Finite-difference model of land subsidence caused by cluster loads in Zhengzhou, China

Groundwater exploitation has been regarded as the main reason for land subsidence in China and thus receives considerable attention from the government and the academic community. Recently, building loads have been identified as another important factor of land subsidence, but researches in this sector have lagged. The effect of a single building load on land subsidence was neglected in many cases owing to the narrow scope and the limited depth of the additional stress in stratum. However, due to the superposition of stresses between buildings, the additional stress of cluster loads is greater than that of a single building load under the same condition, so that the land subsidence caused by cluster loads cannot be neglected. Taking Shamen village in the north of Zhengzhou, China, as an example, a finite-difference model based on the Biot consolidation theory to calculate the land subsidence caused by cluster loads was established in this paper. Cluster loads present the characteristics of large-area loads, and the land subsidence caused by cluster loads can have multiple primary consolidation processes due to the stress superposition of different buildings was shown by the simulation results. Pore water migration distances are longer when the cluster loads with high plot ratio are imposed, so that consolidation takes longer time. The higher the plot ratio is, the deeper the effective deformation is, and thus the greater the land subsidence is. A higher plot ratio also increases the contribution that the deeper stratigraphic layers make to land subsidence. Contrary to the calculated results of land subsidence caused by cluster loads and groundwater recession, the percentage of settlement caused by cluster loads in the total settlement was 49.43% and 55.06% at two simulated monitoring points, respectively. These data suggest that the cluster loads can be one of the main causes of land subsidence.