Stability Analysis Of Rock Mass Research Articles

Semi-automatic recognition of rock mass discontinuity based on 3D point clouds

Information on rock mass discontinuities is crucial for rock mass stability analysis. Due to the low efficiency, incompleteness, and potential risk of the traditional compass methods in measuring discontinuities, three-dimensional light detection, ranging, and other remote sensing methods have become essential. In this study, voxel filtering was used to subsample a point cloud so that its feature points were retained while reducing the computational load. An improved regional growing (RG) algorithm was then used to extract rock mass discontinuities. A software Geocloud v1.0 was developed based on the proposed method to semi-automatically recognize discontinuities. Additionally, two groups of sensitivity experiments were performed to analyze the influence of different numbers of nearest neighbors and maximum RG angles on the extraction of discontinuities. Results showed that most of the discontinuities could be accurately recognized with different thresholds. Furthermore, the accuracy of the proposed method was verified by real geometries, on a real highway slope, and in a natural quarry. Finally, the efficiency of the proposed method was proven using comparative computational experiments.

A precise modeling method of three‐dimensional discrete fracture network based on rectangular joint model

AbstractAs the weak structure and main seepage channel of rock mass, the discrete fracture network (DFN) has a significant influence on the physical and mechanical properties of rock mass. In this paper, based on the rectangular joint model, two algorithms are proposed to realize the precise modeling of the DFN in any polyhedron. First, the equivalence of DFN modeling with the rectangular joint model and the elliptical joint model is theoretically deduced. On this basis, the chain splicing algorithm suitable for the rectangular joint model is proposed, which can generate the DFN model according to the actual distribution of joint spacing, trace, and bridge length. Aiming at the concave boundary in the model domain, the segmentation‐stitching operation is put forward, and the continuity of the joint when passing through the interface is ensured. Finally, the effectiveness of the above algorithm is verified by several simple cases, and the relationship between the size of the geometrical representative elementary volume (REV) and discontinuity parameters is discussed. The results show that when the mean values of the joint distribution parameters are the same, even if the distribution rules are different, the number of joints generated in the same spatial region is approximately equal. The size of the geometrical REV is independent of the spacing and bridge length and is approximately three to five times the mean of the trace. The relevant algorithms and conclusions in this paper can be used as the basis for subsequent rock mass stability analysis and seepage calculation.

Implementing close-range remote surveys for the digitally supported rock mass stability analysis

A digitally supported rock mass stability analysis is herein presented for the implementation of non-contact close-range remote surveys against landslide hazard in sheltered environments, such as Marine Protected Areas. An airborne photogrammetric survey was carried out at the Lachea Islet (Sicily), which is part of a small volcanic archipelago with a peculiar geological history, hosting unstable rock masses belonging to the first eruptive stages of Mount Etna. The digital model built for this study allowed extracting the discontinuity orientation data, performing a kinematic analysis along the recognized discontinuity clusters, and quantifying the volume of potentially unstable boulders. Laboratory tests allowed achieving the main physical-mechanical parameters of involved rocks, which were used to perform a quantitative stability analysis under both deterministic and probabilistic approaches, based on the extracted digital data. Finally, a 3D rockfall trajectory analysis was carried out by simulating statistical rockfall path on the digital model built for the study. Results highlighted a poor stability in the studied islet sector, which is worsened by taking into account the high seismicity that characterizes the area. The main tourist elements of the islet must be considered at risk, as they are located within the simulated trajectories of the landslides. The methodological protocol carried out for this study, based on conventional procedures but using remotely derived and digitally processed information, can be considered a useful tool in the frame of nature-based solutions for hydro-meteorological hazards connected to climatic changes.

