Strength Properties Of Rock Mass Research Articles

Wpływ ograniczenia naprężenia na stabilność masy skalnej

A huge number of factors controls rock mass failure, but it is mainly influenced by the state of stress and in particular on the bearing capacity and failure mechanism of the massif. The evaluation of rock mass strength in confined and unconfined compression, as well as its tension strength, are key issues to understand rock mass behaviour prior to failure. A connection between the laboratory analyses of the rock mass and the practical use of the obtained data is presented in the current work. The strength properties, confinement effect and failure mechanisms are successfully studied in volcanic rock specimens from an underground mine. In order to estimate the confinement effect on rock mass strength properties, different confined compression stresses on rock specimens are applied. In addition, the crack initiation and propagation in rock samples are observed and rock mass failure mechanisms are studied. The obtained data is used for stability analyses of an underground openings through determination of the safety factor. The obtained results of the safety factors underlined the influence of the confining stress on the rock mass. The tendency of increasing values of the shear safety factor and decreasing values of the tensile safety factor as confinement increases is found. This is an important observation that would allowed more accurate predictions of the stable and unstable zones of the underground openings to be carried out, and thus the stability of the rock mass to be improved.

Geotechnical and Geophysical Investigations of Estimating Rock Mass Properties

Accurate assessments of the deformation and strength properties of rock masses are essential for analysing the foundations, subsurface excavation, and construction of slopes, however, identifying geotechnical properties, particularly weak rock masses, is challenging for geoscientists, geologists, and geotechnical investigators. To determine the rock mass properties, geophysical techniques, and rock mass classification methods are widely used. Although rock classification methodologies exist, they are rarely employed in foundation construction analysis due to being predominantly established for tunnelling purposes. This study aims to employ classification methods, and geophysical and geotechnical investigation approaches to provide realistic rock mass properties for a building foundation, compare results, and assess techniques' effectiveness; it also reviews current state-of-the-art methods for classification techniques and investigations. Results show that compressional and shear wave velocities increase with depth indicating a change from poor to satisfactory mechanical behaviour, and empirical equations provide highly valuable and satisfactory deformation modulus values when compared to field seismic values. Almost all classification methods provided reasonable results compared with the seismic results, however highly overestimated and underestimated outcomes were obtained from some empirical equations applying the Rock Quality Designation index and Rock Mass Rating system. Empirical equations that gave the practical deformation modulus outcomes are the Rock Mass Rating based equations and Q-based equations and Geological Strength Index-based equations. Overall, the Rock Quality Designation index underestimated the seismic result, whereas the Rock Mass Rating, Q, and Geological Strength Index systems produced good agreement and realistic results. To conclude, classification methods were effectively applied to a building foundation. Since the Rock Quality Designation is a key value and feature for other systems including Q, and Rock Mass Rating systems, it is an essential factor. Although the Q systems provided practical consequences, this system mainly relied on the Rock Quality Designation value not the compressive strength of the intact rock. The Rock Mass Rating and being the most feasible and essential systems due to detailed geotechnical observations as inputs more significantly the uniaxial compressive strength of the intact rock, and various factors including deformation modulus, strength, Poisson’s ratio, equivalent cohesion, and friction angle of rock mass as outcomes.

A method to interpret fracture aperture of rock slope using adaptive shape and unmanned aerial vehicle multi-angle nap-of-the-object photogrammetry

The aperture of natural rock fractures significantly affects the deformation and strength properties of rock masses, as well as the hydrodynamic properties of fractured rock masses. The conventional measurement methods are inadequate for collecting data on high-steep rock slopes in complex mountainous regions. This study establishes a high-resolution three-dimensional model of a rock slope using unmanned aerial vehicle (UAV) multi-angle nap-of-the-object photogrammetry to obtain edge feature points of fractures. Fracture opening morphology is characterized using coordinate projection and transformation. Fracture central axis is determined using vertical measuring lines, allowing for the interpretation of aperture of adaptive fracture shape. The feasibility and reliability of the new method are verified at a construction site of a railway in southeast Tibet, China. The study shows that the fracture aperture has a significant interval effect and size effect. The optimal sampling length for fractures is approximately 0.5–1 m, and the optimal aperture interpretation results can be achieved when the measuring line spacing is 1% of the sampling length. Tensile fractures in the study area generally have larger apertures than shear fractures, and their tendency to increase with slope height is also greater than that of shear fractures. The aperture of tensile fractures is generally positively correlated with their trace length, while the correlation between the aperture of shear fractures and their trace length appears to be weak. Fractures of different orientations exhibit certain differences in their distribution of aperture, but generally follow the forms of normal, log-normal, and gamma distributions. This study provides essential data support for rock and slope stability evaluation, which is of significant practical importance.

