CORNER EFFECTS IN DEEP EXCAVATIONS-ESTABLISHMENT OF A FORECAST MODEL FOR TAIPEI BASIN T2 ZONE

Abstract

This study attempts to establish a novel model for forecasting wall deformation and ground surface settlement of deep excavations. The model is developed by considering the corner effect and examining the data from relevant case histories. The study is specifically limited to the construction works in the T2 zone of the Taipei Basin. The following results were obtained: (1) The maximum wall deformation during each excavation step was approximately 0.2%-0.5% of the excavation depth, and was influenced by the corner effect. (2) The maximum ground surface settlement took place approximately at the center of the wall; and settlements at the corners were smaller due to the corner effect, they were generally 20%-60% of the maximum settlement. (3) The area within a distance of two times the excavation depth had a relatively large settlement or relatively steep slope of settlement trough, which can be defined as the primary influence settlement area. The area at a distance of 2-3 times the excavation depth had a gentler slope of settlement trough and can be defined as the secondary influence settlement area. (4) If the analysis is carried out with theoretical hydrostatic pressure or with measured water pressure, the same tendency ”the deeper the wall embedment depth, the greater the factor of safety for overall stability” is found. This study also makes two specific contributions. First, the corner effects in deep excavations are further confirmed through more case studies. Secondly, a simple hazard analysis for estimating settlements induced by deep excavations is presented.