Excavation Of Rock Slope Research Articles

Automatic interpretation of geometric information of discontinuities and its influence on the stability of highly-jointed rock slopes

The discrete fracture system of a rock mass plays a crucial role in controlling the stability of rock slopes. To fully account for the geometric shape and distribution characteristics of jointed rock masses, terrestrial laser scanning (TLS) was employed to acquire high-resolution point-cloud data, and a developed automatic discontinuity-identification technology was coupled to automatically interpret and characterize geometric information such as orientation, trace length, spacing, and set number of the discontinuities. The discrete element method (DEM) was applied to study the influence of the geometric morphology and distribution characteristics of discontinuities on slope stability by generating a discrete fracture network (DFN) with the same statistical characteristics as the actual discontinuities. Based on slope data from the Yebatan Hydropower Station, a simulation was conducted to verify the applicability of the automatic discontinuity identification technology and the discrete fracture network-discrete element method (DFN-DEM). Various geological parameters, including trace length, persistence, and density, were examined to investigate the morphological evolution and response characteristics of rock slope excavation under different joint combination conditions through simulation. The simulation results indicate that joint parameters affect slope stability, with density having the most significant impact. The impact of joint parameters on stability is relatively small within a reasonable range but becomes significant beyond a certain threshold, further validating that the accuracy of field geological surveys is critical for simulation. This study provides a scientific basis for the construction of complex rock slope models, engineering assessments, and disaster prevention and mitigation, which is of great value in both theory and engineering applications.

Experimental Study on Creep Characteristics of Unloaded Rock Masses for Excavation of Rock Slopes in Cold Areas

Seasonal freeze–thaw environments are one of the key factors that aggravate the mechanical strength decay of excavated and unloaded rock masses on reservoir banks in cold areas. To study the time-dependent mechanical properties of an excavated and unloaded rock mass on a bank slope under freeze–thaw action, triaxial unloading tests were carried out on sandstone, freeze–thaw tests simulating freezing strength were conducted, and triaxial creep tests were implemented with graded incremental loading on unloaded specimens subjected to freeze–thaw action. The test results showed that the total deformation of the unloaded specimens is significantly increased compared with the conventional specimens, and the lateral direction is more likely to produce creep behaviour than the axial direction. The level of confining pressure determines the level of creep deformation of unloaded specimens and affects the variation law of creep rate. The creep behaviour of the unloaded specimens is aggravated by freeze–thaw action and, the longer the freezing period, the larger the creep strain share, and the creep rate increases significantly. The creep damage pattern of the unloaded specimens subjected to freeze–thaw action is mainly manifested as shear damage, and the creep process intensifies the derivation of tension-type cracks in the specimens. The higher the confining pressure of the unloaded specimen, the more obvious the plastic characteristics and the weaker the brittle characteristics during creep failure. The freeze–thaw action significantly reduces the long-term strength of the unloaded specimen, which is approximately 50~55% of the instantaneous strength. The long-term strength decays significantly with an increasing freezing period, and the research results can provide a theoretical reference for the evaluation of the long-term stability of excavated and unloaded rock masses in cold areas.

Discussion on blasting vibration monitoring for rock damage control in rock slope excavation

Discussion on blasting vibration monitoring for rock damage control in rock slope excavation

Effect of confining pressure on damage accumulation of rock under repeated blast loading

In-situ stress has complex impacts on the blasting excavation of rock mass, but the effect of confining pressure on the crack propagation under repeated blast loading is still unclear. This study investigated the effect of confining pressure on blasting damage through theoretical, experimental and numerical analyses. First, the stress distribution around blasthole under static loading was theoretically analyzed. Then, the parameters of Riedel-Hiermaier-Thoma (RHT) model were determined and validated by repeated blast tests. The effect of confining pressure on the failure mode of granite sample was included. Finally, pre-split blasting of rock slope was numerically simulated to explore the failure behaviors of rock mass under in-situ stress conditions. The numerical results indicate that the RHT model can well reproduce the tensile failure behavior and dynamic crack propagation of granite sample. Confining pressure significantly changes the failure mode of granite sample and the blast-induced cracks mainly propagate along the direction of maximum principal stress. Repeated blast loading has little contribution to rock breakage in the direction of minimum principal stress. The pre-split blasting technology can considerably improve the stability of remaining rock mass in the blasting excavation of rock slope. A plum-blossom-shape arrangement of blastholes and delayed initiation of production holes can promote the quality of blasting operations under pre-stress conditions.

