自平衡试桩Q-s曲线理论解析方法研究

Research on theoretical analytical method of Q-s curves of self-balancing test piles

为实现自平衡试桩理论方法更好地应用于基桩承载力测试,提出一种适用于层状地基中单桩承载力自平衡法测试的理论解析转换方法。基于自平衡上、下段桩加载受力模型,假定桩侧荷载传递函数符合理想弹塑性模型,推导出层状地基中上、下段桩弹性和塑性状态的荷载传递矩阵。再用MATLAB编程得到上、下段桩各微段处轴力、侧摩阻力及竖向变微量,代入精确转换公式中将自平衡试桩结果转换成传统静载测试Q-s曲线,并利用等荷载法求解其极限承载力。结合青岛胶州湾大桥工程试桩实例,采用锚桩法和自平衡法2组试桩工况结果验证该理论解析方法的准确性。研究结果表明:自平衡理论解析计算上、下段桩身各点轴力和侧摩阻力与锚桩法实测数据比较均在误差允许范围内;与传统静压测试、简化转换法相比,该解析转换法Q-s曲线与传统静压试验吻合效果明显优于简化转换法;同时对比2种转换法得到承载力值,简化转换法对于准确测定单桩承载力偏于保守,且不能分析桩身内力特征及承载能力,解析转换方法求解结果精度提高约12.3%。因此,证实了该理论解析方法在实际工程层状地基中有很大的适用性,可在基桩承载力自平衡测试工程中大量推广与应用。

In order to realize the better application of the self-balanced test theory method to the bearing capacity test of pile foundation,a theoretical analytical method is proposed for the self-balanced test of single pile in stratification foundation.Firstly,based on self-balanced upper and lower section pile loading force model,the load transfer matrix of the upper and lower piles in stratification foundation is derived under the assumption that the load transfer function of the pile side accords with the ideal elastic-plastic model.The axial force,the internal forces and the vertical displacements at each micro-element of the upper and lower sections of the pile are obtained using MATLAB programming,and the results of the self-balanced test pile are converted into the Q-s curve of the conventional static load test by substituting the accurate conversion formula,the ultimate bearing capacity is solved by equal load method.Finally,combined with the test pile of Qingdao Jiaozhou Bay Bridge,two groups of test results of anchor pile method and self-balanced method were used to verify the accuracy of the theoretical analytical method in this paper.The results show that:the axial force and lateral friction resistance of each point of upper and lower section pile calculated by self-balanced theory were within the allowable error range compared with the measured data of anchor pile method.Compared with the traditional static pressure test and simplified conversion method,the Q-s curve of the theoretical analytical method agrees better with the traditional static pressure test than the simplified transformation method.Meanwhile,comparing the two conversion methods to get the bearing capacity value,the simplified conversion method is conservative for the accurate determination of the single pile bearing capacity,it can’t analyze the internal force characteristics and bearing capacity of the pile,the accuracy of the analytical conversion method is improved by about 12.3%.Therefore,it is proved that the theoretical analysis method has great applicability in practical engineering layered foundation,which confirms the accuracy of the conversion method,and can be widely used in the self-balancing test engineering of pile bearing strength.