Cohesive Subgrade Soils Research Articles

Undrained Cyclic Loading Response of Subgrade Soil Subjected to Varying Moisture Content and Stress Level

Subgrades that are constructed from fine-grained cohesive soils undergo large settlements; therefore, the study of their deformation behavior is important to avoid early deterioration in the traffic infrastructure. In this study, the deformation behavior of two different types of cohesive subgrade soils at different compaction states has been addressed that considered the effect of influencing factors, such as water content, deviatoric stress, and confining pressure (σ3). The results from the unconsolidated undrained cyclic triaxial tests show that the deformation behavior of soil is highly influenced by the level of applied deviatoric stresses and moisture content on the wet side of optimum (WS) and is slightly affected by σ3 and moisture content on the dry side of optimum (DS). The elastic strain (ɛe) component showed a decreasing trend with an increase in the number of load cycles (N) and then attained a steady value toward a higher N; however, the plastic strain (ɛp) component continuously increased for a given magnitude of applied cyclic deviatoric stresses (σd,c). From the test results, logarithmic strain models were proposed to predict the long-term total (ɛt) strain and ɛp that developed in cohesive subgrade soils, which were subjected to various combinations of variations in moisture content and stresses. The proposed model has been compared with the existing model and shows better prediction ability with a coefficient of correlation (R2) of >95% in most cases.

Compaction characteristics of natural cohesive subgrade soil stabilized with local sustainable materials

In traditional road construction, the most common source materials for roadbed layers are the borrow pits. During the construction process, the source’s materials, excavation, loading, and handling have been considered significant factors on total construction cost. Improving the geotechnical properties of the locally available source materials using the waste materials of the local industry (as additives) is helped in avoiding undesirable additional costs in the field construction. The present paper explains the results of an experimental study of compaction characteristics for subgrade material of districts of Baghdad, Iraq with two different types of local byproduct materials “cement dust and fly ash materials,”. The selected soil, cement dust, and fly ash mixtures were made ready for use in the laboratory, and the mixtures’ compaction properties were investigated. Both light and heavy manual compaction tests were carried out and compared. The effect of selected stabilizers on the compaction behavior of the subgrade soil was determined to obtain the optimal values of stabilizer materials. The finding of this paper indicates that the compaction characteristics and behavior of the subgrade soil greatly depend on the type of additives used. However, the subgrade stabilization with local byproduct materials is beneficial from economic and environmental points of view.

Dummy Regression to Predict Resilient Modulus of Cohesive Subgrade Soils

Dummy Regression to Predict Resilient Modulus of Cohesive Subgrade Soils

Hybrid Formulation of Resilient Modulus for Cohesive Subgrade Soils Utilizing CPT Test Parameters

AbstractIn the present study, a novel model is introduced for the prediction of a resilient modulus (MR) of cohesive subgrade soils considering cone-penetration test parameters to establish correla...

Development of genetic-based models for predicting the resilient modulus of cohesive pavement subgrade soils

The accurate determination of resilient modulus (Mr) of pavement subgrade soils is an important factor for the successful design of pavement system. The important soil property Mr is complex in nature as it is dependent on several influential factors, such as soil physical properties, applied stress conditions, and environmental conditions. The aim of this study is to explore the potential of an evolutionary algorithm, i.e., genetic algorithm (GA), and a hybrid intelligent approach combining neural network with GA (ANN-GA), to estimate the Mr of cohesive pavement subgrade soils. To achieve this aim, a reliable database containing the results of repeated load triaxial tests (RLT) and other index properties of subgrade soils was utilized. GA was employed to develop a precise equation for predicting Mr of subgrade soils. In addition, GA was used as a tool for determining the optimal values of the weights and the bias of the ANN-GA approach. The developed ANN-GA model was then transferred to a functional relationship for further application and analyses. Several validation and verification phases were conducted to examine the performance of the developed models. The results indicated that both GA and ANN-GA models could accurately predict the Mr of cohesive subgrade soils, and performed better than other models in the literature. Finally, a sensitivity analysis was conducted to evaluate the effect of the utilized parameters on Mr.

