再生混凝土骨料包裹桩承载特性试验研究

采用再生混凝土骨料替换包裹碎石桩碎石芯料，形成一种新型地基处理方式——再生混凝土骨料包裹桩，以改善采用包裹碎石桩处理液化及软弱土地基时碎石强度未能充分发挥的问题.开展了模型试验，研究包裹长度、刚度及长径比对再生混凝土骨料包裹桩单桩承载特性和骨料破碎度的影响.研究结果表明：包裹长度为1倍～6倍桩径时，延长包裹长度可显著提高桩体承载力，包裹长度小于1倍或大于6倍桩径时，包裹长度对承载力改善不明显；包裹材料的临界刚度约为100 kN/m，当小于临界刚度时，增加包裹刚度能显著提高桩体承载力，大于临界刚度时，增加包裹刚度不再明显改善桩体承载力；再生混凝土骨料包裹桩桩长不变时，长径比大于10的桩体承载力较低，桩体主要在10～30 cm深度内产生不同程度的局部弯曲，长径比小于7的桩体承载力较高，桩体主要发生轻微鼓胀变形，无局部弯曲；混凝土骨料的破碎度与桩体能承受的极限荷载呈正相关，增加包裹长度、刚度及桩径均会增加芯料的破碎度.因此，进行再生混凝土骨料包裹桩单桩设计时应充分考虑包裹长度、刚度和长径比与芯料破碎度之间的关系，以获取最优设计方案.

Experimental Study on Bearing Capacity of Geosynthetic-Encased Recycled Concrete Aggregate Column

Recycled concrete aggregates are used to replace the gravel core material of encased stone columns, forming a new foundation treatment method—recycled concrete aggregate encased column, to improve the problem that the gravel strength cannot be fully exerted when the encased stone column is used to treat liquefied and soft soil foundations. Laboratory model tests were performed to study the effect of encasement length, stiffness, and the ratio of column length to diameter on the bearing characteristics and aggregate fragmentation degree of the encased recycled concrete aggregate column. The results show that when the length of encasement is 1 to 6 times the column diameter, the bearing capacity of the column can be significantly increased by increasing the encasement length. When the length of encasement is less than 1 or more than 6 times the column diameter, the length change of encasement does not significantly influence the bearing capacity of the column. The critical stiffness of encasement is about 100 kN/m. When the stiffness of the encasement is less than the critical stiffness, increasing the encasement stiffness can prominently improve the bearing capacity of the column. However, when the stiffness of the encasement is greater than the critical stiffness value, increasing the encasement stiffness cannot significantly improve the bearing capacity of the column. When the length of the geosynthetic-encased recycled concrete aggregate column is fixed, columns with a length-to-diameter ratio greater than 10 have a lower bearing capacity, and mainly produce local bending to varying degrees within the depth range from 10 cm to 30 cm, while columns with a length-to-diameter ratio less than 7 have a relatively higher bearing capacity and mainly experience slight bulging deformation without local bending. Besides, there is a positive correlation between the fragmentation degree of the recycled concrete aggregate and the ultimate load that the column can withstand. Increasing the encasement length, stiffness and column diameter will increase the fragmentation degree of the core material. Therefore, when designing a single geosynthetic-encased recycled concrete aggregate column, full consideration should be given to the relationship between the encasement length, stiffness, the ratio of column length to diameter, and the fragmentation degree of the concrete aggregate, to obtain the optimal design scheme.