Browsing by Author "Showkat, Rakshanda"

Now showing 1 - 20 of 20

The 7th victor de mello goa lecture: climate resilient design of embankment using geocomposites
(Brazilian Association for Soil Mechanics and Geotechnical, 2025) Showkat, Rakshanda
Climate change is driving non-stationary rainfall patterns, intensifying both the frequency and magnitude of extreme precipitation events, which pose significant risks to earthen embankments. Traditional Intensity-Duration-Frequency (IDF) curves, based on stationary climate assumptions, often underestimate future hydrological loads. This study investigates the stability of embankments with and without geocomposite drainage layers under both stationary and non-stationary IDF scenarios, focusing on return periods of 10, 30, 50, and 100 years. Bengaluru, India, a monsoon-affected urban region, serves as the case study, with future rainfall projections derived from the CMIP6 SSP5-8.5 scenario to represent high-emission pathways. Numerical simulations reveal that unreinforced embankments under non-stationary conditions experience rapid pore-water pressure accumulation and a significant drop in Factor of Safety (FOS), reaching critical saturation in as little as 12 hours for 50-year return events. In contrast, geocomposite-reinforced embankments exhibit improved drainage, delayed saturation, and maintain FOS above 1.5 under stationary scenarios, and up to 18 hours of stability in the 100-year non-stationary case.
Analysing Shallow Footing on Compacted Embankment Under Rainfall
(Springer, 2025-10) Showkat, Rakshanda
Using the Barcelona Basic Model (BBM) in the FLAC software, the study examines the behaviour of a shallow footing placed on a compacted, unsaturated embankment. The effectiveness of BBM and the Mohr-Coulomb model in foretelling the consequences of water infiltration is compared. It is predicted that soils modelled using BBM result in higher settlements as BBM is capable of modelling the loss of suction upon infiltration. Using the finite difference method in FLAC, hydromechanical coupling analysis is performed to assess the influence of rainfall infiltration in conjunction with load-deformation response. The two stages of the analysis are as follows: the first stage uses the footing to load the embankment, and the second stage incorporates infiltration. It is discovered that the loading phase is influenced by the net stresses, producing load-displacement curves that may be observed. Suction is a major factor during the infiltration phase, which causes changes in pore pressure. This work emphasizes how crucial it is to take suction effects into account when simulating unsaturated embankments that are prone to infiltration.
Analysis of a shallow footing resting on compacted unsaturated embankment under infiltration
(ASCE, 2023-03) Showkat, Rakshanda
Compacted embankments are usually found to be in unsaturated condition. In this study, a shallow footing resting on an unsaturated compacted embankment modeled using Barcelona Basic model (BBM) was numerically analyzed. BBM was implemented in FLAC to consider the variation of strength and stiffness with the change in suction. A comparison of the observed responses in the footing-loaded embankment upon infiltration using BBM was made with Mohr-Coulomb model. It was observed that BBM accurately models the collapse load and shows higher settlement compared to the Mohr-Coulomb model as it considers the loss of suction upon infiltration. This involved two phases, viz, loading the embankment by footing and second with infiltration. It was found that net stresses affect the loading, and load-displacement curves are observed while suction is the dominating factor during infiltration and pore pressure variation is observed.
Bearing capacity of shallow footing on an unsaturated embankment upon infiltration
(EDP Sciences, 2023) Showkat, Rakshanda
Due to rapid urbanization and population growth, construction activities have been increased on slopes of unsaturated hilly regions. Thus, constructing shallow footings on these slopes is a common method for supporting infrastructure construction. The main factor causing instability of these unsaturated slopes is the loss of suction upon infiltration resulting in footing failures. Thus, in this study, a shallow footing restingon an unsaturated embankment modelled using Barcelona basic model (BBM) has been numerically analysed to investigate the influence of various factors affecting the bearing capacity upon infiltration. The influence of various critical design parameters, like the distance from the crest of the slope and water table positions, slope angle, and infiltration rate, has been studied comprehensively. As the footing distance increases from the crest (setback distance), soil provides higher bearing capacity upon infiltration due to the confinement. Moreover, it is noticed that the bearing capacity reduces monotonically as the water table rises above the toe, thus depicting the Prandtl-type of failure. Further, as the slope angle increases, bearing capacity decreases at various footing distances upon infiltration. The effect of infiltration rate on bearing capacity of footings depends on the air entry value of the soil. As the air-entry value increases, bearing capacity reduces drastically upon infiltration. This approach helps the design engineers consider these factors while constructing footings on unsaturated slopes.
