Development of In-situ Testing Equipment for Friction Between Ground and Structure Foundation

在目前的桩和地锚设计中，摩擦阻力的估计取决于载荷试验和/或具有相当大的不确定性的弹性。为了更好地理解和估算摩阻，研制了一套现场摩阻和正应力测试装置.综述了土与建筑材料间摩擦力的研究现状。这些研究通常使用摩擦阻力作为作用在界面上的剪应力与法向应力的比值。为了合理利用这些研究结果，有必要对正应力进行估算.综述了原位测试的实验研究。在试验研究中所研制的仪器大多是测量原位侧应力或测量仪器与地面之间的摩擦阻力。用一台仪器同时测量侧应力和摩阻力是很少见的。理论研究还没有成功地计算出作用在已安装桩表面上的准确的侧应力.设计并制作了一种能同时测量摩擦阻力和侧向应力的装置。该设计是基于压电圆锥孔压计同时测量桩端阻力、局部侧摩阻力和孔隙水压力。摩擦套的一部分从内部加工成约0.3mm的壁厚。弯曲应变的测量是通过电阻应变片粘贴到摩擦套的薄的部分的内侧。在压缩载荷和液压下对测量值进行了标定.实验室试验进行了控制密度下施加边界（侧向和覆盖层）压力的大型砂样。试验结果表明，该装置能够同时测量侧向阻力和摩擦阻力。

In the present design of piles and earth anchors, the estimation of frictional resistance is dependent on the loading test and/or empiricism with a considerable uncertainty. For better understanding and estimation of frictional resistance, a testing apparatus is developed for the measurement of in-situ friction and normal stress.1. Studies on friction between soils and construction materials are reviewed. These studies often use the frictional resistance as the ratio of the shear stress to the normal stress acting on the interface. It is necessary to estimate the normal stress for appropriate use of the results of these studies.2. Experimental studies on the in-situ tests are reviewed. Most apparatus developed in the experimental studies are either to measure the in-situ lateral stress or frictional resistance between ground and the apparatus. It is rare to measure both lateral stress and frictional resistance with one apparatus. The theoretical studies have not yet succeeded to evaluate the accurate lateral stress acting on installed pile surface.3. A new apparatus is designed and fabricated to measure both frictional resistance and lateral stress at the same time. The design was based on the piezo-cone penetrometer which measure tip resistance, local side friction and pore water pressure at the same time. One part of the friction sleeve was machined from the inside to a wall thickness of some 0.3mm. The bending strain was mesured by means of electric resistance strain gauges bonded to the inside of the thin part of the friction sleeve. The measured values were calibrated under the compressive load and hydraulic pressure.4. Laboratory tests were carried out in large sand samples with controlled density under imposed boundary (lateral and overburden) pressure. The test results showed that the new apparatus is capable of measuring the lateral and frictional resistance at the same time.