Orientation Of Discontinuities Research Articles

Interaction between block caving and rock slope deformation kinematics as a function of cave position and orientation of discontinuities

Several operations are considering the transition from surface mining to underground block caving to access deeper resources. Depending on the geometry of the orebody, the undercut may be positioned beneath the foot of a large open pit slope, or behind its crest. The latter scenario also arises where a natural rock slope is present. Results are reported here from a numerical modelling study investigating the mechanics of deep-seated slope displacements in response to caving. Different failure models are investigated as a function of the orientation of the jointing pattern relative to the location and progressive development of the block cave. A 2-D discontinuum modelling approach is utilised based on the distinct-element method. The results show that the cave location and the resultant strain field, plays a significant role in the rock mass interactions that develop and the subsequent kinematic response of the slope with respect to translational, rotational and toppling behaviour.

Stepwise heat-capacity change at an orientation transition in liquid crystals.

During a phase transition in a bulk material, heat is exchanged with matter to balance the changes in the internal energy and the entropy of the system. Here we report on the thermal detection of a surface-mediated anchoring transition, a spontaneous and discontinuous orientation change between planar (P) and homeotropic (H) alignments within a single nematic phase by changing temperature. In this case a stepwise change in the heat flow, similar to a glass transition, is observed by means of high-resolution differential scanning calorimetry. We found that the jump in the specific heat does not depend on the sample volume, although the contribution of molecules in the vicinity of surfaces, which trigger the transition, becomes less with increasing the sample volume. This means that different molecular orientations, H and P, with respect to surfaces have different thermodynamic free energies. We also address why the anchoring transition occurs by means of grazing-incidence x-ray diffraction measurements, which clearly reveal the formation of quasismectic layers parallel to surfaces in the nematic phase.

Using terrestrial 3D laser scanning and optical methods to determine orientations of discontinuities at a granite quarry

Using terrestrial 3D laser scanning and optical methods to determine orientations of discontinuities at a granite quarry

APPLICATION OF LASER SCANNING SURVEYING TO ROCK SLOPES RISK ASSESSMENT ANALYSIS

Abstract. The methods for understanding rock instability mechanisms and for evaluating potential destructive scenarios are of great importance in risk assessment analysis dedicated to the establishment of appropriate prevention and mitigation actions. When the portion of the unstable rock mass is very large, effective actions to counteract the risks are complex and expensive. In these conditions, an optimal risk management cannot ignore procedures able to faster and accurately acquire i) geometrical data for modeling the geometry of the rock walls and implementing reliable forecasting models and ii) monitoring data able to describe the magnitude and the direction of deformation processes. These data contributes to the prediction of the behavior of a landslide if the measurements are acquired frequently and reliable numerical models can be implemented. Innovative geomatic techniques, based on GPS, Terrestrial Laser Scanning Surveying (TLS), automated total station and satellite and ground SAR Interferometry, have been recently applied to define the geometry and monitoring the displacements of unstable slopes. Among these, TLS is mainly adopted to generate detailed 3D models useful to reconstruct rock wall geometry by contributing to the estimation of geo-mechanical parameters, that is orientation, persistence and apparent spacing of rock discontinuities. Two examples of applications of TLS technique to the analysis of a large front in a quarry and of a rock shoulder of a dam are presented.

Assessment of Excavation Method of Obajana and Ewekoro Limestone Deposits

The research work assessed the optimum excavation method of limestone deposits at Obajana in Kogi State and Ewekoro in Ogun state. Geological mapping was carried out to measure the orientations of discontinuities. The orientation data obtained were plotted on stereonets to determine pole concentration and major joint sets using Dips 5.0 software from Rocscience. Two joint sets were identified in Obajana with orientations of 720/0890 and 880/2210 while three joint sets with orientations of 610/0480, 160/2800 and 900/1400 were identified in Ewekoro quarry face. Schmidt hammer hardness and Unit weight tests were performed. The results obtained were used to evaluate the Uniaxial Compressive Strength (UCS) and consequently, the Point load index (Is) of the rock studied. The excavation method was assessed using Discontinuity Spacing Index (If), the Point load index (Is) and the Geological Strength Index (GSI). The discontinuity spacing index was evaluated from the major joint sets identified and the determination of the volumetric joint count (Jv).The geological strength index was estimated using an inbuilt chart of RocLab 1.0 from Rocscience. Excavation assessments revealed that “Very Hard Ripping” is a possible method of excavating Obajana and Ewekoro Type III deposits while the less dense Type I deposit of Ewekoro can be “Ripped”. The only feasible excavation method for Ewekoro type II deposit is “Blasting”.

