Resistance Of Rock Mass Research Articles

Determining the Relevance of Commonly Used Hydraulic Parameters for Representing the Water Erosive Force in Rock Mass Erosion within Dam Spillways

Spillways are essential control structures in hydroelectric dams for evacuating excess water during periods of high-water flow. These structures are generally excavated within a rock mass, without lining, and they take the form of a flow channel or a plunge pool. Rock mass erosion is an important issue facing engineers when designing unlined spillways. Methods commonly used to analyze this phenomenon are based on the threshold line concept, i.e., the correlation between rock mass resistance and its destruction against the erosive force of water. Multiple indices have been proposed for both rock mass quality and water energy (or erosive force) to assess rock mass erosion. The selection of appropriate indices is critical when evaluating hydraulic erosion. The erosive force of water is often represented by energy dissipation; however, other parameters, including average flow velocity and shear stress at the bottom of the flow channel, may also be relevant. Thus, a critical question is framed: which index best represents the erosive force of water? Here, we develop an approach to assess the applicability of the various indices used to represent the erosive force of water by relying on erosional events at more than 100 study sites. We determine that the most relevant parameters are linked to water pressure, as pressure head and flow velocity better explain the erosive force of the water than shear stress and water dissipation energy.

Selection of the optimal composition and analysis of the detonating characteristics of low-density mixed explosives applied to break thin ore bodies

Purpose is to select the optimal composition of the mixed low-density explosive (Es) applied in the form of blasthole charges which provide high efficiency of blasting operations while mining of thin ore deposits. The abovementioned becomes possible while studying features of the foamed polystyrene chemical decomposition and gasification; role of additional water components as well as catalyzator being sodium carboxymethyl cellulose; and analysis of explosive characteristics of the compositions. Methods. The research involved lab-based experiments to define application efficiency of the recommended low-density blasting agents through identification of the basic explosive characteristics of the model mixed Es. Findings. The optimal composition of the mixed low-density Es has been developed. It consists of ammonia nitrate, diesel fuel, granulated foamed polystyrene, water, and sodium carboxymethyl cellulose to be used to break thin ore bodies. Owing to it, the possibility has arisen to control over a wide range both detonation velocity and pressure of blasting fumes during the charge density increasing or decreasing. The main detonative characteristics of the proposed compositions of low-density Es have been determined helping perform explosive rock mass loading in terms of extremely low values of both energy and explosive characteristics. The developed composition of the mixed low-density Es makes it possible to control quantity of Es energy in a volume well unit by means of increase or decrease in the charge energy concentration depending upon the changes in the rock mass resistance; in such a way, efficient breakage of thin ore bodies is provided inclusive of less dilution indicators. Originality. For the first time, dependence of the relative efficiency of the mixed low-density Es upon the foamed polystyrene volume content has been identified as well as dependence of pressure of blasting fumes upon the charging density. Practical implications are the development of procedures for blasting operations while thin ore body mining. The procedures are based upon formulating of the optimal composition of low-density Es differing in its simplicity, safety, and efficiency; and helping reduce prime cost of the extracted mineral at the expense of the decreased degree of the ore dilution. An empiric formula to define specific consumption of the low-density Es has been proposed for Akbakay mine.

