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The reaction of geosynthetic-encased stone columns (GECs) in soft soils under embankment loading was modeled with an indoor physical model test and numerical models using three dimensional and two dimensional finite element methods. The experimental and three dimensional numerical modeling results showed that the failure of the GECs is caused by th...
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... embankment was constructed using steel weights in three stages (stages 1e3) as shown in Fig. 2. The embankment was constructed in three stages using steel weights. Each loading stage was 10 min (time to place the weights) followed by a resting period for the dissipation of excess pore water pressure, which is about of 30e40 min based on the monitored data from piezometers shown in Fig. 3. After the construction of the ...
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... place the weights) followed by a resting period for the dissipation of excess pore water pressure, which is about of 30e40 min based on the monitored data from piezometers shown in Fig. 3. After the construction of the embankment, sand bags with equivalent pressure of 21 kPa were applied on the embankment surface to fail the structure (stage 4 in Fig. 2). The deformation of the ground before the last loading stage is shown in Fig. 4. The shape of the deformed ground shows that large settlement has occurred below the embankment, with heave in the soils in front of the toe. The largest curvature of the deformed ground contour is located below the toe of the embankment, where is also the ...
Citations
... They contributed to enhancing the understanding of the behavior of such reinforced soil structures and the factors influencing their stability. Chen et al. (2015) conducted physical model tests and 3-D numerical finite element modeling to study the behavior of a uniformly loaded embankment placed on a soft soil treated with geosynthetics encased stone columns. They observed a bending failure of the reinforced columns. ...
The increase in urbanization has led governments to build on sites with certain geotechnical hazards, such as liquefaction, low bearing capacity, etc. In recent decades, as governments have focused their efforts on the environmental and economic aspects, researchers have emphasized the need to use suitable alternative materials for the best design features, also the issue of plastic pollution is a significant global problem that requires urgent attention, current initiatives focus on the use of technical solutions to integrate non-biodegradable plastics into the construction of buildings and road pavement. In this paper, a series of direct shear tests were performed to evaluate the benefits of plastic wastes, such as polypropylene (PP) pots, and the engineering properties of sand reinforced with such materials. To highlight the contribution of the reinforcement to the shear strength, the tests were carried out on sand reinforced with variable fibre contents (0.2, 0.4, 0.6, and 0.8%) for loose-density sand and medium-density sand. The experimental results showed that the increase in shear strength is relatively more significant for specimens prepared with dry deposition mode as compared to those prepared with wet deposition mode and it is increased with the fibre content. The inclusion of randomly distributed fibres has a significant effect on the shear strength and dilatation of sandy soils. Furthermore, the recycling fibre used in this study shows a better performance in terms of shear strength. In conclusion, the use of plastic waste as reinforcement would lead to at least two solutions: soil reinforcement and reducing the environmental impact of waste.
... They contributed to enhancing the understanding of the behavior of such reinforced soil structures and the factors influencing their stability. Chen et al. (2015) conducted physical model tests and 3-D numerical finite element modeling to study the behavior of a uniformly loaded embankment placed on a soft soil treated with geosynthetics encased stone columns. They observed a bending failure of the reinforced columns. ...
The granular columns treatment is widely used in the weak soils. The present paper focuses on the numerical modeling of a direct shear test on granular columns in soils. The finite difference code Fast Lagrangian Analysis of Continua in 3 Dimensions (FLAC3D) was used in this research work, to evaluate the equivalent properties of granular column-improved soils with different diameters of the columns, and different plan configurations. The results of these numerical tests are discussed in terms of increases the shear load-strength and decreases the horizontal displacement due to the variation of arrangements, Young's modulus and the friction angle of the granular columns. Different types of failures observed in the granular columns. Bending failure mode is the main in the granular column with large values of Young's modulus and the friction angle when subjected a lateral load.
... Khabbazian et al., 2010a,b), or loading condition (Yoo and Kim, 2009). Further, most of papers focused on the GESC embedded in soft clay (Chen et al., 2015 but there was few study (Kadhim et al., 2018) on encased sand column in loose sand. ...
