20th International Conference on Soil Mechanics and Geotechnical Engineering, 2022
A research study was conducted to evaluate the applicability of utilizing crystalline silica-rich... more A research study was conducted to evaluate the applicability of utilizing crystalline silica-rich waste products for mitigating ettringite-induced heaving in lime-treated sulfate-rich expansive soils. Free swell strain tests were conducted on cured lime-treated soil specimens, both with and without crystalline silica admixture. The impacts of the curing period and silica admixture dosage on the post-treatment swelling characteristics were studied. An attempt was made to estimate the ettringite-induced volumetric expansion using stoichiometric analysis. The ettringite-induced swell strains interpreted from swell test results were compared with those estimated stoichiometrically. Microstructural studies were also performed to detect ettringite and cementitious compounds formed in treated soils. Test results suggest that crystalline silica admixture may suppress the availability of reactive alumina from clay minerals, react with lime and form cementitious compounds, and reduce the ettringite-induced heaving. The beneficial influence of crystalline silica admixture increased with an increase in dosage and curing period. Overall, this study indicates that crystalline silica-rich waste products may be utilized as a sustainable co-additive with calcium-based stabilizers for stabilizing sulfate-rich soils. RÉSUMÉ : Une étude de recherche a été menée pour évaluer l'applicabilité de l'utilisation de déchets riches en silice cristalline pour atténuer le gonflement induit par l'ettringite dans les sols expansifs riches en sulfate traités à la chaux. Des essais de déformation par gonflement libre ont été réalisés sur des échantillons de sols traités à la chaux, avec et sans adjuvant de silice cristalline. Les impacts de la période de maturation et du dosage de l'adjuvant de silice sur les caractéristiques de gonflement après traitement ont été étudiés. Une tentative a été faite pour estimer l'expansion volumétrique induite par l'ettringite en utilisant une analyse stoechiométrique. Les contraintes de gonflement induites par l'ettringite interprétées à partir des résultats des tests de gonflement, ont été comparées à celles estimées stoechiométriquement. Des études microstructurales ont également été réalisées pour détecter l'ettringite et les composants cimentaires formés dans les sols traités. Les résultats des tests suggèrent que l'adjonction de silice cristalline peut supprimer la disponibilité de l'alumine réactive des minéraux argileux, réagir avec la chaux et former des composants cimentaires, et réduire le gonflement induit par l'ettringite. L'influence bénéfique de l'adjonction de silice cristalline a été amplifiée avec l'augmentation du dosage et de la période de durcissement. Dans l'ensemble, cette étude indique que les déchets riches en silice cristalline peuvent être utilisés comme co-additif durable avec les stabilisateurs à base de calcium pour stabiliser les sols riches en sulfate.
Lime stabilization is widely used to improve the engineering properties of expansive soils. Howev... more Lime stabilization is widely used to improve the engineering properties of expansive soils. However, the durability of the lime-treated high-sulfate soil has been a persistent cause of concern for researchers and engineers. Treatment of a sulfate-rich soil with calcium-based stabilizers results in the formation of a highly deleterious compound known as ettringite. Ettringite crystals undergo substantial swell due to moisture ingress and cause considerable damage to pavements and light-weighted structures. In addition, the moisture intrusion during the early curing period has a detrimental impact on the strength and durability of the treated layers. An attempt was made in this research study to enhance the durability of lime-treated sulfate-rich soil using a crystalline silica-based admixture. The improvement in engineering properties over the traditional lime stabilization method was determined using a volumetric swell and strength test before and after subjecting the samples to moisture conditioning. Furthermore, the scanning electron microscope imaging was performed to identify the new reaction products in the treated soil and corroborate the observations of the engineering tests. The results indicate that the addition of crystalline-silica admixture has reduced ettringite-induced volumetric swelling from 45% to 3% and enhanced the retained UCS from 5 to 40 kPa.
Transportation Research Record: Journal of the Transportation Research Board, 2021
The longevity and performance of a pavement section depend on the characteristics of the subgrade... more The longevity and performance of a pavement section depend on the characteristics of the subgrade soil. A majority of the pavements in North Texas, U.S., are constructed on expansive soils. The deterioration of the pavement performance because of rutting, cracking, and differential heaving is a regular phenomenon in the regions predominantly distributed with expansive soils. The pavements, particularly those built for low-volume traffic conditions, experience distress because of the high swelling and shrinkage characteristics of the underlying problematic soils. Geosynthetics have been traditionally used to improve such poor subgrades because of their many benefits, such as ease of installation, and ample mechanical and hydraulic properties. In the last decade, a newly available wicking geotextile, with a moisture redistribution capacity, has been developed to improve the performance of pavements constructed over expansive and frozen soils. In this study, small-scale laboratory and full-scale field studies were conducted to comprehend the wicking ability of this innovative geotextile in an expansive soil environment. Full-scale test sections were constructed with reclaimed asphalt pavement aggregate and traditional crushed stone aggregates in the base layer near North Texas. Details of the construction and instrumentation procedure are discussed in this paper. A comparative study between the performance of the pavement sections subjected to traffic loads and moisture intrusion was also performed. Furthermore, the rutting life of the sections, estimated using a linear elastic model, was compared and validated using the in situ data. The observations during the initial phase indicated that the wicking geotextile has the potential to improve the long-term pavement performance.
