Engineering Approach to the Evaluation of Bearing Capacity of Pile Considering the Ground Crushability

可碾碎的沙质土壤在世界各地都可以找到，并且具有非常可压缩的特点。这类地基中的桩基存在承载力极低、沉降量大的工程问题。为发展合理的岩土工程方法评价桩的承载能力，揭示了桩的动员承载机理。在此基础上，根据单粒破碎试验、三轴试验、环剪试验和模型桩在不同恒应力水平下的单粒破碎试验、环剪试验和载荷试验结果，讨论了应力状态和土性对砂土承载能力的影响。可压碎土具有高压缩性、大剪切模数和大内摩擦角等材料特性。对于这类土体，桩的抗沉动员能力较低的机理是明确的。桩端承载力是由可压碎土的材料性质和桩周边界应力的影响引起的。(3)滑移破坏时，具有光滑表面的桩与土之间通常会产生侧摩阻力。在这种情况下，它可以用库仑定律来表示，库仑定律是不同粉碎性砂土的摩擦角和法向压力的分量。另一方面，它注重在大应力比情况下的侧摩阻力的估计。(4)根据(1)-(3)的结果，可以给出一种合理的承载力评估方法。

Crushable sandy soils can be found throughout the world and are characterized very compressible. It have engineering problems of very low bearing capacity and large settlement of the pile foundation in such grounds. In this study, in order to develop a rational geotechnical method for the evaluation of the bearing capacity of pile, it showed the mechanisms of the mobilized bearing capacity. And then the influence of the stress condition and the soil properties on the bearing capacity in sands is discussed based on the theoretical considerations and the experimental results of the individual particle fragmentation tests, the triaxial tests, the ring shear tests and the loading tests of model pile in some types of sand with different crushabilities at various constant stress levels.The main conclusions obtained are :(1) Crushable soil particles are generally angular and easy to break as compared with standard geomaterials. The crushable soils have material properties such as high compressibility, large shear modulus and large internal friction angle. And a large deformation is needed to get enough soil strength.(2) For such soils, the mechanism for the much lower mobilizing bearing capacity of the pile against settlement is clear. The end bearing capacity is caused by the material properties of crushable soils and by the effects of boundary stress around the pile.(3) The skin friction of the pile with a smooth surface is usually occurred between the pile and the soil on slip failure. At that case it can be expressed by Coulomb's law which is the component of the friction angle and the normal pressure in different crushabilities of sands. On the other hands, it pays attention to estimate the skin friction in the case of large stress ratio.(4) It can be shown a rational method to evaluate the bearing capacity from the results of(1)-(3).