Search Results (6)

The surrounding rock during a coal mine excavation is prone to significant engineering disasters such as considerable deformation and rock bursts. Pressure release can improve the stress field of a deep rock mass and prevent the occurrence of dangers such as roadway collapse and coal and gas outbursts. This paper uses the ANSYS 19.0/LS-DYNA finite element software to simulate the crush area and fracture zone of a detonation charge with different diameters under in situ stress. The stability of the surrounding rock was analyzed based on the impact stress and velocity, and was verified by field tests. The research results show that the blasting load primarily affects the damaged area near the borehole, while the in situ stress affects far-field crack propagation. The crack propagates in the direction of high surrounding rock pressure. When the uncoupling index is 1.5, the impact pressure of a 60 mm diameter cartridge is eight times that of a 20 mm diameter cartridge. The impact speed can reach two times that of the 20 mm diameter cartridge. The high-energy event at the roof is transferred to the front of the working face, the distribution is no longer concentrated, and a better pressure-relief blasting effect is achieved. The research results can help guide the prevention and control measures of rock bursts and other mining disasters. Full article

The China Society of Explosives and Blasting required a larger than 20% annual increase in the national use of digital electronic detonators since 2018. So, this article conducted a large number of on-site tests and then used the Hilbert–Huang Transform method to analyze and compare the vibration signals of digital electronic and nonel detonators during the excavation process of minor cross-sectional rock roadways from the perspective of time, frequency, and energy. Then, through vibration energy analysis, identification of actual delay time, and formula derivation, it was proved that the delay time error of the detonator can control vibration wave random interference and reduce vibration. The analysis results showed that when using a segmented simultaneous blasting network for excavation in small-sectioned rock tunnels, nonel detonators may provide more excellent protection to structures than digital electronic detonators. In the same segment, the timing error of nonel detonators produces a vibration wave with a random superposition damping effect, resulting in an average vibration reduction of 19.4% per segment compared to digital electronic detonators. However, digital electronic detonators are superior to nonel detonators for the fragmentation effect on rock. The research conducted in this paper has the potential to facilitate a more rational and comprehensive promotion of digital electronic detonators in China. Full article

In order to solve the problem of serious deformation and failure of surrounding rock and difficult maintenance of gob-side entries with strong mining-induced small coal pillars, taking the A110607 return airway of the Shanwenjiaba Coal Mine as the engineering background, the key parameters of roof-cutting and pressure relief control technology for roadway excavation with strong mining-induced small coal pillars were studied by using two-way concentrated blasting roof-cutting and pressure relief technology, combined with theoretical analysis, numerical simulation and a field industrial test. A collaborative control scheme of “roof-cutting pressure relief + anchor cable combined support” is proposed. The test results show that when the height of roof-cutting is 8 m, the angle of roof-cutting is 15°, and when the width of the coal pillar is 3 m, the effect of roof-cutting and pressure relief is the best. Through the field blasting test, it was determined that the blast hole spacing was 800 mm, 321 charge structure was used in the intact roof, and 221 or 211 charge structures were used in the broken roof and geological structure zones. During the driving and strong mining period, the roof and floor movement of the roof-cutting section of the roadway excavation was reduced by about 38% compared with the uncut section, and the deformation of the two sides of the roadway was reduced by about 44% compared with the uncut section. It shows that the collaborative control scheme of “roof-cutting pressure relief + anchor cable combined support” has a good effect on the roadway excavation driving of small coal pillars in strong mining. Full article

Many problems exist in the layout of working surfaces in high-gas mines, such as the low efficiency of roadway excavation, difficulties in maintenance after excavation, and serious resource wastes due to difficulties in recovering coal pillars between roadways. Taking the project profile in the west wing mining area of Sihe Coal Mine as the background, this work proposed an optimization plan for the staggered-layer arrangement of roadways. The minimum retained size of the coal pillar was calculated through theoretical analysis, and the plastic failure and deformations of surrounding rocks under different coal pillar sizes and roadway layouts were compared based on finite difference numerical simulations. The reasonable retained size of the coal pillar was determined to be 45 m, and the roadway layout was determined according to the distribution of coal and rock strata in the mining field. The technical measures of base angle pressure relief blasting and strengthening support were proposed to ensure the safety and stability of surrounding rocks of roadways during the service period after the layout plan was optimized. Similar simulation tests were used to study the damage deformations and stress changes of the blasting pressure relief floor. On-site tests showed that the optimized roadway layout greatly improved the recovery rate of coal resources. In addition, surrounding rocks had good stability, and they could be simply repaired or serve the next working surface directly without being repaired. These research results provide a scientific basis and useful reference for similar projects. Full article

In this paper, a Fiber Bragg Grating (FBG) stress sensor is developed to measure the stress variation between the lower Excavation Damaged Zone (EDZ) and the upper undistributed rock. The disturbance brought by the environmental temperature can be differentially compensated with two FBGs mounted symmetrically on the spokes. Through finite element analysis, it can be known that the direct stress and shear stress are pointed at the angles of 45° and 60° on both sides of the coal mine roadway, respectively. The anchor ends of the sensors are installed into the upper undistributed rock and the bolt tails of the mine roadway with a depth of 700 m and fastened by nuts to secure the load sensing device on the surface of the rock. When the shallow foundation of surrounding rock is pressed and deformed toward the coal mining road, the structural modifications can be converted into the stress of rock bolt and the strain of spoke. Thus, the FBG mounted on the surface of the spoke receives the shift information of the Bragg wavelength. The monitoring results indicate that the FBG stress sensors are sensitive to the variation of the EDZ. During the blasting, the stress amplitude varies from 40.256 to 175.058 kPa, and the creep time changes from 21 to 74 min. The proposed method can be applied in the field of underground coal mines for safety condition monitoring of the EDZ and forecasting the coal mine roadway stability. Full article

Excavation-damaged zones (EDZs) induced in underground mining and civil engineering potentially threaten tunnel safety and stability, and increase construction and support costs. In this paper, an investigation of the excavation damaged zone (EDZ) around roadways in Fankou lead-zinc mine in Guangzhou, China is performed by applying a seismic velocity method accompanied by SET-PLT-01 nonmetallic ultrasonic detector. Meanwhile, the in situ stress in the mining area was measured based on the stress relief method with the Swedish high-precision LUT system. The results indicate that the stress field is dominated by the maximum horizontal tectonic stress, and the extents of the EDZ on the roof-floor region are greater than that on the sidewall. In addition, both of the in situ stresses and EDZs show an increasing trend with an increase of depth. Analytical solutions of EDZ around circular openings in the brittle rock mass subjected to non-hydrostatic stress fields are presented in terms of the Mohr–Coulomb and generalized Hoek–Brown criteria, and validated by several cases mentioned above. The extents of EDZ solved by closed-form solutions were found to be in a great agreement with those obtained in the field. Finally, a series of parametric studies are conducted to investigate the effects of cohesion (c), friction angle (φ), geological strength index (GSI), m_i, uniaxial compressive strength (σ_c), and disturbance factor (D) on EDZ. It is shown that the effects of c, φ, GSI, and σ_c are significant; however, more attention should be paid to consider the dynamic disturbances induced by mechanical drilling, blasting, and seismic waves in tunnel excavations or operations. Full article