地中弹性边界对盾构近距离掘进位移场的影响

EFFECTS OF ELASTIC BOUNDARY IN GROUND ON DISPLACEMENT FIELD INDUCED BY SHIELD TUNNELING

通过工程实践发现,地下构筑物的存在对盾构穿越施工引起的位移场分布有较大影响,从而对盾构穿越构筑物的变形预测与控制也有较大影响。为分析预测盾构超近距离穿越地中构筑物施工过程中的地层变形特性,将地中构筑物视为弹性边界,运用边界单元法进行模拟分析。根据弹性理论的小变形假设及弹性边界的变形协调条件,地层中的位移场可以认为是由盾构推进和弹性边界上作用力同时引起的位移场的叠加。计算结果表明:考虑弹性边界时土层中的位移场与常规不考虑弹性边界的影响有较大的差别,其计算结果对盾构近距离掘进中位移场的精确预测及超前控制具有重要意义。实际工程问题可以根据所提的理论计算得出盾构与弹性边界的关键控制距离,以超前控制盾构掘进施工,确保近距离保护对象的安全。

Engineering practices show that the existence of underground structures or obstacles severely influence the distribution of displacement produced by shield tunneling across them. To analyze and predict magnitudes and the characteristics of the ground deformation induced by shield tunneling across the adjacent underground objects, the boundary element method is deduced considering the underground objects as the elastic boundary. According to the small deformation hypothesis of the elastic theory and coordination conditions of elastic boundary, the ground displacement fields can be obtained by superposition of the displacement fields produced by shield tunneling and reaction forces on the elastic boundary. The displacement caused by reaction on the elastic boundary can be achieved by the theory of Winkler elastic foundation. Analytical results based on the above mentioned principles indicate that there are great differences about the characteristics of the ground displacement fields with/without considering the elastic boundary. The existence of the underground objects obstructs the propagation of the ground movement and makes the accumulated displacement near them. So, there is an important signification in accurate prediction and precontrol of the displacement fields subjected to the adjacent advance of the shield by considering the effect of the elastic boundary. In practice, the critical control distance can be calculated by the proposed method, which could be employed in precontrol of shield construction and secure the safety of adjacent protected objects.