Analysis of P-wave propagation in filled jointed rock mass with viscoelastic properties

Stress wave propagation in filled jointed rock mass is an important basis for the analysis of rock dynamic stability. The presence of small cracks in rock mass often causes the rock to exhibit viscoelastic behavior, resulting in the amplitude attenuation and time delay of the stress wave. In view of the incomplete understanding of stress wave propagation in viscoelastic media, this study presents an analysis on stress wave propagation in filled jointed rock mass with viscoelastic properties based on the time-domain recursive analysis method. By introducing the quality factors of stress wave in viscoelastic medium, the propagation equation of plane P-wave in filled jointed rock mass with viscoelasticity is established. Subsequently, the transmission and reflection characteristics of P-wave are accordingly analyzed. The results indicate that the transmission and reflection coefficients of P-wave through the filled joint decrease obviously due to the attenuation effect of rock viscoelasticity on wave amplitude, but the coefficients gradually stabilize as the quality factor increases. As the propagation distance of the P-wave increases in viscoelastic rock masses, the transmission and reflection coefficients decrease gradually. The normal stiffness of joint contact interface has a decisive influence on the wave propagation. Specifically, a higher normal stiffness leads to stronger transmission and poorer reflection. The larger the thickness of filled joint, the more obvious the attenuation of P-wave becomes. Additionally, the viscoelasticity of filling layer further aggravates the influence of joint thickness on the attenuation of P-wave. The study comprehensively takes into account the effect of viscoelasticity of both the rock mass and the filling layer on transmission and reflection of waves. The research results provide certain theoretical support for the dynamic response and stability analysis of rock mass containing structural planes.

Analytical Solution for Rock Discontinuity Prediction Without Stereonet

Stereographic projection has been used in Rock Engineering for decades to represent rock mass discontinuities in graphical form and to carry out further stability analysis. Currently, there are computer programs available for this purpose. The objective of this technical note is to present some closed form expressions related to stereographic projections such as the prediction of a possible joint set. These solutions can be implemented in spreadsheets or in computer programs and would benefit stability analysis of rock masses with discontinuities. This helps to reduce the work load with hand solutions and enhance the analysis in modern computational tools with stereonet, where the rotation and snap features are not available yet.

Experimental study on effect of freeze-thaw cycles on dynamic mode-Ι fracture properties and microscopic damage evolution of sandstone

The investigation of dynamic fracture characteristics of sandstone after freeze-thaw (F-T) treatments is of great significance for the optimization of blasting parameters and stability analysis of rock masses engineering in cold or high-elevation regions. In the present study, the P-wave velocity, porosity, T2 spectrum curve, and micromorphology of sandstone specimen after different F-T cycles were measured using nuclear magnetic resonance (NMR) and scanning electron microscopy (SEM) techniques. The F-T damage factor was defined according to the reduction in wave impedance. Moreover, the dynamic mode-Ι fracture test was carried out using notched semicircular bend (NSCB) sandstone specimen. Meanwhile, the fracture process of NSCB specimen was captured by adopting a high-speed photography system. Test results show that F-T cycles can irreversibly deteriorate the microscopic pore structure and the cementation between mineral particles, which is manifested by an increase in the proportion of macropores and mesopores. The dynamic fracture pattern of sandstone specimen is affected by the coupling of F-T cycle number and loading pressure. Furthermore, the dynamic fracture toughness of sandstone constantly increases with the increase of loading rate at a specified F-T cycle number, while the F-T cycle treatment has a significant weakening effect. There has a negative exponential correlation between dynamic fracture toughness and F-T damage factor.

Mechanical property and thermal degradation mechanism of granite in thermal-mechanical coupled triaxial compression

Mechanical properties of rocks under high temperature and high pressure are important for the design and stability analysis of rock mass in deep-buried underground engineering. This study is devoted to investigating the strength and deformation behaviors of granite as well as the thermal degradation mechanism under coupled high-temperature and high-pressure conditions in triaxial compression tests. Two groups of triaxial compression test under six different temperatures (20, 50, 70, 90, 110, 180 °C) and five different pressures (0, 2, 15, 30, 40 MPa) designed by the orthogonal method were performed by a self-developed thermo-mechanical true triaxial testing device on the granite samples drilled from the borehole at the depth of 600 m. The multi-scale features of the sliding surface of the post-failure samples were characterized by field optical microscopy and 3D laser scanning. Temperature effects on the granite mechanical properties, especially the friction properties were identified and discussed. It is found that increasing temperature induces obvious thermal degradation of strength and elastic modulus of the tested granite under triaxial compression. The deformation and failure pattern of the tested granite are dominantly governed by the confining pressure rather than temperature when the temperature varies between 20 °C and 180 °C. Temperature plays a crucial role in the friction behavior in triaxial compression, and the increase in temperature leads to the increase of gouge particles and the linear decrease of the roughness of the sliding surface. Both thermal cracking and friction weakening contribute to the thermal degradation of strength at high pressure. The findings are helpful in comprehensively understanding the mechanical behavior of granite under coupled high temperature and high pressure, and in revealing the thermal degradation mechanism of hard rocks.

