Failure Modes Of Rock Slopes Research Articles

Numerical Investigation on Dynamic Response and Failure Modes of Rock Slopes with Weak Interlayers Using Continuum-Discontinuum Element Method

In order to better understand the dynamic response and failure modes of rock slopes containing weak interlayers subjected to earthquake excitation, a series of numerical simulations were carried out using the continuum-discontinuum element method (CDEM), considering the influence of seismic amplitude and weak interlayers inclination. The seismic response characteristics of slopes were systematically analyzed according to the waveform characteristics, amplification effect, equivalent crack ratio, etc. The numerical results show that the acceleration waveform characteristics and peak ground displacement (PGD) amplification coefficient have good correspondence with the dynamic failure process of landslides. Comprehensive analysis of waveform characteristics and PGD amplification coefficient can determine the damage time, damage location, and damage degree of landslides. The landslide process can be divided into three stages according to the equivalent crack ratio: rapid generation of a large number of microcracks, expansion and aggregation of microcracks, and penetration of micro-cracks and the formation of slip surfaces. The equivalent crack ratio provides a new idea for evaluating slope stability. In addition, under the combination of different amplitudes and weak interlayers, these earthquake-induced landslides exhibit different failure modes: the failure of the gentle-dip slope is mainly local rockfall; The mid-dip and steep-dip slopes with small amplitudes experience “tensile cracking-slip-collapsing” failure; The steep-dip slopes under strong earthquake failed in the form of “tensile cracking-slip-slope extrusion-collapsing”. The research results are of great significance for a deeper understanding of the formation mechanism of rock landslides with weak interlayers and the prevention of such landslide disasters.

Anchorage design analysis and field monitoring of large key blocks in high and steep rock slope

One of the main failure modes of rock slope is the instability of the key block formed by cutting combination of structural planes. In view of the block stability and control problem caused by the combination of structural planes in the high and steep rock slope in Southwest China, the key block theory method and on-site monitoring method are used to study the stability of the key block after the excavation of the slope, the optimization of the design parameters of anchor cable support, and the deformation characteristics and change laws of the slope with the construction process are analyzed. The research results show that the large block formed by the discontinuity layer and layer fracture of the slope reaches 26000 m3, sliding along the structural plane on both sides, with low safety factor. The safety monitoring data show that the block is stable after the reinforcement with anchor cable.

Research on the deformation and failure mode of rock slope with multiple locking segment failure characteristics

Landslides are the most critical types of geological disasters in China, seriously threatening the safety of life and property of the inhabitants in the surrounding areas. Most landslides in China are large and giant rock landslide slope failures of large and giant rocks. Brittle failure of multiple locking sections usually accompanies rock slope failure. The locked section is significant for the early identification of rock slopes, slope deformation control, and slope failure prevention. This study uses the ground-based synthetic aperture radar technology to obtain the surface deformation data of the entire process of slope failure. By analyzing the development law of slope surface deformation before landslide failure, the dynamic process and evolution model of the time–space evolution of slope deformation and failure are proposed. The finding of the research shows that the deformation time-series curve of slope failure with multiple locking sections completely differs from the typical three-stage theory of slope failure deformation with creep characteristics. The failure process of each locking segment before the failure of the critical locking segment is accompanied by the transverse expansion of the shear failure of the sliding surface and the pulling failure of the trailing edge. After the failure of the last key-locking section, the final landslide failure will be formed. The entire process is a process of energy accumulation and downward movement, manifested by the stage displacement of the sliding mass, the mixed deformation characteristics of oscillation, and rising trend of the monitoring curve. Based on the characteristics of the entire surface deformation data in the landslide failure process, the research results prove the typical failure mode of rock slope with three sliding-tension cracking-shearing sections. The research results are critical in identifying the failure mode, analyzing slope stability, predicting landslide failure, and judging the scale of the landslide.

Investigating the Effect of Rock Bridge on the Stability of Locked Section Slopes by the Direct Shear Test and Acoustic Emission Technique.

As a portion of intact rock separating joint surfaces, rock bridge plays a significant role in the stability of rock slopes. This paper aims to investigate the effect of different rock bridges on the mechanical properties and failure mode of rock slope by means of the direct shear test and acoustic emission technique. Field conditions were simulated in direct shear tests which were carried out on specimens with rock bridges at different continuity rates, normal stress, arrangements, and joint angles. Experimental results indicate that the strength of specimens is controlled by the rock bridge and the structural plane. The rock bridge contributes to the strength of the specimen, while the through plane weakens the strength of the specimen. The increase of normal stress can weaken the stress concentration near the tip of the rock bridge and improve the shear resistance of the specimen. The different arrangement of rock bridge has little effect on the normal displacement of the specimen, and has a great influence on the shear strength. The shear capacity of the specimen is related to the angle of the crack, and the angle of the crack is approximately proportional to the peak shear strength. For the specimens with different joint occurrence, the mode of crack propagation at the initial stage is basically the same, and the specimen is finally damaged due to the generation of through cracks in the core area of rock bridge. The instantaneous release of the huge energy generated during the experiment along the shear direction is the root cause of the sudden failure of the rock bridge. The formation, aggregation, and transfixion process of rock bridge is of concern and has been experimentally investigated in this paper for the prevention and control of the locked section rock slope with sudden disasters.