Granitic inselberg erosion controlled by dike swarm array in semiarid Brazil

Numerous inselbergs rise above the regional erosional surface in semiarid northeastern Brazil. The inselbergs are underlain by the Quixadá Pluton and cut by cm-thick granite dike swarms. Five inselbergs with abundant dikes from two different parts of the pluton were selected to investigate the role of dike patterns in the evolution of residual granite topography, including morphological features of hillslopes. The methods included field mapping of landforms, structural measurements of accessible dike arrays, and rock strength determinations using a Schmidt hammer. Unmanned Aerial Vehicle (UAV) photogrammetry was used to build detailed digital surface models of inselbergs and to recognize geometric patterns of dike arrays. In addition, 34 rock samples were collected to determine rock composition and evaluate their resistance to weathering. The results show that >60 % of dikes display a sub-horizontal array composed of low- and medium-angle dikes (up to 45° dip), which tend to increase rock-mass resistance, providing effective barriers against weathering and vertical fracturing, and are associated with the most prominent, steep-sided residual hills. Besides, dike swarm geometry controls the slope outlines of some inselbergs, which commonly conform to dike attitudes. By contrast, steeply-dipping dikes (>60° dip) promote weathering along the dike-host rock interface and are hypothesized to underlie the plains between the inselbergs. At a small scale, dikes control the occurrence and evolution of minor rock landforms such as weathering pans, solution runnels, overhangs, and split boulders. Our findings show that the resistance of inselbergs to erosion is not homogeneous in the granitic pluton but is controlled by local factors such as dike occurrence and dip.

A Simplified Approach to Estimate Anchoring Capacity of Blocky Rock Mass with Pressure Arch Theory

In this paper, a simplified method for predicting rock mass resistance against tensile forces from rock anchors (anchor) is presented. The interaction of anchors and rock mass was investigated using three-dimensional discontinuous numerical modelling. Several patterns of rock discontinuities were assumed in the numerical modelling while a single anchor is embedded in it. The numerical results show that the existence of a discontinuity set sub-parallel to the anchor significantly improves the rock mass resistance against the tensile force from the anchors. This phenomenon is due to the rock block interlocking at the sub-parallel discontinuity set. Rock block interlocking generates a zone of stress concentration inside the rock mass which has an arch shape (i.e., a pressure arch), resisting against the anchor's tensile force. The load-bearing capacity of the pressure arch plays a significant role in the resistance of the rock mass against the forces from the rock anchor. A voussoir beam analogy was utilised to study the load-bearing capacity of the pressure arch. A simplified analytical approach was developed to assess the load-bearing capacity of the voussoir beams. Then, it was used in combination with the weight of the mobilised rock mass by the anchor to assess the maximum anchoring resistance of the rock mass (anchoring capacity). The suggested method was calibrated by numerical modelling and relevant published pull-out test results. The technique developed in this paper shows the significance of rock block size, shear behaviour of rock discontinuities, Young's modulus of the rock mass, and uniaxial compressive and tensile strength of the intact rock in anchoring capacity of rock masses.

The Effect of Clay-Soil on Landslide: Case Study from Central Java, Indonesia

Landslides are caused by triggering factors such as rainfall, geological factor, geotechnical properties of surface rock, and human activity. Weathering is an essential phenomenon that generates clay minerals and influences the landslide mechanism because the process will reduce rock mass resistance. In the study area, intensive rain contributed to the weathering and increased the water content in the clay soil that affected the stability of the slopes. The clay mineral in the soil in the study area was investigated. The type of clays was determined by plasticity index and liquid limit value and X-Ray diffraction analysis. Some geotechnical properties also were determined, including grain size, shear strength, and atterberg limit. As a result, the clay minerals within the study area’s volcanic rock formations play an important role in causing landslides because of illite and smectite, which reduce shear strengths and have high swelling potentials.

Effects of Normal Stress and Joint Inclination Angle on Rock Failure Characteristics Under Compression–Shear Conditions

In this study, cement mortar was used to make specimens containing groups of parallel joints with different inclination angles to simulate natural rock mass, and the specimens were subjected to shear tests under different normal stresses. By analyzing the crack propagation path, failure modes, and strength characteristics of these rock specimens, the effects of normal stress and joint inclination angles on the strength and failure characteristics of this type of rock mass were studied. The following conclusions are drawn: 1) when the inclination angles of the joints are 0° and 15°, the changing of the normal stress did not affect the failure mode of the rock mass. The rock mass was mainly in the mode of shear failure, and the increase in the normal stress only increased the spalling area of the rock mass. 2) When the inclination angles of the joints are 30°, 45°, and 60°, with the increasing of the normal stress, the number of those approximately parallel cracks in the specimens increased, the friction marks caused by shearing increased, and the failure mode of the rock mass changed from tension failure to tension–shear composite failure. 3) Under different joint inclination angles, the propagation and penetration paths of cracks generated in the rock mass and the damage mode of the rock mass were different. With an increase in the joint inclination angles, the damage mode of the rock mass gradually changes from shear damage to tensile–shear composite damage and the α and β angles between the through cracks and the vertical direction on the left and right sides of the specimens tended to decrease. 4) The shear resistance of the rock mass was affected by the inclination angle of the joints and the normal pressure. The shear resistance of rock mass was improved due to the increasing of normal stress. Within a certain range, with the increasing of the inclination angles of the joint, the shear resistance of the rock mass tended to decrease first and then to increase.