The seismic response of a highly heterogeneous hydraulic fill dam was evaluated by studying the n... more The seismic response of a highly heterogeneous hydraulic fill dam was evaluated by studying the natural frequencies of the first and second modes of vibration and analyzing the crest accelerations of different two-dimensional or 2D sections of the dam when subjected to two different earthquake excitations. The existing methods for determination of the natural frequency of earthen embankment structures can only be used to analyze the structural response at small strain levels. However, during seismic events, the natural frequency of an earthen dam is significantly affected by the nonlinear material behavior exhibited by the geomaterials at high strain levels. Hence, a novel method was devised to evaluate the strain-dependent natural frequency for plane strain 2D dam sections, using a synthesized multi-sine base excitation. The degradation of first and second natural frequencies of transverse vibration for all the 2D sections followed a linear trend when plotted against the respective crest's root mean square strain on a logarithmic scale. The slope of the degradation curve was found to depend on the constituent material properties prevalent in the individual sections. The observed variations in natural frequencies and crest accelerations of the 2D dam sections were also used to assess the suitability of using two-dimensional plane strain analyses for studying the response of a long earthen dam having variability in material properties. Results indicate that there is a considerable chance of erroneous estimation of the seismic response of such highly heterogeneous earthen dams that are conventionally analyzed using plane strain models. A 2D analysis was found to merely capture the seismic response of the individual sections of the dam as independent entities while ignoring the stiffening or weakening effect of the adjacent neighboring segments that may have different material properties.
Geo-Congress 2020: Foundations, Soil Improvement, and Erosion, 2020
The resilient modulus (MR) is regarded as an important stiffness parameter for pavement design. D... more The resilient modulus (MR) is regarded as an important stiffness parameter for pavement design. Determining the MR of expansive subgrades is critical because of their high swell-shrink potential. Lime stabilization has been adopted to treat expansive subgrade soils in North Texas for decades. Due to severe greenhouse effects of lime use and production, an alternative to lime stabilization has gradually emerged. A liquid ionic soil stabilizer (LISS), an environmentally friendly soil stabilizer can be used as an alternative soil stabilizer for its significant effect in enhancing soil stiffness and strength. However, engineers are still reluctant to accept the use of LISS because of the proprietary patent and limited literature review. In this study, the MR of expansive soils before and after LISS treatment was evaluated in the laboratory. The LISS used is composed of sulfuric acid, phosphoric acid, surfactant, and water. LISS was diluted in water to treat expansive soils and the soils were cured for 7 and 28 days. The experimental MR results of expansive soils treated with LISS were validated by comparing them with the results of the M-EPDG model and Ooi et al. (2004) model.
Geo-Congress 2020: Engineering, Monitoring, and Management of Geotechnical Infrastructure, 2020
The operation of dams at times requires a sudden decrease in the existing reservoir level. This a... more The operation of dams at times requires a sudden decrease in the existing reservoir level. This abrupt change in the upstream water level, known as rapid drawdown, results in the development of unbalanced forces and occasionally causes catastrophic failure of the upstream shell. The drawdown-induced slope stability analyses are typically performed assuming that geomaterials used to build the dam exhibit isotropic permeability; even though, in reality, the geomaterials mostly exhibit anisotropic properties. The principal objective of this study is to comprehend the impact of anisotropic permeability on the drawdown-induced stability analysis of earthen dams and assess the impact of erroneously assuming isotropic permeability properties for numerical analyses. The influence of dam geometry, rate of drawdown, and depth of reservoir water before drawdown were also studied. The results of this research study highlight that the assumption of isotropic permeability inevitably leads to erroneous estimation of deformations incurred during drawdown. The extent of error was observed to increase with an increase in the dam slope and drawdown velocity.
Geo-Congress 2020: Geotechnical Earthquake Engineering and Special Topics, 2020
Earthquake excitations often cause an increase in pore water pressure in contractive sands result... more Earthquake excitations often cause an increase in pore water pressure in contractive sands resulting in liquefaction, which can lead to catastrophic consequences. Therefore, it is imperative to assess the earthquake-induced excess pore water pressure and deformations to evaluate the post-earthquake serviceability of the important structures such as earthen dams. The analyses are usually performed using the equivalent linear method or the non-linear method. The purpose of this research is to evaluate and compare the excess pore water pressure and associated deformations predicted using these two methods of analyses. Two numerical models of a typical zoned earthen dam were subjected to two earthquake time-history data with significantly different frequency contents to comprehend the differences in the outcome. The analyses results are similar for dams with dense sand shells when subjected to low-intensity earthquake excitations with the predominant frequency significantly different from the first natural frequency of the structure.
Proceedings of the Indian Geotechnical Conference, 2019
Pavements often suffer from different distresses such as rutting and cracking due to the presence... more Pavements often suffer from different distresses such as rutting and cracking due to the presence of underlying expansive subgrade soils. The ingress and egress of water have a detrimental effect on the performance of the pavements due to the swell-shrinkage behavior of the subgrade soil. Millions of dollars are invested annually for the maintenance and rehabilitation of such pavements. Traditionally, lime has been used for treating problematic subgrade soils to enhance the strength, stiffness and other engineering properties. However, previous studies have shown that lime treated soils often incur a significant strength loss when exposed to moisture intrusion, especially in the early curing periods. This research work explores the possibility of using a novel silica-based admixture to enhance the engineering properties of lime treated soil, reduce the swelling potential and deter the moisture-induced strength loss incurred during early curing periods. Laboratory test results suggest that an expansive soil treated with lime and silica-based admixture has a significant reduction in water-absorbing potential and strength loss during the early stages of curing as compared to the soil treated with lime only.
