Study on the Elasto-plastic Behavior of Open or Closed end Pile

1.由于直径的增大，管桩的承载力是超静定的。当荷载增大时，单位面积桩力随桩厚与桩径比的变化趋势，并形成了在桩端直径的2倍范围内将桩端阻力传递到桩上部的机制，但在荷载较小时，单位面积桩力也可随桩径的变化而变化.用有限元法模拟了开口桩和封闭桩的工作性状，认为桩顶附近的极限摩阻力状态使地基沉降主要集中在主应力方向形成的锥下。(1)由于桩内土随桩沉降，桩端内摩阻力除桩端外可忽略不计，但在桩端，由于砂粒的夹持，桩端的外摩阻力或内摩阻力大于其它部位。(2)在开放桩的情况下，靠近尖端的沙子没有失败，但靠近顶部失败。 ...更多信息 (3)对于桩端以下5m处的刚性土层被混凝土堵塞在2倍桩径范围内的封闭桩，桩侧摩阻力从裂缝处到上部依次达到极限值，桩端附近的砂土破坏。(4)从上述的极限摩擦状态和砂土的破坏状态中，依次观察到通常的屈服荷载和岸田和高野命名的“第一极限荷载”。对于该方法中的摩擦单元和砂土破坏后卸荷单元的改进，必须引入位移控制或柔度法。砂体在端部附近的应力值达到颗粒破碎范围，本构关系也需改进。对称轴附近的周向应变误差或应力和应变的精确定义必须进行研究.针对上述改进，建立了端部无摩擦试件三轴试验方法，并采用应变控制进行试验。少

1. The bearing capacity of pipe piles is statically indeterminate on account of increasing in diameter. The force per unit area shows a tendancy to vary as the ratio of thicknes to diameter as the load is made larger and the mechanism, which transfers end resistance to the upper part of piles between the extent which is twice as long as diameter at the tip ,is formed, but it may vary as the diameter as long as the load is small.2. The behaviours of open or closed pile were simulated by the F.E.M analysis, and then it is presumed that the ground will be settled by the pile mainly under the cone formed by the principal stress direction due to the ultimate state of friction near the pile top.(1) The inner soil settles with the pile so that the inner friction is negligible except the pile tip At the pile tip, however, outer or inner friction is larger than other part owing to arching of sand particles.(2) In the case of the open pile, sand near the tip did not fail but near the top failed. … More (3) In the case of the closed pile, in which the rigid stratum at 5m under the tip which plugged by the concrete between the extent which is twice as long as pile diameter, the friction reached the ultimate value in order from the rip to the upper part and the sand near the tip was failed.(4) From the above mentioned ultimate state of friction and the failure of sand, the usual yielding load and 'the first ultimate load', named by Kishida and Takano, were observed in order.3. For improvement of friction element and unloading element of sand after failure in the method, the displacement control or flexibility method must be introduced. The stres values of sand near the tip reach the particle crushing range so that the constitutive law must be improved also. Errors of circumferential strain near the axis of symmetry or the precise definition of stress and strain must be investigated.4. For the above mentioned improvement, triaxial test method with end frictionless pieces was established and the test will be conducted by strain control. Less