Shear Strength Of Rock Mass Research Articles

Effect of nano-Al2O3/epoxy resin composite on the shear strength recovery of fractured rock masses with various crack widths and SCA interfacial treatments

The mechanical properties of grout and the effect of the bonding between grout and the repaired material are the two main factors affecting the shear strength of the material. To study the effect of repairs carried out with nano-Al2O3/epoxy resin composite (NAEC) on the shear strength of rock masses, cracks with different widths and treatments by silane coupling agent (SCA) solutions with various surface treatment concentrations (kSCA) were considered. The mass percentage ratio of nano-Al2O3 in the composite (kAl) was optimized based on the obtained uniaxial compressive strength (UCS). The selected NAEC was used to fill cracks of different widths, and the bonding effect was analyzed using a bilateral shear strength test that effectively avoids the bending effect. Solutions with diverse kSCA values were used to treat the rock surfaces with the 3-mm-wide cracks. The results showed that the UCS of the NAEC tended to increase with increasing kAl when the mass ratio (kCE) of the curing agent to epoxy resin was 0.25. When kAl= 0.01, the UCS of the composite peaked at 97.82 MPa. With increasing crack width, the shear strength first increased and then decreased. When the crack width was 3 mm, the shear strength reached a maximum of 29.02 MPa. However, without nano-Al2O3, the shear strength was 23.66 MPa, and the shear strength of ultrafine Portland cement (UPC) material was only 8.37 MPa. With increasing kSCA, the shear strength tended to first increase and then decrease. For a kSCA of 2%, the shear strength reached a maximum of 39.40 MPa, corresponding to an increase of 35.8%. Nevertheless, the composite shear strength as degraded at 5% kSCA. In summary, the NAEC exhibited a sound bonding effect, SCA surface treatments effectively improved the shear strength, and the bonding shear strength was related to the crack width.

Experimental study of the shear strength criterion of rock structural plane based on three-dimensional surface description

Abstract The failure of rock mass is mainly due to the failure of the structural plane, which is an important factor to reduce the mechanical properties and stability of rock mass. The shear strength of rock mass is one of the parameters for the stability calculation of large-scale rock mass engineering. The shear strength of a rock structural plane is strongly influenced by surface morphology. Considerable research has been conducted regarding the correlation between two-dimensional structural plane morphology and shear strength. However, quantitative research on three-dimensional (3D) morphology is relatively limited. In this study, 3D printing technology was used to create molds. Using cement and sand as the main materials, additives such as early strength and water-reducing agents were added, and test samples of irregular surface topography were created. The 3D roughness was quantified by formula calculation. Using a ZScanner® 800 hand-held 3D laser scanner to perform scanning on the structural surface, the parameter curve was analysed by generating 3D coordinate information and a 3D image of the fracture surface, and the quantitative parameter M p 3 D {M}_{\text{p}}^{3\text{D}} describing the 3D morphology of the structural surface was constructed. The change rule of R p 3 D {R}_{\text{p}}^{3\text{D}} and joint roughness coefficient (JRC) were analysed under different scanning resolutions, Δ(r), the scanning precision was suggested, and the functional relationship between JRC and M p 3 D {M}_{\text{p}}^{3\text{D}} was established. Finally, a formula for shear strength parameters considering the 3D characteristics of a structural plane surface was established. The model validation results show that the experimental data were within the 95% confidence band of the model curve, the average error of the shear strength was 10.4%, the errors of friction angle and cohesion, C, were 3.4 and 9.4%, and the reliability was fine.

Displacement Back Analysis of Reservoir Landslide Based on Multi-Source Monitoring Data: A Case Study of the Cheyiping Landslide in the Lancang River Basin, China

Landslides that occur in the littoral zone of a reservoir can directly damage the hydraulic structures and threaten the lives and property around the reservoir. Due to the spatial variability and heterogeneities of rock mass, a limited amount of data obtained from laboratory and in situ tests cannot comprehensively characterize the mechanical properties of rock and soil masses. Therefore, displacement back analysis is often performed to determine the mechanical parameters of rock and soil masses. The spaceborne Interferometric synthetic aperture radar (InSAR) has proved to be a powerful tool for geodesy in the measurement of landslide movement. However, InSAR can only measure the surface motion of the landslide without the subsurface information. This study uses multi-source monitoring data in the landslide displacement back analysis, including surface InSAR and an internal borehole inclinometer. The identified material parameters and finite element simulation are used to predict the landslide deformation. The case study of the Cheyiping landslide located in the Lancang River basin demonstrates the necessity and feasibility of using multi-source monitoring data in landslide displacement back analysis. The Cheyiping landslide is currently in the creep deformation stage. The decrease in shear strength of rock masses due to the rheological deformation and the change in reservoir water level are the internal and external factors leading to excessive landslide deformation. The numerical modeling can accurately simulate the landslide movement using the identified material parameters. By combing multi-source monitoring data and numerical modeling, the reservoir landslide deformation analysis can help evaluate the landslide deformation state and stability, which is vital for reservoir risk mitigation and the sustainable development of hydropower resources.

