Modulus Of Rock Research Articles

Evaluation of Carbonate and Heterogenous Rock Masses for the Dam Foundation: A Case Study at Kanarwe River Basin, Sulaimaniyah, NE Iraq

Evaluating rock masses for dam foundations, especially heterogeneous rock (flysch), becomes imperative and requires accurate geomechanical classifications. The rocks at the Kanarwe river basin, especially at a proposed dam site (Goma-Qazan near Khewata, Sura Qalat villages), mainly consist of interlaying massive carbonate rocks of the Aqra Formation with flysch rocks of Tanjero Formation. Therefore, selecting appropriate dam types is challenging and very risky. This study conducted a detailed study of lithology, discontinuity condition, rock sampling and laboratory tests to determine the site suitable for dam construction using the quantitative GSI, Rock Mass Rating, and Dam Mass Rating geomechanical classification systems. A new procedure was suggested for calculating stress relaxation and damage level (disturbance factor D) in rock masses. The Dam mass rating related to the foundation stability shows a good stability indication ranging from 43.7–82.9, indicating foundation suitability for all dam types. The foundation excavation desirability and consolidation grouting were evaluated based on dry basic rock mass rating, which shows that the site is suitable for earth fill and hardfill dams. However, the rock mass units require spot and systematic grouting for gravity and Arch dams, respectively. Ec/Em (deformation modulus of the dam/deformation modulus of foundation rocks) values for massive carbonate rock range from 0.18–0.93; they indicate site suitability for arch, gravity dam, earth fill and hardfill dams. While the Ec/Em values for flysch rock mass units range from 1–6.4, they indicate some units have a serious problem situation and need treatment based on the types of dams.

Preliminary Study on In-Situ Modulus Measurement Using Knocking Ball Test; A Case Study on Setul Limestone

The in-situ elastic modulus (E) is a vital parameter for describing rock strength in many engineering projects on rock slopes. The elastic modulus and uniaxial compressive strength (UCS) are typically investigated via laboratory tests using core samples. However, the direct determination of E is costly and time-consuming in preparing many intact samples from highly weathered Setul limestone. The knocking ball testing method is a non-destructive test that can quickly and easily obtain the elastic modulus of rock in-situ by striking the surface of a rock mass with a spherical steel hammer. This study presents the relationship between the elastic modulus of knocking ball (Ekb) and the uniaxial compressive strength of the Schmidt hammer (UCS-Schmidt). Results show that the regression coefficient correlation, R2 is 0.851, indicating a positive trend with a few outliers. The measured Ekb were also verified with mineral properties and correlated to differential weathering grades to confirm the accuracy of measurement results. The finding compared to previous similar studies tested on several types of rock show a statistically significant. This research highlights the effectiveness of the knocking ball method for determining the modulus of rock slope at different weathering grades. A high elastic modulus corresponds to a high uniaxial compressive strength, verified by the laboratory test. This study shows that the knocking ball can be useful for predicting in-situ elastic modulus.

A bulking model to simulate stope convergence in deep tabular excavations

This paper investigates the use of a novel time-dependent bulking model in a displacement discontinuity code to simulate the convergence between the roof and the floor of deep tabular stopes. This study is important as the current layout design criteria that are based on elastic theory have become outdated. This approach ignores rock failure and fails to predict the actual magnitude and the time-dependent nature of the stope convergence. This has implications for support design and for estimating the stress acting on remnants in mature mines. A rock mass modulus reduction strategy, often used to circumvent this problem, reflects the expected lower effective rock modulus for near-stope fractured material, but must be applied for the entire rock mass region in the displacement discontinuity solution procedure for tabular layout problems. As an alternative, it is proposed in this paper that the rock bulking can be expressed as a function of the elastic closure by using a constitutive rule for the reef-normal compressive reaction stress that is expressed as a function of the compaction strain. The proposed model was tested using convergence data collected from a shaft pillar extraction in a deep gold mine. The bulking model, in conjunction with a limit equilibrium model to simulate the face crushing, seems capable of replicating the underground behaviour. As the stresses on remnants and pillars can be more accurately simulated, this approach holds promise of improving current design criteria. Calibration of the model nevertheless remains a challenge and a programme of routine convergence measurements will have to be implemented on the mines.

