Subgrade Strength Research Articles

Microcrystalline Cellulose-A Green Alternative to Conventional Soil Stabilizers.

Biopolymers are polymers of natural origin and are environmentally friendly, carbon neutral and less energy-intense additives that can be used for various geotechnical applications. Biopolymers like xanthan gum, carrageenan, chitosan, agar, gellan gum and gelatin have shown potential for improving subgrade strength, erosion resistance, and as canal liners and in slope stabilization. But minimal research has been carried out on cellulose-based biopolymers, particularly microcrystalline cellulose (MCC), for their application in geotechnical and geo-environmental engineering. In this study, the effect of MCC on select geotechnical properties of kaolin, a weak, highly compressible clay soil, like its liquid and plastic limits, compaction behavior, deformation behavior, unconfined compression strength (UCS) and aging, was investigated. MCC was used in dosages of 0.5, 1.0, 1.5 and 2% of the dry weight of the soil, and the dry mixing method was adopted for sample preparation. The results show that the liquid limit increased marginally by 11% but the plasticity index was nearly 74% higher than that of untreated kaolin. MCC rendered the treated soil stiffer, which is reflected in the deformation modulus, which increased with both dosage and age of the treated sample. The UCS of kaolin increased with dosage and curing period. The maximum UCS was observed for a dosage of 2% MCC at a 90-day curing period. The increase in stiffness and strength of the treated kaolin with aging points out that MCC can be a potential soil stabilizer.

Stabilization of Fibrous Peat Soils with Addition Palm Shell Ash Waste

South Sumatra Province has a peat area of 1.4 million Ha. The distribution of peat soil in Ogan Ilir is 23,687.91 Ha. Peat soil has a low bearing capacity. This research aims to explain the effect of stabilization on peat soil characteristics. Peat soil samples were taken using the Block Sampling method. The research locations are Parit Village and Lorok Village, Ogan Ilir Regency. Peat soil needs better properties and is unsuitable for foundation soil for civil construction. To overcome this, one method of soil improvement is required, namely the chemical stabilization method: changing the chemical properties of the soil by adding a mixture. The mixture used is palm shell ash waste with variations of 0%, 10%, 15%, 20%, 25%. Soil properties (physical and chemical), SEM, EDS, PTS, and CBR tests were carried out to determine the effect of this mixture. Soil properties test results: water content () in Parit Village 226.39%, and Lorok Village 252.39%. The fiber content (FC) test results for Parit Village were 25.18% and for Lorok Village 28.01%. Peat soil is classified as fibrous peat soil. The CBR value for Parit Village was 4.60%, and Lorok Village was 4.16%. The results of the immersion CBR test showed that Parit Village had a curing period of 7 days, a variation of 5%, namely 4.68%. Look Village obtained the most outstanding results: a curing period of 14 days, a variation of 25%, and 4.76%. The CBR value obtained in this study is 3%-5% (average) when used for subgrade strength with compaction conditions depending on the road category.

Effect of Wetting and Drying Cycle on the Behavior of Teff Straw Ash-Stabilized Expansive Soil

This study explores the impact of wetting and drying cycles on teff straw ash-stabilized expansive soil, with a focus on enhancing its mechanical properties for road subgrade applications. Expansive soil, characterized by continuous swell and shrink behavior, undergoes cyclic testing to establish equilibrium and critical density. The mitigating effects of teff straw ash on soil damage and its influence on expansive soil’s mechanical attributes are investigated. Laboratory results classify natural expansive soil as A-7-5 and CH according to AASHTO and USCS standards, respectively. Using a one-dimensional odometer apparatus, six wetting–drying cycles are conducted on teff straw ash-stabilized expansive soil to observe its behavior at equilibrium. Scanning electron microscopy reveals a disordered bond between soil particles and teff straw ash, intensifying with increased wetting–drying cycles. X-ray diffraction analysis is performed on samples subjected to different curing times, indicating heightened cation exchange and pozzolanic reactions as curing duration increases, thereby reducing soil expansiveness. A 96-hr socked California Bearing Ratio (CBR) test assesses subgrade strength. The CBR values for natural soil fall below the Ethiopian Road Authority (ERA) standards for low-volume roads. In contrast, expansive soil stabilized with teff straw ash at 10%, 15%, and 20% exhibits substantial increases in CBR values (3.7, 6.7, and 8.9, respectively), meeting the ERA standards. This suggests that teff straw ash stabilization renders expansive soil suitable for low-volume road subgrades, aligning with ERA standards. This comprehensive study provides valuable insights into the potential use of teff straw ash as an effective stabilizer for expansive soils, offering sustainable solutions for road construction in regions characterized by expansive soil challenges.

