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自平衡法测试基桩抗压承载力时转换系数取值的合理性直接影响到检测结论的准确性。为确定砂性土中转换系数?的准确性,选取3个工程,主要土层均为砂性土,同一场地均进行了自平衡法和传统静载试验。每个工程中选取自平衡检测的基桩与传统静载的基桩为对比组,其地质条件、施工工艺、桩的几何尺寸、桩顶和桩底高相近或一致,以传统静载法测得结果为基准,采用Matlab编程对自平衡法测得等效荷载-位移曲线进行拟合,得出与传统静载法结果拟合度最佳的?取值。将?的拟合值和?=0.6、0.7和?原工程取值分别得到的等效位移荷载曲线与传统静载试验结果进行对比。结果表明,(1)3个工程中所得转换系数γ拟合值取值范围在0.42~0.71之间,与原工程中采用的γ值相比均偏小;(2)?取值对等效受压桩上段桩总摩阻力和弹性压缩量的影响很大;(3)采用转换系数γ拟合值计算的等效转换曲线与原工程中采用的?值相比更接近传统静载法所得结果,表明3个工程中?的取值均过大,导致所测极限承载力过于保守;(4)砂性土中自平衡转换系数建议取值为0.6~0.7左右。
The rationality of the value of conversion coefficient when testing the compressive bearing capacity of pile foundation by the self-balance method has a direct impact on the accuracy of the test conclusion. In order to determine the accuracy of the conversion coefficient in sandy soil, three projects were selected. The main soil layer was sandy soil. Both self-balance method and traditional static load test were conducted on the same site. Each project selected from the balanced detection of the pile and the traditional static load of the pile as a control group, the geological conditions, construction technology, pile geometry, pile top and bottom height similar or consistent with the traditional static method Based on the results, the equivalent load-displacement curves measured by self-balance method were fitted by Matlab programming, and the best fitting value with the traditional static load results was obtained. The fitting values and the equivalent displacement load curves obtained from the original values of 0.6, 0.7 and the original engineering values are compared with the traditional static load test results respectively. The results show that (1) the fitting values of the conversion coefficients γ obtained in the three projects range from 0.42 to 0.71, which are both smaller than the γ values used in the original project; (2) (3) The equivalent conversion curve calculated by the fitting coefficient of conversion coefficient γ is closer to the traditional static load method than the value used in the original project The results show that the values of 3 are too large, resulting in the ultimate bearing capacity is too conservative; (4) sand soil self-equilibrium conversion coefficient suggested value of about 0.6 to 0.7.