The American Society of Civil Engineers ranks the existing pavement infrastructure in the USA at ... more The American Society of Civil Engineers ranks the existing pavement infrastructure in the USA at a sub-par 'D' grade. Population growth, fast-paced industrialisation and infrastructure ageing put significant strain on the road and highway network. To enhance the sustainability of existing and upcoming pavement infrastructure, researchers have developed numerous models and tools for quantifying the resource consumption, environmental impact and socioeconomic consequences of these systems. However, these models do not incorporate the robustness of construction nor consider the performance and reliability of such infrastructure. Cognisant of the need to balance the sustainability and resilience elements of transportation infrastructure, this research introduces a quantitative framework for their combined assessment. As part of this multi-criteria analysis, the individual metrics (impact categories) of sustainability and resilience are identified and a quality index, I Q , is introduced to evaluate the combined degree of sustainability and resilience of a pavement project in north Texas, USA. The pavement was constructed on sulfate-rich expansive clays, and the subgrade was stabilised with materials such as lime and fly ash. The framework provides a powerful decision-making tool to engineers, owners, state and federal agencies and other stakeholders for the selection of appropriate pavement design or construction alternatives while balancing both the sustainability and resilience aspects.
Geotechnical Characterisation and Geoenvironmental Engineering, Lecture Notes in Civil Engineering, 2019
The quality and acceptability of a waveform data collected during spectral analysis of surface wa... more The quality and acceptability of a waveform data collected during spectral analysis of surface waves (SASW) testing is judged based on the coherence function over the measured range of frequencies. However, many trials and repetitions are required during SASW testing to obtain data with acceptable coherence value (>0.95). This makes the test time-consuming, and in most cases, only small portion of the collected data that satisfies the acceptable coherence criteria can be used for analysis. In this research study, an attempt was made to study the effect of using an impact source of constant energy on the coherence function as compared to the use of traditional handheld hammers. Laboratory experimental studies were performed on sandy clay soil bed filled in a metal box of dimensions 1.5 m  0.61 m  0.45 m. Also, a series of field tests were performed to validate the applicability of the laboratory findings. In both laboratory and field testing, a 2.5 kg hammer was used with height of fall as variable parameter. Two sets of tests were performed. One with random height of fall that is similar to current practice and the other with fixed height of fall of 0.13 m to simulate impacts with same energy conditions. Test results depicted that unlike the conventional procedure of testing, the use of constant energy of impact leads to coherence close to 1 over a significantly large frequency bandwidth. This research highlights the effect of using constant and varying impact energy on coherence value over a wide range of frequencies obtained during SASW testing.
ASCE IFCEE 2018 Geotechnical Special Publication, 2018
In this research, a sensitivity analysis was performed to study the effect of variation in maximu... more In this research, a sensitivity analysis was performed to study the effect of variation in maximum shear modulus (Gmax) values of different layers of a levee structure on the seismic response and stability of the levee slopes. The analysis was implemented by systematically varying the Gmax values of the different layers to simulate the effect of possible variation in estimated Gmax values obtained from in-situ/laboratory tests and correlation equations. The Gmax values of the layers were altered in two ways: variation in (1) individual layers; and (2) group of layers; thus, simulating the effect of incorrect estimation in Gmax values of a particular layer and a group of layers, respectively. The levee was subjected to the acceleration time-history data of two earthquakes with considerably different predominant frequencies. It was observed that the inaccurate estimation of Gmax values, especially for the deeper layers, significantly affects the natural frequency and peak crest acceleration. Moreover, a prominent change in the factor of safety of slopes under seismic loading conditions was observed with variation of Gmax values for the near resonance condition. The effects were pronounced when the Gmax values were varied for a group of layers, rather than individual layers.
A method is proposed to estimate the degradation of the first natural frequency of vibration of e... more A method is proposed to estimate the degradation of the first natural frequency of vibration of earthen dams with increase in strain levels induced due to seismic events. A synthesised wave, referred to as the 'sum of sines', generated by the superposition of sinusoidal waves with frequencies ranging from 0.01 Hz to 25 Hz, is scaled to different peak accelerations and used to simulate seismic excitations at the base of the dam. The natural frequency is then determined by studying the response of the structure in the frequency domain. For this study, four dams with varying complexities of geometry, constituent material properties, and known natural frequencies were at first selected from previously published literature to establish the validity of the proposed method for determining natural frequencies of the dams at small strain levels. Plane strain models of these structures were constructed and analysed, using a commercially available finite element method-based software that is capable of performing time-history analyses. Results from the analyses indicate a good agreement between the natural frequencies predicted using the proposed method and the frequency values reported in the literature for the corresponding structures at small strain levels. The method was later used to determine the strain-dependent natural frequency of a hydraulic-fill dam in North Texas. Twenty-one different earthquake conditions, with different peak ground accelerations, frequency contents, and mean periods, were used to thoroughly validate the applicability of the developed methodology. Numerical analyses indicate that the strain-dependent variation of the first natural frequency follows a similar trend as that obtained using the 'sum of sines' excitation when the dam is subjected to widely different earthquake conditions.
The quality and acceptability of the results of the spectral analysis of surface waves (SASW) fie... more The quality and acceptability of the results of the spectral analysis of surface waves (SASW) field test are dependent upon the coherence function, in conjunction with the transfer function. The coherence value is a measure of the quality of the test, and the transfer function denotes the phase lag between signals that are received by the geophones. This article presents a methodology for obtaining high-quality field test data, using a source capable of producing constant impact energy for several repeated impact strikes in an SASW test. Both laboratory and field investigations were performed to assess the effectiveness of the constant impact energy source at improving the coherence value. Tests were conducted on the surface of the soil compacted in a metal box and on the crest of an earthen dam using (a) handheld hammers, resulting in variable impact energy and (b) a drop hammer, dropped from a predetermined fixed height, resulting in constant impact energy. The variation in the shear wave velocity (Vs) profile obtained using the two testing methodologies and its impact on the seismic response analysis of an earthen embankment structure were studied. The SASW tests performed in the laboratory using constant impact energy were more efficient and repeatable than those performed using varying impact energy, and the results showed increased coherence values over a wide range of frequencies. A similar improvement in coherence data was observed in the field studies, and the Vs profiles were found to be significantly different for tests conducted using both methodologies. It was observed that the peak and spectral accelerations at the crest of embankments are significantly different when embankments with different Vs profiles are subjected to seismic excitation. This study emphasizes the importance of performing the SASW test, using a constant impact energy source to obtain a reliable estimate of Vs profiles of subsurface layers.