Dynamic mechanical properties and failure behaviors of brittle rock materials with a tunnel-shaped opening subjected to impact loads

Since the surrounding rocks of underground tunnels are frequently suffered from the dynamic disturbance of mechanical percussion drilling and explosive blasting, it is significantly meaningful to investigate the mechanical properties and failure behaviors of rock material with a tunnel-shaped opening under dynamic loads. In this work, seven groups of prismatic samples, including the intact samples and the samples with a circular opening of three kinds of diameters, a square opening, a horseshoe-shaped opening and a D-shaped opening, were prepared for dynamic compressive loading. The results show that the prismatic specimens satisfy the stress uniformity condition in impact tests using SHPB testing system with a bar diameter of 50 mm. The weakening effects of the existed openings on the dynamic compressive strength, elastic modulus and peak strain of rocks are closely associated with the size and shape of opening and the loading direction. Based on the energy parameters of the samples, the dissipated energy density of each group of samples can be solved. The failure degree of the samples characterized by dissipated energy density and fractal dimension are in good agreement. Besides, the failure mode of the intact specimen belongs to splitting tensile failure, while that of the pre-holed specimens can be classified as shear-dominated failure due to the coalescence of the openings and the shear cracks occurring along the diagonals of the specimens. The test results provide some insights into the mechanical behavior of rock materials under dynamic loads and lay an important theoretical foundation for support design and rock disaster prevention of underground tunnel.

Numerical validation of Gassmann’s equations

Derived several decades ago, Gassmann’s equations continue to be widely used in applied geophysics. Gassmann’s equations allow us to calculate the elastic moduli of a fully saturated rock from dry rock moduli knowing the porosity, fluid bulk modulus, and bulk modulus of the solid grains. These equations are treated as exact in the scientific community, but there is a lack of comprehensive numerical validation. Furthermore, recently several publications have appeared in the literature postulating a logical error in the derivation of Gassmann’s equations. Therefore, I develop a numerical validation of Gassmann’s equations. For that, I use a 3D finite-element approach to resolve the conservation of linear momentum that is coupled with the stress-strain relations for the solid phase and the quasistatic linearized compressible Navier-Stokes momentum equation for the fluid phase. Finally, a convergence study validating the correctness of Gassmann’s equations for a particular yet arbitrarily chosen “generic” pore geometry is presented. The arbitrary model geometry is simple as compared with real rocks; however, it is sufficiently complex with elements resembling wider pore bodies and narrower pore throats to, in general, validate Gassmann’s equations. MATLAB routines to reproduce the presented results are provided.

Acoustoelastic Mori-Tanaka model for third-order elastic constants of fractured rocks

Insights into the stress-dependent elastic moduli of fractured rocks are important in monitoring geopressure and tectonic stress. This can be addressed by the theory of acoustoelasticity that describes elastic nonlinearity due to the cubic strain-energy function through third-order elastic constants (TOECs). The acoustoelastic TOECs are strictly valid for an isotropic homogeneous medium. The extension to fractured rocks remains largely unaddressed. A group of fractures (ellipses) is embedded into a homogeneous background medium subjected to a uniform confining pressure. We formulate an acoustoelastic Mori-Tanaka (MT) model for the effective TOECs of fractured rocks which can be defined as the weighted average of individual TOECs between the background and fractures in terms of respective volume fractions and stiffnesses. For homogeneously distributed fractures, the stress-induced strains are isotropic in the background and in the fractures. For aligned fractures, the resulting anisotropic strains over the background and fractures make the rock a vertical transverse isotropic medium. The effective elastic moduli and TOECs of fractured rocks depend on background elastic moduli, fracture contents, aspect ratios, and fracture orientations. The prestressed aligned fractures induce nonlinear effects on the effective TOECs that increase with increasing fracture contents and decreasing aspect ratios. We validate the acoustoelastic MT model by experimental data and investigate its limitation by comparing it with finite-element simulations.

