Study on the construction parameters of shield tunnelling in short-distance undercrossing the existing tunnel

Using the methods of numerical simulation, earth pressure distribution below the existed tunnel of different buried depth was studied. It is shown that the lateral range and the depth of earth pressure affected by the existing tunnel are both 1.5 times of the tunnel external diameter. The affected partition can be divided into three areas along the lateral direction, including gradually reducing area before traversing, keeping minimum traversing and gradually resuming area after traversing. The relationship between the minimum earth pressure and the buried depth of the existing tunnel is negative exponential, while the relationship between the minimum earth pressure and the distance from the bottom of the existing tunnel is logarithmic. According to the distribution law of earth pressure under the existing tunnel, it is proposed that the construction parameters of shield tunnelling in short-distance undercrossing the existing railway should be divided into three areas. The formulas which are used to calculate the length of different areas and the recommended set construction parameters are provided. Based on a typical project of shield tunnelling in short-distance undercrossing the existing tunnel in operation, the measured construction parameters agree well with the recommended set values, and the vertical deformation of the existing tunnel is controlled within 5 mm.