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.

Uncertainty consideration in rock mass blastability assessment in open pit mines using Monte Carlo simulation

Blastability is defined as the resistance of rock mass to fragmentation due to the dynamic stress of blasting. Comprehensive study and understanding of geomechanical conditions of the in-situ rock mass are necessary to analyze the blastability along with optimal blasting design. Blastability Index (BI) is one of the most widely applied methods for the classification of rock mass and predicting the specific charge of blasting in open pit mines. Regarding the existence of uncertainty in the geomechanical characteristics of in-situ rock masses, accurate BI assessment requires a wide range of field studies. It could lead designers to a wrong decision about rock mass classification. Simulation is one of the reliable and applicable approaches to overcome the geomechanical uncertainties in rock mass studies. Therefore, in this paper, the Monte Carlo simulation method has been applied to blastability assessment in Sungun Copper Mine, Iran. For this purpose, the geological factors, including rock mass description, joint plane spacing, joint plane orientation, specific gravity influence, and hardness, were measured and implemented in 46 points of the pit wall. Statistical analysis was carried out to find out the best fit-distribution functions of all mentioned parameters. After that, the Monte Carlo simulation program was developed and carried out in MATLAB software. The overall results of the simulation reveal that the Monte Carlo method could provide a better vision of any possible combination of geological factors. It is also found out that less than two percent of the rock masses do have challenging blastability conditions, and the average blastability of rock masses in the studied mine is 18, which is close to an average score of blastability classification as well.

Determination of the rock mass resistance index (GSI) based on image processing

More and more often, and on an increasingly large scale, the geological resistance index (GSI) system is used for the design and practice of the mining process. The GSI, is a unique system for classifying the mass of rocks, linked to the parameters of rock strength and mass distortion, based on the generalized criteria of Hoek-Brown and MohrCoulomb. The GSI can be estimated using standard and in situ tables by direct surface observations in underground or surface mining. The GSI value provides a numerical representation of the overall Geotechnical quality of the rock mass. The method for determining GSI using photographic images of the in situ rock mass, with image processing technology, fractal theory and artificial neuronal network (ANN), is already known and successfully applied in several projects.

Study of Elastic, Elastoplastic and Post-Limiting States of Rock Mass in the Vicinity of Openings Using the Measurement Data at Their Boundaries

The problem of determining the stress-strain state in the vicinity of an opening with an arbitrary shape using the measurements of the Cauchy stress vector and displacement vector is solved. The states of elasticity, plasticity, and post-limiting straining are considered. The obtained results allow rapid determining of the resource capabilities of rock mass resistance to failure on the boundary both in a buried opening and in opencast mining.

Bemessungskonzept für Druckschächte bei Nutzung des passiven Gebirgswiderstands

AbstractThe proposed method can be seen as an adaption of the ”Seeber“ concept considering developments in geomechanics, calculation methods and steel technology over the last decades. When exposed to inner pressure, the cracking condition is transgressed and steel linings will not protect the rock mass against cracking. Accordingly, the post‐failure behaviour of the rock mass is an essential basis for structural design. The effects of crack water pressure on radial displacements and the width of gaps are considered. The resistant behaviour of the rock mass is determined by its minor primary principal stress. Under mountain ridges and slopes, there is no correlation between the minor stresses and the height of overburden. Obviously damage cases in concrete lined tunnels are the result of inappropriate assessment of principal stresses. A better approach is proposed based on fundamental considerations and FE calculations. Crack water pressure close to the level of the minimal principal stress will induce progressive hydraulic fracturing in the rock mass, which requires safe waterproofing sealing of the shaft. Grouting the coaxial gap in rock mass is a firm part of any design concept. In shafts sealed by membranes, the capability to bridge fissures must be proved by tests. In steel lined shafts, the usable passive resistance of rock mass is determined by the acceptable radial displacement.