Mechanical Characterization of Coarse-Grained Waste Rocks Using Large-Scale Triaxial Tests and Neuroevolution of Augmenting Topologies

Mining operations produce large quantities of waste rocks, which are usually disposed of in waste rock piles, but can also be valorized in mine haul roads. The engineering performance of these haul roads significantly depends on the mechanical characteristics of the materials used for the construction. However, available experimental studies on coarse-grained waste rocks are relatively limited, mainly because of their large grain size and the scarcity of adapted testing equipment. In this study, a series of repeated load and monotonic triaxial tests (specimens 300 mm in diameter and 600 mm in height) were carried out to evaluate the resilient modulus, permanent deformation, and shear strength of coarse-grained waste rocks (up to 60 mm in diameter) with different gradations. Results showed that an increasing in maximum particle size and compaction effort resulted in a larger resilient modulus and shear strength and smaller permanent deformation. The optimal gravel-to-sand ratio to maximize resilient modulus and shear strength was around 5. Permanent strain was relatively constant when the gravel-to-sand ratio was between 1 and 5, but it decreased significantly when the ratio increased to 8. The impact of fines content and water content on the mechanical properties was relatively limited. Also, the MR-θ model and Rahman and Erlingsson model showed good fitting performance for resilient modulus and permanent strain, respectively. Finally, neuroevolution of augmenting topologies (NEAT) was used to develop a machine learning model for predicting the resilient modulus of waste rocks, based on 265 data sets. The model showed reliable accuracy, simple topology, and high generalizability capacity. The findings described in this article should be beneficial for the valorization of waste rocks in pavement engineering.

Prediction of Strength and Modulus of Jointed Rocks Using P-wave Velocity

Strength and deformation characteristics of jointed rocks are important parameters for the design of many civil and mining engineering structures. These parameters are difficult to obtain from direct testing of jointed rocks; hence it is usual practice to derive them through indirect approaches. In the present study, an attempt is made to obtain rough estimates of strength and modulus of jointed rocks through P wave velocity. Jointed specimens of a model rock were prepared for laboratory testing. Joints at different orientations and comprising of different joint roughness coefficients were used (JRC $$=$$ 2–4, 12–14 and 14–16). Ultrasonic P-wave velocity and UCS tests were conducted on the specimens. The effect of joint orientation and joint wall roughness on P-wave velocity was studied. An index, Joint Factor was used to quantify the effect of joint attributes on strength and modulus of jointed rock. It was observed that P-wave velocity is closely linked with Joint Factor. This study suggests a correlation to obtain Joint Factor Jf from P-wave velocity. P-wave velocity may be measured in the field and Jf may be computed through the suggested correlation. The computed Jf may then be used to get the strength and modulus values of jointed rocks. Charts are also suggested to roughly assess the shear strength parameters, cmass and ϕmass of the jointed rock.

A numerical assessment of local strain measurements on the attenuation and modulus dispersion in rocks with fluid heterogeneities

SUMMARY The forced oscillation method is widely used to investigate intrinsic seismic wave dispersion and attenuation in rock samples by measuring their dynamic stress–strain response. However, using strain gauges to locally measure the strains on samples surfaces can result in errors in determining the attenuation and moduli of rocks with mesoscopic scale heterogeneities. In this study, we developed a 3-D numerical model based on Biot's poroelastic theory to investigate the effect of strain gauge location, number and size on attenuation and dispersion in response to wave-induced fluid flow. Our results show that increasing the strain gauge length, number, and size can reduce the error between local and bulk responses. In a homogeneous and isotropic rock with a quasi-fractal fluid heterogeneity at 12 per cent gas saturation, the relative error between local and bulk responses stays below 6 per cent when the strain gauge length surpasses 8.6 times the correlation length. As the gas saturation becomes larger, the ratio minimally changes non-monotonically, initially increasing and then decreasing. We also used the Monte Carlo method to demonstrate that local laboratory measurements can approximate the reservoir-scale response with a minimum relative error of 1.5 per cent as the sample number increases. Our findings provide guidance for (i) interpreting local low-frequency measurements in terms of bulk properties of rock and (ii) upscaling lab measurements to reservoir-scale properties.