Permanent deformation behavior of cohesive subgrade soils classified as A-4a and A-6a

The subgrade layer, upon which the pavement is constructed, will have a large impact on structural design. The study aims at characterizing permanent deformation properties of cohesive subgrade materials including. A new testing procedure, stage loading, was used to test the permanent deformation of subgrade materials at different stress levels and load repetitions; this technique allows researchers to explore the effect of stress history on the accumulation of plastic deformation besides saving time, effort, and test specimens. The permanent deformation results showed a constant increasing rate of plastic strain at higher stress levels. The results obtained could be used to help engineers in characterizing the cohesive subgrade materials. Statistically, soil type and water content were found to be statistically significant at the 0.05 significance level, whereas, at the 0.1 significance level stress level, soil type and water content were found to be significant factors in affecting permanent stain.

Resilient Behavior of Sodium Alginate–Treated Cohesive Soils for Pavement Applications

AbstractNatural weak cohesive subgrade soils are considered low quality foundations for pavement structures that may lead to significant pavement distresses. Several solutions can be proposed to en...

Predictive modelling of the MR of subgrade cohesive soils incorporating CPT-related parameters through a soft-computing approach

Performance of pavements is significantly influenced by the characteristics and behaviour, e.g. compaction and deformation, of their underlying layer as subjected to different loadings. This can be experimentally or theoretically estimated through the subgrade soil resilient modulus (MR) parameter. The MR found by laboratory tests does not completely describe the actual in situ conditions of subgrade soils. Additionally, almost all of the predictive models proposed in the literature relate the MR parameter to lab-related soil indices and conditions of stresses applied in laboratory tests. This study explores the feasibility of producing a new MR equation using key soil lab and in situ related parameters for the pavements subgrade cohesive soils through gene expression programing (GEP) approach. A database comprising several experimental data acquired by conducting cone penetration test and corresponding resilient moduli tests on various cohesive subgrade soils is employed for modelling of the pertinent MR factor and a new empirical mode is suggested. In order to examine the proposed model from both precision and engineering perspectives, various validation and verification analyses are done. The results present that the strength of GEP approach and the proposed formula for indirect estimation of the MR of pavements subgrade soils.

Effectiveness of lime in stabilising subgrade soils subjected to freeze–thaw cycles

Periodic freeze–thaw conditions are known to alter the geotechnical behaviour of soils. Although lime stabilisation is used to enhance the mechanical properties of subgrade soils, Jordan lacks the experience with such utilisation where seasonal frost takes place during cold winters. An investigation is carried out on the impact of freeze–thaw cycles on the behaviour of lime-stabilised fine-grained soils widely available throughout the country. Five lime contents ranging from 0 to 8% are used to stabilise the soil. To study the effect of environmental factors on durability, soils are subjected to freeze–thaw cycles ranging from 0 to 20 and subsequently tested for unconfined compressive strength. Measurements show that lime stabilisation substantially improves the geotechnical properties of untreated soil. Benefits are measured in terms of reduced soil plasticity, higher optimum moisture content, lower maximum dry density, and higher unconfined compressive strength. Experimental results show that freeze–thaw cycles decrease the unconfined compressive strength of soil with further reduction as freeze–thaw cycles are increased. However, this effect is much higher on untreated soil as compared to stabilised soil. Findings of the present study confirm the appropriateness of lime for increasing the durability of cohesive subgrade soils exposed to freezing conditions. Such stabilisation offers lower life-cycle cost and enhanced pavement performance advantages to earthwork construction.

Effect of moisture content of cohesive subgrade soil

A good subgrade for road pavement is required to support the traffic load that passes through. The characteristics of the subgrade is determined by the stress-strain behaviour that is expressed as a resilient modulus. The performance of the pavement is affected by characteristics of the subgrade. Characteristics of clay soil generally have a low of bearing capacity, especially to support the load induced by the wheel load of vehicles. Clay soil is very sensitive to changes of temperature and moisture content. The changes of moisture content cause the changes on the subgrade‚s resilient modulus value. This paper studies the resilient modulus of the subgrade of clay soil by laboratory testing. To investigate the effect of moisture content, this testing is done on a dry side, OMC condition and wet side. The result shows the difference of the resilient modulus characteristic and deformation that is influenced by the moisture content.

