Jointed Rock Slope Research Articles

Limit state analysis of stepped sliding of jointed rock slope based on tensile-shear composite failure mode of rock bridges

Limit state analysis of stepped sliding of jointed rock slope based on tensile-shear composite failure mode of rock bridges

The role of discontinuities in rock slope stability: Insights from a combined finite-discrete element simulation

Rock slope failure is particularly detrimental to the safety of human life and engineering infrastructure. The pre-existing discontinuities in the jointed rock slopes play a key role in the slope stability, and the destabilization process often related to the complex interaction between the discontinuities and the intact rock bridge. Understanding the failure mechanism and accurately predicting the failure process are essential for the safety of jointed rock slopes. In this paper, a jointed rock slope analysis model (Y-slopeJ) is developed to evaluate the stability state and simulate the progressive failure process of jointed rock slopes based on the combined finite-discrete element method (FDEM). The accuracy and robustness of the proposed model are validated by numerical tests. Then this Y-slopeJ is applied to investigate the failure mechanism and failure process of rock slopes with various types of discontinuities, with an emphasis on crack initiation, propagation and coalescence. This work proposed a promising tool in understanding and predicting the progressive failure process of jointed rock slopes.

Impact of Groundwater Table Fluctuation on Stability of Jointed Rock Slopes and Landslides

Groundwater level plays an important role in triggering landslides. In this paper, Distinct Element Method is used to investigate the impact of groundwater table fluctuation on the stability of jointed rock slopes. For this purpose, 110 cases including different number of joint sets, joint friction angles, joint spacings, and joint angles are considered and the influence of changing groundwater level on the stability of a jointed rock slope is investigated through a series of parametric studies. This study shows that the factor of safety for slopes can decrease significantly with increasing the groundwater level, and the impact is more significant on slopes with steeper joints. Furthermore, as the spacing of the joints decreases, the impact decreases. However, as the joint spacing increases, the groundwater table should rise to a higher elevation to be able to have an impact. Moreover, the impact on the factor of safety is similar for different joint friction angles when the groundwater level elevation is high. This study provides a better understanding of the impact of groundwater table fluctuation on the stability of jointed rock slopes.

Identification of the Potential Critical Slip Surface for Fractured Rock Slope Using the Floyd Algorithm

A rock slope can be characterized by tens of persistent discontinuities. A slope can be massive. The slip surface of the slope is usually easier to expand along with the discontinuities because the shear strength of the discontinuities is substantially lower than that of the rock blocks. Based on this idea, this paper takes a jointed rock slope in Hengqin Island, Zhuhai as an example, and establishes a three-dimensional (3D) model of the studied slope by digital close-range photogrammetry to rapidly interpret 222 fracture parameters. Meanwhile, a new Floyd algorithm for finding the shortest path is developed to realize the critical slip surface identification of the studied slope. Within the 3D fracture network model created using the Monte Carlo method, a sequence of cross-sections is placed. These cross-sections containing fractures are used to search for the shortest paths between the designated shear entrances and exits. For anyone combination of entry point and exit point, the shortest paths corresponding to different cross-sections are different and cluttered. For the sake of safety and convenience, these shortest paths are simplified as a circular arc that is regarded as a potential slip surface. The fracture frequency is used to determine the probability of sliding along a prospective critical slip surface. The potential slip surface through the entrance point (0, 80) and exit point (120, 0) is identified as the final critical slip surface of the slope due to the maximum fracture frequency.

The Effect of Discontinuity Orientation and Thickness of the Weathered Layer on the Stability of Lesser Himalayan Rock Slope

Abstract The effect of discontinuity orientations and thickness of the weathered layer in the stability of jointed phyllite rock slopes of the Lesser Himalayan region was examined in this study. Numerical simulation was performed using the Rocscience RS2 V9 finite element software package. The performance of the slope was assessed for varying slope height, slope angle, weathered layer thickness, and orientation of the main joint and the cross joint set. The results indicate that the stability of rock slope depends on the relative orientation and distribution of the contained joint sets and the thickness of the weathered layer. Based on numerical simulation, the order of percentage reduction of a factor of safety (FOS) for the critical combination of joint sets has been identified. It was deduced that while keeping all the parameters constant, the effect of cross joint orientations is prominent in the case of shallow weathered layer and reduces as the thickness of the weathered layer increases. The effect of main joint orientations is prominent in the case of a deep weathered layer and reduces as the thickness of the weathered layer decreases. Analysis of variance (ANOVA) of the obtained result indicates that all the independent variables (slope height, slope angle, weathered layer thickness, main joint set, and cross joint set) are significantly predicting the dependent variable (FOS of rock slope) and the reducing order of significance is weathered layer thickness, slope angle, main joint orientation, slope height, and cross joint orientation.