International Journal of Pavement Engineering, Taylor & Francis, 2017
This paper presents a rational approach to answer the questions of how many field tests need to b... more This paper presents a rational approach to answer the questions of how many field tests need to be performed at a test site to determine its subgrade strength properties, and what inferences can be drawn from limited number of field tests. MATLAB simulations were performed to generate various data sets that corresponded to site variability, with the coefficient of variation (CoV) ranging from 10 to 80%. Studies were performed based on coefficient of variation (CoV) and regression analysis. This study provides two important charts for evaluating subgrade properties at test sites: (1) to determine the number of field tests to be performed, after which there would not be any significant change in the inferences drawn from the test results; (2) inferences pertaining to subgrade soil property of a field test site, based on a limited number of tests. In order to demonstrate the applicability of the charts developed through this research, light weight deflectometer (LWD) spot tests that were performed at a test site, were considered. The results were used to draw inferences about the modulus of the subgrade material and the possible variability of the test site, in addition to the maximum number of tests that might be performed.
International Journal of Pavement Engineering, Taylor & Francis, 2018
Long-term performance of pavement sections depends on the structural integrity and strength of it... more Long-term performance of pavement sections depends on the structural integrity and strength of its individual layers. Clay-rich soils do not often meet the structural requirements needed to perform as an effective subgrade material. Among the different in situ techniques available to enhance the engineering properties of these clay-rich soils, lime stabilisation is the most preferred alternative. Although lime treatment improves the strength properties of clay-rich soils due to sustained pozzolanic reactions, the intrusion of external water can deter the benefits of stabilisation processes. The objective of this study was to identify the possible causes of strength and durability loss in lime stabilised subgrade soil during moisture exposure and determine the effect of curing period on the extent of moisture-induced damage incurred. Reasons for immediate strength loss observed in stabilised materials when exposed to moisture conditions were also investigated as part of the study. Thermal analysis techniques, such as differential scanning calorimetry, differential thermal analysis and thermo-gravimetric analysis were used in identifying and quantifying the calcium silicate hydrate (C-S-H) phases precipitating in lime-treated soils and also to determine the water retention properties of these cementitious materials. Results suggest the inherent affinity and water holding capacity of the precipitated C-S-H phases are partially responsible for the deterioration in strength properties observed in stabilised layers exposed to water, especially during early curing periods. As curing proceeds, the increased suction potential created by the C-S-H phases is counteracted by a higher matrix strength. This phenomenon causes a reduction in external water movement and associated strength loss in stabilised layers.
Road Materials and Pavement Design, Taylor and Francis, 2017
Durability is a major concern for all stabilised materials as it can reduce the structural capaci... more Durability is a major concern for all stabilised materials as it can reduce the structural capacity of pavement layers. One of the primary factors influencing the long-term performance of stabilised subgrade layers is moisture. The structural properties of these engineered materials starts to deteriorate with ingress of external water. The detrimental effect of soaking depends on the level of pozzolanic reaction achieved by the stabilised layer prior to water intrusion. Although the affinity for water is reduced after stabilisation, some amount of water is held within the matrix by the precipitated Calcium Silicate Hydrate (C-S-H) phases due to their inherent water adsorption capacity. The extent of damage in turn depends on the type and concentration of different cementitious phases due to the structural, compositional and morphological differences. This study tries to determine the type of hydrated cementitious phase that is more resilient to moisture-induced damage. Results indicate the presence of C-S-H II phase to be beneficial for durability of lime-treated soil when compared to C-S-H I phase.
M.Tech Thesis, Indian Institute of Technology Kanpur, 2015
Durability or longevity of stabilized subgrade soil is a critical parameter that defines the stru... more Durability or longevity of stabilized subgrade soil is a critical parameter that defines the structural capacity and long term performance of pavement layers. Moisture is known to be one of the detrimental factors affecting the long-term performance of stabilized subgrade layers. Although the presence of water (optimum moisture conditions) is needed to sustain long term pozzolanic reactions, ingress of external water is known to degrade the structural properties of these stabilized layers. The magnitude of damage due to intrusion of water has been shown to depend on the extent of pozzolanic reaction achieved. Even though lime treatment reduces the affinity for water in clayey soils, the stabilized matrix can hold external water due to the inherent water holding capacity of the precipitated Calcium Silicate Hydrate (C-S-H) phases. Hence the amount of water held in the stabilized layer may further depend on the type and concentration of individual cementitious phases formed during lime-soil interaction. However the structure, composition and morphology of cementitious phases vary with the physiochemical conditions existing in the stabilized layer during the time of precipitation. Being the major strength contributor in stabilized soil, moisture exposure and the subsequent changes in physiochemical properties of C-S-H phases can significantly influence the strength and durability of the treated soil. A differential scanning calorimeter with thermo gravimetric analyzer was used to study the changes in type and concentration of different C-S-H phases formed in treated soils. This study primarily focuses on determining the probable cause behind durability issues in stabilized layers due to moisture intrusion, mainly during the early stages of curing when the stabilized soil has not achieved appreciable strength. The study also focuses on the impact of different C-S-H phases on the durability of lime stabilized soils. Results suggest that different C-S-H phases are formed in a given soil depending on the amount of lime added. Furthermore, a difference in concentration and type of individual cementitious phases may also contribute to difference in behavior of stabilized layers.
