# A DEM Study on Bearing Behavior of Floating Geosynthetic-Encased Stone Column in Deep Soft Clays
## 1 Introduction  
Stone columns, which are composed of granular material, have been widely used to improve the bearing capacity, reduce settlement, and enhance the stability of foundation in soft clay [1; 2; 3; 4]. As the granular material is cohesionless, it may lead to lateral expansion failure of stone columns. The strength and stiffness of stone columns is mainly provided by the confining stresses of the surrounding soil. However, in extremely weak soil (cu < 15 kPa), the confining stresses may not be enough [5; 6; 7; 8]. In order to provide the required confining stresses, [PERSON] proposed the concept of encasing stone columns in 1989 [9; 10; 11; 12]. The stone columns are encased by high-strength, creep-resistant geosynethties. The geosynthetic encasement can provide sufficient confining stresses, prevent lateral deformation of granular material, and maintain the drainage capacity of stone columns [13; 14; 15; 16; 17; 18]. The geosynthetic-encased stone columns (GESCs) have the advantages of low pollution, low cost, and easy construction [19; 20], and the GESCs are widely used in foundation treatment. Due to the encasement, the bearing and deformation characteristics of geosynthetic-encased stone columns (GESCs) and ordinary stone columns (OSCs) are different. Many researchers have studied the GESCs through the finite element method, laboratory tests, and field monitoring [21; 22; 23; 24; 25; 26; 27]. [PERSON] and [PERSON] [28; 29; 30] investigated the GESC through laboratory model tests and the finite element method. Theypointed out that the GESC had a much higher stress concentration compared with the OSC. [PERSON] and [PERSON] [31] investigated the effective encasement depth of GESCs in the same conditions for various diameters. [PERSON] and [PERSON] [32] used 3D finite element program to simulate the GESC under vertical stresses and pointed out the effect of geosynthetics stiffness on the lateral bulging. [PERSON] et al. [33] found that the 3D numerical analysis had more advantages than the 2D analysis to study the GESCs under the embankment and could obtain more required information. [PERSON] et al. [34] investigated the behavior of GESCs and OSCs through uniaxial compression tests. They reported that the bearing capacity of GESCs was larger than that of OSCs. [PERSON] and [PERSON] [35] conducted a series of small-scale model tests to observe that the bugling of the column occurred directly beneath the encasement. [PERSON] et al. [36] studied the floating deep mixed columns through laboratory model tests and finite element analysis. They found that the settlement of the floating column composite foundation was mainly affected by the depth improvement ratio. [PERSON] et al. [37; 38; 39] carried out a series of field tests and finite element numerical simulations to study the bearing characteristic of the GESC. They found that the GESC could effectively reduce the lateral displacement of the soil mass. [PERSON] et al. [40] used the construction and demolition waste to construct the GESC. Their study indicated that the construction and demolition waste could be considered as a sustainable and valuable resource for GESC. The studies mentioned above did not consider the discreteness of the aggregates that make up the column, especially the finite element method. In actual engineering, it is sometimes uneconomical for GESCs to penetrate soft clay; therefore, the GESCs are in a floating state. [PERSON] et al. [41] presented the application of an FGESC in an embankment project in Sao Paulo, Brazil. The columns were 80 cm in diameter, 11 m in length, and implemented on 2 m center-to-center spacing on a square pattern. The bearing capacity of the treated foundation was 150 kPa, which is significantly greater than the shear strength of the soil of 15 kPa. The load-bearing deformation mechanism of the floating geosynthetic-encased stone column (FGESC) is different from those of GESC. There are still relatively few studies on FGESCs in the available literature.