A simulation study of the activity characteristics and genetic mechanism of coupled ground fissures: Exemplified by the Songzhuang ground fissure in Beijing

The active characteristics and genetic mechanism of coupled ground fissures mainly induced by fault activities and pumping are studied, and the Songzhuang Town in Tongzhou District of Beijing is taken as the research archetype. The damage of surface planes and stratigraphic profiles caused by ground fissure activities are clarified through field investigation, and the variation characteristics of the displacement field and stress field of the strata caused by different dislocation amounts and groundwater level drop are revealed. The response processes of the model stratum under the two conditions of fault misalignment and groundwater extraction are simulated and studied respectively by using the finite difference method. Finally, the relationship between this type of ground fissure and the main inducing factors is discussed. The results show that (1) the ground fissure is characterized by three-dimensional activities, which causes the vertical tension of the shallow stratum and wall to be 0.3−1.2 cm, and the vertical dislocation of the deep stratum gradually increases with the burial depth. (2) Stress changes caused by fracture activities are concentrated in the ground fissure development area and lead to significant vertical displacements in the hanging wall, the stratum located in the ground fissure area has large shear and traction deformation, and the vertical displacement difference between the two sides is the largest. The gradual increase of fault dislocations causes the hidden fractures to extend upward, and cause secondary cracks on the shallow surface of the hanging wall, resulting in the overall distribution of ground fissures with a certain width. (3) The vertical extension and horizontal expansion of ground fissures are aggravated by the lowering of groundwater levels, and the surface on both sides of the crack produces continuous settlement response, making the center of the subsidence funnel become a concentrated development area of ground fissures, with the maximum settlement of 10.2 cm in the model stratum at the fissure in its central area, and the settlement range of about 38 m in the hanging wall and about 16 m in the foot wall. (4) This type of ground fissures is obviously controlled by faults, but the increased activity in this period is mainly due to groundwater over-exploitation. This work will be of great theoretical and practical significance to understand ground fissure mechanism, establish quantitative relationship between formation and fault with groundwater, and prevent and reduce disasters.