End bearing response of open-ended pipe piles embedded in rock

Prediction of bearing capacity of steel pipe piles in rock masses is an important consideration in civil engineering especially as such prediction influences the safety of the supported superstructures as well as the pile integrity in pile driving operations. Provided that the rock mass is described as a linear elastic and perfectly plastic material obeying the Hoek-Brown failure criterion, a finite element analysis is performed to investigate the embedment depth effect on the annular base bearing capacity and the failure mechanism of typical open-ended pipe piles in sedimentary rock masses. The pipe pile has smooth walls and rough toe surface. Annular toe resistance of pipe piles can serve as an estimate of the rock mass resistance to driving in a fully coring mode which is usually expected for large diameter open-ended pipe piles. Pipe pile results are also extended to circular piles and embedded strip foundations socketed in rock masses. The analysis is shown to highlight the influence of the annular geometry of the pipe pile causing an unsymmetrical failure mechanism with respect to pipe wall center as well as an inclination of rock mass reaction, which if sufficiently large, may lead to pile convergence and damage during pile driving operations. The failure mechanism legitimates the plug tendency to rise up in the pipe and explains the plug formation. The study demonstrates that in most practical applications, the bearing capacity of pipe piles approaches a limiting value, which is less than or at most equal to the end bearing capacity of an embedded strip foundation of width equal to the pipe wall thickness. A comparison has been made with experimental data. It is shown that the results are relatively in good agreement with test data in terms of rock mass resistance and the mechanism of rock plug formation.

Evaluation of mechanical performance and optimization design for lattice girders

The present study investigated the mechanical performance of the LG and its cost-efficiency. The analyses were performed using loading capacity test and numerical approach. Influential factors such as main steel bar, diagonal bar, welding and stirrup were considered. First, different cases were designed to investigate the contribution of each component. An experimental system which could simulate the resistance of rock mass was developed. Then, a performance index was introduced to evaluate the relationship between the ultimate loading capacity and cost of construction material. A simple design procedure for engineers to optimize the LG was also provided. After that, a series of plain lattice girders, shotcreted lattice girders were studied and optimized. Meanwhile, refined numerical models were developed in ABAQUS to further validate the results. Finally, the structural performance of lattice arch girders was studied. The results revealed that under the large eccentric mechanical model, the main steel bar on the rock mass side, the diagonal bar, welding length and the stirrup have limited contribution to the ultimate loading capacity of the lattice girders. Thus, the researchers proposed the optimization strategies for the lattice girders: decrease in the diameter of the main steel bar on rock mass side and the diagonal bar, reduction of the welding length, and cancellation the stirrup.

Comparing rockfall scar volumes and kinematically detachable rock masses

Scenario-based risk assessment for rockfalls, requires assumptions for different scenarios of magnitude (volume). The magnitude of such instabilities is related to the properties of the jointed rock mass, with the characteristics of the existing unfavourably dipping joint sets playing a major role. The critical factors for the determination of the maximum credible rockfall volume in a study site, the Forat Negre in Andorra, are investigated. The results from two previous analyses for the rockfall size distribution at this site are discussed. The first analysis provides the observed size distribution of the rockfall scars, and it is an empirical evidence of past rockfalls. The second one, calculates the kinematically detachable rock masses, indicating hypothetical rockfalls that might occur in the future. The later gives a maximum rockfall volume, which is one order of magnitude higher, because the persistence of the basal planes is overestimated. The tension cracks and lateral planes interrupt systematically the basal planes, exerting a control over their persistence, and restricting the formation of extensive planes and large rockfall failures. Nonetheless, the formation of basal planes across more than one spacings of tension cracks is possible and small step-path failures have been observed too. Concluding, the key factor for the determination of the maximum credible volume at the study-site is the maximum realistic length of the basal planes, penetrating into the rock mass, their spacing, and, if applied, the contribution of the rock bridges to the overall rock mass resistance.