Asperity degradation characteristics of soft rock-like fractures under shearing based on acoustic emission monitoring

Shear failure of rock masses along pre-existing discontinuities is one of the predominant failure modes of rock slopes and underground tunnels. The monitoring and prediction of the impending shear failure is of great significance to ensure the stability of the rock structures and the safety of the workers. In this study, direct shear tests under normal stress ranging from 0.5 to 10 MPa are conducted on rock fractures (analogous to soft rock discontinuities), which are obtained by artificial splitting, during which the AE parameters are monitored. Test results show that the AE parameters (hit, energy and events) increase with the shear stress, and peak at or near the peak shear strength, after which the AEs gradually decay with the decrease of shear stress. The number of AE events first increases and then decreases with increasing normal stress, which may be associated with the ductile deformation of the porous structure of cement mortar under higher normal stress. The degradation of asperities on the fracture surface can be inferred from the accumulative AE hits and events, which are characterized by “S” shapes and can be divided into slow growth, fast growth and slow growth stages. Conceptual and mathematical asperity damage models are proposed respectively based on the temporal characteristics of AE events and the curve fitting, which can be used to predict the asperity damage for a given shear stress curve. The AE b-value fluctuates and remains high in the shear process. There is no strong correlation between the shear stress and the b-value, which indicates that the b-value may not be an effective index to predict the quasi-static shear failure of jointed rock masses possessing similar properties like cement mortar. Results of this study will not only contribute to a better understanding of the asperity degradation characteristics but also provide valuable knowledge for AE monitoring applications in jointed rock masses.

Experimental study on vibration instability model of rock slope based on parallel chaotic algorithms

Abstract In view of the irrationality of sensor arrangement scheme in the model test method of anti-dip rock slope vibration instability, the accuracy and efficiency of test data acquired are reduced, which cannot meet the requirements of real-time vibration simulation process. There are some limitations in the authenticity and scientificity of test results. A model test of rock slope vibration instability based on parallel chaotic algorithm is proposed. The method uses cement, sand, iron powder, clay and admixture to prepare rock mass materials, sets Teflon cloth with very low surface friction coefficient to simulate discontinuous joints of rock slope according to certain rules in the interior of slope, and adopts parallel chaotic genetic algorithm to optimize sensor placement scheme based on the corresponding relationship between algorithm and optimal parameters of sensor placement. The experimental results show that the failure modes of rock slope under vibration are as follows: crack development, slope spalling and collapse sliding; acceleration response enlarges obviously along the slope face, and horizontal acceleration dominates; the optimization effect and operation time of sensor placement scheme are significantly improved to avoid premature convergence and fall into local optimum solution.

Research on the Influence of Interconnectivity Structure Parameters to Stability of Stratified Rock Slope

Based on the slope engineering of the expansion project from Laiwu to Linyi section of Beijing-Shanghai Expressway, this paper uses numerical simulation method and strength reduction theory to analyze the change law of stability and failure mode of rock slope under the change of structural plane inclination, cohesion and internal friction angle. The results show that: with the increase of structural plane inclination, the change law of the failure mode of the bedding layered slope is pull-bedding slip→shearing-slip→toppling failure; The change rule of the failure mode of the inverse-dip layered slope is from shearing-slip to toppling-slip; the stability of bedding layered slope and inverse-dip layered slope with steep structural plane inclination are increased with the growth of the structural plane cohesion, while the safety factors of the inverse-dip layered slope with a small structural plane inclination have no significant changes. The stability of bedding layered slope increases with the growth of the structural plane friction angle, while the inverse-dip layered slopes have obvious differences trend between steep and gentle structural plane inclination. The research can provide reference for similar projects.

