Policy-Driven Land Deformation in Coastal Megacities Quantifying Coupled Subsidence–Uplift Dynamics and Infrastructure Risks via a Viscoplastic Framework

Over the past century, groundwater overexploitation has triggered severe land subsidence in coastal megacities like Tianjin, China. However, with policy changes such as enforced extraction restrictions and large-scale water diversion, the downward trend has now been reversed, unexpectedly leading to strange phenomena. Long-term monitoring in Tianjin (2013–23) reveals a complex spatiotemporal pattern where areas of persistent land subsidence coexist with zones of recent uplift, following shifts in groundwater policy. The mechanisms governing this transition, particularly the lagged, nonelastic nature of the uplift, remain poorly quantified. The decade-long leveling data and field experiments were integrated to elucidate the differential hydromechanical response of layered soils. Especially, the field experiments reveal distinct deformation mechanisms: Sand layers exhibit primarily elastoplastic behavior, whereas clay layers are dominated by viscoplastic deformation. These contrasting responses, combined with variations in layer thickness, lead to spatially heterogeneous ground movement. These insights inform the development of a 3D visco-elasto-plastic hydromechanical coupling model, explicitly incorporating state-dependent parameters to capture hysteresis and inelasticity. The validated model not only reproduces the observed decadal deformation field but also enables a quantitative, scenario-based risk assessment for critical infrastructure, projecting differential displacement under various groundwater management futures. This study reveals how policies restricting groundwater extraction in coastal cities can unexpectedly cause ground uplift alongside subsidence, creating new risks for infrastructure like railways and tunnels. By analyzing a decade of data from Tianjin, China, we show that rising groundwater levels lead to uneven ground movement—some areas lift while others sink—due to differing soil properties. Our predictive model helps cities anticipate these shifts, enabling proactive protection of critical infrastructure. This work is vital for urban planners and policymakers seeking to balance water resource management with public safety, especially as global coastal cities face similar challenges from climate adaptation strategies.