Underpinning Methods of Diaphragm Wall of Subway Station Constructed by Cut and Cover Reverse Method under Foundation Pit Cover Plate

The connection between the auxiliary structure and the subway station usually requires breaking the diaphragm wall, which is more difficult and risky when a temporary cover plate is installed on the diaphragm wall. Based on the demolition construction of the diaphragm wall of a subway station constructed by cover and top-down construction method, a construction method of underpinning demolition using a local demolition body as temporary vertical support was proposed, and the problem was solved. First of all, the influence of different underpinning distances on the structural system of the cover plate was calculated numerically, and considering the construction progress and workspace, the temporary underpinning columns with a width of 1 m and a breaking distance of no more than 12 m were determined as the control indicators, which can meet the load-bearing performance requirements of each stressed structural system under temporary underpinning construction. Secondly, the demolition of the diaphragm wall under the cover plate and the transfer construction of the cut blocks were detailed, and the control indicators and practices of key construction links such as block size, cutting block hoisting, and reserved column nodes were given. The implementation results showed that using the existing diaphragm wall as a temporary underpinning structure for the construction of the diaphragm wall is safe, reliable, fast in construction, and economical in cost.