Kinematic Assessment of Rock Slope Stability at Obajana and Ewekoro Quarries

The research work assessed the stability of rock slopes for optimum exploitation of limestone deposits at Obajana in Kogi State and Ewekoro in Ogun state. Geological mapping was carried out to measure the orientations of discontinuities. The orientation data obtained were plotted on stereonets to determine pole concentration and major joint sets using Dips 5.0 software from Rocscience. Two joint sets were identified in Obajana with orientations of 720/0890 and 880/2210 while three joint sets with orientations of 610/0480, 160/2800 and 900/1400 were identified in Ewekoro quarry face. The Dips software was further used to perform kinematic analyses for toppling, planar and wedge failures for each of the faces investigated. The friction angles for the kinematic analyses were obtained using Roclab 1.0 software (Rocscience, 2002). The results of the analyses show that toppling failure cannot occur in Obajana while planar and wedge failures may occur. The three failure modes (toppling, planar and wedge) were identified in Ewekoro.

Predicting penetration rate of hard rock tunnel boring machine using fuzzy logic

Predicting the penetration rate of a tunnel boring machine (TBM) plays an important role in the economic and time planning of tunneling projects. In the past years, various empirical methods have been developed for the prediction of TBM penetration rates using traditional statistical analysis techniques. Soft computing techniques are now being used as an alternative statistical tool. In this study, a fuzzy logic model was developed to predict the penetration rate based on collected data from one hard rock TBM tunnel (the Queens Water Tunnel # 3, Stage 2) in New York City, USA. The model predicts the penetration rate of the TBM using rock properties such as uniaxial compressive strength, rock brittleness, distance between planes of weakness and the orientation of discontinuities in the rock mass. The results indicated that the fuzzy model can be used as a reliable predictor of TBM penetration rate for the studied tunneling project. The determination coefficient (R 2), the variance account for and the root mean square error indices of the proposed fuzzy model are 0.8930, 89.06 and 0.13, respectively.

Terrestrial laser scanning of rock slope instabilities

ABSTRACTThis manuscript presents a review on the application of a remote sensing technique (terrestrial laser scanning, TLS) to a well‐known topic (rock slope characterization and monitoring). Although the number of publications on the use of TLS in rock slope studies has rapidly increased in the last 5–10 years, little effort has been made to review the key developments, establish a code of best practice and unify future research approaches. The acquisition of dense 3D terrain information with high accuracy, high data acquisition speed and increasingly efficient post‐processing workflows is helping to better quantify key parameters of rock slope instabilities across spatial and temporal scales ranging from cubic decimetres to millions of cubic metres and from hours to years, respectively. Key insights into the use of TLS in rock slope investigations include: (a) the capability of remotely obtaining the orientation of slope discontinuities, which constitutes a great step forward in rock mechanics; (b) the possibility to monitor rock slopes which allows not only the accurate quantification of rockfall rates across wide areas but also the spatio‐temporal modelling of rock slope deformation with an unprecedented level of detail. Studying rock slopes using TLS presents a series of key challenges, from accounting for the fractal character of rock surface to detecting the precursory deformation that may help in the future prediction of rock failures. Further investigation on the development of new algorithms for point cloud filtering, segmentation, feature extraction, deformation tracking and change detection will significantly improve our understanding on how rock slopes behave and evolve. Perspectives include the use of new 3D sensing devices and the adaptation of techniques and methods recently developed in other disciplines as robotics and 3D computer‐vision to rock slope instabilities research. Copyright © 2013 John Wiley & Sons, Ltd.

Study of Seepage Properties of Fractured Rock Mass Based on Improved K-Means Clustering Algorithm

Seepage properties of fractured rock mass are of prime importance for hydraulic engineering and accurate description of rock fracture geometry parameters is an important and basic task in rock hydraulics. In this paper, an improved K-means clustering algorithm for structural plane of fractured rock mass was first brought forward and the corresponding Matlab program for discontinuity orientations partitioning was compiled and then used in the fitting analysis of dominant orientations of certain dam foundation rock mass. On this basis, combining calculation formulas of multi-group fractures, the permeability tensor and principle value was calculated for the actual dam foundation. The results provide a theoretical and computational reference for other similar projects.

