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Calibration of the UBC3D-PLM model to liquefaction strength curve for loose sand from cyclic simple shear element data.
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This study aims to predict the effect of liquefaction on an embankment resting on liquefiable foundation soil. A numerical model has been simulated in PLAXIS 2D with plane strain idealization. An effective stress-based elastoplastic UBC3D-PLM model has been used to represent the constitutive behavior of foundation sandy soil. The embankment soil ha...
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... atmospheric pressure. The bottom boundary has been considered fully fixed. A viscous boundary generally updates the stress condition at the boundary to nullify the effect of reflected stresses back into the domain. In this manner, it is attempted to simulate the realistic boundary condition with a certain amount of accuracy ( Yang et al. 2003). Fig. 10(a) shows effective vertical stress distribution during the initial soil condition for the benchmark model. Similar stress distribution at the end of reconsolidation (250 s) after the application of cyclic loading (amplitude 0.1 g) is depicted in Fig. 10(b). To study the effectiveness of stone column mitigation, a detailed parametric study ...
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... the realistic boundary condition with a certain amount of accuracy ( Yang et al. 2003). Fig. 10(a) shows effective vertical stress distribution during the initial soil condition for the benchmark model. Similar stress distribution at the end of reconsolidation (250 s) after the application of cyclic loading (amplitude 0.1 g) is depicted in Fig. 10(b). To study the effectiveness of stone column mitigation, a detailed parametric study has been executed to highlight the effect of the stone column diameter (D), the spacing of stone columns (S), and the input ...
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... study. The variation in the crest settlement with an increasing number of stone columns has been the main focus of this study. As an input motion, 10 cycles of 1.6 Hz frequency have been applied with an acceleration of 0.1 g amplitude. The crest settlement for the no stone column condition has been taken as a benchmark. It can be observed from Fig. 11 that with a single stone column below the toe, settlement reduces by nearly 11.20%, whereas with 3 and 5 stone columns, settlement reductions are 60% and 70%, respectively. With an increase in the number of stone column, settlement reduces. However, with a minimum of three stone columns in each region under the embankment toe, a ...
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... dynamic loading condition when the soil experiences the maximum value of change in pore pressure, this condition represents the maximum excess pore pressure ratio (r u,max ). Variations in r u,max for different diameters of the stone column throughout the length of the profile of liquefiable foundation soil at 5 and 3 m depth are compared in Fig. 12. For a constant S/D ratio of stone columns, the diameter of the stone columns has been varied in this section. Three different diameters (0.6, 0.8, and 1.0 m) were considered in this study. The stone column-encased zone has been demarcated as an effective zone. The effect of the stone columns in this zone below the embankment toe is ...
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... density (%) 65 60 γ dry (kN/m 3 stone columns, and the compressibility of the soil reduces. At a 3-m depth, this phenomenon is more predominant than at a 5-m depth. At 5-m depth, the stone columns are more effective than at 3-m depth. This may be attributed to the presence of a denser sand layer at a 6-m depth. Fig. 13 shows the effect of the stone column in restraining the lateral outflow deformation of foundation soil below the embankment. The variation in the lateral displacement U x along the depth of the liquefiable foundation soil layer are compared for all three diameters. In the case of the benchmark model, the maximum outflow horizontal ...
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... of the stone columns, 65.50%, 70.76%, and 77.20% reduction in U x,max can be observed for the 0.6, 0.8, and 1-m-diameter stone columns, respectively. The stone columns are efficient in reducing the lateral outflow of foundation soil under the embankment. With an increase in the diameter (D) of the stone column, a reduction in U x can be observed. Fig. 14 shows an embankment crest settlement time history plot for the benchmark model and models with different diameters of a stone column. At the end of cyclic loading, the crest settlement value was observed to be 0.192 m in the case of the benchmark model. This value reduced by 59.8%, 65.52%, and 68.75% for the models with 0.6-, 0.8-, and ...
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... to be 0.192 m in the case of the benchmark model. This value reduced by 59.8%, 65.52%, and 68.75% for the models with 0.6-, 0.8-, and 1-m-diameter stone column models, respectively. This observation shows a considerable justification that with the restraining of the lateral outflow of the embankment foundation soil, crest settlement also reduces. Fig. 15 shows a profile for the ground surface deformation after the cyclic event. In the case of the benchmark model, considerable heaving has been observed in the free surface region due to the excessive settlement of the embankment. Maximum heaving has been noticed at a location 6 m away from the embankment toe. On the other side, heaving ...
