Showing papers by "Sai K. Vanapalli published in 2019"
TL;DR: In this article, a series of laboratory tests were conducted on intact specimens of two loess soils to characterize their collapsibility, shear strength, microstructure and mineralogy, and microstructural observations were performed on the specimens after various mechanical tests (oedometercollapse tests and triaxial tests).
Abstract: A series of laboratory tests were conducted on intact specimens of two loess soils to characterize their collapsibility, shear strength, microstructure and mineralogy. In addition, microstructural observations were performed on the specimens after various mechanical tests (oedometer-collapse tests and triaxial tests). The micrographs were processed using MATLAB program and the morphology properties of soil pores (including area, major axis length, eccentricity and orientation) were obtained. The micrographs and variations in distributions of the pore morphology properties were used to interpret the microstructural evolution of loess soils due to loading and wetting. Results of the study highlight that collapsible loess soils have an open structure, where clay-coated silts and clay-silt aggregates functioning as fundamental units are connected to each other with a few cementations. Upon loading and wetting, disintegration of clay aggregates (cementations), breakdown of carbonate cementations and other bonding agents initiate the failure of soil structure. This is followed by particle movement and rearrangement, transforming the initial open structure into a closer one. The microstructural evolution is dependent on the stress level and stress path. With the increase in stress level, large-sized inter-aggregate pores transform into small-sized intra-aggregate pores; the pores are flatter and still randomly orientated. Fissures with the size and connectivity related to the stress level may develop in the specimen under a triaxial stress state, depending on the stress path.
94 citations
TL;DR: In this article, the microstructures of intact and remolded loess were investigated and the evolution of the microstructure and PSD (poresize distribution) due to consolidation.
Abstract: It is widely acknowledged that the mechanical behavior of a soil is significantly influenced by the soil microstructure; and the microstructure can evolve as a result of any mechanical, hydraulic, chemical or thermal change taken place on soil sample. The present study aimed to investigate the microstructures of intact loess and remolded loess and to explore the evolution of the microstructure and PSD (pore-size distribution) due to consolidation for both intact and remolded loess. A loess from the Loess Plateau of China was used as test material. A series of intact loess specimens were consolidated to various vertical pressures in oedometer cells. The same loess was remolded at the optimum water content state to various compaction degrees using static compaction method. It is equivalent to consolidate the remolded loess with the least compaction degree under various stress levels. The microstructures of intact loess specimens after consolidation tests and remolded loess specimens are characterized using the SEM (scanning electron microscope) and MIP (mercury intrusion porosimetry) techniques. The micrographs and PSDs under various consolidation pressures (or compaction energies) were compared to investigate the evolution of the microstructure and PSD induced by mechanical loading for each kind of soil. The microstructure of intact loess is more homogeneous and is less dependent on consolidation stress than remolded loess. In both soils, the pores with entrance diameter smaller than 6 μm are almost not influenced by consolidation. In intact loess, inter-aggregate pores with entrance diameter greater than 6 μm are compressed randomly due to loading. However, in remolded loess, the pores are compressed until all larger pores have been compressed. The cumulative pore volume curve of remolded loess of any compaction degree can be divided into two segments, large-pore segment (6–50 μm) and small-pore segment (< 6 μm). The large-pore segment is simplified into a horizontal line and a straight line which slope is independent on the compactness. Remolded loess has very different microstructure and PSD from intact loess even though they may have the same GSD (grain-size distribution), mineralogical composition, and some other physical properties. The microstructural evolution induced by mechanical loading also varies in both kinds of soils. Based upon the measured PSDs, a method is proposed for predicting the PSD of remolded loess of any compaction degree using a reference PSD.
67 citations
TL;DR: In this article, the similarity between the soil-freezing characteristic curve (SFCC) and soil-water characteristic curve is discussed. But, the authors highlight that rigorous investigations are required for better understanding the SFCC to facilitate its use for cold-region engineering practice applications.
Abstract: The drying–wetting and freezing–thawing cycles significantly influence the soil pore water in the vadose zone in permafrost and seasonally frozen regions. The soil-freezing characteristic curve (SFCC) describes the relationship between unfrozen water content and subzero temperature in a soil at frozen condition. Several studies suggest that the SFCC of a frozen saturated soil is similar to soil-water characteristic curve (SWCC), which describes the relationship between water content and suction for a soil under unfrozen unsaturated condition. In the present study, the similarity between SFCC and SWCC, and possible reasons for the hysteresis of SFCC are succinctly reviewed. The SFCC and SWCC of two Canadian soils were measured and critically interpreted to understand the fundamental behavior of SFCC in comparison with the SWCC. The observed hysteresis of SFCC for the two soils was mainly associated with the supercooling of pore water. The measured SFCC and SWCC of the two soils show quantitative dissimilarity rather than similarity. This may be attributed to the experimental limitations and possible fundamental differences between drying–wetting and freezing–thawing processes. In addition, several concerns regarding the similarity between SFCC and SWCC are discussed. The present study highlights that rigorous investigations are required for better understanding the SFCC to facilitate its use for cold-region engineering practice applications.
