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Design of Rectangular Roadside Drains | Drainage Sewers and Channels

By
Anuoluwapo Kolade
-

Roadside drains or channels are structures that are used for conveying storm water away from roads or streets. The complete design of rectangular roadside drains involves hydraulic design, geotechnical design, and structural design.

The hydraulic design involves the proper sizing of the drain to ensure that the design flood is properly discharged, while the geotechnical design involves the verification of the capacity of the supporting soil to carry the weight of the channel and the water. It also involves the verification of the soil-structure interaction since drains are buried structures. The structural design of drains involves the selection of the proper material, thickness, and reinforcement to withstand the pressures and forces exerted by the soil and water.

In previous articles, we extensively discussed how to determine the best hydraulic cross-section of roadside drains and the construction and cost comparison of rectangular and trapezoidal drains. In this article, you will discover everything you need to know about the geotechnical and structural design of rectangular roadside drains.

Similar to the design of retaining walls, roadside drains are also subjected to active and earth pressures. In the example treated below, active and passive earth pressures, surcharge loads and water pressures are considered.

Worked Example on the Design of Rectangular Roadside Drains

The rectangular drain shown below is backfilled with a typical cohesionless granular material, having a unit weight (γ) of 18 kN/m3, zero cohesion (C), and internal angle of friction (ϕ) of 30°. The allowable bearing pressure of the soil is 150 kN/m2, the coefficient of friction (μ) is 0.5, the unit weight of reinforced concrete is 24 kN/m3, and surcharge loads of 15 and 5 kN/m2 on both sides of the drain. The drain has been designed to cater to a flow of 400mm depth and the unit weight of water (γw) should be taken as 9.8 kN/m3.

design of rectangular roadside drains
All drain dimensions in mm

Given the information above, design the drain wall and base reinforcements assuming fcu = 20 N/mm2, fy = 460 N/mm2, cover to reinforcement = 40 mm, diameter of reinforcements = 10 mm, and thickness of walls and base = 150 mm.

Geotechnical Design

Wall pressure calculations

Ka = (1 – sinϕ) / (1 + sinϕ)
Ka = (1 – sin30°) / (1 + sin30°) = 0.333

Wall 1

active 093917
Active pressure on drain wall

Active pressure at the top of the drain wall = qKa = 15 × 0.33 = 4.95 kN/m2
Active pressure at the base of the drain wall = qKa + KaγZ = 4.95 + (0.33 × 18 × 0.85) = 4.95 + 5.049 = 9.999 kN/m2

passive 093919
Passive pressure on drain wall

Passive pressure at the top of the drain wall = 0
Passive pressure at the base of the wall = γwZ = (9.8 × 0.55) = 5.39 kN/m2
Net pressure at the base of the wall = 9.999 – 5.39 = 4.609 kN/m2

Wall 2
Active pressure at the top of the drain wall = qKa = 5 × 0.33 = 1.65 kN/m2
Active pressure at the base of the drain wall = qKa + KaγZ = 1.65 + (0.33 × 18 × 0.85) = 1.65 + 5.049 = 6.699 kN/m2

Passive pressure at the top of the drain wall = 0
Passive pressure at the base of the wall = γwZ = (9.8 × 0.55) = 5.39 kN/m2
Net pressure at the base of the wall = 6.699 – 5.39 = 1.309 kN/m2

Total vertical load (N)
Walls (Wws) = 2(0.15 x 0.7 x 24) = 5.04 kN/m
Base (Wb) = 1.1 x 0.15 x 24 = 3.96 kN/m
Water (Ww) = 0.4 x 0.8 x 9.8 = 3.136 kN/m
Total vertical load Wws + Wb + Ww (N) = 5.04 + 3.96 + 3.136 = 12.136 kN/m

Horizontal forces on drain walls due to surcharge load and backfill

combination 093919
Resultant pressure on drain wall

Wall 1 = qKaZ + (0.5 × KaγZ × Z) – (0.5 × γwZ × Z) = (15 × 0.333 × 0.85) + (0.5 × 5.049 × 0.85) – (0.5 × 5.39 × 0.85) = 4.246 + 2.146 + 2.291 = 4.101 kN/m

Wall 2 = qKaZ + (0.5 × KaγZ × Z) – (0.5 × γwZ × Z) = (5 × 0.33 × 0.85) + (0.5 × 5.049 × 0.85) – (0.5 × 5.39 × 0.85) = 1.403 + 2.146 – 2.291 = 1.258 kN/m

Net horizontal force (PA) = 4.101 – 1.258 = 2.843 kN/m

Resistance to sliding

Frictional Force (Ff) = μN = 0.5 × 12.136 = 6.068 kN/m
F.O.S = Ff / PA = 6.068/2.843 = 2.134
The factor of safety 2.134 > 1.5. Therefore, the drain is very safe from sliding.

Resistance to overturning

Taking moment about wall 1;

Sum of overturning moments (Mo) = (4.101 – 1.258) × (0.85/3) = 0.806 kNm per m
Sum of restoring moments (MR) = (W1 × 0.075m) + (Ww × 0.55m) + (W2 × 1.025) + (Wb × 0.55) = (2.52 × 0.075) + (3.136 × 0.55) +(2.52 × 1.025) + (3.96 × 0.55) = 0.189 + 1.725 + 2.583 + 2.178 = 6.675 kNm/m

F.O.S = MR / MO = 6.675/0.806 = 8.281
The factor of safety 8.281 > 2. Therefore, the drain is very safe from overturning.

Bearing capacity check

Bending moment about the centerline of the base;

M = (W2 × 0.475m) + (4.101 × 0.85/3) – (W1 × 0.475m) – (1.258 × 0.85/3) = (2.52 × 0.475m) + (4.101 × 0.85/3) – (2.52 × 0.475m) – (1.258 × 0.85/3) = 1.197 + 1.162 – 1.197 – 0.356 = 0.806 kNm per m

Total vertical load (N) = 12.136 kN/m
Eccentricity (e) = M/N = 0.806/12.136 = 0.066m

Check: D/6 = 1.1/6 = 0.183m
Since e < D/6, there is no tension in the drain base.

Maximum pressure in the drain base (qmax) = P/B (1 + 6e/B) = 12.136/1.1 [1 + (6 × 0.066)/1.1] = 15.005 kN/m2
Minimum pressure in the drain base (qmin) = P/B (1 – 6e/B) = 12.136/1.1 [1 – (6 × 0.066)/1.1] = 7.061 kN/m2

Since qmin and qmax are lower than the allowable bearing pressure of the soil (150 kN/m2), bearing capacity check is satisfied.

Structural Design

Design of the Walls

Since the horizontal force due to surcharge load and backfill on Wall 1 > Wall 2, we adopt Wall 1 parameters for design. Using the centroid formula of a parallelogram for the pressure diagram of wall 1 to determine the distance (x) from the centroid to the base of the wall and distance (y) from the centroid to the top of the wall;

x = 0.85 [((4.609 + (2 x 4.95)) / (3(4.609 + 4.95))] = 0.43m

Thus, y = 0.85 – 0.43 = 0.42m
Taking moment at the top of the drain wall due to the active force;
M = 4.101 x 0.42 = 1.722 kNm per m

Taking moment at the base of the drain wall due to the active force;
M = 4.101 x 0.43 = 1.763 kNm per m

Since the moment at the base of the drain wall is greater than that at the top, we adopt the moment at the base for design.

At ultimate limit state;
M = 1.4 × 1.763 = 2.468 kNm per m

Flexural Design (Bending)

Given: Thickness of wall (h) = 150mm, Cover = 40mm, fcu = 20 N/mm2, fy = 460N/mm2, Rebars = 10mm

Effective depth (d) = 150 – 40 – (10/2) = 105 mm

K = M/(fcubd2) = (2.468 x 106) / (20 x 1000 x 1052) = 0.0112 (K < 0.156)
la = 0.5 + (0.25 – k/0.9)0.5 = 0.5 + (0.25 – 0.0112/0.9)0.5 = 0.987
Since 0.987 > 0.95, la = 0.95

As,req = M/(0.95fy.la.d) = (2.468 x 106) / (0.95 × 460 x 0.95 x 105) = 56.62 mm2/m
ASmin = (0.13bh)/100 = (0.13 x 1000 x 150) / 100 = 195 mm2

Provide Y10 @ 300mm c/c (ASprov = 260 mm2/m)

Steel ratio check

4.0 > (100ASprov / bh) > 0.13
4.0 > (100 x 260) / (1000 x 150) > 0.13
4.0 > 0.17 > 0.13 (Steel ratio is satisfied)

Shear check

Ultimate design shear force on drain wall (V) = (1.4 × 4.101) = 5.741 kN/m

Shear stress (v) = V/bd = (5.741 × 1000) / (1000 × 105) = 0.055 N/mm2

Shear strength (vc) = 0.632 × (100As/bd)1/3 × (400/d)1/4 × (fcu/25)1/3
vc = 0.632 × [(100 × 260)/(1000 × 105)]1/3 × (400/302)1/4 × (20/25)1/3 = 0.632 × 1.3529 × 1.3971 × 0.9283 = 1.109 N/mm2
Since v < vc, no shear reinforcement required.