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... this section, the effect of spacing (S) was taken into consideration by varying S/D ratios as 2, 2.5, and 3. The uniform 0.6-m-diameter stone column was considered in the parametric study. Variations in r u,max along the horizontal distance are compared in Fig. 16 for different S/D ratios. The r u,max below the embankment toe was seen decreasing with a decrease in the spacing of the stone columns. The area enclosed by the stone columns and the nearby surrounding soil was found to be mitigated quite ...
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... Except for the results for S/D = 2.5, for the other two spacings, it can be predicted that the stone columns showed better mitigation with increasing depth. In the case of the benchmark model at a depth of 3 m below the center of the embankment, the r u,max value was found to be 0.191. The same was observed to be 0. 188, 0.196, and 0.194 Fig. 17 shows the embankment crest settlement time history after 10 cycles of cyclic loading for various spacings of stone columns under the toe regions along with the benchmark model results. A small marginal difference in the crest settlement has been observed with the variation in spacing for the 0.6-m-diameter stone column. A maximum ...
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... been seen that not only the efficiency of the reduction of EPP is important for reducing the settlement of the embankment, but also the effective length of mitigation is important. A maximum reduction in settlement can be obtained only if mitigation has been done up to the required length of the mitigation zone under the toe of the embankment. Fig. 18 shows the time history of the EPP plot for different locations at the middepth of the liquefiable layer (S/D = 2.5) for both the benchmark model and the mitigated model. The location P 1 toward the free field shows an approximately 13.92% reduction in the maximum EPP value due to the presence of a stone column. However, locations P 2 ...
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... this study primarily focuses on the region below the embankment toe (effective zone), because this location is most critical for the liquefaction-induced settlement of embankments. The contour of r u after 10 cycles of loading for the benchmark model and the model with the 0.6-m-diameter stone columns at 2.5D spacing have been compared in Fig. 19. A clear effect of the stone columns in reducing EPP in the area below the embankment toe can be noticed from the contours of r u ...
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... model considered previously. Material properties were kept similar to those of the dynamic stage only. The contours of r u after a reconsolidation for 41.75 s post liquefaction are compared in Fig. 20 for the benchmark model and the model with the 0.6-m-diameter stone column. A clear effect is noticed in the values of r u below the embankment. Fig. 21 depicts a 41.75 s postliquefaction reconsolidation EPP time history for locations P 1 to P 4. It can be easily interpreted that the stone column was efficient enough to dissipate the EPP that built up during the dynamic loading stage in a short span of time. At location P 1 in the case of the benchmark model, the maximum EPP can be observed to be ...
Citations
... The numerical simulation is frequently used as a complementary approach for the widely used simplified liquefaction analysis procedure to perform a detailed analysis on the damage of a liquefaction hazard on structure (Chou and Lin, 2020; Chaloulos et al., 2020; Tsai et al., 2020; Chou et al., 2023) or to evaluate the effectiveness of mitigation design plans (Chakraborty and Sawant, 2022;Su et al., 2022;Phyo et al., 2021). It is important the constitutive model used in the numerical simulation having the same cyclic resistance with the simplified liquefaction analysis procedure to obtain reasonable and comparable evaluation results. ...
Liquefaction hazards can cause damage to structures and loss of life and property. The simplified prediction equation, numerical simulation and model test are three commonly used approaches to evaluate the damage of the liquefaction hazards or the effectiveness of the mitigation plan. Because the numerical simulation can include the site-specific conditions into the evaluation and perform a parametric study under a reasonable time and affordable budget, many research and engineering projects choose this approach as an evaluation tool. In order to obtain rational and comparable simulation results, appropriate constitutive models and model inputs are essential. Many liquefaction constitutive models (Finn model, UBCSAND model, SANISAND model, PM4Sand model etc.) have been introduced and coded for numerical programs (PLAXIS, FLAC, MIDAS etc.) to study liquefaction hazards and many related topics. Among these constitutive models, PM4Sand model has been frequently used in recent projects to model the soil liquefaction. PM4Sand model is modified from the bounding surface plasticity model for geotechnical earthquake engineering applications and coded as a user-written constitutive model in FLAC. In this study, inputs of PM4Sand (version 3.1) model are calibrated against the triggering curve of simplified liquefaction analysis procedures suggested by Seismic Design Specifications and Commentary of Buildings of Taiwan for future liquefaction evaluation projects. In addition, model responses of PM4Sand model are discussed and compared with laboratory tests
... To model the behavior of coarse-grained SCs, the Mohr-Coulomb elastic-perfectly plastic model has been employed, as described by Noui et al. (2019). Recently, the impact of liquefaction on an embankment supported by liquefiable foundation soil has been evaluated numerically (Chakraborty and Sawant 2022). Simulations were performed using PLAXIS 2D. ...