A comparison between SMR and SSPC classification systems for the assessment of rock slope stability in the context of Pelotas Batholith, Canguçu, Rio Grande do Sul, Brazil

Rock mass classifications are a simple yet useful tool to provide a practical assessment of rock slope stability. Among the available classifications for this purpose, Slope Mass Rating - SMR (Romana, 1985) is the most commonly used. It is based on the basic Rock Mass Rating - RMR (Bieniawski, 1989) and on adjustment factors related to the geometry and method of excavation of rock slopes. While SMR is a discrete method, the Slope Stability Probability Classification - SSPC (Hack et al., 2002), a less-known classification, is a probabilistic one. SMR gives better results when applied to structural-controlled rock masses, while SSPC provides solutions for both structural-controlled and nonstructural-controlled rock masses. The aim of this study was to assess the stability of cutting slope sections by SMR and SSPC along a BR-471 Highway segment, in Canguçu, state of Rio Grande do Sul, Brazil. The chosen area lies in the Pelotas Batholith, a 400 km-length unit, whose geometry and structures are regionally controlled by transcurrent shear zones. The location is characterized by a subtropical climate with high humidity and rainfall along the year. The analysis showed that the rock mass is structural-controlled, and many of the sections analyzed present stability problems. Comparing the methodologies applied, SMR indicates ten geotechnical zones as unstable or completely unstable, while SSPC indicates six unstable ones, which are all related to sliding failure, including both planar and wedge failures. Both methods applied showed good results. Yet, adjustments regarding the original criteria have real potential to improve further analyzes in the area. For SMR, the main suggestions include: adjustment of kinematic analysis weight in comparison to the weight of RMRb features, adjustment of weathering grade weight in relation to IRS, and inclusion of weight for large scale roughness. The suggestions for SSPC regarding structural-controlled stability are: adjustment of the susceptibility to weathering weight, focusing on the weathering of discontinuities, and the inclusion of the effect of water percolation.

Testing Method for the Range of Fracture Zone of Rock Slope under Blasting Load

In engineering blasting, the determination of the range of rock blasting fracture zone has important guiding significance for blasting construction. This paper proposes a method that can accurately and directly obtain the range of rock blasting fracture zone. Based on the theory of elastic wave propagation, test rods which are made of appropriate material are selected and prepared. A certain number of boreholes are drilled for subsequent insertion of the test rods along the direction perpendicular to the free surface of the excavation at a certain distance from the blast hole. Based on the field blasting test results, the deepest fracture position of the test rod is used as the boundary of the blasting fracture zone, and the range of the rock blasting fracture zone is obtained. A numerical analysis model is established according to the Mohr–Coulomb constitutive relationship and the Von Mises yield criterion. Then, the range of the fracture zone and the maximum horizontal radius of the fracture zone are analyzed and obtained. The numerical analysis results are compared with the field measured data. It is demonstrated that the range of the fracture zone obtained by the numerical simulation is in good agreement with the blasting test results of the pre‐embedded test rods. The research results can provide references for the safety control of blasting and excavation of rock slopes.

Blasting cushion pad of reducing vibration start a new era of decreasing disaster in civil and mining engineering explosion with micro-damage