Stress wave propagation and incompatible deformation mechanisms in rock discontinuity interfaces in deep‐buried tunnels

AbstractComplex weak structural planes and fault zones induce significant heterogeneity, discontinuity, and nonlinear characteristics of a rock mass. When an earthquake occurs, these characteristics lead to extremely complex seismic wave propagation and vibrational behaviors and thus pose a huge threat to the safety and stability of deep buried tunnels. To investigate the wave propagation in a rock mass with different structural planes and fault zones, this study first introduced the theory of elastic wave propagation and elastodynamic principles and used the Zoeppritz equation to describe wave field decomposition and develop a seismic wave response model accordingly. Then, a physical wave propagation model was constructed to investigate seismic waves passing through a fault, and dynamic damage was analyzed by using shaking table tests. Finally, stress wave attenuation and dynamic incompatible deformation mechanisms in a rock mass with fault zones were explored. The results indicate that under the action of weak structural planes, stress waves appear as a complex wave field decomposition phenomenon. When a stress wave spreads to a weak structural plane, its scattering may transform into a tensile wave, generating tensile stress and destabilizing the rock mass; wave dynamic energy is absorbed by a low‐strength rock through wave scattering, which significantly weakens the seismic load. Wave propagation accelerates the initiation and expansion of internal defects in the rock mass and leads to a dynamic incompatible deformation. This is one of the main causes for large deformation and even instability within rock masses. These findings provide an important reference and guide with respect to stability analysis of rock mass with weak structural planes and fault zones.

Empirical shear strength criteria for filled jointed of metasedimentary sandstone

Rock joint shear failure criteria constitute numerical simulation that significantly governs the calculation for rock mass stability analysis. The presence of joint infilling potentially reduces the estimation accuracy for the deformation of rock joint. This study discovers the role of infilling thickness in governing the empirical calculation of linear Mohr-Coulomb failure criterion and non-linear Barton-Bandis failure criterion. A series of direct shear tests with constant surface roughness and controlled infilling material composition facilitates the joint shear strength with various infilling thicknesses. The results indicate that the joint shear strength decreases primarily with infilling material within the joint aperture. Although all the friction angles are closely similar, different cohesion values show the influence of infilling material thickness on shear strength characteristics. The joint shear strength values indicate significant differences where the filled joint shear strength reduction depends on associated infilling thicknesses and the adopted failure criterion. Multiplication to the Filled Joint Factor (FJF ) normalized from the τfilled joint/τcleaned joint ratio will precisely evaluate the filled joint shear strength. Hence, the shear strength estimation from Mohr-Coulomb and Barton-Bandis failure criteria to the various thicknesses of joint infilling will provide sufficient filled joint deformability characteristics.

Damage mechanism and stability analysis of rock mass in the high geo-stress tunnel subjected to excavation

High geo-stresses and complicated geological conditions are two typical characteristics in the traffic tunnel of the tailrace surge chamber at the Shuangjiangkou hydropower station, Southwest China. Rock failures such as spalling and rockbursts induced by excavation were encountered repeatedly in this tunnel. To evaluate the stability of rock mass of the tunnel during excavation, the high-precision microseismic (MS) monitoring technology was introduced. Through analysing the tempo-spatial distribution characteristics of MS events, the main damage areas and their influencing factors were studied. The rock fracturing mechanisms of MS clusters were revealed based on the source parameters of MS events. A three-dimensional model was established to obtain the stress and deformation characteristics of rock mass. Results indicated that the MS events mainly occurred between July 10 and 26, 2017 and the energy release was higher during this period. The main damage areas of rock mass were located at the Stake K0 + 110m–K0 + 170m. Weak structures and multi-cavern effect aggravated rock mass damage subjected to excavation-unloading. Tensile failure was the main fracturing type of rock mass. Rock mass damage influenced by weak structures was especially prominent. The numerical simulation results are consistent with the MS monitoring results. The results could provide significant references for safety evaluation and construction design of similar tunnels.

