Subgrade Soil Types Research Articles

Enhanced in-situ measurement and evaluation methods for subgrade modulus utilizing falling weight deflectometer

Falling Weight Deflectometer (FWD) tests have gained increasing popularity in evaluating the stiffness modulus of pavement subgrade. This paper presents an enhanced method for in-situ testing and evaluation of subgrade modulus using FWD apparatus. The method comprises three components: 1) guidelines for conducting field FWD tests with appropriate loading magnitudes and repetitions; 2) selection of optimal deflection positions for modulus back-calculation; and 3) determination of the suitable depth of the semi-infinite rigid layer. This method was developed based on measurements and analysis of FWD data from five highway subgrade sites, covering various subgrade soil types and climatic conditions. The enhanced method helps to promote the robustness and accuracy of modulus back-calculation results. Furthermore, to validate the proposed method, the back-calculated modulus was compared with moduli obtained from the other two commonly used tests, named the Portable Seismic Pavement Analyzer (PSPA) modulus test and the triaxial modulus test. Comparison results indicate strong correlations between the modulus values obtained from the proposed method and those from the PSPA and triaxial modulus tests, affirming the practicality of the proposed method in determining subgrade stiffness modulus.

Evaluation of sand subgrade seepage erosion caused by buried pipeline leakage

Leakage from buried pipelines can lead to an increase in the water content of the subgrade soils and a rise in the water table, leading to soil loosening, erosion and ultimately the formation of hidden voids and roadway collapses. This study presents a discrete-element method and validates its accuracy by utilising cavity data from model experiments. It investigates the mechanism of seepage erosion resulting from pipe leakage and analyses the development of the soil arch effect. Furthermore, it discusses the influence of sand void ratio and particle size on sand seepage erosion. The results indicate that the erosion area is primarily affected by the void ratio and particle size. In comparison to soil particles ranging from 0.1 to 5 mm and from 2 to 5 mm, those with sizes between 0.1 mm and 2 mm generate areas of erosion and loosening that are approximately 40% larger. The proposed model offers a precise analysis of the developmental process and the extent of seepage erosion, thereby contributing to the prediction of potential road cavity areas based on dynamic changes in key factors such as subgrade soil type and groundwater level.

A mobilised bearing capacity approach to the performance-based design of unpaved roads

Unpaved roads are used on low traffic or temporary roads such as for materials transport across construction sites or mines. Performance is usually expressed as a rut depth and if it becomes too large, the passage of vehicles may be hindered and repairs needed. A new design method to calculate the required aggregate thickness to avoid excessive rutting both at the surface and at subgrade level is proposed. Tyre size is an input parameter allowing application of the method to a wide range of cases from heavy haul roads to lightly trafficked local roads. A wide range of rut depths and axle passes may be specified, even as low as values typically required in proof roll testing. The proposed method takes a mobilised strength approach to predict permanent deformation on the first pass by means of newly derived hyperbolic relationships. The permanent deformation on the first pass is then coupled with a separately derived deformation accumulation (logistic) function to predict rut depths following the first pass. The adaptation of well-established bearing capacity design methods with fundamental soil strength parameters has provided a framework for the method’s application to a wide range of aggregate and subgrade soil types, including low-quality or recycled aggregates as well as those mechanically stabilised by geogrid.

Impact of sea level rise on asphalt pavement responses considering seasonal groundwater and moisture gradient in subgrade

Sea level rise (SLR) has been found to have a great impact on the transportation infrastructure in coastal areas. This study developed an analysis approach with numerical modeling to analyze the impact of SLR-induced groundwater rise on critical responses of coastal pavements. The numerical model employed a stress-, moisture content- and matric suction-dependent modulus model to consider the unsaturated characteristics of subgrade soil and non-linear distribution of moisture content. The model results were validated using Falling Weight Deflectometer (FWD) tests in the field. Based on the realistic moisture content collected from Long-Term Pavement Performance (LTPP) database, the critical responses of pavements were evaluated. The in-situ moisture content is non-linearly distributed along the depth, which differs from traditional assumption of monotonic distribution. The seasonal groundwater table (GWT) and subgrade soil type are two factors impacting the critical pavements responses under SLR scenarios. The pavement will be significantly impacted by SLR in the seasons with the higher GWT. The modulus of clay soil is more sensitive to moisture content than that of sandy or silty soil and thus causes the greater increase of pavement responses as sea level rises. On the other hand, the compressive stain on subgrade increases more remarkably than tensile strains at the bottom of asphalt layer under the impact of SLR.