The sustainable management of coal slag, a prevalent solid waste byproduct resulting from coal combustion, remains an enduring and paramount subject of investigation. This paper presents an approach of exploring the viability of coal slag as a sustainable substitute for conventional gravel in geosynthetic-encased columns by large-scale model tests and numerical simulation, with a focus on its potential to enhance loose sand foundation performance. The properties of coal slag were characterized through X-ray fluorescence (XRF), X-ray diffractometry (XRD), and leaching tests. The bearing and deformation characteristics of a 250-mm diameter geosynthetic encased coal slag column (GECSC) installed in loose sand foundation were compared with those of an untreated foundation by large scale physical model tests. The parametric study involving the stiffness and encased length of geosynthetic encasement, as well as the relative density of surrounding sand was performed based on the three-dimensional finite element model verified by experimental tests. The results show that the coal slag tested is an environmentally friendly material with huge potential as an alternative to gravel for encased columns in foundation treatment. Increasing the encasement stiffness enhances bearing capacity and reduces circumferential deformation. The GECSC technology is particularly well-suited for loose sand, exhibiting a noteworthy improvement ratio of 2.73 in sand with a relative density of 10 %. The cost-effective encasement length (i.e., double times of diameter) for partially encased GECSC is recommended in terms of controlling the maximum bulge.
... Road embankments built over soft and extremely soft soils may undergo excessive total deformations and lack of stability due to high compressibility and low undrained shear strength of underlying soil. Using compacted granular columns is a common ground improvement technique to enhance embankment performance over soft deposits (Deb et al. 2008;Han 2015;Chen et al. 2015;Deb and Behera 2016;King et al. 2017;Bahadori et al. 2018;Zheng et al. 2020;Aghili et al. 2021;Basack and Nimbalkar 2023). Granular columns installed in a regular pattern, attract most portion of the embankment applied load due fill arching thus the total vertical stress transferred to the soft soil and the subsequent deformations significantly reduce. ...
In this study, undrained behavior of a road embankment overlying ordinary and geosynthetic-encased granular columns is evaluated through fully coupled nonlinear stress analysis. In this contribution, the equivalent area methodology is used to convert the strengthened zone into an equivalent area including soft soil and granular columns. Diameter and internal friction angle of granular columns, undrained shear strength of soft soil, encasement stiffness, and encasement length are all varied aiming to compare the performance of embankment in undrained condition. Results show that enlarging columns size from 0.6 to 1.2 m reduces total deformations to half. However, this improvement can be 30% enhanced as granular columns are fully encased. Also, the computed failure mode alters from deep-seated to surficial failure surface as column size, internal friction angle of column filling material, and encasement stiffness increase. Unlike encased columns, embankment on ordinary granular columns in soft soil with threshold cu value of 11.5 kPa fails due to lack of sufficient lateral support from very soft soil. In addition, encasement stiffness is found to be the most critical factor affecting deformations and stability of embankment, among others.
... Under the influence of inclined soft soil foundations and dam self-weight, engineering problems such as the uneven settlement and excessive lateral deformation of roadbeds and slope instability are prone to occur during the construction of dam substations on sloping soft soil foundations [3]. For soft soil foundation problems, concrete piles [4,5], stone piles [6,7], deep cement mixing piles [8,9], inclined piles [10,11], and T-shaped deep cement mixing piles [12] are often used to improve the strength and stiffness of such subsoils before dam substations are constructed. ...
For the construction of dam substations in coastal or mountainous areas, inclined soft soil foundations are very common. The unique engineering characteristics of inclined soft soil foundations can bring great difficulties to the construction of dam substations. In this paper, a pile foundation reinforcement dam slope model on an inclined soft soil foundation is established; the influence of different pile spacings, the pile length, and the soft soil foundation angle on the slope safety factor is studied; and the failure mechanism and stability of pile-supported dam slope foundation are analyzed. The research results indicate that pile foundation reinforcement can reduce the deformation of the dam slope foundation and improve stability. The pile layout has an important impact on stability, but a change in the pile spacing has little effect on the settlement surface at the bottom of the dam slope. The pile length has a significant impact on the safety of the slope within a certain range. The main stress area of the pile is 0–2 m above the pile, and its main deformation is the lateral deformation of the upper part of the pile. The research results of this article can provide parameter support and theoretical guidance for the construction of dam substations.
