Instability Mode and Movement Characteristics of Dangerous Rock Body in Steep Rock Slope

The cutting relationship and development degree of structural plane control the instability mode and scale of rock slope. The trajectory of rock mass after instability is an important basis for the design of dangerous rock prevention. The back slope of a residential area was investigated in this paper. Based on the survey data of the field structure surfaces, the possible instability mode of the slope rock mass was analyzed by using the stereographic projection method. The shear strength parameters of the rock mass were inverted through the investigation of dangerous rock mass. Finally, ANSYS/LS-DYNA was used to simulate the dangerous rock mass motion trajectory. This study provides a reference for the analysis of the instability process of single rock.

Stability Assessment of Dangerous Rock Mass of an Overhanging Slope in Puerdu Town, Southwestern China

Dangerous rock mass in the overhanging slope of Puerdu town has good free-face condition, high position, and great potential energy, identification and stability evaluation of which is a difficult problem in the disaster prevention. In this paper, the limit equilibrium method was used to evaluate the dangerous rock mass stability in the overhanging slope. Firstly, geomorphic characteristics and the distribution of dangerous rock mass are determined by the field geological survey. Secondly, six dangerous rock masses which may cause more threat are studied, with defining their failure modes and characteristic parameters. Finally, a simplified geological model is established, the stability coefficient of dangerous rock mass under different conditions is calculated by the limit equilibrium method, at the same time, stability analysis of dangerous rock mass is carried out based on the stereographic projection, and the hazard probability is estimated by the empirical formula. Results show that joints obviously developed in the dangerous rock mass of W1, W2, W3, W4, W5, and W6, with falling-type and toppling-type failure modes. In the natural condition, the dangerous rock mass is understable and unstable under the rainstorm and earthquake conditions. Consequently, rainstorm and earthquake are the key triggering factors of the instability and collapse of dangerous rock mass.

Trajectory Analysis and Risk Evaluation of Dangerous Rock Mass Instability of an Overhang Slope, Southwest of China

Analysis of the movement trajectory and risk assessment of the high-slope dangerous rock mass collapse are of great significance for preventing and controlling the geological disasters of collapse. This study firstly takes the dangerous rock mass of the high slope in Pu’erdu Town, Yanjin County, Zhaotong City, Yunnan Province, as the research object, calculates and analyzes the trajectory of collapse movement of several groups of dangerous rock mass with great threat, and RocFall are used to carry out numerical simulation analysis and verification. Secondly, the risk and vulnerability of the dangerous rock mass in the study area are analyzed, and the risk evaluation is carried out through the risk evaluation matrix to clearly define the risk level. Results show that if the dangerous rock mass collapses, the horizontal movement distance was approximately 53–88 m, and the maximum bounce height of the platform was approximately 3–18 m, which will seriously threaten the life and property safety of residents. There is little difference between the simulation of the collapse of dangerous rock mass by RocFall software and the calculation result of the formula. Although RocFall software is more intuitive and can be directly compared with charts, software cannot completely simulate the actual situation, and it is only suggested as a reference from design rather than a basis of design. The result of risk evaluation shows that there are 2 high-risk dangerous rocks, 3 medium-risk dangerous rocks, and 1 low-risk dangerous rock in this area. It is suggested that a reasonable and scientific engineering treatment scheme should be put forward as soon as possible in combination with the collapse trajectory of the collapsing movement.

Calculation Method of Bonding Section of Joint Surface of Dangerous Rock Mass Based on Amplitude Ratio

In this study, through an analysis of vibration response characteristics of joint surface stiffness on dangerous rock mass, the relationship formula between amplitude ratio of the dangerous rock mass to the bedrock and the length of the bonding section of the joint surface is determined. The stability of the rock mass can be evaluated by combining the formula with the existing rock-mass limit equilibrium theory. This study proposes the existence of a resonance bonding length for the dangerous rock mass. When the length of the bonding section reaches the resonance bonding length, the dangerous rock mass has the largest response to the bedrock vibration. The study found that when the length of the bonding section of the dangerous rock mass is longer than the resonance bonding length, the amplitude ratio increases with the decrease of the bonding section and increases with the increase of the vibration frequency of the bedrock. When the length of the bonding section of the dangerous rock body is shorter than the resonance bonding length, the amplitude ratio decreases with the decrease of the bonding section and decreases with the increase of the vibration frequency of the bedrock. Indoor experiments were conducted by collecting the vibration time-history curves of rock blocks and stone piers and performing analysis and calculation, which proved the accuracy of the analytical results. Through the amplitude ratio of the dangerous rock mass and the bedrock, the bonding length can be calculated. This method can improve the calculation accuracy of the stability coefficient K of the dangerous rock mass.