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为深入研究桩基础破坏特征,解决桩基础承载机理和破坏条件问题,自行设计桩基础承载力室内试验,对桩顶外力、位移、桩侧摩阻力与桩底反力进行了全方位测试。采用临近桩基破坏时减小加载量的方法,结合数值模拟极限方法分析,在两种方法所得P-s曲线中可以找到陡降的破坏点。两种方法的极限承载力、桩底反力吻合较好,表明室内试验可信,数值极限方法可行。依据以上两种方法,提出了桩基的三点破坏特征:(1)破坏时桩顶位移突变,破坏后有时会有所反弹;(2)破坏时桩底反力突变并出现明显反弹;(3)破坏时桩侧摩阻力出现先降低后增大现象。这些特征表明桩基破坏后桩侧与桩底承载力还将提高,使桩基仍然维持力学平衡状态,表明桩基这种破坏特征与其他基础形式不同。综合桩基础破坏特征,提出应按第一次桩顶位移突变作为控制桩基础承载力的条件。本次研究只是探索,还需现场试验的验证。
In order to deeply study the failure characteristics of pile foundation, solve the bearing mechanism and failure conditions of pile foundation, the pile foundation self-designed indoor test was carried out to test the pile top external force, displacement, pile side friction and pile bottom reaction force in all directions. Using the method of reducing the loading near the failure of pile foundation and combining with the limit analysis of numerical simulation, it is found that the sharp drop point can be found in the P-s curve obtained by the two methods. The ultimate bearing capacity of the two methods, the reaction at the bottom of the pile is better, indicating that the indoor test credible, the numerical limit method is feasible. Based on the above two methods, the three-point failure characteristics of pile foundation are proposed: (1) The displacement of the top of the pile changes suddenly when the failure occurs, and sometimes it will rebound after the failure; (2) The reaction force at the bottom of the pile breaks down suddenly and rebounds obviously; 3) when the pile friction resistance appears to reduce the first increase after the phenomenon. These characteristics show that the bearing capacity of pile side and pile bottom will increase after the pile foundation is damaged, so that the pile foundation still maintains the mechanical equilibrium state, which shows that the damage characteristics of pile foundation are different from other foundation forms. Based on the failure characteristics of the pile foundation, it is proposed that the first pile top displacement mutation should be taken as the condition to control the bearing capacity of pile foundation. This study is only to explore, but also the field test verification.