A Review on Existing Methods to Assess Hydraulic Erodibility Downstream of Dam Spillways

In recent years, rock scouring or erosion downstream of dams has become an increasing dam safety concern. Several theoretical, semi-theoretical, semi-analytical and numerical methods can be used to assess the rock erosion in hydraulic structures. Semi-theoretical approaches determine the correlation between the erosive intensity of fluid flow and the resistive capacity of rock. Such approaches establish the scour thresholds as a function of erosive intensity of water and several rock mass indices by using in situ data and a curve-fitting approach. In some studies, the excavatability index, initially developed for rock mass stability analysis, was used to analyse the rock mass resistance in hydraulic erodibility analysis. The effectivity and weight of the geomechanical parameters used are yet to be determined on the basis of the erodibility phenomenon. The semi-analytical methods are developed on the basis of the mechanical and hydraulic interaction of rock mass and water. Four methods developed by Bollaert et al. are important in determining the erodibility in the plunge pool, but they are not applicable in the case of spillways. They used the comprehensive fracture mechanics for closed-end joints, quasi-steady impulsion, and dynamic impulsion (DI) for blocky rock erosion. The application of these methods to each site is necessary to identify constants that are difficult to determine. Few numerical methods are available to assess the rock mass erosion in hydraulic structures. In the case of numerical methods, the erosive agent is indistinct, and the hydraulic hazard parameter on the spillway surface is almost challenging to apply. This study comprehensively reviews the mechanism of erosion and the methods for assessing the risk of potential rock mass erosion downstream of dams and hydraulic structures. The advantages and disadvantages of all methods are discussed and the potential future research directions in this domain are proposed.

Study of Creep Mechanical Properties and a Rheological Model of Sandstone under Disturbance Loads

The stress environments of rock masses are complex. To explore the mechanical properties of sandstone under earthquake or disturbance loads, laboratory triaxial creep tests under different disturbance loads were conducted on sandstone from Fuxin, Liaoning Province, China. Given the disturbance load, a creep deformation pattern for sandstone was analyzed, and the influence of the disturbance load on the mechanical properties of rock was considered. Thus, a constitutive model of rock under creep disturbance load was established. The results show that (1) the creep curve can be divided into four stages: attenuation creep, steady creep, disturbance creep, and acceleration creep; the increment of disturbance creep varies for different disturbance loads and the larger the disturbance load, the larger the disturbance creep deformation; (2) with increasing disturbance loads, the long-term strength, failure time, and elastic modulus of sandstone decreases linearly, while the peak strain increases; and (3) considering the influence of the disturbance load and introducing an acceleration element to modify the Nishihara model, a constitutive model describing the whole deformation process of sandstone under creep disturbance load was established. The accuracy of the model was verified by test data and provides a theoretical basis for rock mass stability analysis.

COMPARING THE HOEK-BROWN AND MOHR-COULOMB FAILURE CRITERIA IN FEM ANALYSIS

This paper revisits the issue of a potential substitutions of the Hoek-Brown failure model by the standard Mohr-Coulomb model in the stability analysis of rock masses. The derivation of equivalent shear strength parameters of the Mohr-Coulomb proposed by Hoek et al. [1] is addressed with emphases on the suitable range of stresses for which the equivalence of the two failure criteria applies. To that end, a simple numerical analysis of the oedometric test is carried out. It is seen that a correct choice of the upper limit of the minimum compressive principal stress is crucial for the Mohr-Coulomb model to provide predictions comparable to the Hoek-Brown model. This issue is addressed next in the light of the solution of slope stability problem. All the presented results were derived with the help of the GEO5 FEM finite element software [2].