Bentonite swelling behavior under physicochemical controls: A critical review on thermal–electrolytic conditions and mineralogical determinants for nuclear waste management
(Elsevier, 2025-12) Showkat, Rakshanda
High-level radioactive waste in deep geological repositories relies on bentonite buffers to ensure long-term containment by sealing canisters and limiting groundwater transport. Swelling behavior of bentonite, arising from its unique mineralogical and physico-chemical characteristics, is therefore central to repository integrity. Current knowledge gaps governing its swelling capacity include, (i) exploring individual and coupled effects of temperature and electrolyte concentration and (ii) understanding key physico-chemical properties (montmorillonite content, cation exchange capacity (CEC), specific surface area (SSA), and exchangeable sodium percentage (ESP)) influence on thermo-chemical stress mechanisms. This review critically examines the understanding of how temperature, electrolyte concentration, and mineralogical parameters interact to influence bentonite swelling, hydraulic sealing, and long-term stability. Experimental results, international repository programs and case studies consistently show that montmorillonite content, multi-barrier microstructural states, and electrolyte chemistry are decisive in predicting buffer performance. Evidence indicates that swelling pressure follows a temperature-dependent duality, governed by interlayer and interparticle mechanisms, while salinity and pH strongly suppress swelling through diffused double layer (DDL) compression and ion exchange. Comparisons of globally prominent monovalent cations (Na+) dominated bentonites with divalent cations (Ca+-Mg2+) bentonites revealed that Na-rich bentonites exhibited superior swelling, however, its performance declines sharply in electrolyte conditions. At intermediate dry densities, collapse yields isotropic swelling; low and high densities preserve anisotropy, modulating crystalline vs. DDL expansion. Despite clear trends, anomalies remain, this review aims to improve understanding of thermo-chemical swelling responses to identify the most suitable buffer material for nuclear waste repositories, thereby supporting environmental safety and protection.
Bio-stabilisation of soils using crude urease enzymes: mechanisms, applications and challenges
(Taylor & Francis, 2026-01) Showkat, Rakshanda
The shift towards sustainable, low-carbon ground improvement has positioned enzyme-induced carbonate precipitation (EICP) as a promising bio-mediated soil stabilisation technique. Crude plant-derived urease, especially from jack bean and soybean, has shown potential in enhancing soil strength and reducing permeability through calcium carbonate precipitation within pore spaces. Compared with microbial-induced carbonate precipitation (MICP), EICP avoids biosafety concerns and bacterial viability constraints and exhibits improved transport potential in fine-grained soils. The reported strength, however, from crude urease-based EICP generally remains within the sub-megapascal to low-megapascal range and is comparable to, but not exceeding, those achieved by optimised MICP treatments under laboratory conditions. The performance of EICP shows substantial variability across soil types and treatment procedures, and current evidence is dominated by small-scale laboratory studies. This review focuses on EICP using crude urease extracts, examining enzyme extraction methods, treatment strategies, and the influence of various additives. Laboratory-based durability assessments, including wet-dry and freeze-thaw cycles, are critically discussed, while emphasising the absence of long-term field monitoring data. Key constraints related to pore-scale transport, environmental sensitivity, ammonium by-products and scalability are addressed. Also, several research gaps are identified to guide future mechanistic modelling, controlled field trials and the development of hybrid stabilisation approaches.
