Experimental investigation of ground fissure reactivation and differential deformation under layered groundwater pumping–recharge conditions

Groundwater-level fluctuations can induce differential deformation at ground-fissure sites, yet systematic experimental investigations of hydraulic and layered deformation responses across fissures during pumping-recharge remain limited. This study focuses on the F 4 ground-fissure area in Yuhuazhai, Xi’an, and employs a large-scale physical model to investigate hydro-mechanical responses under layered groundwater pumping-recharge conditions. Under the present experimental conditions, hydraulic and deformation responses varied markedly among different layers and between the two sides of the fissure. Recharge restored approximately 85%–88% of the pumping-induced hydraulic-head drawdown during the first three stages. Under the deep 6-Sand Layer condition, the maximum pore water pressure decrease reached 37.05 kPa, exceeding that under the 4-Sand Layer condition, while the degree of recovery after recharge was relatively lower. pore water pressure disturbances were strongest in the sand layers, attenuated markedly in the adjacent silty clay layers, and propagated across the fissure, although asymmetric responses occurred between the hanging wall and footwall. The silty clay layers contributed more than 70% of the total deformation during multiple pumping stages and exhibited delayed recovery during recharge. As the experiment progressed, stratal and differential deformation generally decreased; under the same cumulative pumping volume of 840 L, the total surface deformation in the later stage was 51.1% lower than that in the earlier stage. These results demonstrate that a high degree of hydraulic-head recovery does not necessarily correspond to synchronous recovery of stratal deformation. Therefore, groundwater management in ground-fissure areas should incorporate coordinated monitoring of layered hydraulic responses and stratal deformation, rather than relying solely on groundwater-level recovery, thereby providing a basis for groundwater regulation and deformation-risk mitigation.