Plastic Zone Of Surrounding Rock Research Articles

Quantitative Characterization and Disturbance Law of Key Parameters Influencing Deformation of Overlying Strata during Strip Filling in a Goaf

Strip filling mining in a goaf is of great significance for solving the ‘three under’ coal-pressure and mining-area ecological environment problems in Central and Eastern China, but the disturbance characteristics of filling parameters on overlying rock are not clear at present. Taking the geological conditions of the CT30101 working face in Mahuangliang coal mine and the short-wall interval strip filling as a background, the strength parameters (cohesion and friction angle), deformation parameters (elastic modulus and Poisson’s ratio), and structural parameters (strip width and spacing) of the filling body were selected as experimental factors, and the maximum settlement of the direct roof and the ground surface was taken as the evaluation index. The influence degree of each factor was quantitatively characterized via a variance analysis and an F test, and the main control factors of the strip filling overburden settlement were proposed. The roof and surface displacement, the stress evolution law of the filling body, and the shape change of the surrounding rock plastic zone under different levels of main control factors in the entire process of mining filling coupling were analyzed in detail. The results showed that the cohesion of the backfill had a highly significant impact on the direct roof settlement, the strip spacing and the friction angle of backfill had a significant impact on it, the cohesion of the backfill and the strip spacing had a certain impact on the surface settlement, and the two had a cross-coupling effect. In the process of mining and filling, the stress evolution of the filling body was extremely complex, and it finally presented a saddle shape that was high on both sides and low in the middle; the majority of the strata and the filling body primarily exhibited shear damage, with a small amount of tensile failure zones appearing only in the direct roof and mid-section of the filling body. The above conclusions have a certain guiding significance for the optimal design of strip filling in a goaf.

Unified strength-based elastoplastic solution for frost heaving force of cold-region tunnels considering dual non-uniform frost heaving of surrounding rock

Precise evaluation of the frost heaving force and surrounding rock plastic zone is an important basis of the prevention of freezing damage in cold-region tunnels. The temperature gradient along the radial direction of cold-region tunnels surrounding rock results in the dual non-uniform frost heaving of surrounding rock, namely, the gradual change of frost heave ratio along the radial direction and the unequal frost heaving deformation in the circumferential and radial directions. A new elastoplastic solution of tunnel frost heaving force considering double non-uniform frost heave and intermediate principal stress was derived based on the elastoplastic mechanics theory, thick-cylinder theory, and unified strength theory to better guide the frost resistance design of tunnels in cold regions. The rationality and advantages of the unified plastic solution of tunnel frost heaving force were verified by model tests and engineering examples. Results showed that the theoretical calculation value of frost heaving force was in good agreement with the measured value. When the gradual change in the frost heave ratio of surrounding rock in the radial direction was ignored, the frost heaving force and radius of the surrounding rock plastic zone were large and conservative. The solution in this paper can accurately evaluate the tunnel frost heaving force and surrounding rock plastic zone. Finally, this paper studies the influences of intermediate principal stress coefficient, the frost heaving coefficient of unit temperature of frozen surrounding rock, non-uniform frost heaving coefficient in different directions, and maximum freezing depth on the evolutionary law of frost heaving force and plastic zone of cold-region tunnels are studied.

The Change in the Shape Characteristics of the Plastic Zone in the Surrounding Rock of an Auxiliary Retracement Channel and a Reasonable Channel Spacing Determination Method

