钢管桩单桩复合地基加固隧道软土地基试验研究

Experimental Study on the Improvement of Soft-Soil Tunnel Foundation by Composite Foundation with Steel Pipe and Single Piles

为了对宝兰客运专线王家沟隧道软弱地基进行加固处理,并了解加固后的桩基受力状态,通过现场试验及数值模拟,研究钢管桩单桩复合地基的荷载沉降特性及钢管桩轴力、桩侧摩阻力以及桩身弯矩的变化规律。研究结果表明:由现场试验所得的P-s(荷载-位移)、s-lgt(位移-时间的对数)以及s-lgp(位移-荷载的对数)曲线没有明显可以确定极限承载力的特征点,根据规范采取控制沉降的方式给出极限承载力特征值为200 kPa,并可以此作为设计依据。根据数值模拟中钢管桩的总沉降量以及荷载沉降"归一化曲线",数值模拟可以作为现场试验的必要补充。数值模拟结果显示:桩身轴力呈"D"状分布,最大值为59.8 kN;在距桩顶2 m桩长范围内有负摩阻力产生,其余部位均为正摩阻力,负摩阻力最大值约为130 kPa,正摩阻力最大值约为50 kPa,且桩身中性点并不唯一;桩身上部有弯矩产生,但数值很小,对钢管桩稳定性的影响可以忽略。

The load-settlement characteristics of a single-pile composite foundation with steel pipe piles are studied through field tests and numerical simulation with the aim of strengthening the weak foundation of a passenger-dedicated line tunnel and understanding the stress state of the pile foundation after reinforcement.The variation rule of side friction,axial force,and bending moment of the pile body are also discussed.Results show that the P-S,S-lg t,and S-lg p curves obtained through field tests lack distinct feature points that are useful for determining ultimate bearing capacity.The characteristic value of the ultimate bearing capacity is 200 kPa in accordance with the code.Numerical simulation can be used as a necessary supplement to field tests in accordance with the total settlement of steel pipe piles in numerical simulation and the normalized curve of load settlement.Numerical simulation results show that the axial force distribution of the pile body has a D-shaped pattern and a maximum value of 59.8 kN.Negative skin friction resistance falls in the range of 2 m from the top of the pile with a maximum value of 130 kPa,and the rest of the pile exhibits positive friction resistance with a maximum value of 50 kPa.The neutral point of the pile is not unique.A small bending moment exists in the upper part of pile body,and its influence on the stability of the steel pipe pile can be neglected.