241 / 2023-09-29 21:06:47

Study on the Coordinated Settlement Patterns between Loose Aquifer Loss and Surface Ground Due to Groundwater Depletio

Distributed Fiber Optic,SBAS-InSAR,Aquifer Compression,Aquitard Weakening,Concurrent Subsidence of Loose Layer and Surface

Mining-induced disturbance in coal mining can indirectly cause the loss of groundwater, resulting in compression of loose layers and surface subsidence, posing a threat to coal mine safety and production. In order to analyze in-depth the effects of such non-mining factors on the loss of groundwater and subsidence in loose aquifers, the study area is divided from top to bottom into First aquifer, First aquiclude, second aquifer, secondary aquiclude, third aquifer, third aquiclude, and fourth aquifer based on existing geological and hydrogeological data. Using distributed fiber optic sensing technology as the main method supplemented by time-series InSAR technology, and combined with conventional leveling and ground-based measurement methods and groundwater monitoring, a three-dimensional integrated observation network for ground subsidence, known as the "sky-ground-underground" system, was constructed to explore the synergistic subsidence patterns of strata and the surface.

The results indicate: (1) Continuous compression in the quaternary aquifer and tertiary confining layer is the main cause of surface subsidence in the study area. The two layers contributing the most to strata deformation are the third aquiclude, and fourth aquifer. The deformation in the near-surface loose layer exhibits seasonal characteristics, rising in spring and summer and subsiding in autumn and winter, while the quaternary aquifer and tertiary confining layer exhibit continuous subsidence throughout the observation period. (2) The overlying clay layer above the fourth aquifer in the study area is weakened due to the influence of groundwater in the quaternary aquifer. The degree of weakening is inversely proportional to the burial depth and directly proportional to the groundwater permeability. Weakening of the clay layer leads to compression of the aquitard at the top of the aquifer, exacerbating surface subsidence. (3) Deformation in the fourth aquifer is consistent with the trend of water head changes in the fourth aquifer. The two exhibit a linear relationship, and the observed results match the theoretical calculations. This suggests that water loss in the quaternary aquifer is the main cause of its compression and deformation. (4) The study area is experiencing continuous subsidence. Using Sar data as the dependent variable (y) and deformation variables in the quaternary aquifer and tertiary confining layer as independent variables (x1 and x2, respectively), a multiple linear regression was performed, yielding the equation y=3.987 x1-0.135 x2-1.114 with an R2 of 0.517. This demonstrates a certain linear relationship between surface deformation and deformation in the tertiary confining layer and quaternary aquifer, further confirming that the decrease in water head in the quaternary aquifer is the main cause of surface subsidence in the study area.