天津滨海新区软黏土吸附力预测方法

Absorption Force Prediction Method of Tianjin Coastal Soft Clay

吸附力广泛存在于黏性土地基的上拔或卸荷问题中,对于桩靴迁航移位、拔桩、打捞沉船等工程问题,它是一种需要克服的阻力;而对于正常工作状态的桶形基础、吸力锚等结构物,则是抵抗外部荷载的有利因素,但这种保护作用又会随着土体固结效应而消失。为了合理预测吸附力的大小及规律,通过黏土地基中沉箱上拔模型试验,研究上拔阻力和基底负孔隙水压力的发展变化规律。研究表明,基础底面卸荷应力与孔压增量可用Skempton公式计算,得出孔压系数A与归一化入泥深度的经验关系;沉箱底面粘着强度约为1. 3倍原位不排水抗剪强度;最大吸附力出现于沉箱与土体脱离时刻,此时吸附力由箱底真空吸力和粘着力组成,提出最大吸附力的经验计算方法。

Absorption force is widely appeared on uplift or unloading problem,mainly in cohesive soil. When any foundation in saturated clay foundation is used to provide stable working environment for the upper structure,suction force between the base and foundation is beneficial to resist the external load. However,a structure,such as spud can,need to be pulled out and moved to other areas,it will become a hindrance and restricting factor. Therefore,the absorption force prediction has a great significance to engineering construction. By caisson model test,uplift resistance and the development of negative pore water pressure was analyzed. Results show that the relationship between pore pressure increment and unloading stress on bottom of foundation accord with Skempton pore pressure formula,and the experience formula is proposed. Adhesion force is calculated which is approximately equal to 1. 3 times situ undrained shear strength. The largest absorption force is proved to appear at the moment when the bottom separates from the soil,constituted by negative pore water and adhesion force. Finally the experiential calculation method is proposed.