再生混凝土骨料包裹桩复合地基承载特性及计算理论

Bearing Capacity Characteristics and Calculation Theory of Recycled Concrete Aggregate Encased Column Composite Foundation

利用再生混凝土骨料替代包裹碎石桩中的天然碎石骨料,形成一种新型再生混凝土骨料包裹桩复合地基。通过开展复合地基承载特性的模型试验,研究了长径比、包裹长度、包裹刚度和面积置换率对再生混凝土骨料包裹桩复合地基的影响,并基于试验结果对该复合地基的承载力计算理论进行了推导。研究结果表明:再生混凝土骨料包裹桩复合地基能明显提高被加固土体的承载特性;在进行再生混凝土骨料包裹桩复合地基设计时,单桩长径比宜为6~7,桩径宜为800~1200 mm,土工材料包裹长度宜为5~6倍桩径,包裹材料刚度宜为1000~4500 kN/m,桩间距最优置换率宜选取在0.1~0.2;桩体底端与顶端应力之比随承压板顶面位移的增大逐渐稳定在15%~20%;再生混凝土骨料包裹桩侧土压力由桩顶向下呈先增大后减小的现象,最大应力出现在距桩顶约300 mm(3d,d为桩径)深度处。根据再生混凝土骨料包裹桩复合地基桩、土和土工包裹材料的变形协调原理,及桩体的鼓胀变形特性对再生混凝土骨料包裹桩复合地基承载力计算公式进行了推导,所得结论可为该新型复合地基的设计提供理论依据。

A new type of recycled concrete aggregate encased column(RCAEC)composite foundation can be formed by replacing the natural gravel aggregate in the wrapped gravel pile with recycled concrete aggregate.Some model tests have been performed on RCAEC,the effects of the ratio of column length to diameter,geosynthetic encasement length,geosynthetic encasement stiffness,and the optimal replacement rate on RCAEC composite foundation were studied,and the calculation theory of bearing capacity of the composite foundation was deduced based on the test results.According to the results,the RCAEC composite foundation could effectively improve the foundation bearing capacity of reinforced soil.In the design of RCAEC composite foundation,the ratio of column length to diameter should be 6~8,the column diameter should be 800~1200 mm,the encased length of geotechnical should be 5~6 times to the column diameter,and the encased stiffness should be 1000~4500 kN/m.In the design of column spacing,the optimal replacement rate should be selected as 0.1~0.2.With the increase of the settlement,the ratio gradually stabilized at 15%~20%.The lateral stress of RCAEC increases first and then decreases from the column top to the bottom.At the same time,the maximum lateral stress occurs at the depth of about 300 mm(3d,d is pile diameter)from the column top.According to the column-soil and geosynthetics deformation coordination principle of RCAEC composite foundation as well as the bulging deformation characteristics of column,the calculation formula of bearing capacity of RCAEC composite foundation was deduced.In short,the conclusion can provide a basis for the design of this composite foundation.