Effect of Joint Roughness and Infill Thickness on Shear Characteristics of Rock Mass

The joint planes in fractured rock mass will reduce the tensile strength and shear strength of rock mass, which has a decisive influence on the deformation and failure mode of engineering rock mass. Furthermore, infill also exists between the joint surfaces, which will also affect the shear characteristics of the joint. A method of importing standard joint profile into PFC2D was proposed, and a series of numerical simulation tests were carried out to study the effect of joint roughness and infill thickness on the shear characteristics of joints. The numerical results revealed that rock bolts profoundly improved the shear strength of the infilled rock joints, enhanced the toughness of the joint surface, increased the number of micro-cracks, and made the dilatation more obvious. The shear stress and the normal displacement of unbolted or bolted infilled rock joints increased with increasing the joint roughness and decreasing the infill thickness. The maximum horizontal compression stress in the middle of the bolt gradually increased with the increase of joint roughness coefficient. Different roughness has different effects on the number of micro-cracks in the sample. The number of total cracks and tensile cracks of the bolted and unbolted specimens increased with the increase of joint roughness coefficient, while the shear cracks remained almost the same. Through the study of the coupling effect of joint roughness and infill thickness on peak shear stress, results can be obtained as follows. The unbolted samples are highly sensitive to JRC changes. The greater the infill thickness, the greater the sensitivity of unbolted samples to JRC changes. The reinforcement effect of the bolt will strengthen the meshing strength between the joint surface and the filling material; that is, the meshing strength is positively correlated with joint roughness and negatively correlated with filling thickness.

An integrated UAV photogrammetry-discrete element investigation of jointed Triassic sandstone near Sydney, Australia

Over the last decade, UAV Structure-from-Motion photogrammetry and digital rock mass mapping tools have been rapidly adopted into geotechnical engineering practice. As computing power has increased, numerical models and remote sensing methods have become more sophisticated, and much research has been applied to the development of digital rock mass classification and data collection methods. This investigation presents a case study of UAV photogrammetry mapping, discrete fracture network analysis and discrete element method modelling of jointed sandstone exposed in coastal cliffs and wave-cut platforms near Sydney, Australia. The aim of the study is to investigate a selection of digital mapping and numerical modelling approaches for rock mass geomechanical characterisation. A cohesive workflow is presented for UAV photogrammetry survey, discontinuity mapping, simulation of rock mass scale laboratory tests, and 3D DFN simulations of roof reinforcement in a large-span road tunnel.Digital discontinuity mapping is undertaken using two different software tools, and results are compared with historical conventional mapping. A novel GIS-based workflow is demonstrated to interrogate the mapping data, using a cellular grid approach to measure fracture intensity and fracture network connectivity. The discontinuity statistics are used as inputs to a series of 3D discrete element method numerical UCS, triaxial, and biaxial load tests that investigate the rock mass anisotropy and the impact of confining stress on rock mass shear strength, stiffness, and failure mechanisms. Next, the mapping data are applied to DFN simulations of a 31 m span tunnel, based on upcoming proposed road tunnels in Sydney. The tunnel simulations show how predicted displacements in the tunnel roof are proportional to fracture intensity.

Influence of material bridges on shear strength of unfilled intermittent rock joints

According to the well-known Jaeger's theory, the minimum possible rock mass shear strength as a discontinuum actually corresponds to the shear strength of rock joints. Since failures in rock masses due to loads caused by civil structures or civil works occur mainly by exceeding their shear strength, the shear strength of rock joints has huge practical significance. Therefore, in this paper it was decided to analyse a factor which can have a very important influence on the shear strength of unfilled rock joints. Namely, the influence of the presence of material bridges and initial joints between them, their number, size, mutual distance and orientation relative to the shearing direction were analyzed using results of laboratory or numerical CNS direct shear tests which were carried out by different researchers around the world. Except for increasing its peak and residual value, the professional public is currently unaware of the impact of this factor on the shear strength of intermittent rock joints. Based on the carried out analysis, appropriate conclusions have been made.

