Rock Stress Field Research Articles

Numerical analysis for mining-induced stress and plastic evolution involving influencing factors: high in situ stress, excavation rate and multilayered heterogeneity

PurposeThis study aims to analyse the deep resource mining that causes high in situ stress, and the disturbance of tunnelling and mining which may induce large stress concentration, plastic deformation and rock strata compression deformation. The depth of deep resources, excavation rate and multilayered heterogeneity are critical factors of excavation disturbance in deep rock. However, at present, there are few engineering practices used in deep resource mining, and it is difficult to analyse the high in situ stress and dynamic three-dimensional (3D) excavation process in laboratory experiments. As a result, an understanding of the behaviours and mechanisms of the dynamic evolution of the stress field and plastic zone in deep tunnelling and mining surrounding rock is still lacking.Design/methodology/approachThis study introduced a 3D engineering-scale finite element model and analysed the scheme involved the elastoplastic constitutive and element deletion techniques, while considering the influence of the deep rock mass of the roadway excavation, coal seam mining-induced stress, plastic zone in the process of mining disturbance of the in situ stress state, excavation rate and layered rock mass properties at the depths of 500 m, 1,500 m and 2,500 m of several typical coal seams, and the tunnelling and excavation rates of 0.5 m/step, 1 m/step and 2 m/step. An engineering-scale numerical model of the layered rock and soil body in an actual mining area were also established.FindingsThe simulation results of the surrounding rock stress field, dynamic evolution and maximum value change of the plastic zone, large deformation and settlement of the layered rock mass are obtained. The numerical results indicate that the process of mining can be accelerated with the increase in the tunnelling and excavation rate, but the vertical concentrated stress induced by the surrounding rock intensifies with the increase in the excavation rate, which becomes a crucial factor affecting the instability of the surrounding rock. The deep rock mass is in the high in situ stress state, and the stress and plastic strain maxima of the surrounding rock induced by the tunnelling and mining processes increase sharply with the excavation depth. In ultra-deep conditions (depth of 2,500 m), the maximum vertical stress is quickly reached by the conventional tunnelling and mining process. Compared with the deep homogeneous rock mass model, the multilayered heterogeneous rock mass produces higher mining-induced stress and plastic strain in each layer during the entire process of tunnelling and mining, and each layer presents a squeeze and dislocation deformation.Originality/valueThe results of this study can provide a valuable reference for the dynamic evolution of stress and plastic deformation in roadway tunnelling and coal seam mining to investigate the mechanisms of in situ stress at typical depths, excavation rates, stress concentrations, plastic deformations and compression behaviours of multilayered heterogeneity.

Water Inrush Mechanism of Fault Zone in Karst Tunnel under Fluid-Solid Coupling Field considering Effective Stress

At present, the tunnel construction engineering is increasingly transferring to southwest mountainous areas with complex terrain and geological conditions in China and presents a trend of “large buried depth, long tunnel line, high stress, strong karst, high water pressure, complex structure and frequent disasters.” Taking water inrush disaster of karst tunnel fault zone as the research object, an evolutionary mechanical model of rock damage under the coupling action of stress-seepage is proposed in this paper. Besides, based on Comsol Multiphysics numerical software, the tunnel excavation is simulated, and the stress field, seepage field, and rock damage during the excavation are analyzed; thus, the mechanical mechanism of water inrush disaster from tunnel fault in karst area is obtained. The research results indicate that the tunnel excavation is a dynamic construction process, and the construction disturbance redistributes the original rock stress field and changes the state of seepage field. With the increase of excavation steps, the contour distribution of vertical stress ratio near the tunnel face is a circle shape, indicating that the rock mass is obviously disturbed by excavation, and the ratio of principal stress difference of rock mass at arch crown and bottom plate is large. Besides, the fault fissures expand and penetrate under the influence of tunnel excavation disturbance, increasing the permeability of fault zone in karst tunnel. In addition, the water seepage erosion takes away the granular rock mass, and the lithology becomes more weaker, which makes it possible for the occurrence of water inrush disaster in karst tunnel. Therefore, the advanced geological prediction is important in tunnel construction in karst area. The research results can be treated as an important theoretical basis for the prevention and treatment for water inrush disaster of fault zone in karst tunnel.

