Prevention and control of land subsidence and earth fissures in Suzhou–Wuxi–Changzhou region

Abstract: [ Objective] The Suzhou–Wuxi–Changzhou region is one of the most severely affected areas by land subsidence, both in China and globally. In the early 1970s, land subsidence occurred and resulted in the formation of ground fissures caused by differential subsidence, thus resulting in significant economic losses. In this century, the rate of ground subsidence has decreased, with some areas experiencing regional ground resilience. The unique developmental history of ground subsidence allows one to comprehensively interpret its evolutionary process and causal mechanisms. This study aims to unravel the life cycle and driving forces of land subsidence in the Suzhou–Wuxi–Changzhou region. [ Methods ] To achieve this, a multifaceted approach was employed, including long-term and large-scale monitoring of three-dimensional seepage, stress, and strain, complemented by physical experimental models and numerical simulations. An analysis was conducted to synthesize the macro-evolutionary patterns and causal mechanisms of land subsidence and the formation of ground fissures. [ Results and Conclusion ] The findings indicate that land subsidence in the Suzhou–Wuxi–Changzhou region exhibits distinct characteristics that evolve through five discernible stages: initiation, rapid development, deceleration, stagnation, and rebound. The development of land subsidence is intricately connected to groundwater extraction, with stratum deformation arising predominantly from the compaction and dewatering of aquifers and aquitards due to pumping. During the subsidence phase, primary aquifer sand and contiguous aquitards are identified as the primary contributors to subsidence. By dissecting the causal mechanisms of land subsidence and ground fissures, this study delineates the spatiotemporal evolution of the structural compression and rebound of strata under varying conditions of deep groundwater exploitation, restriction, and prohibition, along with their respective contributions to subsidence. Ground fissures, which act as a secondary geological hazard at certain stages of subsidence, exhibit a spatial distribution and occurrence time that are closely related to groundwater levels, land subsidence, bedrock undulations, and soil-layer structural disparities. The life cycle of ground fissures can be encapsulated by the mechanical processes of compression, tension, shearing, and rebound, which highlights the triggers and critical thresholds for fissure formation due to differential subsidence. An integrated “sky–air–ground” monitoring system that can perform full-section fiber-optic monitoring in geological boreholes and amalgamates diverse technical methods is established to obtain scientific and granular data support for land-subsidence control and prevention. Furthermore, an innovative finite-element coupling interface element method customized for regional and site-specific scales is developed. This method successfully simulates the mechanical mechanisms of stratum deformation as well as the genesis and propagation of ground fissures under complex three-dimensional geological conditions, thus facilitating the precise identification and management of subsidence- and fissure-prone areas. [ Significance ] This study highlights the government’s land-subsidence control measures at various stages, which are characterized by technological innovations such as groundwater extraction restrictions and bans, thus setting a precedent for land-subsidence management and groundwater-resource stewardship in other provinces and cities across China.