Deterministic and probabilistic analysis of the response of shallow footings on unsaturated soils due to rainfall
(Elsevier, 2023-11) Showkat, Rakshanda
Due to rainfall, footings are usually subjected to effects of water table fluctuations which results in the variation of ultimate bearing capacity in unsaturated soils. However, the conventional bearing capacity theories don’t account for the variation of suction as the water table position changes. In this paper, an equation based on Terzaghi theory is proposed to evaluate the variation of bearing capacity due to suction variations due to rainfall. The proposed equation results in higher bearing capacity values compared to the conventional Terzaghi equation. Further, a comparison of the bearing capacity obtained using the proposed equation is made with those obtained from Barcelona Basic model (BBM), Mohr-Coulomb model and Terzaghi equation. It is observed that BBM results in lower values of bearing capacity compared to Mohr-Coulomb model as the former considers the loss of suction upon infiltration. Soil properties like porosity, permeability and soil water characteristic (SWCC) influence the bearing capacity in unsaturated soils. Thus, probabilistic analysis is carried out by using an efficient kriging surrogate model in order to analyze the impact of variation of the associated parameters on the bearing capacity. The surrogate model can predict the surface displacements of footing upon infiltration with enhanced accuracy and computational efficiency. Considering the uncertainty associated with rainfall loads, it is observed that as the return period of rainfall increases, failure probability increases.
Effect of rainfall infiltration on the stability of compacted embankments
(ASCE, 2022-05) Showkat, Rakshanda
Rainfall infiltration causes the collapse of unsaturated embankments due to loss of suction. In this paper, the Barcelona Basic Model (BBM), a constitutive model developed for unsaturated soils, was implemented in Fast Lagrangian Analysis of Continua (FLAC) for simulating the effect of varying rainfall intensities on compacted embankments. It was observed that large vertical deformations occur and considerably high positive pore-water pressures get developed, accounting for the collapse of an embankment. The results also show that rainfall intensity and duration affect the slope stability. A comparison was made between the results obtained using the Mohr–Coulomb model and BBM. It was found that the soil undergoes larger deformations when modeled using BBM as BBM accurately models the loss of suction upon saturation. Reliability analysis of embankment shows that probabilistic analysis provides a better assessment of slope stability rather than the factor of safety and shows that suction and hydraulic conductivity are critical parameters influencing slope reliability for unsaturated soil slope embankments.
Estimation of soil water characteristic curve using machine-learning algorithms and its application in embankment response
(ASCE, 2025-01) Showkat, Rakshanda
The parameters of the soil water characteristic curve (SWCC) play a pivotal role in the examination of unsaturated soil behavior. This study employs three machine learning models—random forest (RF), extreme gradient boosting (XGBoost), and multiexpression programming (MEP)—to predict the SWCC using key soil properties. Among them, the RF model demonstrated the most robust performance in SWCC prediction. The Shapley Additive Explanation (SHAP) analysis further reveals that suction is the most influential factor affecting SWCC predictions, with other input parameters also contributing significantly. Additionally, the MEP model offers a straightforward expression for SWCC estimation and, thus, proved practical for predicting embankment responses and exhibited superior accuracy over traditional methods, such as the Arya and Paris model (ACAP). For a precise assessment of the hydromechanical response of the embankment subjected to infiltration, an increase in pore pressure is observed when employing the MEP model compared to the ACAP model for fine-grained soils. The findings emphasize the potential of RF and MEP in enhancing SWCC prediction and their practical implications for soil engineering applications.