Research on Three-Dimensional Stress Monitoring Method of Surrounding Rock Based on FBG Sensing Technology.

Research on the stress state of rock mass is essential for revealing the distribution characteristics and evolution law of the surrounding rock stress field in the roadway, studying the coal–rock dynamic disaster and the design of roadway support. This thesis proposes a three-dimensional stress monitoring method for surrounding rocks based on fiber Bragg grating (FBG) sensing technology and a cube-shaped three-dimensional stress fiber grating sensor is developed based on the principle of this monitoring method. According to the fiber grating strain obtained by numerical simulation, the calculated three-dimensional stress value is basically consistent with the theoretical value. The margin of error was plus or minus one percentage point. The sensing performance of the sensor was tested using a uniaxial compression experiment instead of a triaxial compression experiment. The experimental results show that in the range of 0~50 Mpa, the sensor’s sensitivity to X, Y and Z axis stress is 25.51, 25.97 and 24.86 pm/Mpa, respectively. The relative error of measured stress is less than 4%. Meanwhile, the sensor has good linearity and repeatability, and has broad application prospects in the field of underground engineering safety monitoring such as in coal mines and tunnels.

Fracture Development and Multifield Coupling Evolution Law of Soft Overburden Rock in a Medium-Thick Coal Seam Mine

To study the fracture development and multifield coupling evolution law of soft overburden rock for medium-thick coal seam mining, taking the first 50105 working face of the Faer coal mine as the research background, a numerical simulation, a fractal theoretical analysis, and network parallel electric method experiments were conducted; the fracture development and coupled stress field and energy field evolution law of soft overburden rock for medium-thick coal seam mining are analyzed. The results showed that the overburden collapse process could be divided into three stages: pseudo-top collapse to key layer breakage, key layer breakage to overburden bending, and overburden bending to collapse and compaction. The fractal dimensions of the overburden fracture before and after breakage of the key layer showed a rising-stable-declining trend, and the experimental analysis showed that fracture development began in the unmined area at the front end of the working face under the influence of overstress. In addition, the height of fracture development after stabilization was 53.7 m. A relationship was established between the height of the overburden fracture, peak stress, and dissipation of the energy density of the key layer, and their associated disaster mechanism induced by mining in a medium-thick coal seam progressed as follows: coal mining → stress redistribution → dissipation energy increase → fracture development → stress concentration → key stratum breaking → stress transfer → energy release → dynamic disaster. These results can be used as a reference for observing and mastering the development law of overburden fractures and preventing disasters under such conditions.

Study on the influence of hole defects with different shapes on the mechanical behavior and damage law of coal and rock.

To study the effect of different shapes of hole defects in coal and rocks on their mechanical behavior and macro damage law, the microscopic mechanical parameters required for particle flow code (PFC) simulation were calibrated with laboratory test data, and then the evolution process of crack and stress field in coal and rocks with circle, square, triangular and trapezoidal holes under uniaxial compression were researched. The findings indicate that: the existence of hole defects lowers the elastic modulus, peak stress, peak strain and other mechanical parameters of coal and rock, and the reduction degree is influenced by the shape of defect. Meanwhile, the existence of hole defects promotes the generation and evolution of meso-cracks in coal and rock. For coal and rock with hole defects, the crack initiation stress and expansion stress are less than those of intact coal and rocks. The crack initiation stress and expansion stress of coal and rocks with trapezoidal hole defects are the smallest, and the coal and rocks with circular hole defects are the largest. The existence of hole defects weakens the damage degree of coal and rocks to some extent. With the increase of axial strain, the evolution curve of the number of meso-cracks shows stage characteristics, which consists of the calm period before the crack initiation point, the stable growth stage between the crack initiation point and the dilatation point, and the accelerated growth stage after the dilatation point. Before the initiation of crack, the concentration zone of compressive stress is located on the left and right sides of the hole defect, and the concentration zone of tensile stress is located on the upper and lower sides of the hole defect. The concentration of tensile stress is the main reason for the initiation and propagation of cracks, while the existence of compressive stress chain among macroscopic cracks is the cause of the residual strength of coal and rocks after failure.