In underground coal mines, the stability of the retracement channel in the surrounding rock is crucial for the safe and efficient retracement of the equipment and to guarantee the continuity of the retracement work. To reveal the deformation and damage mechanism of the surrounding rock of an auxiliary retracement channel (ARC) and the determination method for the reasonable spacing of two retracement channels during the end of the mining period, the deviatoric stress field in front of the working face and the change in the shape characteristics of the plastic zone in the ARC are investigated in this paper. The formation of ultimate stress equilibrium, high deviatoric stress, decreasing deviatoric stress, and low deviatoric stress environments in front of the working face during the end of mining occur successively, and the different deviatoric stress environments are the main reasons for the different shape characteristics of the plastic zone in the surrounding rock. The changes in the shape characteristics of the plastic zone correspond to the changes in the shape characteristics in the zone with deviatoric stress and exhibit the following order: full plastic deformation zone, butterfly-shaped zone, elliptical zone, and circular plastic zone. A reasonable spacing determination method for the two retracement channels is proposed: the ARC is arranged in the decreasing deviatoric stress environment, where the surrounding rock plastic zone shape is elliptical, and the ARC is relatively stable. Based on this research result, the spacing of the double retracement channels at the Lijiahao 22-116 working face was determined to be 25 m, which achieved a positive application effect and allowed the safe and efficient retracement of the working face equipment.

Numerical Simulation Research and Application of Support Design of Broken Rock Mass in Submarine Gold Mine

In order to solve the problem that the broken rock mass is easy to collapse and fall during the excavation of a submarine gold mine, two kinds of bolt-mesh-concreting combined support schemes are designed by means of field engineering geological investigation, indoor rock mechanics test, rock mass quality classification, and theoretical analysis. We use the numerical simulation for verification and carry out the field industrial test. The results show that the stability grade of broken surrounding rock is III–IV; both schemes can effectively control the deformation and failure of surrounding rock. Compared with the unsupported scheme, the maximum roof displacement in the scheme using roadway roof and sidewall support is reduced by 26.9%, the maximum thickness of the roof plastic zone is reduced by 58.2%, and the volume of the surrounding rock plastic zone is reduced by 26.32%. The bolt-mesh-shotcrete support has good control effect on the loose deformation of surrounding rock, which can effectively prevent the roof collapse and sidewall spalling of roadway. The field industrial test of support scheme meets the stability control requirements of broken rock mass in mines, and the application effect is obvious. The research results presented in this study provide valuable technical guidance and essential insights for the design of support systems in other similar mining projects, contributing to the effective control and stability of broken rock masses during excavation.

Study on deflection of principal stress and deformation characteristics of roadway surrounding rock under mining action in close-distance coal seams

The traditional index to determine the width of the stopping coal pillar (WSCP) is generally only the front abutment pressure, but the direction of the principal stress will deflect due to the mining action, which brings significant challenges to controlling the surrounding rock. Based on theoretical calculation and numerical simulation, we studied the deflection law of principal stress under mining action, quantified the bearing capacity of roadway surrounding rock, and determined WSCP. The results show that: (1) With the deflection of the principal stress, the distribution of the surrounding rock plastic zone also rotates; (2) λ and repeated mining dominate and aggravate the deflection angle and range of the principal stress in front of the working face, respectively. When λ is close to 1, the deflection of principal stress should be paid attention to in determining WSCP; (3) The anchorage composite bearing structure (ACBS) provides a scientific basis for quantifying the bearing capacity of surrounding rock. WSCP of the lower coal seam is determined to be 60–75 m, and the corresponding principal stress deflection is about 135°. The control of the surrounding rock in the diagonal direction where the maximum principal stress is concentrated should be paid attention to.

Theoretical analysis of drilling cuttings considering stress zoning of surrounding rock and its application in stress detection

AbstractDrilling cuttings method is a commonly used method to detect the risk of rockburst, which has been widely recognized and applied in coal mines. However, in the current theoretical research on the relationship between drilling cuttings method and coal stress, it is generally considered that the mechanical parameters of coal at different positions of roadway are unchanged, and the influence of surrounding rock plastic zone and elastic zone is not considered. Therefore, according to the secondary distribution characteristics of roadway side stress, the theoretical calculation formula of drilling cuttings in the plastic zone and elastic zone of the roadway side is established in this paper. The example shows that the distribution of cuttings on the roadway side is obviously consistent with the abutment pressure. The cuttings in the plastic zone and the elastic zone are in linear and power function with the coal stress, respectively, and the cuttings in the plastic zone are greater than those in the elastic zone. With the increase of the hole diameter, the slope of the relationship curve between the drill‐cutting weight and stress gradually increases, and the response of the drill‐cutting weight with a large hole diameter to the change of coal stress is more obvious. The numerical simulation results show that the error of the theoretical calculation formula of the drilling cuttings method is less than 9%, which can meet the engineering application needs of estimating the drill‐cutting weight in coal and the stress of coal. Using the theoretical formula, the stress field in the leading area of the working face is measured, and the leading influence range and the accurate position of the high stress concentration area are determined, which provides more comprehensive stress information for the early warning of impact danger and pressure relief.

