DMRB Flexible Road Pavement Design Using Re-Engineered Expansive Road Subgrade Materials with Varying Plasticity Index
1
Civil Engineering Cluster, Department of Geography and Environmental Management, Faculty of Environment and Technology, University of the West of England, Bristol BS16 1QY, UK
2
Faculty of Environment and Technology, University of the West of England, Bristol BS16 1QY, UK
*
Author to whom correspondence should be addressed.
Geotechnics 2022, 2(2), 395-411; https://0-doi-org.brum.beds.ac.uk/10.3390/geotechnics2020018
Submission received: 23 April 2022
/
Accepted: 30 April 2022
/
Published: 12 May 2022
Abstract
:Pavement thickness is a very vital component during the design stage of a road construction project. Pavement design helps to determine the costs of the project over a certain period to ascertain how the cost of road pavement construction affect the life cycle cost of the road. Road pavements are designed based on the type of subgrade material and the expected traffic load to help clients and decision-makers make decisions on the project. In this study, expansive road subgrade materials were improved using lime and cement and their California Bearing Ratio (CBR) was used in road pavement design. The study used the Design and Manual for Roads and Bridges (DMRB) as a guide to investigating the effect of stabilised expansive road subgrade with varying CBR values on road pavement design. The mineral structure, characteristics, Atterberg limit, compaction CBR, swell and microstructural analysis (scanning electron microscopy (SEM) and Energy Dispersive X-ray (EDX)) of stabilised subgrade materials were investigated. The results show an increase in California Bearing Ratio (CBR) values and a reduction in swell values while curing age increased for stabilised subgrade materials. Treated samples show high Calcium Silicate Hydrate (C-S-H) gel formation after 7 and 28 days of curing. The thickness of road pavement was observed with an increase in CBR values. The study established that the thickness of road pavement and overall construction cost can be reduced using cement and lime as additives in subgrade stabilisation.
1. Introduction
In this study, flexible road pavement design was carried out for various traffic loads, and California Bearing Ratio CBR values were achieved in this study in accordance with the Design Manual for Road and Bridges (DMRB) for re-engineered Artificially Synthesised Subgrade (ASS). The impact of using treated and untreated expansive road subgrade with varying plasticity CBR values in flexible road pavement design used for light and heavy traffic were investigated. A mixture of untreated bentonite and kaolinite at various percentages was used to form an Artificially Synthesised Subgrade (ASS) with properties similar to an already existing expansive subgrade. The study conducted Atterberg limits and compaction test for untreated ASS materials to determine their moisture content and characteristics. ASS materials were further stabilised using cement and lime to improve their engineering properties for use as subgrade materials in road construction. Road pavements are superimposed processed materials placed over natural subgrade to carry traffic load and provide adequate skid resistance. Pavements are designed based on various factors, such as traffic load, CBR and many more, which helps in decision-making by determining the cost of the road project based on the design [1,2]. Road pavement construction takes more than 50% of the overall constriction cost, especially where weak subgrade is involved, which can cause defects and failure, leading to a high cost of maintenance and sometimes a total reconstruction of the road [3,4]. China, the United States and the UK have spent up to $US30 billion and £3 billion on maintenance costs due to infrastructure built on expansive soils [5,6]. Reference [7] stated that millions of dollars are spent on damage caused by expansive road subgrade. In this study, cement and lime were used as binders in subgrade stabilisation. Cement and lime have been used for decades in the improvement of subgrade materials due to their ability to form calcium silicate hydrate gel (C-S-H) gel during the hydration process responsible for strength gain [4,8]. C-S-H gel binds subgrade particles together, making cement suitable for subgrade stabilisation [3,9]. Reference [10] used cement in proportions of 4% and 15% in subgrade stabilisation. During lime hydration, C-S-H gel is produced on enhancing strength in a mix [11]. Lime stabilisation is recommended for subgrade with a liquid limit from 25% to 50% and plasticity between 20% and 30% [12]. Reference [13] achieved good CBR values after using 3–8% lime in subgrade stabilisation, while reference [14] used 1% of lime in expansive subgrade stabilisation. Figure 1a–d shows wet and dry expansive soil and road pavement defects caused by expansive subgrade. Figure 2 shows how the results achieved in this study can be applied in real-life road construction, and Table 1 shows the merits and demerits of treating road subgrade and subgrade removed and replaced with imported materials.