Evaluation of dynamic properties of unsaturated soils under cyclic loading
(Elsevier, 2025-03) Showkat, Rakshanda
This study investigates the cyclic response of unsaturated soils, focusing on the dynamic properties such as damping characteristics and soil stiffness, under varying matric suction and confining stress conditions during cyclic triaxial loading. Despite challenges in evaluating unsaturated soils compared to saturated ones, cyclic triaxial testing emerges as an efficient method for exploring their cyclic behavior. Through a series of experiments with different loading frequencies, stress levels, and suction conditions, the research reveals that as matric suction increases, stiffness rises while the damping ratio decreases. Additionally, comparisons between isotropic and anisotropic stress conditions show that the shear modulus is higher under anisotropic consolidation due to particle reorientation. The study proposes a semi-empirical equation to address the stress and suction dependency of shear modulus, finding a consistent trend between predicted and measured values. Ultimately, the findings underscore the significance of stress state, suction, cyclic shear strain, number of loading cycles and confining pressure in determining soil shear modulus.
Experimental and numerical evaluation on the response of unsaturated compacted soils under triaxial conditions
(ASCE, 2025-02) Showkat, Rakshanda
This paper presents the findings from a series of constant suction triaxial tests conducted on compacted sand and silty sand under unsaturated conditions. These tests were carried out using a fully automated double-walled triaxial cell employing the axis translation technique. The net mean stresses applied ranged from 50 to 250 kPa, while matric suctions were maintained at 0, 100, and 200 kPa. The primary objective of this study was to elucidate the mechanical behavior of the two compacted soils under triaxial conditions, particularly focusing on the influence of suction on variables such as peak stress, apparent cohesion, critical state stress, postpeak softening, and strain-induced dilatancy. The experimental results were utilized to calibrate and validate two prominent critical state-based models for unsaturated soils: the Barcelona basic model (BBM) and the Morvan model. While the BBM accurately predicted the deviatoric stress values at the critical state under controlled suction conditions, it did not adequately capture the postpeak softening behavior. Conversely, the Morvan model, after appropriate calibration and validation, successfully replicated both the critical state and postpeak behaviors, demonstrating a strong correlation between its predictions and the experimental data for both soil types.
Experimental investigation on reuse of dredged soils improved using waste rubber tyre powder (WRTP) and cement as admixtures
(Taylor & Francis, 2024-03) Showkat, Rakshanda
Dredged soils possessing low-bearing capacity and high compressibility were tested incorporating waste rubber tyre powder (WRTP) at varying percentages in increments of 1.5% up to 15% by dry weight of the soil and 2% cement. It was observed that maximum dry unit weight (MDUW) decreased to 11.75 and 12 kN/m3 for combinations of 15% WRTP and 15% WRTP + 2% cement respectively. Direct shear test (DST) parameter ‘c’ at 4.5% WRTP and 2% cement increased from 44 to 49 kN/m2 whereas angle of internal friction, ‘ϕ’ showed an increase up to 37°. The Unconfined compressive strength (UCS) of soil-WRTP-cement mixture enhanced from 110 kN/m2 in the untreated state to 596 kN/m2 at 28 days curing and 6% WRTP + 2% cement. Further, California bearing ratio (CBR) values increased up to an optimum addition of 6% WRTP + 2% cement, both in unsoaked (6 to 13%) and soaked condition (2 to 7%). Soil improvement using WRTP and cement can improve the strength and durability of road subgrades and embankments. WRTP in addition to cement can be used in locations with weak or problematic soils to improve load-bearing capacity and reduce settlement-related problems.
Hydro-mechanical simulations of unsaturated soil slope
(Springer, 2021-07) Showkat, Rakshanda
Rainfall-induced landslides, which are frequent in various parts of the world, cause a substantial loss in infrastructure and are always a risk to public safety. The assessment of such landslides is critical, and therefore, the effect of rainfall on unsaturated soil slope is modeled, and the results of numerical simulations are presented in this paper. Coupled hydro-mechanical simulations are performed using the elastoplastic Barcelona Basic Model (BBM), and the results are presented in terms of the displacement values, the evolution of pore water pressure (PWP), and saturation zones. The obtained results are compared with those of the traditionally used model, i.e., Mohr–Coulomb. As BBM considers the effect of confining pressure and suction, which the Mohr–Coulomb Model does not consider, a considerable difference in the displacement values is found. Moreover, initial failure gets developed upslope as the tensile volumetric plastic strains are concentrated at the top of the slope, suggesting that soil slope does not have to be entirely saturated to experience failure.