Automated rockmass discontinuity mapping from 3-dimensional surface data

Remote sensing technologies, specifically terrestrial-based static LiDAR and photogrammetry, are transforming from state-of-the-art to state-of-practice tools for engineering geologists. The complexity of available software packages to perform standard geomechanical analyses is slowing the widespread adoption of these technologies within the geotechnical community. The development of automated processing tools for feature extraction and data interpretation is aimed at eliminating the need for complex software and manual analysis. This paper presents the development of the algorithms used in the software program PlaneDetect for the automated identification and mapping of planar discontinuities within a 3-dimensional surface model of a jointed rockmass. The software employs a five stage procedure of: surface smoothing, edge detection and masking, blast damaged detection and masking, discontinuity identification, and discontinuity set clustering. The software outputs a stereonet of discontinuity orientations colored by joint set family, an image of the 3-dimensional model with each mapped discontinuity colored by the set family, and a text file of discontinuity orientations. The results of the geomechanical analyses computed by PlaneDetect in comparison to the manual mapping results are more statistically reliable based on less user bias. The time saving realized through using PlaneDetect for mapping discontinuities is approximately ten times compared to the manual mapping approaches.

Terrestrial Photogrammetry and Numerical Modelling for the Stability Analysis of Rock Slopes in High Mountain Areas: Aiguilles Marbrées case

Several high-altitude slope instability phenomena, involving rock blocks of different volumes, have been observed in recent years. The increase in these phenomena could be correlated to climatic variations and to a general increase in temperature that has induced both ice melting with consequent water seepage and glacial lowering, with a consequent loss of support of the rock face. The degradation of the high-altitude thermal layer, which is known as “permafrost”, can determine the formation of highly fractured rock slopes where instabilities can concentrate. The present research has developed a methodology to improve the understanding and assessment of rock slope stability conditions in high mountain environments where access is difficult. The observed instabilities are controlled by the presence of discontinuities that can determine block detachments. Consequently, a detailed survey of the rock faces is necessary, both in terms of topography and geological structure, and in order to locate the discontinuities on the slope to obtain a better geometric reconstruction and subsequent stability analysis of the blocky rock mass. Photogrammetric surveys performed at different times allow the geostructure of the rock mass to be determined and the rock block volumes and detachment mechanisms to be estimated, in order to assess the stability conditions and potential triggering mechanisms. Photogrammetric surveys facilitate both the characterisation of the rock mass and the monitoring of slope instabilities over time. The methodology has been applied in a case study pertaining to the North Face of Aiguilles Marbrées in the Mont Blanc massif, which suffers from frequent instability phenomena. A slope failure that occurred in 2007 has been back-analysed using both the limit equilibrium method (LEM) and 3D distinct element modelling (DEM). The method has been supported and validated with traditional in situ surveys and measurements of the discontinuity orientation and other rock mass features.

A Simple Method for Measuring Discontinuity Orientations from Terrestrial LIDAR Data

The measurement of discontinuity (joint) orientations is critical in assessing the stability of discontinuous rock slopes. The discontinuity orientations are used as input to all discontinuous modeling programs and methods, including kinematic screening methods and limited equilibrium sliding methods. ### Manual Discontinuity Measurements Traditionally, discontinuity orientations are measured manually using a compass (Figure 1). The drawbacks of this method include the fact that these measurements are slow, are tedious, often subject the user to physical danger (from rock falls and/or the need to scale slopes for measurements at heights), and may be inaccurate due to sampling biases when measurements are restricted to accessible areas only. Figure 1. Manual measurements of joints are slow, tedious, expose the user to danger, and are often limited to locations that are easily accessible. ### LiDAR Measurements Terrestrial LiDAR (light detection and ranging) scanners (Figure 2) can return detailed three-dimensional (3-D) maps or point clouds of rock slopes. These include highly accurate maps of planar features such as joints and other discontinuities. Joint orientations can be measured on these point clouds in various ways. LiDAR scanners are increasingly being used for the purpose of measuring discontinuity orientations (Bulut and Tudes, 1996; Feng, 2001; Post, 2001; Donovan et al., 2005; Strouth and Eberhard, 2006; Haneberg, 2008; Olariu et al., 2008; Lato et al., 2009; Sturzeinegger and Stead, 2009; Gigli and Casagli, 2011; and Otoo et al., 2011). Figure 2. Leica ScanStation II in Saudi Arabia. #### Systematic LiDAR Orientation Measurements One way to automatically generate orientations from LiDAR scans is to use advanced algorithms to create solid models (polygonal models) where each polygon represents a planar face. The typical LiDAR measurements work well in general when using scans from vegetation-free continuous rock cuts or slopes where the exposure is entirely composed of discontinuity surfaces. Where vegetation is present, or blast- or …