Millisecond delayed blasting has been widely used in reducing vibration of engineering blasting practice before. Pre-splitting blasting has been widely used in reducing vibration of rock slope excavation by blasting up to now. There was still damage to surrounding rock by millisecond delayed blasting and pre-split blasting even smooth blasting. The recurrent blasting vibration will produce cumulative damage to surrounding rock mass of underground and rock slope engineering, even induce rock mass fracture, collapse, roof fall or instability landslide . The damage area is much larger than the blasting excavation area, so rock mass would be damaged several times and result in accumulative damage. Not only the disturbance of single blasting on the surrounding rock should be controlled during blasting construction of anchorage roadway or tunnel, but the emphasis should be put on the accumulative vibration effect of surrounding rock induced by frequent circle short-distance blasting and the corresponding control measures should be taken. This paper introduces a cushion pad which has simple structure and is easy used in blasting engineering. This device can not only avoid large amount of cracks on the rock slope and cumulative damage to surrounding rock mass and rock mass of engineering to instability induced after blasting, but also cushion and hold up at large extent heavy detonation shock after blasting. It is first used in Panzhihua Xujiagou iron open pit, Huayinshan coal mine with gas in SiChuan province, Miaowei hydropower station in Yunnan province and Minshui tunnel blasting engineering in Xin-Fen highway in Hebei-Shanxi province. It effectively cushion the heavy detonation shock from explosion avoiding the damage surface of surrounding rock and accumulated damage of rock, thus improve stability of rock mass and save a large amount of support costs. The vibration velocity with cushion is 50% less than with pre-splitting blasting, even less than the threshold of blasting vibration accumulated damage. Ratio of semi--hole archive 95%. Achieve China patent, the number: ZL 201220107888.5, ZL201220230579.7, ZL 201220750552.0., ZL 201220016697.8.

Rock slope stability along road cut of Kulikawn to Saikhamakawn of Aizawl, Mizoram, India

Landslide is a natural hazard which carries water, mud, debris and sometimes large boulders. Earthquakes, heavy rainfall and tectonic forces are natural responsible factors for landslides, whereas overpopulation and rapid development in the hilly region are unnatural factors which involve human activities such as construction/maintenance of roads, highways, railways and buildings by the unplanned excavation of rock slopes. Both natural and unnatural factors have been accountable for the increase in the probability of landslides in the past few decades. In the present study, stability analysis of rock slopes has been carried out along Kulikawn to Saikhamakawn road section of Aizawl. Kinematic analysis has been performed to identify the road cut slopes which have the potential to fail, and mainly two types of failures were found, i.e., wedge and topple failure. In order to check the stability of road cut slopes, Geological Strength Index, slope mass rating (SMR) and continuous slope mass rating (CoSMR) have been used in this study. Numerical modelling has also been performed to assess the stability of the road cut slope. The maximum displacement of 0.79 m with a maximum velocity of 0.78 m/s has been found for rock slope at location L1 using numerical modelling which confirms the finding from kinematic analysis, SMR and CoSMR analysis.

Bayesian updating for progressive excavation of high rock slopes using multi-type monitoring data

Systems for monitoring the deformation and stress conditions of excavated high rock slopes are usually implemented for safety reasons and to predict the stability of future works. This paper adopts Bayesian methods for updating important geomechanical parameters namely: E(III1), E(III2), E(IV2), E(f8), c(III1), c(III2), c(V1) and c(f8) in these types of cases. The proposed method utilizes parametric sensitivity analysis, the BP neural network (back propagation neural network), and Bayesian updating to effectively reduce the number of variables, improve the computational efficiency and gradually update the random variables by using progressive monitoring information. The high rock slope excavation on the left bank at the Lianghekou Hydropower Station in China is illustrated as a detailed case study. Initially, only one type of measurement is first used for Bayesian updating (measured displacements or anchorage forces), and then both types of measurements are used. Compared to using only one type of measurement, the parameter uncertainty is reduced and the model accuracy is improved when both types of measurements are employed.

Reliability Analysis of Rock Slope Excavation Considering the Stochasticity and Finite Persistence of Wedges

With a focus on wedge failure during rock slope excavation and considering stochasticity and finite persistence based on a stochastic structural-plane network simulation and Lajtai’s rock resistance criteria, we present a simplified method combined with binary particle swarm optimization (BPSO) to calculate the shear strength of 3D rock masses. The probabilities of rock slope failure under excavation surfaces of various sizes were obtained using the Monte Carlo method. These probabilities can provide a theoretical basis for determining excavation stability. The approach was applied to a rock slope excavation project in Chongqing, China, and yielded satisfactory results.