Failure Mechanism and Stability Control of Soft Roof in Advance Support Section of Mining Face

There is a great risk of roof falls in the advance support section of the mining face (ASSoMF), and it is difficult to control the roof. Based on the soft roof of Lijiahao coal mine, this paper studies the stress distribution of the ASSoMF and the space-time evolution of the surrounding rock plastic zone by using theoretical analysis and numerical simulation, and reveals its failure mechanism. Based on the control effect of support resistance on plastic zone, it is proposed that the advance support should mainly adapt to the roadway deformation. Advance equipment without repeated support for mechanized movement has been developed, and the support timing analysis and strength check have been carried out. Results show that the roadway at ASSoMF is in a non-uniform stress field, the confining pressure ratio reaches 1.5~7, and the surrounding rock forms asymmetric failure; the principal stress direction deflects, the angle between it and the vertical direction is about 10°~25°, and the plastic zone of the surrounding rock also rotates to the roadway roof. The proposed equipment can adapt to the characteristics of an unsymmetrical large deformation of a soft roof, and can effectively bear the roof load and maintain the stability of the roadway.

Failure mechanism and support system of roofs in advance areas affected by mining under the condition of soft rock stratum

The advance area affected by mining (AAAM) of the Lijiahao coal mine is influenced by the superposition of the side and advance abutment pressure, and the roadway roof is considerably damaged. General support technology and equipment cannot economically and effectively maintain the stability of the roadway roof of AAAM. Through field detection, theoretical analysis, and numerical simulation, this study analyzes the structure of the surrounding rock, the evolution characteristics of the regional stress field, the distribution of the surrounding rock plastic zone, and the influencing factors of the plastic zone in the AAAM of the Lijiahao mine. The results show the following: 1) the direct roof and floor of the roadway comprise coal, siltstone, and sandy mudstone, which has low strength and can be easily broken. 2) The maximum and minimum principal stresses in the AAAM reach 2.3 and 1.5 times of in situ stress, respectively, and the ratio of the two stresses reaches 2–8, which causes the shape of the plastic zone of the surrounding rock to turn into a butterfly shape. 3) The principal stress direction of AAAM deflects at a large angle, which causes the deepest failure direction of the surrounding rock to rotate to the roof and floor of the roadway. Accordingly, a self-moving foldable support system is proposed to support the AAAM of the Lijiahao coal mine. The system will not support the roof repeatedly and is suitable for soft rock stratum. In addition, it can also adapt to the heave of roadway floor and avoid dumping. The mechanized operation of the system makes the roof support in AAAM more efficient and safer.

Analysis of Surrounding Rock Pressure of Deep Buried Tunnel considering the Influence of Seepage

This paper takes the surrounding rock of deep tunnel as the research object and considers the action mechanism under the influence of seepage. Based on the Mohr-Coulomb criterion, the stress mechanism of surrounding rock of deep buried tunnel is analyzed by a convergence constraint method. Based on the elastic-plastic solution, the nonlinear elastic-plastic solution of the interaction between surrounding rock and lining structure considering the effect of seepage force is proposed, and the radius of surrounding rock plastic zone is obtained. The relationship between surrounding rock stress and displacement, radial deformation of lining, and support reaction force was observed. At the same time, considering the effects of seepage, strain softening, and intermediate principal stress, the surrounding rock is divided into a plastic residual zone, plastic softening zone, and elastic zone, and the stress distribution expressions of the plastic zone and each zone of surrounding rock of circular tunnel are derived. The results show that with the change of nonuniform permeability coefficient, the seepage shows anisotropy in different directions, and the closer to the horizontal or vertical direction, the more obvious the influence of nonuniform permeability coefficient on pore water pressure distribution. Seepage and material softening have different effects on the distribution of surrounding rock stress field and the size of plastic zone. Material softening is more unfavorable to the stability of surrounding rock than seepage. The intermediate principal stress coefficient has a significant impact on the tangential stress and plastic zone of surrounding rock. When the intermediate principal stress effect is not considered, the calculation results are relatively conservative and cannot give full play to the strength of surrounding rock effectively. The research conclusion can provide a theoretical reference for studying the stability of surrounding rock in tunnel excavation under water-bearing rock.