Key group analysis based on DDA method for rock slope stability analysis

Inhomogeneity and discontinuities play a key role in resistance and behavior of rock masses. Today engineers have a wide range of methods to analyze the stability of rock slopes. Due to its simplicity and speed of evaluation, static analysis methods continue to play a special role in the stability assessment of jointed rock slopes. One of the most well-known static methods used in the stability analysis of rock slopes is the Key Block method (KBM), which is based on the key block finding and analyzing. In this method, if none of the key blocks are unstable, it implies that rock mass is stable. Occasionally, the combination of a number of stable blocks has led to formation a group of blocks that sometimes leads to instability. Therefore, the stability analysis of the jointed rock masses leads to study of groups of blocks that are potentially dangerous for the stability of a rock slope. The Key Group method (KGM), with its progressive approach, finds these critical groups and focuses the stability calculations on these groups. In order to increase the efficiency, accuracy and speed of this method and to develop it in three dimensions, it is decided to combine it with one of the numerical methods. The standard Discontinuous Deformation Analysis method (DDA) is an implicit method based on the finite element method. This is a sophisticated numerical method for modeling the quasi-static and dynamic behavior of rock block systems in discontinuous rock masses. The goal of this paper is to use of the potency of the numerical method of DDA to analyze the candidate key group. For this purpose, the DDA computer program was developed with Mathematica programming language and combined with the KGM software. The resulting package, after selecting the key group by the KGM method, proceeds to analyze it with the DDA method. Two examples solved illustrating the reasonable results and the efficiency of this developed method compared to that of the original KGM and SKGM. The results validated the proper accuracy and good performance of the procedure developed in this research.

Failure of Rock Slopes with Intermittent Joints: Failure Process and Stability Calculation Models

Abstract Rock slopes with intermittent joints in open-pit mines are complex geological bodies composed of intact rock and discontinuous structural planes, and their stability analysis are necessary for mine disaster prevention. In this study, a series of base friction tests were performed to determine the failure process and displacement field evolution of rock slopes with intermittent joints using the speckle technique of a noncontact measurement system. Next, stability calculation models of the slopes were established from the energy perspective using the plastic limit analysis theory, and the effects of the joint inclination angle and coalescence coefficient of rock bridges on the slope stability were evaluated. The four main conclusions are as follows: (1) The failure of rock slopes with intermittent joints shows the feature of collapse-lower traction-upper push. (2) Based on the failure modes of rock bridges in slopes, the failure of rock slopes with intermittent joints could be divided into three types: tensile coalescence (type A), shear coalescence (type B), and tensile–shear coalescence (type C). (3) Among the three slope types, the stability of the type A slope is significantly influenced by rock cohesion, whereas that of the type B slope is significantly influenced by joint cohesion. The stability of type C slope is significantly influenced by the joint inclination angle and joint friction angle. (4) The local-stable slope is unstable while the first through-tensile crack in the zone of the potential sliding body higher than the critical instability height appeared. This study guides the stability evaluation and instability prediction of jointed rock slopes in open-pit mines.

