The location of the groundwater level observation hole for the CL and its water level dynamic changes are shown in Fig. 7.
From July 2000 to July 2006, the drainage of the No. 1 well mainly occurred in the − 150 m West Wing and the − 250 m West Wing discharge roadways, and the discharge volume was stable at 800 m3/h. The 4–92 observation hole, which was close to the two discharge roadways, changed from + 6.0 m to -210.0 m, and continued to decrease by 216 m. From July 2006 to March 2012, the main drainage was in the − 250 m West Wing discharge roadway, the drainage water volume was 1373.5 m3/h, and the water level of the 4–92 observation hole was basically stable at -220~-225 m. With the implementation of the hydrophobic scheme, the water in the East Wing − 106 m water inrush point disappeared, indicating that the groundwater of the CL at the shallow elevation of -150 m and F125 fault was closely related to underground water.
From July 2006 to March 2012, while the − 250 m West Wing drainage roadway was draining, drainage also occurred in the − 250 m East Wing drainage roadway, with a drainage volume of 2,580.0 m3/h. The water level of the 4–99 observation hole on the east side of the F125 fault decreased from − 11.0 m to -42.2 m, or only 31.2 m. The water level of the S1 observation hole decreased from − 29.2 m to -60.5 m, which only decreased by 31.3 m, reflecting the poor water conductivity of the F125 fault as a whole. These results showed that the groundwater hydraulic connection of the CL on both sides of the fault was not very close.
From April 2012 to September 2013, the water volume of the − 250 m East Wing roadway remained steady at 500 m3/h, and the water levels of observation holes 2–7 and 3 − 1 (Fig. 6) near the − 250 m East Wing discharge roadway decreased from − 162.5 m and − 184.1 m to -232.4 m and − 230.5 m, respectively, while the groundwater level tended to be consistent. These data indicate that the aquifer of the CL on the west side of the F125 fault was well connected. In addition, the water levels of 4–99 and S1 on the east side of the F125 fault were stable at -42.7 m and − 66.8 m. Compared with holes 2–7 and 3 − 1 on the west side, the water level difference was above 160 m, which proved that the hydraulic connection of the groundwater in the CL on both sides of the F125 fault was not close . Additionally, there was a difference between the 4–99 and S1 water levels of the 386 m east side of the F125 fault is 24.1 m, indicating that the groundwater hydraulic connection of the CL in the east side of the F125 fault was not close.
From April 2012 to October 2015, a hydrophobic decompression project was carried out in the − 300 m West Wing discharge roadway (Fig. 6). The total hydrophobicity volume was 600 m3/h, and the water level of S12, 1–1, and 1–2 decreased from − 244.8 m, -219.9 m, and − 231.5 m to -310.0 m, -315.0, m and − 305.4 m, respectively. As seen from Fig. 6, the distances between S12 and the 1–1 and 1–2 holes were 1,000 m and 350 m, respectively, and the water level elevations of the three boreholes were basically the same in October 2015, which confirmed the hydraulic connection of the CL groundwater in the west part of the F125 fault and the shallow part of the elevation of -300 m is relatively close.
From May 2014 to May 2017, drilling holes were constructed along the − 390 m West Wing discharge roadway and − 350 m East Wing discharge roadway, and underground water drainage was performed. The drainage volume of the − 350 m East Wing discharge roadway is only 3 m3/h, the 4 − 1 water level remains at about − 310 m, and there was little change, indicating that the groundwater hydraulic connection of the CL in the deep No. 1 well was not close.