Stability Analysis of Surrounding Rock in Multi-Discontinuous Hydraulic Tunnel Based on Microseismic Monitoring

The diversion tunnel of a hydropower station is characterized by low quality surrounding rock and weak structural planes. During excavation, rock mass spalling and cracking frequently occur. To evaluate the stability of a rock mass during tunnel excavation, high-precision microseismic monitoring technology was introduced to carry out real-time monitoring. Based on the temporal and spatial distribution characteristics of microseismic events, the main damage areas and their influencing factors of tunnel rock mass were studied. By analyzing the source characteristic parameters of the concentration area of microseismic activities, the rock fracture mechanism of the concentration area was revealed. The 3D numerical model of diversion tunnel was established, and the deformation characteristics of the rock mass under the control of different combination types of weak structural planes were obtained. The results showed that the microseismic event was active between 29 October 2020 and 6 November 2020, and the energy release increased sharply. The main damage areas of the rock mass were located at Stakes K0 + 500–K0 + 600 m. Microseismic source parameters revealed that shear failure or fault-slip failure induced by geological structures had an important influence on the stability of the surrounding rock. The numerical simulation results were consistent with the microseismic monitoring results and indicated that among the three kinds of structural plane combination types, including “upright triangle”, “inverted triangle” and “nearly parallel”, the “upright triangle” structure had the most significant influence on the stability of the surrounding rock. In addition, the maximum displacement of the surrounding rock had a trend of lateral migration to the larger dip angle in the three combined structural plane types. The research results will provide significant references for the safety evaluation and construction design of similar tunnels.

A Practical Method for the Automatic Recognition of Rock Structures in Panoramic Borehole Image during Deep-Hole Drilling Engineering

Digital panoramic borehole imaging technology has been widely used in the practice of drilling engineering. Based on many high-definition panoramic borehole images obtained by the borehole imaging system, this paper puts forward an automatic recognition method based on clustering and characteristic functions to perform intelligent analysis and automatic interpretation researches, and successfully applied to the analysis of the borehole images obtained at the Wudongde Hydropower Station in the south-west of China. The results show that the automatic recognition method can fully and quickly automatically identify most of the important structural planes and their position, dip, dip angle and gap width and other characteristic parameter information in the entire borehole image. The recognition rate of the main structural plane is about 90%. The accuracy rate is about 85%, the total time cost is about 3 h, and the accuracy deviation is less than 4% among the 12 boreholes with a depth of about 50 m. The application of automatic recognition technology to the panoramic borehole image can greatly improve work efficiency, reduce the time cost, and avoid the interference caused by humans, making it possible to automatically recognize the structural plane parameters of the full-hole image.

Research on Search Method of Potential Sliding Surface of Rock Slope with Embedded Structural Plane

Slope stability has been a key issue in the field of geotechnical engineering. Determining the potential sliding surface of a slope is an important link in evaluating the stability of the slope. For rock slope with embedded structural plane, the potential sliding surface is greatly affected by the embedded structural plane. When determining the potential sliding surface, the influence of the position of the embedded structural plane should be considered. According to the distribution characteristics of the embedded structural plane of the rock slope, the structural plane in rock slope is divided into two types: (1) front embedded and (2) rear embedded structural plane. Considering the influence of two types of structural planes, a search method for potential sliding surfaces of rock slope is proposed combined with the finite random tracking method. The location of the sliding surface is controlled through the cut-in point, cut-out point, and arc height so that the range of search variables does not need empirical assumption. An engineering example is used to verify the search method. The results show that the method could accurately obtain the potential sliding surface of the rock slope with embedded structural plane, which proves the effectiveness of the search method.

Effects of External Dynamic Disturbances And Structural Plane On Rock Fracturing Around Deep Underground Cavern

The occurrence of disasters in deep mining engineering has been confirmed to be closely related to the external dynamic disturbances and geological discontinuities. Thus, a combined finite-element approach was employed to simulate the failure process of an underground cavern, which provided insights into the failure mechanism of deep hard rock affected by factors such as the dynamic stress-wave amplitudes, disturbance direction, and dip angles of the structural plane. The crack-propagation process, stress-field distribution, displacement, velocity of failed rock, and failure zone around the circular cavern were analyzed to identify the dynamic response and failure properties of the underground structures. The simulation results indicated that the dynamic disturbance direction had less influence on the dynamic response for the constant in situ stress state, while the failure intensity and damage range around the cavern always exhibited a monotonically increasing trend with an increase in the dynamic load (stress-wave amplitudes). The crack distribution around the circular cavern exhibited an asymmetric pattern, possibly owing to the stress-wave reflection behavior and attenuation effect along the propagation route. Geological discontinuities significantly affected the stability of nearby caverns subjected to dynamic disturbances, during which the failure intensity exhibited the pattern of an initial increase followed by a decrease with an increase in the dip angle of the structural plane. Additionally, the dynamic disturbance direction led to variations in the crack distribution for specific structural planes and stress states. These results indicate that the failure behavior should be the integrated response of the excavation unloading effect, geological conditions, and external dynamic disturbances.

Numerical Simulation and Analysis of Tunnel Failure Mode by Stochastic Fracture Model

The dip angle, length, spacing, and fracture distance of rock fissure affect the morphology of roadway after collapse. The numerical simulation software CDEM is used to simulate the morphology of roadway collapse. The Monte Carlo model is used to simulate different types of crack models in two-dimensional plane and generate different crack models. The effects of crack angle, crack length, fracture distance, and spacing on the deformation of surrounding rock are analyzed. The influence of different rock burst on the failure strap-fall modes of fissure roadway and roadway in different sections is analyzed, and the stability law of roadway is studied. Under the condition of high stress, the roadway shape has little influence on the distribution of the principal stress difference of surrounding rock, but the equivalent excavation radius determines the distribution of the plastic zone of surrounding rock. The larger the ineffective reinforcement zone is, the larger the deformation around the roadway will be. The decrease of the angle between the structural plane and the vertical stress increases the failure range of the roadway under the gravity burst pressure. Under the horizontal tectonic stress type rock burst, when the structural plane inclination angle is 0°, the two-sided caving body fills the roadway and the roof caving range becomes smaller.

Surrounding Rock Stability Control Technology of Roadway in Large Inclination Seam with Weak Structural Plane in Roof

The surrounding rock control technology of mining roadways in large inclination seams with a weak structural plane in the roof is one of the most challenging fields in underground roadway support. In view of the serious deformation of the surrounding rock of the transportation roadway in the 1201 working face of a mine, the deformation and failure characteristics and instability mechanism of the surrounding rock of the roadway are analysed. The self-stability mechanical model of the roof block structure of the roadway with a large inclination under the support effect is established, and the support concept of “high pre-stressed asymmetric” and the combined support method of bolts, wire mesh, and cables are proposed. The rationality of the supporting scheme is verified by numerical simulation. The results show that: compared with bolt and wire mesh support, the maximum shear displacement of the roof’s weak layer under the combined support of bolt, wire meshes, and cable before and after mining is reduced by 86.78% and 83%, respectively, and the maximum total displacement of surrounding rock surface is reduced by 49.22% and 37.1%, respectively. The field monitoring results show that the combined support scheme can effectively control the deformation of the surrounding rock.