Compensated Raft Foundation on a Preloaded Soil Improved by Vertical Drains

Compensated raft foundation is used to support heavily loaded structures resting on soft and low-permeable soils, and aids in the reduction in settlement due to lowering of the stress transferred to the underlying soil. Such soils often require preloading and pre-treating with vertical drains to arrest the majority of the final settlement under the actual construction in lesser time. This paper reports the attainable efficacy in adopting the above methods for the foundation of the 10 th Boy's Hostel at the Indian Institute of Technology, Guwahati. Soft clayey and marshy fill soil is prevalent in the hostel site. FEM modelling using PLAXIS 2D v2012 has been used to interpret the possible benefit of the adopted method. In comparison to the condition when no preload was used, it has been observed that the application of staged preloading resulted in a reduction of the total settlement in the range of 45- 90%. Moreover, in comparison to the untreated soil, the application of vertical drains significantly accelerated the rate of consolidation and dissipation of pore-pressure (~30-50% and 15-25 times respectively). The comparative results reveal that the adoption of above methods will substantially help to improve the settlement characteristics of the soft soil site in discussion.