Study on the size effect of elastic modulus of rock considering the joint spacing

The relationship between the rock’s elastic modulus and deformation characteristics, affected by joint spacing and ductility, was not determined. This study investigates the size effect of the elastic modulus of rock with parallel joints using numerical simulation and regression analysis. The results showed an exponential relationship between elastic modulus and spacing of parallel joints and a negative exponential relationship between elastic modulus and rock size. The characteristic size of elastic modulus has a power function relationship with the parallel joints spacing, and the characteristic elastic modulus of rock has a power function relationship with the parallel joints spacing. The general and specific forms of these relationships are provided. Establishing these relationships allows for predicting and calculating the elastic modulus of the mine rock mass and serves as a reference for the deformation analysis of the rock.

Effect of Tip Diameter on Static Penetration of a Button Tip into Rock

Rock drills have been widely used for blast hole drilling in tunnel construction and ore extraction. For the advancement of performance and efficiency of rock drills, it is essential to understand the penetration behavior of a button bit and each of the button tips into rock. In this study, static penetration tests were conducted with three rocks using each of button tips with six diameters. The test results showed that the force-penetration curves are linear in the loading phase and convex downward in the unloading phase for sandstone and andesite and that the curves are convex downward in both the loading and unloading phases for granite, if rock chipping does not occur. The force-penetration curves in the loading phase and deformation mechanisms of the rocks could be explained with the contact mechanics; plastic deformation is dominant for sandstone and andesite, and in contrast elastic deformation is dominant for granite. In addition, the relations of the diameter of a button tip, the Young’s modulus and yield stress of rock to the force-penetration curves were clarified. These results indicate that force-penetration curves are estimated beforehand from mechanical properties of the target rock. Occurrence of rock chipping was found to be influenced by not only the diameter of a button tip but also the heterogeneity of rock texture.

Factors affecting casing equivalent stress in multi-cluster fracturing of horizontal shale gas wells: finite element study on Weirong Block, southern Sichuan Basin, China

Multi-cluster fracturing technology was often used in horizontal well reservoir reconstruction to achieve production increase, which also affected casing equivalent stress distribution. This paper focuses on multi-cluster fracturing and establishes a fracturing model in line with the reality. The three-dimensional finite element model of multi-cluster fracture-formation-cement sheath-casing was proposed, the influence of cluster spacing and fracturing cluster number on casing equivalent stress was studied. On this basis, a single segment 8-cluster three-dimensional finite element model was developed. The influence of rock elastic modulus, casing inner wall pressure, geostress change and elastic modulus of cement sheath on casing equivalent stress was simulated from two aspects of uniform and non-uniform extrusion of wellbore. Actual data was used and analyzed for the fracturing section of a well in Weirong Block, southern Sichuan Basin, China. The results showed that the casing equivalent stress decreased with the increase of fracture dip angle. The casing equivalent stress increased with the increase of cluster spacing; however, it decreased with the increase of rock elastic modulus. The casing equivalent stress increased with the increase of casing wall pressure. Also, the cracks extrude the casing evenly did not affect the change on casing equivalent stress. It was also found that, when casing was uniformly squeezed by multiple fractures, the difference of ground stress had little effect on casing equivalent stress, while non-uniform extrusion had greater effect on casing equivalent stress. Further, when there was no wellhead pumping pressure, the casing equivalent stress increased with the increase of the elastic modulus of the cement sheath, and decreased on the contrary. The elastic modulus of rock was lower than that of cement sheath, and the casing equivalent stress increased with the increase of the elastic modulus of cement sheath, and decreased on the contrary. The research results had certain guiding significance for the prevention and control of casing damage in fracturing section.

