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

在目前的桩和土锚设计中，摩阻力的估计依赖于载荷试验和/或经验，具有相当大的不确定性。为了更好地了解和估计摩擦阻力，研制了一种用于测量现场摩擦和法向应力的测试装置。综述了土体与建筑材料之间摩擦的研究现状。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之比。为了正确使用这些研究的结果，有必要估计法向应力。对现场试验研究进行了综述。在试验研究中开发的仪器大多是为了测量地应力或地面与仪器之间的摩擦阻力。用一个仪器同时测量侧向应力和摩擦阻力是很少见的。理论研究还没有成功地准确计算出作用在安装桩表面上的侧向应力。设计并制作了一种能同时测量摩擦阻力和侧向应力的新型装置。该设计基于压电式圆锥贯入仪，同时测量顶端阻力、局部侧摩阻力和孔压。摩擦套的一部分从内加工到壁厚约0.3 mm。用粘贴在摩擦套薄壁内侧的电阻应变片测量弯曲应变。在压缩载荷和水压作用下对测量值进行了标定。在施加边界(侧向和覆岩)压力下，对密度受控的大砂样进行了室内试验。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.