Determination of Safe Depth and Lateral Distance of Unsupported Excavation Near Mat Foundation in Cohesive Soils Using PLAXIS

Abstract

Deep excavations are essential to harbor the urban needs of the present age. The excavation of pits for foundation construction in an already limited space in urban centers poses damage to the neighboring structures. In this study, two mat foundations on two different types of clay soils have been modeled in PLAXIS to determine the maximum depth of excavation and the minimum safe distance of the excavation pit from these mat foundations. The failure modes under consideration are excessive settlement, angle of distortion of the mat foundation, and pit face failure. A co-relation to determine the safe maximum depth of unsupported excavation pit and minimum horizontal distance from adjacent mat foundation is presented based on results from 195 models. The ratio of critical unsupported excavation depth and critical horizontal distance from an existing building first drops to 1:3 in all cases and then rises in a non-linear manner. The modes of failures at various stages have been highlighted based on 44 critical cases.

Keywords

• plaxis
• mat foundation; cohesive soils
• unsupported excavation
• safe depth
• safe lateral distance