Evaluating the Shear Strength of Subbase-subgrade Interface Using Large Scale Direct Shear Test

The inclusion of geogrid in road pavements can improve pavement performance through increasing the lateral confinement, bearing capacity, and overall rigidity of the pavement, as well as reducing the vertical and lateral pavement deformations. The materials used in the present study are: subbase granular materials Type B, two types of subgrade soil; clay and sandy soil, and two nonwoven biaxial geogrids (G1 and G2) used as reinforcing materials. Direct shear testing was adopted by manufacturing a large-scale direct shear apparatus consisted of an upper, square box of size 20 cm × 20 cm × 10 cm, and a lower, rectangular box of size 200 mm × 250 mm × 100 mm is used in the present study. The results show that, for the four normal stresses equal to 25, 50, 75 and 100 kPa, the interface shear stress curves increased and followed similar trend. For clay-subbase interface, installation of geogrid decreases the apparent cohesion of the material from 16.5 kPa (without reinforcement) to be 8 kPa and 13.5 kPa for G1 and G2, respectively. At sand-subbase interface, using geogrid leads to increase the cohesion of the material from 3.5 kPa to be 15.5 and 16 kPa for G1 and G2, respectively. The friction angle increases slightly from 30o (without reinforcement) to be 35o for G1 and G2 when the interface is subbase over clay. While, it decreased from 35.8o to be 32.1o for G1 and G2 at sand-subbase interface. The interaction coefficient for G1 and G2 increased when the normal strength increased at the clay-subbase interface. Otherwise, the behavior of interaction coefficient of the sand-subbase interface appears deferent trend, where increasing normal stress leads to decrease the interaction.

Dispersive Soil Stabilization Using Biopolymers, Bioenzymes, Additives as a Subgrade Material: A Review Paper

The overall performance of pavement is dependent on the subgrade soil type and its properties. Soil stabilization has always been a substantial concern in construction of highways. In situ soil remoulding is an essential criterion to enhance the fundamental engineering properties of subgrade and to meet the standards of road construction. Various stabilization techniques are utilized to annihilate the inadequate properties of sub-grade soils. Principally, traditionally used soil stabilizers like lime, cement, bitumen, etc. and combinations of these have been utilized widely to enhance the properties of problematic soil. These traditionally soil stabilizers are uneconomical and use of gravel or sand to enrich soil properties are depleting. This scenario has led to lots of researches in order to identify and introduce cost efficient and eco-friendly materials, in particular, different types of inorganic to organic stabilizers have been experimented at laboratory level and also in field level in order to scrutinize their suitability as soil stabilizer. This paper elaborates the various research conducted on enhancing sub-grade of the road by stabilizing dispersive soil with biopolymers, bioenzymes, and additives. These stabilizers are environmentally friendly and a cost-effective alternative to traditionally soil stabilizers.

Evaluation of different types of soil subgrade using glass powder for Low-Volume Roads (LVRs)

Flexible pavement structure consists of number of layer to pose the various function required to maintain a durable pavement over long durability. In order to provide the durable pavement structure over the week subgrade, it consumes larger thickness of natural materials. To avoid such problem and stabilize the available week sub-grade soil. The use of industrial waste in pavement structure gains attention to reduce the natural resource in pavement structure. Last few decades, the utilization of industrial material waste had become immensely in the growing world of construction. In pavement to strengthen the weak sub-grade soil, these products are fulfil the requirements and also showed the outmost performance in pavement structure. In view of the above, this study was conducted on weak sub-grade soil with the different other practically with the additives of glass powder. The glass powder were added in various percentages to the soil mass of sub grade. The experimental study were carried-out The Standard Proctor Test (SPT), Shear Strength (SS), California Bearing Ratio (CBR) Test to determine the optimum (%) of glass powder with the different type of sub-grade soil. This study concluded that, the use of glass is pozzolanic material improved the strength of weak sub-grade soil. The optimum glass powder is found as 15% for the both the types of soil sub-grade.

