Mechanical Parameters Of Rock Mass Research Articles

Multiscale method for identifying and marking the multiform fractures from visible-light rock-mass images

Multiform fractures have a direct impact on the mechanical performance of rock masses. To accurately identify multiform fractures, the distribution patterns of grayscale and the differential features of fractures in their neighborhoods are summarized. Based on this, a multiscale processing algorithm is proposed. The multiscale process is as follows. On the neighborhood of pixels, a grayscale continuous function is constructed using bilinear interpolation, the smoothing of the grayscale function is realized by Gaussian local filtering, and the grayscale gradient and Hessian matrix are calculated with high accuracy. On small-scale blocks, the pixels are classified by adaptively setting the grayscale threshold to identify potential line segments and mini-fillings. On the global image, potential line segments and mini-fillings are spliced together by progressing the block frontier layer-by-layer to identify and mark multiform fractures. The accuracy of identifying multiform fractures is improved by constructing a grayscale continuous function and adaptively setting the grayscale thresholds on small-scale blocks. And the layer-by-layer splicing algorithm is performed only on the domain of the 2-layer small-scale blocks, reducing the complexity. By using rock mass images with different fracture types as examples, the identification results show that the proposed algorithm can accurately identify the multiform fractures, which lays the foundation for calculating the mechanical parameters of rock masses.

Experimental study on the size effect and anisotropy in mechanical properties of fractured rock mass based on 3D printing

The size effect and anisotropy of fractured rock mass mechanical parameters are difficult problems to solve in the field of engineering. This study taken full advantage of sand 3D printing technology to batch-reproduce complex structures and prepare rock-like specimens with different sizes and rotation directions. The size effect and anisotropy of the fractured rock mass were investigated. Digital image correlation was used to conduct noncontact full-field observations of the specimen. The results showed that the sand 3D printing specimens have the advantages of high precision and brittleness and can reproduce the deformations and failure processes of natural rock. The compressive strength and failure mode of the fractured rock have significant size effect characteristics. Assessing the size effect on the compressive strength of the specimen, 100 × 100 mm is the mechanical representative elementary volume (mREV) scale. The compressive strength and failure mode of the fractured rock under the mREV scale show obvious anisotropy. Based on the size effect of fracture density, 80 × 80 mm was identified as the geometric representative elementary volume (gREV) scale. The gREV scale was smaller than and close to the mREV scale was found. In addition, the differentiation rate of standard deviation (DRSD) is defined to provide information on the dispersion of the strain field and the precursor information of crack initiation during the deformation and fracture of the rock mass. This study provides a new method for laboratory experimental studies on the size effect and anisotropy of complex fractured rock masses from the perspective of 3D printing.

A new method for determining strength parameters of rock using digital drilling technology

Fast and accurate prediction for mechanical parameters of rock mass is an important prerequisite for guiding the safe construction of rock engineering. At present, the rock strength parameters test requires well-prepared samples; sample preparation is time consuming, costly, and difficult as well as destructive, in particular the polishing and rectification of the sample ends. In this paper, the mathematical model of the drilling process is established based on the force characteristics of the drill bit and the principle of mechanical limit equilibrium. The digital drilling tests are carried out on four types of rocks to drilling characteristics using the digital drilling system. The concept of cutting strength ratio is proposed to analyze the correlation between cutting strength ratio and rock internal friction angle and cohesion. A new method is proposed for determining the compressive and tensile strength of rock. The results show that the cutting strength ratio increases with the increasing of internal friction angle and cohesion. The uniaxial compressive strength and tensile strength of rock increase linearly with the cutting strength ratio. The average error of rock tensile strength is 12.29%, and the average error of uniaxial compressive strength is 20.44%. The internal friction angle of rock obtained based on the digital drilling technology is consistent with the value measured by the laboratory standard test. This method can provide a new way to determine rock strength parameters in real time.