20th International Conference on Soil Mechanics and Geotechnical Engineering, 2022
A research study was conducted to evaluate the applicability of utilizing crystalline silica-rich... more A research study was conducted to evaluate the applicability of utilizing crystalline silica-rich waste products for mitigating ettringite-induced heaving in lime-treated sulfate-rich expansive soils. Free swell strain tests were conducted on cured lime-treated soil specimens, both with and without crystalline silica admixture. The impacts of the curing period and silica admixture dosage on the post-treatment swelling characteristics were studied. An attempt was made to estimate the ettringite-induced volumetric expansion using stoichiometric analysis. The ettringite-induced swell strains interpreted from swell test results were compared with those estimated stoichiometrically. Microstructural studies were also performed to detect ettringite and cementitious compounds formed in treated soils. Test results suggest that crystalline silica admixture may suppress the availability of reactive alumina from clay minerals, react with lime and form cementitious compounds, and reduce the ettringite-induced heaving. The beneficial influence of crystalline silica admixture increased with an increase in dosage and curing period. Overall, this study indicates that crystalline silica-rich waste products may be utilized as a sustainable co-additive with calcium-based stabilizers for stabilizing sulfate-rich soils. RÉSUMÉ : Une étude de recherche a été menée pour évaluer l'applicabilité de l'utilisation de déchets riches en silice cristalline pour atténuer le gonflement induit par l'ettringite dans les sols expansifs riches en sulfate traités à la chaux. Des essais de déformation par gonflement libre ont été réalisés sur des échantillons de sols traités à la chaux, avec et sans adjuvant de silice cristalline. Les impacts de la période de maturation et du dosage de l'adjuvant de silice sur les caractéristiques de gonflement après traitement ont été étudiés. Une tentative a été faite pour estimer l'expansion volumétrique induite par l'ettringite en utilisant une analyse stoechiométrique. Les contraintes de gonflement induites par l'ettringite interprétées à partir des résultats des tests de gonflement, ont été comparées à celles estimées stoechiométriquement. Des études microstructurales ont également été réalisées pour détecter l'ettringite et les composants cimentaires formés dans les sols traités. Les résultats des tests suggèrent que l'adjonction de silice cristalline peut supprimer la disponibilité de l'alumine réactive des minéraux argileux, réagir avec la chaux et former des composants cimentaires, et réduire le gonflement induit par l'ettringite. L'influence bénéfique de l'adjonction de silice cristalline a été amplifiée avec l'augmentation du dosage et de la période de durcissement. Dans l'ensemble, cette étude indique que les déchets riches en silice cristalline peuvent être utilisés comme co-additif durable avec les stabilisateurs à base de calcium pour stabiliser les sols riches en sulfate.
Lime stabilization is widely used to improve the engineering properties of expansive soils. Howev... more Lime stabilization is widely used to improve the engineering properties of expansive soils. However, the durability of the lime-treated high-sulfate soil has been a persistent cause of concern for researchers and engineers. Treatment of a sulfate-rich soil with calcium-based stabilizers results in the formation of a highly deleterious compound known as ettringite. Ettringite crystals undergo substantial swell due to moisture ingress and cause considerable damage to pavements and light-weighted structures. In addition, the moisture intrusion during the early curing period has a detrimental impact on the strength and durability of the treated layers. An attempt was made in this research study to enhance the durability of lime-treated sulfate-rich soil using a crystalline silica-based admixture. The improvement in engineering properties over the traditional lime stabilization method was determined using a volumetric swell and strength test before and after subjecting the samples to moisture conditioning. Furthermore, the scanning electron microscope imaging was performed to identify the new reaction products in the treated soil and corroborate the observations of the engineering tests. The results indicate that the addition of crystalline-silica admixture has reduced ettringite-induced volumetric swelling from 45% to 3% and enhanced the retained UCS from 5 to 40 kPa.
Transportation Research Record: Journal of the Transportation Research Board, 2021
The longevity and performance of a pavement section depend on the characteristics of the subgrade... more The longevity and performance of a pavement section depend on the characteristics of the subgrade soil. A majority of the pavements in North Texas, U.S., are constructed on expansive soils. The deterioration of the pavement performance because of rutting, cracking, and differential heaving is a regular phenomenon in the regions predominantly distributed with expansive soils. The pavements, particularly those built for low-volume traffic conditions, experience distress because of the high swelling and shrinkage characteristics of the underlying problematic soils. Geosynthetics have been traditionally used to improve such poor subgrades because of their many benefits, such as ease of installation, and ample mechanical and hydraulic properties. In the last decade, a newly available wicking geotextile, with a moisture redistribution capacity, has been developed to improve the performance of pavements constructed over expansive and frozen soils. In this study, small-scale laboratory and full-scale field studies were conducted to comprehend the wicking ability of this innovative geotextile in an expansive soil environment. Full-scale test sections were constructed with reclaimed asphalt pavement aggregate and traditional crushed stone aggregates in the base layer near North Texas. Details of the construction and instrumentation procedure are discussed in this paper. A comparative study between the performance of the pavement sections subjected to traffic loads and moisture intrusion was also performed. Furthermore, the rutting life of the sections, estimated using a linear elastic model, was compared and validated using the in situ data. The observations during the initial phase indicated that the wicking geotextile has the potential to improve the long-term pavement performance.