Investigation of the mechanical response of recovered geogrids under repeated loading

This study investigates the mechanical response and performance of biaxial polypropylene geogrid specimens cyclic loading. This work assesses the influence of embedment depths and subgrade strengths on the of geogrids. The experimental program involved subjecting the geogrid specimens to 100 repeated tensile loading cycles at four distinct load targets: 20%, 40%, 60%, and 80% of the geogrid ultimate tensile strength. The analysis focused evaluating the effects of preloading factors such as California Bearing Ratio (CBR) values, embedment depth, and the response to cyclic testing. Results show trends in stiffness reduction and changes in damping ratio with increased number of cycles. A comparative analysis was conducted with a control specimen from the same batch, highlighting the difference in mechanical response attributed to precycling variables. The findings indicate that the overall mechanical behavior of recovered geogrids is comparably consistent with new geogrids. However, variations in strain and stiffness reduction were observed among the recovered specimens, suggesting a pattern of yielding before failure. The findings suggest a minimal effect of embedment depth on the damping ratio at lower CBR. Overall, it was found that precycling and subgrade conditions have minimal effect on the mechanical response of the recovered specimens when tested in isolation.

РІЗНІ ПРАКТИКИ ОЦІНЮВАННЯ МІЦНОСТІ ШАРІВ ҐРУНТОВОЇ ОСНОВИ І ДИСПЕРСНИХ МАТЕРІАЛІВ ЗА РЕЗУЛЬТАТАМИ ДИНАМІЧНОГО ВИПРОБУВАННЯ КОНУСНИМ ПЕНЕТРОМЕТРОМ

Introduction. The introduction to the paper highlights the methods of standard geotechnical tests for in situ measurements of subgrade strength or strength estimation. Problem statement. The issue of the paper concerns the interpretation and the application of the results of testing of the subgrades or granular layers of a road pavement by the dynamic cone penetrometer. Purpose. The goal of the paper consists of the analysis of practices of the subgrade strength evaluation by the conversion of the dynamic cone penetration test (DCPT) results to the nominal values of the California bearing ratio (CBR) or by plotting the subgrade profile and also of practices for the layer thickness evaluation and compaction control. Results. The main principles of DCPT were reviewed with performing the analysis of factors affecting the test results. The equations of the dependence of the nominal CBR values on the penetration index as the main result of DCPT was analyzed. The assumption was made that the difference in such equations may be determined by the differed confinement conditions under testing in accordance with which the calculated values provided by the results of testing under the triaxial confinement are higher. Also the stair-stepping effect appeared when performing DCPT on cohesive soils was reviewed.

Subgrade Strength Recovery of Fine-Grained-Soil-Containing Roads in Western Oregon Forest

Forest roads are composed of surface and subsurface layers. Determining the seasonal strength and associated moisture changes in these roads is required to understand their capacity. This study looks at changes in the subgrade layer. Laboratory and field studies were conducted to determine the changes in subgrade conditions by measuring moisture content and subgrade strength for fine-grained, non-plastic soils in Western Oregon. One field and one laboratory experiment were conducted. Drying in the field experiment occurred during the summer months in the absence of rainfall, while the laboratory study allowed drying for 48 h under controlled suction. In both cases, there was a slight reduction in the subgrade’s moisture content and no significant improvement in subgrade strength. These findings are supported by the soil physics theory that shows that limited water content reduction is expected for these fine-grained soils, as the numerous tiny soil pores can hold water at high capillary tensions. Adding rock layers adds an insulation effect for the subgrade, further reducing evaporation. Consequently, the moisture content remains high, and there will be little change in subgrade strength during the measurement periods.

