The Experts below are selected from a list of 360 Experts worldwide ranked by ideXlab platform
H Rahardjo - One of the best experts on this subject based on the ideXlab platform.
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effects of unsaturated properties on stability of slope covered with caesalpinia crista in singapore
Environmental geotechnics, 2018Co-Authors: H Rahardjo, Alfrendo Satyanaga, Chien Looi Wang, Johnny Liang Heng Wong, Vincent Han LimAbstract:Rainfall plays an important role in affecting the slope stability in a tropical country such as Singapore. The Soil in Singapore is mainly Residual Soil with a deep groundwater table that is common...
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modeling of suction distributions in an unsaturated heterogeneous Residual Soil slope
Engineering Geology, 2012Co-Authors: Azman Kassim, Nurly Gofar, Lee Min Lee, H RahardjoAbstract:The formation of Residual Soil of Grade V and Grade VI due to tropical weathering process introduces small hydraulic heterogeneities in the Soil mantle which greatly alter the suction distribution during rainfall infiltration, and hence the stability of the Residual Soil slopes. This paper presents field evidences of suction distributions in a heterogeneous Residual Soil slope. Several modeling approaches were attempted to simulate the observation by considering the presence of thin layer of Grade VI, the variation in the hydraulic conductivity of Grade V layer as well as the effect of evaporation. The Soil hydraulic heterogeneity in Grade V layer was modeled by adopting continuum method, in which the Residual Soil was subdivided into three zones of average hydraulic conductivities. The analysis results show that the presence of thin layer of Grade VI Residual Soil and the relict discontinuities in Grade V Soil must be considered in the analysis as these features introduced permeability disparity and thus a natural capillary barrier effect that limited the downward movement of infiltrated rainwater even during the exceptionally wet condition. The results also show that the inclusion of evaporation effect provided a better prediction to the suction distributions during wet condition than dry condition.
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effect of antecedent rainfall on pore water pressure distribution characteristics in Residual Soil slopes under tropical rainfall
Hydrological Processes, 2008Co-Authors: H Rahardjo, E. C. Leong, R B RezaurAbstract:Characteristics of changes in pore-water pressure distribution are the main parameters associated with slope stability analysis involving unsaturated Soils, which are directly affected by the flux boundary conditions (rainfall infiltration, evaporation and evapo-transpiration) at the Soil-atmosphere interface. Four slopes were instrumented in two major geological formations in Singapore to provide real-time measurements of pore-water pressures and rainfall events on the slopes. The field monitoring results were analysed to characterize pore-water pressure distributions under various meteorological conditions and to study the effect of antecedent rainfall on pore-water pressure distributions in typical Residual Soil slopes under tropical climate. Slope stability analyses were also conducted for the best and worst pore-water pressure distributions recorded in each slope to determine the range of factor of safety for the slopes. Results indicate that, antecedent rainfall, initial pore-water pressures prior to a significant rainfall event as well as the magnitude of the rainfall event play a crucial role in the development of the worst pore-water pressure condition in a slope. The role of antecedent rainfall in the development of the worst pore-water pressure condition was found to be more significant in Residual Soils with low permeability as compared with that in Residual Soils with high permeability. Pore-water pressure variation due to rainfall was found to take place over a wide range in Residual Soils with higher permeability as compared to Residual Soils with lower permeability. The worst pore-water pressure profiles occurred when the total rainfall including the 5-day antecedent rainfall (in most cases) reached a maximum value during a wet period. The factor of safety of Residual Soils with low permeability was found to be unaffected by the worst pore-water pressure condition.
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response of a Residual Soil slope to rainfall
Canadian Geotechnical Journal, 2005Co-Authors: H Rahardjo, Eng Choon Leong, R B RezaurAbstract:Rainfall-induced landslides are a common problem in Residual Soil slopes of the tropics. It is widely known that rainfall-induced slope failures are mainly caused by infiltration of rainwater; however, the response of a Residual Soil slope to infiltration is not fully understood. The difficulties lie in the quantification of the flux boundary condition across the slope surface with respect to infiltration and its effect on the pore-water pressure conditions in the slope. Therefore, it is important to understand the response of a slope to different rainfall conditions and the resulting changes in pore-water pressures and water contents. A Residual Soil slope in Singapore was instrumented with pore- water pressure, water content, and rainfall measuring devices, and studies were carried out under natural and simulated rainfalls. Results indicate that significant infiltration may occur in a Residual Soil slope during a rainfall. Small total rainfalls can contribute a larger infiltration percentage than large total rainfalls. The percentage of infiltration usually decreases with increasing total rainfalls. The study has indicated the existence of a threshold rainfall of about 10 mm for runoff generation to commence. Infiltration during wet periods may lead to the development of positive pore-water pressures as a consequence of a perched water table condition. Matric suctions are recovered gradually during dry peri- ods due to redistribution. Soil water contents tend to be higher near the toe of the slope than at the crest irrespective of rainfall events, indicating subsurface movement of water in the downslope direction. The study has also indicated a correlation between rainfall amount and relative increase in pore-water pressure. The results can be used to quantify the flux boundary conditions required for the seepage analyses associated with rainfall-induced slope failures.
