摘要
宁波市地下水为消耗型开采,在时间、空间和程度上,地面沉降与地下水开采量有极密切的关系。由于各土层所处的释水条件及物理力学性质的差异,土层变形各具特点;地层组合关系的不同,地面沉降存在分区性。宁波地面沉降主要由粘土释水固结所致。根据土层应力——应变关系分析,提出了“预压固结线”,该曲线表示宁波土层预固结压力增加速率及土层显著压缩的孔隙水压力逐渐下降的趋势。目前,当含水层水位在-25米范围内升降,土层以弹性变形为主,地面不产生显著沉降。因此,-25-0.427n米(n为某年距1986年的年数)作为今后宁波控制地面沉降的地下水元许水位值。据水位——水量相关计算,每年6—9月为地下水高峰开采期,地下水月安全开采量为100+3.133n万米~3。
The exploitation of ground water in Ningbo City is of exploiting type, and therefore, the surface subsidence is initially associated with exploitation quantity of groundwater in time space and degree. The deformations of different soil layers have different features since the water-releasing conditions and physieo-mechanical properties of the soil layers are different. Different stratum associations lead to the difference of various surface subsidence regions. The surface subsidence in Ningbo City is mainly caused by the water release and consolidation of clay beds. According to stress-strain analysis, the authors make a'pressure consolidation line' expressing the pressure increase rate when the soil Iayer is preconsolidated and the pore water pressure decrease trend when the soil layer is remarkably compressed. If the water level of aquifer changes at present around -25m, then the deformation of soil layers will mainly be elastic and the surface subsidence will not be striking, in this regard, the authors advance -25-0.427n(m) as the permissive ground water level for controling the surface subsidence in Ningbo City (where,n stands for year number from 1986 on). A calculation on water level-ground water exploitation quantity relation proves that the monthly safe exploitation quantity of ground water is 100+3.133n×104~m^8.