The seismic response of a highly heterogeneous hydraulic fill dam was evaluated by studying the n... more The seismic response of a highly heterogeneous hydraulic fill dam was evaluated by studying the natural frequencies of the first and second modes of vibration and analyzing the crest accelerations of different two-dimensional or 2D sections of the dam when subjected to two different earthquake excitations. The existing methods for determination of the natural frequency of earthen embankment structures can only be used to analyze the structural response at small strain levels. However, during seismic events, the natural frequency of an earthen dam is significantly affected by the nonlinear material behavior exhibited by the geomaterials at high strain levels. Hence, a novel method was devised to evaluate the strain-dependent natural frequency for plane strain 2D dam sections, using a synthesized multi-sine base excitation. The degradation of first and second natural frequencies of transverse vibration for all the 2D sections followed a linear trend when plotted against the respective crest's root mean square strain on a logarithmic scale. The slope of the degradation curve was found to depend on the constituent material properties prevalent in the individual sections. The observed variations in natural frequencies and crest accelerations of the 2D dam sections were also used to assess the suitability of using two-dimensional plane strain analyses for studying the response of a long earthen dam having variability in material properties. Results indicate that there is a considerable chance of erroneous estimation of the seismic response of such highly heterogeneous earthen dams that are conventionally analyzed using plane strain models. A 2D analysis was found to merely capture the seismic response of the individual sections of the dam as independent entities while ignoring the stiffening or weakening effect of the adjacent neighboring segments that may have different material properties.
Geo-Congress 2020: Foundations, Soil Improvement, and Erosion, 2020
The resilient modulus (MR) is regarded as an important stiffness parameter for pavement design. D... more The resilient modulus (MR) is regarded as an important stiffness parameter for pavement design. Determining the MR of expansive subgrades is critical because of their high swell-shrink potential. Lime stabilization has been adopted to treat expansive subgrade soils in North Texas for decades. Due to severe greenhouse effects of lime use and production, an alternative to lime stabilization has gradually emerged. A liquid ionic soil stabilizer (LISS), an environmentally friendly soil stabilizer can be used as an alternative soil stabilizer for its significant effect in enhancing soil stiffness and strength. However, engineers are still reluctant to accept the use of LISS because of the proprietary patent and limited literature review. In this study, the MR of expansive soils before and after LISS treatment was evaluated in the laboratory. The LISS used is composed of sulfuric acid, phosphoric acid, surfactant, and water. LISS was diluted in water to treat expansive soils and the soils were cured for 7 and 28 days. The experimental MR results of expansive soils treated with LISS were validated by comparing them with the results of the M-EPDG model and Ooi et al. (2004) model.
Geo-Congress 2020: Engineering, Monitoring, and Management of Geotechnical Infrastructure, 2020
The operation of dams at times requires a sudden decrease in the existing reservoir level. This a... more The operation of dams at times requires a sudden decrease in the existing reservoir level. This abrupt change in the upstream water level, known as rapid drawdown, results in the development of unbalanced forces and occasionally causes catastrophic failure of the upstream shell. The drawdown-induced slope stability analyses are typically performed assuming that geomaterials used to build the dam exhibit isotropic permeability; even though, in reality, the geomaterials mostly exhibit anisotropic properties. The principal objective of this study is to comprehend the impact of anisotropic permeability on the drawdown-induced stability analysis of earthen dams and assess the impact of erroneously assuming isotropic permeability properties for numerical analyses. The influence of dam geometry, rate of drawdown, and depth of reservoir water before drawdown were also studied. The results of this research study highlight that the assumption of isotropic permeability inevitably leads to erroneous estimation of deformations incurred during drawdown. The extent of error was observed to increase with an increase in the dam slope and drawdown velocity.
Geo-Congress 2020: Geotechnical Earthquake Engineering and Special Topics, 2020
Earthquake excitations often cause an increase in pore water pressure in contractive sands result... more Earthquake excitations often cause an increase in pore water pressure in contractive sands resulting in liquefaction, which can lead to catastrophic consequences. Therefore, it is imperative to assess the earthquake-induced excess pore water pressure and deformations to evaluate the post-earthquake serviceability of the important structures such as earthen dams. The analyses are usually performed using the equivalent linear method or the non-linear method. The purpose of this research is to evaluate and compare the excess pore water pressure and associated deformations predicted using these two methods of analyses. Two numerical models of a typical zoned earthen dam were subjected to two earthquake time-history data with significantly different frequency contents to comprehend the differences in the outcome. The analyses results are similar for dams with dense sand shells when subjected to low-intensity earthquake excitations with the predominant frequency significantly different from the first natural frequency of the structure.
Proceedings of the Indian Geotechnical Conference, 2019
Pavements often suffer from different distresses such as rutting and cracking due to the presence... more Pavements often suffer from different distresses such as rutting and cracking due to the presence of underlying expansive subgrade soils. The ingress and egress of water have a detrimental effect on the performance of the pavements due to the swell-shrinkage behavior of the subgrade soil. Millions of dollars are invested annually for the maintenance and rehabilitation of such pavements. Traditionally, lime has been used for treating problematic subgrade soils to enhance the strength, stiffness and other engineering properties. However, previous studies have shown that lime treated soils often incur a significant strength loss when exposed to moisture intrusion, especially in the early curing periods. This research work explores the possibility of using a novel silica-based admixture to enhance the engineering properties of lime treated soil, reduce the swelling potential and deter the moisture-induced strength loss incurred during early curing periods. Laboratory test results suggest that an expansive soil treated with lime and silica-based admixture has a significant reduction in water-absorbing potential and strength loss during the early stages of curing as compared to the soil treated with lime only.