Study on the mechanism of displacement mutation for jointed rock slopes during blasting excavation

During blasting excavation of jointed rock slopes, the rock masses of the slopes often suffer an abrupt change in displacement, which is called displacement mutation. This kind of displacement mutation seriously threatens the stability of jointed rock slopes. Taking the left-bank spandrel groove slope in the Baihetan hydropower station as an example, the displacement behaviour of the jointed rock slope under excavation was surveyed based on the field monitoring. It is found that the displacement mutation of the jointed rock slope is closely related to the dynamic disturbances of blasting excavation. Then the numerical simulations based on the FLAC3D program were conducted to study the mechanism and influencing factors of the displacement mutation caused by blasting excavation. The results show that the displacement mutation is attributed to the combined actions of blast loading and transient in-situ stress release occurring on blast-created free surfaces if high in-situ stress exists. Under the compression of blasting pressure and in-situ stress, strain energy is accumulated and stored in the rock masses of slopes. As the blasting pressure decays, the accumulated rock strain energy due to blast loading is rapidly released. Meanwhile, the stored rock strain energy under in-situ stress is also quickly released as blasts create a free surface and the in-situ stress initially exerted on this face is suddenly released over a very short period. It is the rapid release of the rock strain energy that causes joint opening and displacement mutations in jointed rock slopes. Magnitude of the joint opening displacement is positively related to the strain energy release rate. The blasting load at higher peak pressure, longer rise time and shorter fall time and the transient in-situ stress release with a higher initial stress and a shorter period correspond to greater strain energy release rates, and thus will result in larger joint opening displacement.

An Enhanced Discrete Element Modeling Method Considering Spatiotemporal Correlations for Investigating Deformations and Failures of Jointed Rock Slopes

The discrete element method (DEM) is commonly employed to analyze the deformations and failures of jointed rock slopes. However, when the iterative calculation process of the DEM modeling should be terminated is still unclear. To solve the above problem, in this paper, a discrete element modeling method based on the energy correlation coefficient is proposed to determine when the iterative calculation process could be terminated, and then applied the proposed method to analyze the deformations and failures of jointed rock slopes. Compared with the existing discrete element modeling method based on the displacement variation coefficient, the proposed method based on the energy correlation coefficient is much more applicable for jointed rock slopes. The main advantage of the proposed method is that there is no need to determine the position of the potential sliding surface, and the displacements of all blocks are no longer counted as statistics, but the spatiotemporal correlations between all blocks are considered. The effectiveness of the proposed method is verified by comparing with the existing method based on the displacement variation coefficient for an abbreviated jointed rock slope. Moreover, the proposed method is successfully applied to analyze a real-world jointed rock slope without an obvious potential sliding surface in which the existing method cannot work.

INFLUENCE OF SWELLING ON SHEAR STRENGTH OF SHALE-LIMESTONE INTERFACE

Rock slope stability is almost controlled by the behaviour of the interface between rock layers. The presence of shale layers between limestone layers complicates this behaviour. As the shale layer undergoes swelling with moisture, it causes the shear interface properties to change with a specific behaviour different from the dry state. The behaviour will depend on the shale’s degree of saturation, swelling percentage, and stress level over shale. An experimental program was carried out to determine the shear interface behaviour parameters of shale-limestone during swelling phenomena to guide stability checks. The interface cohesion and friction angle results are reported along the swelling process and compared with the dry state condition. These results help engineers assign adequate and accurate values for joint shear and normal stiffness in jointed rock slopes, including swelling layers.

A Qslope-based empirical method to stability assessment of mountain rock slopes in multiple faults zone: A case for North of Tabriz

The present article provides an empirical relationship for rock slope stability assessment based on Qslope classification. The relationship is used as a correction procedure for classic Qslope for mountain regions with multiple fractures related to several faults. The relationship is derived from 25 distinct jointed slopes near the North Tabriz Fault (NTF). The NTF triggered numerous micro-faults and fractures in rocky landscapes, resulting in sliding on a variety of scales. The present empirical method is introduced based on a field survey and a stability analysis of the studied slopes based on Qslope principles. The results indicate that the classic formulation of Qslope can be modified to β = 62.6 log10 (Qslope) + 36 for mountain regions with multiple fault zones.• This empirical method can be useful for fast stability assessment on jointed rock slopes.• This relationship can use as a modification for the original formula in multiple faults zones.