Comparative Study on the Plastic Zone of Circular Hole Surrounding Rock in Anisotropic In Situ Stress Conditions

Anisotropic in situ ground stress is an objective stress state of rock mass that should be taken into account when calculating the plastic zone of the circular hole surrounding rock. The point stress method and approximate plastic condition method for calculating plastic zone are derived, and the finite element numerical calculation is carried out. Different analytical and finite element approaches are employed for calculation based on the representative parameters. The outcomes of the calculations are thoroughly examined. There are four shapes of plastic zone, among which the butterfly plastic zone can be obtained only by approximate plastic condition method and finite element method. The distribution of plastic zone calculated by using the point stress method and the Ruppneyt formula is identical, with only small deviations. The modified Fenner formula should not be used to calculate the plastic zone under in situ stress anisotropy since it would result in an underestimation of the maximum plastic radius. The detailed calculation and results comparison of this paper can provide a reference for more comprehensive and reasonable evaluation of the surrounding rock plastic zone.

Numerical Simulation of Coupling Support for High-Stress Fractured Soft Rock Roadway in Deep Mine

Aiming at the difficulties during the support of high-stress fractured soft rock roadway in deep mine, a comprehensive surrounding rock management method of bolt-net-cable-grout coupling support is proposed and the mechanism of interaction between coupling support and surrounding rock is analyzed by numerical simulation. The effectiveness of the coupling support is proved by an application in the east wing return-air roadway in the Qingdong Coal Mine of Huaibei Mining Group. The results show that the surrounding rock plastic zone near the sidewall and floor of high-stress fractured soft rock roadway is larger than that near the roadway roof, and its distribution range can be reduced by using the coupling support. And, the coupling support can improve the reliability of roadway support and the stability of surrounding rock by reducing the axial stress of anchor bolts, the stress concentration of surrounding rock caused by anchor bolt, the roadway surface displacement, and deep displacement of surrounding rock.

The shape characteristics of circular tunnel surrounding rock plastic zone in the complex stress field

The shape characteristics of circular tunnel surrounding rock plastic zone in the complex stress field

Analysis of Plastic Zone and Pressure Variance Features of Surrounding Rock of High-Altitude Macker Tunnel: A Case Study in Jiangluling Macker Tunnel in Qinghai

Due to the special mechanical properties of macker rock, problems may be caused easily if the pressure of the surrounding rock calculated from the standard empirical equation is used in the structural design of tunnel support, such as obviously insufficient bearing capacity of the support structure, large deformation, and collapse. Taking the Jiangluling Macker Tunnel in Gonghe-Yushu Highway as an example, the distribution pattern of plastic zone of the surrounding rock and the calculation method and reasonable values of pressure of the surrounding rock are studied in this paper, by means of theoretical analysis, numerical computation, and field measurement data. The results show that the elastic-plastic analysis method is suitable for the pressure of the surrounding rock of macker tunnel. The influence radius of the plastic zone of the surrounding rock can be 32 m, and the lateral pressure of the surrounding rock of the tunnel is equivalent to the vertical pressure. In the absence of test conditions and measured data, the pressure of the surrounding rock can be approximately 0.83 MPa for the purpose of design of tunnel support structure. This conclusion provides technical support for projects in similar conditions.

