软土地层大断面管幕箱涵顶进竖向姿态的理论与实测分析

针对千斤顶产生的偏心顶推力作用下箱涵发生的“抬头”现象，采用局部弹性地基模型，首先, 从理论上推导得到箱涵顶进竖向姿态变化的解析解; 然后，结合现场实测分析，探究偏心顶力作用下大断面管幕箱涵的“抬头”机制及变化规律。研究表明： 1) 千斤顶顶推力与顶进阻力合力的作用线不重合而产生的使管节上抬的力矩是首节箱涵“抬头”的核心诱因； 2) 缓解首节箱涵“抬头”问题的主要施工措施有减小掘进机顶推力或正面土压力、增加上排管幕刚度、对箱涵上表面进行局部减摩、对箱涵下部进行冲洗卸土等，其中，减小掘进机顶推力或正面土压力效果最为明显。

Theoretical and Practical Analysis of Vertical Jacking Attitude of LargeCross section Pipe Roof Box Culvert in Soft Soil Stratum

Under the effect of eccentric jacking force caused by lifting jack, the lifting phenomenon of box culvert occurs. By adopting the Winkler foundation model, the analytical solution of the vertical attitude variation of box culvert is derived theoretically. And then the mechanism and variation regulars of lifting phenomenon of box culvert under eccentric jacking force are explored based on field measurement analysis. The research results show that: (1) The imbalance torque caused by the different action elevation of jacking force and the combined force of thrust resistance is the core cause for the lifting phenomenon. (2) The main construction measures to mitigate lifting phenomenon include reducing the jacking force or the earth pressure of soil ahead of pipe jacking machine, increasing the stiffness of the upper row of pipe roof, reducing local friction on the upper face of box culvert, flushing and unloading soil from the bottom of the box culvert, etc.〖KG-*3〗, in which the measure of reducing jacking force or the earth pressure of soil ahead of pipe jacking machine is the most effective.