Design of the base

The pressure distribution diagram on the base at serviceability limit state is shown below;
qmin = 7.061 kN/m2
qmax = 15.005 kN/m2

bearing capacity 082251
Pressure distribution on the drain base

At the ultimate limit state;

qmin = 7.061 x 1.4 = 9.885 kN/m2
qmax = 15.005 x 1.4 = 21.007 kN/m2

On investigating the maximum design moment at point A;

Water = 1.4 × [9.8 × 0.4 × 0.8 × (0.8/2 + 0.15) = 2.415 kNm/m
Base = 1.4 × [24 × 0.15 × 0.8 × (0.8/2 + 0.15) = 2.218 kNm/m
Earth pressure = [9.885 × 1.1 × (1.1/2)] + [(21.007 – 9.885) × 1.1 x 0.5 × (1.1/3)] = 8.223 kNm/m

Net moment = 8.223 – 2.415 – 2.218 = 3.59 kNm/m

On investigating the maximum design moment at point B;

Water = 2.415 kNm/m
Base = 2.218 kNm/m
Earth pressure = [9.885 × 1.1 × (1.1/2)] + [(21.007 – 9.885) × 1.1 × 0.5 × (2 × 1.1/3)] = 10.466 kNm/m

Net moment = 10.466 – 2.415 – 2.218 = 5.833 kNm per m

Since net moment at B > moment at A, we adopt 5.8833 kNm for design.

Flexural Design (Bending)

Given: Thickness of base(h) = 150 mm, Cover = 40 mm, fcu = 20 N/mm2, fy = 460 N/mm2, Size of rebars = 10mm

Effective depth (d) = 150 – 40 – (10/2) = 105mm

K = M/(Fcubd2) = (5.833 × 106) / (20 × 1000 × 1052) = 0.0265 (K < 0.156)
la = 0.5 + (0.25 – k/0.9)0.5 = 0.5 + (0.25 – 0.0265/0.9)0.5 = 0.97

Since 0.97 > 0.95, La = 0.95

ASreq = M/(0.95Fy.La.d ) = (5.833 × 106) / (0.95 × 460 × 0.95 × 105) = 133.82 mm2/m
ASmin = (0.13bh)/100 = (0.13× 1000 × 150) / 100 = 195 mm2

Provide Y10 @ 300mm c/c (ASprov = 260 mm2/m)

Shear Check

Calculating the maximum shear force at any section of the drain base;

Water = 1.4 × (9.8 × 0.4 × 0.8) = 4.39 kN/m
Base = 1.4 × (24 × 0.15 × 0.8) = 4.032 kN/m
Earth pressure = 0.5 × (21.007 + 9.885) × 0.8 = 12.356 kN/m

Net shear force = 12.356 – 4.39 – 4.032 = 3.934 kN/m

Shear stress (v) = V/bd = (3.934 × 1000) / (1000 × 105) = 0.037 N/mm2

Shear strength (Vc) = 0.632 × (100As/bd)1/3 × (400/d)1/4 × (fcu/25)1/3 = 0.632 × (100 × 260)/(1000 × 105)]1/3 × (400/302)1/4 × (20/25)1/3 = 0.632 × 1.3529 × 1.3971 × 0.9283 = 1.109 N/mm2

Since v < Vc, no shear reinforcement required.

Detailing

detailing 082508
Typical drain section

Conclusion

This article has discussed the geotechnical and structural design of rectangular roadside drains. However, readers must note that only one load case has been treated. Therefore, a designer must consider other load cases or load combinations to ascertain the accuracy of the design. For example, it would be appropriate to rerun the design with the drain filled and when the drain is empty to determine the most critical load case or combination.

Causes of Deterioration of Used Concrete Sewer Pipes

By
Charity Mmuo
-

Concrete is the building material that is most usually used for sewer systems because of its favorable structural qualities, capacity for prefabrication, and freedom from form restrictions. For a variety of reasons, such as the effects of (bio)chemical deterioration, ageing, and the loss of soil support, the structural integrity of concrete sewer pipes degrades with time.

The design life of a sewer system is several decades. Due to the capital-intensive nature of maintaining a sewer system as well as the severe societal and financial consequences of catastrophic failure, accurate condition evaluation has become increasingly important over time.

Concrete sewer pipe
Figure 1: Installation of concrete sewer pipes

The two most frequent sources of data used to determine whether to repair or replace sewers are Closed-Circuit Television (CCTV) inspection and age. The difficulty of revealing deterioration on the outside of the sewer pipe wall, the low accuracy and reliability of visual inspection data, and the weak correlation between visual inspection data and material properties are just a few drawbacks that have recently been discovered with regard to these inspection methods.

Additionally, the majority of nations lack a database that contains precise information on the state of the subsurface infrastructure. Thus, it is obvious that clear knowledge about the real structural state of sewer systems is required in order to enhance current inspection techniques and enable adequate condition assessments.

The structural state of sewer networks has been the subject of numerous study investigations during the past few decades. Much emphasis has been paid to the biogenic sulphuric acid-induced degradation process that typically occurs in concrete sewer pipes.

Investigations into the sulphuric acid-producing bacteria and the chemical deterioration mechanisms that result at the inner surface of sewer pipes have revealed that the concrete’s calcium hydroxide and calcium silicate hydrate react with the acid to create gypsum and/or ettringite, which frequently causes an increase in porosity and, as a result, a decrease in strength and stiffness.

deterorating sewer
Figure 2: Deteriorated concrete sewer pipes

Additionally, naturally occurring carbondioxide in soil may migrate to the outside of concrete sewer pipes, where it may interact with hydrated cement in the presence of moisture. The strength, porosity, and pore size distribution of the cement paste may change as a result of this carbonation process. The assessment of the structural failure behavior of sewer pipes was the focus of additional experimental researches.

Despite the fact that the aforementioned investigations have focused  on important issues and facts, a complete understanding of how (bio)chemical attack affects the mechanical performance of in-situ concrete sewer pipes is still lacking. However, this information is necessary to boost the suitable recommendations that municipalities and other stakeholders can use when making decisions about the upkeep and replacement of concrete sewer pipe systems.

Evaluation of Deterioration of old Sewer Pipes

Recently, researchers (Luimes et al, 2022) from the Department of the Built Environment, Eindhoven University of Technology, Eindhoven, The Netherlands, and Department of Hydraulic Engineering, Deltares, MH Delft, The Netherlands,  studied the effects of biochemical attack on the mechanical performance of used concrete sewer pipes which they published in the journal, Construction and building materials (Elsevier).

Thirty-five used, unreinforced concrete sewer pipes provided by The Netherlands’ Municipalities of The Hague and Arnhem were used for the experimental program. The tested pipes, which range in age, size, and geometry, have been in use as combined sewer systems (i.e., the tested pipes installed in the 1920s and 1950s) or as improved separated systems (i.e., the tested pipes installed in the 1990s) up until July/August 2019 (pipes from Arnhem) and January 2020 (pipes from The Hague), respectively, without undergoing rehabilitation or protection treatments.

The test program involved concrete sewer pipes that had been in use for between 22 and 95 years. During that time, exposure to particular in-situ circumstances had resulted in some chemical attack, which may have been accompanied by mechanical damage from traffic loads and excavation. This might have reduced the concrete’s mechanical qualities, which might have affected the pipe’s ability to support structural loads. The inner and outer surfaces of the sewer pipes were first given a rigorous visual inspection during the study, and were then classified using various surface condition classes in order to explore these issues in more detail.

samples
Figure 3: Four examples of unreinforced concrete sewer pipe specimens of different age that were considered in the experimental program (Luimes et al, 2022)

The cross-sections of the sewer pipes were also tested for residual alkalinity using a phenolphthalein method, where a pH indicator was provided by a 1 percent solution of phenolphthalein. The solution turns from pink to magenta in moderately alkaline conditions with a pH in the range of 9.2 to pH 10. The solution turns magenta in extremely alkaline surroundings with a pH > 10, but it stays colorless in somewhat alkaline and acidic conditions with a pH 9.2.

The dissolution of solid calcium-hydroxide in the pore solution causes the pH of the concrete to rise to a level above 12.5 to 13, which is shown by the magenta zones. On the other hand, the colorless zones indicate the presence of a chemical attack in the past, which may have been brought on by carbonation (8.3 <  pH < 9) and biogenic suphuric acid corrosion (1< pH < 3).

X-ray diffraction (XRD) data were used by the researchers to further analyze the type of chemical attack. A total of 6 different surface condition classes were identified, and a particular place may be described by many surface conditions. The surface conditions were classified as follows in accordance with nomenclature generally used by the sewer asset management community:

  1. Smooth – A surface that is virtually intact and aesthetically comparable to the surface of a brand-new sewer pipe
  2. Exposed granulates – Exposed granulates and porous mortar between granulates referred to chemically harmed surfaces where the granulates are now visible and/or have fallen off due to the loss of the thin outer mortar layer. In the latter class, the mortar that once held the exposed granulates together has degraded into a porous, loose material that is simple to spall off.
  3. The deposits class — As a result of variations in the wastewater level, dark colored bands indicate obvious color changes and adhering deposits along the inner pipe surface.
  4. Rough – A surface with minor chemical assault symptoms, wherein a portion of the thin outer mortar layer is still covering the granulates.
  5. Excavation damage – This refers to relatively big scraped or broken off pieces brought about by bulldozers and excavators during the mechanical removal of the sewer pipes from the soil.
different levels of pipe deterioration
Figure 4: Representations of the 6 surface condition classes: (1) Smooth, (2) Exposed granulates, (3) Porous mortar between granulates, (4) Deposits — Dark coloured bands,
(5) Rough, and (6) Excavation damage, as observed on the inner and outer surfaces of the tested concrete sewer pipes (Luimes et al, 2022)

The types and degree of biochemical attack were respectively assessed by performing XRD analyses and phenolphthalein tests. The following conclusions were obtained from the findings.