Real-Time Assessment of Blasting Damage Depth Based on the Induced Vibration During Excavation of a High Rock Slope

Abstract Blasting is a major means for excavation of rock slope, and the blast-induced damage to reserved rock mass must be strictly limited to ensure safety of the high slope and reduce the cost for support. As a traditional and widely used technique, the sonic wave testing is usually adopted to detect the extents of blasting damage, but the workload of detecting is considerably heavy during excavation of large-scale rock slopes with a height of several hundred meters. Thus, a simple but efficient method of blasting damage assessment based on comprehensive vibration survey was presented in this paper. In total, 5 bench blasting experiments were conducted at the excavation site of the left dam-abutment slope of the Bai-he-tan Hydropower Station in southwestern China. A semi-empirical and semi-theoretical approach for predicting the blasting damage depth based on the Peak Particle Velocity (PPV) of blasting vibration at certain distance was established. The method was used to predict the damage depth of the subsequent bench blasting with monitored vibration, and the predicted results agreed well with those obtained by field damage testing, which indicated that the method proposed in this paper is reasonable and credible. Although there is no rigorous theoretical basis, this real-time damage assessing approach is simple and convenient to use, and it can significantly reduce the massive workload of sonic wave testing and greatly improve efficiency. The accuracy of damage assessment is heavily dependent on the engineering geological conditions of excavation site and the vibration monitoring quality. Thus, careful investigation of the engineering geological conditions before blasting excavation and field experiments are necessary for the application of this method.

Effects of freeze–thaw on the determination and application of parameters of slope rock mass in cold regions

Freeze–thaw could significantly affect the deterioration of mechanical properties of slope rock mass, and should be taken into consideration when determining the parameters of slope rock mass in cold regions. In this paper, we first measured the freeze–thaw coefficient using the freeze–thaw cycle test on intact slope rock mass from Mengku Mine, then determined the freeze–thaw correction coefficient by taking field geological investigation and rock hardness into consideration, and established a linear relationship between Geological Strength Index (GSI) and Tianshan slope rock mass rating (TSMR) system (a rock mass classification method applicable in cold regions) by incorporating the freeze–thaw correction coefficient into the expression of rock mass effect. The results show that freeze–thaw correction coefficient varies between 0.71 and 0.93, and GSI varies between 45 and 63. We further determined the parameters of slope rock mass by employing the generalized Hoek–Brown criterion and using it established a numerical rock slope excavation model and analyzed the rock mechanic features and stability status. The results indicate that the maximum ground deformation of slop rock mass is 15mm, and the floor rebound is about 42mm. Overall, the method described in the present paper can be used to select slope rock mass in cold regions and calculate the slope rock stability.

Numerical Simulation of Unloading Zone Division for Excavated Rock Slope

Excavation unloading zone corresponds to stress decreased area of slope rock mass after excavation. Quality of slope rock mass in this area will be degraded due to excavation disturbance, and the mechanical parameters of rock mass will be also degraded accordingly. Therefore, determining the range of excavation unloading zone accurately is one of the key factors to ensure the rationality and validity of numerical simulation results of rock slope excavation. In this paper, the range of excavation unloading zone is determined by comparing stress field before and after excavation, choosing stress component perpendicular to excavation face as comparative standard in calculation, which can be calculated by computer program with FLAC software. Stress adjustment of slope rock mass due to excavation is a dynamic and changing progress, so the range of excavation unloading zone is changing during excavation, which can be achieved by a cycling program in numerical simulation. The correctness and usefulness of this method is proved by the calculation results of example analysis.

Spatial distribution of excavation induced damage zone of high rock slope

The excavation induced damage zone (EDZ) can significantly influence the overall performance of an excavated slope. Determining the spatial distribution characteristics of the EDZ is very important to both design and construction of high rock slope. Based on the case study of the excavation of high rock slope at the Xiluodu Hydropower Station in Sichuan province of China, spatial distributions of EDZ of the slope surface and berm were determined using sonic logging and cross-hole sonic tests. The results showed that the vertical damage depth increases non-linearly from the inner side to the outer flank of the berm, whereas the horizontal damage scope increases non-linearly from the bottom to the top of the slope. The maximum horizontal damage scope and the maximum vertical damage depth are found to be at the outer flank of the berm. To reproduce and predict the EDZ for high rock slope excavation with Dynamic Finite Element Method, a modified tensile–compressive damage model was introduced into the simulation of the EDZ of Xiluodu high rock slope. Four other frequently used damage models were used as comparisons. The results demonstrate that the damage zone obtained by the modified tensile–compressive damage model agreed with observations better than the other four existing blasting damage models.

