الفهرس 
CHAPTER (1): INTRODUCTIONOnly 14 pages are availabe for public view
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Abstract
Raft foundations are usually used for medium heavy structures constructed on soft clay. Soft soils are present in many regions all over the world and the places of them are in important cities along rivers and seas. There are two main problems encountered when undertaking civil constructions in soft soil deposits, excessive settlement and low shear strength. In many situations, granular piles are common type of ground improvement technique applied in order to reduce settlement, improve the soil bearing capacity and accelerate the consolidation of soft compressible soils beneath the raft. Granular piles beneath the raft may be fully penetrated and based on strong soil layer (i.e., end bearing granular piles) or partially penetrated (i.e., floating granular piles). In this study, a three dimensional finite element analysis has been carried out using PLAXIS 3D to investigate the performance of a uniformly loaded rigid raft resting on soft and very soft clay soil improved by granular piles. A parametric study has been performed to investigate the effect of various parameters on the performance of the raft foundation such as shear strength of the clay; thickness of sand pad; granular pile materials such as crushed concrete, crushed ceramic, crushed red brick as recycled aggregates and basalt as a natural aggregates; the granular piles type as floating or end bearing pile; the area replacement ratio and the effect of using encasement. In addition, the effect of area replacement ratio on the bending moment of raft and the lateral bulging of granular pile has been studied. The results indicate that the use of granular piles to reinforce soft soil under rigid raft improves the bearing capacity, settlement and bending moment of the raft. More improvement occurs due to the increase of shear strength of clay, thickness of sand pad, granular pile length, and area replacement ratio. Additionally, the results show that recycled aggregates may be effectively utilized as granular pile materials in place of conventional natural aggregates for the improvement of soft clay. Using geogrid and geotextile as an encasement for granular piles in very soft clay enhances the ultimate bearing capacity of the raft.