Erratum to: Mechanical response and stability analysis of rock mass in high geostress underground powerhouse caverns subjected to excavation

Erratum to: Mechanical response and stability analysis of rock mass in high geostress underground powerhouse caverns subjected to excavation

Slope stability analysis of rock mass using Rock Mass Rating and Slope Mass Rating

The rapid development in the construction of infrastructure on the hilly terrain has led to excavation of large bodies of rock mass to form cut slopes, resulting in the deformation and reduction in the stability of the rock material. As the slopes were cut more than 10 years ago, it is worried that there should be strength deterioration of the rock slope that could affect the stability of the slope. A study should be carried out to evaluate the recent condition of the slope in terms of its stability and safety after a long period of the exposure. A field study was conducted to collect the discontinuity data and laboratory test for the purpose of stability analysis using the existing stability analysis scheme of Rock Mass Rating (RMR) and Slope Mass Rating (SMR). The study was taken place at an exposed cut slope of a highway in Sri Jaya, Pahang. The objective of this study is to determine and evaluate the stability of the rock cut slope. A classification of the discontinuity parameters such as the strength, Rock Quality Designation (RQD), spacing, aperture, infilling, persistence, weathering, and groundwater have been used to determine the rock mass condition. The classification also need laboratory test for the point load strength (PLT) parameter. The RMR classification showed the rock to be very good condition, while the SMR showed the slope to be completely stable to stable. This study provide a good database in assessing the rock slope condition from time to time for the slope authority management.

Numerical Investigation and Analysis of Intermediate Principal Stress Effects on Rock Failure Behaviors

A series of numerical experiments have been conducted to investigate the intermediate principal stress effects on rock failure behaviors. The numerical results show that the strength and deformation of the rock samples are significantly affected by the intermediate principal stress. The effects are inconsistent in different intervals. As intermediate principal stress ratio b increases, the rock strength increases initially and finally decreases. When b is approximately equal to 0.5, the strength of the rock sample reaches the maximum. In the microlevel, the intermediate principal stress affects the number and distribution of microcracks. The increase of the intermediate principal stress makes the projection of the microcracks on the loading plane change from uniform to uneven. On the one hand, the intermediate principal stress restricts the propagation of microcracks in the normal direction along the intermediate principal stress (or with a component in this direction), which will lead to an increase in the strength of the rock samples. On the other hand, the propagation of microcracks along the normal direction with small principal stress (or with a component in this direction) is promoted, which leads to a decrease in the strength of the rock sample. End friction can make the intermediate principal stress effect more significant because the friction of the loading end to the rock sample can result in stress deviation between the actual value and experimental value. Inhomogeneity of stress field induced by the change of stress states or end friction forces is the external factor of the intermediate principal stress effect. Also, the inhomogeneity of rock material itself is the internal factor. Intermediate principal stress will promote or restrict the failure of certain directions, thus affecting the overall strength of the rock samples. The numerical results can be very meaningful for stability analysis of rock masses in practical engineering.

Mechanical response and stability analysis of rock mass in high geostress underground powerhouse caverns subjected to excavation

To investigate the stability of rock mass in high geostress underground powerhouse caverns subjected to excavation, a microseismic (MS) monitoring system was established and the discrete element method (DEM)-based numerical simulation was carried out. The tempo-spatial damage characteristics of rock mass were analyzed. The evolution laws of MS source parameters during the formation of a rock collapse controlled by high geostress and geological structure were investigated. Additionally, a three-dimensional DEM model of the underground powerhouse caverns was built to reveal the deformation characteristics of rock mass. The results indicated that the MS events induced by excavation of high geostress underground powerhouse caverns occurred frequently. The large-stake crown of the main powerhouse was the main damage area. Prior to the rock collapse, the MS event count and accumulated energy release increased rapidly, while the apparent stress sharply increased and then decreased. The amount and proportion of shear and mixed MS events remarkably increased. The maximum displacement was generally located near the spandrel areas. The MS monitoring data and numerical simulation were in good agreement, which can provide significant references for damage evaluation and disaster forecasting in high geostress underground powerhouse caverns.