Analysis of the impact of rating methods for assessing the rock mass on its physical and mechanical characteristics and on the calculation of the support of a vertical shaft

The purpose of the work is to review the existing techniques for evaluating the stability of rock around the vertical shaft and to make the comparative analysis of the effect of using different rating techniques on the assessment of the strength and stability of the massif, as well as on the results of stress calculation on the inner contour of the lining. The relevance of the work. The forecasting of the development of deformations of the vertical shaft rock contour during mining operations is an important element of geomechanics. Its reliability depends on the correctness of determining the mechanical characteristics of the rock mass. For this purpose, it is necessary, by means of application of one of existing methods of massif evaluation, to pass from characteristics of tested core samples to the characteristics of the massif. Due to the need for the mineral’s extraction, vertical shafts and other underground structures are vital, therefore, the relevance of identifying the strengths or limitations of existing techniques for assessing the stability of the host rock massif should not be underestimated. The research’s methods. This work is a theoretical study, during which logical, analytical methods of scientific knowledge, quantitative and qualitative statistical analysis and synthesis of data, methods of mathematization and functional analysis were used. Based on the data of the borehole drilling, the transition was made from the physical and mechanical characteristics of the sample to the physical and mechanical characteristics of the massif, using different rating methods of rock evaluation, after which the deformation modulus of the massif and the stress on the contour of the mount were determined, and a comparative analysis of the results was carried out. The results of the work and its area of application. The paper gives a review of rating systems of rock massif structural disturbance estimation, presents some analytical methods of stability determination, reviews evaluation methods using field instruments and numerical simulation. Studies of the influence of different massif rating systems on determining the deformation modulus of the massif and the stresses in the lining on the example of five boreholes in two different fields in tectonically complicated mining and geological conditions are presented. According to the results of the study, the following dependences were established: with the same initial physical and mechanical properties of the sample, after switching to the characteristics of the array using the GSI index, the deformation modulus of the array is significantly higher than when using the RMR rating; when calculating the stresses on the fastener contour using the GSI index, the stresses on the inner fastener contour are significantly lower than when calculating using the RMR rating. The field of application of these results is the science of geomechanics as well as the industrial underground construction industry. Conclusions. When calculating rock modulus and stresses on the lining contour, methods of evaluating the stability of the massif significantly affect the results of the calculations. The assessment of the massif using only rating systems is not reliable; such an engineering problem requires the use of more than two rating systems for a more accurate assessment, as well as the additional use of approaches, in particular, mathematical modeling.

Developing Two Hybrid Algorithms for Predicting the Elastic Modulus of Intact Rocks

In the primary and final designs of projects related to rock mechanics and engineering geology, one of the key parameters that needs to be taken into account is the intact rock elastic modulus (E). To measure this parameter in a laboratory setting, core samples with high-quality and costly tools are required, which also makes for a time-consuming process. The aim of this study is to assess the effectiveness of two meta-heuristic-driven approaches to predicting E. The models proposed in this paper, which are based on integrated expert systems, hybridize the adaptive neuro-fuzzy inference system (ANFIS) with two optimization algorithms, i.e., the differential evolution (DE) and the firefly algorithm (FA). The performance quality of both ANFIS-DE and ANFIS-FA models was then evaluated by comparing them with ANFIS and neural network (NN) models. The ANFIS-DE and ANFIS-FA models were formed on the basis of the data collected from the Azad and Bakhtiari dam sites in Iran. After applying several statistical criteria, such as root mean square error (RMSE), the ANFIS-FA model was found superior to the ANFIS-DE, ANFIS, and NN models in terms of predicting the E value. Additionally, the sensitivity analysis results showed that the P-wave velocity further influenced E compared with the other independent variables.

