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结合天津于家堡南、北地下车库项目开展了2组各3根扩底抗拔桩的极限承载力试验,其中一组试桩有效桩长19 m,另一组试桩有效桩长30 m,试桩均加载至极限破坏状态。载荷试验过程中,两组试桩均对桩顶、有效桩长桩顶以及桩端位置进行了位移测试;其中有效桩长为19 m的试桩还开展了桩身轴力测试。对2组试桩成果从荷载位移曲线、桩身轴力分布、桩侧摩阻力分布规律等方面进行了分析。结合有限元数值模拟分析表明,扩底抗拔桩的承载力由等截面段桩侧摩阻力与扩大头抗力共同组成,首先由等截面段桩土侧摩阻力提供抗拔力;当上拔荷载进一步增大后,扩大头开始逐渐发挥作用,并且扩大头抗力占总承载力的比例逐步上升。极限状态下,有效桩长为19,30 m的试桩,扩大头提供的抗力占总抗拔承载力的比例分别约为50%和35%。扩大头的存在对于等截面段桩侧摩阻力的发挥影响较小。扩大头受周边土体法向力的竖向分量是扩大头抗力的主要组成部分,极限状态下,其可占扩大头抗力的70%左右。
The ultimate bearing capacity tests of 3 sets of 3 deep-grouted piles were carried out in combination with the north and south underground garage project at Yujiapu, Tianjin. The effective length of a group of test piles was 19 m, and the length of another group of test piles was 30 m. The test piles were loaded to the ultimate destruction state. During the load test, the displacement test was performed on the pile top, the effective pile long pile top and the pile end position in the two groups of test piles. The test pile with an effective pile length of 19 m was also tested for axial force of the pile body. The results of the two sets of test piles were analyzed from the aspects of load-displacement curve, distribution of axial force of the pile body, distribution law of pile friction resistance, and other aspects. Combining finite element numerical simulation analysis shows that the bearing capacity of the bottom-lift pile is composed of the friction resistance of the pile section and the expanding head resistance in the equal-section section. The friction resistance of the pile-soil side of the equal-section section is firstly provided; when the upper load is extracted After further increase, the expansion head gradually began to play a role, and the proportion of head resistance increased to the total carrying capacity gradually increased. In the limit state, the test piles with an effective pile length of 19,30 m have a resistance ratio of 50% and 35% respectively. The existence of an enlarged head has little effect on the frictional resistance of the pile section in the equal section section. Expanding the vertical component of the head by the normal forces of the surrounding soil is the main component of the expansion of the head resistance. In the limit state, it can account for about 70% of the head resistance.