Stability Prediction of Residual Soil and Rock Slope Using Artificial Neural Network

A sudden downward movement of the geomaterial, either composed of soil, rock, or a mixture of both, along the mountain slopes due to various natural or anthropogenic factors is known as a landslide. The Himalayan Mountain slopes are either made up of residual soil or rocks. Residual soil is formed from weathering of the bedrock and mainly occurs in gentle‐to‐moderate slope inclinations. In contrast, steep slopes are mostly devoid of soil cover and are primarily rocky. A stability prediction system that can analyse the slope under both the condition of the soil or rock surface is missing. In this study, artificial neural network technology has been utilised to predict the stability of jointed rock and residual soil slope of the Himalayan region. The database for the artificial neural network was obtained from numerical simulation of several residual soils and rock slope models. Nonlinear equations have been formulated by coding the artificial neural network algorithm. An android application has also been developed to predict the stability of residual soil and rock slope instantly. It was observed that the developed android app provides promising results in predicting the factor of safety and stability state of the slopes.

Dynamic Response Characteristics and Cumulative Failure Evolution Process of Jointed Rock Slopes Subject to Continuous Earthquake Excitations Using Discrete Element Method

Dynamic Response Characteristics and Cumulative Failure Evolution Process of Jointed Rock Slopes Subject to Continuous Earthquake Excitations Using Discrete Element Method

Novel methods for quantitative analysis of kinematic stability and slope mass rating in jointed rock slopes with the aid of a new computer application

Novel methods for quantitative analysis of kinematic stability and slope mass rating in jointed rock slopes with the aid of a new computer application

Investigations of a Weathered and Closely Jointed Rock Slope Failure Using Back Analyses

This study presents the case of a landslide triggered by a high groundwater level caused by several days of continuous rainfall in the northeastern region of Taiwan. The slope where this landslide occurred consists of closely jointed and weathered bedrock. By means of finite element limit analysis and the Hoek–Brown failure criterion, this study performed a slope failure simulation similar to the actual landslide and deduced the reasonable value range for the combination of key Hoek–Brown failure criterion parameters through back analyses. The results indicate that the key parameters affecting the bedrock’s slope stability were the geological strength index (GSI) and the disturbance factor (D), whereas the effects of the unconfined compressive strength (σci) were less significant. The results of the back analysis reveal that the suitable D-value range and GSI of closely jointed and weathered sandstone in the northeastern region of Taiwan are 0.8 to 0.9 and 20 to 30, respectively. These back-analyzed value ranges can serve as a reference for broader applications in the preliminary stability analysis of similar rock slopes where it is difficult to perform in situ investigation.

Simulating the entire progressive failure process of rock slopes using the combined finite-discrete element method

This paper presents a novel approach (Y-slope) to simulate entire slope failure processes, from initiation, transport to deposition. The algorithm is implemented in a combined finite-discrete element method code. Absorbing boundary conditions are implemented to improve computational efficiency for the initial stress state equilibrium. Strength reduction methods, considering both tensile and shear failure modes, are implemented to evaluate the slope stability, where the safety factor and critical failure surface are automatically obtained. The energy dissipation mechanism, due to blocks’ friction and collision, is incorporated to accurately simulate the block kinematics during the post-failure stage. The accuracy and robustness of Y-slope are validated by numerical tests, and the failure mechanism and failure progress of a homogeneous and jointed rock slope are presented. Results indicate that Y-slope can not only evaluate the slope stability state (e.g., safety factor and critical failure surface), but also simulate the entire failure process (e.g., slope deformation, failure surface evolution, block transport and deposition). In addition, the critical role of existing discontinuities on the slope stability and failure mechanism are also highlighted. This work proposes a promising tool in understanding the failure mechanism and assessing the potential risk by predicting the entire failure process of rock slopes.

Upper Bound Analysis of Non-Persistent Jointed Rock Slope Using Rigid Block Element Method