On the effect of subgrade strength on the performance of geogrid-reinforced railway ballast

This paper presents the results of a series of ballast box tests aimed at investigating the effectiveness of geogrid reinforcement in reducing track settlement in a 300mm-thick layer of railroad ballast supported by three different artificial subgrades. In each experiment, the ballast layer supports a model tie subjected to cyclic compressive loading applied at a frequency of 0.8Hz with stress extrema at the tie-ballast interface of 57kPa and 400kPa for a total of 40,000 cycles. The three artificial subgrades considered in this study have CBR readings of 25, 13, and 5. For each subgrade, four tests are performed whereby one corresponds to an unreinforced condition (i.e., no geogrid) and three are reinforced with a single geogrid placed at either 150mm, 200mm, and 250mm below the bottom of the tie. The results indicate that geogrids exhibit a superior ability to minimize the tie’s settlement when the ballast layer is supported by a weak subgrade. The experiments further allude to the fact that the influence of the geogrid’s placement depth is exacerbated by the subgrade’s strength. In ballast layers supported by competent subgrades, the geogrid placement depth wields a marginal influence on the resulting tie settlement. However, the geogrid’s location becomes a key factor in ballast beds underlain by soft subgrades, with geogrids placed closer to the bottom of the tie being the most effective at minimizing the tie settlement.

Review of Subgrade Soil Stabilised with Natural and Synthetic Fibres

Subgrade soil is an essential component in the design of road structures as it provides lateral support to the roadway. One of the main reasons for pavement failure is subgrade settlement, which leads to a loss of subgrade strength. If the mechanical properties of subsoils are lower than required, a soil stabilisation method may be an option to improve the soil properties of the weak subsoil. Soil stabilisation is one of the techniques for improving poor subsoil, which results in significant improvement in tensile strength, shear strength and bearing capacity of subsoil. Soil stabilisation can be broadly divided into four types: thermal, electrical, mechanical, and chemical. The most common method of improving the physical and mechanical properties of soils is stabilisation with binders such as cement and lime. However, soil stabilisation with conventional methods using cement and lime has become uneconomical in recent years, so an alternative such as fibres may be sought. This review provides a comprehensive comparison of the effectiveness of natural fibres and synthetic fibres in stabilising subgrade soils.

Comparative Experimental Study on Strength Properties of Red Clay Modified by Cement and Industrial Solid Waste Powder

Because of the existence of clay minerals such as montmorillonite in red clay, the strength of red clay decreases significantly as water content increases. This study aims to improve the strength of red clay by using three different kinds of industrial solid waste powder, i.e., steel slag (SS) powder, fly ash (FA), and ground-granulated blast furnace slag (GGBS). At the same time, the ordinary Portland cement (OPC) was selected as a comparison of the improvement effect on the strength of red clay modified by the aforementioned industrial solid waste powder. The properties of the red clay and the industrial solid waste powder were documented comprehensively. The unconfined compressive strength (UCS) tests were conducted on the specimens of the red clay and the red clay modified by the OPC, SS, FA, and GGBS, which had been cured for 3, 7, and 21 days at a temperature of 25°C, respectively. The results showed that the strength of red clay can be significantly improved by the three kinds of industrial solid waste powder. After a 21-day curing period, the experimental results showed that the UCS of the red clay modified by 7% SS, 5% FA, and 5% GGBS increased by 252%, 131%, and 140% compared to that of the red clay without modification. However, the modification effects of the SS, FA, and GGBS on the red clay were generally inferior to that of the OPC. By observing the microstructures of the modified clay, the mechanism of industrial solid waste powder and cement improving the strength of the red clay was analyzed. The findings in this study can provide a reference for improving subgrade strength by a soil-modification method in road constructions.