2. Materials and Methods
In this study, bentonite and kaolinite were used to form ASS subgrade ASS 1 (25% bentonite + 75%koilinte), ASS 2 (35% bentonite + 65% kaolinite) and ASS 3 (75% bentonite + 25% kaolinite). Details regarding the suppliers of the materials used, their oxide, chemical, mineralogy and particle size distribution can be found in reference [15]. Laboratory synthesised expansive road subgrade were formulated in accordance with BS 1924-1:2018 [16] and was used as the target material in this study. The Atterberg limits, compaction, swell and CBR tests were carried out on stabilised and unstabilised ASS materials to determine their bearing capacity and swell potentials for use in road construction. Microstructural properties were conducted for stabilised ASS to ascertain the effect of additives on strength development in subgrade materials. Further details including sample preparation and laboratory testing exercise are as reported in the authors’ previous study [15]. Flexible road pavement design was conducted using the CBR values achieved in this study in accordance with DMRB, CD 226 [17], DMRB HD 26/06 [18] and IAN 73/06 [19] using varying design traffic loads to determine the effect of varying traffic load and CBR on road pavement design. KENPAVE road pavement analysis software was used to analyse the stresses at various response points within the layers of the selected pavement structure. Compaction and Atterberg limits tests were conducted in accordance with BS EN 13286-2-2012 [20], BS EN ISO 17892-12-2021 [21], BS 1377-4-1990 [22], ASSHTO T265 [23], ASTM D2216-19 [24], ASTM D4318-17e1 [25], AASHTO T90 [26] and ASSHTO T89 [27] were used in their optimum moisture content (OMC) and maximum dry density (MDD) determination. Figure 3 shows the methodological process used in this study to achieve the set aim of this study.
3. Results and Discussion
Californa Bearing Ratio (CBR) and Microstructural Characteristics
Untreated ASS materials recorded the highest CBR values of 9% and 2% for unsoaked and soaked ASS 3 composed of high bentonite content, while ASS 1 recorded a CBR value of 8% for untreated and 0.9% for untreated soaked and ASS 2 observed 5% CBR for untreated and 0.8% for untreated soaked ASS samples. The CBR values achieved for soaked untreated ASS materials are unacceptable for use in road construction. Ref. [18] states that CBR values <2% are unacceptable for use in road construction. Treated ASS 2 recorded the highest CBR value of 100%, while ASS 1 and ASS 3 recorded CBR values of 90% and 80% after 28 days of curing. CBR value for treated ASS materials decreases with an increase in bentonite content. According to [15], high plasticity subgrade exhibits high bearing capacity. High plasticity soil has good CBR values [28]. After treating ASS samples using cement and lime, CBR values for ASS 1 (8%) increased to 80% and 90% after 7 and 28 days of curing; a CBR value of 5% was recorded for ASS 2, and increased to 60% and 100% after 7 and 28 days of curing; and a CBR value of 9% for ASS 3 increased to 30% and 80% after 7 and 28 days of curing. An overall decrease in CBR value was observed as bentonite content increased. The increase in CBR value observed after treating ASS materials using cement and lime was due to the formation of calcium silicate hydrate (C-S-H) gel in the mix, which is responsible for strength gain. C-S-H gel acts as a binder to hold soil particles together. Cement and lime produce C-S-H gel during the hydration process, which is responsible for strength gain [3,29]. The formation of C-S-H gel in treated samples increased with an increase in curing age. This accounts for the high increase in CBR values for treated ASS materials as curing age increases. The formation of C-S-H gel was observed after conducting Scanning Electron Microscopy (SEM) analysis on treated ASS materials. A clear formation of calcium silicate hydrate (C-S-H) gel and calcium aluminate hydrate (C-A-H) gel was observed in ASS samples, and the C-S-H formation in ASS samples increased as curing age increase. ASS 1 recorded calcium formation of 16.21%, ASS 2 at 30.51% and ASS 3 at 21.96% after 7 days of curing. After 28 days of curing, C-S-H gel formation increased with ASS 1 recording calcium formation of 24.75%, ASS 2 at 32.56% and ASS 3 at 33.08%, respectively [15]. This translated into an increase in CBR value with an increase in curing age. According to references [3] and [30], the continuous formation of C-S-H gel with an increase in curing age within a pore structure can contribute to strength development in a mix. Further details including Energy Dispersive X-ray (EDX) results are reported in the authors’ previous study [15]. Table 2 shows CBR results for treated and untreated ASS materials. Figure 4a–f shows SEM images of ASS sample after 7 and 28 days of curing.