Research on failure mechanism and support technology of fractured rock mass in an undersea gold mine

The surrounding rock control has been a difficult problem for fractured rock mass in hard rock mines. This article describes a case study of the failure mechanisms and the support design technology for fractured rock mass drifts in Xinli Gold Mine. Based on field investigation, the geology characteristics, failure types, influencing factors, support types, and their failure types were analyzed. The rock mass classification, rock mass physical and mechanical parameters were obtained by using Q, RMR, and GSI systems. The zoning of surrounding rock, stability analysis and zoning support schemes design were carried out based on rock mass classification results. The pretension is designed by China underground mine experiences and verified by numerical simulation. RS2 was used to compare the plastic zone under pre- and post-support conditions. The plastic zone is significantly reduced after support is installed, which indicates that the designed support schemes can effectively control the failure of surrounding rock. In view of difficulties in the excavation and support of fractured rock mass, the short excavation and short support technology was proposed to ensure the success excavation of the drift in fractured rock mass. The field application shows that the short excavation and support technology are effective.

Progressive Failure of Surrounding Rock in Underground Engineering and Size Effect of Numerical Simulation

The analysis and simulation of progressive failure of surrounding rock is very important for analyzing the stability of surrounding rock in underground engineering. Size effect is also a key problem worth further study in engineering. Taking the underground powerhouse on the right bank of Baihetan as an example, the acoustic test results are collected and the relaxation and failure characteristics of the surrounding rock are summarized. Then, the numerical simulation of progressive failure of surrounding rock of underground powerhouse is carried out by using the finite discrete element method CDEM (continuum-based discrete element method). The results are compared with the acoustic test results of the surrounding rock relaxation layer, and the stress and displacement of surrounding rock characteristic points are analyzed. At the same time, the size effect of grid and mechanical parameter in the process of numerical simulation are discussed. The calculated fracture depth of surrounding rock is in good agreement with the acoustic test results, which shows the reliability of progressive failure simulation of surrounding rock of the underground powerhouse. When CDEM is used to simulate the excavation of tunnels with different tunnel diameters, the minimum grid size should be about 1% of the tunnel diameter. The mechanical parameters of rock mass have significant size effect, which needs to be analyzed in detail. The research results prove the superiority of the CDEM method in simulating the progressive failure of hard surrounding rock and its unique size effect characteristics, which can provide technical reference for the application of the CDEM method in other similar engineering problems.

A 3D microseismic data-driven damage model for jointed rock mass under hydro-mechanical coupling conditions and its application

Rock mass is a fractured porous medium usually subjected to complex geostress and fluid pressure simultaneously. Moreover, the properties of rock mass change in time and space due to mining-induced fractures. Therefore, it is always challenging to accurately measure and model rock mass properties. In this study, a three-dimensional (3D) microseismic (MS) data-driven damage model for jointed rock mass under hydro-mechanical coupling conditions is proposed, and it is a 3D finite element model that takes seepage, damage and stress field effects into account jointly. Multiple factors (i.e. joints, water and microseismicity) are used to optimize the rock mass mechanical parameters at different scales. The model is applied in Shirengou iron mine to study the damage evolution of rock mass and assess the crown pillar stability during the transition from open-pit to underground mining. It is found that the damage pattern is mostly controlled by the structure, water and rock mass parameters. The damage pattern is evidently different from the two-dimensional result and is more consistent with the field observations. This difference is caused by the MS-derived damage acting on the rock mass. MS data are responsible for gradually correcting the damage zone, changing the direction in which it expands, and promoting it to evolve close to reality. For the crown pillar, the proposed model yields a more trustworthy safety factor. In order to guarantee the stability of the pillar, it is suggested to take waterproof and reinforcement measures in areas with large damage degrees.