Investigation of subgrade conditions on the Airbara – Toboali road section to improve road quality

The Airbara - Toboali Road Section is a national road located in South Bangka Regency, Bangka Belitung Islands Province. Some segments of this road often experience road damage, although road repairs have been carried out several times to overcome the damage. The subgrade layer is the most important layer in the pavement structure because it functions to withstand all the loads above it. CBR (California Bearing Ratio) is penetration test used to evaluate the subgrade strength of roads and pavement. Therefore, this study aims to investigate the subgrade conditions on the Air Bara – Toboali road section in order to improve road quality. This study uses hand boring testing with 4 sampling points and field CBR testing with the DCP tool. Field CBR samples were taken as many as 30 points every 50 meters from STA 0+000 – STA 1+450. The average CBR value obtained shows that the CBR of this subgrade is in the good category (10.77%). Subgrade conditions per layer, namely at a depth of 0-2 meters the roads have almost the same soil characteristics. However, the soil depth of more than 2 meters in several locations on the road segment has a different character. The results of this investigation are expected to assist road planning so that road quality can improve.

Viability of calcinated wastepaper sludge ash geopolymer in the treatment of road pavement subgrade materials

Problematic ground conditions constituted by weak or expansive clays are commonly encountered in construction projects and require some form of chemical treatment such as lime and cement to re-engineer their performance. However, in the light of the adverse effects of these traditional additives on the climate, alternative eco-friendlier materials are now sourced. In the current study, the viability of calcinated wastepaper sludge ash geopolymer in enhancing the engineering behaviour of a problematic site condition is evaluated. A highly expansive clay (HEC) constituted with a blend of kaolinite and bentonite clays is treated with calcinated wastepaper sludge ash (CPSA) geopolymer. Activation of the precursor is actualised at room temperature using a combination of NaOH and Na2SiO3 at various activator to soil + binder ratios (AL/P), and molarity (M). The mechanical, microstructural, and mineralogical characteristics of the treated clay were investigated through unconfined compressive strength (UCS), swell, water absorption, SEM, and EDX analysis. The performance of the stabilised samples was then compared with the requirements for road subgrade and subbase materials and that of OPC and lime-GGBS treatment. The results showed that CPSA-geopolymer enhanced the engineering properties of the treated clay better than traditional binders (OPC and Iime-GGBS). UCS improvement of 220 % was observed in the CPSA-stabilised soil over that of OPC-treated ones, while the swell potential and water absorption were drastically reduced by over 95 and 97 % respectively after 28-day soaking. The SEM and EDX results showed improved crystallisation of earth-metal-based cementitious flakes (NASH) with increasing CPSA, molarity, and AL/P ratios, which enhanced the inter-particle bonds with simultaneous reduction in porosity. The modified characteristics of the stabilised materials meet the requirements for pavement subgrades. Further, the equivalent carbon emission (CO2-e) from the stabilised materials were also evaluated and compared with that of traditional binders. The results also showed that CPSA-geopolymer had lower CO2-e at higher subgrade strengths than OPC, making it more eco-friendly. Therefore, wastepaper sludge, a common landfill waste from paper recycling is a viable geopolymer precursor that could be utilised in enhancing the engineering properties of subgrade and sub-base materials for road and foundation construction.

Subgrade Strength Performance Behavior of Alkali-Activated Binder and Cement Stabilized Expansive Soil: A Semifield Study

Subgrade Strength Performance Behavior of Alkali-Activated Binder and Cement Stabilized Expansive Soil: A Semifield Study

Experimental Investigation of the Effects of Subgrade Strength and Geogrid Location on the Cyclic Response of Geogrid-Reinforced Ballast

Experimental Investigation of the Effects of Subgrade Strength and Geogrid Location on the Cyclic Response of Geogrid-Reinforced Ballast

Predicting California bearing ratio of HARHA-treated expansive soils using Gaussian process regression