4. DMRB Road Pavement Design
Road pavement design is the process of determining the type and composition of road pavement structure based on various factors, such as type of traffic, the California Bearing Ratio (CBR) of subgrade and many more. Pavement design helps the client and decision-makers to determine the costs of the project over a certain period and investigate the effects of cost, service life and economic inputs on the life cycle cost of the road when making investment decisions [2]. Pavement designs are based on the principle that the flexural strength of the cement-bound roadbase should be greater than the combined traffic and thermal warping stresses experienced during service [31]. There are two major types of road pavement—these are flexible and rigid pavements. Flexible pavement is a pavement structure that includes a combination of aggregate and bitumen; it is heated and blended precisely and then placed and compacted on a bed of granular layer. Traffic load is transferred to the subgrade through the combination of layers. Flexible pavements require proper maintenance to avoid crumbling due to heavy traffic load because it is made up of asphalt, whose viscous nature permits plastic distortion. Although almost all asphalt pavements are constructed on a gravel base, some full-depth asphalt surfaces are constructed directly on the subgrade. There are three different classifications of asphalt depending on temperature: (i) hot mix asphalt (HMA), (ii) warm mix asphalt (WMA), and (iii) cold mix asphalt (CMA) [32]. Rigid pavement is a combination of aggregates and cement. It is blended precisely and then placed and compacted on a bed of granular layer. Rigid road pavement has no subbase and is non-flexible; they are constructed from reinforced concrete. Rigid road consists of three layers and is mostly used to build airport runways and highways and typically provide heavy-duty industrial floor slabs, ports and dock plant pavements and heavy, high traffic park or concluding pavements. Rigid pavements are designed to be long-lasting structures, with high-quality surfaces for the purpose of safe driving. The structural layers of rigid pavement transmit the traffic load to the subgrade. The differences between flexible and rigid pavement are shown in Figure 5.
In this study, flexible road pavement design was carried out based on the CBR values achieved for treated and untreated ASS materials in accordance with the Design Manual for Roads and Bridges (DMRB) CD 226 [17], DMRB HD 26/06 [18] and IAN 73/06 [19], respectively. In this study, a traffic design of 8 msa and 80 msa (million standard axles) were adopted for the pavement design to see the effect of heavy and light traffic design on pavement thickness using varying CBR values. Acceptable CBR values above 2% were achieved in this study, and a stiffness modulus above 30 MPa was adopted (Road Pavement Design Guide, 2000 [34] and IAN73/06 [20]).
A flexible composite pavement construction with performance design Class 3 was adopted due to its durability and cost-effectiveness, compared to a fully flexible pavement [31]. Heavy-duty road pavements are usually built using flexible composite pavement options because it is cheaper, can carry up to about 100 msa and provide the same quality as fully flexible pavement [31]. Composite pavement structures have a Cement Bound Granular Materials (CBGM) base with an asphalt overlay. In this study, a three-layer flexible composite pavement structure was adopted as shown in Figure 6.
Surface Course: a carefully proportioned mixture of bitumen-bound minerals mixed to the required specification. It provides skid resistance, weather resistance and low traffic noise. It can withstand traffic load and transfer the load to lower layers [1].
Base Course: the area immediately under the wearing surface (surface course). The materials used in a base course are extremely high quality, as the base course lies close under the pavement surface and is subjected to severe loading [1].
Subbase Course: this is the lower layer of the road pavement and is made up of cement-bound granular materials containing crushed rock or gravel. It is the foundation of the road and it transfers the load from above to the lower layers [1].
Subgrade: the existing ground, whether improved by stabilisation or compacted to the appropriate level of strength required to carry traffic load. In situations where subgrade materials are not strong enough on their own, a capping course can be provided as a construction platform to work on [1]. Capping courses are generally a layer of granular product from crushed rock quarry and recycled materials. In some circumstances, depending on the particular need of the road being built, a pavement structure may require a binder course at the lower part of the surfacing. Binder course carries part of the load the surface course carries and helps to waterproof lower layers. Binder courses are made up of a type of asphalt concrete with different gradings of aggregate types and quantities [31]. Figure 7a,b were used to determine the thickness and stiffness modulus for the various pavement layers. Based on the design, a hydraulic-bound class (B) CBGM B–C8/10 (or T3) was adopted as subbase materials (See Table 3). A hydraulic bound mixture (HBM) category (B) was adopted as base material (Marked in Table 3) and a hot-rolled asphalt (HRA) was adopted as surface materials in accordance with DMRB CD 226 [17].