Seismic Bearing Capacity of Strip Footings Placed Adjacent to Rock Slopes

ABSTRACT The bearing capacity of strip footings placed adjacent to the rock slopes subjected to pseudo-static horizontal earthquake body forces has been investigated by using the upper bound (UB) finite element limit analysis (FELA) in combination with a mesh adaptive strategy. The generalized Hoek–Brown (GHB) failure criterion is applied to describe the strength properties of rock masses, which can be treated as its native form without the smoothing of the yield surface while employing the second-order cone and power cone programming to solve the optimization models. Based on the UB FELA method, the seismic bearing capacity factor is determined considering the effect of different governing parameters, namely the horizontal earthquake acceleration coefficient k h , the normalized slope height H/B, the rock strength ratio σ ci /γB, the geological strength index GSI and the material constant m i . For design purpose, a series of non-dimensional charts are provided, and typical failure mechanisms are also discussed in detail.

Characterization of rock formation at Toshka fourth depression – Egypt

ABSTRACT Recently, the Egyptian south valley has been considered as one of the most promising developments for the mega projects such as power stations, roads and bridges. Fresh water channels were extended through to transfer water from Nasser Lake to the irrigated land in the western desert in order to save the groundwater storage for the later usage. Rock formations generally represent a great challenge in civil engineering due to their wide spatial variability, whether vertically or horizontally. This paper presents the results of a geotechnical study that was carried out across the Toshka fourth depression, Egypt. The study comprises a comprehensive investigation programme in the field and complemented with laboratory testing programme to evaluate the physical and mechanical rock properties. The geotechnical investigation included executing boreholes with a depth up to 100 m; core and bulk samples were extracted and recovered. Moreover, an extensive laboratory testing programme was conducted on the samples. Additionally, Rock Mass Rating System was used to identify the rock mass properties, considering the effect of discontinuities planes, layers joint roughness conditions, slaking rate and in addition to the effect of wetting and drying on Rock Mass strength parameters. The results indicated that the geological formation generally composed of limestone intercalated with layers of silty claystone or clayey siltstone. The results of this study cover, among others, rock mass strength properties that should be considered as a design parameters or regarded as guidelines for the design of any future development in the region.

Results of the research, development and production seminar for drilling and blasting

The article provides the results of the research, development and production seminar on drilling and blasting in surface and underground mine workings and special blasting. The seminar was organized by the Ural Association of Shotfirers (Vzryvniki Urala) and held on 26 May, 2022 on the territory of the UMMC Museum Complex in the town of Verkhnyaya Pyshma, with the participation of the Institute of Mining UB RAS and the Ural Department of Rostekhnadzor. Reports on the following topics were presented: special blasting in explosive welding of metals and explosive demolition; experience with nonexplosive mixtures and devices, including pulsed gas generators, in dense urban areas; the outcome of developing and testing the procedure of studying rock mass strength properties in the course of blasthole roller drilling in open pits; forthcoming innovations in Federal Law no. 116 on Industrial Safety of hazardous production sites; relevance, features and conditions of blasting under safety shelters; mining conditions for underground mining at the Donskay Mining and Processing Plant in Kazakhstan. The theoretical part of the seminar was followed by a tour of the exhibition centers of the UMMC Museum Complex including military and automotive museums, the “Wings of Victory” aviation exhibition, the “Ceremonial Regiment” exhibition centre, and an open exposition site with railway and artillery equipment.

О научно-производственном семинаре взрывников Урала

The article presents information on the outcomes of the scientific and practical workshop on drilling and blasting operations in surface and underground mines and special blasting operations, which was organized by the Blasting Specialists of the Urals Association and held on May 26, 2022, at the Museum Complex of the Urals Mining and Metallurgical Company in the City of Verkhnyaya Pyshma with participation of the Institute of Mining of the Urals Branch of the Russian Academy of Sciences and the Urals Department of the Federal Service for Environmental, Technological and Nuclear Supervision (Rostekhnadzor). The workshop included presentations on the following topics: dedicated blasting operations in explosion bonding of metals and demolition of buildings; experience in working with non-explosive mixtures and devices, including ‒ pulse gas generators in restrained urban conditions; results of development and testing of a method to study the rock mass strength properties during roller-bit drilling of blast holes in open-pits; forthcoming innovations in Federal Law No.116 "On industrial safety of hazardous facilities"; relevance, specific features and conditions of blasting operations below the safety covers; mining and technical conditions of underground operations in the Donskoy GOK mine in Kazakhstan. A tour of the four exhibition centres of the Museum Complex, i.e. those of the military and automobile equipment, the "Wings of Victory" aviation exhibition, the "Ceremonial Regiment" exhibition centre, and the open exhibition site with railway and artillery equipment, was held upon completion of the theoretical part of the event.