Prediction of Shear Strength of Fully Weathered Coastal Red Sandstone: Influence of Water Content, Fine Content, and Relative Compaction

Xu, H.; Cai, L.; Shao, Z.; Wang, Z.; Li, Z., and Huang, C., 2021. Prediction of shear strength of fully weathered coastal red sandstone: Influence of water content, fine content, and relative compaction. Journal of Coastal Research, 37(4), 827–841. Coconut Creek (Florida), ISSN 0749-0208.Shear strength of coastal rock mass can be characterized by parameters such as cohesion and internal friction angle, which are relatively difficult to measure with accuracy on coastal engineering sites. This paper aims to predict shear strength of fully weathered coastal red sandstone with physical property parameters—water content, fine content, and relative compaction—that are easily measured on site. The variation of shear strength parameters with physical property parameters was obtained with indoor direct shear tests, and the real-time prediction of shear strength of fully weathered coastal red sandstone was realized by employing a decision tree model. The results show that the variation of shear strength parameters with physical properties can be accurately characterized by cubic polynomials and that the cohesion and internal friction angle can be well predicted by a 10-layer decision tree model with high accuracy. This study sheds light on the variation of shear strength of fully weathered coastal red sandstone and similar rock mass with physical properties and has practical significance for engineering conducted in such strata, which require in-time monitoring of shear strength of rock mass.

Empirical Model for Shear Strength of Artificial Rock Containing a Single Nonpersistent Joint

Abstract This paper proposes an empirical equation to evaluate the shear strength of rock mass with nonpersistent joints. A novel specimen preparation method is proposed and is used to created plas...

Characteristics and mechanism of a landslide at Anqian iron mine, China

Owing to the heavy rainfall, a landslide occurred at the Anqian Iron mine, at 18:00(UTC + 8) on November 24, 2019, in China. The landslide was about 3.0 × 104 m3 and caused damage to the road of transporting waste materials. Failure characteristics and the mechanism of this landslide were analyzed in this study. The landslide area was divided into three parts: the rear tension cracking area, the middle sliding deformation area, and the front colluvium area. A contact-free measuring technique using the new ShapeMetrix3D system was applied and 204 joints were analyzed based on equal-angle stereographic projection. Thus, a conceptual model of the mechanism of the landslide was constructed and the formation process of the landslide was divided into three stages: the first shearing and dislocation stage; the second sliding, front bulging, and rear tractive cracking stage; and the third local rock mass collapse and colluvium depositing stage. Numerical modeling was performed to discover the landslide mechanism by progressively reducing the shear strength of rock mass. The results showed that the original slope was stable, whereas heavy rainfall triggered the landslide, and the predicted failure surface matched closely the field investigations. The factor of safety obtained by real three-dimensional analyses was slightly higher than that obtained by plane problem analyses, and the difference was attributed to the three-dimensional effect of the landslide. This paper also presents the results obtained from the parametric analysis in order to understand the impact of shear strength parameters on the overall stability of the slope.

Profiles of Near‐Surface Rock Mass Strength Across Gradients in Burial, Erosion, and Time

AbstractRock mass strength is recognized as an important control on landscape morphology and evolution. However, the controls on rock strength in mountainous topography remain poorly characterized, in part because strength remains challenging to quantify at spatial scales relevant to geomorphology. Here we quantify the mechanical properties of rock masses using subsurface S‐wave velocities, Schmidt hammer hardness values, and Geological Strength Index (GSI) observations. We produce shallow depth profiles of rock mass shear strength using intact rock hardness as measured from a Schmidt hammer, and assessment of the structure and surface conditions of fractures using GSI. We apply these techniques to the Western Transverse Ranges, southern California, USA, where gradients in stratigraphic age and erosion rate allow us to evaluate our methodology. We resolve strength differences of 200 kPa to ∼5 MPa that appear to be related to diagenetic changes associated with the maximum burial depth of young clastic sedimentary rocks. For rocks of the same lithologic type, stratigraphic age, and inferred burial histories, we resolve smaller differences in strength (300 kPa–1.5 MPa) that appear to be positively correlated with mean erosion rates. We suggest that the increase in strength with increasing erosion rate reflects decreased residence time in the weathering zone for ranges experiencing faster fault slip rates. These findings demonstrate up to an order of magnitude variability in strength with respect to burial, erosion, and time for lithologically similar rocks. As such, lithology alone is unlikely to adequately capture the role of rock strength in landscape evolution.

