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桩端后注浆可以较大幅度地减小超长桩桩顶沉降量,同时改善桩基承载性能。根据东明黄河大桥采用桩端后注浆技术与未注浆桩2根试桩的现场竖向抗压静载试验结果,通过对桩基承载性状、桩身轴力及侧摩阻力的综合分析,可以发现,后注浆试桩较未注浆试桩Q-s曲线更加平缓。在最大桩顶荷载时,桩顶沉降量减小33.2%。在特征承载力条件下,试桩为纯摩擦桩,超长桩的桩顶沉降主要来自桩身压缩,后注浆对桩基沉降减小幅度有限。在沉降控制条件下,可以通过提高桩身质量以及提高桩身钢筋密度或混凝土标号等措施有效减小桩顶沉降量。规范推荐侧摩阻力值仅与土层物理力学性质有关,建议桩基设计时考虑侧摩阻力的深度效应。在渗透、劈裂及压密等综合作用下,桩端及桩侧下部形成较大体积的水泥-土体复合固结体,较好地改善了桩基承载性能。
Pile tip grouting can greatly reduce the settlement of overlength pile, and improve the bearing capacity of pile. According to the vertical static load test results of two pile test results of the post-grouting pile tip and the pile of the Dongming Yellow River Bridge, through the comprehensive analysis of the pile foundation bearing capacity, axial load and lateral friction, It can be found that post-grouting test pile is more smooth than un-grouting test pile Qs curve. At the maximum pile roof load, the settlement of pile top decreased by 33.2%. Under the characteristics of bearing capacity, the test pile is a pure friction pile. The pile top settlement of the extra-long pile mainly comes from the compression of the pile body, and the post grouting reduces the pile foundation settlement to a limited extent. Under settlement control conditions, the settlement of pile top can be effectively reduced by improving the quality of pile body and increasing the density of pile or concrete marking. The standard recommended lateral frictional resistance value is only related to the physical and mechanical properties of the soil. It is suggested that the depth effect of the lateral frictional resistance should be taken into account when designing the pile foundation. Under the combined effect of infiltration, splitting and compaction, a larger volume of cement-soil composite consolidation body is formed on the pile end and the lower part of the pile, which improves the bearing capacity of pile foundation.