Improvement of cohesive soils by using stone columns
(International Journal of Technical Research and Applications, 2018) Showkat, Rakshanda
Soil being natural and non-manufactured material has proven itself to be most potentially problematic and complex materials to tackle with. The complexity does not arise only because of soil as a material, but also by the fact that various methods to characterize the soil for estimations of constituents, behavior and strength are potentially difficult. In this paper , a study on the effect of stone columns on the behaviour of cohesive soils has been done, it was found that the installation of the stone columns plays a very significant role in improving the bearing capacity of the cohesive soils. The main improvement in cohesive soils takes place by virtue of densification while inserting the stone column, the increase in drainage also plays a great role. The length of the stone columns was found to greatly influence the behaviour of the improvement of the soils. The improvement is very significant for a length of 1B where B is the width/diameter of the footing.
A laboratory study on the mechanical behaviour of dredged soil admixed with waste rubber tyre powder and cement
(Springer, 2021-04) Showkat, Rakshanda
Due to the rapid development in automobile industry, the amount of tyre wastes has been increasing every year throughout the world. An attractive method to reduce the tyre waste produced is the use of recycled waste materials for civil engineering application, and also, it may be used as a stabilizer in soils so that it may help in improving the engineering properties of soft soil. Dredge material which belongs to soft soil deposits usually has low bearing capacity, high compressibility and undergoes settlement over a long period of time, hence cannot be used as a construction or foundation material. In this study, tyre rubber powder has been used to see its influence on the mechanical properties of dredged soil. Dredged soil was collected from the catchment of Dal Lake- Nishat. Various tests like specific gravity, gradation analysis, Atterberg’s limit, compaction tests, direct shear tests, unconfined compressive strength, California bearing ratio tests have been done in order to characterize and find the shear strength parameters. This study involves performing compaction test and UCS on the soil incorporated with rubber powder (passing 425µ) at varying percentages of 1.5, 3, 4.5, 6, 9, 12 and 15%. Also, to further improve the strength, cement at a constant percentage (2%) was added to rubberized soil and the effect on UCS characteristics at various curing periods of 3 and 7 days was analysed.
Physical and mechanical behavior of dredged soil acquired from dal lake—a laboratory study
(Springer, 2021) Showkat, Rakshanda
This chapter delves into the physical and mechanical behavior of dredged soil acquired from Dal Lake, a significant water body in Srinagar, India. The study begins with an introduction to Dal Lake, its importance, and the challenges it faces due to urbanization and pollution. The authors collected soil samples from three different sites on the lake and conducted extensive laboratory tests to determine various geotechnical properties. Key findings include the classification of the dredged material as inorganic silt with medium plasticity, low specific gravity, and low shear strength parameters. The chapter also discusses the compaction characteristics and California Bearing Ratio (CBR) values of the dredged soil, indicating its limited suitability for construction purposes without stabilization. The study concludes with a call for proper management and treatment of the dredged material to enhance its potential for engineering and environmental applications. This chapter is a valuable resource for professionals seeking to understand the geotechnical aspects of dredged soil and its potential reuse.
Probabilistic analysis of compacted embankments using kriging surrogates
(ASCE, 2026-03) Showkat, Rakshanda
The natural variability of material properties in both soil deposits and earth structures is often disregarded in geotechnical design. To address this gap, this study proposes a probabilistic approach for evaluating the impact of soil variability on embankment response, utilizing a probabilistic finite difference model that employs kriging surrogates with randomly varying values of preconsolidation stress, porosity, and suction. To enhance computational efficiency, an intelligent surrogate model was developed. The study uses a coupled hydro-mechanical analysis to calculate crest settlement at various stages of rainfall. The anisotropic Barcelona basic model characterizes soil mechanical behavior, while van Genuchten relationships describe water retention and permeability. By using unsaturated soil mechanics and a probabilistic approach, the study consistently analyzes rainfall-induced displacements. The results of the study indicate that displacements can be vastly underestimated if the variability of parameters and partial saturation are not taken into account at the same time. The variability of settlements and their statistical characteristics during rainfall are dependent on soil variability statistics. The intelligent surrogate model accurately predicts embankment failure under infiltration, with superior computational efficiency.
