下穿式箱涵顶进施工过程土体受力规律研究

为了研究下穿式箱涵顶进过程中土体应力变化规律,以新长铁路丁溪河中桥的疏浚拓宽工程为背景,实时监测了箱涵顶进开始到就位过程中桥台处土体的应力变化。基于ABAQUS建立了箱涵与土的三维有限元模型,定义了箱涵底板、侧墙与土之间的法向接触对和切向接触对,从而将实际箱涵顶进施工的过程等效为给定箱涵初始位移的接触分析问题。根据实际施工中土层切土高度的变化情况,模拟了切土高度分别为4.51 m和6.51 m的两种箱涵顶进工况。计算结果表明,数值模拟得到的侧向土压力整体要大于实测土体的压应力,这主要是由于数值模拟中采用的是接触压应力,而顶进过程中可能出现箱涵侧墙与土体分离而导致的空顶。切土高度为6.51 m时数值模拟得到的箱涵摩阻力与箱涵的实际顶力非常接近,实现了二者的近似平衡,而切土高度为4.51 m时计算的摩阻力要小于实际顶力。

Research on Soil Stress Law During Jacking of Under-Crossing Box Culvert

In order to study the variation of soil stress during the jacking of under-crossing box culverts, the dredging and widening project of Dingxi River Railway Bridge located on Xinchang Railway is taken as an example. The variation of soil stress at the bridge abutment was recorded in real time during the whole process of the box culvert jacking. A three-dimensional finite element model of the box culvert and soil was then established based on ABAQUS. The normal contact and tangential contact between the box culvert bottom, the side wall and the soil were defined. Thus, the construction process of the actual box culvert jacking was equivalent to the nonlinear contact analysis of the box culvert with an initial displacement. According to the change of soil cutting height in actual construction, the condition of box culvert jacking with soil cutting heights of 4.51 m and 6.51 m was simulated respectively. Results show that the lateral earth pressures based on numerical simulation were generally larger than the measured values. The main reason is that the contact stress was adopted during the numerical simulation, whereas the side wall of the box culvert and the soil could be separated during the jacking process. When the soil height was 6.51 m, the calculated frictional resistance of box culvert was very close to the recorded jacking force, and an approximate equilibrium was realized. However, when the soil height was 4.51 m, the calculated frictional resistance was less than the actual jacking force. Conclusions show that it is reasonable to investigate the box culvert jacking based on the finite element method and real time monitoring technology.