Numerical study to evaluate the effect of encased stone columns technique for liquefaction mitigation of sandy soil by PLAXIS 2D

The present paper investigates the effectiveness of using geotextile encased stone column for mitigating the liquefaction phenomenon in saturated sandy deposits. Reduced scale 1-g model tests were conducted using a uniaxial shake table to study the behavior of loose saturated sand reinforced with encased stone columns when subjected to harmonic (sinusoidal) loading. Additionally, the response of saturated sand reinforced with stone column, with and without geotextile encasement is also studied and compared. The test results show that the installation of stone column in the saturated loose sand increases the liquefaction resistance of sand. The presence of geotextile allows quicker dissipation of pore water which results in an improved liquefaction resistance of sand. Moreover, the acceleration amplitude influences the response of both the unreinforced and reinforced sand. The increase in acceleration amplitude increases the magnitude of excess pore water pressure ratio. Furthermore, the presence of stone column also reduces the settlement of the shallow foundation.

Ground improvement techniques are frequently employed in construction sites characterized by weak soil conditions that may result in suboptimal performance. The use of ordinary and encased stone columns aims to enhance endurance, shear strength, and soil hardness, thereby mitigating settlement issues and expediting the consolidation of contaminated sand soils. In this research, a comprehensive investigation involving 74 cases was conducted to assess the behavior of both ordinary stone columns and encased stone columns under strip footing in contaminated sand subgrade. The objective was to discern the impact and characteristics of encapsulation in comparison to encapsulated stone columns, employing a Finite Element Model (FEM) within the PLAXIS 3D software package. The study focused on stone columns with two different diameters (D = 0.5 m and 0.6 m), while the column length was 12 m across all cases. As the contamination level increases—at the variable contaminated sand levels of (2%, 5%, and 10%)—the viscosity of the soil rises, leading to a reduction in cohesion between soil granules. Consequently, the internal friction angle decreases, with values diminishing from 31° to 27° and then to 24°, respectively. The clean sand was placed to achieve relative density, a medium dense sand state (Dr = 50%). The two categories of stone columns examined were ordinary stone columns (OSC) without encapsulation and encased stone columns (ESC) encapsulated with varying degrees of hardening. Results obtained at variable internal friction angles (35, 40, and 45 degrees) revealed a notable increase in the endurance of ordinary stone columns on untreated soil conditions, reaching 100%, 125%, and 148% for column diameters (D = 0.5 m) and 130%, 145%, and 180% for column diameters (D = 0.6 m), respectively. The corresponding increase in the endurance of encased stone columns under untreated soil conditions was found to be 275%, 33%, and 345% for column diameters (D = 0.5 m) and reached 313%, 350%, and 375% for column diameters (D = 0.6 m), respectively. All preceding results were obtained under the condition of a contaminated sand content of 5%. The investigation aimed to provide valuable insights into the performance and efficacy of ordinary stone columns (OSC) and encased stone columns (ESC) as a geotechnical solution for improving soil conditions in construction projects.

Dissipation of excess pore water pressure of saturation clay was discussed in the paper. Monotonic loading, unloading-reloading, and creep tests of one dimensional compression were performed to study the orderliness of dissipation of excess pore water pressure. In the drained consolidated tests, strain rate was changed step by step to check the effects of excess pore water pressure on effective axial stress. Creep tests were performed in different stage of loading and unloading procedure under different effective axial stress. In order to estimate the effects of excess pore water on effective axial stress more precisely, excess pore water pressure ratio was introduced. Test results show that: (1) excess pore water pressure changed gradually as strain rate changed abruptly, while excess pore water pressure ratio changed quickly; (2) excess pore water pressure maintained constant shortly after the change of strain rate during monotonic loading tests under small strain rate; (3) excess pore water pressure may be smaller than back pressure during unloading-reloading tests, in which, excess pore water pressure ratio is negative; (4) there neutral creep existed in unloading-creep-unloading procedure. Excess pore water pressure ratio equal to 0 and excess pore water pressure maintained a constant value equal to the back pressure in neutral creep.