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response of a Residual Soil slope to rainfall
Canadian Geotechnical Journal, 2005Co-Authors: H Rahardjo, Eng Choon Leong, T T Lee, R B RezaurAbstract:Rainfall-induced landslides are a common problem in Residual Soil slopes of the tropics. It is widely known that rainfall-induced slope failures are mainly caused by infiltration of rainwater; howe...
Bujang B. K. Huat - One of the best experts on this subject based on the ideXlab platform.
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The effect of size and replacement content of nanosilica on strength development of cement treated Residual Soil
Construction and Building Materials, 2016Co-Authors: Sayed Hessam Bahmani, Nima Farzadnia, Afshin Asadi, Bujang B. K. HuatAbstract:In this study, effects of size and replacement content of nanosilica on physical, chemical, and microstructural characteristics of cemented Residual Soil were investigated. Accordingly, UCS and electrical resistivity tests were conducted on cemented specimens with replacement contents of 0.2%-1% nanosilica of 15 and 80 nm at 7, 14 and 28 days. XRD, Zeta potential, CEC, FTIR, and SEM tests were performed to identify chemical and microstructural changes over time. The results showed that smaller size nanosilica had an accelerated influence on samples while nanosilica of larger size was more effective at ages after 14 days of curing.
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stabilization of Residual Soil using sio2 nanoparticles and cement
Construction and Building Materials, 2014Co-Authors: Sayed Hessam Bahmani, Afshin Asadi, Bujang B. K. Huat, Nima FarzadniaAbstract:An experimental study was performed to determine the effect of SiO2 nanoparticles on consistency, compaction, hydraulic conductivity, and compressive strength of cement-treated Residual Soil. Also, SEM, XRD and FTIR tests were carried out to identify the underlying mechanisms. The addition of nanoparticles was found to advantageously affect the compactability, hydraulic conductivity. Besides, addition of 0.4% nanosilica to the cement treated Soil improved the compressive strength by up to 80%. XRD, FTIR and SEM test results showed that silica nanoparticles promoted the pozzolanic reaction by transforming Portlandite into calcium silicate hydrate (C–S–H) gel.
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relationship between shear strength and Soil water characteristic curve of an unsaturated granitic Residual Soil
American Journal of Environmental Sciences, 2006Co-Authors: Thamer Ahmed Mohamed, Shahrir Hashim, Bujang B. K. HuatAbstract:Shear strength parameters are crucial for stability analyses of slopes against slope failures and landslides. The three shear strength parameters that are required to define a failure envelope of an unsaturated Soil are c’ (apparent cohesion), Φ’ (effective angle of friction) and Φb (shear strength change with change in matric suction). A Soil-water characteristic curve (SWCC) that relates the water content of a Soil to matric suction is another important relationship for the unsaturated Soil mechanics. The SWCC essentially shows the ability of an unsaturated Soil to retain water under various matric suctions. This study concentrates on the shear strength-SWCC relationship that has been carried out on an unsaturated granitic Residual Soil. It is observed that the failure envelope of an unsaturated Soil is non-linear due to the non-linear Soil water characteristic curve (SWCC). At low matric suctions, where the suction is lower than the air-entry value of the Soil, the Soil is at or near saturation condition and behave as though it was saturated. Consequently an increase in matric suction produces the same increase in shear strength as does an increase in net normal stress. However, at matric suctions higher than the air-entry value of the Soil, the Soil starts to desaturate. The increase in shear strength with respect to matric suction becomes less than the increase with respect to the net normal stress.
W G Zhang - One of the best experts on this subject based on the ideXlab platform.
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Numerical study of the effects of groundwater drawdown on ground settlement for excavation in Residual Soils
Acta Geotechnica, 2019Co-Authors: A. T. C. Goh, R.h. Zhang, W. Wang, H L Liu, W G ZhangAbstract:For deep excavations in Residual Soils that are underlain by highly fissured or fractured rocks, it is common to observe the drawdown of the groundwater table behind the excavation, resulting in seepage-induced ground settlement. In this study, finite element analyses are firstly performed to assess the critical parameters that influence the ground settlement performance in Residual Soil deposits subjected to groundwater drawdown. The critical parameters that influence the ground settlement performance were identified as the excavation width, the excavation depth, the depth of groundwater drawdown, the thickness of the Residual Soil, the average SPT N60 value of the Residual Soil, the location of the moderately weathered rock, and the wall system stiffness. Subsequently, an artificial neural network (ANN) model was developed to provide estimates of the maximum ground settlement. Validation of the performance of ANN model was carried out using additional data derived from finite element analyses as well as with measured data from a number of excavation sites.