The American Society of Civil Engineers ranks the existing pavement infrastructure in the USA at ... more The American Society of Civil Engineers ranks the existing pavement infrastructure in the USA at a sub-par 'D' grade. Population growth, fast-paced industrialisation and infrastructure ageing put significant strain on the road and highway network. To enhance the sustainability of existing and upcoming pavement infrastructure, researchers have developed numerous models and tools for quantifying the resource consumption, environmental impact and socioeconomic consequences of these systems. However, these models do not incorporate the robustness of construction nor consider the performance and reliability of such infrastructure. Cognisant of the need to balance the sustainability and resilience elements of transportation infrastructure, this research introduces a quantitative framework for their combined assessment. As part of this multi-criteria analysis, the individual metrics (impact categories) of sustainability and resilience are identified and a quality index, I Q , is introduced to evaluate the combined degree of sustainability and resilience of a pavement project in north Texas, USA. The pavement was constructed on sulfate-rich expansive clays, and the subgrade was stabilised with materials such as lime and fly ash. The framework provides a powerful decision-making tool to engineers, owners, state and federal agencies and other stakeholders for the selection of appropriate pavement design or construction alternatives while balancing both the sustainability and resilience aspects.
Geotechnical Characterisation and Geoenvironmental Engineering, Lecture Notes in Civil Engineering, 2019
The quality and acceptability of a waveform data collected during spectral analysis of surface wa... more The quality and acceptability of a waveform data collected during spectral analysis of surface waves (SASW) testing is judged based on the coherence function over the measured range of frequencies. However, many trials and repetitions are required during SASW testing to obtain data with acceptable coherence value (>0.95). This makes the test time-consuming, and in most cases, only small portion of the collected data that satisfies the acceptable coherence criteria can be used for analysis. In this research study, an attempt was made to study the effect of using an impact source of constant energy on the coherence function as compared to the use of traditional handheld hammers. Laboratory experimental studies were performed on sandy clay soil bed filled in a metal box of dimensions 1.5 m  0.61 m  0.45 m. Also, a series of field tests were performed to validate the applicability of the laboratory findings. In both laboratory and field testing, a 2.5 kg hammer was used with height of fall as variable parameter. Two sets of tests were performed. One with random height of fall that is similar to current practice and the other with fixed height of fall of 0.13 m to simulate impacts with same energy conditions. Test results depicted that unlike the conventional procedure of testing, the use of constant energy of impact leads to coherence close to 1 over a significantly large frequency bandwidth. This research highlights the effect of using constant and varying impact energy on coherence value over a wide range of frequencies obtained during SASW testing.
ASCE IFCEE 2018 Geotechnical Special Publication, 2018
In this research, a sensitivity analysis was performed to study the effect of variation in maximu... more In this research, a sensitivity analysis was performed to study the effect of variation in maximum shear modulus (Gmax) values of different layers of a levee structure on the seismic response and stability of the levee slopes. The analysis was implemented by systematically varying the Gmax values of the different layers to simulate the effect of possible variation in estimated Gmax values obtained from in-situ/laboratory tests and correlation equations. The Gmax values of the layers were altered in two ways: variation in (1) individual layers; and (2) group of layers; thus, simulating the effect of incorrect estimation in Gmax values of a particular layer and a group of layers, respectively. The levee was subjected to the acceleration time-history data of two earthquakes with considerably different predominant frequencies. It was observed that the inaccurate estimation of Gmax values, especially for the deeper layers, significantly affects the natural frequency and peak crest acceleration. Moreover, a prominent change in the factor of safety of slopes under seismic loading conditions was observed with variation of Gmax values for the near resonance condition. The effects were pronounced when the Gmax values were varied for a group of layers, rather than individual layers.
A method is proposed to estimate the degradation of the first natural frequency of vibration of e... more A method is proposed to estimate the degradation of the first natural frequency of vibration of earthen dams with increase in strain levels induced due to seismic events. A synthesised wave, referred to as the 'sum of sines', generated by the superposition of sinusoidal waves with frequencies ranging from 0.01 Hz to 25 Hz, is scaled to different peak accelerations and used to simulate seismic excitations at the base of the dam. The natural frequency is then determined by studying the response of the structure in the frequency domain. For this study, four dams with varying complexities of geometry, constituent material properties, and known natural frequencies were at first selected from previously published literature to establish the validity of the proposed method for determining natural frequencies of the dams at small strain levels. Plane strain models of these structures were constructed and analysed, using a commercially available finite element method-based software that is capable of performing time-history analyses. Results from the analyses indicate a good agreement between the natural frequencies predicted using the proposed method and the frequency values reported in the literature for the corresponding structures at small strain levels. The method was later used to determine the strain-dependent natural frequency of a hydraulic-fill dam in North Texas. Twenty-one different earthquake conditions, with different peak ground accelerations, frequency contents, and mean periods, were used to thoroughly validate the applicability of the developed methodology. Numerical analyses indicate that the strain-dependent variation of the first natural frequency follows a similar trend as that obtained using the 'sum of sines' excitation when the dam is subjected to widely different earthquake conditions.
The quality and acceptability of the results of the spectral analysis of surface waves (SASW) fie... more The quality and acceptability of the results of the spectral analysis of surface waves (SASW) field test are dependent upon the coherence function, in conjunction with the transfer function. The coherence value is a measure of the quality of the test, and the transfer function denotes the phase lag between signals that are received by the geophones. This article presents a methodology for obtaining high-quality field test data, using a source capable of producing constant impact energy for several repeated impact strikes in an SASW test. Both laboratory and field investigations were performed to assess the effectiveness of the constant impact energy source at improving the coherence value. Tests were conducted on the surface of the soil compacted in a metal box and on the crest of an earthen dam using (a) handheld hammers, resulting in variable impact energy and (b) a drop hammer, dropped from a predetermined fixed height, resulting in constant impact energy. The variation in the shear wave velocity (Vs) profile obtained using the two testing methodologies and its impact on the seismic response analysis of an earthen embankment structure were studied. The SASW tests performed in the laboratory using constant impact energy were more efficient and repeatable than those performed using varying impact energy, and the results showed increased coherence values over a wide range of frequencies. A similar improvement in coherence data was observed in the field studies, and the Vs profiles were found to be significantly different for tests conducted using both methodologies. It was observed that the peak and spectral accelerations at the crest of embankments are significantly different when embankments with different Vs profiles are subjected to seismic excitation. This study emphasizes the importance of performing the SASW test, using a constant impact energy source to obtain a reliable estimate of Vs profiles of subsurface layers.
