Research On The Characteristics And The Influence Of The Construction Cross Beneath The Existing Line In Beijing

The degree of the influence of cross beneath construction on the existing line subsidence is an important part of assessing the operation safety of existing lines. Studying the influencing factors and the general rules of how cross beneath construction causes the existing lines subsidence is of great significance to control the settlement and ensure the operation safety of the existing lines. In this paper, the cross beneath construction in Beijing area is selected as a sample, and theoretical analysis, field monitoring and numerical simulation methods are used to discuss the characteristics of the cross beneath construction and study the influencing factors and the general rules of subsidence of existing lines due to cross beneath construction has obtained:(1) The characteristics of cross beneath construction is summarized by analyzing the crossing project in proximity and the method of cross. Comprehensive comparison about the applicability between the shallow excavation method and the shield method is made by stratum condition, the adaptability of structural section, safety, impact on the surrounding environment, the construction progress and project cost to provide a reference for the construction option.(2) The mechanism of influence of new tunnels cross beneath construction on the existing lines is studied. It is pointed out that both shallow excavation method and shield method causes stratum disturbed, and that will have negative effects on tunnel structure, track structure and in-line auxiliary facilities of the existing lines. Because shield method construction will provide thrust on the tunnel face, and limit the stratum in front of the tunnel face squeezing out, under the same conditions, lower influence on stratum deformation degree and the existing lines is caused by shield method construction compared with the shallow excavation method.(3) Influence on the existing line caused by cross beneath construction is analyzed by the study on monitored data about the deformation of existing tunnel structure and track structure caused by cross beneath construction in Beijing area. And it is shown that the influence of cross beneath construction on the existing lines has significant "space effect" and "time effect":the existing lines within the range of1to1.5times of the new tunnel cave span had obvious subsidence; the subsidence generated in the process of new tunnels cross beneath construction suppresses the final subsidence degree. (4) Numerical simulation is obtained in studying the rule of influence on existing line caused by the span of the new tunnel and the vertical distance to the existing line. It is shown that the maximum subsidence value and the influenced range of the existing line increases with the increasing of the new tunnel span, but the ratio of affected range and the new tunnel span reduces; the increase of vertical distance between the newly built tunnel and the existing line has little influence on the maximum subsidence value of the existing line, but the influenced range of existing line will decreased significantly.