Development of Guidelines for Retrofitting Of Shallow Foundations

Abstract

Risalpur being part of semiarid climate zone consists of hot humid and dry climate conditions. The soil in the region is mostly alluvial and loess deposits with the traces of carbonates. Such soil deposits together with climatic conditions favours formation of collapsible soil deposits. These deposits shows remarkably good strength, stiffness and bearing capacity under controlled conditions but behavior changes suddenly if the soil is exposed to wet/humid environment. Research shows that the soil has a moderate to severe collapse potential within the zone of influence of shallow foundations. The current study aims at finding out a technically viable and economically feasible solution for retrofitting of damaged foundations/structures. The main aspect of study was to confirm the results of laboratory test carried out by the previous researchers in the mitigation of collapse susceptibility of Risalpur soil. Verification of the laboratory test results was carried out through full scale field testing with the aim to provide some recommendations to designers and engineers for future construction in collapsible soils. A total of five walls were constructed as per Military Engineering Services (MES) specifications and loaded so as to produce a contact pressure of 1 tsf at the foundation-soil interface. Two of the walls were loaded in dry conditions and then the foundations were flooded; two walls were constructed on stone columns improved soil and the fifth wall was constructed on original soil but foundation was treated with compaction grouting before loading/flooding. Settlements increased from 6mm in dry conditions to about 24mm due to flooding. Differential settlements were also observed due to flooding. The wall that was treated with stone columns with an area replacement ratio of 15% reduced the settlement by about 50% under flooded condition whereas the wall treated with grout columns affected a reduction of 75% in total settlement. Also the treated walls showed no signs of differential settlements. The study showed that both stone columns and compaction grouting can be used effectively to control collapse settlement of foundation soil. Compaction grouting using in-situ soil with 5% cement can provide an economical soil to rehabilitate damage structures in the area.