Pre-stressed anchor cable force evolution laws of plane sliding bedding slopes

This paper aims to understand how anchor cable force evolution laws can improve reinforcement designs. The self-developed weak plane sustained deterioration technology was conducted in the indoor test on the reinforced bedding rock slope containing a linear type weak plane. The force evolution laws of anchor cables with the weak plane sustained deterioration was studied. Furthermore, the theoretical equations were derived on the basis of the rigid assumption of the rockmass and the limit equilibrium method, and the equations have been verified to be reliable through comparison with the test results. The numerical simulations in different rockmass mechanical parameters reveal that the theoretical equations are suitable for hard rockmass. The results indicate that, with the weak plane sustained deterioration, the anchor cable axial forces increase gradually, and the axial force increase is inversely proportional to the length of the free sections. The findings could provide the theoretical guideline for the pre-stress safety reserves during the reinforcement designs of anchor cables in different positions of bedding rock slopes.

Prediction of mode I fracture toughness of rock using linear multiple regression and gene expression programming

Prediction of mode I fracture toughness (KIC) of rock is of significant importance in rock engineering analyses. In this study, linear multiple regression (LMR) and gene expression programming (GEP) methods were used to provide a reliable relationship to determine mode I fracture toughness of rock. The presented model was developed based on 60 datasets taken from the previous literature. To predict fracture parameters, three mechanical parameters of rock mass including uniaxial compressive strength (UCS), Brazilian tensile strength (BTS), and elastic modulus (E) have been selected as the input parameters. A cluster of data was collected and divided into two random groups of training and testing datasets. Then, different statistical linear and artificial intelligence based nonlinear analyses were conducted on the training data to provide a reliable prediction model of KIC. These two predictive methods were then evaluated based on the testing data. To evaluate the efficiency of the proposed models for predicting the mode I fracture toughness of rock, various statistical indices including coefficient of determination (R2), root mean square error (RMSE), and mean absolute error (MAE) were utilized herein. In the case of testing datasets, the values of R2, RMSE, and MAE for the GEP model were 0.87, 0.188, and 0.156, respectively, while they were 0.74, 0.473, and 0.223, respectively, for the LMR model. The results indicated that the selected GEP model delivered superior performance with a higher R2 value and lower errors.

Three-dimensional failure behavior and cracking mechanism of rectangular solid sandstone containing a single fissure under triaxial compression

In actual rock engineering, fissures play an important role in determining the mechanical parameters of rock mass, whereas it is very difficult to construct fissures in cylindrical specimens. Therefore, the pre-fissured rectangular rock specimens were constructed innovatively. Moreover, a series of triaxial compression experimental results on the failure mechanical behavior of rectangular solid sandstone specimens containing a single fissure were reported. The lateral strain in different directions was monitored and the experimental results show that elastic modulus and axial strain increase non-linearly with confining pressure, and the average Poisson’ s ratio parallel to fissure (μ2) is larger than that vertical to fissure (μ3). The cohesion, Hoek-Brown parameters of peak strength show similar trends with that of crack damage threshold to the fissure angle (α), and the parameters of the peak strength are larger than those of crack damage threshold. However, the internal friction angles of the peak strength and crack damage threshold are almost equal. Based on the geometries and properties of cracks, ten typical crack types are identified. Cracks vertical to pre-existing fissures occur in specimens under uniaxial compression, whereas cracks parallel to pre-existing fissures occur under triaxial compression. Finally, X-ray micro-computed tomography (CT) observations are conducted to analyze the internal damage mechanism of sandstone specimens with respect to various fissure angles. Reconstructed 3-D CT images indicate obvious effects of confining pressure and fissure angle on the crack system of sandstone specimens. This research elucidates the fundamental nature of rock failure under triaxial compression.