Study on the Evolution Law and the Orientation Criterion of a Plastic Zone in Rock Surrounding a Circular Roadway in a Three-Dimensional Non-Isobaric Stress Field

The original rock stress field is mainly divided into the σHZ-dominant stress field, the σZ-dominant stress field, and the σH-dominant stress field. Via theoretical analysis, the plastic zone morphology and the orientation of roadway surrounding rock under a three-dimensional stress field are studied in depth, and the theory is verified by numerical simulation. The results show that in the σHZ-dominant stress field, the plastic failure mode changes from elliptical to quasi-circular to butterfly, and the optimized angle range of the roadway orientation is determined by three principal stresses. In the σZ-dominant stress field, the shape of the plastic zone transforms from butterfly to ellipse, the optimized angle range of the roadway orientation is 50–90°, and the butterfly hidden danger zone is in the 0–50° range. In the σH-dominated stress field, the shape of the plastic zone transits from ellipse to butterfly. The optimized angle range of the roadway orientation is 0–40°, and 50–90° is the butterfly hidden danger zone.

Quantitative Study on the Stress Distribution Characteristics of Coal Rock with Faults

To quantitatively describe the distribution characteristics of stress field of coal rock in fault area, a finite element model was established to study the influence mechanisms of different fault parameters on the stress distribution characteristics of coal rock and a prediction model of the tectonic stress field of a fault-containing coal rock was established based on the numerical simulations. The numerical simulation results show that the coal rock in the hanging wall of a normal fault forms an area of disturbance significantly larger than that in the footwall of the normal fault and reverse fault. With the increase in fault throw, the stress concentration factor and fault influence range decrease in both the normal and reverse fault scenarios. Additionally, for both the normal and reverse fault scenarios, with the increase in fault dip angle, the coal rock stress concentration zone gradually collapses to the fault plane and the stress concentration coefficient gradually increases due to the reduction in the area of pressure relief. The prediction model of the tectonic stress field can better describe the quantitative relationship between the fault parameters and the stress of coal rock, which can provide guidance for the excavation design of mining engineering and early warning for possible coal and gas outburst disasters.

Characteristics of Stress Field and Damage Law of Coal Rock in Residual Pillar of Top Slice and Its Application

This article presents a theoretical analysis and numerical simulation studies to determine the suitable position for the lower slice roadway in a residual pillar area after top slicing a thick coal seam. We considered the load concentration on the coal pillar, the goaf floor, and the stress distribution characteristics of the coal pillar area before and after the top slice. With a mechanical model built of the residual pillar load propagation in the floor and the failure model of the floor surrounding rock, the analytical formula we deduced for the coal pillar floor stress and the expression of the floor failure depth of the roadway provides a basis for the reasonable determination of the position of the lower slicing roadway. Studies proved that after mining the top slice working face, the floor stress field of the residual pillar area presented characteristics of the non-uniform distribution. The stress concentration occurred below the coal pillar. The stress variation area appeared at the edge of the coal pillar, with a stable stress area appearing far away from the coal pillar area. Therefore, the roadway layout should avoid the areas below the coal pillar and the coal pillar edge with high stress levels and a large stress variation gradient. High stress concentration formed on the coal pillar transferred to the lower layered coal and floor strata, and decreased the stress concentrations layer by layer. However, mining of the top-layered working face affected the coal, and rock mass damaged the coal pillar floor area and weakened the mechanical properties, which was not conducive to the control of the roadway surrounding rock. The research results applied to No. 30117 working face of the lower slice of the Shancheng Coal Industry, and the proper position of the return airway of the working face was determined to be 8 m outside the east side of the residual pillar in the top slice, achieving a good surrounding rock control effect.