... Although many studies have been published in the literature on stone column-supported embankments on soft ground (e.g., Tan et al. 2008;Borges et al. 2009;Chen et al. 2009Chen et al. , 2015Chen et al. , 2022Castro and Sagaseta 2011;Castro et al. 2013;Deb and Mohapatra 2013;Elsawy 2013;Yapage and Liyanapathirana 2014;Almeida et al. 2015;Basack et al. 2017;Castro Vol:. (1234567890) 2017; Marques and Borges 2018a,b;Miranda et al. 2021;Marques 2021;Miranda et al. 2021;Zhou et al. 2021;Zhang et al. 2022;Abdelhamid et al. 2023;Bhochhibhoya et al. 2023), the number of studies in which basal geosynthetic reinforcement is combined with stone columns is much smaller. ...
... Theoretically, however, the use of such methods may raise some limitations, since rigid-plastic behaviour is tacitly assumed for the materials, which means that strains before overall failure, as well as stress redistribution due to elastoplastic behaviour of the materials, are not considered in the analysis. An alternative approach that allows to overcome such limitations is the use of finite element (FE) modelling (Borges and Cardoso 2002;Borges 1995;Hinchberger and Rowe 2003;Chen et al. 2015;Da Silva et al. 2017;Rowe and Soderman 1987). Two types of finite element methods have been used in practice: (1) the ''strength reduction method'' (SRM) and (2) the "non-reduced strength method" (NRSM). ...
Although stone-column embankments on soft ground have been widely studied, there is a limited number of studies in the literature in which overall stability is analysed when geosynthetic reinforcement is also incorporated at the embankment base. In the paper, a finite element-based stability analysis method is proposed and applied to analyse overall stability of geosynthetic-reinforced and stone column-supported embankments on soft soils. Fully mechanical-hydraulic coupled analyses are performed, a critical state model is used for soil constitutive behaviour and hardening non-linear elastoplastic models are incorporated to model the geosynthetics and soil-geosynthetic interfaces. Comparisons of the proposed method with other published methods are included in which the influence of the geosynthetic constitutive curve and of the area replacement factor of stone columns are analysed. Regarding the geosynthetic constitutive curve, its influence on other key variables - namely, excess pore pressure, geosynthetic tensile force, stress concentration ratio, settlement and horizontal displacement - is also analysed.
... In this analysis, the load versus settlement behaviour in soft soil reinforced by single-layer geosynthetic encased stone columns (SL-GESC) and dual-layer geosynthetic-encased stone columns (DL-GESC) were compared to that of unreinforced soil and ordinary stone column (OSC). Tis study used the Mohr-Coulomb model, which has been used by many scholars in the past to analyse the behaviour of soft soil and stone columns [27,31,[37][38][39]. It was decided that the geosynthetic encasement should be modelled as a linear elastic material. ...
Stone columns are being used to reduce soft soil settlement and increase load-carrying capacity. Since there is inadequate lateral support from the local native soil, soft soil undergoes excessive settlement under vertical loading. This issue is effectively resolved by suitably encasing stone column material by geosynthetic with significant axial stiffness, which provides the required additional confinement reported in the literature. In the current study, an effort has been made to examine the load settlement behaviour of the dual-layered geosynthetic-encased stone column (DL-GESC) under vertical loading. In order to simulate the behaviour of stone column-reinforced soft soil, a FEM analysis was performed using PLAXIS-3D and three-dimensional (3D) models made utilising the unit cell idealisation technique for a single column. The stone column diameter, spacing to diameter (s/d) ratio, and encasement layers were varied to determine their influence on load-settling behaviour. The vertical load-carrying capacity of the ground was significantly improved when an additional layer of geosynthetic encasement was inserted into the stone column as compared to SL-GESC. Improvement of 15–25% was observed for the analysis of a single column installed in soft clay, according to the result obtained. Improvement ratios have been discussed in detail for various encasement conditions.
