Development of a Practical Test Method for Friction Between Cohesive Soil and Structure Foundation

本研究的目的是建立一种实用的粘性土与结构基础间摩擦阻力估算的测试方法。首先，几组摩擦试验(1。为了评估试验装置的效率，更好地掌握摩擦的基本特性，系统地进行了试验。然后，采用原位土样进行摩擦试验(3)，估算桩周摩阻力。通过本研究获得的知识如下：1。粘土与钢的摩擦试验：(1)粘土试样只有剪切变形，直到剪应力达到最大值。(2)对于光滑表面钢，界面发生滑动，粘土试样在达到最大剪应力后停止剪切变形。(3)存在边界钢材粗糙度R_b，当钢材粗糙度大于R_b时，界面不发生滑动，摩擦阻力达到上限，该上限等于粘土试样的抗剪强度2。黏性土与钢的摩擦试验：采用粘土-砂混合物作为黏性土样品。(1)最大剪应力不受粘土-砂混合比和钢材粗糙度的影响。(2)土壤样品含沙量越大，R_b越大。(3)土样剪切变形与界面滑动同时发生的复杂行为。原位土样摩擦试验：采用从桩周地面提取的原状土样进行两组摩擦试验。由于桩周摩阻力与桩周表皮摩阻力较为一致，本研究的试验方法有应用于实际的可能。

The purpose of this study is development of a practical test method for estimating the frictional resistance between cohesive soil and structure foundation. To start with, several sets of friction tests (1. and 2.) were carried out systematically to evaluate the efficiency of the test apparatus andto have a good grasp of the fundamental behavior of the friction. After that, friction tests (3.) were practiced with in-situ soil samples for estimating the skin frictions around piles.The knowledge acquired through this study are as follows :1. Friction tests between clay and steel :(1) There is only the shear deformation of a clay sample until the shear stress reaches the maximum value.(2) For smooth surface steel, the interface sliding occurs and the shear deformation of a clay sample stops after reaching the maximum shear stress.(3) There is the boundary steel roughness, R_b : if the steel roughness is larger than R_b, the interface sliding does not occur and the frictional resistance reaches the upper limiting value which is equal to the shear strength of a clay sample.2. Friction tests between cohesive soil and steel :Clay-sand mixtures have been used as cohesive soil samples.(1) The maximum shear stress is not affected by the clay-sand mixture ratio and steel roughness.(2) The more richly a soil sample has sand, the larger R_b is.(3) There is a complex behavior that the shear deformation of a soil sample occurs simultaneously with the interface sliding.3. Friction tests with in-situ soil samples :Two sets of friction tests were practiced by using undisturbed soil samples extracted from the ground around piles.Since the frictional resistances were in reasonably agreement with the skin frictions around piles, there is a possibility of the application of the test method of this study to practical use.