Life-cycle assessment and multi-criteria performance evaluation of pervious concrete pavement with fly ash

Pervious concrete pavement has great potential in reducing surface water runoff and improving water quality. This study aims to conduct life cycle assessment (LCA) and multi-criteria assessment of pervious concrete pavement with the use of fly ash. The research significance lies in the integration of hydraulic and structure designs for developing functional unit of pervious concrete pavement and combining environmental impacts with engineering and economic indicators. A full LCA of pervious concrete pavement system was conducted including the stages of material, construction, transportation, use, maintenance, and end-of-life stage. The impact assessment included global warming potential, energy consumption, and eutrophication potential due to runoff purification. The pervious concrete pavement structures were designed based on mechanical properties of mixtures, hydrological requirement of reservoir layer, and subgrade soil type to meet equivalent performance on parking lot and highway shoulder. Multi-criteria analysis of pervious concrete mixes and pavement systems were presented based on the normalization of environmental impacts, engineering performances, and economic costs. The LCA results showed that the environmental impacts of pervious pavement system were mainly generated from material stage in terms of 81% to 92% GHG emissions and 70% to 83% energy consumption. The performance rankings of pervious concrete mixes were different from those of pervious pavement structures. The pervious concrete pavement with fly ash can cause greater or less environmental impact, depending on mechanic properties of pervious concrete and the required surface layer thickness to achieve equivalent structural performance.

Study on effect of laboratory roller compaction on unconfined compressive strength of lime treated soils

Expansive soils are problematic due to their swell—shrinkage behavior and low compressive strength. They are modified generally with additives such as lime, fly ash, and various other inorganic and organic materials. Chemical stabilization treatments can improve expansive soil properties for its reuse in geotechnical applications. The present study investigates the properties of two types of subgrade soil treated with Lime and compacted by three different methods in the laboratory. The study is mainly focused to bring out the effect of different methods of compaction on the unconfined compressive strength of Lime treated soils and untreated soils. Laboratory investigation included pH, Atterberg limits, cation exchange capacity (CEC), compaction, unconfined compression strength (UCS), California Bearing Ratio (CBR), Scanning Electron Micrographs (SEM) and EDAX before and after lime treatment. Tests were performed on lime treated soils (2, 4, 6 and 8% of lime). The soil samples for unconfined compressive strength test were prepared by static, dynamic and roller compaction methods in the laboratory. Roller compaction was performed using indigenously fabricated Roller compactor cum Rutting Analyzer (RCRA). The results indicate that dry unit weight and UCS of roller compacted lime treated soil is lower than that of dynamic compacted soil. However, dry unit weight and UCS of lime treated roller compacted soil are closer to that of statically compacted soil. Cation exchange capacity of both soils before and after treatment with lime were examined, CEC reduced with increase in lime content.

Evaluation of the bearing capacity of poor subgrade soils stabilized with waste marble powder according to curing time and freeze-thaw cycles

In this study, pavement subgrade soils were stabilized with two difference types of waste marble powder, and California bearing ratio (CBR) tests were conducted to evaluate the improvement in their bearing capacity. To this end, highly plastic silt (MH) and highly plastic clay (CH) layers were used as the subgrade soil material. A number of unsoaked CBR tests were conducted on the test samples by adding a varying percentage of calcitic marble powder (CMP) and dolomitic marble powder (DMP) using different freeze-thaw cycles (0, 1, 3, 5, 7, and 11 cycles) and curing times (0, 7, 30, and 60 days) in the laboratory. The waste marble powder ratios were taken as 5, 10, 20, 30, and 50% by the dry weight of each soil specimen. SEM and energy dispersive X-ray (EDAX) analyses were also performed on the specimens to determine the efficiency of the marble powders. According to the comparison based on the CBR values, the inclusion of an appropriate amount and type of waste marble powder positively affected the bearing capacity of the subgrade soil samples regardless of curing time and number of freeze-thaw cycles. Moreover, both curing time and freezing-thawing cycles influenced the CBR values depending on the waste marble powder type and content and subgrade soil type.