Development and Application of the 3D Model Test System for Water and Mud Inrush of Water-Rich Fault Fracture Zone in Deep Tunnels

In order to study the evolution process, damage characteristics, and occurrence mechanism of water and mud inrush disaster in deep tunnel fault zone with infiltration instability under complex conditions, a set of the three-dimensional physical model test systems of water and mud inrush flow-solid coupling in tunnel fault zones is developed. The system mainly comprises a rigid test frame, ground stress loading system, hydraulic loading system, multiple information monitoring and acquisition system, and mud and water protrusion recovery system. The system’s main features are that it can meet the model’s simulation of the ground stress field, water pressure, and other complex environments subjected to ground stress, and water pressure gradients can be controlled. The system is characterized by high rigidity, high-pressure strength, visualization, good sealing, and expandability. Taking the water fault zone of a well in the Dazhu Mountain Tunnel of the Darui Railway as the research object, the new fault zone and surrounding rock similar materials applicable to the flow-solid coupling model test are designed using the self-developed flow-solid coupling similar materials. The system is used for model tests to reveal the spatial and temporal changes of the surrounding rock stress field and seepage field during the tunnel excavation process. The test results show that the system is stable and reliable, and the research method and results are of guiding significance to the research of the same type of underground engineering.

Long-term degradation, damage and fracture in deep rock tunnels: A review on the effect of excavation methods

Rocks are frequently host materials for underground structures, particularly for deep Tunnels. Their behavior plays a fundamental role in the overall stability of these structures. In fact, the erection of deep tunnels imposes rocks excavations around the defined routes. These excavations are generally carried out by various methods of which the most used are Drill-and-Blast (DB) and Tunnel Boring Machine (TBM). However, regardless of the tunnelling method used, the impacts such as the perturbation of the initial stress field in rocks and the release of the stored energy are always significant. The impacts produce damage, fractures and deformations which are generally time-dependent and influence the long-term stability of deep tunnels built in rocks. Thus, by considering the aforementioned excavation methods, this paper identifies, reviews and describes the relevant factors generated during and after rock excavations. Interestingly, such factors directly or indirectly influence the long-term stability and therefore the structural integrity of deep rock tunnels. In addition, some recommendations and proposals for future works are presented. This paper can provide useful references in understanding the degradations, damage and fractures generated by tunnelling methods and facilitate suitable actions to ensure long-term stability of deep underground structures.

Fracture processes in coal measures strata under liquid CO2 phase transition blasting

Liquid carbon dioxide phase-transition blasting (LCO2-PB) has been applied to improve the permeability coal seam and enhanced coalbed methane recovery (ECBM). However, the mechanical behavior of crack generation and propagation in LCO2-PB under true triaxial stresses, has not been studied in detail. In this paper, five small-scale experiments of LCO2-PB were carried out with different restraint stresses on concrete blocks (150 × 150 × 150 mm3). Three uniaxial strain-gauges were used to monitor the surface strain of the blocks. The results show that the dynamic shock and expansion exists in the process of LCO2-PB. The release pressure markedly affected the relationship between shock and expansion. The expansion of the borehole and the fracture zone decrease with the increase in the confining pressure stress, and it cannot affect the number and direction generated of the blast cracks. The release pressure plays a decisive role in the number of fractures. The propagation process of LCO2-PB fracture was affected by the combination of LCO2 volume and surrounding rock stress field. The increase in the volume of LCO2, mainly influenced the length of cracks rather than the number of those. The propagation direction of fractures can be determinate by the effects of confining pressure. The research results will help enhance CBM recovery and reduce the occurrence of the gas disaster.

Simulating the Formation of Blasting-Excavation-Induced Zonal Integration in Deep Tunnels with an Elastoplastic Damage Model

More deep tunneling projects will be constructed due to the increasing demand of underground energy and resource. The zonal disintegration phenomena are frequently encountered with the surrounding rock of deep tunnels. To explain the mechanisms underlying the formation of zonal disintegration, an elastoplastic damage model and failure criterion are proposed in this study based on the strain gradient theory and the damage property of rock mass. A coupling calculation subroutine is thereafter developed by the ABAQUS code. The dynamic formation and development regularity of zonal disintegration in the deep tunnel are simulated by this subroutine. The radial displacement, radial stress, and tangential stress show the oscillated variation of peaks and troughs alternately. The coupling effect of the blasting load and the initial geostress transient unloading leads to the variation of alternation oscillation in the surrounding rock stress field, which is an important reason for the zonal disintegration of the surrounding rock. The morphological characteristics of fractured zones and nonfractured zones obtained from numerical simulations are in good agreement with the results from the in situ observations, which confirm the correctness and feasibility of the damage and numerical approach. The method proposed in the current study can be utilized to provide a basis for the prediction and supporting design of fractured modes.