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Performance of braced excavation in Residual Soil with groundwater drawdown
Elsevier, 2018Co-Authors: W G Zhang, A. T. C. Goh, K.h. Goh, O.y.s. Chew, D. Zhou, Runhong ZhangAbstract:In densely built-up Singapore, relatively stiff secant-bored piles and diaphragm walls are commonly used in cut-and-cover works to minimize the impact of ground movement on the adjacent structures and utilities. For excavations in stiff Residual Soil deposits, the associated wall deflections and ground settlements are generally smaller than for excavations in soft Soil deposits. However, if the Residual Soil permeability is high and the underlying rock is highly fissured or fractured, substantial groundwater drawdown and associated seepage-induced settlement may occur. In this study, the excavation performance of four sites in Residual Soil deposits with maximum excavation depths between 20 and 24 m is presented. The maximum wall deflections were found to be relatively small compared to the significantly larger maximum ground settlements, owing to the extensive lowering of the groundwater table. In this paper, details of the subsurface conditions, excavation support system, field instrumentation, and observed excavation responses are presented, with particular focus on the large groundwater drawdown and associated ground settlement. Specific issues encountered during the excavation, as well as the effectiveness of various groundwater control measures, are discussed. The case studies will provide useful references and insights for future projects involving braced excavations in Residual Soil. Keywords: Residual Soil, Braced excavation, Wall deflection, Ground settlements, Groundwater drawdown, Strut forc
Gang Wang - One of the best experts on this subject based on the ideXlab platform.
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mechanical response of granite Residual Soil subjected to impact loading
International Journal of Geomechanics, 2021Co-Authors: Xinyu Liu, Lingwei Kong, Cheng Chen, Xianwei Zhang, Gang WangAbstract:Abstract When constructing subway tunnels, blasting is commonly used to deal with granite boulders in weathered granite formations. It is, therefore, crucial to evaluate how the blasting-induced im...
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effect of cementation on the small strain stiffness of granite Residual Soil
Soils and Foundations, 2021Co-Authors: Xinyu Liu, Lingwei Kong, Xianwei Zhang, Gang WangAbstract:Abstract It is widely acknowledged that Residual and sedimentary Soils differ considerably because of how they formed. However, despite extensive advances regarding sedimentary Soil, little is known about the small-strain stiffness of Residual Soil. This paper concerns granite Residual Soil from Xiamen in China, for which a typical profile is established by in situ investigations. How the stiffness varies with the Soil current state, including effective mean stress, void ratio and strain, is established via systematic resonant-column tests on high-quality undisturbed and remolded specimens. Highlighted are the unique properties of the studied Soil and how they affect the Soil stiffness. It is found that cementation among Soil particles plays a critical role in the Soil stiffness. Although some existing methods can confirm the existence of cementation in the studied Soil, they cannot quantify it. Therefore, a new parameter Rn is proposed to quantify the degree of cementation, with lower Rn corresponding to a more cemented structure. According to the proposed Rn, the studied Residual Soil in Xiamen has a different degree of cementation from that of some well-studied weathered materials, thereby necessitating separate characterization of this Soil. This study improves the understanding of Residual Soil stiffness at small strain, especially the key effect of cementation in natural Soil.
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engineering geology of Residual Soil derived from mudstone in zimbabwe
Engineering Geology, 2020Co-Authors: Lingwei Kong, Cheng Chen, Xinyu Liu, Xianwei Zhang, Gang WangAbstract:Abstract As increasing amounts of civil engineering work are carried out on mudstone-derived Residual Soils, it has become important to systematically assess their geological engineering properties. Thus, the properties of mudstone-derived Residual Soils were evaluated in this study via a series of comprehensive laboratory tests to assess physical, mechanical, mineralogical, and microstructural variations. Results show that the physical properties of these Soils are inadequate in terms of engineering applications; these Soils can be classified as highly plastic clays that are hard to compact. Natural mudstone-derived Residual Soils undergo severe disintegration underwater while remolded examples are similar but tend to exhibit more stable responses. Natural mudstone-derived Residual Soils behave in a structured way when subjected to shear and compression; these Soil types possess superior natural shear resistance but their strength decreases significantly following saturation as well as in wetting and drying cycles. Data show that the microstructures of mudstone-derived Residual Soils are characterized by the presence of aggregations with fissures; although iron-bearing cementation between these aggregations is responsible for high Soil strength, bonds can be damaged, or even destroyed, when samples are saturated or subjected to wetting and drying cycles leading to a reduction in shear strength. The results of this research provide clear parameters for related engineering applications and enhance our understanding of Residual mudstone-derived Soils.
