Geocell-Sand Mattress overlying soft clay subgradei: Behaviour under circular loading

Abstract

The soft soil often poses design, construction and maintenance hazards to civil engineering structures, so any development activities on such areas are generally avoided. However, the advancement of technology has led to the emergence of numerous ground improvement techniques that render such sites suitable for constructional purposes. Among others, soil reinforcement technique is a viable alternative to enhance the strength of the soft soils. The latest adaptation of this technique involves the use of geocell mattress which is a three dimensional, polymeric, honeycomb like structure interconnected at joints. The geocells provide an all round confinement to the material by virtue of their interconnected cells and prevent their lateral spreading on the application of load, thus resulting in a much stiffer material with higher load carrying capacity. Available literature on geocell reinforcement indicates that substantial improvement in performance can be obtained with the provision of geocell reinforced sand mattress over soft clay subgrade. However, the influence of various key parameters on the overall performance and behaviour of geocell-sand mattress reinforced clay subgrade system are not well understood. Under the present investigation, a detailed parametric study through a series of experiments has been carried out to develop an understanding of the behaviour of the soft clay subgrade supported geocell-sand mattress system under circular loading. The influence of various parameters pertaining to geocell-soil configuration such as depth of placement of geocell mattress from the base of the footing, pattern of formation of geocells, pocket size of geocells, height of geocell mattress and relative density of the infill sand in geocells have been studied extensively in a systematic manner. Tests have also been carried out with an additional layer of geogrid placed at the base of the geocell mattress. The influences of the height of geocell mattress, pocket size of geocells and iv relative density of infill sand on the overall performance of the geocell-geogrid composite system have been evaluated. The results of the model load tests show that the stiffness and the load carrying capacity of the clay subgrade improve substantially with the provision of geocell reinforcement. The load carrying capacity of the reinforced foundation bed is found to be influenced by the depth of placement of geocell mattress, pocket size of geocells, height of geocell mattress and relative density of infill sand in geocells. Based on the analysis of the test data, the critical values of the geocell-sand mattress giving maximum beneficial effect are determined. The heaving on the fill surface is found to reduce due to increased confinement provided by the geocell reinforcement to the infill sand. The reduction is relatively more with geocell mattress of higher height and of smaller pocket sizes. An additional geogrid layer at the base of the geocell mattress further enhances the load carrying capacity of the foundation bed. The beneficial effect of the basal geogrid layer is, however, dependent on the pocket size of geocells, height of geocell mattress and relative density of the infill sand. Multiple-variable regression analysis has been performed on the experimental data to develop models in order to predict the bearing capacity of the reinforced foundation bed as a func...