Combined effect of anisotropy and uncertainty on the safe mud pressure window of horizontal wellbore drilled in anisotropic saturated rock

The investigation of safe mud pressure window of horizontal wellbore drilled in the saturated rock by accounting for the combined effect of anisotropy and uncertainty is the main purpose of this work. To this aim, the deterministic solution of collapse and fracture initiation pressures are firstly presented in three cases that describe the behavior of wellbore: (1) immediately after drilling (i.e., undrained problem); (2) at long term due to the steady-state fluid flow (permeable boundary case) and (3) by neglecting the variation of initial pore pressure (i.e., impermeable boundary condition case). Based on these deterministic solutions, the key parameters of different sources of anisotropy (initial stress state, poro-elastic and strength properties of rock mass) are highlighted through sensitivity analysis. Then, the famous Monte Carlo Simulation (MCS) is undertaken to quantify the uncertainty effect on the probability of success of safe mud pressure window of the wellbore. We also present an adaptation of the Kriging metamodeling technique to study the stability of wellbore. In comparison with the referent solution of MCS, the Kriging metamodel provides a high accuracy and can be used as a performant tool for the probabilistic assessment of wellbore. The consideration of anisotropy combined with uncertainty, and the hydraulically boundary condition around wellbore in this work allows us to complete the contributions in the literature and confirm their strong effect on the design of wellbore.

Duration of the final phase of mining area deformation process in the conditions of Upper Silesia (Poland)

The ability to estimate the duration of mining impact on the surface is important for both active and decommissioned mines. It allows to plan rational land development and to assess the time of exploitation impact on buildings. The data concerns cases of exploitation with roof caving in 20 hard coal mines in Upper Silesia and cases of exploitation with hydraulic stowing in 4 mines. Based on the analysis of geological and mining documentation, the duration of the final stage of the subsidence process was established — from the end of mining operations to the final stage of the subsidence. It was assumed that the subsidence reached its final state when the increments between two consecutive measurements did not exceed 10 mm. Further analyses were carried out using the regression method using the Statistica program, looking for the relationship between the duration of the final phase of the subsidence process and the quantities characterizing the operating conditions. The obtained results indicate a significant impact of the depth of exploitation and the value of the parameter characterizing the rock mass strength properties on the duration of the final phase of the deformation process. As a result of statistical analyses, appropriate empirical formulas were proposed. In the case of performing exploitation with caving and when the variation in the value of tgβ parameter characterizing the rock mass is small, which currently occurs in the considered basin, one can use the proposed formula, linking the duration of the process with the depth of mining exploitation.

Effects of spatial variability of weak layer and seismic randomness on rock slope stability and reliability analysis

Rock slope stability is a key research issue in geotechnical engineering. Weak layer is a distinct feature distinguishing the rock slopes from soil types, and its existence considerably controls the slope stability. Taking in to account the differences in mineral composition, sedimentary conditions, stress history and other geological processes, the physical and mechanical parameters of rock mass generally show certain spatial variability. On the other hand, for slope failures such as landslides, rockfall and debris flows, earthquake is one of the main triggering factors. In this paper, an efficient framework is presented to evaluate the stability of the rock slope with weak layers considering spatial variability of rock mass strength properties under seismic loading. A rock slope model with weak layer is established, followed by modeling of both the spatial variability of cohesion (c) as well as friction angle (ϕ) of rock material and weak layer characterized by random field method. Random seismic loading is applied via the pseudo-static method. The Latin Hypercube Sampling (LHS) is adopted to calculate the failure probability of rock slope. The results indicate that the spatial variability of weak layer has more influence on the slope stability than that of rock material, and the influence of seismic randomness cannot be neglected. In addition, under different seismic loadings, the spatial variability of weak layers and seismic randomness have different effects on slope failure probability.

Management of Explosive Crushing of Rock Mass in Quarries

The article deals with improving the quality of rock blast crushing due to increase in delay intervals. The recent decades change in understanding of the rock destruction mechanism under the blast loads influence is shown. The blast mechanical effect reveal itself in rock crushing as well as in the loss of strength away from a charge. The blast waves are acting as compressive and tensile loads in this area. Existing micro-defects and micro-cracks grow as a result. The rock mass strength properties changes. A new condition of the rock mass is called pre-destroyed. The blasts time delay increasing causes cracks merging and a gradual size decrease of the rocks structural elements.