After carrying out road pavement design, the results obtained for traffic design 8 msa and 80 msa using subgrade CBR values 5, 8 and 9% obtained in this study are shown in Figure 8a–d. A pavement design software KENPAVE was used to analyses different wheel configurations under linear elastic layer behaviour to determine the behaviour of the layers at various response points in the pavement structure. The study has shown that a significant change in pavement thickness can only be observed for subgrade CBR values from 2–5% when using DMRB in road pavement design guidance. This is because the subbase layer forms a major of the road pavement structure, and class 3 subbase chart offers the thicker subbase layer only for subgrade CBR values between 2–10.5% after which the subbase thickness remains the same (180 mm). Hence, no significant change in pavement thickness was observed, even with a CBR value of 100% achieved for ASS 2 as shown in Table 4c,d. A reduction in road pavement thickness with a rise in subgrade CBR values was observed. Pavement design structure showing the thickness of various layers was carried out for untreated CBR values 5%, 8% and 9% as an example in this study. The results show that a subgrade CBR value of 5% has a thicker pavement structure compared to that of subgrade CBR values of 8% and 9% for traffic design 8 msa and 80 msa, respectively. This shows a reduced pavement thickness with respect to high CBR values. Due to the low CBR values (5%), a thicker pavement is required to limit the rate of pavement deterioration due to stresses from traffic load. According to [31], the thickness of asphalt layers is required to limit stresses and reduce the severity of reflective cracking. Pavement design for the remaining CBR values for treated ASS samples achieved shows similar pavement thickness, with a small change in thickness achieved for the selected traffic design load and their corresponding layer thickness. A reduction in elastic modulus for various layers was observed with a reduction in the CBR value during analysis using KENPAVE, resulting in the determination of layer thickness. Layers with high elastic modulus require thinner layer thickness, and low elastic modulus require thicker layer thickness. Low elastic modulus in a pavement layer means stresses in that layer are high due to applied traffic load, and the thickness of that layer must be increased to reduce the stresses to avoid fatigue. The thickness of asphalt layers is required to limit stresses and reduce the severity of reflective cracking [31]. Pavement thickness for treated and soaked ASS samples are summarised in Table 4a–f of this study.
5. Conclusions
After conducting pavement design for re-engineered artificially synthesised expansive subgrade materials with varying plasticity index using DMRB design guidance, it was observed that pavement thickness increased or reduced in relation to CBR values and elastic modulus within the various layers of the pavement structure. The study also concluded with the following:
- There was no significant difference in pavement thickness for low and high CBR values when using DMRB in road pavement design. A significant change in pavement thickness can only be observed for subgrade CBR values from 2–5% when using DMRB in road pavement design. CBR values and elastic modulus influenced the overall thickness of road pavement.
- This study would benefit the industry in many ways, as road contractors can quickly refer to this study to determine road pavement layer thickness when they encounter subgrade materials with CBR characteristics similar to what was used in this study.
- ASS samples with high bentonite content recorded a high plasticity index with unacceptable swell values greater than 2.5% and acceptable CBR values below 2%.
- Lime and cement were able to improve the engineering properties of ASS materials and reduce swell to the lowest minimum of 0.04%
- CBR value increased with an increase in bentonite content in treated and untreated ASS samples. This proves that bentonite has a high bearing capacity.
- Based on the finding in this study, it is recommended that subgrade materials are stabilised on-site to reduce the cost of construction instead of removing them and replacing them with imported materials.
Author Contributions
Conceptualisation, S.J.A. and S.Y.O.A.; methodology, S.Y.O.A. and S.J.A.; validation, S.Y.O.A. and S.J.A.; formal analysis, S.Y.O.A. and S.J.A.; investigation, S.Y.O.A. and S.J.A.; resources, S.J.A. and C.A.B.; data curation, S.Y.O.A. and S.J.A.; writing—original draft preparation, S.Y.O.A. and S.J.A.; writing—review and editing, S.Y.O.A., S.J.A. and C.A.B.; visualisation, S.J.A. and C.A.B.; supervision, S.J.A. and C.A.B.; project administration, C.A.B. and S.J.A. All authors have read and agreed to the published version of the manuscript.
Funding
This research did not receive any specific grant from funding agencies in the public, commercial or not-for-profit sector.