Back-analysis of Donghekou landslide using improved DDA considering joint roughness degradation

Currently, the dynamic behavior of high-speed long-runout landslides triggered by earthquakes remains unclear due to the complexity of such phenomena. Degradation in the shear strength of rock masses is considered a primary factor contributing to the high velocities and long runout distances of these landslides. In this study, the strength degradation induced by changes in rock joint morphology is analyzed considering a numerical model of the Donghekou landslide, by using discontinuous deformation analysis (DDA). First, an exponential joint roughness degradation function (i.e., JRCm) that depends on displacement is incorporated with the nonlinear Barton–Bandis (B–B) shear strength criterion, and this modified B–B criterion is combined with the DDA. Moreover, a virtual joint is introduced in the DDA to model the propagation of cracks in intact rock masses, in order to simulate the dynamic phenomenon of earthquake-induced landslides. Subsequently, this improved DDA (IDDA) is validated via simulations of a shear test and a sliding block over an inclined plane. Finally, the IDDA is employed to simulate the Donghekou landslide, which was induced by the 2008 Wenchuan earthquake in China. Furthermore, the entire dynamic process of the landslide, including crack propagation, instability, initiation, and motion, is depicted. The simulated deposit patterns obtained via the IDDA are in good agreement with the results of field investigations. The simulation results also prove that the IDDA can reflect key movement behaviors of Donghekou landslide and that the degradation of rock joints significantly influences the long runout distance and high velocity of sliding mass.

Applicability of powder-based 3D printing technology in shear behavior analysis of rock mass containing non-persistent joints

To evaluate the shear strength of rock mass containing non-persistent joints, a comprehensive knowledge of the shear mechanism of both joint and rock bridge is required. In this study, different joint configurations were initially designed, then the 3D printed and plaster specimens were made applying 3D printing technology and casting process, respectively. A novel procedure was applied to build plaster specimens embedding finite (closed/open) joints surrounded by intact material from all sides. Subsequently, joint persistence (rock bridge ratio) and joint dispersion effects of both single joint and coplanar intermittent joints on the shear strength of the specimens were experimentally examined by conducting several direct shear tests under constant normal load (CNL) condition. The experimental results obtained from the plaster and 3D printed specimens were compared to assess the applicability of powder-based 3D printing technology to shear behavior analysis of weakness planes containing non-persistent joints. Moreover, the joint friction contribution to the shear strength of the plaster specimens containing a single non-persistent joint was investigated thanks to the proposed casting procedure. It was found that the embedded joints of the specimens with greater rock bridge ratios have less contribution to the shear strength.

Predicting long-term stability of tunnels considering rock mass weathering and deterioration of primary support

One distinctive feature of tunnels is the direct interaction between the primary support and the surrounding rocks. For this reason, loads applied to tunnels may vary significantly over time due to changes in rock mass behavior and environmental actions. In this paper, a methodology is proposed for predicting long-term stability of tunnels that accounts for weathering of rock and deterioration of primary support. Chemical weathering of sedimentary rocks around tunnels results in degradation of rock mass shear strength (cohesion and friction angle) and Young’s modulus with time. Two semi-empirical logarithmic equations for modelling of the diminution of rock mass characteristics are presented. Tunnel support systems may also deteriorate and lose their load bearing capacity over time when exposed to aggressive agents. Therefore, main mechanisms of deterioration in common support systems i.e. rock bolts, steel sets and shotcrete are investigated and equations for quantifying damages to their mechanical properties with time are derived. The suggested procedure has been fully illustrated through numerical simulation of a freeway tunnel in Iran (Torshan tunnel) using finite difference method. The tunnel behavior has been evaluated using long-term ground reaction curves (GRC), ground-support interaction diagrams and lining factor of safety FS. Results show that there is a marked increase in the overall ground pressure and rising of internal forces acting on the final lining with time, especially bending moments at the tunnel sidewalls. After 60 years, the lining FS drops below the minimum acceptable value, 1.5 in this case, thus the tunnel rehabilitation is recommended.