Factors affecting performance of sprayed seals in rural Victoria

ABSTRACT Factors that significantly affect performance of in-service sprayed seals have been identified through developing comprehensive models using a multilevel analysis approach. Subjective condition data of surface distresses from five rural road networks in Victoria/Australia have been used. They include cracking, deformation, texture loss, stone loss and patching. Evaluations of individual distresses for representative segments are combined into a composite index called Surface Inspection Rating (SIR) which is used to trigger the need for resealing. Contributing factors considered include surface age, traffic volume, aggregate size, subgrade soil type, shoulder seal width, rainfall and temperature. For each network, statistically significant factors for each distress are identified and used in developing their SIR models. An overall SIR model has also been developed using condition data from all five networks. Predictions of this model have been compared with an existing model that has been developed using Markov Chains with surface age as the only predictor. The results show that both models have roughly similar deterioration rates of SIR up to 8 years of seal life, after which deterioration rate of the newly developed model becomes higher.

Combined effect of compaction level and matric suction conditions on flexible pavement performance using construction and demolition waste

The characteristics of the unbound base layer have been recognized to influence the performance of flexible pavements to wide extents depending on climate conditions, construction quality, material source, traffic level, and pavement structure. Recently, unsaturated soil modeling has become generally accepted in predicting the pavement performance as pavement layers are typically placed well above soil water table, and tend to remain unsaturated during pavement service life. This paper investigates the combined impact of compaction level and initial matric suctions of construction and demolition (C&D) waste material used as a based layer on simulated pavement performance using the AASHTOWare Pavement ME Design software. Towards the preparation of the software inputs as per level 1 requirements, a laboratory experimental program was conducted on C&D material which includes the construction of soil water characteristic curve (SWCC) and determination of resilient modulus at four different moisture contents and two levels of compaction effort. The simulated pavement performance analyses consider two climatic conditions (dry and wet), two groundwater table levels (shallow and deep), two types of subgrade soil (strong and weak), and two thickness levels for the base and asphalt surface layers (thin and thick). Full statistical analyses of the main and interaction effects were performed on the results of AASHTOWare Pavement ME Design software. The results showed that the compaction level has more significant effect on the base and subgrade rutting and bottom-up fatigue cracking than the initial matric suction. In addition, both initial matric suction and SWCC input level were found to have a significant effect on all simulated distresses. Furthermore, the interaction between the compaction and initial matric suction was found to be significant.

Using artificial neural network and genetics algorithm to estimate the resilient modulus for stabilized subgrade and propose new empirical formula

Abstract This paper presents the results of using rigorous modeling artificial neural network and genetic algorithm to examine the proper stabilization of very weak subgrade soils at high moisture contents. The experimental database was performed in Louisiana transportation research center for four types of soft soil, 125 samples data were prepared and used in development ANN and genetic algorithm models. For two models, the input variables include eight parameters, namely cement percentage, lime percentage, PI, silt percentage, fly ash, optimum moisture content OMC, moisture content M.C, and clay percentage, the output variable includes resilient modulus for different types of stabilized subgrade. Furthermore, mathematical models were proposed to predict the resilient modulus for stabilized weak subgrade with different types of stabilizer agent such as cement, lime, and fly ash with four different subgrade soil types of different plasticity indices. Besides, the proposed models for estimating resilient modulus for stabilized subgrade were derived by an artificial neural network model and genetic algorithm. The scheme method displayed is a particular process of which resilient modulus for stabilized subgrade can be determined directly. The results show impressive due to obtain a high value for regression for sets of models; we obtained another accurate result for Mr by using Gene expression programming. Following the model design is stablished; the powers and deficiencies of the proposed models are tested by matching the resilient modulus proposed from two models with the resilient modulus extracted from experimental test concerning the R2 values. Further, in the neural network model, an exact assessment was achieved using r2 = 0.97. Genetic algorithm with a coefficient of determination (R2) of 0.95 to determine the resilient modulus of stabilized subgrade. Achievement estimation of the ANN and genetic algorithm pointed out that the theses methods were capable to predict resilient modulus of stabilized with powerful and higher efficiency and outcomes of these models was more conventional to the experimental results. Finally, sensitivity analysis of the achieved models has been performed to examine the impact of input variables on output (Mr) and determines that the cement percentage, lime percentage, fly ash percentage, PI, clay percentage, MC, OMC, and silt percentage are the powerful variables on the resilient modulus of stabilized subgrade.