Institutional Review Board Statement
Not applicable.
Informed Consent Statement
Not applicable.
Data Availability Statement
The data presented in this study are openly available in Materials at https://0-www-mdpi-com.brum.beds.ac.uk/1996-1944/15/8/2773.
Acknowledgments
The authors acknowledge the advice, comments and suggestions from anonymous reviewers significantly improved the quality of this paper.
Conflicts of Interest
The authors declare that they have no conflict of interest associated with this publication, and no financial support has been given to influence the outcome of this work.
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Figure 1.
(a) Typical wet expansive soil [4]; (b) Typical dry expansive soil [4]; (c) Uplifting of flexible pavement [4]; (d) Typical longitudinal crack on road pavement due to expansive subgrade [4].
Figure 2.
The application process of binder agent in real-life road construction.
Figure 3.
The methodological process used in this study.
Figure 4.
(a) Scanning Electron Microscopy (SEM) image results for ASS 1 after 7 days of curing; (b) SEM image results for ASS 2 after 7 days of curing; (c) SEM image results for ASS3 after 7 days of curing; (d) SEM image results for ASS 1 after 28 days of curing; (e) SEM image results for ASS 2 after 28 days of curing; (f) SEM image results for ASS 3 after 28 days of curing.
Figure 4.
(a) Scanning Electron Microscopy (SEM) image results for ASS 1 after 7 days of curing; (b) SEM image results for ASS 2 after 7 days of curing; (c) SEM image results for ASS3 after 7 days of curing; (d) SEM image results for ASS 1 after 28 days of curing; (e) SEM image results for ASS 2 after 28 days of curing; (f) SEM image results for ASS 3 after 28 days of curing.
Figure 5.
Difference between flexible and rigid pavement [33].
Figure 5.
Difference between flexible and rigid pavement [33].
Figure 6.
Three-layer flexible composite pavement structure.
Figure 7.
(a) Class 3 design—single foundation layer (Interim Advice Note (IAN) 73/06) [19]; (b) nomograph for determining the design thickness for flexible pavement (Design Manual for Roads and Bridges (DMRB) CD 226) [17].
Figure 8.
(a) Results for DMRB pavement design traffic 8 msa for untreated subgrade; (b) pavement thickness and three-layered flexible pavement system from KENPAVE for ASS 1, 2 and 3; (c) results for DMRB pavement design traffic 80 msa for untreated subgrade; (d) pavement thickness and three-layered flexible pavement system from KENPAVE for ASS 1, 2 and 3.
Figure 8.
(a) Results for DMRB pavement design traffic 8 msa for untreated subgrade; (b) pavement thickness and three-layered flexible pavement system from KENPAVE for ASS 1, 2 and 3; (c) results for DMRB pavement design traffic 80 msa for untreated subgrade; (d) pavement thickness and three-layered flexible pavement system from KENPAVE for ASS 1, 2 and 3.
Table 1.
Merits of in situ stabilised subgrade and demerits of subgrade removal and replacement [15].
Table 1.
Merits of in situ stabilised subgrade and demerits of subgrade removal and replacement [15].
| Cement/Lime Treated Subgrade | |
|
|
 | |
| In situ soil stabilisation process (Wirtgen-group.com (accessed on 7 May 2022)) | In situ soil treatment process in mixing chamber |
| Removal and Replacement | |
 |
|
| Removal and replace subgrade | |
Table 2.
CBR results for treated and untreated ASS materials.
| Subgrade Type | Mix Design | Treated | Soaked | Curing Days | CBR Values (%) |
|---|---|---|---|---|---|
| ASS 1 | (25%B + 75%K) | x | x | 0 | 8 |
| ASS 1 | (25%B + 75%K) | x | √ | 0 | 0.9 |
| ASS 2 | (35%B + 65%K) | x | x | 0 | 5 |
| ASS 2 | (35%B + 65%K) | x | √ | 0 | 0.8 |
| ASS 3 | (75%B + 25%K) | x | x | 0 | 9 |
| ASS 3 | (75%B + 25%K) | x | √ | 0 | 2 |
| ASS 1 | (8%L + 20%C) | √ | x | 7 | 80 |
| ASS 1 | (8%L + 20%C) | √ | x | 28 | 90 |
| ASS 1 | (8%L + 20%C) | √ | √ | 0 | 50 |
| ASS 2 | (8%L + 20%C) | √ | x | 7 | 60 |
| ASS 2 | (8%L + 20%C) | √ | x | 28 | 100 |
| ASS 2 | (8%L + 20%C) | √ | √ | 0 | 40 |
| ASS 3 | (8%L + 20%C) | √ | x | 7 | 30 |
| ASS 3 | (8%L + 20%C) | √ | x | 28 | 80 |
| ASS 3 | (8%L + 20%C) | √ | √ | 0 | 30 |
Where B = Bentonite K = Kaolinite L = Lime and C = Cement.