Method for calculating the shear strength of rock masses with different combined structural planes based on the 3D printing technology

The mechanical behavior of rock masses with different combined structural planes is poorly understood because of the difficulties associated with the performance of rock observations and analyses from the surface, collection of samples during field investigations, specimen preparation, and laboratory tests. The combination of rock mass structural planes has a significant effect on the rock mass mechanical properties. The three-dimensional (3D) printing technology can conveniently create 3D entities with complex structures, thereby providing an unprecedented opportunity to break through this bottleneck. In this study, model samples of structural surface models with different combinations are printed using the 3D printing technology, and a cement slurry with 3:1 water–cement ratio is used as the structural body to produce rock masses with different combined structural planes. The method replicates well the morphological features of natural joints. Moreover, the shear properties and the failure characteristics are stable and consistent. Direct shear tests are also performed on the rock masses of different combined structural planes from the intersection line parallel and perpendicular to the structural planes to obtain the relevant mechanical parameters and rock mass failure modes. The results prove the feasibility of the 3D printing technology in the experimental study of rock mass mechanics and show that the strength and failure modes of rock masses with different combined structural planes are different. A calculation method for the shear strength of rock masses with different combined structural planes is proposed herein based on the experimental data and the Mohr–Coulomb theory, and the method’s feasibility is verified by several examples.

A shear strength model for anisotropic blocky rock masses with persistent joints

The Mohr-Coulomb (MC) shear strength parameters, cohesion c and angle of friction φ, are required in numerical models. Currently, the geological strength index (GSI) system has been widely used for estimating shear strength of blocky rock masses in rock engineering. However, the GSI system does not include the effect of joint orientation β on the mechanical properties of a rock mass, which means that the shear strength model cannot reflect anisotropic rock mass strength behavior caused by joint orientation. In this research, UDEC-based synthetic rock mass models, which are calibrated by experimental data, are adopted to study the effect of joint orientation on the shear strength of blocky rock masses with two perpendicular joint sets. The values of cohesion c and angle of friction φ estimated from the numerical simulation are compared with those calculated from the empirical shear strength models based on the GSI system. Comparison of the results shows that the existing empirical model overestimates the shear strength of rock mass when 10° <β < 45°, which may impose a risk on engineering design. To rectify the problem, based on the analysis of shear strength parameters of rock masses with various joint orientations, anisotropic weighting factors are proposed to modify the existing model. The proposed modified model is capable of providing conservative but more accurate estimation of the shear strength of rock mass, which is important for safe engineering designs.

Displacement monitoring, displacement verification and stability assessment of the critical sections of the Konak tunnel, İzmir, Turkey

The main focus of this study is vertical displacement monitoring and verification along with preliminary support design for the four geotechnical sectors of the twin tube Konak tunnel that was constructed in a highly populated area in İzmir. The displacements of the tunnel that were obtained through numerical analysis were verified by comparing them with the displacements obtained by construction monitoring. In the study area, volcanics, pyroclastics and some sedimentary deposits (sandstone, mudstone and conglomerate) often intertongue with each other especially in the exit portal area. The accurate estimation of the shear strength and deformation parameters of these units is important for the displacement predictions and for the assessment of tunnel stability. Rock mass classification systems, namely, RMR, Q system and GSI have been employed to obtain the rock mass shear strength and deformation parameters along with performing empirical tunnel support design. Numerical analysis has been performed by using the finite element analysis for assessing tunnel support design and for predicting the vertical displacements at five different measurement points around the tunnel periphery and in the four geotechnical sectors of the tunnel.An evaluation of the results revealed that about 70% of the predicted displacements matched the measured displacements while only about 12.5% of the displacement predictions exceeded the measured displacements by more than about 50%. Moreover, it was observed that neither the support system elements nor the rock mass have yielded due to the redistribution of the stresses imposed by the disturbance related with the tunnel excavation.

New Modified Model for Estimating the Peak Shear Strength of Rock Mass Containing Nonconsecutive Joint Based on a Simulated Experiment

In the Jennings criterion, which is commonly used to estimate the shear strength of nonconsecutive jointed rock masses, the estimated values deviate from the actual values due to the criterion failure to consider the joint undulating angle and the weakening of the mechanical properties of the rock bridge during shearing. Based on the modified Jennings criterion, this paper considers the influence of normal stress and joint continuity on the degree of weakening of the rock bridge’s mechanical parameters and presents a new correction method to further modify the Jennings criterion. The collection of undisturbed rock samples from the study area and the creation of joint(s) for laboratory testing is a cumbersome task. To overcome these limitations, a methodology to simulate the failure of jointed rock mass using the rock-like material, cement mortar, containing a single joint was adopted and its details are presented in this paper. Specifically, the direct shear tests were conducted on artificially prepared jointed rock masses with different joint continuity and undulating angles. The influence of joint continuity and the undulating angle on the shear strength of the nonconsecutive joints was studied. Then, the influence of the normal stress and joint continuity on the deterioration of the mechanical properties of the rock bridge during shearing was analyzed based on the experimental results. A new model for estimating the shear strength of a nonconsecutive jointed rock mass was proposed based on the experimental results and previous studies. The test results show that the smaller the undulating angle and the greater the penetration, the lower the shear strength of the nonconsecutive joint. Besides, the normal stress level and the joint continuity have a significant influence on the weakening of the mechanical properties of the rock bridge. When the normal stress decreases or the joint length increases, the mechanical properties of the rock bridge are significantly weakened. Compared with our estimation of the nonconsecutive joint shear strength based on the original Jennings criterion and the modified Jennings criterion, the calculation results of the newly modified Jennings criterion developed in this study are generally more consistent with the measured values, and thus, they more accurately predict the shear strength of the nonconsecutive jointed rock mass with a regular joint undulating angle.

