Xiaofeng Qin’s research while affiliated with China University of Mining and Technology and other places

Anchored surrounding rock is prone to large nonlinear deformation and instability failure under dynamic disturbances. The fissures and defects within the surrounding rock make the rock mass’s bearing characteristics and deformation instability behavior increasingly complex. To investigate the effect of the fissure angle on the dynamic mechanical response of the anchored body, a dynamic loading model of the anchored, fissured surrounding rock unit body was established based on the finite difference–discrete element coupling method. The main conclusions are as follows: Compared to the indoor test results, this numerical model can accurately simulate the dynamic response characteristics of the unit body. As the fissure angle increased, the dynamic strength, failure strain, and dynamic elastic modulus of the specimen generally decreased and then increased, with a critical angle at approximately 45°. Compared to 0°, when the fissure angle was 45°, the dynamic strength, failure strain, and dynamic elastic modulus decreased by 17.08%, 15.48%, and 9.11%, respectively. Additionally, the evolution process of cracks and fragments shows that the larger the fissure angle, the more likely cracks are to develop along the initial fissure direction, which then triggers the formation of tensile cracks in other regions. Increasing the fissure angle causes the specimen to rupture earlier, making the main rupture plane more directional.

This work examines the effect of loading rate () on the mode III fracture behavior of sandstone. Edge‐notched diametrically compressed (ENDC) disc sandstone specimens were tested under different static and dynamic mode III fracture loadings, revealing a clear loading rate effect on both mode III and mode I fractures. Specifically, the peak load and fracture toughness ( K IIIC, K IC ) increase as the increases across both static and dynamic scales. At the static scale, the K IIIC is about 1.28–1.38 times of the K IC , whereas at the dynamic scale, the K IIIC is less than the K IC . The relationship between K IIIC and K IC is affected by the loading scale and the shape of the specimen, but the data collected thus far indicate that the origin and type of rock have minimal effect on this relationship. In addition, the fracture surface morphology characteristics were quantitatively analyzed.

Coal mining has gradually entered the deep mining era, and large-height mining is an important way to mine thick coal seams in the deep. The high coal wall will inevitably make the distribution of the overburden structure in the coal mining face more complicated, and the large buried depth will also cause more intense mine pressure. The study of the distribution and evolution of the overburden structure and stress in the mining site can provide theoretical guidance for safe mining. In this work, a physical similarity modeling test was carried out based on the physical–mechanical parameters of overburden rock and similarity theory, taking the mining of a deep, large-height working face in Pingdingshan Coal Mine as an example. The results show that the deformation and breakage of overburden rock in deep, large-height workings occurring during mining is persistent and not only in a short period of time. The breakage form of overburden can be categorized into two types based on the deformation characteristics: (I) non-separation-induced type, and (II) separation-induced type. Among these, the breakage induced by separation can be divided into two categories: (i) dominated by self-weight stress, and (ii) affected by shear cracks. It also summarizes the form of the overburden structure and the structural morphology of the stope. The overburden structure shows a “combined cantilever beam structure-articulated rock-slab structure-non-articulated rock-slab structure”. Among these, the periodic breakage of the upper cantilever beam evolved articulated and non-articulated rock-slab structure in the lower part, which weakened the supporting effect of the lower gangue and further aggravated the breakage of the upper overburden rock. The shape of the main structure of the stope mainly depends on the fracture line from the advancing coal wall to the upper overburden: from a rectangular shape without collapse to a trapezoidal shape at the initial stage of collapse, to a trapezoidal shape with multiple steps after the main roof collapse.

Due to the influence of the ground stress, mining disturbance, and other factors, the roadway surrounding rock in deep underground engineering such as mines, tunnels, and underground caverns is prone to looseness and deformation with the excavation of roadways. In such engineering, the bolt support is frequently employed to stabilize the surrounding rock. In this work, a part of the anchor and the surrounding rock were taken as a simplified model of the anchorage rock mass, and the laboratory compression test was performed on the similitude model. Then, the FLAC3D software was used to simulate varying numbers of bolts and different lateral pressure conditions, and the peak stress, the maximum principal stress field, and the anchor stress field distribution of the anchorage rock mass were obtained. The influence of bolt pretightening force and row spacing on the stability of surrounding rock was discussed using the combined arch theory. The results show that increasing the number of bolts and lateral pressure in the anchorage rock mass can significantly improve the stress value and distribution range of the maximum principal stress field and the anchorage stress field. The fluctuation of the anchorage stress field at different anchorage distances can be lessened by increasing the number of bolts (bolt density). When the lateral pressure exceeds 3 MPa, the anchorage mechanical characteristics of the anchorage rock mass tend to remain stable. The coverage of the effective anchorage stress field and the thickness of the surrounding rock anchorage composite arch can be increased by increasing the bolt pretightening force and decreasing row spacing, consequently improving the anchorage mechanical characteristics of the anchorage rock mass. The research results can be used as a theoretical reference for choosing appropriate bolt support parameters for the roadway surrounding rock.

In the process of deep underground resource development and utilization, the surrounding rock mass is not only affected by high temperatures, but also dependent on the dynamic stress environment. In this paper, the dynamic impact loading tests were carried out on the cracked straight-through Brazilian disc (CSTBD) granite specimens after heat treatment using the spilt Hopkinson pressure bar (SHPB) system. The effects of temperature and loading mode on the dynamic fracture toughness, fracture growth path, strain distribution, and fracture angle were analyzed. The results showed that, the fracture toughness of CSTBD granite specimen under dynamic loading decreases gradually as the mixed coefficient increases. The pure mode II fracture toughness is linearly related to that of pure mode I. High temperatures shows a negative effect on the fracture property of granite. Dynamic fracture toughness decreases with the increase of temperature, first gently (25∼400 °C) and then sharply (400∼800 °C). Under dynamic loading, the main crack initiates from the pre-crack tip, accompanied by obvious strain concentration, and then extends gradually to the loading end. The fracture angle of the main crack presents a generally increasing trend with the increase in loading angle, but is not closely related to the temperature of heat treatment.

It is of great significance to study the fracture and deformation characteristics of rock with different moisture conditions for the safety assessment of “fragile surface with cracks” in rock engineering such as dams and underground chambers affected by groundwater. Therefore, in this work, three-point bending tests were conducted on single-edge notched beam sandstone specimens with different moisture conditions (natural condition, dried condition, and saturated condition) under complex stress environment. Additionally, the digital image correlation (DIC) method was used to quantitatively research the fracture parameters and deformation behavior of specimens during pure mode I fracture and mixed mode I-II fracture. The results show that (1) the average peak load of dried sandstone is 42.18-116.08% higher than that of saturated sandstone. (2) By increasing the offset distance of the pre-notch (0-72 mm), the specimen is transformed from pure mode I fracture to mixed mode I-II fracture, with an increase in average peak load of 152.83%-284.24%. (3) When the pure mode I fracture occurs in saturated sandstone, the fracture toughness is 66.74% of that natural sandstone, which is 46.28% of that dried sandstone. (4) In the mixed mode I-II fracture, the effective fracture toughness of sandstone with a consistent moisture condition is 1.05-1.70 times that of the pure mode I fracture. (5) The fracture toughness of saturated sandstone is most significantly affected by the loading mode. When the offset distance of pre-notch increases from 0 to 72 mm, the average effective fracture toughness increases from 4.324 MPa·mm0.5 to 7.357 MPa·mm0.5, increasing by 70.14%. Besides, according to the trend of the ap, which was calculated by the DIC method, the post-peak macroscopic crack propagation is divided into two stages: the post-peak stable propagation stage and the post-peak unstable propagation stage.