Stability Analysis of a Large Gold Mine Open-Pit Slope Using Advanced Probabilistic Method

A large gold reserve was recently discovered at Haveri district of Karnataka state of India where open-pit mining was planned to extract these deposits. Stability analysis for open-pit mine slope at this site is presented in the article. Extensive geological investigations and laboratory testing suggested high variability in geological features of discontinuities, rock mass quality and intact rock properties. Hence, it was decided to perform stability analysis of the rock slope using probabilistic approach along with deterministic approach. Deterministic analysis was carried out with average properties of rock, and reliability analysis of the rock slope was carried out using both traditional and advanced probabilistic methods. In traditional probabilistic method, rock mass strength properties were treated as random variables without considering spatial variation of rock properties and reliability index was evaluated by Monte Carlo (MC) simulation on augmented radial basis function-based response surface. In advanced probabilistic analysis, spatial variability of rock mass strength properties was considered by generating anisotropic random field using Fourier series method with spatial averaging over finite difference zones. Reliability index was then estimated by performing MC simulation using random finite difference method. A comparison was provided between the results of stability analysis of slope from all these approaches. Rock slope was found to be stable in both deterministic and probabilistic approaches; however, the degree of stability predicted was different for both methods. Deterministic approach was found to be inappropriate to analyse the stability of slope having rock mass with variable properties. Further, reliability index and expected performance level of slope were highly underestimated by traditional probabilistic method as compared to advanced probabilistic method.

Assessment of roof stability in a room and pillar coal mine in the U.S. using three-dimensional distinct element method

This paper examines the effect of different geological and mining factors on roof stability in underground coal mines by combining field observations, laboratory testing, and numerical modeling. An underground coal mine in western Pennsylvania is selected as a case study mine to investigate the underlying causes of roof falls in this mine. Three-dimensional distinct element analyses were performed to evaluate the effect of different parameters, such as the variation of immediate roof rock mass strength properties, variation of discontinuity mechanical properties, orientations and magnitudes of the horizontal in-situ stresses, and the size of pillars and excavations on stability of the immediate roof. The research conducted in this paper showed that the bedding planes play an important role on the geo-mechanical behavior of roofs in underground excavations. Therefore, an appropriate numerical modeling technique which incorporates the effect of discontinuities should be employed to simulate the realistic behavior of the discontinuous rock masses such as the layered materials in roof strata of the underground coal mines. The three-dimensional distinct element method used in this research showed the capability of this technique in capturing the important geo-mechanical behavior around underground excavations.

Preliminary estimation of rock mass strength using diamond bit drilling operational parameters

In many mining engineering applications such as prospecting, development, production and grouting, diamond bit drilling is widely used due to high penetration rate, core recovery and its ability to drill with less deviation. It has been well known that the operational parameters of diamond bit drilling are closely related with rock mass strength properties. One of the most widely discussed subjects in drilling is the possibility of using diamond drill bit operational parameters for preliminary estimation of rock mass strength and deformability properties used in many mining engineering design projects. Once such rock properties are estimated, it will be possible to make tactical planning decisions as mining progresses. In this study two different techniques, multiple regression and adaptive neuro-fuzzy inference system (ANFIS) were used to develop the models for preliminary estimation of rock mass strength. The variables used in the models are widely known and recorded operational parameters of diamond bit drilling such as bit load, bit rotation and penetration rate. To develop the models, a database covering the rock properties and the machine operational parameters collected from seven different drill holes in Turkey was constructed. Results indicate that both regression and ANFIS-based models can successfully be used to predict the rock mass strength. Adaptive neuro-fuzzy inference model exhibits better performance according to statistical performance indicators. By means of the developed models it is possible to estimate the strength of rock mass during drilling operation, especially in weak and highly fractured rock masses. The estimated strength parameters can be related to further mining engineering applications such as the assessment of excavatability, blast design and even mine design studies.

Strength hardness rock testing

Rock hardness is an important parameter which characterizes the strength properties of rock mass. The essential aim of this work is to study the influence of different parameters related to the elastic moduli, density and P-velocity. Samples were taken from the Hassi Messaoud site investigation. The tests were carried out (wells OMN602 and OMN402) at different depth ranging from 1900m to 2900m). The method and procedure of the laboratory test are also presented. The obtained results have proved a useful correlation between rock hardness and its strength properties.