Dynamic shear modulus and damping ratio of thawed saturated clay under long-term cyclic loading

Dynamic properties of subgrade soil under the long-term traffic loading are crucial for designing the subgrade structures and evaluating the long-term performance of traffic infrastructures in seasonally frozen regions. In this study, the dynamic shear modulus and damping ratio were employed to evaluate the long-term dynamic behaviors of thawed saturated clay by conducting a series of cyclic tri-axial tests. Effects of freeze-thaw cycles, dynamic stress amplitude, confining pressure and multi stage cyclic loading on the evolution rules of dynamic shear modulus and damping ratio versus shear strain were analyzed. The results indicate that both dynamic shear modulus and damping ratio decrease with the increasing shear strain during the long-term cyclic loading. Repeated freeze-thaw cycles have tremendous effects on decreasing the dynamic shear modulus and increasing the damping ratio. Increasing dynamic stress amplitude has a decreasing effect on dynamic shear modulus, and an increasing effect on damping ratio. Increasing confining pressure has no obvious effect on the evolution of damping ratio, but has an increasing effect on increasing the dynamic shear modulus before the shear strain reaches a certain level. Multi stage cyclic loading can be an alternative method to determine the evolution of dynamic shear modulus during the long-term cyclic loading, but it is not applicable for the damping ratio. Finally, the Martin-Davidenkov model and a hyperbolic model which can be used for predicting the evolution of dynamic shear modulus and damping ratio, respectively, were proposed and validated. The results show that both the two models can give satisfactory prediction. The results achieved in this study contribute to a better understanding of the long-term dynamic behavior for cohesive subgrade soils in seasonally frozen region.

Accumulative plastic strain of thawed saturated clay under long-term cyclic loading

Accumulative strain of subgrade soil is crucial for designing the subgrade structures and maintaining the long-term performance of pavements. Due to the effects of freeze-thaw cycles in seasonally frozen region, subgrades filled with clayey soil usually are exposed to an increasing risk of turning into a saturated condition. The thawed saturated clay can generate notable accumulative strain under long-term cyclic loading. This study investigated the effects of freeze-thaw cycles, dynamic stress amplitude, confining pressure, number of cyclic loading and multi-stage cyclic loading on the evolution of accumulative plastic strain for thawed saturated clay by using dynamic tri-axial tests. An empirical model for calculating the accumulative strain was proposed based on the experimental data. The test results indicate that the normalized accumulative strain increases with the increasing number of freeze-thaw cycles, as well as the increasing dynamic stress amplitude and loading cycles, but decreases with the increasing confining pressure. Evolution of the accumulative strain under multi-stage cyclic loading can be divided into three phases by two threshold CSRs (cyclic stress ratio), i.e., the gradual stabilization phase, the rapid growth phase and the failure phase. The accumulative plastic strain model, which can reflect the effects of freeze-thaw cycles, dynamic stress amplitude, confining pressure and loading cycles, was proposed and validated. Results achieved in this study contribute to a better understanding of deformation behavior for cohesive subgrade soils in seasonally frozen region.

Resilient Modulus Characterization of Compacted Cohesive Subgrade Soil

Soil investigations concerning cyclic loading focus on the evaluation, in particular, of design parameters, such as elastic modulus, Poisson’s ratio, or resilient modulus. Structures subjected to repeated loading are vulnerable to high deformations, especially when subgrade soils are composed of cohesive, fully-saturated soils. Such subgrade soils in the eastern part of Europe have a glacial genesis and are a mix of sand, silt, and clay fractions. The characteristic of, e.g., Young modulus variation and resilient modulus from repeated loading tests, is presented. Based on performed resonant column and cyclic triaxial tests, an analytical model is proposed. The model takes into consideration actual values of effective stress p′, as well as loading characteristics and the position of the effective stress path. This approach results in better characterization of pavement or industrial foundation systems based on the subgrade soil in undrained conditions. The recoverable strains characterized by the resilient modulus Mr value in the first cycle of loading was between 44 MPa and 59 MPa for confining pressure σ’3 equal to 45 kPa, and between 48 MPa and 78 MPa for σ’3 equal to 90 kPa. During cyclic loading, cohesive soil, at first, degrades. When pore pressure reaches equilibrium, the resilient modulus value starts to increase. The above-described phenomena indicate that, after the plastic deformation caused by excessive load and excess pore water pressure dissipation, the soil becomes resilient.