32 citations
TL;DR: In this article, a method that is based on easy-to-obtain parameters from constant water content oedometer tests and the wetting soil-water characteristic curve is used for predicting the long-term wetting-induced collapse deformation.
25 citations
TL;DR: In this article, an artificial neural network (ANN) model was proposed and validated for estimating the resilient modulus of five Canadian soils that are widely used as pavement subgrades were determined under wetting and freeze-thaw conditions.
25 citations
TL;DR: In this paper, the behavior of a single model pile and pile groups in sand under both saturated and unsaturated conditions was investigated, and 40 different mode modes were used to investigate their behavior.
Abstract: The research focus of this paper is directed to investigate the behavior of a single model pile and pile groups in sand under both saturated and unsaturated conditions. Forty different mode...
22 citations
TL;DR: In this article, a three-step computer program is developed for simulating the load-displacement response of a single pile in unsaturated expansive soil taking account of influence of water infiltration.
21 citations
TL;DR: In this article, a model is proposed to estimate the lateral earth pressure (LEP) considering the variation in LSP behind fixed rigid retaining structures with respect to the matric suction during the infiltration process.
12 citations
TL;DR: Buried pipeline systems form vital infrastructure, all over the world, to transport resources such as water, oil, and gas from the production stage to the locations of consumption as discussed by the authors.
Abstract: Buried pipeline systems form vital infrastructure, all over the world, to transport resources such as water, oil, and gas from the production stage to the locations of consumption. Failure or ruptu...
10 citations
TL;DR: Several pipeline projects have been proposed in the world in recent years owing to the rapid growth of the petroleum industry as mentioned in this paper, but these pipelines are usually buried above the natural ground level.
Abstract: Several pipeline projects have been proposed in the world in recent years owing to the rapid growth of the petroleum industry. Onshore pipeline systems are usually buried above the natural groundwa...
6 citations
TL;DR: In this paper, a one-parameter model is proposed to describe the variation of the soaking collapse with the pre-soaking degree of saturation under virgin condition once a soil's yielding point can be clearly defined and the degree of saturated condition is known.
Abstract: In this paper, the volumetric collapse of an unsaturated soil, upon soaking to saturation under a certain stress level, is referred to as soaking collapse. The soaking collapse for a soil under virgin condition is assumed equal to the difference between the soil’s virgin compression line (VCL) and its normal consolidation line (NCL) at saturated condition based on results of oedometric constant water content compression and soaking tests performed on a compacted Nanyang expansive clay. A one-parameter model is proposed to describe the variation of the soaking collapse with the pre-soaking degree of saturation under virgin condition once (1) a soil’s yielding point can be clearly defined and (2) the degree of saturation during virgin compression is known. This model can be used to predict the VCL from the NCL. Data of the Nanyang expansive clay, along with published data of nine soils that were derived from constant water content or constant suction compression tests (including oedometric and triaxial compression), were used to calibrate and validate the model. It is shown that the model, when combined with a degree of saturation-volume model and the information of yielding and NCL, can predict reasonable VCLs for all examined soils and suitably capture several characteristics of the VCL including the nonlinearity and pressurised saturation. A constant model parameter of 1.5 is found suitable for all examined soils. The model is also used to predict the VCLs of two compacted soils from the constant degree of saturation compression, which is a recently developed testing technique to evaluate the compression behaviour of unsaturated soils, with reasonable agreement achieved.
TL;DR: In this article, the authors used commercial software VADOSE/W that can account for climatic factors to predict variation of matric suction with respect to time for an expansive soil cut slope in China, which is reported in the literature.
Abstract: Shallow failures occur frequently in both engineered and natural slopes in expansive soils. Rainfall infiltration is the most predominant triggering factor that contributes to slope failures in both expansive soils and clayey soils. However, slope failures in expansive soils have some distinct characteristics in comparison to slopes in conventional clayey soils. They typically undergo shallow failures with gentle sliding retrogression characteristics. The shallow sliding mass near the slope surface is typically in a state of unsaturated condition and will exhibit significant volume changes with increasing water content during rainfall periods. Many other properties or characteristics change such as the shear strength, matric suction including stress distribution change with respect to depth and time. All these parameters have a significant contribution to the expansive soil slopes instability and are difficult to take into consideration in slope stability analysis using traditional slope stability analysis methods based on principles of saturated soil mechanics. In this paper, commercial software VADOSE/W that can account for climatic factors is used to predict variation of matric suction with respect to time for an expansive soil cut slope in China, which is reported in the literature. The variation of factor of safety with respect to time for this slope is computed using SLOPE/W by taking account of shear strength reduction associated with loss of matric suction extending state-of-the art understanding of the mechanics of unsaturated soils.