Characterization of bi-planar and ploughing failure mechanisms in footwall slopes using numerical modelling

Footwall slopes refer to unbenched rock slopes in which the slope face is parallel to a set of persistent discontinuities (e.g. bedding planes, foliation, faults). These are commonly encountered in weak, thinly bedded, orthogonally jointed, sedimentary rock sequences. Common failure mechanisms include bi-planar failures where shallow dipping crosscutting structures daylight near the slope toe, enabling sliding to occur along steep dipping bedding planes. In the absence of crosscutting structures, failure occurs through deformation and rock mass yielding involving the formation of inter block shear and toe breakout surfaces. Because of the complexity of the toe breakout mechanism, evaluation methods are not well understood. An improved understanding of the failure mechanism, the role of adverse discontinuities, and characterization of the discontinuity, intact rock and rock mass strength properties are key for a successful footwall stability analysis. This paper investigates the development of the inter block shear and toe breakout surfaces with three approaches: i) continuum-based frictional plasticity theory; ii) discontinuum-based distinct-element modelling with Voronoi tessellation using the commercial software UDEC; and iii) hybrid continuum/discontinuum finite-/discrete-element brittle fracture modelling using the commercial software ELFEN. Numerical simulations using ELFEN and UDEC demonstrated a good agreement with frictional plasticity theory. Ploughing failure of footwall slopes is also evaluated, specifically the influence of cross-cutting discontinuity dip angle relative to the slope face. The effects of different geometrical parameters (e.g., slope angle and depth/height ratio) on bi-planar and ploughing failure are assessed using a sensitivity analysis approach. A “Damage Intensity” parameter is introduced and used to quantify damage in the numerical simulations using ELFEN.

Erratum to Volcanic rock-mass strength properties from Snowdonia and Tenerife: implications for volcanic edifice strength

Erratum to Volcanic rock-mass strength properties from Snowdonia and Tenerife: implications for volcanic edifice strength

Rock strength and development of glacial valley morphology in the scottish highlands and northwest iceland

Using data from the Scottish Highlands and northwest Iceland, the present study indicates that bedrock strength properties are an important control on the morphology of glacial valleys. Results indicate that on closely jointed metasedimentary bedrock of low rock mass strength, broad U‐shaped valleys are developed, whilst steeper sided, narrower cross‐profiles have been developed on igneous bedrock of high rock mass strength. Findings suggest it is the interplay of the mass strength of the subglacial bedrock and the dynamic properties of the eroding glacier that control valley morphological development. The implication is that realistic models of topographic development beneath ice sheets need to consider the rock mass strength properties of the eroded bedrock as well as the glaciological variables.

Study on the coalescence mechanism of splitting failure of crack-weakened rock subjected to compressive loads

It is of important significance to study the coalescence mechanism of splitting failure of crack-weakened rock masses under compressive loads. In this paper, a simplified mechanism of crack propagation, in which the crack grows along the direction of maximum principal compressive stress, is proposed. Thus, only mode I is taken into account in the formulation and solution. On the basis of the near crack line analysis method, the elastic–plastic stress field near the crack line is analyzed, and the law that the length of the plastic zone along the crack line is varied with an external loads have been established by the matching condition of the elastic- plastic fields on the boundary, the coalescence stress and the strength properties of rock masses have been determined. The solution is a function of the geometry of the crack array. The results show that the crack coalescence depends on the crack interface friction coefficient, the sliding crack spacing, orientation of the cracks, and the crack half-length. The conclusions are of important significance for rock mass engineering.

Determination of rock mass strength properties by homogenization

AbstractA method for determining fractured rock mass properties is presented here on the basis of homogenization approach. The rock mass is considered to be a heterogeneous medium composed of intact rock and of fractures. Its constitutive model is studied numerically using finite element method and assimilating the fractures to joint elements (Coste, Comportement Thermo‐Hydro‐Mécanique des massifs rocheux fracturés. Thèse de Doctorat, Ecole Nationale des Ponts et Chaussées, Paris, 1997). The method has been applied to a granite formation in France. Geological data on different families of fractures have been used for the statistical representation of the fractures. A mesh‐generating tool for the medium with high density of fractures has been developed. The mechanical behaviour of the rock mass (elasticity, ultimate strength and hardening law) has been determined assuming linear elasticity and Mohr–Coulomb strength criterion both for the intact rock and the fractures. Evolution of the mechanical strength in different directions has been determined as a function of the mean stress, thanks to various numerical simulations. The mechanical strength appears to be anisotropic due to the preferential orientation of the fractures. The numerical results allowed us to determine an oriented strength criterion for the homogenized rock mass. A 2D constitutive law for the homogenized medium has been deduced from numerical data. A 3D extension of this model is also presented. Copyright © 2001 John Wiley & Sons, Ltd.