  • The process of biogenic sulphide corrosion can be blamed for a major portion of the structural deterioration of old sewer lines. This process often results in a porous mortar layer between the granulates and a weak, corroded layer that looks like exposed granulates at the inside of the pipe.
  • Carbonation may have an impact on the sewer pipe’s outside, but it seems to have a very small impact on the pipe’s surface condition and is thought to be less detrimental to the structural integrity.
  • In contrast to the relatively new pipes from the 1990s, the old pipes from the 1920s and 1950s typically exhibit quite significant levels of chemical attack. Despite the fact that the level of chemical attack tends to increase with pipe age, an explicit relationship between pipe age and the degree of chemical attack cannot be determined from measurement data because the pipe’s specific material composition and the surrounding environment also have a significant impact on the level of chemical degradation.

According to the researchers (Luimes et al, 2022), the study’s findings can be used to develop and improve inspection and condition assessment standards. Further research has shown that biogenic sulphide corrosion can significantly contribute to the mechanical deterioration of sewer pipes, making it prudent to keep an eye on how this corrosion process is progressing inside in-situ sewer pipes.

Source:
Luimes R. A., Scheperboer I.C., Suiker A.S.J., Bosco E., and Clemens F.H.L.R. (2022): Effect of biochemical attack on the mechanical performance of used concrete sewer pipes. Construction and Building Materials 346 (2022) 128390 https://doi.org/10.1016/j.conbuildmat.2022.128390

The contents of the cited original article published by Construction and Building Materials (Elsevier) is open access, under the CC BY license (http://creativecommons.org/licenses/by/4.0/) which allows you to share and adapt (remix) the article provided the appropriate credit is given, and the link to this license provided.

Corrosion of Buried Mild Steel Corrugated Sheets

By
Charity Mmuo
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A high moisture content, good aeration, a high level of acidity, and a considerable number of soluble salts,  can make a soil become corrosive. Metal alloys may undergo a dealloying process in corrosive soils as a result of the hostile surroundings there. The combination of soil corrosivity and dealloying corrosion is to blame for the spread of corrosion in buried steel structures.

Corrugated metal pipes (CMPs) and corrugated metal culverts (CMCs) are subterranean steel structures that have been utilized in traffic networks and water supply systems in North America and Europe since the 1850s . Corrugated profiles are being used in pipelines and culverts in  order to help these structures interlock with the surrounding backfill soils and increase confinement properties as well as overall capacity. In cold coastal regions, salt used to melt the snow causes significant chloride deposits in the soil, which exposes buried corrugated steel structures to, resulting in the formation of thick rust layers.

corrugated metal culvert

Corrosion, which results from exposure to hostile conditions where chlorides attack metals with or without protective coatings, is the main reason why buried steel constructions deteriorate. Such deterioration is characterized by thickness loss and a decline in the axial and flexural stiffness of the steel. To avoid structural failure, it is necessary to reevaluate the structural capability and estimated service life. Around the years, soil corrosion has had an impact on several underground steel constructions all over the world (Ezzeldin et al., 2022).

Temperature variations, humidity, airborne sea salt, salts dissolved during snow thawing, and other chemical elements can all contribute to corrosive situations that cause steel to deteriorate over time. The risk of corrosion in buried steel structures is brought on by the very variable soil conditions in the area.

The corrosion process is accelerated by repeated daily and seasonal exposure to salt and water, particularly when there is an increase in temperature fluctuation in cold regions due to the effects of global warming. To monitor potential structural degradation and damage, regular in-service inspection of culvert performance is therefore essential.

The US Pipelines and Hazardous Material Safety Administration states that exterior corrosion is typically to blame for pipeline system ruptures brought on by corrosion. In addition to causing environmental issues, corrosion is a major element in the aging of networks and facilities, needing maintenance and rehabilitation that can put a large financial strain on the nation’s budget.

Recent Research Study on Corrosion

Recent research from the Department of Civil and Resource Engineering and the Department of Mechanical Engineering at Dalhousie University in Nova Scotia, Canada, studied the accelerated laboratory corrosion test on corrugated mild steel structures buried in cohesionless soils. The study utilized repeated wet/dry cycles to simulate the effects of chloride deposits on the buried steel structures. The findings of the study were published in the journal, Case Studies in Construction Materials.

corrugated steel pipe
Corrugated steel pipe

For the purpose of simulating the effects of chloride deposits on corrugated mild steel structures buried in cohesionless soil, the researchers (Ezzeldin et al., 2022) devised an accelerated laboratory corrosion test using multiple wet/dry cycles. The test was initiated by applying a 3.5% NaCl electrolyte solution to cohesionless soil above buried corrugated steel coupons, which were then subjected to repeated wet/dry cycles.

The study also examined the structural profile geometry’s loss of thickness and the degree to which the steel’s tensile strength, ductility, and hardness had been degraded. This investigation focused on the deterioration of mild steel coupons as a result of corrosion. Both micrometer gauge measurements and the weight loss method were used to calculate the corrosion damage.

Corrugated mild carbon steel (CS) type B coupons were used for the tests. The coupons had a corrugation depth of 13 mm, a wavelength of 68 mm, and a thickness of 1.5 mm. Each coupon’s total projection dimensions were 110 mm by 110 mm in order to accommodate multiple waves, one crest and two valleys at the surface facing the dirt. The interface geometry of buried CMPs and CMCs was simulated by the corrugated specimens.

Each coupon was buried beneath a layer of finely graded, well-compacted, cohesionless dirt. The system included two timers to regulate the wetting (spraying) and drying stages, a tank of distilled deionized water, a pump to transfer water from the tank, stainless steel pipes and fittings to carry the water from the tank to an oven, a convection oven to distribute heat evenly to the coupons during the drying stages, and other components.

Two programmed timers were used to regulate the timing for each stage while the wet/dry cycles were repeated. The process of soaking (spraying) took 4 seconds. The soil above each coupon was sprayed with the distilled water as it was transferred by the pump from the tank. To provide dissolved oxygen and keep the water at normal temperature, the tank containing the distilled water was left open to the atmosphere. The heat from the oven was then used to finish the drying process. The soil temperature rose gradually during the drying stage, reaching a nearly dry state (i.e., a recorded soil temperature of about 90 ℃) in about 60 minutes.

The Experimental Setup of the Corrosion test.
The Experimental Setup

Each full wet/dry cycle took about 60 minutes to complete because the spraying was done right away at the start of the cycle. When the soil was sprayed during the wetting stage, the temperature abruptly dropped from around 90℃ to about 60 ℃, a drop of about 30 degrees. Prior to the start of the following wetting stage, the temperature was raised once again during the ensuing drying stage in order to evaporate the majority of the remaining water.

To keep the salt content in the soil at the same level (i.e., 3.5 percent) during subsequent wetting procedures, which were carried out using just distilled water, the electrolyte solution was added just once, using the same quantity of distilled water as utilized for each wetting stage.

Gravity caused the salts to settle onto the steel coupons as a result of the repeated wetting process used to completely saturate the soil throughout each cycle. In order to provide aeration and break up salt crusts that had collected, a spatula was used to mix only the top layer of soil and then compact it on top of each coupon after every 20 wet/dry cycles.

In order to reduce any potential impact on corrosion propagation, the soil adhering to the metal surface’s interface was kept undisturbed by the researchers. To assess the spread of corrosion caused by each set of cycles, five coupons were evaluated with varying totals of wet/dry cycles (50, 100, 200, 400, and 800 cycles).

Findings from the Study

At the end of the experiment by Ezzeldin et al (2022), the following conclusions were made;

  • Mild steel corrosion was accelerated by repeated wet/dry cycles in the absence of a protective layer (such as zinc coating).
  • In the steel coupons, where more induced stresses were created during the production of the corrugated steel sheets, the degree of corrosion was greater at the corrugation crests and valleys.
  • Rust layers of a similar nature and morphology developed on all of the test specimens, imitating the effect of acidic environments on buried steel structures in cold climates. This effect could be clearly observed in both valleys of the coupon treated to 800 wet/dry cycles.
  • While the rate of corrosion steadily decreased, the level of corrosion damage increased when the number of wet/dry cycles was increased. Mixed corrosion modes, such as deep pitting that produced cavities, were a part of the corrosion that eventually evolved.
  • The structural geometry, which lost thickness, and the mechanical qualities, such as tensile strength, ductility performance, and hardness, all degraded as a result of the steel coupons’ deterioration. Due to the reduced axial and flexural rigidity, subterranean steel structures like CMPs and CMCs would no longer be able to function to their full potential. 

A mathematical model, requiring the measurement of four physicochemical parameters at the interface between the soil and the mild steel surface, was used by the researchers to provide an approximate prediction of the depth of corrosion damage in buried steel structures. The present study suggests employing this mathematical model to make approximate predictions of corrosion damage over time, based on the following Eqs. (1,2):

νp = C0exp[-(q1pH + q2ρ + q3ERedox + q4Es-p)] ——– (1)

z(t) = νpt + [(υ0 – νp)/q0] [1 – exp(- q0t)] ——– (2)

Where:
νp = the average long-term corrosion rate;
υ0 = the initial corrosion rate = 0.6743
C0 = constant 1, = 12.2652,
q0= constant 2, = 1.7326,
q1 = pH constant = 0.6623,
q2 = resistivity constant, = 0.0069 Ωm,
q3 = redox potential constant, i.e., 0.0027 mV/SHE,
q4 = soil-structure electric potential constant, i.e., 0.981 V/Cu/CuSO4,
z(t) = the maximum depth of corrosion damage at time (t).