... This encasement increases the overall stiffness as a higher vertical load will be transferred to the surrounding soil by the bulging phenomenon. (Alkhorshid et al. 2019, Murugesan and Rajagopal 2010, Pulko et al. 2011, Kong et al. 2018, Gniel and Bouazza 2010, Gholaminejad et al. 2020, Xu et al. 2021, Xue et al. 2019, Basack et al. 2017, Gu et al. 2020, Ou-Yang et al. 2017, Almeida et al. 2015, Chen et al. 2015, Li et al. 2020, Zhang et al. 2012, Elsawy 2013, Alexiew et al. 2005, Brokemper et al. 2006, Maheshwari and Chauhan 2013, McCabe et al. 2013, Shahu and Reddy 2014, Ali et al. 2014, Zhou and kong, 2019a. ...
... The plane of the slip circle traversing the stone column functions as the shear failure plane for the column body, which is the most common mode of failure for compacted sand or gravel (Abusharar and Han 2011). Bending moment and shear force diagrams from the study of Chen et al. 2015, demonstrated that failure initiates in the columns at the edge of the slope because of the lower amount of lateral resistance. Granular columns under the embankment edge have an increased risk of failure, as Khabbazian et al. (2015) found through numerical analysis. ...
... Field load tests show that the additional restraint provided by the geogrid improves the stiffness of the stone column, which improves the bearing capacity of the stone column and reduces the settlement of soft soil foundations [15]. To avoid the limitation of test conditions, many scholars studied the shear strain and load transfer mechanism of stone columns by numerical simulation and further explored the reinforcement mechanism of GESCs on soft foundations [16][17][18][19][20][21]. Few scholars have studied the dynamic load-bearing performance of soft foundation single-stone columns. ...
The “method of overlap” replaces traditional welding to solve the problem of how the geosynthetic-encased stone column is limited by the welding frame during site construction, making the site construction simplified and economical, but its bearing mechanism is not clear. Therefore, the bearing mechanism and failure mode of the stone column was studied through the compression test of the multi-layer geosynthetic-encased stone column under dynamic and static loading. The research shows that the multi-layer encasement improves the modulus and lateral restraint of the stone column, which increases the stress transfer rate and reduces the damage degree of the stone column. The vertical ultimate bearing capacity increase in multi-layer geosynthetic-encased stone columns under dynamic and static loading is significantly different, and the difference can be up to 47.1%; the corresponding number of encasement layers should be selected according to the actual situation. The influence of the difference between dynamic and static loading on the location of the main radial strain of the stone column can be ignored, but the lateral restraint of the stone column under dynamic loading is weakened, the stress transfer rate is reduced, and the radial strain is reduced and more uniform along the stone column height. The vertical ultimate bearing capacity of the one- and two-layer geogrid-encased stone column under dynamic loading is lower than that of static loading. When treating soft foundations, the influence of traffic loads should be considered, and the bearing capacity of the geosynthetic-encased stone column should be appropriately increased in design value.
... These studies generally indicate that the geosynthetic encasement could significantly improve the bearing capacity and restrict the lateral deformations of stone column. Stone columns under the toe of an embankment are primarily subjected to lateral loading, and thus shear failure is the predominant failure mode (Abusharar and Han 2011;Almeida et al. 2015;Chen et al. 2015). However, research on the shear strength of GESC is limited and the shear reinforcement mechanism of GESC remains to be studied. ...
This paper presents a numerical study to evaluate the contribution of geosynthetic on the shear strength of geosynthetic encased stone column (GESC) under direct shear loading conditions. The backfill soil was characterized using the linearly elastic-plastic Mohr-Coulomb model. The geosynthetic encasement was simulated using linearly elastic liner elements. The interaction between the geosynthetic encasement and soils on both sides was modeled through two interfaces. The three-dimensional numerical model was validated using experimental data from direct shear tests of GESC models. The shear stress-strain response and the development of longitudinal and circumferential strains of GESC during the shear process were first discussed, and then a parametric study was conducted to investigate the effects of various design parameters on the shear strength of GESC and the contribution of geosynthetic. Results indicate that the shear resistance provided by the geosynthetic encasement develops slowly, which depends on the mobilization of tensile strains. At the failure condition, the longitudinal strains are larger than the circumferential strains, which indicates that the longitudinal tensile rupture is more critical for GESC under shear loading. The vertical stress, geosynthetic encasement stiffness, stone column diameter and spacing have the most important influences on the shear strength contribution of geosynthetic encasement.