Reliability analysis of compacted embankment with geocomposite under infiltration
(Emerald, 2023-04) Showkat, Rakshanda
Embankment failures can be prevented by introducing geocomposites to act as drains. The effect of the geocomposite layer on the pore pressure distribution and surface displacements of an unsaturated embankment upon infiltration has been studied numerically using deterministic and probabilistic approaches. The inclusion of the geocomposite layer leads to an increase of suction below the interface and a decrease in suction above it by functioning both as a capillary barrier and a drainage layer, thereby reducing the surface displacements upon infiltration. The load in the form of rainfall and the resistance such as suction of the embankment material being variable leads to a variability in the displacements; therefore, reliability analysis has been carried out using hydraulic permeability and soil water characteristic curve (SWCC) parameters as random variables. To assess the probability of failure (Pf), a surrogate model based on augmented radial basis function has been used. Probabilistic analysis revealed that the embankment with geocomposite has less Pf compared to the embankment without geocomposite considering the rainfall infiltration. Moreover, sensitivity analysis predicted that SWCC parameters influence the Pf of embankment containing geosynthetics under infiltration to a larger extent.
Response of anisotropy modeled compacted embankment during infiltration
(Springer, 2024-07) Showkat, Rakshanda
During rainfall, collapse compression predominates due to the slippage of particles, resulting in the rearrangement of soil fabric toward a configuration dependent on the fabric of the initial stress state. Consequently, these alterations in soil fabric induce anisotropic mechanical behavior in unsaturated soils. In this study, an anisotropic model, denoted as ABBM and based on the Barcelona Basic Model (BBM), was implemented into FLAC to analyze the wetting behavior of a typical compacted embankment during infiltration. The research findings indicate that prolonged rainfall durations result in the evolution of the yield surface, consequently amplifying vertical surface displacement. Moreover, as the anisotropic evolution parameter surpasses a defined threshold, the degree of anisotropy diminishes, ultimately resembling the isotropic behavior observed in the Barcelona Basic Model (BBM) due to changes in preconsolidation pressure. The study presents an innovative approach to evaluate embankment performance under rainfall-induced conditions by considering changes in fabric anisotropy relative to the degree of saturation. The results demonstrate that alterations in the degree of saturation lead to rotation of the yield surface, nearly erasing anisotropy upon reaching full saturation. To account for parameter variability, a reliability analysis was performed using the Monte Carlo method, assessing the performance of embankment using different constitutive models, viz, the Mohr–Coulomb model, BBM, and ABBM. Notably, the analysis revealed that embankment failure probabilities simulated using the ABBM exceed those obtained using the Mohr–Coulomb criterion or BBM, suggesting a greater susceptibility to failure in terms of deformations. This observation has practical significance in a sense that use of appropriate constitutive models in embankments is required.
Soil constitutive models and their application in geotechnical engineering: a review
(International Journal of Engineering Research & Technology, 2018-04) Showkat, Rakshanda
Various constitutive models have been developed for modeling the stress strain behavior of soils and apply such models in finite element modeling for application in geotechnical engineering and also for analysis of soil structure problems under different loading conditions. Simple as well as complex models have been formulated based upon the mechanical principle (hooks law of linear elasticity and columbs law of perfect plasticity).However soils are not entirely linearly elastic and perfectly plastic for the entire range of loading. In fact, actual behavior of soils is very complicated to understand and it shows range of behaviors under different conditions. Hence, different models have been proposed to describe its response. Moreover, no model can completely describe the complex behavior of soils. This paper presents brief introduction of various soil models and particularly the cam clay Model and also their application.