The corrosion damage and reduction in nominal thickness (%) related to number of cycles from the accelerated wet/dry test and number of years from the mathematical model is shown in the Table below;

corrosion model table

Reference(s)
Ezzeldin I., El Naggar H., Newhook J. and Jarjoura G. (2022): Accelerated wet/dry corrosion test for buried corrugated mild steel. Case Studies in Construction Materials 17 (2022) e01152. https://doi.org/10.1016/j.cscm.2022.e01152

The contents of the cited original article published by Case Studies in Construction Materials (Elsevier) is open access, under the CC BY license (http://creativecommons.org/licenses/by/4.0/) which allows you to share and adapt (remix) the article provided the appropriate credit is given, and the link to this license provided.

Number and Depth of Borings for Soil Investigation

By
Ubani Obinna
-

The entire area of a project site cannot be fully explored for site investigation due to logistical and financial constraints. To provide enough information for the design and construction of the foundation of a building or highway, geotechnical engineering consultants must make good decisions about the location, number, and depth of borings for soil investigation. The zone of soil that will be affected by the structural loads should be covered by the number and depth of borings. There are no fixed guidelines to adhere to.

More often, the number and depths of borings are governed by experience based on the geological nature of the ground, the importance of the structure, the structural loads, and the availability of equipment. The minimum number and depth of borings may be specified by building regulations and regulatory authorities in the local area.

Whenever possible, boreholes should always be dug close to the intended foundation location. Where the bearing stratum’s depth is uneven, this is crucial. The boreholes should be precisely positioned in relation to the proposed structures, both in terms of level and location.

A grid of holes that are evenly spaced serves as an appropriate design of boreholes when the layout of the structures has not been established at the time the soil investigation is being conducted. It is feasible to use a grid of boreholes with in-situ probes of some kind, such as dynamic or static cone penetration tests, spaced more closely apart within the borehole grid for large areas. EC 7 recommends, for category 2 investigations, that the exploration points forming the grid should normally be at a mutual spacing of 20 — 40 m.

A challenging issue that is intimately related to the relative costs of the soil investigation and the project for which it is done is the necessary number of boreholes that must be sunk at any specific place. Normally, as more boreholes are drilled, more information about the soil conditions becomes available, allowing for more efficiency in the foundation design. Additionally, the likelihood of encountering unforeseen or challenging soil conditions, which would significantly raise the cost of the foundation work, decreases over time.

An economic limit, however, is reached when the cost of borings outweighs any savings in foundation cost and merely drives up the project’s overall cost. In order to determine the true dip of the strata, it is recommended that at least two and ideally three boreholes be drilled for all but the smallest structures. However, inaccurate assumptions about stratification can still be made.

However, it is very important that the number of boreholes be sufficient to detect any variances in the soil of the site. If the loads placements (such as column footing positions) on the structure’s footprint are known (which is frequently not the case), you should think about drilling at least one borehole where the heaviest load is.

number and depth of borings

The depth to which boreholes should be sunk is governed by the depth of soil affected by foundation-bearing pressures. The vertical stress on the soil at a depth of one and a half times the width of the loaded area is still one-fifth of the applied vertical stress at the foundation level, and the shear stress at this depth is still appreciable. Thus, borings in soil should always be taken to a depth of at least one to three times the width of the loaded area.

The borings are relatively shallow for narrow, widely spaced strip or pad foundations, but for big raft foundations, the borings must be deep unless rock is present within the required depth. When strip or pad footings are placed closely together, the pressure zones overlap, and the entire loaded region effectively becomes a raft foundation with correspondingly deep borings. To cover the zones of soil affected by loading transmitted through the piles in the case of piled foundations, the ground should be studied below the pile-point level.

EC 7 recommends a depth of five shaft diameters below the expected toe level. It is usual to assume that a large piled area in uniform soil behaves as a raft foundation with the equivalent raft at a depth of two-thirds of the length of the piles.

As a guide, a minimum of three boreholes should be drilled for a building area of about 250 m2 (2500 ft2) and about five for a building area of about 1000 m2 (10,000 ft2). Some guidelines on the minimum number of boreholes for buildings and for due diligence in subdivisions are given in Table 1.

Area (m2)Numbers of boreholes (minimum)
< 1002
2503
5004
10005
20006
50007
60008
80009
1000010
Table 1: Guidelines for the Minimum Number of Boreholes for Buildings

Some general guidance on the depth of boreholes is provided in the following:

  • In a compressible soil such as clays, the borings should penetrate to at least between 1 and 3 times the width of the proposed foundation below the depth of embedment or until the stress increment due to the heaviest foundation load is less than 10%, whichever is greater.
  • In very stiff clays and dense, coarse-grained soils, borings should penetrate 5 m to 6 m to prove that the thickness of the stratum is adequate.
  • Borings should penetrate at least 3 m into the rock.
  • Borings must penetrate below any fills or very soft deposits below the proposed structure.
  • The minimum depth of boreholes should be 6 m unless bedrock or very dense material is encountered.

Guidelines for the Minimum Number and Depth of Borings for Common Geostructures

For foundation construction on compressible soils (clay and similar materials) with sufficient strength to initially support the structure, it is important to ensure that borings penetrate these compressible layers. Alternatively, borings should reach a depth where the additional stress placed on deeper strata is minimal, ensuring negligible consolidation that wouldn’t significantly impact the proposed structure’s settlement.

Exceptions exist for exceptionally heavy loads or situations where seepage or other factors are paramount. In such cases, borings may be terminated upon encountering bedrock or penetrating a stratum of exceptional bearing capacity and rigidity for a short distance.

However, this is only advisable if prior explorations in the vicinity or regional stratigraphic knowledge confirm that these strata possess adequate thickness or are underlain by even stronger formations. If these confirmations are lacking, a subset of the borings must be extended further to verify the thickness of the strong strata, regardless of the underlying material’s characteristics.

The recommended guidelines for the number and depth of borings for common civil engineering structures are provided below;

Shallow Foundation for Buildings

Minimum number of boreholes
1, but generally boreholes are placed at node points along grids of sizes varying from 15 x 15m to 40 x 40 m.

Minimum depth
The minimum depth of soil exploration for foundations should be 5 m or 1B to 3B, where B is the width of the foundation. Additionally, the depth of exploration should extend to a depth where the increment in stress is equal to or less than 10% of the maximum foundation pressure.

Deep (Pile) Foundation for Buildings

Minimum Number of Boreholes
1 boring, but generally boreholes are placed at node points along grids of sizes varying from 15 x 15m to 40 x 40 m

Minimum Depth of Boring
25m to 30m;
If bedrock is encountered, drill 3m into it

Bridge

Minimum number of boreholes
Abutments – 2
Piers – 2

Minimum Depth of Boring
25m to 30m;
If bedrock is encountered, drill 3m into it

Retaining Walls

Minimum Number of Boreholes
Length < 30 m: 1
Length > 30 m: 1 every 30 m, or 1 to 2 times the height of the wall

Minimum Depth of Boring
1 to 2 times the height of the wall. For walls located on bedrock, drill 3m into the bedrock

Cut Slopes

Minimum Number of Boreholes
Along the length of slope: 1 every 60 m;
if the soil does not vary significantly, 1 every 120 m
On slope: 3

Minimum Depth of Boring
6m below the bottom of the cut slope

Embankments, Including Highways

Minimum Number of Borings
1 every 60 m;
if the soil does not vary significantly, 1 every 120 m

Minimum Depth of Boring
The greater of 2 x height or 6 m

Evaluation of Pykrete in the Design of a Lattice Tower

By
Charity Mmuo
-

Pykrete is a material used for temporary buildings in cold climates. It is made of a mixture of water and a number of additives, such as wood chips, cellulose sheets that have been dissolved, sand, gums, and combinations of any of those. It was initially created so that ships could be built in cold environments. In the past ten years, this substance has typically been used in shell buildings that have been built with ropes and inflatable fabric formwork (see Figure 1).

The usage of Pykrete in linear element constructions has recently been studied, and some low-rise structures have been constructed as a result. According to Pronk et al (2022), the year 2019 saw the construction of a tower-like Pykrete structure for the International Ice and Snow Innovation Design and Construction Competition, based on an idea from the Eindhoven University of Technology. It is the tallest pykrete structure with linear elements to date, this structure has a height of 11 m.

pykrete dome
Figure 1: Pykrete dome (Pronk et al, 2022)

Researchers (Pronk et al, 2022) from the Department of the Built Environment, Eindhoven University of Technology, Netherlands have carried out a study on the mechanical performance of pykrete beam elements. Experimental tests from the study were compared with previously conducted studies. Furthermore, the researchers presented the optimization  and numerical model of a pykrete tower’s design, followed by a description of the construction techniques. The article was published in the journal, Structures (Elsevier).

Making and Design Concept of the Lattice Tower

In the study conducted by Pronk et al (2022), a preliminary design of the tower was developed, considering a uniform cross-section for the primary elements and secondary elements. The preliminary design of the tower was symmetrical, made up of five similar partitions.

Ten principal load-bearing parts, five of which are exterior (shown in blue in Figure 2) and five of which are internal, extend vertically from the bottom to the top (green elements in Figure 2). Self-weight and wind pressure of 0.5 kN/m2 were taken into account. Recent research literature served as the source for the material’s mechanical properties.

preliminary view of the pykrete tower
Figure 2. Preliminary design of the tower (Pronk et al, 2022)

Fire hoses filled with pykrete were used to create the members of the lattice tower. They transfer the wind loads in addition to the dead weight of the structure to the foundations. Compression in the inner columns is primarily produced by the structure’s self-weight. Due to the additional weight of the structural elements, these compressive forces are low at the top of the tower and increase at ground level, as typical in all structures. As a result, it is anticipated to have a larger cross section close to the foundation.