Rock physics and seismic reflectivity parameterization and amplitude variation with offsets inversion in terms of total organic carbon indicator

Total organic carbon (TOC) prediction with elastic parameter inversions has been widely used in the identification and evaluation of source rocks. However, the elastic parameters used to predict TOC are not only determined by TOC but also depend on the other physical properties of source rocks. Besides, the TOC prediction with the elastic parameters inversion is an indirect method based on the statistical relationship obtained from well logs and experiment data. Therefore, we propose a rock physics model and define a TOC indicator mainly affected by TOC to predict TOC directly. The proposed rock physics model makes the equivalent elastic moduli of source rocks parameterized by the TOC indicator. Combining the equivalent elastic moduli of source rocks and Gray’s approximation leads to a novel linearized approximation of the P-wave reflection coefficient incorporating the TOC indicator. Model examples illustrate that the novel reflectivity approximation well agrees with the exact Zoeppritz equation until incident angles reach 40°. Convoluting the novel P-wave reflection approximation with seismic wavelets as the forward solver, an AVO inversion method based on the Bayesian theory is proposed to invert the TOC indicator with seismic data. The synthetic examples and field tests validate the feasibility and stability of the proposed AVO inversion approach. Using the inversion results of the TOC indicator, TOC is directly and accurately estimated in the target area.

A characterization method for equivalent elastic modulus of rock based on elastic strain energy

Energy is an internal variable during rock deformation and failure, and its dissipation and conversion law can reflect the rock’s internal damage and deterioration state. Analysis of rock deformation and failure process from the perspective of energy is helpful to deeply understand the mechanism of rock damage, fracture and instability failure, and has important theoretical and practical significance for the stability evaluation and support control of surrounding rock. In this study, through single cyclic loading and unloading (SCLU) experiments, cyclic triaxial loading and unloading (CTLU) experiments and conventional triaxial compression (CTC) experiments, the equivalent elastic modulus method based on elastic strain energy is proposed to analyze the energy conversion of rock. The results show that the error of the elastic strain energy calculated by the strain energy formula method is generally higher than 10% with the secant and tangent modulus of the loading and unloading curve as input parameters. Taking the equivalent elastic modulus proposed in this study as an input parameter, more accurate elastic strain energy can be obtained by the strain energy formula. During the rock failure process, the equivalent elastic modulus shows a three-stage characteristic of increase, steady and decrease. The equivalent elastic modulus can be estimated by the quadratic function between the equivalent elastic modulus and confining pressure and axial strain. Under the same deformation and deviatoric stress, the elastic strain energy stored in rock increases with increasing confining pressure. The local maximum energy dissipation rate corresponds to stress drop, and the peak energy dissipation rate appears near the peak strength. High energy dissipation mainly occurs in a short time after peak strength, and energy release and dissipation are more sudden and severe under high confining pressure.

Seismic pre-stack inversion for physical and anisotropic parameters in fractured shale reservoirs

AbstractThe estimation of physical and anisotropic parameters is of great importance for the characterization of fractured reservoirs. Vertical fractures developing in a laterally isotropic (VTI) setting are equivalent to orthotropic anisotropic (OA) media common in stratified fractured shale reservoirs. To obtain independent anisotropic and physical information, a novel reflection coefficient approximation containing physical and anisotropic parameters is derived to improve the stability of the inversion for orthotropic media. To simplify the equation for the reflection coefficient, an approximate rock physics model is constructed using the approximate theory of rock modulus. The estimated parameters are reduced from nine to six. The accuracy analysis reveals that the new reflection coefficient is appropriate and suitable for inversion. In addition, a stepwise Bayesian amplitude versus angle and azimuth (AVAZ) inversion method with smooth background constraints is developed to estimate the anisotropic and physical parameters from the azimuthal seismic data. The smooth background constraint improves the robustness of the inversion. And the stepwise inversion strategy solves the problem that the contribution of the fracture parameter to the reflection coefficient is smaller than the other parameters. Synthetic cases show that the proposed stepwise Bayesian AVAZ inversion method is feasible in estimating the anisotropic parameters for OA media even when the signal-to-noise ratio is 2. The field cases show that the proposed inversion method has good stability and robustness in predicting shale reservoirs with vertical or near-vertical fractures.

