水平往复大位移作用下整体桥台后土压力计算方法

为研究强震和温度作用下，整体桥台产生的水平往复大位移对桥台与台后填土相互作用的影响，进行了整体桥台-H形钢桩-土相互作用拟静力试验，并基于试验结果研究了大位移作用下整体桥台后土压力的分布规律；根据台后土压力分布，提出了台后土压力合力作用点位置与加载位移之间的关系式，并在现有研究的基础上给出了改进的整体桥台后土压力计算方法。研究结果表明:正向加载(桥台挤压台后土)时，台后各处土压力随加载位移的增加先增大后减小；台背处和台后20%桥台高度处土压力受桥台位移的影响更大，沿深度方向呈梯形分布；台背处土压力分布中，由于台底H形钢桩的约束，最大土压力位于入土深度0.875 m处，台底位置的土压力则略有减小；台后60%桥台高度和1.4倍桥台高度处土压力受桥台位移影响较小，沿深度方向呈三角形分布；负向加载(桥台背离台后土)时，台后土压力沿深度方向呈三角形分布，且台后各处土压力与加载位移不相关，其值相对于正向加载时可忽略；水平往复大位移作用下，整体桥台后土会产生脱空现象，脱空范围超过桥台高度的37.5%；台后土压力沿纵桥向呈指数型衰减，且相比小位移作用下衰减得更快；台后土压力合力作用点位置随加载位移的增大而逐渐降低，且台后土压力系数与加载位移具有明显的非线性关系，呈现先增大后减小的规律；现有土压力计算方法未考虑桥台位移的影响或认为台后土压力在桥台发生小位移时随桥台位移的增大而增大，发生大位移时则基本不变；提出的土压力拟合公式的判定系数为0.92，计算值与试验值的相对误差为6.2%，可作为现有土压力计算方法的有益补充。 

Calculation method for earth pressure behind integral abutment under horizontal reciprocating large displacement

To analyze the effect of horizontal reciprocating large displacement generated by the abutment on the interaction between the abutment and the backfill behind the abutment under the actions of strong earthquake and temperature, a quasi-static test for the interaction among the integral abutment, H-shaped steel pile, and soil was carried out. On the basis of the test results, the distribution law of the earth pressure behind the integral abutment under the action of large displacement was studied. According to the distribution of the earth pressure behind the abutment, the relational expression between the action point location of the resultant earth pressure behind the abutment and the loading displacement was proposed, and an improved calculation method for the earth pressure behind the integral abutment was given based on the existing research. Research results indicate that when the abutment is loaded in the positive direction (the abutment squeezes the soil behind the abutment), the earth pressure behind the abutment first increases and then decreases as the loading displacement rises. Earth pressures at the abutment back and 20% of the abutment height behind the abutment are highly affected by the abutment displacement and has a trapezoidal distribution along the depth direction. In the earth pressure distribution at the abutment back, due to the constraint of H-shaped steel pile at the bottom of the abutment, the maximum earth pressure is located at a depth of 0.875 m, and the earth pressure at the bottom of the abutment decreases slightly. Earth pressures at 60% of the abutment height and 1.4 times the abutment height behind the abutment are less affected by the abutment displacement and is triangularly distributed along the depth direction. When the abutment is loaded in the negative direction (the abutment deviates from the soil behind the abutment), the earth pressure behind the abutment is triangularly distributed along the depth direction, and the earth pressure behind the abutment has no connection with the loading displacement, and its value can be neglected relative to the positive loading. Under the action of a horizontal reciprocating large displacement, the soil behind the integral abutment will face a void phenomenon, and the void range will exceed 37.5% of the abutment height. The earth pressure behind the abutment reduces exponentially along the longitudinal direction, and it reduces faster than that under the action of a small displacement. The action point location of the resultant earth pressure behind the abutment decreases gradually as the loading displacement increases, and the earth pressure coefficient behind the abutment has an obvious nonlinear relationship with the loading displacement, which is reflected by the law of first increasing and then decreasing. Existing earth pressure calculation methods do not take into account the effect of the abutment displacement or consider that the earth pressure behind the abutment rises with the increase in the abutment displacement when small displacements occur and remains basically unchanged when large displacements occur. The determination coefficient of the proposed earth pressure fitting formula is 0.92, and the relative error between the calculated value and the test value is 6.2%, which can be a useful supplement to the existing earth pressure calculation methods.