Excavation-induced microseismicity: microseismic monitoring and numerical simulation

The volume of influence of excavation at the right bank slope of Dagangshan Hydropower Station, southwest China, is essentially determined from microseismic monitoring, numerical modeling and conventional measurements as well as in situ observations. Microseismic monitoring is a new application technique for investigating microcrackings in rock slopes. A microseismic monitoring network has been systematically used to monitor rock masses unloading relaxation due to continuous excavation of rock slope and stress redistribution caused by dam impoundment later on, and to identify and delineate the potential slippage regions since May, 2010. An important database of seismic source locations is available. The analysis of microseismic events showed a particular tempo-spatial distribution. Seismic events predominantly occurred around the upstream slope of 1180 m elevation, especially focusing on the hanging wall of fault XL316-1. Such phenomenon was interpreted by numerical modeling using RFPA-SRM code (realistic failure process analysis-strength reduction method). By comparing microseismic activity and results of numerical simulation with in site observation and conventional measurements results, a strong correlation can be obtained between seismic source locations and excavation-induced stress distribution in the working areas. The volume of influence of the rock slope is thus determined. Engineering practices show microseismic monitoring can accurately diagnose magnitude, intensity and associated tempo-spatial characteristics of tectonic activities such as faults and unloading zones. The integrated technique combining seismic monitoring with numerical modeling, as well as in site observation and conventional surveying, leads to a better understanding of the internal effect and relationship between microseismic activity and stress field in the right bank slope from different perspectives.

Road High Cutting Slope Stability Analysis under the Influence of Blasting for Excavation

The impact of blasting effect is an important factor of dynamic stability in the excavation of rock slope. Based on the sub-grade engineering in Jin-hai Lake of the New Countryside Construction Project, this paper sets up a finite element analysis model for the dynamic response of the cutting slope under the blasting loading. It discusses the stress field, displacement field and the propagation law of the blasting seismic wave, and analyzes the security evaluation criteria of the dynamic stability of cutting slope. What’s more, it makes a systematic analysis on the effects of blasting excavation on the stability of the cutting slope according to blasting vibration monitoring. The research provides referential value to form a correct understanding towards slope damage caused by blasting excavation.

DEVELOPMENT OF STATIC FRACTURING METHOD OF ROCK MASS AND CONCRETE BY HYDRAULIC PRESSURE

Although blasting is an effective method of fracturing rock mass, the method involves tremendous shock waves and noise. Due to recent increase in rock excavation near residential areas, there have been growing demands for alternative methods of excavation to avoid excessive noise pollution. A new static fracturing method of rock excavation and demolition of concrete structures using pressurized fluid was developed to satisfy such demands.This paper describes the outline of fracturing machine and fracturing system used in the method, function check experiments of the machine and applicability of the method to rock slope excavation and demolition of top of concrete piles.It is confirmed that the method shows sufficient function to fracture rock mass and concrete structures.

The effective failure modes and stability of slopes in rock mass with two discontinuity sets

The stability of rock slopes in discontinuous rock mass associated with the construction of power plants, highways and open pits is always of paramount importance during the lifetime of these structures. The likely forms of instabilities observed in the excavation of rock slopes and some mathematical methods for the stability analyses are well documented in literature. Since most of the mathematical approaches used are based on the limiting-equilibrium concept, there seems a need to check the validity of these approaches under some controlled conditions. In this paper, the authors describe methods for the stability of a blocky column and discontinuous rock slopes derived on the basis of dynamic equilibrium equations and compare the results calculated according to the developed method with those of experiments on model blocky columns and model slopes in the laboratory. Test results confirm that the limiting equilibrium approache is valid and an effective way of dealing with the stability problems in discontinuous rock mass as long as the likely forms of instability are properly treated in these approaches.