TL;DR: Hysteretic soil water retention behavior is the key information required for interpreting and predicting the hydromechanical responses of unsaturated soils during drying and wetting process as discussed by the authors. But it is difficult to measure water retention in unsaturated soil.
Abstract: Hysteretic soil water retention behavior is the key information required for interpreting and predicting the hydromechanical responses of unsaturated soils during drying and wetting process...
01 Jan 2019
TL;DR: In this paper, the authors present recent advancements in the mechanics of unsaturated soils that can be used in the reliable mechanistic pavement design methods, such as predicting the soil-water characteristic curve (SWCC) and the variation of the resilient modulus (MR) with moisture content and suction.
Abstract: Cost-effective and high-quality transportation systems are critical to the regional, national as well as international development. The design and maintenance of the pavements, which form a critical component of the transportation systems, should address the geotechnics challenges that arise from the influence of external environment, which include the seasonal drying–wetting and freeze–thaw cycles. Environmental factors influence on the pavements can contribute to their deterioration or even failure in certain scenarios. This paper presents recent advancements in the mechanics of unsaturated soils that can be used in the reliable mechanistic pavement design methods. Simple yet reliable approaches that have been developed for predicting the soil–water characteristic curve (SWCC) and the variation of the resilient modulus (MR) with moisture content and suction are introduced and integrated. The proposed integrated approaches provide reliable predictions of the SWCC and the MR using limited experimental data that can be determined from conventional geotechnical tests, and can be used in the rational pavement design practice.
TL;DR: In this article, an infinite slope formulation is proposed to address the mechanism of shallow slope failure, where the unsaturated soil is described by the extended Mohr-Coulomb elasto-plastic constitutive law, in particular, the material parameters of the yield surface is altered according to the accumulation plastic deviatoric strain (extended to unsaturated soils from the classic softening), to simulate the degradation of mechanical properties.
Abstract: Unsaturated swelling soils expand in volume significantly during a wetting event (for example, rainfall infiltration, snow melting, or irrigation), which can lead to substantial change in the stress regime within and degradation of mechanical properties of the shallow soil mass. These changes can, though not completely, interpret many likelihoods of shallow landslides in swelling soils that has been frequently observed. In this work, an infinite slope formulation is proposed to address the mechanism of the shallow slope failure, where the unsaturated soil is described by the extended Mohr–Coulomb elasto-plastic constitutive law, in particular, the material parameters of the yield surface is altered according to the accumulation plastic deviatoric strain (extended to unsaturated soils from the classic softening), to simulate the degradation of mechanical properties. In this way, the influence of (i) the wetting induced swelling, (ii) the swelling induced stress change, and (iii) the associated softening behavior, on the stability of shallow layer is quantitatively examined. The proposed infinite slope formulation is applied to two typical swelling soil slopes: a synthetized one and a real field case. A good agreement between prediction and available experimental data from a published field study is obtained, illustrating the important implications for the engineering design of swelling soil slopes.
01 Jan 2019
TL;DR: In this article, an experimental investigation program was undertaken to study the behavior of a prototype steel pipeline of 114.3 mm outer diameter and 1.35 m length in a sand subjected to a parallel soil mass movement in the longitudinal direction under saturated and unsaturated conditions.
Abstract: An experimental investigation program was undertaken to study the behavior of a prototype steel pipeline of 114.3 mm outer diameter and 1.35 m length in a sand subjected to a parallel soil mass movement in the longitudinal direction under saturated and unsaturated conditions. The experimental program included several axial load-displacement tests that were performed by varying the water table level. These tests were performed in a specially designed soil container that has provision of water/supply drainage system which facilities achieving different soil-matric suction profiles. The results of the experimental study suggest that matric suction has significant influence on the mechanical behavior of pipeline systems. The axial load that was transferred from unsaturated sand onto the pipe was determined to be 2–2.5-folds greater in comparison to saturated condition. Such an external axial force increment that is not anticipated from conventional design calculations may jeopardize the integrity of energy pipeline systems. For this reason, careful reevaluation is required of the existing design models and code provisions that are presently based on conventional soil mechanics. The study summarized in this paper suggests that the rational interpretation of the pipeline systems is possible by extending the principles of unsaturated soil mechanics.