Mechanical and Microcrack Evolution Characteristics of Roof Rock of Coal Seam with Different Angle of Defects Based on Particle Flow Code

The creation of the natural ceiling rock of the coal seam is rife with fractures, holes, and other flaws. The angle of the defects has a significant influence on the mechanical characteristics and crack evolution of coal seam roof rock. Multi-scale numerical simulation software PFC2D gets adapted to realize the crack propagation and coalescence process in the roof rock of a coal seam with different angles of defects under uniaxial compression. The effect of flaw angles on the micro and macro mechanical characteristics of rock is also discovered. The results show that: (1) the defect angle has influence on the stress-strain, elastic modulus, peak strength, peak strain, acoustic emission (AE) and strain energy of roof rock of coal seam. When the defect angles are different, the starting position of the roof rock in a coal seam fracture is different. The quantity of microcracks firstly reduces with an increase in defect angles before gradually increasing. At the same fault angle, the cracks are mostly tensile ones and only a few shear ones. (2) When the defect angle is less than 90°, tensile and shear fractures are mostly localized at the defect's two tips and propagate along the loading direction. When the defect angle is 90°, the tensile and shear cracks are not concentrated at the tip of the defect. (3) As the defect angles increase, the elastic strain energy rises initially and then falls, and the dissipated energy and total input energy both increase continuously. The elastic strain energy is greatest at the highest strength. The study provides a certain reference for the use of various analysis methods in practical engineering to evaluate the safety and stability of rock samples with pre-existing defects.

Research on Floor Heave Mechanisms and Control Technology for Deep Dynamic Pressure Roadways

In order to study the influencing factors of floor deformation and floor heave mechanisms of deep mining roadways, this paper takes the deep dynamic pressure mining roadway of a mine as the engineering background and adopts a research method combining theoretical analyses, numerical simulations and field observations to study the influence of various factors on floor deformation and floor heave mechanisms. It is determined that the influencing factors on floor heave are a large buried depth, a long duration of dynamic pressure, unique characteristics of the surrounding rock and an insufficient support strength. A bearing mechanics model of the roadway floor beam is established, and it is determined that the displacement of the roadway floor is negatively correlated with the elastic modulus and floor thickness and positively correlated with the buried depth of roadway, the roadway width and the width of fracture zone. A numerical simulation method is used to study the influence of the original geological conditions, strengthening the elastic modulus of floor, strengthening the strength of the side wall rock and increasing the thickness of the floor rock on the displacement of the roadway floor. It is determined that increasing the thickness of floor rock controls the floor heave the most, followed by strengthening the elastic modulus of the floor rock and then strengthening the strength of the side walls. The results of the numerical simulation agree well with those of the theoretical analysis. After the control method of “bottom lifting + bottom angle bolt + floor bolt ” is adopted on site to treat the floor heave, the floor heave volume of the roadway is small during the service period of the 303 working face return air roadway, which meets the application requirements of the roadway. Meanwhile, the theoretical analysis and numerical simulation results are indirectly verified.

Experimental Study and Mathematical Description of Gradation Effect on the Mechanical Characteristics of Crushed Waste Rocks

Crushed waste rocks, generated from mining operations, have been widely used for mining infrastructure constructions such as haul roads because of their low cost, high strength, and availability. Crushed waste rock gradation can, however, vary greatly, depending on blasting, mineralogy, and crushing process, but it is a key factor influencing the mechanical properties of crushed waste rocks (including resilient modulus, permanent deformation, and shear strength). Gradation should therefore be optimized to enhance their performance in the field. A series of repeated load and monotonic triaxial tests were carried out on crushed waste rocks with different gravel-to-sand (GS) ratios and fines contents (FC). Results showed that the optimum GS ratio was between 1 and 1.5 and contributed to provide higher resilient modulus and shear strength, and lower permanent strain. An increase in FC could, to the contrary, result in the decrease of resilient modulus and permanent strain and also a significant increase in shear strength. The structure state of crushed waste rocks was quantified using the cm model, and the mechanical properties of crushed waste rocks were dominated by sand and fines when the content of sand and fines was higher than 80%, while it was dominated by gravel particles as the content of sand and fines was lower than 60%. Here, the MR − θ model and the Rahman and Erlingsson model (extended using time-hardening approach) were well adapted to describe resilient modulus and accumulated permanent strain, respectively. Prediction models were also developed based on correlation analyses to predict the resilient modulus and permanent strain of crushed waste rocks based on gradation parameters.