Geostructural stability assessment of cave using rock surface discontinuity extracted from terrestrial laser scanning point cloud

The use of terrestrial laser scanning (TLS) in the caves has been growing drastically over the last decade. However, TLS application to cave stability assessment has not received much attention of researchers. This study attempted to utilize rock surface orientations obtained from TLS point cloud collected along cave passages to (1) investigate the influence of rock geostructure on cave passage development, and (2) assess cave stability by determining areas susceptible to different failure types. The TLS point cloud was divided into six parts (Entry hall, Chamber, Main hall, Shaft 1, Shaft 2 and Shaft 3), each representing different segments of the cave passages. Furthermore, the surface orientation information was extracted and grouped into surface discontinuity joint sets. The computed global mean and best–fit planes of the entire cave show that the outcrop dips 290° with a major north-south strike. But at individual level, the passages with dip angle between 26° and 80° are featured with dip direction of 75°–322°. Kinematic tests reveal the potential for various failure modes of rock slope. Our findings show that toppling is the dominant failure type accounting for high-risk rockfall in the cave, with probabilities of 75.26%, 43.07% and 24.82% in the Entry hall, Main hall and Shaft 2, respectively. Unlike Shaft 2 characterized by high risk of the three failure types (32.49%, 24.82% and 50%), the chamber and Shaft 3 passages are not suffering from slope failure. The results also show that the characteristics of rock geostructure considerably influence the development of the cave passages, and four sections of the cave are susceptible to different slope failure types, at varying degrees of risk.

A discussion on the adjustment parameters of the Slope Mass Rating (SMR) system for rock slopes

Rock mass classification systems are common tools used in the design and construction of rock engineering. Numerous classification systems have been developed for rock slopes, of which the Slope Mass Rating (SMR) system is the most popular. Consequently, many rock slope classification systems have been derived from the SMR system. However, these systems are not good at determining the values of the two adjustment parameters F1 and F3, implying that the original SMR system may contain theory defects. In this paper, we propose some corrected methods for determining F1 and F3 and perform a series of analyses considering the three failure modes of rock slopes: plane, wedge, and toppling failures. The results of the discrepancy analysis from F1 illustrate that, with respect to each of the aforementioned three failure modes the calculated original SMR index is larger than, or equal to, the real value, and the designed slope is possibly in danger. The results of the discrepancy caused by the F3 illustrate that for each of the aforementioned three failure modes, the calculated original SMR index is smaller than, or equal to, the real value, and the designed slope might be conservative and not economical.

Effect of rock mass structure and block size on the slope stability

This paper studies the stability of jointed rock slopes by using our improved three-dimensional discrete element methods (DEM) and physical modeling. Results show that the DEM can simulate all failure modes of rock slopes with different joint configurations. The stress in each rock block is not homogeneous and blocks rotate in failure development. Failure modes depend on the configuration of joints. Toppling failure is observed for the slope with straight joints and sliding failure is observed for the slope with staged joints. The DEM results are also compared with those of limit equilibrium method (LEM). Without considering the joints in rock masses, the LEM predicts much higher factor of safety than physical modeling and DEM. The failure mode and factor of safety predicted by the DEM are in good agreement with laboratory tests for any jointed rock slope.

均質岩盤斜面の崩壊過程に関する数値解析的検討

The knowledge for the failure process of rock slope is of fundamental importance to asses the slope stability.In this paper, a numerical procedure to analyze the failure process of rock slope by the Displacement Discontinuity Method (DDM) is proposed, then the failure process and the failure mode of homogeneous rock slope are discussed.In the numerical analysis, the rock slope is modeled as the elastic material and the process of crack initiation and crack propagation is analysed by DDM. The cohesion of the crack surfaces is treated to be dependent on the displacement discontinuity of the crack. It is made clear that the failure process and the failure mode of rock slope is closely connected with the strength characteristics of the crack surfaces as well as the slope angle by demonstrating the numerical results. It is shown that the slope failure occurs by connecting the conjugated shear cracks, in the case that the critical value of crack shear displacement (CSD) is relatively small. On the other hand, the tensile fracture occurs at the crack tip of the shear crack plays an important role in progressing the slope failure, in the case that the critical value of CSD is relatively large.The critical value of stability factor obtained by the present analysis agrees with the experimental value reported by OKAMURA et al., but dose not with that obtained by the conventional limiting equilibrium analysis.It is pointed out that the influence of the slope angle on the slope stability is less than that predicted by the conventional limiting equilibrium analysis, although the critical value of stability factor increases with decreasing the slope angle.

石灰石鉱山における長大残壁の安定性評価へのブロック理論の適用

Rock slopes left after surface mining in limestone quarry grow gradually larger and higher year after year. Recently, the stability evaluation of these large rock slopes has become an important engineering problem.Rock mass contains many discontinuous planes, such as joint, fault, etc, and the failure mode of rock slope is usually influenced by the geometrical conditions of the discontinuous planes.The block theory is the way to analyze three dimensional stability problems of discontinuous rock masses. In this theory, the critical block is named as the key block, and its character is defined by a topological concept. After the judgement of the key block, it is possible to determine the most suitable way to support these blocks.This paper describes the valid way of treating trace map including many discontinuous planes in order to find out the key block by vector calculation, and applies to stability evaluation of large rock slopes for three limestone quarries.