垫层对水泥土搅拌桩复合地基沉降的影响研究

Study of influence of cushion on settlement of cement-soil mixing pile composite foundation

根据静载荷试验和数值模拟的结果,研究垫层厚度对水泥土搅拌桩复合地基沉降的影响规律。针对珠海地区广泛存在的淤泥质土,进行了天然地基和4种垫层厚度的水泥土搅拌桩复合地基现场静载荷试验。在地基中预埋沉降管和沉降磁环,利用带刻度的探头感应加载过程中沉降磁环位置的变化,获取地基的分层沉降量,据此分析复合地基的沉降规律。在现场试验的基础上,对水泥土搅拌桩4桩复合地基进行了数值分析,将数值计算得到的不同垫层厚度复合地基中桩、土的分层沉降进行比较,结果表明垫层的设置减小了桩的沉降量,但过厚的垫层不能够有效地提高复合地基的承载力,反而会增大沉降。建议对褥垫层厚度的选取,除了要综合承载力和沉降两方面因素之外,还要考虑实际的地质条件。垫层厚度可取20～40cm,当淤泥层位于桩身中部以下取高值,位于桩身中上部取低值。

The influence of cushion thickness on the settlement of cement-soil mixing pile composite foundation was studied by the static load tests and numerical simulation. The static load tests of natural foundation and four cement-soil mixing pile composite foundations in which the cushion thickness was different were carried out for the silt soil in Zhuhai area. The settlement-tubes and magnetic rings were pre-buried in the foundation. And the probe with scale was used to detect the positions of the magnetic rings and obtain the data of the layered settlements. According to these experimental data of composite foundation for four cement-soil mixing piles, the settlement law was analyzed; and layered settlements of piles and soil in different composite foundation were calculated by numerical calculation. The comparison between the different composite foundation shows that the settlement of pile could be reduced by the cushion, but the thickness of cushion has a significant influence on the supporting capacity of composite foundation -- a much thicker cushion could weaken the supporting capacity and increase the settlement of composite foundation. For choosing the optimal thickness of cushion, the geological condition was suggested to be considered except for the supporting capacity and settlement of composite foundation. The cushion thickness could be from 20 cm to 40 cm - the higher value is selected when the silt layer is below the middle sector of pile, conversely the lower value is selected.