宁波平原地面沉降时空分析与防治对策

SPATIOTEMPORAL ANALYSIS AND PREVENTION COUNTERMEASURES OF LAND SUBSIDENCE IN NINGBO PLAIN

精准识别复杂因素影响下地面沉降时空演化规律是地面沉降风险防控的关键。利用宁波市地面沉降监测中心对土层压缩变形和地下水位进行精准监测,并统计分析1985~2017年监测数据,探讨地下水开采量、含水层水位、粘性土孔隙水压力与土体分层沉降的相互作用机制,重建1985年以来宁波平原地面沉降时空演化过程。结果表明:在地下水开采期,含水层水位快速下降导致粘性土释水压密,地面沉降主要来自于软土层、硬土层的压缩变形;在地下水禁限采过渡期,含水层水位逐渐回升,主沉降层位由软土层、硬土层逐渐转移到浅部软土层;在城市建设快速推进期,大规模工程建设活动导致20m以浅软土层成为地面沉降的唯一贡献者,其他土层出现了微量压缩或回弹。城市化建设引发地面沉降已成为宁波市地面沉降防控的重点,需要从城市规划、建设与管理全周期管控。

Accurate identification of the spatiotemporal evolution of land subsidence under the influence of complex factors is the key to the prevention and control of land subsidence risk. Both soil compression deformation and groundwater level are accurately monitored by the Ningbo land subsidence monitoring center, the monitoring data from 1985 to 2017 were analyzed, the interaction mechanism between groundwater exploitation, aquifer water level, pore water pressure of cohesive soil and layered settlement of soil is discussed, the spatiotemporal evolution of land subsidence is reconstructed in Ningbo plain since 1985.The results show that the rapid decrease of aquifer water level leads to the release of water pressure of cohesive soil, and land subsidence mainly comes from the compression deformation of soft and hard soil during the period of groundwater exploitation.During the transition period of groundwater mining prohibition and restriction, the water level of aquifer gradually rises, and the main settlement layer gradually shifts from soft soil layer and hard soil layer to shallow soft soil layer. In the period of rapid development of urban construction, large-scale engineering construction activities lead to the only contributor of land subsidence in the shallow soft soil layer less than 20 m, and other soil layers appear micro compression or rebound. Land subsidence caused by urbanization has become the focus of land subsidence prevention and control in Ningbo, which needs to be controlled from the whole cycle of urban planning, construction and management.