Study on Gas Comprehensive Control Technology in Steep and Extra Thick Coal Seam

In order to improve the gas drainage amount and drainage rate of steeply inclined and extra thick coal seam and realize the safe and efficient mining of coal mine, the distribution and evolution law of surrounding rock stress field and fracture field of horizontal slicing mining face in steeply inclined coal seam were revealed by using numerical simulation method, and the gas flow process and law from lower pressure relief gas to slicing mining face were analyzed The comprehensive control measures of the combination of pressure relief gas interception and drainage and buried pipe drainage in the goaf of this layer have realized the effective gas control of the mining face in the mine production process. The research results play a typical demonstration role for the comprehensive control of rock burst and gas in steep and extra thick coal seam in Xinjiang and even in the whole country, and have promotion significance.

Research on the Evolution Characteristics of Floor Stress and Reasonable Layout of Roadways in Deep Coal Mining

The safe and efficient mining of deep coal resources is severely restricted by the dynamic disasters caused by high gas and high ground stress. Taking a deep mine in China as the research background, a mechanical model of the front supporting stress with the working face was constructed through theoretical calculations. Based on the limit equilibrium theory, the stress distribution in the plastic zone and the elastic zone of the lateral working face was derived; based on semi-infinite plane mechanics model, the floor vertical and horizontal stress distribution was deduced. Then, the roadway surrounding rock stress and displacement field distribution evolution characteristics were revealed through numerical simulation. On this basis, the reasonable floor gas drainage roadway (FGDR) layout was determined: internal staggered layout was used with FGDR, the vertical distance to the working face is 20 m, and the horizontal distance to the working face end is 15 m; the open-off cut of FGDR was arranged in an external staggered layout, the vertical distance to the working face is 20 m, and the horizontal distance to the open-off cut of the working face is 15 m. It is an important practical significance for the layout of FGDR, the control of surrounding rocks, and the improvement of gas drainage effects under similar conditions through the research results.

Numerical Simulation Research on Distribution Characteristics of Overlying Rock Stress Field in Floor Roadway

In order to explore the distribution characteristics of the overlying rock stress field in the floor roadway at different locations, FLAC3D software was used to simulate and analyze the surrounding rock directly above the floor roadway and the surrounding rock within 15m on both sides of the floor roadway when the distance between the floor roadway and the coal roadway and the horizontal distance were changed. The stress field distribution characteristics are obtained, and the stress field distribution characteristics of different areas directly above and on both sides of the floor roadway are obtained, which provides a theoretical basis for the location selection and support of the floor roadway.

Experimental study on mechanical and optical properties of printable photopolymer used for visualising hidden structures and stresses in rocks

Abstract The visualization and quantification of the internal complex structure, stress field, and fluid flow behaviour of subsurface rocks is crucial for the enhanced recovery of deep earth resources and protection of their formation environment. Replicating natural rocks using models produced by three-dimensional printing (3DP) technology is a promising method for visualising and quantifying the hidden structural changes, stress evolution, and fluid flow within subsurface rocks. The development of model materials that are suitable for 3DP and reflect the physical and mechanical properties of rocks is the key to achieving this goal. In this study, the mechanical and optical properties of the printable stress-sensitive photopolymer VeroClear were measured at temperatures in the range from −50 to 125 °C to evaluate the suitability of this photopolymer for modelling actual rocks. The contact angles of the material in different solutions used for evaluating the fluid flow behaviour of rocks were also measured. The reported datasets experimentally support the use of additively printed models for evaluating the solid and fluid mechanics of subsurface rocks.