Geosynthetic encased stone columns (GESCs) are a newly developed technique in which stone columns are wrapped with geosynthetic to overcome some of the limitations of ordinary stone columns (OSCs) through the additional confinement provided by the geosynthetic. This paper presents the behavior of GESCs under circular oil storage tank and its comparison with OSCs under the same in situ conditions using PLAXIS 3D. In this paper, initial studies were carried out to understand the mechanism of load carrying capacity of soils reinforced with stone columns and the later observations from the parametric studies supported the conclusions. The various parameters considered in this investigation include the effect of encasement stiffness and length on settlement and lateral deformation of stone columns. The results show that with an increase in stiffness value, there is a considerable reduction in the long-term settlement and lateral deformation of GESCs. It was found that settlement reduced by up to 55% and lateral deformation by up to 68% with an increase in geosynthetic stiffness from 1000 to 10,000 kN/m. Meanwhile the encasement length up to six times the diameter was found as the optimum encasement length to get the same performance as that of fully encased stone columns. Further a suitable arrangement of encased stone columns in terms of encasement length has been developed to economize the consumption of geosynthetic without compromising the performance of GESCs.

Purpose: This study aims to study the load – settlement behaviour of circular footing rested on encased single stone column. Design/methodology/approach: The effect of vertical, horizontal and combined verticalhorizontal encasement of stone column on the load carrying capacity were examined numerically. The effect of stone column dimension (80 mm and 100 mm), length (400 mm and 500 mm), and spacing of reinforcement on the load carrying capacity and reinforcement ratio were assessed. Findings: The obtained results revealed that the load carrying capacity of geotextile encased stone columns are more than ordinary stone columns. For vertically encased stone columns as the diameter increases, the advantage of encasement decreases. Whereas, for horizontally encased stone column and combined vertical- horizontal encased stone column, the performance of encasement intensifies as the diameter of stone column increases. The improvement in the load carrying capacity of clay bed reinforced with combined verticalhorizontal encased stone columns are higher than vertical encased stone columns or horizontal encased stone column. The maximum performance of encasement was observed for VHESC1 of D = 80 mm. Research limitations/implications: For this study, the diameter of footing and stone column was kept same. The interface strength factor between stone column and clay bed was not considered. Practical implications: The encased stone column could be use improve the laod bearing capacity of weak soils. Originality/value: Many studies are available in literature regarding use of geosynthetic as vertical encasement and horizontal encasement of stone column. The study on combined effect of vertical and horizontal encasement of stone column on load carrying capacity of weak soil is very minimal. Keeping this in view, the present work was carried out.

Finite-difference solution for dissipation of excess pore water pressure within liquefied soil stabilized by stone columns with consideration of coupled radial-vertical seepage

The advantage of utilizing stone columns in very low bearing capacity of soil has been demonstrated as an effective strategy to improve the load bearing characteristics of soils. For stone columns, the load bearing capacity primarily relies upon the circumferential confinement given by the local delicate soils. In this research article, several tests were performed on group of 3 and 4 stone columns having diameter of 40 mm and length of stone columns of 300 mm. Stone columns were tested for both unreinforced and geotextile reinforced stone columns, i.e. encased stone columns and horizontally reinforced stone columns. Reinforced stone columns have been considered to explore the load settlement behaviour and failure mechanism. The principle target of this exploration is to compare the adequacy of encased stoned columns and horizontally reinforced stone columns. Results show that horizontal reinforced stone columns provide better ground improvement in comparison with encased stone columns. Utilizing of geotextile helps reduce failure due to the lateral bulging. Finite element modelling (FEM) has also been performed with Plaxis 2D and 3D software. The FEM results show that the load bearing capacity of reinforced stone columns is better than unreinforced stone columns both depicting failure due to bulging. The validation of experimental and FEM results are found in good agreement within permissible range of variation.

The engineering structures constructed on thick deposits of soft soil strata have problems of low bearing capacity, excessive total and differential settlement, lateral spreading etc. To mitigate such problems, different ground improvement techniques are available namely; vertical drains, lime/cement column, stone (granular) column etc. in view of their proven performance, short time schedule, durability, constructability and low costs. Stone column technique seems to be very suitable and favourable ground improvement technique for deep soft soil improvement. Further to prevent excessive bulging, squeezing of stone into soft soil, stone column can be encased with suitable geosynthetic. Another advantage of encasement is having high load carrying capacity and lesser settlement of composite foundation. This paper presents the current state of the geosynthetic encased stone column as a ground improvement technique. A review is provided aiming to: (a) identify key considerations for the general use of encased stone columns, (b) provide insights for design and construction, (c) compile the latest research developments. Case histories of field applications and observed field performance are cited to portray different stone column applications and observed effectiveness. The paper identifies areas where more research is needed and includes recommendations for future research and development.