According to the research, the tower’s construction was separated into three stages:

  1. Preparing the rope and pipes: The ropes and fire hoses are trimmed to the correct length. Pykrete is injected into the fire hoses from one side. The hoses were linked together after being frozen. The secondary components, the ropes, are tied together and attached to the fire hoses in accordance with the prescribed pattern. The anchors are made of earth connectors. The hoses are hermetically sealed below ground. To keep the shape while the pykrete is being applied, a low tension is applied to these ropes.
  2. Pipe and rope installation without the use of Pykrete: Here, the structure is raised and positioned using a crane (see Figure 3).
  3. Application of pykrete: As soon as the necessary sections are achieved, the pykrete will be gradually applied by spraying and extrusion on the hoses and ropes. Pykrete can be sprayed on the structure until the desired member thickness is achieved after the desired form has been achieved. The top portion, which is currently being lifted by the crane, will be sawn off once enough pykrete has been put, and the tower will then stand on its own.
lifting the structure with crane
Figure 3: Lifting the structure with crane

Based on the preliminary tower design, two main types of samples were evaluated. The cross-section of the first kind of sample is made up of pykrete and a fire hose. A tube with a 64 mm diameter was used as the hose. Pykrete is poured into the tube, and a 44 mm thick second layer of pykrete is applied around the tube, making the section’s overall diameter 154 mm. The mixture of additives in Pykrete contains cellulose at a concentration of 20 g/L (2%).

The second type of sample, which has a smaller cross-section was used to test for secondary elements. It was made up of a rope with a diameter of 12 mm that is encircled by a layer of pykrete measuring 15 mm. The additive concentration is 80 g/L (8%).

The greatest length that can be tested corresponds to a sample length of 450 mm for both types of samples. Testing was done using three different methods: compression, tension, and 4-point bending. For pykrete samples, there aren’t any currently available standardised tests. It is important to understand that pykrete’s mechanical characteristics vary depending on temperature.

Mechanical Performances of Pykrete in Beam Elements

In comparison to common building materials, pykrete’s mechanical characteristics are still being extensively studied. Tests have been done on a large number of samples in order to compare different pykrete compositions. The force–displacement relationship obtained by the bending and compression tests in the current study generally followed the major trends already observed in previous studies. However, some of the takeaways from the study were;

  • Regarding the 4-point bending tests, it appears that the fire hose behaviour during bending shows a hardening phase. The authors however recommended that further research should examine additional samples with composite sections to corroborate this.
  • The compression tests revealed that when using slender linear elements, which weren’t taken into account for shell structures in Pykrete, it will be required to pay attention to buckling.
  • The tests conducted on the fire hose sections produced an elastic modulus that is relatively low and especially much below what is described in the literature. Although the cause of this outcome is unclear, a lack of uniformity in the parts may be to blame.
  • The tensile tests reveal that while the rope does not increase the section’s tensile strength, it does allow for the preservation of the element’s integrity after failure, which is not possible for an element constructed simply of pykrete.

The full results of the test data are available in the publication.

Optimization and Numerical Model of the Tower

Grasshopper® software was used to optimize the tower’s design based on the results of the investigation. It is a Rhino® visual programming plugin that enables the execution of parametric designs based on scripts. A Live Physics engine called Kangaroo2® allows for interactive simulation, optimization, and form-finding within Grasshopper.  Kangaroo2® uses dynamics relaxation With this approach, a nonlinear equation system’s solution is reduced to an explicit iterative calculation. Therefore, a damped dynamic process led to the proposed static solution.

pykrete models
Figure 4: The initial design and the optimised design

The algorithm consists of the subsequent phases. The anchor points, the self-weight, the major element stiffness, and the secondary element stiffness are first defined as the constraint conditions. Then, utilizing Newton’s second law, masses are defined at each node. The total residual forces for each node, the speed, and the position are computed at each iteration. When the geometry reaches its static state, the algorithm will terminate.

The optimum design consists of a series of curves that can be connected to form a mesh. In other words, the gradient of the energy that is in the direction of the forces (masses) defined at each node is used to move the nodes in order to minimize the elastic energy.

The next step is to assess the design’s structural performance in SCIA® under wind loads and self-weight. The elements’ cross-sections are manually modified (decreased or increased). For the primary and secondary parts, there can only be three different sections. Finally, the original design and the new cross-sections are added as a new input in Grasshopper®, and Kangaroo2® generates a new shape.

cross sections of the tower
Figure 5: Final cross-sections of the tower.

Conclusion

Pykrete is a promising and environmentally friendly material for constructing buildings in cold areas. Up until now, inflatable shell structures were the only types of pykrete structures. However, this restricts the kind of constructions that can be made to the shapes of inflatables that can be built.

According to the study, producing truss structures would present new opportunities. By recommending a construction method and performing testing on the sections, the research enabled the creation of an 11 m tall tower made up of linear elements. By using form-finding, the design was optimized, and SCIA® was used to verify the structure under actual loading. The experimental testing have demonstrated that, before constructing more ambitious structures, research on the buckling of these components is required.

Reference(s)
Pronk A., Mergny E., and Li Q. (2022): Structural design of a lattice pykrete tower. Structures 40 (2022) 725-747. https://doi.org/10.1016/j.istruc.2022.03.079

The contents of the cited original article published by Structures (Elsevier) is open access, under the CC BY license (http://creativecommons.org/licenses/by/4.0/) which allows you to share and adapt (remix) the article provided the appropriate credit is given, and the link to this license provided.

Construction and Cost Comparison of Rectangular and Trapezoidal Drains

By
Anuoluwapo Kolade
-

Cost is often a major determiner of decision-making on projects. Therefore, for all civil engineering works, it is required to know the probable construction cost before the project’s commencement. This is known as the estimated cost, which comprises the cost of labour, materials, equipment, and other general overhead costs. The construction and cost comparison of rectangular and trapezoidal drains can be an important consideration during highway design.

In a previous article, determining the best hydraulic section of roadside drains was discussed whereby a particular peak discharge was designed, resulting in rectangular and trapezoidal cross-sections. However, the cost comparison of both cross-sections will be discussed in this article to determine which cross-sections will result in greater savings on cost.

The details of both drain cross-sections are provided below. However, it must be noted that it is assumed that the construction is in-situ, and the cost comparison is based on 1m length of the drain cross-sections. Furthermore, the cost of labour is proportional to the quantity of materials.

Construction Process of Reinforced Concrete Drains

The procedures for the construction of reinforced concrete drains are stated below:

Marking of alignment: This involves a surveyor marking out the alignment for the trench to be dug. This alignment includes horizontal and vertical alignment. The projection of the drain in the horizontal plane is termed as the horizontal alignment, while the projection in the vertical plane is termed the vertical alignment. Survey instruments are used in this operation.

Excavation: After the surveyors have marked out the trench alignment, the depth is also marked out. Excavation is then carried out through the use of manual labour or mechanical means by the use of excavating machine.

Concrete blinding: This is the process of pouring a thin layer of concrete over the bed of the trench to seal in the underlying soil material and prevent dirt and mud from interfering with the drain structure. It is also done to correct any irregularities in the bed of the excavated surface, and to provide smooth, level and regular surface to receive the concrete base. The concrete blinding is a mass concreting and usually 50mm in thickness.

DSC03386
Construction of a rectangular concrete drain

Positioning of reinforcements: U-shape or trapezoidal-shape rebars, as the case may be, are usually placed in position on the blinded surface at the designed spacing. Furthermore, the rebars are positioned with the aid of concrete biscuit to create a concrete cover. It must be ensured that the center of the base aligns with the center alignment provided by the surveyor in order to have a uniform alignment.

Concrete base: After the positioning of rebars, the next step is to cast the concrete base. Usually, a concrete base of 150mm in thickness is cast on the blinded bed of the drain. A guiding panel or formwork is placed into position to guide in casting the concrete base to achieve a uniform alignment base edge, thickness, width, and to manage the concrete while pouring.

Concrete wall: After the casting of the base, and setting and hardening of the concrete, the formwork for the drain walls are positioned to allow for the casting of the wall. The fair-finished panels to be used as formwork should be lubricated, clipped and prepared to receive the concrete. After casting, setting and hardening of the walls, the panels are removed and the concrete is cured.

Backfilling and compaction: After the casting of the drain walls, the excavated portion left beside the drain is backfilled and compacted to avoid settlement of the backfill.

