地下水位变化模式下含水砂层变形特征及上海地面沉降特征分析

土体变形特征与其经历的应力状态有关。由于抽灌水位置和水量的变化,同一土层中不同时期的地下水位可以呈现不同的变化模式,土层表现出不同的变形特征。论文根据上海1400多个水位孔近40a的水位观测资料和各土层的变形资料,从土层变形角度将地下水位的变化方式划分为5种模式。分析了每种地下水位变化模式下土层的变形特征,并进一步分析了上海地面沉降在时间和空间上的特征。分析结果表明:地下水位的变化模式对上海土层的变形有显著影响。同一土层在不同的水位变化模式下可表现为弹性、弹塑性或粘弹塑性的变形特征;地面沉降与地下水开采量、地下水开采层次与主要沉降层具有密切的关系,开采地下水是上海地面沉降的主要原因;与现阶段含水层的水位变化模式相联系,第四承压含水层是上海最近几年来地面沉降的主要沉降层。

Analysis of deformation of sand strata and land subsidence based on modes of groundwater level changes in Shanghai City

Soil deformation relies on the stress states it has experienced.As the variation of the quantity of discharge and recharge and the place change of wells,the groundwater level changes in distinct modes during different periods at the same site,thus the soil deforming in different ways.Based on the groundwater level data from more than 1400 observation wells,the change patterns of groundwater level are classified into five types from the point of soil deformation.According to the deformation data of each soil layer monitored by extensometer groups,the characteristics of soil deformation are analyzed under each mode of groundwater level change.Then the characteristics of land subsidence of Shanghai in time and space are studied.The analysis shows that the mode of groundwater level variation has remarkable effects on the deformation of soils.An identical soil stratum may exhibit elasticity,elasto-plasticity or visco-elasto-plasticity under different modes of groundwater changing.It is also found that there are close relationships between land subsidence and the amount of groundwater pumping, and between the pumped aquifers and the main subsidence layer.This indicates that extracting groundwater is the main cause of land subsidence in Shanghai.The fourth confined aquifer is the main compressive layers in recent years in Shanghai.It is corresponding to the current mode of groundwater changes.