The upper bound method analyzing the stability of the non-persistent jointed rock slopes is proposed by considering rock bridge mechanical effects, which combines the upper bound theorem, the discretization technique of rigid block element and the nonlinear mathematical programming. The kinematically admissible velocity fields of non-persistent jointed rock are constructed. The non-linear mathematical programming models are established for solving the rigorous upper bound solution of ultimate load or safety coefficient by using successive linear programming algorithm. two numerical examples are performed and analyzed. The proposed method is successfully validated by comparing the simulation with those produced by other classical methods. The method has the following advantages: (1) it can simultaneously simulate the discontinuous mechanism properties of the rigid rock blocks and the continuous medium mechanism properties of the rock bridge failures. Both the tensile and shear mechanism effects of the rock bridges can be considered simultaneously; (2) comparing with the exiting numerical methods such as finite element method or discrete element method, this method can not only consider the tensile and shear effects of the rock bridges simultaneously, but also avoid the complex constitutive relationship between the rock masses and the joints. The safety factor and its corresponding failure mechanism can be obtained simultaneously; (3) comparing with the traditional rigid limit equilibrium method, this method does not need to make any assumption of the failure surfaces. The final critical failure mechanism can be directly obtained through mathematically programming method; (4) this method has the characteristics of clear concept, simple in the program composition and high computational efficiency.

Reliability back analysis of a 3D wedge slope based on the nonlinear Barton-Bandis failure criterion

Due to the development of joints, wedge failure has become the main failure type of rock slopes. Obtaining accurate parameters is an important prerequisite in studying slope stability. However, these are difficult to obtain due to the restrictions of field conditions. Based on a real and simple wedge, the method of stability analysis and parameter acquisition of a wedge with the nonlinear Barton-Bandis failure criterion is discussed, and then this method is extended to the conventional form of a wedge. With minimal available data, a simple field test and the reliability back analysis method are combined to propose a specific method for determining the most likely combination of nonlinear strength parameters when wedge failure occurs. This approach can provide a simple and practical method for determining the nonlinear strength parameters for engineering applications. Thus, the small frequent collapse incidences in jointed rock slopes can be effectively utilized to provide a reference for the prevention and control of large-scale failure.

An Energy-Based Discrete Element Modeling Method Coupled with Time-Series Analysis for Investigating Deformations and Failures of Jointed Rock Slopes

The discrete element method (DEM) can be effectively used in investigations of the deformations and failures of jointed rock slopes. However, when to appropriately terminate the DEM iterative process is not clear. Recently, a displacement-based discrete element modeling method for jointed rock slopes was proposed to determine when the DEM iterative process is terminated, and it considers displacements that come from rock blocks located near the potential sliding surface that needs to be determined before the DEM modeling. In this paper, an energy-based discrete element modeling method combined with time-series analysis is proposed to investigate the deformations and failures of jointed rock slopes. The proposed method defines an energy-based criterion to determine when to terminate the DEM iterative process in analyzing the deformations and failures of jointed rock slopes. The novelty of the proposed energy-based method is that, it is more applicable than the displacement-based method because it does not need to determine the position of the potential sliding surface before DEM modeling. The proposed energy-based method is a generalized form of the displacement-based discrete element modeling method, and the proposed method considers not only the displacement of each block but also the weight of each block. Moreover, the computational cost of the proposed method is approximately the same as that of the displacement-based discrete element modeling method. To validate that the proposed energy-based method is effective, the proposed method is used to analyze a simple jointed rock slope; the result is compared to that achieved by using the displacement-based method, and the comparative results are basically consistent. The proposed energy-based method can be commonly used to analyze the deformations and failures of general rock slopes where it is difficult to determine the obvious potential sliding surface.

A novel dynamic stability analysis method for jointed rock slopes based on block-interface interaction

The dynamic stability evaluation of jointed rock slopes is a complex problem of solving nonlinear and uncertain systems. The interactive method of partitioned finite element and interface element is applied to the solution of the seismic response of jointed rock slopes under earthquake. The contact status of the weak interlayer can be calculated at each moment by the method. Since the balance of the slope slider can be inferred by contact status on weak interlayer, a novel criterion of rock slope instability based on the contact status of the contact surface is proposed. The criterion not only satisfies the requirement for the sudden change of residual deformation but also meets the completely broken of the weak interlayer. Since the interactive method can still converge in the state of slope failed, an adaptive strength reduction method is proposed to search for the safety factor automatically. To verify the effectiveness of the method, the dynamic stability of a classical rock jointed slope is calculated, and then compared with the result in the reference paper. Moreover, the proposed method is applied to analyze the dynamic stability of a high steep rock slope with complex internal joints and the safety factor is calculated successfully.