Establishment of landslide early-warning indicator using the combination of numerical simulations and case matching method in wushan open-pit mine

Landslides seriously threaten the safety of human life and property. In order to predict the on-set of potential landslides, this paper first characterizes the physical and mechanical parameters of rock mass on the basis of core rock quality designation identification, the geostatistics interpolation method, and the Hoek-Brown criterion. Then, the rock-mass physical and mechanical parameters characterization model was transformed to the slope numerical models, and the characteristics of potential landslides were predicted combined with the monitoring data and numerical simulation. Finally, on the basis of pairing between potential- and historical landslide cases, an early-warning indicator of a potential landslide was set as a posterior indicator of a historical landslide with the highest similarity. The results show that the potential landslide mode of the west and the southwest slope of the Wushan open-pit mine, the case study considered here, was a single-step wedge landslide and an integral-incline landslide. These two types of landslides were found to be most similar to those in the Anjialing open-pit mine and the Fushun West open-pit mine. Based on the posterior-warning indicator of the most similar landslide cases, the warning indicators of the west and southwest slope are set as 12.7 mm/d and 135.2 mm/d. The proposed method here provides a reference for the establishment of early-warning indicators for landslides in open-pit mines.

Calibration of Water Inrush Channel and Numerical Simulation of Water Inrush Process in Coal Mine Roof

The surrounding rock of a coal mine roof fractures with the excavation of the underground working face in coal mining. These mining-induced fractures are connected and extended upward to form water inrush channels. A water inrush accident may occur when there is a sufficiently large water source. To elucidate the formation mechanisms of the roof water inrush channel and the characteristics of water inrush in goafs, we performed a case study of No.18401 Panel of Xiqu Coal Mine in China and determined whether the roof water inrush channel is connected by theoretical calculation and microseismic monitoring. The modified mechanical parameters of rock masses were embedded into the numerical model based on microseismic data. Microseismic monitoring and numerical simulation were organically combined to analyze the connection process of the water inrush channel, after which the roof water inrush channel is calibrated on the No.18401 Panel. We established a non-Darcy flow model for water inrush in the water-conducting fractured zone of mines by coupling the Darcy, Forchheimer, and Navier–Stokes equations. Finite element language and its compiler (FELAC) was used to study the water inrush mechanism of non-Darcy seepage. The results show that the pressure, velocity, and porosity in the water-conducting fractured zone are non-uniform in water inrush occurrence and development, and the mixed fluid mainly passes through the “dominant channel.” The development of water inrush is accompanied by the release of the hydrostatic pressure in the aquifer, the sudden increase of the velocity at the water inrush position, and the increase in fluid concentration. Hence, the underground water inrush can be predicted and prevented by monitoring the aforementioned indicators. This research is of great significance for the calibration of the water inrush channel of the roof and the prediction of water inrush disasters.

Application of the Maximum Sensitivity Principle in the Optimization of Measuring Point Arrangement in Transversely Isotropic Rock Mass Engineering

The inverse analysis method based on in situ measurement information provides a new approach to determine the mechanical parameters of rock mass. The accurate on-site monitoring data is the prerequisite and basis for the success of displacement back analysis. To improve the accuracy of requirement parameters, a reasonable layout program should be developed to optimize the layout of the measuring position. In order to study the optimal arrangement of measuring points in anisotropic rock mass, the layout optimization of measuring points around a tunnel in the transversely isotropic rock mass is studied according to the maximum sensitivity criteria. The influence of the spatial location of the measuring points on the measurement of the tunnel deformation is obtained. The results indicate that the measuring point should be arranged close to the extreme point in the direction of the larger principal stress.

Freeze-Thaw Effects on Stability of Open Pit Slope in High-Altitude and Cold Regions

The cycle of the freeze-thaw action must be taken into account in the stability analysis of an open pit slope in the high-altitude and cold regions, because the natural process of freeze-thaw poses a significant effect on mechanical properties of the rock mass. To achieve this purpose, a linear relationship between the geological strength index (GSI) and the Tianshan slope rock mass rating (TSMR) system is established considering the effect of the freeze-thaw action by introducing a freeze-thaw correction coefficient δ. The GSI value is modified for rock mass in high-altitude and cold regions. The improved Hoek-Brown criterion considers the influences of the freeze-thaw action and steep and gentle slopes. The research outcome is applied in the No. 4 minefield open pit coal mine in the Muli mining area. Numerical calculations are performed by inputting rock mass mechanical parameters obtained in traditional and modified criterions, to discuss the influences of the freeze-thaw action on the stabilities of both the present mining slope and the final slope at the end of the designed mining. The results show that the safety factors of the original slope are 2.33 and 1.67, respectively, while after the modification, they are 2.14 and 1.61, respectively. In terms of the No. 4 minefield open pit coal mine, the slope stability meets the design requirement, although taking the freeze-thaw cycle into account.

