扬州市城区地面沉降现状与防治对策

扬州市城区第四纪地层覆盖差异很大，明显分成两个不同的区域：扬州城区西南部仅为全新统和上更新统沉积，厚度较薄；而扬州城区东北部，第四纪地层发育较全，厚度较大。地层上的差异使得扬州市城区地下水的开采也呈现出差异性：城区地下水主采层第Ⅱ、第Ⅲ承压含水层主要在城区东北部，西部、南部缺失。由于主要开采层集中在东北部，加之较长期的地下水过量开采，使得本区地下水水位降落漏斗主要分布在城区北部。通过对20年前测量过的一些水准点和监测井的水准复测，证实扬州市城区确实有地面沉降的发生。但扬州城区的地面沉降量并不是很大。结合地质水文条件的分析，文章提出地下水位控制在一定范围之上（-30m）对地面沉降的影响较小的观点，认为应合理控制开发地下水。针对扬州市城区的地面沉降现状，提出在现有地面沉降监测设施的基础上，再补建一些地面沉降监测GPS标石点，对一些重点区应加密布设。同时，密切关注地下水位的变化，预防严重地面沉降灾害的发生。

The Present State and Preventive Measures of Ground Subsidence in Yangzhou City

There are big differences in the overlay of the Quaternary sediments in different areas in Yangzhou urban area.Geologically,it can be divided into two areas: the south-west area with thinner Holocene and the upper Pleistocene sediments and the north-east area with thicker Quaternary stratums.These result in the different distribution of groundwater.The main exploitation layers of groundwater(the No.II and III confined aquifer) are located in the north-east area of the city.There is no main confined aquifer in south-west area.Because of the excessive groundwater extraction in a long period,the descent filler of groundwater are mainly located in the north-east area.Relevelling the bench marks and monitoring wells that surveyed 20year ago proves the ground subsidence in Yangzhou city.But the subsidence rate is low.Based on the analysis on the local geological and hydrological condition,it is thought that the effect of groundwater level on ground subsidence should be light if the groundwater level maintains around-30 m.So the groundwater mining should be reasonably controlled.To the present condition of ground subsidence in Yangzhou city,the authors suggested that,in addition to the available ground subsidence monitoring facilities,some other GPS bench marks should be added and,in key areas,more GPS bench marks should be built.In order to prevent the hazard due to ground subsidence,we should keep close watch on the changes of groundwater level.