管幕箱涵顶进施工中迎面土压力研究

管幕法是在始发井与接受井之间,利用微型顶管技术在拟建的地下建筑物四周顶入钢管或其他材质的圆管,钢管之间采用锁口连接并注入防水材料而形成水密性地下空间,在此空间内采用开挖或箱涵顶进方案修建地下建筑物的一种新型暗挖技术。管幕箱涵顶进工法是管幕法与箱涵法的结合。上海市中环线虹许路—北虹路地下立交隧道工程是世界上首次在软土地区采用不加固软土方法进行管幕箱涵顶进施工的工程,由于该工程采用常规方法监测箱涵顶进前端迎面土压力非常困难,所以笔者将静力触探探头进行改装,水平固定于网格前端实测端阻力,并采用经典球孔扩张理论推导换算公式,用以计算迎面土压力。通过实测和计算分析,得到迎面土压力在箱涵侧壁和中隔墙附近较大,平均值接近被动土压力等规律。

A study on the front earth pressure during box culvert jacking within pipe-roof

Pipe-roof method is an innovative excavation technique.Steel pipes or tubes of other materials are jacked into the soil between the starting shaft and the receiving shaft to form a type of closed underground space,within which the box culvert structure is constructed by jacking.It is the first time in the world that the pipe-roof culvert-box advancing scheme,without reinforcing the saturated soft soil to reduce cost,was adopted in the Shanghai Middle Ring Road subway project,crossing under the intersection of Hongxu Road and Beihong Road.In the project it is difficult to measure the pressure caused by the soil in front of the box culvert jacking if using the conventional method.The front earth pressure was measured by cone resistance of a CPT to the soil in front of the box culvert.Based on the theory of spherical cavity expansion,the conversion formula from cone resistance to earth pressure was introduced to calculate the front earth pressure.According to the calculation and analysis of the measured data,it is concluded that the front earth pressure of a box-culvert is larger than that in other areas and the average value is less than but close to that of passive earth pressure.