Table 3.
Examples of hydraulic bound base materials (HBM) (DMRB CD 226) [17].
Table 3.
Examples of hydraulic bound base materials (HBM) (DMRB CD 226) [17].
| HBM Category | A | B | C | D |
| Crushed rock coarse aggregate: (using aggregate with a coefficient of thermal expansion < 10 × 10−6 < per °C | - | CBGM B–C8/10 (or T3) SBM B1–C9/12 (or T3) FABM1–C9/12 (or T3) | CBGM B–C12/15 (or T4) SBM B1–C12/16 (or T4) FABM1–C12/16 (or T4) | CBGM B–C16/20 (or T5) SBM B1–C15/20 (or T5) FABM1–C15/20 (or T5) |
| Gravel coarse aggregate: (using aggregate with a coefficient of thermal expansion ≥ 10 × 10−6 per °C) | CBGM B–C8/10 (or T3) SBM B1–C9/12 (or T3) FABM1–C9/12 (or T3) | CBGM B–C12/15 (or T4) SBM B1–C12/16 (or T4) FABM1–C12/16 (or T4) | CBGM B–C16/20 (or T5) SBM B1–C15/20 (or T5) FABM1–C15/120(or T5) | - |
| Pavement layers | Materials Description | |||
| Surface course | Hot Rolled Asphalt (HRA) | |||
| Base course | Hydraulic Bound Mixture (HBM) | |||
| Subbase | Cement Bound Granular Mixture (CBGM) | |||
Table 4.
(a) DMRB pavement design for traffic load 8 msa. (b) DMRB pavement design for traffic load 80 msa. (c) DMRB pavement design for traffic load 8 msa. (d) DMRB pavement design for traffic load 80 msa. (e) DMRB pavement design for traffic load 8 msa. (f) DMRB pavement design for traffic load 80 msa.
Table 4.
(a) DMRB pavement design for traffic load 8 msa. (b) DMRB pavement design for traffic load 80 msa. (c) DMRB pavement design for traffic load 8 msa. (d) DMRB pavement design for traffic load 80 msa. (e) DMRB pavement design for traffic load 8 msa. (f) DMRB pavement design for traffic load 80 msa.
| (a) | |||||||||||||||||||||||
| ASS 1 (25% Bentonite + 75% Kaolinite) High Plasticity | ASS 2 (35% Bentonite + 65% Kaolinite) Very High Plasticity | ASS 3 (75% Bentonite + 25% Kaolinite) Extremely High Plasticity | |||||||||||||||||||||
| Flexible Pavement Layers | Material | Thickness (mm) | Treated | Curing (Days) | Soaked | CBR (%) | Design Traffic (msa) | Flexible Pavement Layers | Material | Thickness (mm) | Treated | Curing (Days) | Soaked | CBR (%) | Design Traffic (msa) | Flexible Pavement Layers | Material | Thickness (mm) | Treated | Curing (Days) | Soaked | CBR (%) | Design Traffic (msa) |
| Surface Course | HRA | 130 | Surface Course | HRA | 130 | Surface Course | HRA | 130 | |||||||||||||||
| Base Course | HBM | 160 | Base Course | HBM | 160 | Base Course | HBM | 160 | |||||||||||||||
| Subbase | CBGM | 180 | Subbase | CBGM | 180 | Subbase | CBGM | 180 | |||||||||||||||
| Subgrade | ASS | ∞ | √ | 7 | × | 80 | 8 | Subgrade | ASS | ∞ | √ | 7 | × | 60 | 8 | Subgrade | ASS | ∞ | √ | 7 | × | 30 | 8 |
| Total pavement thickness | 470 | Total pavement thickness | 470 | Total pavement thickness | 470 | ||||||||||||||||||
| (b) | |||||||||||||||||||||||
| ASS 1 (25% Bentonite + 75% Kaolinite) High Plasticity | ASS 2 (35% Bentonite + 65% Kaolinite) Very High Plasticity | ASS 3 (75% Bentonite + 25% Kaolinite) Extremely High Plasticity | |||||||||||||||||||||