International Journal of Pavement Engineering, Taylor & Francis, 2017
This paper presents a rational approach to answer the questions of how many field tests need to b... more This paper presents a rational approach to answer the questions of how many field tests need to be performed at a test site to determine its subgrade strength properties, and what inferences can be drawn from limited number of field tests. MATLAB simulations were performed to generate various data sets that corresponded to site variability, with the coefficient of variation (CoV) ranging from 10 to 80%. Studies were performed based on coefficient of variation (CoV) and regression analysis. This study provides two important charts for evaluating subgrade properties at test sites: (1) to determine the number of field tests to be performed, after which there would not be any significant change in the inferences drawn from the test results; (2) inferences pertaining to subgrade soil property of a field test site, based on a limited number of tests. In order to demonstrate the applicability of the charts developed through this research, light weight deflectometer (LWD) spot tests that were performed at a test site, were considered. The results were used to draw inferences about the modulus of the subgrade material and the possible variability of the test site, in addition to the maximum number of tests that might be performed.
International Journal of Pavement Engineering, Taylor & Francis, 2018
Long-term performance of pavement sections depends on the structural integrity and strength of it... more Long-term performance of pavement sections depends on the structural integrity and strength of its individual layers. Clay-rich soils do not often meet the structural requirements needed to perform as an effective subgrade material. Among the different in situ techniques available to enhance the engineering properties of these clay-rich soils, lime stabilisation is the most preferred alternative. Although lime treatment improves the strength properties of clay-rich soils due to sustained pozzolanic reactions, the intrusion of external water can deter the benefits of stabilisation processes. The objective of this study was to identify the possible causes of strength and durability loss in lime stabilised subgrade soil during moisture exposure and determine the effect of curing period on the extent of moisture-induced damage incurred. Reasons for immediate strength loss observed in stabilised materials when exposed to moisture conditions were also investigated as part of the study. Thermal analysis techniques, such as differential scanning calorimetry, differential thermal analysis and thermo-gravimetric analysis were used in identifying and quantifying the calcium silicate hydrate (C-S-H) phases precipitating in lime-treated soils and also to determine the water retention properties of these cementitious materials. Results suggest the inherent affinity and water holding capacity of the precipitated C-S-H phases are partially responsible for the deterioration in strength properties observed in stabilised layers exposed to water, especially during early curing periods. As curing proceeds, the increased suction potential created by the C-S-H phases is counteracted by a higher matrix strength. This phenomenon causes a reduction in external water movement and associated strength loss in stabilised layers.
Road Materials and Pavement Design, Taylor and Francis, 2017
Durability is a major concern for all stabilised materials as it can reduce the structural capaci... more Durability is a major concern for all stabilised materials as it can reduce the structural capacity of pavement layers. One of the primary factors influencing the long-term performance of stabilised subgrade layers is moisture. The structural properties of these engineered materials starts to deteriorate with ingress of external water. The detrimental effect of soaking depends on the level of pozzolanic reaction achieved by the stabilised layer prior to water intrusion. Although the affinity for water is reduced after stabilisation, some amount of water is held within the matrix by the precipitated Calcium Silicate Hydrate (C-S-H) phases due to their inherent water adsorption capacity. The extent of damage in turn depends on the type and concentration of different cementitious phases due to the structural, compositional and morphological differences. This study tries to determine the type of hydrated cementitious phase that is more resilient to moisture-induced damage. Results indicate the presence of C-S-H II phase to be beneficial for durability of lime-treated soil when compared to C-S-H I phase.
M.Tech Thesis, Indian Institute of Technology Kanpur, 2015
Durability or longevity of stabilized subgrade soil is a critical parameter that defines the stru... more Durability or longevity of stabilized subgrade soil is a critical parameter that defines the structural capacity and long term performance of pavement layers. Moisture is known to be one of the detrimental factors affecting the long-term performance of stabilized subgrade layers. Although the presence of water (optimum moisture conditions) is needed to sustain long term pozzolanic reactions, ingress of external water is known to degrade the structural properties of these stabilized layers. The magnitude of damage due to intrusion of water has been shown to depend on the extent of pozzolanic reaction achieved. Even though lime treatment reduces the affinity for water in clayey soils, the stabilized matrix can hold external water due to the inherent water holding capacity of the precipitated Calcium Silicate Hydrate (C-S-H) phases. Hence the amount of water held in the stabilized layer may further depend on the type and concentration of individual cementitious phases formed during lime-soil interaction. However the structure, composition and morphology of cementitious phases vary with the physiochemical conditions existing in the stabilized layer during the time of precipitation. Being the major strength contributor in stabilized soil, moisture exposure and the subsequent changes in physiochemical properties of C-S-H phases can significantly influence the strength and durability of the treated soil. A differential scanning calorimeter with thermo gravimetric analyzer was used to study the changes in type and concentration of different C-S-H phases formed in treated soils. This study primarily focuses on determining the probable cause behind durability issues in stabilized layers due to moisture intrusion, mainly during the early stages of curing when the stabilized soil has not achieved appreciable strength. The study also focuses on the impact of different C-S-H phases on the durability of lime stabilized soils. Results suggest that different C-S-H phases are formed in a given soil depending on the amount of lime added. Furthermore, a difference in concentration and type of individual cementitious phases may also contribute to difference in behavior of stabilized layers.
Uploads