Ground improvement technique for sustainable infrastructure

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Flexible foundations used for roads, railway tracks, pipelines, and earth dams are often built on soft cohesive soil. These structures usually suffer from low bearing capacity and excessive settlement, which are manifested in the form of sinkholes in roads and catastrophic collapses of the infrastructure and loss of life. Stone columns are known as cost-effective, environmentally friendly, easy to install and sustainable soil improvement technique for these types of structures (Wood et al., 2000; Hanna et al., 2013). Stone columns also provide additional drainage path, which will speed up the consolidation process, and accordingly the ground will resistance earthquakes (Sivakumar et al., 2004). Moreover, stone columns are used to improve the stability of natural slopes and to reduce liquefaction potential when installed in loose cohesionless soil (Etezad et al., 2015). The objective of the proposed research is to examine the performance of a flexible foundation overlying a group of stone columns. In order to achieve these objectives, experimental, numerical and analytical models will be developed to simulate the soil-structure-interaction of the problem stated. Experimentally: Laboratory prototype set-up consists of a testing tank, loading frame and measuring devices. The clay sample will be formed from a dry kaolin powder, mixed with water at about 60% saturation. Core samples of 100mm diameter of the reinforced clay will be extracted from the tank and placed in the triaxial set-up for testing. A consolidated undrained (CU) test will be carried out under cell pressure following ASTM, (2004). Reading of measuring devices will be recorded at a regular interval by data acquisition system (DAS), which will be attached to a personal computer. Numerically: High fidelity 3-D numerical models will be developed to examine the synergistic effect of the parameters govern the performance of this system. Three models will be developed to simulate the installation process of the stone columns in the soft soil and the second is to simulate the (CU) triaxial tests. The stresses and deformations measured from the first model will be used as an input data in the second model. The results of the second model will be validated with the results of the present experimental investigation. The third model is to simulate a flexible footing on a soft clay layer reinforced by stone columns. Analytically: The deduced failure mechanism from the present experimental and numerical investigations will be idealized and divided into slices of soft clay and sand, making the columns, a non-circular slip surface will be analyzed using Morgenstern-Price method of slice for non-circular slip surfaces, and the limit equilibrium technique. The results of this model will be used as the base to develop design theories to predict the bearing capacity of the system and to recommend on the number and spacing of the columns for economical design.