砂井联合水泥土搅拌桩复合地基固结解析解

砂井联合水泥土桩复合地基是一种新型的复合地基加固技术,既可以加快软土地基固结时间,又可以增强软土地基的强度。针对该组合型复合地基的布桩特点,该类复合地基可以简化成以水泥土搅拌桩为中心的轴对称固结模型,并假定孔隙水沿径向渗流到砂井体内的流量等同于砂井体内排出的水量,考虑砂井的涂抹效应,推导出该类型下砂井联合水泥土搅拌桩复合地基固结方程。根据实际工程荷载多数单级施加和地基附加应力呈梯形分布的特点,得出了砂井联合水泥土桩复合地基固结解析解。通过对单级荷载情况下的复合地基固结解析解的退化,得出了瞬时施加荷载下的解析解。最后分别针对井径比、加荷历时、桩-土模量比、砂井渗透系数等影响因素,对复合地基固结性状进行了分析。该解答对提高此类复合地基的设计和计算水平有一定的理论指导意义。

Analytical solution for consolidation of composite foundation with sand drains and cement-soil mixing piles

The combined composite foundation improved by both sand drain and cement-soil mixing piles, is a new technique of ground improvement for soft soils. It can not only accelerate the consolidation process but also enhance the bearing capacity of the soft soil foundation. According to the configuration of the pile and sand drains, this type of composite foundation is simplified as an axisymmetric model with the cement-soil mixing piles located at the center of the unit cell. The water is assumed to flow into the sand drain from the center along the radial direction and the water flows into the sand drain is equal to that flows out of it, i.e., the equal flow assumption at the soil-sand drain interface. In this way, the smear effect of the sand drain can be taken into account and the consolidation equation for this type of composite foundation is developed. Then analytical solution is obtained for the loading scheme which is applied gradually and the stress increment is distributed in a trapezoid form in the vertical direction. Furthermore, with degeneration of the obtained solution to the simple cases, the analytical solution under an instant loading is presented. Finally, the influences of the following parameters, including the ratio of influenced zone radius to sand drain radius, the loading period, pile-soil compression modulus and sand-drain’s permeability coefficient, are investigated. This analytical solution has a theoretical significance to improve the design and the calculation of this type of composite foundation.