Research on Displacement Failure Characteristics of Deep Roadway Surrounding Rock

In order to explore the displacement failure characteristics of deep roadway surrounding rock, the surrounding rock stress field model of the uniform stress field in the circular tunnel is simplified. It analyzes the stress evolution features of deep coal rock and discusses the mechanism of zonal disintegration. It observes the deep displacement surrounding rock of Qujiang mine n the depth of 1000m, the displacement shows that the wave crests and troughs appears alternately; wave crest position for damage area, trough part for non-damage zone. The surrounding rock of roadway exists zonal disintegration phenomenon, each roadway section is a total of four fracture zones. Due to different positions of roadway section tunnel excavation time rheological effect, the longer the tunnel is excavated, the more serious the surrounding rock is damaged.

Study on the Stability of Rock Slope Under the Coupling of Stress Field, Seepage Field, Temperature Field and Chemical Field

The research on the stability of rock slopes under the multi-field coupling has important theoretical and practical significance for the analysis and prevention of freeze–thaw disasters of engineering in cold regions. In this paper, COMSOL Multiphysics numerical simulation software and numerical simulation methods are adopted. Based on the coupling theory of rock stress field, seepage field, temperature field, and chemical field, and field test data, the stability of rock slope under the multi-field coupling is studied under the research background of the highway slope of Jinghe to Yining County of G577 line. Based on the study of multi-field coupling theory, a numerical calculation model is established, the rationality of the numerical calculation model is verified, and the maximum frozen thickness of the slope is determined. On this basis, the change rules of the relevant parameters such as stress, temperature, deformation and damage of the highway slope in the engineering area are studied. The slope stability analysis is performed based on the YAI slope stability evaluation method. The stability of the slope is analyzed from the freezing, thawing and freeze–thaw process states of the shallow layer of the slope. It provides a theoretical basis for engineering construction in cold region.

Experimental and theoretical analysis of hydraulic fracturing and gas fracturing of rock under true triaxial compressions

A test system was developed for true triaxial hydraulic fracturing (HF) and gas fracturing (GF) combined with acoustic emission (AE) monitoring and 3D computerized tomography (CT) scanning reconstruction to carry out a series of HF and GF tests under different true triaxial loading conditions. The critical breakdown pressure characteristics, the AE activities, and the fracture propagation and spatial morphologies were obtained during the fracturing process. The test results showed that the GF breakdown pressure was approximately 29.0–31.3% less than the HF breakdown pressure. Moreover, for the GF specimen, the gas pore pressure induced a large number of new microfractures before critical fracture. However, both HF and GF under true axial compression can only produce simple main longitudinal fractures (LFs, along the borehole) and transverse fractures (TFs, across the borehole) that are strictly dependent on the initial true triaxial stress field. Based on the experimental observations, a hypothesis for the initiation of the HF and GF under true triaxial compression was proposed by using the maximum tangential stress on the borehole wall and the maximum axial stress along the borehole. Accordingly, analytical solutions of the critical breakdown pressure for the HF (impermeable) and GF (permeable) specimens were derived. The theoretical predictions agree well with the observations from the 3D numerical simulations and tests. Lastly, a novel pulsed GF method (dynamic loading fracturing) was proposed to overcome the dependence of the in-situ crustal stress field associated with traditional HF and GF methods (static loading fracturing). Laboratory test results showed that the dynamic pulsed GF at moderate pressure can generate a complex and random fracture network independent of the in-situ stress field in rock.

Numerical Study on the Elastic Deformation and the Stress Field of Brittle Rocks under Harmonic Dynamic Load

In order to study the deformation displacement and the stress field of brittle rocks under harmonic dynamic loading, a series of systematic numerical simulations are conducted in this paper. A 3D uniaxial compression simulation is carried out to calibrate and determine the property parameters of sandstone and a model of the cylindrical indenter intruding the rock is proposed to analyze the process of elastic deformation. Four main parameters are taken into account, namely the position on the rock, the frequency and the amplitude of dynamic load, the type of indenter and the loading conditions (static and static-dynamic). Based on the analysis undertaken, it can be concluded that both of the deformation displacement and stress field of the rock change in a harmonic manner under the static-dynamic loads. The frequency and the amplitude of harmonic dynamic load determine the period and the magnitude of the rock response, respectively. In addition, the existence of harmonic dynamic load can aggravate the fatigue damage of the rock and allow a reduction in static load. Our investigations confirm that the static-dynamic loads are more conducive to rock fracture than static load.