The Analysis and Correction of Sampling Bias of Discontinuity Orientation Caused by Linear Sampling Technique

Orientation data of discontinuities are of paramount importance for rock engineering studies because they affect the rock slope stability and control the path of flow. Most orientation data are collected using linear sampling. However, data acquired by such linear sampling techniques are subject to bias, owing to the orientation of the sampling line. Even if a weighting factor is applied to orientation data to reduce this problem, the bias is not be significantly reduced when certain sampling orientations are involved. If the linear sampling orientation nearly parallels the discontinuity orientation, most of these parallel discontinuities are excluded from the survey results. To correct this bias ,a weighting factor is applied to orientation data first of all and then the orientation data in blindzone is corrected by added date from the different sampling line .The comprehensive pole and contour plots diagram is completed at last, which is consistent of the real situation. This method makes up for the deficiency of linear sampling technique and obtains the comprehensive orientation data in rock.

Cut Slope Design Recommendations for Sub-Horizontal Hard Sedimentary Rock Units in Ohio, USA

Although most cut slopes in Ohio consist of inter-layered, sub-horizontal units of hard and soft sedimentary rocks (sandstone, limestone, dolostone, shale, claystone, mudstone), slopes consisting of relatively thick hard rock units are not uncommon. Design of stable cut slopes in hard rock units needs to consider rock mass strength and orientation of discontinuities with respect to slope face. Results of kinematic stability analyses show that hard-rock cut slopes are less likely to have conventional plane and wedge failures, caused by unfavorable orientation of discontinuities. The main cause of failure is identified to be the undercutting-induced toppling, which is not amenable to traditional kinematic or rock mass strength-based analyses. Therefore, to recommend a suitable slope angle, numerical models, using UDEC software, were employed to study how various slope angles affect the process of undercutting-induced toppling failures. The UDEC models showed a slope angle of 45° (1H:1 V) to be the most stable angle. However, a 63° (0.5H:1 V) slope angle can significantly reduce the potential for such failures and is therefore more appropriate than the widely used angle of 76° (0.25H:1 V).

A new method for analyzing the stability of rock wedges

In the analysis of rock slope stability, the method of wedge analysis proposed by Hoek and Bray in their classic textbook Rock Slope Engineering (1981) [1] and the computer program SWEDGE (Rocscience, 2001) [18], which was developed based on this method, are widely applied, especially in practical engineering situations. In the Hoek–Bray method, wedge failure modes are identified by the effective normal forces that act on the two discontinuities forming the wedge. The effective normal forces obtained using this method may be distorted with respect to certain conditions since discontinuities usually cannot bear tensile stress. This may lead to inaccurate estimations of failure modes and incorrect solutions for safety factors. This paper establishes criteria for normal forces to identify failure modes according to kinematic conditions of wedge failure and proposes a modified Hoek–Bray method for the analysis of wedge stability. Considering the scattering in discontinuity orientation data, an optimization procedure for wedge stability is proposed. This involves a genetic algorithm (GA) for searching the critical failure surface with the minimum factor of safety and provides a low-limit solution with conservative advantages for engineering support design to ensure the stability and safety of the rock slope.

Determining the Effects of Discontinuities on Blast Heap Fragment Size Distribution Using a Numerical Modeling Method / Określanie wpływu spękań i nieciągłości na rozkład wielkości brył skalnych po pracach strzałowych w oparciu o metody modelowania numerycznego

There are many factors that determine the size distribution of blast heap fragments. The most important factors are the type and amount of explosive material used and the blast design. However, the geological nature of the work area is also an important parameter. In particular, parameters such as the location and frequency of discontinuities affect the size distribution of heap fragments. The general conclusion reached through laboratory and field studies on discontinuities is that the orientation of the discontinuity and the fillings between the discontinuities determine the blast results. This study presents a numerical model that can be used to determine the relationship between the interval and orientation of discontinuities and blast efficiency. Twelve blast experiments were performed at two quarries to develop a numerical model. The data from the field studies were used as input in the numerical model, and the relationship between the discontinuities and fragment size distribution is investigated in this paper.

