Water is one of the major risk sources in the excavation of deep-large foundation pits in a water-rich area. The presence of intrusive broken diorite porphyrite in the stratum aggravates the risk level of deep foundation pits. Based on a geological survey report and design documents of parameter information, MIDAS/GTS software was used to perform the numerical simulation of an engineering example of a deep foundation pit project of ultradeep and water-rich intrusion into the broken rock station of subway line 4 in a city. The simulation results show the characteristics of seepage path evolution, seepage aggregation areas and points, and the effect of seepage on the deformation of a deep foundation pit during the whole construction of this deep foundation pit. The results show that with the precipitation-excavation of the deep foundation pit, the pore water pressure at the bottom of the foundation pit follows a distribution of three “concave” shapes. High-permeability pressure zones are found around the foundation pit, intruding broken diorite porphyrite zones, and middle coarse sand zones. With further excavation of the foundation pit, the seepage pressure in the middle part of the foundation pit gradually decreases, and the two “concave” distributions in the middle gradually merge together. After excavation to the bottom of the pit, the pore water pressure at the bottom is distributed in two asymmetrical “concave” shapes, and the maximum peak of pore water pressure is found at the intrusion of fractured porphyrites prone to water inrush. The four corners of the foundation pit are prone to form seepage accumulation zones; therefore, suffosion and piping zones are formed. The surface settlement caused by excavation is found to be the largest along the longitudinal axis of the deep foundation pit, whereas the largest deformation is found near the foundation pit side in the horizontal axis direction of the foundation pit. With the excavation of the deep foundation pit, the diaphragm wall converges to the foundation pit with the maximum deformation reaching about 25 mm. After the first precipitation-excavation of the deep foundation pit to the silty clay and the bottom of the pit with the largest uplift, with further precipitation-excavation of the deep foundation pit, the uplift at the bottom of the deep foundation pit changes only slightly.

The height of water-conducting fracture zones (WCFZs) is vital for the prevention of water, gas, and roof accidents in coal mines. However, its dynamic evolution law and maximum height are difficult to be obtained by traditional prediction methods, especially for conditions in which there is high overburden caving strength and a thick coal seam. Therefore, taking the 150,313 fully mechanized caving working face in Yingying Coal Mine as a background, according to the principle of optimized processes, a new predicting approach based on the Brillouin optical time-domain reflectometry (BOTDR) is proposed. Firstly, we estimated the height through empirical formula calculation, theoretical analysis, and similar model simulation tests. Secondly, we studied the optimized layout of optical cables in the overburden in detail for predicting the maximum height of the WCFZ and keeping the cables in good performance during field prediction. Thirdly, we researched and optimized the borehole parameters, optical fiber selection, and the special protection measures. Finally, we applied the aforementioned optimized outcomes in the field experiment to dynamically predict the height of the WCFZ. As a result of the field experiment, the distribution characteristics of optical fiber strain, the maximum height, and the evolution law of the WCFZ were obtained through the regular monitoring of fiber strain using BOTDR. The experiment demonstrated that its maximum height is consistent with the results studied indoors. The validation and feasibility of the approach proposed in this paper were verified via the aforementioned studies. The research in this paper has good reference value and important significance for predicting the height of the WCFZ using BOTDR in coal mines with similar geological and productive conditions.

Improving coal resource mining rates has long been a focus of coal industry research. The gob-side entry retaining by roof cutting (GERRC) is a new coal mining technology that has gained popularity in China due to its high mining rate and safety. Based on the GERRC technology, the precise technical procedure is elaborated, and the fundamental idea of pressure relief is explored through creating a structural mechanics model of the surrounding rock in this paper. The results of mechanical analysis show that the primary mechanism of roof pressure release is to weaken the integrity of the roof, thereby reducing the ultimate bending moment of the rock stratum. In addition, an additional strategy for pressure release is suggested in this research, involving the weakening of the roof rock by the creation of dense pressure-released holes. The results of the engineering field experimentation demonstrate that the dense pressure-released holes can completely replace the conventional blasting technology of the past to achieve the effect of releasing the roof pressure, thus avoiding the use of hazardous and challenging-to-obtain explosives and demonstrating safety, reliability, and feasibility.