苏州城市规划区Ⅱ承压水开采与地面沉降预防控制研究

Research on the exploitation of the second pore confined water and control of land subsidence in Suzhou City

在孔隙承压水开采与地面沉降的关系上存在2种观点。水、土应力平衡理论认为:只要开采承压水,就会引发应力失衡并导致地面沉降;而水、土动态平衡理论则认为:除非开采水压力至水、土应力平衡面以下,否则不会引发地面沉降。苏州城市规划区第Ⅱ承压水开采水位与地面沉降动态观测表明,在-33m处存在一个天然动态水、土应力平衡面。第Ⅱ承压含水层形成后,经上覆堆积物自重压力长期压缩作用,其水压力具较高的压强,这种天然状态下产生的弹性释放储存量可开采利用多少,取决于开采状态下水、土应力平衡时可消耗压力水柱高度中的水头值。因而地面沉降的根本原因是开采水位超过了-33m,突破了天然状态水、土应力平衡面水位。Ⅱ承压含水层在天然状态受上覆堆积物重力产生的高压强弹性释放储存量现象,可以帮助我们确立该地区孔隙Ⅱ承压水开采不产生地面沉降的临界水位(水、土应力平衡面)。这一点对承压水开采条件、可开采资源性质具有重大实际意义。同样可以应用于饱受地面沉降困扰的无锡、常州及周边地区,为地下水开发利用政策由单一的封井停采转为目标水位控制开采提供了科学依据。同时也为此政策在承压水动力学机制上找到了内在原因。

There are two views concerned the relation between the exploitation of the pore confined water and land subsidence. The theory of stress equilibrium between groundwater and soil considers that the land subsidence takes place because of the stress inequilibrium between groundwater and soil induced by exploitation of the pore confined water. While the theory of dynamic equilibrium surface between groundwater and soil insists that the land subsidence would not happen until the groundwater level reaches the equilibrium surface. The analysis resulted from the dynamic measurements of the exploitative level of the second pore confined water and the extent of land subsidence in Suzhou City showed that there was a dynamic equilibrium surface between groundwater and soil located about -33m level under ground. The stress of the second pore confined water is larger than the gravity stress of overlaid accumulation which has been stable after compaction through long times. And the main reason of land subsidence is the second pore confined water level below -33m underground, which breaks through the dynamic equilibrium surface between groundwater and soil. The existence of natural dynamic equilibrium surface between the groundwater stress and the gravity stress of overlaid accumulation is great significant, and it may instruct us how to control the critical level of exploitative groundwater. The result could also be applied in other areas such as Wuxi, Changzhou and so on, where are bothered seriously by land subsidence too. This study provides the scientific evidences for the groundwater utilization policy transforming from prohibition of groundwater exploitation to the aim level.