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本文介绍了应变测量中的线法原理和相应的测量技术——滑动式测微计(Sliding Micrometer—ISETH)及其应用。实测结果表明,该法的原理和仪器设备都大大优于传统方法。静力试桩中,它可提供各土层摩阻力、端承力的发展规律及其极限值,测定值与实际加载值的偏差不大于±2％。负摩阻力长期监测中,它准确提供轴应变,从而可导出中性点位置,端承力大小以及轴向力、正负摩阻力、弯矩、水平位移等轴向分布曲线及其随时间的发展规律。由于实测值与按有效应力公式计算值有较大差别,本文提出了按不排水慢剪强度分析负摩阻力的新途径。不均匀地面堆载条件下,桩中弯矩及水平位移很大,它的危害性可能比负摩阻力还显著。
This paper introduces the principle of line law in strain measurement and the corresponding measurement technique—Sliding Micrometer—ISETH and its application. The measured results show that the principle and equipment of this method are greatly superior to the traditional methods. In the static test pile, it can provide the development law and limit value of the friction resistance and end bearing force of each soil layer. The deviation between the measured value and the actual loading value is not more than ±2%. In the long-term monitoring of negative friction resistance, it accurately provides axial strain, which can derive the neutral point position, end bearing force size and axial force, positive and negative friction resistance, bending moment, horizontal displacement and other axial distribution curves and their time-dependent Development Law. Since the actual measured value is quite different from the calculated value according to the effective stress formula, this paper proposes a new way to analyze the negative friction resistance according to the undrained slow shear strength. Under uneven ground loading conditions, the bending moment and horizontal displacement of the pile are large, and its harmfulness may be more significant than negative friction resistance.