Interaction Between Hoop Stresses and Passive Earth Resistance in Single and Multiple Geocell Structures (2009)

Geocell structures consist of a series of interconnected single cells, made from different polymer materials. The cell walls completely encase the infill material and provide an all-around confinement to the soil. The confinement effect is based on three main mechanisms: active earth pressure within loaded cell, passive earth resistance in the adjacent cells and hoop stresses in the cell walls. To evaluate the interaction between hoop stresses and passive earth resistance radial load tests on single and multiple geocell structures were carried out. Geocell materials with different stiffness and different numbers of interconnected geocells were tested. The tests results have shown that the stiffness of the geocell material and the numbers of adjacent cells are the most important parameters for the confinement effect. Geocell structures consist of a series of interconnected single cells, made from different polymer materials. The geocells are delivered to the construction site, expanded and are filled with soil. The cell walls completely encase the infill material and provide an all-around confinement to the soil. If a vertical load is applied on a geocell structure horizontal active earth pressure is mobilized within the loaded cell. The magnitude of active earth pressure is depending on the friction between the infill material and the cell walls. Due to active earth pressure, hoop stresses within the cell walls and earth resistance in the adjacent cells are mobilized which increases the stiffness and the load-deformation behavior of the soil. Different large scale model tests have shown that geocell reinforcements reduce the vertical and horizontal deformation of the soil and the vertical stresses in the subgrade material (Dash et al., 2001, 2003; Emersleben and Meyer 2008a; Meyer and Emersleben, 2005a, 2006). By the significantly increasing application of geocells for the stabilization of materials with low bearing capacity, especially in regions were qualified material is rarely, a common useable design method for geocells is awfully important for a cost effective solution. For the evaluation of common design method the interaction between hoop stresses, active earth pressure and passive earth resistance in single and multiple geocell structures has to be known very exactly. Different authors have carried out triaxial tests on single geocells and multiple geocell systems to evaluate the influence of geocell walls and mobilized hoop stresses on the shear strength of different infill materials. Bathurst and Karpurapu (1993) have carried out triaxial tests on aggregate materials (silicia sand and crushed limestone) confined by a single geocell manufactured of polymeric material. The test results show that the geocell-soil composite materials have the same angle of friction as the unreinforced materials but that the geocells mobilize an apparent cohesion to the soil. Depending on the infill material the apparent cohesion varied between 156 to 190 kPa. Madhavi Latha and Murphy (2007) studied the influence of two different geocell membranes on the shear strength of river sand. The geocell membranes were manufactured from a geotextile and a polyester film and were self welded to a cylindrical form. Compared to other reinforcement forms (e.g. eight geotextile layers and discrete fiber forms) the geocell forms were found to be highly effective in improving the strength of the used sand. The geocell membrane made of geotextile showed an improvement in strength of 100 percent at all confining pressures compared to unreinforced sand. Because of the formation of indents the strength of geocells made from polyester was increased by 100 percent compared to the geotextile cells. Both geocell materials mobilized an apparent cohesion to the sand of 78 kPa (geotextile) and 273 kPa (polyester) while the friction angle was nearly the same. Rajagopal et al. (1999) carried out triaxial tests on multiple geocells to simulate the real conditions in which a number of geocells are interconnected. Four different types of geosynthetics (polypropylene, woven geotextile, nonwoven geotextile and a soft plaster mesh) were used to fabricate circular shapes