The California bearing ratio (CBR) is one of the basic subgrade strength characterization properties in road pavement design for evaluating the bearing capacity of pavement subgrade materials. In this research, a new model based on the Gaussian process regression (GPR) computing technique was trained and developed to predict CBR value of hydrated lime-activated rice husk ash (HARHA) treated soil. An experimental database containing 121 data points have been used. The dataset contains input parameters namely HARHA—a hybrid geometrical binder, liquid limit, plastic limit, plastic index, optimum moisture content, activity and maximum dry density while the output parameter for the model is CBR. The performance of the GPR model is assessed using statistical parameters, including the coefficient of determination (R2), mean absolute error (MAE), root mean square error (RMSE), Relative Root Mean Square Error (RRMSE), and performance indicator (ρ). The obtained results through GPR model yield higher accuracy as compare to recently establish artificial neural network (ANN) and gene expression programming (GEP) models in the literature. The analysis of the R2 together with MAE, RMSE, RRMSE, and ρ values for the CBR demonstrates that the GPR achieved a better prediction performance in training phase with (R2 = 0.9999, MAE = 0.0920, RMSE = 0.13907, RRMSE = 0.0078 and ρ = 0.00391) succeeded by the ANN model with (R2 = 0.9998, MAE = 0.0962, RMSE = 4.98, RRMSE = 0.20, and ρ = 0.100) and GEP model with (R2 = 0.9972, MAE = 0.5, RMSE = 4.94, RRMSE = 0.202, and ρ = 0.101). Furthermore, the sensitivity analysis result shows that HARHA was the key parameter affecting the CBR.

Strength Performance of Alkali Activated Binder and Cement Stabilized Expansive Soil: A Field Study on Subgrade Layer

The dual character of expansive subgrade soil, which includes swelling and shrinkage, causes a premature collapse on the pavement surfaces. The scopes of the current study include comparison of the field performance of cement and alkali activated binder (AAB) stabilized expansive subgrade soil. To assess the strength properties, a 12 m long semi-field test section with expansive soil that has been treated with AAB, cement, and untreated expansive soil is built. Steel slag and fly ash are used as dry pozzolanic precursors in AAB, while sodium silicate and sodium hydroxide are used as an activator solution in a 0.4 water:solids ratio. AAB provides twin benefits of reducing the need for traditional binders and lowering the cost of fly ash/slag disposal in landfills. It also has a less carbon footprint than a PC-based binder, stronger mechanical strength and longer durability. By embedding a number of stress metres and strain gauges in the subgrade layer and applying a load through a dual-wheel truck load (12-tonne rear axle load) on the field track, the in-situ subgrade strength behaviour is assessed. On samples taken from the field section, the effects of AAB, curing duration, and the proportion of steel slag/fly ash in the alkaline soil mixture on the geomechanical properties of soil are examined. Additionally, using KGP-BACK software, falling weight deflectometer investigations were conducted to assess the elastic moduli of each layer. It has been noted that subgrade layers treated with AAB had larger elastic moduli than those treated with cement or left untreated. In comparison to cement-treated soil, the AAB mixture’s subgrade strength is increased by 23-26% by the combined addition of slag and fly ash. Based on the semi-field test section studies, recommendations for the effective application of AAB stabilisation for expansive soils as subgrade are given.

Strength of Cement Treated Base Courses in the Flexible Pavement Design for Pathlaiya- Nijgadh Section of East-West Highway of Nepal

Rutting and fatigue are the most common pavement distresses that are caused due to overloading, subgrade strength, and poor construction quality. The strength of the pavement layer can be improved by the construction of cement-treated layers. This study suggested that the cement-treated base is the effective modification technique for a granular base course by evaluating the unconfined compressive strength, and modulus of rupture. The unconfined compressive strength revealed that a cement-treated base is an effective treatment for the improvement of strength. Similarly, flexural strength indicated that a cement-treated base is an effective method to reduce the fatigue damage of the base course, and 5% cement content is sufficient to resist crack formation on the base course. 5.34% cement content in CTB developed a stiff mix with a stronger ability towards applied load dispersion that can resists deformation. In the meantime, unconfined compressive strength, modulus of rupture, and modulus of elasticity obtained at 5.34% cement content on a cement-treated base satisfied the minimum requirement as set by the Department of Roads, Government of Nepal.