Cost Analysis of Rectangular Drain

rectangular details 102132
Rectangular drain details

Excavation  
Volume of soil = (1.1 + 0.6) × (0.05 + 0.15 + 0.7) × 1 = 1.53 m3
Unit cost of excavation = ₦1,500 per m3
Cost of excavation = 1.53 x 1,500 = ₦2,295

Concrete in blinding
Volume of concrete = 0.05 × 1.7 × 1 = 0.085 m3
Unit cost of concrete = ₦55,000
Cost of concrete material = 0.085 × 55,000 = ₦4,675

Concrete in drain
Volume of concrete = [(1.1 × 0.15) + 2(0.7 × 0.15)] x 1 = 0.375 m3
Unit cost of concrete = ₦55,000
Cost of concrete material = 0.375 × 55,000 = ₦20,625

Reinforcement
Bar Mark 1 = 6 × 2.6 × 0.617 = 9.626 kg
Bar Mark 2 = 14 × 1 × 0.617 = 8.638 kg
Total weight of rebar = 9.626 + 8.638 = 18.264 kg

Unit cost of rebar = ₦ 450
Cost of rebar = 18.264 x 450 = ₦ 8,220

Formwork
Base = 2(0.15) × 1 = 0.3 m2
Walls = 2(0.7+0.7) × 1 = 2.8 m2
Total area of formwork required = 0.3 + 2.8 = 3.1m2

Unit cost of formwork = ₦5,400 (marine plywood)
Total cost of formwork = 3.1 x 5,400 = ₦16,740

images 1
Rectangular drain construction

Cost Analysis of Trapezoidal Drain

trap 063228
Trapezoidal drain details

Excavation
Volume of soil = [0.5(0.8 + 1.65) × 0.95] × 1 = 1.164m3
Unit cost of excavation = ₦1,500
Cost of excavation = 1.164 × 1,500 = ₦1,745

Concrete in blinding
Volume of concrete = 0.05 × 0.8 × 1 = 0.04m3
Unit cost of concrete = ₦55,000
Cost of concrete material = 0.04 × 55,000 = ₦2,200

Concrete on drain
Volume of concrete = [0.5(1.65 + 0.8) × 0.9] – [0.5(0.5 + 1.35) × 0.75] = (1.1025 – 0.69375) × 1 = 0.409m3
Unit cost of concrete = ₦55,000
Cost of concrete material = 0.409 × 55,000 = ₦22,495

Reinforcement
Bar Mark 1 = 6 × 2.6 × 0.617 = 9.626 kg
Bar Mark 2 = 14 × 1 × 0.617 = 8.638 kg
Total weight of rebar = 9.626 + 8.638 = 18.264 kg

Unit cost of rebar = ₦450
Cost of rebar = 18.264 x 450 = ₦8,220

Formwork
Walls = 2(0.865) × 1 = 1.73m2
Unit cost of formwork = ₦5,400
Total cost of formwork = 1.73 × 5,400 = ₦9,345

images 12
Trapezoidal drain construction

The table below shows the cost comparison of the rectangular and trapezoidal drains;

Cost component Rectangular SectionTrapezoidal Section% reduction or increment
Excavation₦2,295₦1,745– 23.97%
Concrete in blinding ₦4,675₦2,200– 52.94%
Concrete in drain₦20,625₦22,495+ 9.07%
Reinforcement₦8,220₦8,220—
Formwork₦16,740₦9,345– 44.18%
Total₦52,555₦44,005– 16.27%

Conclusion

The article has discussed the cost comparison of rectangular and trapezoidal drain cross-sections per meter run for a particular peak discharge. From the cost analysis, it can be deduced that the cost of concrete in drain required for the trapezoidal drain is 9.07% higher than that of the rectangular drain. However, there are significant reductions of 23.97% in excavation cost, 52.94% in concrete blinding cost, and 44.18% in formwork cost for the trapezoidal drain over the rectangular cross-section.

Furthermore, there is an overall cost reduction of 16.27% if the choice of drain cross-section is trapezoidal. Similarly, suppose the labour cost is directly related to the quantity of materials. In that case, adopting the trapezoidal cross-section is expected to result in savings on the cost compared to a rectangular cross-section. This justifies that trapezoidal cross-sections are usually the most economical, provided there is a right-of-way (ROW).

Standard Penetration Test (SPT) for Foundation Design

By
Ubani Obinna
-

The standard penetration test (SPT) is made in boreholes by means of the standard 50.8 mm outside and 33.8 mm inside diameter split spoon sampler. It is a very useful method for estimating the in-situ density of cohesionless soils, and when modified by a cone end, it can also be used to assess the relative strength or deformability of rocks.

An automatic trip device triggers repeated strikes from a 63.5 kg weight falling freely through 760 mm, driving the sampler to a penetration of 450 mm.The only blows counted as part of the conventional penetration number are those for the final 300 mm of driving (N-value). For the entire 450 mm of drive, it is standard practice to count the blows for every 75 mm of penetration.

By doing so, it is possible to determine the depth of any disturbed soil in the borehole’s bottom and the height at which any obstacles to driving, such as cobblestones, huge gravel, or cemented layers, are encountered. In the test, typically no more than 50 blows are made (including the number of blows necessary to position the sampler below the disturbed zone).

Both the depth at the start of the test and the depth at which it is concluded must be given in the borehole record if the full 300mm penetration below the initial seating drive is not achieved, i.e., when 50 blows are made before full penetration is achieved. Appropriate symbols must be used to indicate whether the test was completed within or below the initial seating drive. The tube is disassembled for analysis of the soil samples after removal from the borehole (see Figure 3).

SPT TEST
Figure 1: Driving sequence in an SPT test

In gravelly soil and rocks the open-ended sampler is replaced by a cone end. Investigations have shown a general similarity in N-values for the two types in soils of the same density.

The standard penetration test was first developed in the USA as a simple tool to determine the density of soils. The test was adopted by various nations throughout the world, and numerous relationships between the test results and soil characteristics and analytical methods were developed.

According to published data, test methodologies vary greatly across different countries. Non-standard types of hammers and samplers were being utilised, and there were several ways to manage the hammer drop, including free-fall or rope and pulley arrangement.

SPT TEST IN PROGRESS
Figure 2: Typical SPT hammer set up

The two most common types of SPT hammers used in the field are the safety hammer and donut hammer. They are commonly dropped by a rope with two wraps around a pulley (see Figure 2).

Correction Factors to SPT Test

There are several factors that will contribute to the variation of the standard penetration number, N, at a given depth for similar soil profiles. These factors include SPT hammer efficiency, borehole diameter, sampling method, and rod length factor.

Split spoon sampler for SPT
Figure 3: Split spoon sampler for SPT

It therefore became evident that if the test data were to be used for correlation with different soil parameters, as will be explained below, corrections to N-values produced by non-standard techniques would be required. The following is a summary of the correction factors that should be applied to the measured blow-count.

The primary correction is focused on the energy that the drill rods and hammer send to the sampler. This has been normalised using a 60% of the theoretical maximum energy ratio (ERM). The term N stands for the measured blow-count , while N60 stands for the hammer energy correction. A further correction is applied to allow for the energy delivered by the drill rods. The N60 value is corrected to N by multiplying N’60 by 0.75 for rod lengths of 3 m or shorter. The correction factor is unity for lengths greater than 10 m. No correction for sampler size or weight is necessary if a British Standard or ASTM standard sampler is used.

Thus;

N60 = N(ERm/60) = NCE ——– (1)

where ERm is the energy ratio and CE is the 60% rod energy ratio correction factor. Correction factors for rod lengths, sampler type, borehole diameter, and equipment (60% rod energy ratio correction) are given in Tables 1 – 4.

SPT TEST SET UP
Figure 4: Set up of SPT in site

In the field, the magnitude of ERM can vary from 30 to 90%. The standard practice now in the U.S. is to express the N-value to an average energy ratio of 60% (≈ N60). Thus, correcting for field procedures and on the basis of field observations, it appears reasonable to standardize the field penetration number as a function of the input driving energy and its dissipation around the sampler into the surrounding soil, or;

N60 = NCHCBCSCR/60 ——– (2)

where N60 = standard penetration number corrected for field conditions
N = measured penetration number
CH = hammer efficiency (%)
CB = correction for borehole diameter
CS = sampler correction
CR = correction for rod length

CountryHammer TypeHammer Release CH (%)
JapanDonut
Donut		Free Fall
Rope and pulley		78
67
USASafety
Donut		Rope and pulley
Rope and pulley		60
45
ArgentinaDonutRope and pulley45
ChinaDonutFree fall
Rope and pulley		60
50
Table 1: Variation of hammer efficiency with hammer type and hammer release

Diameter (mm)Diameter (inches)CB
60 – 1202.4 – 4.71.0
15061.05
20081.15
Table 2: Variation of borehole correction factor with borehole diameter

VariableCS
Standard sampler1.00
With liner for dense sand and clay0.80
With liner for loose sand0.90
Table 3: Variation of sampler correction factor with sampler type

Rod length (m)CR
> 101.0
6 – 100.95
4 – 60.85
0 – 40.75
Table 4: Variation of rod length correction factor with rod length

Worked Example on SPT Number Calculation

The blow counts for an SPT test at a depth of 6 m in a coarse-grained soil at every 150mm are 9, 16, and 19. A donut automatic trip hammer and a standard sampler were used in a borehole 152 mm in diameter.

(a) Determine the N value.
(b) Correct the N value for rod length, sampler type, borehole size, and energy ratio to 60%.
(c) Make a preliminary description of the compactness of the soil.

Strategy:
The N value is the sum of the blow counts for the last 0.304 m of penetration. Just add the last two blow counts.

Solution

Step 1: Add the last two blow counts.
N = 16 + 19 = 35

Step 2: Apply correction factors.
From the Tables above;
CH = 60%
CB = 1.05
CS = 1.00
CR = 0.95

N60 = NCHCBCSCR/60 = (35 × 60 × 1.05 × 1.00 × 0.95)/60 = 34

Step 3: Use Table 5 to describe the compactness.
For N = 34, the soil is dense.

Correlations Using SPT

Although the applications of SPT results are entirely empirical, their extensive use has allowed for the accumulation of vast knowledge regarding the behaviour of foundations in sands and gravels. Relationships between N-values and properties like density and shearing resistance angle have been identified.

BS 5930 gives the following relationship between the SPT N-values and the relative density of a sand as shown in Table 5;

N’60 (blows/300 mm
of penetration)		Relative DensityDr (10%)
Below 4Very loose< 20
4 – 10Loose20 – 40
10 – 30Medium – Dense40 – 60
30 – 50Dense60 – 80
Over 50Very dense> 80
Table 5: Relationship between SPT number and the relative density of soil

Some correlations of the SPT with soil characteristics, in particular the susceptibility of a soil to liquefaction under earthquake conditions, require a further correction to N’60 to allow for the effective overburden pressure at the level of the test. In granular soils, the standard penetration number is highly dependent on the effective overburden pressure.