Assessment of structurally-controlled slope failure mechanisms and remedial design considerations at a feldspar open pit mine, Western Turkey

A variety of structural discontinuities crossing the slopes of Alipasa feldspar open pit mine, in western Turkey, caused different types of slope failures which led to interruptions in ore production. Thereupon, extensive geotechnical investigations, including geological characterization, in-situ and laboratory geotechnical testing, long-term movement monitoring, back-analyses and possible remedial measures, were conducted. Field observations and subsequent analyses suggested that the failures were limited to benches and the movement developed down-slope along discontinuities due to the following reasons: (i) unfavorable orientations of the foliation planes and joints, (ii) low shear strength along discontinuities and (iii) exceptionally heavy rains filling the tension cracks prior to failure. Comparisons between movement vectors and orientation of discontinuities showed a good agreement that indicates two types of instability, namely, planar and wedge failures. A back analysis procedure for the assessment of failures along the rough discontinuities, with non-linear failure envelopes, was successfully applied to the unstable slopes in the pit. The results of the 2-D limit equilibrium back-analyses and movement monitoring data suggested that the wedges and/or planar blocks formed at the uppermost benches tended to move down to fill the gap which resulted from the previous movement of the blocks in the benches. Remedial measures such as dewatering and reduction of height of the benches were suggested. Results of stability analyses conducted for possible remedial measures were presented and discussed.

Verification of a 3-D LiDAR Viewer for Discontinuity Orientations

Light detection and ranging (LiDAR) scanners are increasingly being used to measure discontinuity orientations on rock cuts to eliminate the bias and hazards of manual measurements which are also time consuming and somewhat subjective. Typically LiDAR data sets (point clouds) are analyzed by sophisticated algorithms that break down when conditions are not ideal, for example when some of the discontinuities are obscured by vegetation, or when significant portions of the rock face are composed of fractured facets, weathering generated surfaces, or anything that should not be identified as a discontinuity for the purposes of slope stability analysis. This paper presents a simple LiDAR point cloud viewer that allows the user to view the point cloud, identify discontinuities, pick three points on the surface (plane) of each discontinuity, and generate discontinuity orientations using the three-point method. Additionally, a test of our 3-D LiDAR viewer for discontinuity orientations on rock cuts in the United States of America and Canada is presented.

Utilising of linear and non-linear prediction tools for evaluation of penetration rate of Tunnel Boring Machine in hard rock condition

Predicting Tunnel Boring Machine (TBM) penetration rate is a crucial issue for the successful fulfilment of a mechanical tunnel project. Penetration rate depends on many factors such as intact rock properties, rock mass conditions and machine specifications. In this paper, linear and non-linear multiple regression as well as Artificial Neural Network (ANN) techniques were applied to predict the penetration rate of TBM. In developing of the proposed models, five parameters, which include Uniaxial Compressive Strength (UCS), Brazilian Tensile Strength (BTS), peak slope index (punch penetration), spacing of discontinuities (of weakness planes) and orientation of discontinuities with respect to the tunnel axis (β angle), were incorporated. For this study, 46 datasets were collected. Performance of these models was assessed through the R2, RMSE and MAPE. As a result, these indices revealed that the prediction performance of the ANN model is higher than that of the non-linear and linear multiple regression models.

Assessment of Rockfall Hazard along the Road Cut Slopes of State Highway-72, Maharashtra, India

Rockfall is a major problem in high hill slopes and rocky mountainous regions and construction of highways at these rockfall prone areas often require stable slopes. The causes of rockfall are presence of discontinuities, high angle cut slopes, heavy rainfall, and unplanned slope geometry etc. Slope geometry is one of the most triggering parameters for rockfall, when there are variations in slope angle along the profile of slope. The Present study involves rockfall hazard assessment of road cut slopes for 15 km distance starting from Mahabaleshwar town along State Highway-72 (SH-72). The vertical to subvertical cut slopes are prone to instability due to unfavorable orientation of discontinuities in slope face of weathered and altered basaltic rockmass. The predominant type of instability has been found as wedge type failure involving medium to large size blocks. In order to investigate the existing stability conditions, analyses were carried out at two locations under different slope conditions. The kinematic analysis was performed using stereographic projection method. RockFall 4.0 numerical simulator software was used to calculate the maximum bounce heights, total kinetic energies and translational velocities of the falling rockmass blocks, and a comparative analysis is presented with increasing the mass of blocks and height of the slope. The result of numerical analysis shows that varying slope angle geometry creates more problems as compared to the mass of blocks in the scenario of rockfall.