... In order to simplify the computational process, a plane strain condition is adopted (Kumar et al. 2020;Chakraborty and Sawant 2022). Despite the cylindrical shape of the SCs, the equivalent plane strip is assumed in this study. ...
One effective technique for mitigating the earthquake-induced liquefaction potential is the installation of stone columns. The permeability coefficients of stone columns are high enough to cause a high seepage velocity or expedited drainage. Under such conditions, the fluid flow law in porous media is not linear. Nevertheless, this nonlinear behavior in stone columns has not been evaluated in dynamic numerical analyses. This study proposes a dynamic finite element method that integrates nonlinear fluid flow law to evaluate the response of liquefiable ground improved by stone columns during seismic events. The impact of non-Darcy flow on the excess pore pressure and stress path compared to conventional Darcy law has been investigated numerically in stone columns. Furthermore, the effects of different permeability coefficients and stone column depths have been studied under near and far field strong ground motions. The results indicate that the non-Darcy flow increases the excess pore water pressure as high as 100% in comparison to the Darcy flow.
... Recent studies have shown the effectiveness of stone columns in mitigating the liquefaction of foundation soil using advanced constitutive models [22][23][24]. Recently Chakraborty and Sawant [25] studied the effect of the stone column on the mitigation of liquefaction of embankment foundation soil. The study addressed the influence of the stone column's diameter (D) and spacing (S) to diameter ratio (S/D) below the embankment toes. ...
... The plan view of the arrangement of stone columns is shown in Fig. 1d. This arrangement of stone columns has been taken from a recent study [25]. Stone columns are created using volume elements, with a spacing to diameter ratio (S/D) equal to 2. ...
... The foundation soil layers (layer I and layer II) have been modeled using the UBC3D-PLM material model. The material model properties are considered from the calibration study reported by Chakraborty and Sawant [25,32,33]. However, in the case of model GBM, the gravel berms are considered linear elastic [21], and the stone columns are modeled using the UBC3D-PLM model. ...
The present study focused on gravel berm and stone column improvement techniques for mitigating the effects of liquefaction for an embankment resting on liquefiable ground. Three-dimensional finite element models are developed to evaluate the effectiveness of two countermeasure techniques for embankments resting on liquefiable soil. Three different embankment models are considered in this study as benchmark embankment model (BM), gravel berm embankment model (GBM), and stone column mitigation model (SCM). Foundation soil has been modeled using an elasto-plastic effective stress-based UBC3D-PLM model. Initially, the behaviour of three different embankment models (BM, GBM, and SCM) are evaluated under varying amplitude of cyclic input motion. Later, a seismic study is carried out considering 10 sequential earthquake motions to assess the effect of the aftershock following the main shock event. It can be seen that even small amplitude aftershocks can develop a high excess pore pressure ratio in the foundation soil, especially below the embankment toe. Moreover, a linear correlation has been observed between the input motion Arias intensity and the intensity at the embankment crest. In an overall observation, stone column mitigation was found to be a sound mitigation approach.
... Excessive settlement and loss of stability of offshore structures have been frequently reported when low-strength and highcompressibility soft clay is embedded (Mesri and Funk 2015;Das and Dey 2020;Chakraborty and Sawant 2022). To avoid these problems, the sand compaction pile (SCP) method is widely adopted to improve the properties of soft clay (Feng et al. 2020). ...
... This phenomenon could cause buildings to topple over abruptly, sink, and tilt. Furthermore, [22][23][24][25][26] guided research works to identify some intelligent strategies and practical approaches that can be adopted to mitigate the soil liquefaction problem in construction. They found that employing kaoliniteclay, stone columns, nanomaterials, recycled materials, colloidal silica, bentonite, laponite, and short synthetic fibers could be applied and implemented to improve the soil mechanical characteristics by enhancing its potential to resist the liquefaction problem when an earthquake occurs and making amendments in its structure. ...