The Cement Fly Ash and Gravel (CFG) Pile and Encased Stone Column (ESC) are the ground improvement techniques. The main object of the study is to the numerical analysis of the Both techniques pile group were used to support the Embankment with and without the geotextile both techniques composite foundation by the Finite Element method under static and dynamic load analysis. Numerical simulation has been carried out in Plaxis 3D. A case study from china’s highspeed embankment supported by CFG and ESC have investigated the load caring capacity by soil and pile. While the failure behaviors, settlement, excess pore pressure, and lateral behavior with variable embankment loading and number of geosynthetic effect moreover, the diameter of CFG piles and ESC at various locations in an embankment has been varied to study its influence on the load distribution among the CFG piles/ESC and lateral load displacement of the pile group. The results show that increasing the diameter of both techniques reduced the total settlement and differential settlement of embankment. It observed that the seismic load has a significant effect on the vertical and lateral displacement.

Liquefaction is soil condition associated with the drastic increase in pore water pressure of uniform sandy soil due to an enormous earthquake. Therefore, this study aimed to investigate the correlation of liquefaction potential with excess pore water pressure ratio in nine boreholes located at Kretek 2 Bridge area using empirical and numerical methods. Liquefaction potential was estimated based on a semi-empirical method simplified by Idriss and Boulanger (2008), and safety factor (SF) value of <1.0 was used to represent the existence of its potential. The result showed that liquefaction potential was dominant at depths of 1.5 to 6.0 m, with the exception of BH-9 with 16.5 m and BH-4. Furthermore, the excess pore water pressure ratio was estimated using empirical method developed by Yegian and Vitelli (1981) as well as Serafini and Perlea (2010). Numerical analysis was also conducted for comparison purposes and the process focused on using Deepsoil v7.0 to generate excess pore water pressure by considering soil conditions and dominant seismic sources in Kretek 2 Bridge area. The result showed that the ratio of excess pore water pressure was greater or equaled 0.8. Both empirical and numerical methods produced similar values for BH-1, BH-2, BH-8, and BH-9 at a depth of 1.5–3.0 m, 3–4.5 m, 3.0 m, and 16.5 m, respectively. This showed a correlation between excess pore water pressure ratio and liquefaction potential values at the same depth. However, numerical method tended to overestimate the ru value, necessitating the use of empirical method to obtain a more reliable result.

Booming infrastructure activities demand suitable subsoil conditions to accomplish design requirements in terms of strength and serviceability. Soft soils encountered during such activities may pose problems such as very low strength, poor hydraulic conductivity, shrinkage and swelling with seasonal moisture variations etc. Utilization of sites with soft soils required the invention of various ground modification techniques. Stone columns is one of such techniques used in soft soils to improve its load bearing capacity, dissipate excess pore water pressure rapidly and reduce the total settlement effectively and economically. Stone columns require use of natural aggregates to be transported from a distant place to the construction site that causes an increase in construction cost, carbon footprint and diminish natural resources. This paper presents laboratory investigations of load test results on virgin clay bed and clay bed with stone columns. Two different conditions of stone columns viz. (1) un-encased stone columns with natural and lightweight aggregates (2) encased stone columns with natural and lightweight aggregates. Clay beds were prepared using slurry consolidation method by mixing dry soil with water content equal to 1.5 times liquid limit of the soil. Displacement controlled load tests were performed on clay beds with and without stone columns. Loads against applied displacements were continuously monitored for all the tests conducted. Clay bed with stone columns demonstrated higher load carrying capacity as compared to virgin clay beds. Un-encased stone columns indicated increase in bearing capacity by 31.7% for natural aggregates and 19.5% for light weight aggregates as compared to virgin clay bed. Further, provision of encasement to the stone columns increased load carrying capacity to 36.6% for natural aggregate stone columns and 31.7% for light weight aggregate stone columns as compared to virgin clay bed.

Relationship between earthquake-induced uplift of rectangular underground structures and the excess pore water pressure ratio in saturated sandy soils

Improvement of consolidation settlement beneath square footings using uncased and encased stone columns

Time-Dependent Behavior of Embankment Resting on Soft clay Reinforced with Encased Stone Columns

Effect of clogging of stone column on drainage capacity during soil liquefaction