Effects of geogrid encasement on lateral and vertical deformations of stone columns in model tests

Abstract

Geosynthetic encasement of individual stone columns can provide additional confinement to the columns thus increasing their load capacities and reducing lateral and vertical deformations. Most of past studies have been focused on the load capacities and settlements (i.e. vertical deformations) of the encased stone columns. However, the load transfer mechanism and the lateral bulging deformation pattern of the encased stone columns are not thoroughly understood. In the present study, four series of laboratory model tests in a large-scale testing tank were performed to investigate the effect of geogrid encasement on the lateral and vertical deformations of stone columns installed in a clay bed. For comparison purposes, ordinary stone columns were also tested and evaluated. The main objective of this research is to investigate the lateral and vertical deformation patterns of the encased stone columns and the reinforcement mechanisms of the geogrid encasement with different encasement lengths. In addition, the stress-strain characteristics of the encasement were measured and analysed. The test results show that the ultimate load capacity of the soft soil was greatly increased by the geogrid-encased stone columns. The effective length of the encasement was three to four times of the diameter of stone columns based on the consideration of performance and economy. In comparison with the analytical solution based on the unit cell concept with full encasement of columns, the experimental tests on composite foundations with partially encased columns, which allowed lateral deformations of columns and soils and slippage along the column-soil interfaces (geogrid-soil, stone column-geogrid, and stone column-soil if the column is not encased), resulted in larger settlements, especially at higher vertical pressures.

Geosynthetic Encased Columns Supporting Rail Infrastructure – Perspectives on Research and Case Studies

“…Although small-scale laboratory research has provided valuable information on the behavior of the granular columns, in order to avoid the scaling issues, researchers [20,21] have opted for large-scale tests to study the behavior of granular columns at large scale. In the large-scale studies, the stress concentration ratio of for granular columns have been reported at a wide range between 3 and 20.…”

Settlement Behavior of Soft Subgrade Reinforced by Geogrid‐Encased Stone Column and Geocell‐Embedded Sand Cushion: A Numerical Analysis

“…Malarvizhi and Ilamparuthi [17] conducted small-scale tests to investigate the improved performance of GESC and found that the ultimate bearing capacity of GESC treated beds is three times that of the untreated beds. Gu et al [18] also found that the ultimate load capacity of the soft soil was greatly increased by GESC, and the effective length of the encasement was three to four times of the diameter of stone columns. Orekanti and Dommaraju [8] conducted strain-restricted compression tests on GESC, and the results showed that GESC with lateral reinforcement of end-bearing type and floating type showed a substantial increase in load-carrying capacity relative to clay by 2.44 and 2.01 times, respectively.…”

Model Testing of Encased Stone Column Composite Foundations under Traffic Loads

“…Four series of laboratory model tests were performed in a large-scale testing tank to investigate the effect of geogrid encasement on the lateral and vertical deformations of stone columns installed in a clay bed. In addition, the stress-strain characteristics of the encasement were measured and analysed by Gu et al [8,9]. To provide the theoretical basis for the design and construction of an embankment with an encased stone column composite foundation, two groups of indoor model tests for the embankment with encased stone column composite foundation with different stiffnesses of the encasement were carried out in accordance with the influence of the stiffness of the encasement on the deformation and stability of the composite foundation with the encased stone column by Chen et al [10].…”