Engineering Characterization of Subgrade Soils of Jimma Town, Ethiopia, for Roadway Design

Soils are naturally occurring materials that carry loads of civil engineering structures including roads and buildings. However, not all natural soils are suitable for such uses due to limited strength and instability under varying environmental conditions. A lack of adequate geotechnical investigations and soil characterization can result in the over-design of foundations, unexpected excavations to remove unsuitable soils, cost overruns, construction delays; and, contract disputes. In this research, an experimental plan was executed to determine the engineering properties of subgrade soil in Jimma Town in southwestern Ethiopia by using both disturbed and undisturbed soil samples. The plan included tests to determine the moisture content, specific gravity, grain-size analysis, Atterberg limits, compaction-density relationship, California Bearing Ratio (CBR), unconfined compression strength, and triaxial shear strength. X-ray diffraction (XRD) analysis was also conducted to determine the chemical composition of the soil. The soil characterization indicated that soft clay is the predominant subgrade soil type and that it has a very low load-bearing capacity, high plasticity, low strength and, high compressibility, which makes the soil unsuitable to serve as a highway subgrade without the help of soil improvement techniques.

Interpretation of CBR Test Consequences for Subgrade Soil Preserved Through Geo-Grid

The California Bearing Ratio (CBR) is a parameter for evaluation of the mechanical strength of sub grade, base course and other layers of a new carriage way. It depends on various factors and nature of soil. The service life of pavement on weaker soil sub grade is quite low due to the high compressibility and plasticity behavior of soils. Some soils possess less strength, CBR value and have high affinity to moisture content. Hence it is important to increase the strength of soil for sustainable performance of Indian roads. To increase the sub grade soil strength, geogrids are used in roads. Geogrids are cost effective polymeric materials used as soil reinforcement. It helps to increase the stability and bearing capacity of soil, enables good drainage and involves less maintenance. Increase in CBR value of the sample with use of geogrids leads to reduction in the thickness of pavement. Two soil samples are collected from the nearby construction sites. Basic tests are to be conducted on the samples to determine its engineering and index properties followed by CBR test under optimum moisture content. This paper deals with the experimental results of CBR tests on different types of sub grade soil by increasing the number of geogrid layers in each trial. This gives the optimum number of geogrid layer to attain the maximum CBR value. This paper also includes the application of CBR value in the design of flexible pavements as per IRC recommendations.

Experimental and numerical studies on geotextile reinforced subgrade soil

ABSTRACT Experimental and numerical studies were undertaken to study the effect of geotextile used for subgrade reinforcement. The standard laboratory California bearing ratio (CBR) test was conducted on the soil reinforced with geotextile. Two different types of subgrade soil, sandy and clayey soil, and two types of geotextiles (woven and non-woven) were used in this study. The geotextile reinforcements were placed in samples in various combinations in one, two and three layers. The effects of type of geotextile and position and number of geotextile layers on the strength of subgrade were investigated. An increase in CBR value was observed due to the inclusion of woven geotextile reinforcement in the subgrade. It was also observed that woven geotextile performed better than non-woven geotextile. Finite-element program ABACUS is also used to back analyse the experimentally calculated CBR values and found to be in good agreement with experimental results.

Laboratory testing and analysis of dynamic and static resilient modulus of subgrade soil under various influencing factors

In this study, dynamic and static resilient modulus of subgrade soil were conducted for six types of subgrade soil using the stress level and loading range on top of subgrade under moving vehicle loading. The influences of loading frequency, stress level, compaction degree, and moisture content on dynamic and static modulus were investigated. The prediction models of nonlinear parameters of dynamic resilient modulus and the relationship of dynamic and static resilient modulus were developed. Results showed that dynamic resilient modulus of different soils were significantly affected by loading frequency at the loading frequency range of 0.5–3 Hz. Dynamic and static resilient modulus were both positively related with confining pressure and compaction degree, but negatively related to the moisture content of subgrade soil. The nonlinear parameters of dynamic resilient modulus prediction models had the similar form for different types of subgrade soil, while the coefficients of nonlinear parameters varied with the type of subgrade soil. The parameters of the relationships between dynamic and static resilient modulus for different types of soil were also similar in the equation format with different parameter values. The research findings provide valuable information for using realistic subgrade soil modulus in pavement design and analysis.