Enhancing soft subgrade soil with a sewage sludge ash/cement mixture and nano-silicon dioxide

In this study, a mixture of sewage sludge ash (SSA) and cement was applied to improve the properties of soft cohesive soil. In addition, nano-SiO2 was applied as an additive to the SSA/cement-treated soil. Four different mix ratios of SSA/cement (1:1, 2:1, 3:1, and 4:1) were used as stabilizers to improve the strength of the soft cohesive subgrade soil, and the total amount of SSA/cement added was fixed at 15 % of the soil weight. The effect of 2 % nano-SiO2 was also investigated. Experiments, including Atterberg limit measurements, compaction tests, unconfined compressive strength (UCS) tests, and scanning electron microscopy, were performed. The test results indicated that a mixture of SSA and cement improved the engineering properties of soft subgrade soil, generating a UCS that was 6.5–8.4 times better over 28 days and a CBR value that was 61–97 higher. Furthermore, the addition of nano-SiO2 enhanced the engineering properties after adding various SSA/cement ratios, increasing the UCSs that were 30–47 kPa higher over 28 days and generating CBR values that were 3–9 higher. This study suggests that to best develop the additive efficiency, nano-SiO2 should be added to soil treated with an SSA/cement ratio of 3:1.

Study on Prediction Model of Dynamic Resilient Modulus of Cohesive Subgrade Soils Considering Moisture Variation

The matric suctions were measured by the filter paper method, and the parameters of soil-water characteristic curve were obtained. In order to investigate the effect of moisture content on cohesive subgrade soils dynamic resilient modulus, a series of dynamic-triaxial test were carried out. Based on the matric suctions measured by the filter paper method, the relationship between dynamic resilient modulus and matric suctions were analyzed. The study demonstrated that the dynamic resilient modulus values decrease with the increase of circular deviator stress and moisture content, in reverse of matric suctions. Considering that the dynamic resilient modulus is a function of deviator stress and bulk stress, based on the present three parameters compound constitutive model which reflects the effect of bulk stress and deviator stress, the effect of matric suctions which could indirectly reflect the effect of moisture content was introduced. And then the prediction model incorporating the effect of stress and moisture for cohesive subgrade soils was established. The model was utilized for experimental data regression analysis, a high coefficient of determination shows that the model is accurate and credible. The prediction models not only can evaluate the long-term performance of subgrade soil in Southern China's rainy areas, but also can provide parameters for the pavement design based on dynamic method.

Prediction Model of Dynamic Resilient Modulus of Cohesive Subgrade Soil Based on Triaxial Test System

Resilient modulus (MR) of cohesive subgrade soil is a critical parameter for pavement design and evaluation with mechanistic-empirical method. The objective of this paper was to establish a constitutive model of MR of cohesive subgrade soil on the basis of triaxial repeated loading tests considering moisture condition coupled with stress. Major findings can be seen from this study. Firstly, MR increases with the increase of confining pressure under the condition of the same deviator stress. The increase rate of MR of cohesive subgrade soil with higher water content is more obvious than that of cohesive subgrade soil with lower water content. Secondly, MR decreases with the increase of deviator stress under the condition of the same confining pressure. The decrease rate of MR of cohesive subgrade soil with different water contents keeps the same range, which keeps between 30 percent and 35 percent. Thirdly, the effect of deviator stress on MR is more than that of confining pressure. Cohesive subgrade soil exhibits the feature of the stress softening. Finally, the predicted value of MR based on the established constitutive model has a good relevancy to its measure value. There is litter doubt that these findings provide practical supports for attaining MR in the design of pavement structure.

