水位升降对粗砂地基承载力和沉降影响的试验研究

EXPERIMENTAL STUDY ON BEARING CAPACITY AND SETTLEMENT OF COARSE SAND AFFECTED BY CHANGES OF GROUNDWATER LEVEL

随着城市地下空间的开发和利用,地下水位埋深较浅的地区,例如沈阳市,在施工过程中需要降水,工程完毕后停止降水又使水位恢复。水位的变化可能会导致地基土抗剪强度的变化、地基的回弹或沉降、渗透破坏引起地表塌陷等岩土问题,尤其是地基承载能力和既有建筑物的沉降是工程设计中必须考虑的岩土问题。对于辽沈地区,大多数文献只给出定性的回答,但工程设计需要的是定量回答,这是本文的研究目的。本文通过模型试验模拟粗砂地基上的浅基础,通过静载荷试验、水位观测、水压力和土压力传感器测试等方法测试地下水位升降时,粗砂地基的承载力、土中应力及基础沉降等的变化规律,并对试验结果进行分析和数值仿真分析,提出了利用拟合公式的方法弥补数值仿真分析与模型试验误差的思路。研究结果表明,对于密实的粗砂土地基,其地基承载力特征值在地下水位上升前后会降低,降低幅度达26%,主要原因是地基土抗剪强度降低导致承载力减小;在基础上施加一定荷载后,无论地下水位升和降,基础都会产生附加沉降。水位升高4.3m,沉降为0.565mm,主要原因是地基土的承载能力降低。水位下降4.3m,沉降0.315mm,主要原因是地下水位下降导致土中有效应力增大;数值仿真分析结果表明FLAC3D可以较好地模拟试验过程,可用拟合公式的方法修正饱和砂土出现的误差。

Along with the development of city underground space, the place where buried depth of underground water is low, like Shenyang, dewatering is needed during construction and water level is recovered after completion. Frequent water level change can lead to many geotechnical problems such as bearing capacity change, surface col- lapse caused by additional settlement of foundation and seepage flow in soil. Especially the beating capacity and the additional settlement are key problems. Many researches and papers only supply the qualitative results. The purpose of this paper is to get the quantitative results. This paper is based on the model test. It builds a foundation model on the coarse sand, through the SLT test, monitoring the water level and the stress change using the soil pressure sen- sor and water pressure sensor, and recording the bearing capacity, settlement and stress change along with the wa- ter level change. Then conducted numerical analysis, and used fitting formula to settle the relationship of model test and numerical analysis. The results show that the coarse foundation base characteristic value can lose 26%in maxafter the water level change. If load is applied on the foundation either the water level up or down can cause addi- tional settlement. If the water level rises 4. 3m, the additional settlement can be 0. 565mm （caused by bearing ca- pacity drop）. If the water level drops 4. 3m, the additional settlement can be 0. 315mm（caused by the increase of effective stress）. Numerical analysis shows that for dry sand the numerical analysis fit well. For saturated sand, the tolerance can be fixed by the fitting formula.