Field performance evaluation of asphalt mixtures containing high percentage of RAP using LTPP data

Recycled asphalt pavement (RAP) has been used in production of new mixtures for many decades and has become a common practice in highway agencies. However, concerns about field performance of RAP mixtures have been lingering on since the beginning of RAP usage. In this study, the field performance of RAP was verified through the Long-Term Pavement Performance (LTPP) program. Particularly, pavement overlays constructed with virgin asphalt and those constructed with a significant RAP percentage were examined and compared regarding their field performance. To achieve this goal, data from the Specific Pavement Study experiment 5 (SPS-5) of LTPP were retrieved and statistically analyzed for comparison. A total of eighteen projects comprised of 162 sections were collected. Various performance measures were incorporated, including alligator cracking, longitudinal cracking (wheel path and non-wheel path), transverse cracking, patching, potholes, rutting, roughness, and pavement surface deflections. In addition to the key variables used in the SPS-5 experiment (thickness, materials and pre-overlay treatment), the impacts of other important factors, including climatic conditions, initial surface condition and subgrade soil classification, were also investigated. Exploratory data analyses and logistic regression were used to compare the performance of RAP and virgin asphalt overlays. Results from the analysis results show that RAP had little effects on longitudinal cracking, transverse cracking, and roughness, but slightly increased the risk of fatigue cracking and weakened pavement structure. As expected, use of RAP was beneficial in reducing the rutting potential of thick overlays. For both RAP and virgin asphalt overlays, thicker overlays performed better than thinner ones in all performance measures except for rutting. Pre-overlay treatment methods and subgrade soil types were found to be critical factors affecting fatigue cracking and roughness. The initial surface condition also showed significant effects on pavement structural capacity and fatigue cracking over the long run.

Evaluating the performance of very weak subgrade soils treated/stabilized with cementitious materials for sustainable pavements

Abstract This paper presents the results of laboratory tests that were conducted to determine the proper treatment/stabilization recipe of very weak subgrade soils at high moisture contents, and to evaluate the corresponding performance-related properties [e.g., the resilient modulus and permanent deformation] for use in the design of sustainable pavement structures. Four different subgrade soil types of different plasticity indices were considered in this study. Three different moisture contents were selected at the wet-side of optimum that correspond to a raw soil strength value of 172 kPa (25 psi) or less. All the soils were treated with different combinations of class C fly ash (or Portland cement type I) and hydrated lime to achieve a 7-day target strength values of 345 kPa (50 psi) to create a working platform and 690 kPa (100 psi) to stabilize the subgrade for subbase application. Repeated load triaxial (RLT) tests were performed on laboratory molded specimens to evaluate their resilient modulus and permanent deformation behavior under cyclic loading. The AASHTO T-307 procedure was followed in this study to conduct the resilient modulus tests. A good correlation was observed between the water/additive ratio and the resilient modulus/permanent deformation, such that the soil specimens prepared at low water/additive ratio showed better performance than those prepared at high water/additive ratio. The results of laboratory tests showed that the use of direct correlation between unconfined compressive strength (UCS) and resilient modulus for cementitiously treated/stabilized soils can be misleading.

Enzyme based soil stabilization for unpaved road construction

Enzymes as soil stabilizers have been successfully used in road construction in several countries for the past 30 years. However, research has shown that the successful application of these enzymes is case specific, emphasizing that enzyme performance is dependent on subgrade soil type, condition and the type of enzyme used as the stabilizer. A universal standard or a tool for road engineers to assess the performance of stabilized unbound pavements using well-established enzymes is not available to date. The research aims to produce a validated assessment tool which can be used to predict strength enhancement within a generalized statistical framework. The objective of the present study is to identify new materials for developing the assessment tool which supports enzyme based stabilization, as well as to identify the correct construction sequence for such new materials. A series of characterization tests were conducted on several soil types obtained from proposed construction sites. Having identified the suitable soil type to mix with the enzyme, a trial road construction has been performed to investigate the efficiency of the enzyme stabilization along with the correct construction sequence. The enzyme stabilization has showed significant improvement of the road performance as was evidenced from the test results which were based on site soil obtained before and after stabilization. The research will substantially benefit the road construction industry by not only replacing traditional construction methods with economical/reliable approaches, but also eliminating site specific tests required in current practice of enzyme based road construction.