| Flexible Pavement Layers | Material | Thickness (mm) | Treated | Curing (Days) | Soaked | CBR (%) | Design Traffic (msa) | Flexible Pavement Layers | Material | Thickness (mm) | Treated | Curing (Days) | Soaked | CBR (%) | Design Traffic (msa) | Flexible Pavement Layers | Material | Thickness (mm) | Treated | Curing (Days) | Soaked | CBR (%) | Design Traffic (msa) |
| Surface Course | HRA | 180 | Surface Course | HRA | 180 | Surface Course | HRA | 180 | |||||||||||||||
| Base Course | HBM | 210 | Base Course | HBM | 210 | Base Course | HBM | 210 | |||||||||||||||
| Subbase | CBGM | 180 | Subbase | CBGM | 180 | Subbase | CBGM | 180 | |||||||||||||||
| Subgrade | ASS | ∞ | √ | 7 | × | 80 | 80 | Subgrade | ASS | ∞ | √ | 7 | × | 60 | 80 | Subgrade | ASS | ∞ | √ | 7 | × | 30 | 80 |
| Total pavement thickness | 570 | Total pavement thickness | 570 | Total pavement thickness | 570 | ||||||||||||||||||
| (c) | |||||||||||||||||||||||
| ASS 1 (25% Bentonite + 75% Kaolinite) High Plasticity | ASS 2 (35% Bentonite + 65% Kaolinite) Very High Plasticity | ASS 3 (75% Bentonite + 25% Kaolinite) Extremely High Plasticity | |||||||||||||||||||||
| Flexible Pavement Layers | Material | Thickness (mm) | Treated | Curing (Days) | Soaked | CBR (%) | Design Traffic (msa) | Flexible Pavement Layers | Material | Thickness (mm) | Treated | Curing (Days) | Soaked | CBR (%) | Design Traffic (msa) | Flexible Pavement Layers | Material | Thickness (mm) | Treated | Curing (Days) | Soaked | CBR (%) | Design Traffic (msa) |
| Surface Course | HRA | 130 | Surface Course | HRA | 130 | Surface Course | HRA | 130 | |||||||||||||||
| Base Course | HBM | 160 | Base Course | HBM | 160 | Base Course | HBM | 160 | |||||||||||||||
| Subbase | CBGM | 180 | Subbase | CBGM | 180 | Subbase | CBGM | 180 | |||||||||||||||
| Subgrade | ASS | ∞ | √ | 28 | × | 90 | 8 | Subgrade | ASS | ∞ | √ | 28 | × | 100 | 8 | Subgrade | ASS | ∞ | √ | 28 | × | 80 | 8 |
| Total pavement thickness | 470 | Total pavement thickness | 470 | Total pavement thickness | 470 | ||||||||||||||||||
| (d) | |||||||||||||||||||||||
| ASS 1 (25% Bentonite + 75% Kaolinite) High Plasticity | ASS 2 (35% Bentonite + 65% Kaolinite) Very High Plasticity | ASS 3 (75% Bentonite + 25% Kaolinite) Extremely High Plasticity | |||||||||||||||||||||
| Flexible Pavement Layers | Material | Thickness (mm) | Treated | Curing (Days) | Soaked | CBR (%) | Design Traffic (msa) | Flexible Pavement Layers | Material | Thickness (mm) | Treated | Curing (Days) | Soaked | CBR (%) | Design Traffic (msa) | Flexible Pavement Layers | Material | Thickness (mm) | Treated | Curing (Days) | Soaked | CBR (%) | Design Traffic (msa) |
| Surface Course | HRA | 180 | Surface Course | HRA | 180 | Surface Course | HRA | 180 | |||||||||||||||
| Base Course | HBM | 210 | Base Course | HBM | 210 | Base Course | HBM | 210 | |||||||||||||||
| Subbase | CBGM | 180 | Subbase | CBGM | 180 | Subbase | CBGM | 180 | |||||||||||||||
| Subgrade | ASS | ∞ | √ | 28 | × | 90 | 80 | Subgrade | ASS | ∞ | √ | 28 | × | 100 | 80 | Subgrade | ASS | ∞ | √ | 28 | × | 80 | 80 |
| Total pavement thickness | 570 | Total pavement thickness | 570 | Total pavement thickness | 570 | ||||||||||||||||||
| (e) | |||||||||||||||||||||||