New Approach to the Design of Tunnels in Squeezing Ground

The study of the mechanical behavior of discontinuous rock masses is a rapidly growing subject. Much research has been reported in the literature concerning the estimation of the tunnel support pressures incorporating the real behavior of a rock mass using different types of constitutive models and rock parameters. These studies have favored the introduction of various analytical solutions for the easier geomechanical cases but have not been converted into numerical models suited for commercially available software and therefore could not be used in real and more complex engineering applications. The notable constitutive models used in common practice in rock mechanics are the Mohr-Coulomb and Hoek-Brown failure criteria. Most of the commonly available software supports only these two failure criteria. The difficulties faced in possibly implementing a new constitutive model into the numerical suites already available are so large that the studies using innovative constitutive models result in a mere academic exercise. In this paper, a new methodology is described for the application of the polyaxial constitutive model, which is characterized by the direct influence of all the principal stresses in the resistance of a rock mass. The methodology applied in this research uses the format of the Mohr-Coulomb model using the equivalent angle of friction and cohesion of the rock mass surrounding the tunnel. The equivalent parameters of rock mass resistance, which are directly derived from the common Mohr-Coulomb parameters, are also influenced by the intermediate principal stress σ2, in accordance with what was suggested in the polyaxial strength criterion, and by the approach chosen for quantifying the uniaxial compressive strength σcr of the rock mass. To demonstrate the practical applicability of this constitutive model, it has been used to predict the squeezing of rock observed and measured at three different instrumented sections of a tunnel.

Early Holocene catastrophic mass-wasting event and fan-delta development on the Hua-tung coast, eastern Taiwan

Landslides and debris flows rarely occurred during historical times in the tectonically active Coastal Range of eastern Taiwan. This topographic stability, however, contrasts greatly with the widespread existence of terraced alluvial fans and fan-deltas on the Hua-tung coast which fringes the range. This study focuses on the two largest fan–terrace systems on the Hua-tung coast, both of which consist of alluvial fans (plane-view areas up to 8 km 2) larger than their contributing catchments. Stratigraphic data show that both systems were in sandy, wave-dominated settings during de-glacial times. The systems were then disturbed by a catastrophic landslide/debris-flow event (or events), which brought enormous amounts of gravel (Facies Gm) into the systems, deforming previously-deposited marine sands (Facies Sm) and shallowing the seafloor. The combined Gm/Sm complex yields multiple radiocarbon dates ranging from 11.3 to 8.3 ka cal BP, with a cluster around 8.6 ka cal BP. This mass-wasting event has been unique since the emergence of its contributing catchment 0.2–0.3 Ma ago. The low frequency of such an event could reflect the great resistance of rock mass in the source areas to weathering and erosion. The common blockage of valley floors by giant-boulder piles, which limits channel incision and sediment transport, could also increase the apparent stability of the mountain. The trigger of landslides in the Coastal Range has been linked to large earthquakes. Additionally, we propose that the great magnitude and duration of the observed early Holocene event were caused by the contemporaneous prolonged rainfall (and/or high frequency of typhoons) associated with the East Asian summer monsoon maximum.

Research on Internal Force and Deformation of Supporting Rock-Socketed Piles Based on Ultimate Resistance Mechanics Theory

At present there have rarely studies on internal force and deformation for rock-socketed piles of deep excavation. The current approaches still exist and have many deficiencies and all of them didn't consider the effect of rock-socketed length. Based on the theoretical mechanics analysis of rock mass resistance, the computing methods of ultimate resistance Pult is applied to the analysis of force balance of rock-socketed part, the paper has put forward the detailed procedure for computing internal force and deformation of supporting rock-socketed piles in view of the rock-socketed length, moreover, the influence of the stability of rockmass is comprehensive considered in this method. Finally, an example is analyzed according to the procedure, the calculation results show that the method is much feasibility. The internal force and deformation of the retaining piles computed according to the procedure mentioned above satisfies the stability of rockmass.