Towards a novel auto-rotating lidar platform for cavity surveying

This paper presents the conceptual design, construction, and preliminary testing of a novel auto-rotating platform for cavity surveying. Cavity surveying involves generating a 3D model of an opening from acquired point cloud data. 3D models are used for volume estimation, stope reconciliation, dilution control, convergence monitoring, and rock mass stability analysis. In contrast to conventional cavity monitoring systems (CMS), which employ a rotating light detection and ranging (LiDAR) sensor attached to a stationary boom, the presented novel platform consists of a single point LiDAR sensor attached to an auto-rotating body as a unique solution to the cavity surveying problem. A proof of concept device consisting of a four-blade rotor and a data acquisition system was constructed and dropped from a five-metre overhang. Although auto-rotation was not reached, the set of indoor drop tests provide preliminary results that illustrate the design concept and describes the impact of design parameters. .

Experimental study on stress wave attenuation and energy dissipation of sandstone under full deformation condition

Excavation behaviours not only destroy the balance of original stress in rock mass but lead to the redistribution of initial stress, resulting in rock mass in a new stress environment. The static stress in rock mass has the characteristics of dynamic change. For the purpose of investigating the effect of increasing static stress on attenuation mechanism and energy dissipation of stress wave in sandstone under the overall deformation condition, small disturbance experiments on sandstone bar are carried out with a modified split-Hopkinson pressure bar test system. The stress waveform, p wave velocity, temporal and spatial attenuation of amplitude, and energy dissipation are studied under various static stresses. Results show that stress waveforms at different locations are approximately the same, those at the same locations vary greatly, and the tensile waves that appeared at the tails of stress waves are larger with increasing static stress. With increasing static stress, p wave velocity experiences a dramatic increase, then develops gently, and finally a sharp decrease; the stress demarcation points are σs/σc = 30% and σs/σc = 55%, respectively. P wave velocity can be predicted by a quadratic equation when σs/σc > 63.69%. The relation between longitudinal wave velocity and static stress can be described by a quadratic function. Stress wave amplitudes decrease exponentially with increasing distance and time. Values of temporal spatial response intensity (RI) and spatial RI are approximately equal and present the same development tendency of nonlinear and linear stages due to the same dimensions. Values of temporal attenuation characteristic (AC) and spatial AC are differed by 2 or 3 orders of magnitude although they present the same development tendencies. Ratios of RI and AC can indicate the sensitivity of temporal and spatial attenuation to different static stresses. Full-wave energy declines in an exponential function with increasing static stress and decays as a logarithmic function with increasing distance. Widespread attenuation characteristics like these should provide a theoretical basis for rock mass stability analysis.

A nonlinear elasto‐viscoplastic model for clayed rock and its application to stability analysis of nuclear waste repository

AbstractThe creep behavior is one of the most important topics on the stability analysis of rock mass in underground engineering. In order to characterize the creep deformation of clayey rock more accurately, this study proposes a nonlinear elasto‐viscoplastic (EVP) model based on a new yield surface and a modified Mohr‐Coulomb (MC) flow potential. First, the finite element (FE) formulation for the constitutive creep behavior is derived and a user subroutine to define the material's mechanical behavior (UMAT) is implemented in the commercial finite element package ABAQUS. The numerical simulation is validated against the triaxial creep tests of a cylinder, and the results show that the proposed model can effectively predict the creep responses of clayey rock and thus compensate for the deficiency of the creep model in ABAQUS. Then, the proposed model is used to study the long‐term stability of clayey rock formation surrounding an underground experimental site. Based on the results from triaxial creep tests and in situ monitoring of the lining deformation, the time‐dependent material creep parameters are obtained for rock by using the back analysis method. The predicted lining deformation is in good agreement with the field data with most of the relative errors less than 3.5%. The creep zone in the surrounding rock demonstrates that the horizontal scope is larger than the vertical one. The proposed model is proven to provide accurate prediction on the creep characteristics of clayey rock, showing a potential to assess the long‐term stability and reliability of large‐scale underground engineering structures.