| ASS 1 (25% Bentonite + 75% Kaolinite) High Plasticity | ASS 2 (35% Bentonite + 65% Kaolinite) Very High Plasticity | ASS 3 (75% Bentonite + 25% Kaolinite) Extremely High Plasticity | |||||||||||||||||||||
| Flexible Pavement Layers | Material | Thickness (mm) | Treated | Curing (Days) | Soaked | CBR (%) | Design Traffic (msa) | Flexible Pavement Layers | Material | Thickness (mm) | Treated | Curing (Days) | Soaked | CBR (%) | Design Traffic (msa) | Flexible Pavement Layers | Material | Thickness (mm) | Treated | Curing (Days) | Soaked | CBR (%) | Design Traffic (msa) |
| Surface Course | HRA | 130 | Surface Course | HRA | 130 | Surface Course | HRA | 130 | |||||||||||||||
| Base Course | HBM | 160 | Base Course | HBM | 160 | Base Course | HBM | 160 | |||||||||||||||
| Subbase | CBGM | 180 | Subbase | CBGM | 180 | Subbase | CBGM | 180 | |||||||||||||||
| Subgrade | ASS | ∞ | √ | 3 | √ | 50 | 8 | Subgrade | ASS | ∞ | √ | 3 | √ | 40 | 8 | Subgrade | ASS | ∞ | √ | 3 | √ | 30 | 8 |
| Total pavement thickness | 470 | Total pavement thickness | 470 | Total pavement thickness | 470 | ||||||||||||||||||
| (f) | |||||||||||||||||||||||
| ASS 1 (25% Bentonite + 75% Kaolinite) High Plasticity | ASS 2 (35% Bentonite + 65% Kaolinite) Very High Plasticity | ASS 3 (75% Bentonite + 25% Kaolinite) Extremely High Plasticity | |||||||||||||||||||||
| Flexible Pavement Layers | Material | Thickness (mm) | Treated | Curing (Days) | Soaked | CBR (%) | Design Traffic (msa) | Flexible Pavement Layers | Material | Thickness (mm) | Treated | Curing (Days) | Soaked | CBR (%) | Design Traffic (msa) | Flexible Pavement Layers | Material | Thickness (mm) | Treated | Curing (Days) | Soaked | CBR (%) | Design Traffic (msa) |
| Surface Course | HRA | 180 | Surface Course | HRA | 180 | Surface Course | HRA | 180 | |||||||||||||||
| Base Course | HBM | 210 | Base Course | HBM | 210 | Base Course | HBM | 210 | |||||||||||||||
| Subbase | CBGM | 180 | Subbase | CBGM | 180 | Subbase | CBGM | 180 | |||||||||||||||
| Subgrade | ASS | ∞ | √ | 3 | √ | 50 | 80 | Subgrade | ASS | ∞ | √ | 3 | √ | 40 | 80 | Subgrade | ASS | ∞ | √ | 3 | √ | 30 | 80 |
| Total pavement thickness | 570 | Total pavement thickness | 570 | Total pavement thickness | 570 | ||||||||||||||||||
NOTE: HRA = Hot Rolled Asphalt, ASS = Artificially Synthesised Subgrade, HBM = Hydraulic Bound mixture, CBGM = Cement Bound Granular Mixture.
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Amakye, S.Y.O.; Abbey, S.J.; Booth, C.A. DMRB Flexible Road Pavement Design Using Re-Engineered Expansive Road Subgrade Materials with Varying Plasticity Index. Geotechnics 2022, 2, 395-411. https://0-doi-org.brum.beds.ac.uk/10.3390/geotechnics2020018
AMA Style
Amakye SYO, Abbey SJ, Booth CA. DMRB Flexible Road Pavement Design Using Re-Engineered Expansive Road Subgrade Materials with Varying Plasticity Index. Geotechnics. 2022; 2(2):395-411. https://0-doi-org.brum.beds.ac.uk/10.3390/geotechnics2020018
Chicago/Turabian StyleAmakye, Samuel Y. O., Samuel J. Abbey, and Colin A. Booth. 2022. "DMRB Flexible Road Pavement Design Using Re-Engineered Expansive Road Subgrade Materials with Varying Plasticity Index" Geotechnics 2, no. 2: 395-411. https://0-doi-org.brum.beds.ac.uk/10.3390/geotechnics2020018