The effects of clay on landslides: A case study

Landslides are triggered by geological structures, morphology, climate of the region, geotechnical properties of surface rock, engineering excavation for various purposes and waste water parameters. Weathering is a very important factor in landslide occurrences because it decreases the resistance of rock mass. Clay, a weathering product of rock mass, contributes to landslide occurrence because of their chemical and physical properties. It is believed that the intense rainfall in the East Black Sea region not only contributes to the weathering of the rock mass, but also increases the water content in the clays that leads to reduction in the stability of natural slopes. In this study, the clays forming as a result of completely weathering dacitic rock in Kanlica (Giresun) and surroundings were investigated in association with landslides and determined mitigation measures for landslide in Kanlica Village. The type of clays was determined as illite using Differential Thermal Analysis (DTA). From laboratory tests the geotechnical properties of clays were ascertained to be LL = 47.2%, PI = 19.6%, γ s = 25.89 kN/m 3, γ d = 19.91 kN/m 3, n = 44.7%, ϖ = 25.89%, c′ = 21.58 kN/m 2, ϕ′ = 31°. As a result, both stress increase and strength decrease happen due to the increase of water content, thus a landslide occurred and causes extensive damage to property in the vicinity.

Predicting the Spatial Distribution of Pyrite Concretions and its Influence in Continuous Coal Mining

Mine planning in the coal industry is traditionally developed using a geological model built by discretising relevant geological and engineering attributes into small blocks. Production scheduling is planned based on a 3D geological model representing important features, such as coal cumulation, coal recovery at the plant and other geochemical properties relevant for environmental characterisation. In coal operations using continuous mining systems, rock mechanics properties are deemed relevant as these properties directly influence equipment performance. Rock mass resistance and its abrasiveness impact directly the system productivity. Operational difficulties may arise when using continuous coal cutters within zones containing high concentrations of pyrite concretions. In extreme situations, high pyrite concentration makes unpractical the use of continuous systems with severe costs penalties if not predicted in advance. This paper presents a methodology to forecast pyrite spatial distribution based on kriging. The results proved to be appropriate based on reconciliation obtained comparing pyrite percentage versus bit consumption. A case study in major coal deposit illustrates the methodology.

Distribuição espacial de concreções piríticas e sua influência na performance de conjuntos mecanizados em mina de carvão

O planejamento mineiro na indústria carbonífera é tradicionalmente desenvolvido utilizando um modelo geológico construído pela discretização de atributos relevantes (geológicos, de engenharia, etc.) em blocos de lavra. O planejamento da produção é elaborado com base em modelos geológicos 3D representando importantes características, tais como acumulação de carvão, recuperação na planta de beneficiamento além de outras propriedades geoquímicas relevantes para, por exemplo, a caracterização ambiental. Nas operações de lavra com conjuntos mecanizados, as propriedades mecânicas das rochas são julgadas relevantes na medida em que têm influência direta na performance do equipamento. A resistência da rocha e sua abrasividade têm um impacto direto na produtividade do sistema. Dificuldades operacionais podem surgir quando cortadeiras de frente atuam em zonas contendo altas concentrações de concreções piríticas. Em situações extremas, altas concentrações de concreções podem penalizar de tal forma a atuação de conjuntos mecanizados, em termos de custos, que podem tornar impraticável sua operação, se o esquema de avanço não foi corretamente previsto. Esse artigo apresenta uma metodologia de previsão da distribuição espacial de pirita baseada em krigagem. Os resultados provaram ser apropriados baseando-se em uma reconciliação obtida pela comparação de percentagens de pirita versus consumo de bits. Um estudo de caso em um grande depósito de carvão ilustra a metodologia.