This research is carried out to investigate and assess the critical role of soil properties and their content in influencing the soil liquefaction phenomenon that takes place when an earthquake happens. A case study is considered in this work, representing the Karakaya Dam. Two research approaches were implemented to achieve the research goal, including extrapolation in Excel and numerical optimization using linear regression. The outputs revealed that the annual temperature in the future of zones around the Karakaya Dam, including Azami, Ortalama, and Asgari, would witness a moderate increase of about 3 to 6 degrees Celsius in the next decade. Moreover, the research confirmed that the Euphrates River discharge rate at the Karakaya Dam would witness a significant increase from (100-350 m³) to (2,590-2,640 m³) in 2029, explaining that temperature and discharge rate may influence the liquefaction. Meanwhile, the research outputs indicated that soil temperature under the Karakaya Dam and chemical elements would not vary significantly in the next decade. Notwithstanding, the pH number will change widely from 4.14 to 9.74 in 2029. Besides, the most significant chemical molecule concentration in the soil under the Karakaya Dam is the phosphite anion, corresponding to a minimum and maximum concentration of 1 and 2 μg/m², respectively © The Author 2022. This work is licensed under a Creative Commons Attribution License (https://creativecommons.org/licenses/by/4.0/) that allows others to share and adapt the material for any purpose (even commercially), in any medium with an acknowledgement of the work's authorship and initial publication in this journal
... This phenomenon could cause buildings to topple over abruptly, sink, and tilt. Furthermore, [22][23][24][25][26] guided research works to identify some intelligent strategies and practical approaches that can be adopted to mitigate the soil liquefaction problem in construction. They found that employing kaoliniteclay, stone columns, nanomaterials, recycled materials, colloidal silica, bentonite, laponite, and short synthetic fibers could be applied and implemented to improve the soil mechanical characteristics by enhancing its potential to resist the liquefaction problem when an earthquake occurs and making amendments in its structure. ...
This research is carried out to investigate and assess the critical role of soil properties and their content in influencing the soil liquefaction phenomenon that takes place when an earthquake happens. A case study is considered in this work, representing the Karakaya Dam. Two research approaches were implemented to
achieve the research goal, including extrapolation in Excel and numerical optimization using linear regression. The outputs revealed that the annual temperature in the future of zones around the Karakaya Dam, including Azami, Ortalama, and Asgari, would witness a moderate increase of about 3 to 6 degrees Celsius in the next decade. Moreover, the research confirmed that the Euphrates River discharge rate at the Karakaya Dam would witness a significant increase from (100-350 m3) to (2,590-2,640 m3) in 2029, explaining that temperature and discharge rate may influence the liquefaction. Meanwhile, the research outputs indicated that soil temperature under the Karakaya Dam and chemical elements would not vary significantly in the next decade. Notwithstanding, the pH number will change widely from 4.14 to 9.74 in 2029. Besides, the most significant chemical molecule concentration in the soil under the Karakaya Dam is the phosphite anion,
corresponding to a minimum and maximum concentration of 1 and 2 μg/m2, respectively.
... Dinesh et al. (2022) proved efficacy of advanced constitutive model PM4S and in modelling different mitigation strategies for embankments founded on liquefiable soil. Chakraborty and Sawant (2022) studied liquefaction mitigation of embankment using stone columns beneath the toe. It is observed that an arrangement of three numbers of stone columns with 0.6 m diameter (D) and 2D spacing is efficient enough to reduce the excess pore pressure (EPP) and settlement for lower to moderate earthquake loading. ...
... Hence, a densification width of 6.0 m is only considered on both sides of the embankment toe. In Model 3 (Fig. 1c), Five numbers of the stone column have been provided beneath the embankment toe area as stone column mitigation based on the earlier observations in previous study (Chakraborty and Sawant 2022). It was observed that 0.6 m diameter (D) stone columns with 2D spacing is efficient enough to reduce both the EPP beneath the toe region and the settlement of the embankment. ...