A number of empirical relationships have been proposed to convert the field standard penetration number N60 to a standard effective overburden pressure σ0‘, of 96 kN/m2 (2000 lb/ft2). The general form for standard sampler is;

N’60 = CNN60 ——– (3)

Several correlations have been developed over the years for the correction factor, CN. In standard geotechnical engineering textbooks, two of these given in Equations (4) and (5) are recommended for use (SI Units);

CN = 9.78√(1/σ0‘) ——– (4)

or

CN = 2/(1 + 0.01σ0‘) ——– (5)

Values of CN derived by Seed et al (1984) are shown in the Figure below;

CORRECTION FACTOR
Figure 5: Correction factor to N’ value to allow for overburden pressure

Correlation of SPT with Cohesive Soils (Clays)

The consistency and unconfined compressive strength (qu) of clay soils can be estimated from the standard penetration number N60. It is important to point out that the correlation between N60 and unconfined compressive strength is very approximate. The sensitivity, St, of clay soil also plays an important role in the actual N60 value obtained in the field. In any case, for clays of a given geology, a reasonable correlation between N60 and qu can be obtained as shown in Equation (6).

qu/Pa = 0.58N600.72 ——– (6)

Where Pa is the atmospheric pressure (in the same unit with qu).

Standard Penetration Number N60ConsistencyConsistency IndexUnconfined Compressive Strength kN/m2 (lb/ft2)
< 2Very soft< 0.5< 25 (500)
2 – 8Soft to medium0.5 – 0.7525 – 80 (500 – 1700)
8 – 15Stiff0.75 – 1.080 – 150 (1700 – 3100)
15 – 30Very Stiff1.0 – 1.5150 – 400 (3100 – 8400)
> 30Hard> 1.5> 400 (8400)
Table 6: Approximate Correlation between Consistency Index, N60, and qu

Stroud (1975) has established relationships between the N-value, undrained shear strength, modulus of volume compressibility, and plasticity index of clays as shown in Figure 6.

relationship between SPT and cohesion
Figure 6: Relationship between SPT number, plasticity index, and undrained shear strength of clay soil
relationship between SPT and volume of compressibility
Figure 6: Relationship between SPT number, plasticity index, and compressibility of clay soil

It is not advised to use the SPT in place of the direct approach of conducting laboratory tests on undisturbed samples to determine the shear strength and compressibility of clay soils. This is due to the fact that the correlations between the SPT and the strength and deformability of clays have only been established empirically, with no consideration of time effects, anisotropy, or the composition of the soil.

Correlation of SPT with Cohesionless Soils (Sands)

The drained angle of friction of granular soils, ϕ’, also has been correlated to the standard penetration number. Peck, Hanson, and Thornburn (1974) gave a correlation between (N1)60 and ϕ’ in a graphical form, which can be approximated as;

ϕ'(degrees) = 27.1 + 0.3(N1)60 – 0.00054(N1)602 ——– (8)

Schmertmann (1975) also provided a correlation for N60 versus σ0‘. After Kulhawy and Mayne (1990), this correlation can be approximated as;

ppo

Where Pa is the atmospheric pressure in the same unit as σ0‘.

Terzaghi and Peck also give the following correlation between SPT value, Dr, and φ as shown in Table 7.

ConditionNDr (%)ϕ’
Very loose0 – 40 – 15< 28°
Loose4 – 1015 – 3528° – 30°
Medium10 – 3035 – 6530° – 36°
Dense30 – 5065 – 8536° – 42°
Very dense> 50> 85> 42°
Table 7: Correlation between SPT value, Dr, and φ

Conclusion

The SPT can be completed quickly and easily. The equipment can penetrate dense materials and is widely available  The engineering characteristics of soils such as bearing capacity and foundation settlement have all been linked to SPT results. However, the majority of these correlations are marginal.

Errors can come from a variety of sources, such as test performance and the use of non-standard equipment. The incorrect lifting and dropping of the hammer, inadequate borehole cleaning prior to the test, and failure to maintain the groundwater level, if one exists, are examples of test performance errors. These mistakes result in N values that are not typical of the soil. For coarse gravel, boulders, soft clays, silts, and mixed soils containing boulders, cobbles, clays, and silts, SPT tests are unreliable.

Application of Digital Twin to Zagreb’s Water Distribution Network

By
Charity Mmuo
-

A digital twin is computer software that simulates how a process or product would work using data from the real world. To improve the output, these systems can use artificial intelligence, software analytics, and the internet of things. These virtual models have become a mainstay in contemporary engineering to spur innovation and boost efficiency thanks to the development of machine learning and elements like big data.

To put it briefly, developing the digital twin of a system can enable the advancement of major technological trends, prevent expensive breakdowns in physical items, and test processes and services utilizing enhanced analytical, monitoring, and predictive skills.

According to a report by Bentley Systems, their software OpenFlows and OpenUtilities software have been used to address the water distribution challenges in Zagreb, the capital city of Croatia. A digital twin created for the system/model has also helped in the management of the system. Bentley Systems offer a lot of software solutions in infrastructure.

digital twin
Typical digital twin model [Source: Bentley Systems]

Managing a Water Supply Network that is Over a Century Old

One of the world’s oldest operational water networks, the 144-year-old Zagreb water delivery system was first built in 1878. Around 30,000 people lived in Zagreb, the capital of Croatia, at the time, with 11,150 of them having access to a water delivery system with a 4-kilometer radius and a 53.2 liters per second capacity. Since then, the population has increased, resulting in a daily water intake of 310,000 cubic meters and the need for water services for approximately 900,000 people over an area of 800 square kilometers delivered by an enlarged network extending 3,500 kilometers.

The public water supply and sewerage business in Zagreb, ViO Zagreb, appointed the company Hidroing the duty of digitizing the system to better manage the network because the water loss have increased dramatically over the previous two decades and have become significantly worse since the occurrence of the 2020 earthquakes.

water loss 1

Construction of a Digital Supply System

For the network’s ensuing thirty years of operation, ViO anticipated that Hidroing would provide a thorough master plan and water loss program. Hidroing was required to create a comprehensive hydraulic model for the EUR 1 million project based on an updated GIS model that allowed for full diagnostic of the supply system, district meter area (DMA) zoning, and numerous measurement locations. Hidroing, however, encountered considerable problems with data collecting and had trouble detecting flow, pressure, and chlorine levels.

WATER DISTRIBUTION NETWORK

They concluded they needed an integrated hydraulic modeling solution to enable intelligent water management in order to meet the owner’s expectations for digitizing the water supply network.

Hydraulic Modeling is Provided by Bentley Applications

Hidroing chose Bentley’s OpenFlows and OpenUtilities solutions for GIS (Geographic Information System) creation, 3D modeling, hydraulic modeling, on-site operations, and facility management after carefully weighing their options. A hydraulic model of the complete network was built and calibrated using 3,000 measurement locations, 144 DMA zones with unique situations, and 3,500 kilometers of pipeline.

Analyze and visualize utilities networks EDITED
Bentley OpenUtilities

They established a smooth connection for data integration by sharing statistical data between the model and the GIS platform using Bentley’s cutting-edge technology. One of the biggest digital twin models in Eastern Europe was developed with the help of the hydraulic modeling solution.

Smart Water Management is Powered by Digital Twin

According to Bentley Systems, Hidroing shortened the production and application of the calibrated hydraulic model for water loss reduction by 16 months by utilizing Bentley’s integrated modelling and analysis technologies. The initial timeframe for developing the GIS platform and producing and calibrating the model was 36 months. However, in under 20 months, they were able to create a finished model and digital twin that identified over 50 steps to reduce water loss utilizing OpenFlows and OpenUtilities.

Carbon-Positive Hotel Development in Colorado

By
Charity Mmuo
-

Concrete is one the most utilised construction material in the world because it is strong, readily available, durable, and adaptable. However, numerous studies have shown that can concrete is also one of the most harmful materials to the environment due to its large carbon footprint. The concrete and cement industry contributes to about 8% of the world’s carbon emissions. This therefore reinforces the need for carbon-positive sustainable construction.

According to the Paris Agreement, emissions from iron and steel, as well as cement and concrete and other sectors, must be net-zero by 2050 – 2070 or the owners will suffer the marginal cost of negative emissions at that time.

global CO2 emmisions by industry
Global CO2 emmisions from industry [Source: World Economic Forum]

To achieve net-zero CO2 emissions in these industries, material efficiency must be improved to minimize primary demand for these materials, more and higher-value recycling must be implemented, and production must be decarbonized. As a result, the project team of hotel development in Denver, Colorado, is meticulous about creating and adhering to its carbon budget, because the plans for a new hotel in Colorado call for a concrete structure that is carbon-positive.

According to Grant McCargo, co-founder, CEO, and Chief Environmental Officer of real estate developer Urban Villages, “The built environment, including homes, accounts for 45 percent of the global carbon footprint every year, and as developers, we need to take some responsibility for that impact. Because of this, we made the brave decision to become carbon positive, which means that this hotel will offset more carbon than it produces“.

According to McCargo, Urban Villages is building the hotel with sustainable design and construction elements to stay under its 4,397 MT CO2e structural carbon budget (This equates to the annual energy consumption of 530 houses.)

Exterior of the Hotel

The hotel is being built on a 10,000 square foot triangle-shaped plot of land in downtown Denver, at the junction of 14th Street and West Colfax Avenue. The famous location is next to Civic Center Park, a 12-acre public park encircled by historic government and museum structures, including the Colorado State Capitol.