SWCC Based Prediction Model of Equilibrium Moisture of Clay Subgrade with High Groundwater Table

To accurately calibrate the working range of equilibrium moisture of clay subgrade, according to unsaturated soil mechanics basic theories, the filter paper method was used to measure matrix suction and to establish soil-water characteristic curve (SWCC) model with reflecting function between moisture and metrics suction. The prediction method about the working range of equilibrium moisture of unsaturated clay subgrade was proposed and the model was tested. The results show that equilibrium moisture of clay subgrade out the affected range of the precipitation and evaporation is mainly controlled by the impact of groundwater. The Fredlund & Xing model can better characterize the unsaturated cohesive subgrade soil humidity and the correlation matrix suction and the model parameters possessed highly reliability. The prediction result of clay subgrade's equilibrium moisture on groundwater control area has high uniformity with experimental result. The prediction method is reasonable and reliable. The results provide new perspectives and standpoints to objectively characterize the equilibrium moisture status of unsaturated clay subgrade.

Correlation between Resilient Modulus and Plastic Deformation for Cohesive Subgrade Soil under Repeated Loading

Pavement performance is related to resilient modulus and plastic deformation of pavement materials, which in turn are affected by environmental conditions and traffic loading. A series of triaxial tests was conducted on a residual lateritic soil for 10,000 load repetitions, with some specimens subjected to 100,000 load repetitions, to characterize the behavior of cohesive subgrades under repeated loading, including resilient modulus and plastic deformation. The shakedown concept was used to describe the accumulated plastic deformation and the strain-hardening and softening behavior. Experimental results show that the resilient modulus of cohesive subgrades exhibits strain-hardening behavior under low stress levels. In the meantime, the rate of plastic strain accumulation becomes diminutive. Soil under this condition is in a stable state. Conversely, under high stress levels, cohesive soil tends to soften after a specific number of load applications and accumulates excessive plastic strain and leads to an unstable state. To predict the plastic strain of subgrade soil under repetitive loading, regression models incorporating the strain-hardening behavior for a cohesive soil were used.

Predicting Moisture-Dependent Resilient Modulus of Cohesive Soils Using Soil Suction Concept

The resilient modulus of the materials used in various pavement layers has been used extensively as an important material property in structural design of pavement. The state of stress and moisture content of cohesive soils have been observed to exert significant effects on the measured resilient modulus. Since the moisture content in the cohesive subgrade soils underneath the pavement undergoes seasonal changes due to infiltration of precipitations and since characterization of moisture and stress dependent resilient modulus of cohesive soils is a demanding and tedious task, there is a practical need for a predictive equation for the resilient modulus as a function of stress states and moisture content. This paper presents a new predictive equation for the resilient modulus of cohesive soils using the concept of soil suction. The accuracy of the proposed model is validated against experimental data of A-4 and A-6 soils conducted by the writers as well as by other data available in the literature. The proposed model provides advantages over the existing predictive equations by reducing the number of tests and soil specimens needed for determining the regression coefficients in the equation. The proposed predictive equation compares well with the empirical equation in the new mechanistic empirical pavement design guide (MEPDG) in predicting the effect of moisture content variation on the resilient modulus. The proposed model provides an advantage over the MEPDG empirical equation in taking into account the effects of both the stress state and moisture content on the resilient modulus of cohesive soils.

Prediction of Resilient Modulus of Cohesive Subgrade Soils from Dynamic Cone Penetrometer Test Parameters

Current pavement design procedures recommend the resilient modulus of subgrade materials for pavement design and analysis. The objective of this paper is to develop two statistical models to predict the resilient modulus of subgrade cohesive soils from the dynamic cone penetration (DCP) test parameters and soil properties. The first model correlates resilient modulus to the dynamic cone penetration test parameters, while the second model correlates resilient modulus to both the dynamic cone penetration test parameters and soil properties. Field and laboratory experiments were conducted at 31 sites in Louisiana that contain four common soil types (A-4, A-6, A-7-5, and A-7-6). Field tests included DCP tests and soil sampling, while laboratory tests included determining basic soil properties and resilient modulus. Statistical analyses were conducted on the collected data, and two statistical models were developed for the prediction of resilient modulus of cohesive subgrade soils from the DCP test parameters and soil properties. The models predicted a separate data set that was not used in their development, indicating the success of the application of the dynamic cone penetration test in evaluating the resilient modulus of pavement subgrade soils. The predicted values obtained from the proposed models corresponded well with the measured resilient modulus values from the repeated load triaxial test.