Xianwei Zhang - One of the best experts on this subject based on the ideXlab platform.
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structural characterization of Residual Soil and the effect of drying and wetting cycles on its strength
Civil Infrastructures Confronting Severe Weathers and Climate Changes Conference, 2021Co-Authors: Wei Bai, Lingwei Kong, Xianwei Zhang, Zhiliang Sun, Xiu YueAbstract:A series of indoor tests was performed to obtain the physical and mechanical properties and structural characterization of granite Residual Soil. Experimental results indicated that clot and flocculation are the primary forms of microstructure, and the Residual appearance of the parent rock’s crystal pattern is reserved. Structural strength is provided by strong cementation and Residual chemical bond force. The clay mineral is mostly kaolin, which exhibits a laminated structure. The grain particle of granite Residual Soil presents the mixed features of sand and clay. The coefficient of compressibility is mostly distributed with in the range of 0.30–0.35 MPa−1, which is for medium compressible Soil. Granite Residual Soil demonstrates good mechanical performance even under saturation condition. However, strength variability is notable. Drying and wetting cycles reduce the strength of granite Residual Soil, and strength decreases by approximately 30% after two drying and wetting cycles.
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mechanical response of granite Residual Soil subjected to impact loading
International Journal of Geomechanics, 2021Co-Authors: Xinyu Liu, Lingwei Kong, Cheng Chen, Xianwei Zhang, Gang WangAbstract:Abstract When constructing subway tunnels, blasting is commonly used to deal with granite boulders in weathered granite formations. It is, therefore, crucial to evaluate how the blasting-induced im...
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effect of cementation on the small strain stiffness of granite Residual Soil
Soils and Foundations, 2021Co-Authors: Xinyu Liu, Lingwei Kong, Xianwei Zhang, Gang WangAbstract:Abstract It is widely acknowledged that Residual and sedimentary Soils differ considerably because of how they formed. However, despite extensive advances regarding sedimentary Soil, little is known about the small-strain stiffness of Residual Soil. This paper concerns granite Residual Soil from Xiamen in China, for which a typical profile is established by in situ investigations. How the stiffness varies with the Soil current state, including effective mean stress, void ratio and strain, is established via systematic resonant-column tests on high-quality undisturbed and remolded specimens. Highlighted are the unique properties of the studied Soil and how they affect the Soil stiffness. It is found that cementation among Soil particles plays a critical role in the Soil stiffness. Although some existing methods can confirm the existence of cementation in the studied Soil, they cannot quantify it. Therefore, a new parameter Rn is proposed to quantify the degree of cementation, with lower Rn corresponding to a more cemented structure. According to the proposed Rn, the studied Residual Soil in Xiamen has a different degree of cementation from that of some well-studied weathered materials, thereby necessitating separate characterization of this Soil. This study improves the understanding of Residual Soil stiffness at small strain, especially the key effect of cementation in natural Soil.
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accumulated plastic strain behavior of granite Residual Soil under cycle loading
International Journal of Geomechanics, 2020Co-Authors: Yin Wang, Shixing Zhang, Song Yin, Xinyu Liu, Xianwei ZhangAbstract:Abstract In this study, the accumulated plastic strain (APS) of granite Residual Soil under cyclic loads is investigated by a series of undrained cyclic triaxial tests. Granite Residual Soil is a s...
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engineering geology of Residual Soil derived from mudstone in zimbabwe
Engineering Geology, 2020Co-Authors: Lingwei Kong, Cheng Chen, Xinyu Liu, Xianwei Zhang, Gang WangAbstract:Abstract As increasing amounts of civil engineering work are carried out on mudstone-derived Residual Soils, it has become important to systematically assess their geological engineering properties. Thus, the properties of mudstone-derived Residual Soils were evaluated in this study via a series of comprehensive laboratory tests to assess physical, mechanical, mineralogical, and microstructural variations. Results show that the physical properties of these Soils are inadequate in terms of engineering applications; these Soils can be classified as highly plastic clays that are hard to compact. Natural mudstone-derived Residual Soils undergo severe disintegration underwater while remolded examples are similar but tend to exhibit more stable responses. Natural mudstone-derived Residual Soils behave in a structured way when subjected to shear and compression; these Soil types possess superior natural shear resistance but their strength decreases significantly following saturation as well as in wetting and drying cycles. Data show that the microstructures of mudstone-derived Residual Soils are characterized by the presence of aggregations with fissures; although iron-bearing cementation between these aggregations is responsible for high Soil strength, bonds can be damaged, or even destroyed, when samples are saturated or subjected to wetting and drying cycles leading to a reduction in shear strength. The results of this research provide clear parameters for related engineering applications and enhance our understanding of Residual mudstone-derived Soils.