A Perspective into Development of Pavement Design Methods for Low Volume Roads: A Review

The definition of low volume roads (LVRs) is not time static and it varies from place to place around the world. The importance of such roads for providing access, in connecting communities and link farms to markets is well appreciated worldwide. LVRs are credited as the direct source of social economic development in rural communities, growth, reduction of poverty and sustaining livelihood. Nevertheless, the LVR network is growing at an unsatisfactory rate especially in Sub-Saharan Africa. The slow rate in developing LVR network is attributed to the high cost of construction and maintenance. To the author’s perspective, research has a significant role in lowering both maintenance and construction costs and in turn realise a growth in the network size and adequacy. To demonstrate the importance of research in road development, a comparison has been made between the current and the previous pavement design methods for LVRs in Tanzania. The improvement so far has been in the determination of subgrade strength using the Dynamic Cone Penetration (DCP) method instead of the less accurate and more demanding California Bering Ratio (CBR) method; a simpler approach in estimating design traffic load that is also less conservative; encouraging the use of local natural materials which could be marginal for construction instead of the conventional but expensive crushed rock; and improvement in layer design which result to less pavement thickness. While all these improvements enhance saving in pavement cost, it is argued that further development is possible through research especially in local materials and procedures.

Performance evaluation of silty soil reinforced with glass fiber and cement kiln dust for subgrade applications

In this study, the use of glass fiber and cement kiln dust (CKD) as stabilizing agents for a typical silty soil is investigated. Fibers with three lengths (12 mm, 18 mm and 24 mm) were added as percentages of soil’s dry weight (0.3%, 0.6%, 0.9%, and 1.2%), the cement kiln dust (CKD) was added in three percentages by dry weight of soil (7%, 14% and 21%). The subgrade strength was evaluated in terms of laboratory California bearing ratio (CBR) tests in soaked and unsoaked environment to simulate both dry and inundated conditions for field applications. Chemical and microstructural changes were monitored with Fourier transform infrared spectroscopy (FTIR) and integrated FESEM-EDAX analysis respectively. IITPAVE software was used to compute actual strains on pavement layers and determine the optimum thickness of the pavement sections for untreated and treated subgrade. In comparison to the untreated soil, the overall pavement thickness reduced by approximately 44% when designed on improved subgrade. The cost reduction, using the improved subgrade material was approximately 37.5%. Because the actual strains were significantly lesser than the permissible values, the structural performance of the pavement designed on improved subgrade was enhanced against subgrade rutting and fatigue cracking. The optimum CKD–fiber combination was found to be 14% CKD and 0.6% fiber. The laboratory test results indicated that the proposed ground improvement technique can be effective for subgrade improvement of low-volume roads and also serve as a sustainable disposal solution of CKD.

Statističko modeliranje kolotraženja za ceste s malim volumenom prometa u Indiji

This study considers a road rutting model better-suited for the flexible pavements in the low-volume roads of India. The rutting on a road directly affects various aspects such as the pavement performance, safety, driving comfort, and travel time. Accordingly, this study is conducted on 173 test sections of low-volume roads, and a mathematical rutting model is developed using a multiple regression analysis. In the model, the rutting is the response variable, whereas the commercial vehicles per day, rainfall, subgrade strength (as a modified structural number), and pavement age are the explanatory variables. The model is statistically validated and used to forecast road rutting and the effectiveness of the rutting prediction is confirmed. The error between the field data and estimated values is within 5 %.

System reliability-based design optimization of flexible pavements using adaptive meta-modelling techniques

Recognizing the need for sustainable and long-lasting structures, reliability-based designs have been gaining acceptance in the pavement engineering community. The Reliability Based Design Optimization (RBDO) is formulated to design cost-effective flexible pavements in the presence of uncertainties. Two meta-modelling approaches are considered in this study, the second-order adaptive Response Surface Model (RSM) and the adaptive Polynomial-Chaos based Kriging (PC-Kriging) meta-model. The study highlights the need for adaptive meta-modelling techniques in the reliability-based design of pavement structures, through the quantification of the epistemic uncertainty. For the numerical examples considered in this study, the model uncertainty was found to be around 1% for three-layer sections and below 2.5% for four-layer pavements. To address the correlation between the pavement failure modes, a System Reliability Based Design Optimization (SRBDO) approach is proposed in this paper. The SRBDO methodology is further adapted to design the optimum combination of pavement layer thicknesses and moduli, to meet the target levels of reliability, given the expected traffic demand and subgrade strength at a pavement site. Thus, the SRBDO formulation using adaptive meta-models, presented in this study, efficiently integrates the economic analysis of various pavement design alternatives with the Mechanistic-Empirical procedure in a system reliability framework.