Back analysis of mechanical parameters of rock masses based on multi-point time-dependent monitoring data

The physical and mechanical parameters of rock masses are important factors that affect the numerical simulation and safety evaluation of geotechnical engineering. Due to the discontinuity and heterogeneity of rock mass, the parameters obtained by laboratory test and field test can not represent the actual situation. With the development of computer technology, the parameter identification method based on machine learning provides a new way to solve the above problems. Aiming at the rheological model based on thermodynamics with internal state variables, a back analysis method of mechanical parameters based on IAGA-BP algorithm is proposed. The sensitivity of deformation parameters, damage effect parameters and viscoplastic parameters involved in the model are analyzed using range analysis method. And the parameters which have great influence on the deformation of surrounding rock are selected to reduce the dimension of output layer. The displacement corresponding to the representative time point are selected as the input layer neuron. A numerical model is established to finely simulate the driving process of TBM, which is used to generate training samples and test samples. BP, GA-BP, PSO-BP, APSO-BP and SVM are also used to inverse the parameters of surrounding rock. Two evaluation metrics are used to evaluate the performance of above algorithms, including prediction accuracy and stability. The method is applied to inverse parameters of surrounding rock of a tunnel. The results show that the time-dependent deformation curve of surrounding rock obtained by BP neural network optimized by improved adaptive genetic algorithm (IAGA-BP) fits well with the monitoring curve (the average prediction error is 3.8%, and the prediction stability is 16.3%), which is much better than other algorithms.

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.

Directional rock mass rating (DRMR) for anisotropic rock mass characterization

Rock mass classification systems are used to categorize and estimate the role of the most significant parameters influencing rock mass behavior to represent an equivalent continuum. Generally, in these methods, the impact of the related parameters is considered uniform in all directions. Hence, these systems describe the rock mass as an isotropic medium. In some cases, in particular, for layered strata and systematically fractured rocks, the assumption of isotropic behavior may not provide realistic results. Hence, in this paper, to characterize the rock mass anisotropy, a directional rock mass rating (DRMR) has been proposed based on the well-known rock mass rating (RMR). So, DRMR provides a three-dimensional rock mass rating, quantitatively. By means of statistical distribution of DRMR, a classification for the degree of anisotropy of rock mass has been proposed. Furthermore, a criterion to identify the prominent rock mass, isotropic/transversely isotropic/anisotropic situation, is presented. Then the stereonet has been used to demonstrate an all-round graphical representation of DRMR. This with DRMR provides an illustrative insight into the actual rock mass condition and can assist to select the appropriate method for further analysis. Also, the method can be used as a basis to develop practical solutions for many rock engineering issues, such as characterizing the mechanical parameters of rock mass as an anisotropic equivalent continuum, selective directional rock mass improvement, and proper selection of rock tunnel and rock cavern alignments. Finally, the results of some practical applications of the method, based on field data, are presented.

