Study on reasonable chamber pressure of shield tunneling in undercrossing existing subway construction

Considering the protection of existing tunnel and significant changes of the earth pressure below, it is very difficult to select reasonable chamber pressure in undercrossing existing subway construction. Under the different buried depth of existing tunnel, characteristics of earth pressure distribution below are studied with the numerical simulation. It is shown that the lateral range and depth of affected earth pressure are 1.5 times outer tunnel radius. The affected partition can be divided into three areas along lateral, including gradually reducing area before traversing, keeping minimum traversing and gradually resuming area after traversing. According to the working principle of EPB shield machine, method that setups chamber pressure partition is provided. Based on a typical undercrossing tunnel construction project in Shanghai, the measured chamber pressure proved to be at good coincidence with the recommended values.