The hotel will rise 13 floors and feature 265 guest rooms when it is finished, which is expected to be in late 2023. The hotel’s name, Populus, is derived from the aspen trees of Colorado, scientifically known as Populus tremuloides, which are represented on the spectacular front with domed windows.

Americas First Carbon Positive Hotel Begins Construction in Colorado 3

The first carbon-positive hotel in the United States, according to reports, will be Populus. The project’s carbon-positive objectives will also be helped by a major ecological effort off-site, including a preliminary promise to plant trees equivalent to more than 5,000 acres of forest, according to McCargo. This offset of embodied carbon is roughly equal to 500,000 gallons of gasoline. Urban Villages intends to plant more trees in the future to reduce the energy needed to run the hotel.

A Paradigm Shift in Conventional Design

The initiative got off the ground in 2017 when the city of Denver requested hotel proposal submissions. According to McCargo, his company filed a proposal in an effort to make a lasting impression on Civic Center Park, which was originally created as part of the city’s 1867 bid to become the state capital. Recently, the city invested millions on reviving the park.

According to McCargo, “We appreciated the opportunity to go in and make a huge difference. We were chosen for the project, not because we had the lowest bid, but rather because they trusted us to make a positive change“.

To achieve this, Urban Villages collaborated with renowned architecture firm Studio Gang on a plan that would be both aesthetically pleasing and environmentally beneficial, the latter of which involved completely transforming the location of Denver’s first gas station. The ambitious project attracted Studio NYL, who was keen to take on the role of structural and façade engineer.

According to Chris O’Hara, P.E., founding principal of Studio NYL, “The kind of work that we take on has some aspirational purpose – sometimes it’s performance, sometimes it’s establishing aesthetics.” This project aims to be a carbon-positive building during its lifespan in addition to being an iconic structure in a key location.

The majority of the hotel’s carbon-positive objectives will be met through building operations, but O’Hara points out that a number of structural elements, such as the façade and concrete mix, will significantly boost its effectiveness.

Aerial View of the Hotel’s Roof and Exterior

In order to create a high-performance building and reduce the number of mechanical systems required to maintain it, O’Hara asserts that a tight envelope was crucial. “The main goal for the structure is to reduce the quantity of carbon in the concrete. As structural engineers, we make a great effort to limit material consumption and stick to our carbon budget.

Aerial view of Hotel being built with Carbon-Positive Concrete
Aerial view of the hotel’s Roof and Exterior ( Courtesy of Studio Gang)

Low-Carbon Concrete

The team decided on reinforced concrete despite its high embodied carbon because of the project’s tight design requirements. According to O’Hara, the site’s geometry, height restrictions imposed by sightlines to the state building, and the square footage all contributed to the necessity of using concrete.

According to O’Hara, “All of these many things made a flat slab concrete system most appropriate to the architecture.” So, the true question was, “How can we take a building with so much cement in it and make it efficient from carbon perspective?”

The team is employing a number of strategies to reduce the amount of concrete in the project in order to achieve that goal. According to O’Hara, these include maximizing slab continuity, positioning columns to benefit from external cantilevers, and reducing column transfers while taking into account the effects on the necessary amounts of steel reinforcement.

According to O’Hara, the integration of the column arrangement and cantilevers with the unit layout and the façade support system are the most crucial components. The design team assessed a range of spacing options and cantilevers to work with the unit needs and mechanical circulation, and how those interacted with the main level and amenity needs, with the goal of reducing the amount of material used.

To stay within the carbon budget, the team will employ low-carbon concrete in addition to keeping the amount of concrete in the project to a minimum. For instance, the use of fly ash lowers the carbon content of concrete, and a minimum of 20% fly ash replacement was adopted in the project. The embodied carbon for each form of concrete placement, such as the drilled piers, walls, columns, flat slabs, was kept to a minimum.

According to O’Hara, carbon sequestration, a procedure that turns carbon dioxide into a mineral that is indelibly incorporated into concrete, could further further reduce the amount of carbon in the concrete. Although carbon sequestration is not yet taken into account in the embodied carbon budgets of the project, but O’Hara believes that incorporating carbon sequestration in their mix design is a top priority for the project team.

Façade Style

The hotel’s envelope will be crucial to fulfilling the project’s carbon-positive objectives, just like the concrete mix is. The facade’s style is pleasing to the eye and is reminiscent of the aspen trees seen throughout the state. According to McCargo, “As an aspen tree grows, the branches fall off lower down with most of the canopy up higher. Where those branches fall off, it makes this charcoal gray eye-shaped eyelet. So, when you look at the facade and think, ‘Wow, look at all of those different windows,’ it’s mimicking what the trunk of the tree looks like, and it creates a fun shape”.

aspen tree
Aspen Tree
FACADE STUDIOGANG
Facade Style (CREDIT : Studio Gang)

Fenestration

The positioning and design of the windows are meant to lower the building’s energy requirements in addition as producing quirky patterns on the front. The dome-shaped window design also enables self-shading, which further reduces solar gain, according to O’Hara. “We have a truly opaque system with less vision glass than many buildings of this typology, which means our solar heat gain is substantially less,” he says. “Having that vision glass well shaded was a major part in terms of getting improved building performance in Colorado, with the high solar intensity.”

Window
The rooms inside Populus will be minimal with views of the surroundings

The procedure for fastening the façade to the building is another vital component in attaining the project’s carbon-positive goals. Glass fiber reinforced concrete panels around 20 feet tall by 10 feet wide will make up the façade. The panels will attach at the floor lines every 10 feet with dead weight anchors, as opposed to a standard rain screen that fastens to the structure every 24-48 inches, according to O’Hara. With fewer potential thermal bridges in the façade, he explains, “we can reduce the amount of thermally damaged connections we need.”

Industry Standard

The project team believes that by taking deliberate measures to reduce the amount of carbon in the building’s structure, the hotel will be well-positioned to accomplish the remainder of its carbon-positive goals through building operations. This, according to McCargo, includes composting, off-site renewable energy, and everyday operational effectiveness. When you look at this project holistically in terms of how it will be run and managed, that’s where a lot of the carbon objectives are fulfilled, O’Hara acknowledges, “We can do only so well with a concrete building.”

Although building activities will ultimately turn this project into a carbon-positive one, O’Hara believes that strict carbon budgets like this will eventually become the standard.

Every project that leaves this office is currently undergoing a life-cycle assessment, he says. “We believe that without measurement, management is impossible. As we move through the schematic design, we will begin informing our project partners about the carbon footprints of the various material possibilities, whether or not they want to know. Owners may choose to ignore such information, but it is our responsibility to at least provide them with it so they can make wise judgments.

According to Mere Hall, P.E., S.E., senior associate of NYL Studio, as more developers become aware of this knowledge, it is anticipated that more will take the environmental effects of their projects into account. The major objective, according to her, is to disseminate information so that people may begin having conversations that will advance efforts toward greater environmental sustainability. “I sincerely hope that this becomes the industry norm and a component of the services we offer to advance projects.”

Introduction of Smart Motorways Technology to the Bruce Highway, Queensland Australia

By
Charity Mmuo
-

Motorways with information, communications, and control systems built into and alongside the road are referred to as “smart motorways” (also known as controlled motorways). These technology-based systems are used to actively regulate traffic flows, increase road capacity, and improve road safety. They also provide other significant benefits for road users, such as improved trip reliability and real-time traveller information.

Smart motorway employs traffic management techniques to expand capacity and lessen congestion in particularly congested regions. The hard shoulder can be used as a running lane, and variable speed limits can be used to manage traffic flow. By minimizing the need to add more lanes, Highways England (formerly the Highways Agency) developed smart motorways to manage traffic in a way that minimizes its negative effects on the environment, cost, and construction time.

featured 1

Smart motorways comprise an integrated package of intelligent transport systems (ITS) interventions. This includes coordinated ramp signaling, speed and lane use management, traveler information (using variable message signs) and network intelligence (such as from vehicle detection equipment).

The Department of Transport and Main Roads has disclosed that new traffic control technology would be installed along a 60-kilometer stretch between Pine River and Caloundra Road in Queensland, Australia order to monitor traffic conditions in real-time. Agencies will be able to proactively monitor changing situations like accidents, inclement weather, or congested traffic conditions by using ramp signals, variable speed limit and message signs, vehicle detection systems, and CCTV cameras.

According to the Federal Minister for Infrastructure, Transport, Regional Development, and Local Government, Catherine King, “As part of our commitment to improving the safety and performance of our national highways, the Australian Government has allocated $84 million towards this project, which is part of the 15-year, $13 billion Bruce Highway Upgrade Program.”

An illustration of smart motorways technology.
(Image Credit: LLOT WORLD)

At various sites throughout the project corridor, targeted vegetation clearing, site establishment, investigative activities, and earthworks will also take place. Widening the southbound entry ramp to the Bruce Highway and installing a number of technology, such as ramp signaling, variable speed limit signs, and a new shared route across the highway, are both being prepared for near Caboolture-Bribie Island Road.

To track vehicle travel durations, traffic flow, and speed, the initiative will install wireless traffic sensors at strategic spots along the highway. The coverage and resolution offered by these traffic sensors will be sufficient to track the operation of the highway in real-time.

The majority of the work will be done at night to minimize inconveniences due to the high traffic loads. The safety of drivers and road workers will be ensured by traffic controllers, slower speed restrictions, and signs.

Weather and building circumstances permitting, construction is anticipated to be finished in 2024. The Australian and Queensland governments split the $105 million cost of the Bruce Highway – Managed Motorways Stage 2 – Gateway Motorway to Caloundra Road Interchange project 80:20.

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