... With keeping this viewpoint in consideration, a hybrid mitigation has been introduced in this study considering a pile-stone column combined mitigation method. However, the location and width of mitigation is based on the observations from past studies (Adalier et al. 1998;Okamura and Matsuo 2002;Chakraborty and Sawant 2022) and few trials with varying configurations on the overall performance of embankment under dynamic loading. The stone columns and the pile have been modelled in structure mode in PLAXIS 2D. ...
Three different liquefaction mitigation techniques for an earthen embankment resting on saturated loose cohesionless soil have been compared in the present study as densifica-tion of foundation soil, stone column mitigation, and hybrid pile-stone column mitigation. Numerical modelling has been done using finite element modelling assuming plane strain condition. Liquefaction behaviour of the foundation soil has been modelled using the effective stress-based elasto-plastic UBC3D-PLM model. All the three mitigation models along with the benchmark model have been analysed under 25 different real ground motions. The maximum embankment crest settlement has been occurred in the Imperial Valley (1979) ground motion having the maximum Arias Intensity. The maximum crest settlement and the maximum excess pore pressure ratio in the mitigation zone below embankment toe found to be increasing with Arias Intensity of ground motions. In case of mitigation using densification of region below the embankment toe, the mitigated zone away from the toe towards the free field liquefies. The stone column mitigation reduces the excess pore pressure more efficiently beneath the embankment toe region than other two mitigation techniques. The hybrid mitigation with a combination of gravel drainage and pile found to be more effective to reduce the excess pore pressure as well as the shear-induced and post-shaking settlement due to the rapid dissipation of excess pore pressure of the foundation soil.
The fragility curve, which specifies the likelihood that a structure would sustain damage that exceeds a certain threshold for different levels of loading intensity, is a newly developed method for the seismic risk assessment of all at-risk projects. Median and log-standard distribution are the two parameters constituting the cumulative lognormal distribution function, typically used to describe fragility curves. An investigation of the response of a road embankment geotechnical structure exposed to liquefaction-induced deformation driven by earthquakes is presented in the current work. The elasto-plastic and effective stress-based UBC3D-PLM model is used in the numerical analyses based on 2D FE analysis. A rigorous calibration process is carried out to generate the model parameters concerning laboratory test findings from past literature. With increasing intensity of ground motion (PGA), permanent embankment settlement (PES) is used to indicate the extent of the damage. A collection of 9 separate ground motions, scaled to different intensity levels, were used in the incremental dynamic analysis (IDA) that has been used to perform the fragility analyses. It has been observed that the embankment experiences more settlement even with low to moderate ground motion intensity due to the existence of the liquefiable foundation layer. To assess the vulnerability of an earthen embankment exposed to liquefiable foundation soil, different factors have been taken into account, including the relative density of the liquefiable underlying soil, the thickness of the liquefiable layer, and the geometry of the embankment (height and width). It has been noticed that liquefiable layer properties are the primary and embankment properties are the secondary parameters influencing the vulnerability of embankment supported on liquefiable soil deposit.
The fragility curve, which specifies the likelihood that a structure would sustain damage that exceeds a certain threshold for different levels of loading intensity, is a newly developed method for the seismic risk assessment of all at-risk projects. Median and log-standard distribution are the two parameters constituting the cumulative lognormal distribution function, typically used to describe fragility curves. An investigation of the response of a road embankment geotechnical structure exposed to liquefaction-induced deformation driven by earthquakes is presented in the current work. The elasto-plastic and effective stress-based UBC3D-PLM model is used in the numerical analyses based on 2D FE analysis. A rigorous calibration process is carried out to generate the model parameters concerning laboratory test findings from past literature. With increasing intensity of ground motion (PGA), permanent embankment settlement (PES) is used to indicate the extent of the damage. A collection of 9 separate ground motions, scaled to different intensity levels, were used in the incremental dynamic analysis (IDA) that has been used to perform the fragility analyses. It has been observed that the embankment experiences more settlement even with low to moderate ground motion intensity due to the existence of the liquefiable foundation layer. To assess the vulnerability of an earthen embankment exposed to liquefiable foundation soil, different factors have been taken into account, including the relative density of the liquefiable underlying soil, the thickness of the liquefiable layer, and the geometry of the embankment (height and width). It has been noticed that liquefiable layer properties are the primary and embankment properties are the secondary parameters influencing the vulnerability of embankment supported on liquefiable soil deposit.