Numerical simulation of the morphological effect of rock joints in the processes of concentrating elastic strain energy: a direct shear study

Rockburst in coalmines is the result of the release of the elastic strain energy (ESE) stored in rock and coal masses. The examination of the elastic strain energy (ESE) along rock joint is important to evaluate the shear strength of rock masses. The morphology of joints and the strength of rock masses are considered as the key factors influencing the distribution of the ESE. In this study, a three-dimensional model is developed to quantify the influence of the morphological effect of rock joint (by varying the amplitude and wavelength of the joint) and different materials (coal or rock) on the distribution of the ESE. The results show that when the wavelength of the joint reaches about 5~20% of the length of the model and the amplitude of joint reaches about 2~10% of the height of the model, a relative high concentration of the ESE was found at the left and right crests, together with a low concentration in the middle crests. For most cases, the maximum ESE generally has a similar order of magnitude (108~109 J) and approximately arched trend for different wave amplitudes for the joints. However, in cases of the flattest joint only reaches about 10−16 J. Regarding the influence of different materials on ESE, the rock-rock system generally has a similar distribution of ESE with the rock-coal system, but the latter one concentrates much more ESE. The coal-rock system has the smallest ESE. This recognition of the highly unbalanced distribution of ESE will certainly help to effectively reduce the potential failure of rocks under the CNL boundary conditions.

Load-displacement response of drilled shaft tip in soft rocks of sedimentary origin

A database of in situ drilled shaft and plate load tests in soft rock mass is developed. Analyses of the in situ load tests suggest that (i) the development of tip contact pressures is related to the rock mass shear strength, rock mass deformation modulus, and the vertical displacement of the drilled shaft tip, (ii) embedding the drilled shaft tip contributes to the development of punching shear failure mechanism in the underlying rock mass, however, the mobilized tip contact pressures do not significantly increase as the embedment depth increases unless the rock mass shear strength and deformational properties drastically increase with embedment depth, and (iii) the drilled shaft diameter does not significantly influence the development of the contact pressures, especially in large diameter drilled shafts. A framework for the analysis of the load-displacement response of the drilled shaft tip in soft rock mass is proposed using the in situ load tests. The proposed framework accounts for the observed nonlinear load-displacement response of soft rock mass and is a function of the initial normal stiffness and the initial yield pressure of the rock mass under the drilled shaft tip. Simple equations are developed for the initial normal stiffness and the initial yield pressure of soft sedimentary rocks. Additionally, in situ and laboratory test results are used to provide recommendations for the prediction of the parameters that are required in the proposed models for the initial normal stiffness and the initial yield pressure, namely the unconfined compressive strength and deformation modulus for the rock mass.

Mechanical model of safety thickness for resource recovery of complex & difficult mining ore body

In view of the difficulty in calculating the safe thickness of complex and difficult-to-mine orebody in the process of resource recovery, based on the elastic-plastic theory and mechanics method, the mechanical models of the safe thickness of orebody recovery above the collapse area and that of orebody recovery at the side of the collapse area are constructed respectively. The results show that: 1. Using the fixed beam model to calculate the safety thickness, the additional load on the roof, the volume weight and span of the rock stratum, the width of the rock stratum and the water pressure are the important influencing factors. When the water pressure exists, the safety thickness can be reduced; 2. When the safety thickness is calculated by the elastic plate model with fixed support around, the safety thickness decreases with the increase of the tensile strength or shear strength of rock mass, and increases with the increase of the external load; 3. When the collapse area is located at the side of the ore body to be mined, the safety thickness decreases with the increase of the tensile or shear strength of rock mass, and with the increase of the external force. The load increases with the increase of load. The research can provide theoretical support for mining residual mineral resources.