Inverse analysis for rock mechanics based on a high dimensional model representation

Mechanical parameters of rock mass are essential in rock engineering for stability analysis, supporting design, and safety construction. The inverse analysis has been commonly used in rock engineering to determine the mechanical parameters of the rock mass. In this study, a novel inverse analysis approach was proposed through combing high dimensional model representation (HDMR), Excel solver, and numerical model. HDMR was employed to approximate the nonlinear function between the mechanical parameters of rock mass and the response of rock based on the numerical model. Excel Solver was adopted to search the mechanical parameters of rock mass based on the HDMR model for the inverse analysis. The proposed method was verified and illustrated the performance of the proposed method by two tunnels. The mechanical parameters of rock mass were determined based on the displacement of surrounding rock mass and HDMR model using the Excel solver for the tunnels. The displacement and stress of surrounding rock mass were computed based on the determined mechanical parameters of rock mass by the proposed method. There was an excellent agreement with the real value or contour that was computed based on the actual mechanical parameters of the rock mass. The results demonstrated that the proposed method was practical and accurate. It also made it convenient to be applied to determine mechanical parameters of rock mass based on monitored information.

Study on Mechanic Parameters Selection of Rock Slope Based on BP Neural Network Displacement Back Analysis

Natural rock mass is a complex three-phase composition, and its internal structure, physical characteristics such as fragmentation and water content have significant temporal and spatial variability. The method of assigning the mechanical parameters of rock mass according to the code ignores this important feature. In order to obtain the mechanical parameters of natural rock mass more accurately, based on a rock slope in NO.2 section of Ganxian-Xingguo expressway, a method for calculating mechanical parameters based on displacement back analysis of BP neural network was proposed on the basis of traditional code assignment. The back analysis model was optimized by neuron weight, inertia correction and algorithm step control, and then the mechanical parameters of the whole slope were back analyzed. Fatherly, the finite element numerical simulation software ANSYS was used to establish the grid model of the slope to judge the whole stability of the slope. The field monitoring was used to verify the calculation results. Facts and figures showed that the mechanic parameters gotten from the back analysis is more reliable than those in the code. The study can provide reference for mechanic parameters assignment of the rock slope.

Reliability Assessment of an Open Pit Slope on Bong Iron Ore Mine

Slope stability on Bong mine is crucial for securing a balance in the gross national product of Liberia. The mine is being operated using conventional open pit methods with slope angles optimally designed to maximize ore stripping quantity. However, a working slope has displayed signs of uncertainty. The overall inclination of the slope is 56°, and the proposed maximal excavation is 315.42 m, but current depth in ore is approximately 50%. Based on the study of slope geological characteristics, the physical and mechanical parameters of rock mass and the geometrical calculation of stoping, the study is tailored on the mechanism of inspecting stress-strain behavior in response to seasonal variation of rock moisturization as a more suitable means of stope slope stability analysis in this case. This study took full account of local rainfall and other meteorological conditions. Slope stability is investigated via stereographic projections and stability assessment using the Shear Strength Reduction (SSR) method based on FLAC (Fast Lagrangian Analysis of Continua) numerical modeling technique in three dimensions to predict the stress-strain behavior of the open-pit slope and evaluate its stability state. Global stability has been analyzed under natural and saturated conditions and it is found that the slope is critically stable and needs proper attention.

Study on Finite Element Numerical Simulation of Rock Slope Based on Ground Penetrating Radar Detection

Weathering degree of natural slope and its mechanical parameters have significant spatio-temporal variability. At present, the method of determining the mechanical parameters according to the suggestions of the specification ignores this phenomenon. In order to improve the accuracy of finite element numerical simulation results, a method for obtaining rock mass mechanical parameters based on ground penetrating radar (GPR) detection was proposed. Based on a rock slope of Xianyang international airport in Shaanxi province, the degree of fracture and water-rich inside the slope were detected by GPR, and the slope was divided into several units with different levels. Then, the mechanical parameters such as elastic modulus, Poisson’s ratio and cohesion force of different units were obtained according to the specification. Fatherly, the finite element numerical simulation software MIDAS-GTS was used to establish the grid model of the slope, and the recommended values provided by the specification were used to calculate the sliding displacement of the slope. Compared with the field displacement monitoring data, the results showed that the numerical simulation values were closer to the monitoring values, indicating that the mechanical parameters obtained by this method were more consistent with the actual value of the rock mass.