Mechanical Characteristic and Length Optimization of System Anchor in Loess Tunnel Based on Field Measurement and Analytical Solution

In this paper, field measurement is used to obtain the force of system anchor in its actual working condition and stress situation of system anchors in different parts of loess tunnel is analyzed based on field test results, indicating the reasons why values of measured axial force of system anchor are different in different parts of loess tunnel. Based on the displacement solution of Mindlin problem, this paper deduces the analytical solution to stress distribution of system anchors in the sidewall of loess tunnel under the pull-out force, analyzes the distribution forms and influencing factors of shear stress and axial force. At the same time, analytical solutions to system anchor stress and surrounding rock plastic zone radius are tentatively applied to the analysis of stress characteristics and length optimization of system anchor in loess tunnel. The research results are of great significance to understand the mechanical characteristics of anchors in loess tunnel and to optimize the design of anchors in the primary support system of loess tunnel, which leads to accelerated construction progress and low economically cost, especially in loess tunnels with large cross section and long span.

A mechanical model for the circular tunnel considering the interaction between the surrounding rock and support structure based on the unified strength criterion

It is very significant to study the stress and displacement fields in the surrounding rock induced by the tunnel excavation and its support. First of all, in order to take into account the effect of the intermediate principal stress on the tunnel surrounding rock mechanical behavior, the unified strength criterion (USC) is adopted to describe the plastic yield behavior of the surrounding rock. Secondly, the model proposed by Kastner does not consider the effect of the initial elastic displacement of the tunnel surrounding rock before the support structure is constructed and the interaction between the surrounding rock and the support structure. Therefore, a new mechanical model for the circular tunnel, which can overcome these shortcomings, is finally proposed by considering the tunnel practical construction process on basis of Kastner’s method. The effects of the calculation parameters such as the intermediate principal stress coefficient b, the initial elastic displacement u0 at the tunnel wall, the rock internal friction angle and the stiffness ks of the support structure on the surrounding rock plastic zone, and radial displacement of the tunnel wall are studied in detail. The results of the calculation examples show that the tunnel surrounding rock relative plastic zone rp/r0 and ground radial displacement us of the tunnel wall decrease with increasing b. With increasing u0, rp/r0 and us both increase, while with increasing ks and the rock internal friction angle, rp/r0 and us both decrease. In sum, it indicates that the proposed model for the circular tunnel can perfectly reflect the tunnel mechanical behavior.

Deformation and Failure Mechanism of Surrounding Rock in Mining-Influenced Roadway and the Control Technology

Aiming at the problem of surrounding rock deformation and failure of mining roadway and its control, a mechanical model of the circular roadway under the mining environment is established, and the implicit equation of the plastic zone boundary is derived. By analyzing the morphologic evolution law of the surrounding rock plastic zone in the mining roadway, the key factors affecting the morphologic change of the plastic zone are obtained, that is, the magnitude and direction of principal stress. The influence law of the magnitude and direction of principal stress on the plastic zone of the mining roadway is analyzed by using numerical simulation software, and the deformation and failure mechanism of surrounding rock of the mining roadway is revealed. The results showed that the size and morphology of the plastic zone were closely related to the confining pressure ratio (η). Taking the boundary of η valuing 1, the larger or smaller η value was, the more serious the deformation and failure of surrounding rock would be; the morphology of the plastic zone changed with the deflection of the principal stress, with the location of the maximum plastic zone influenced by the principal stress direction. For the surrounding rock control in the mining-influenced roadway, it is advised to take the following methods: firstly, it is necessary to consider how to reduce or remove the influence of mining on surrounding rock, improve the stress environment of surrounding rock, and reduce the failure depth of the plastic zone, so as to better maintain the roadway. Secondly, in view of the deformation and failure characteristics of the mining roadway, the fractional support method of “yielding first and then resisting” should be adopted, which applies the cable supplement support after mining instead of the one-off high-strength support during roadway excavation, so as to control the malignant expansion of the surrounding rock plastic zone and prevent roof falling accidents.

Stability Analysis and Reasonable Layout of Floor Drainage Roadway above Confined Water and under Mining Influence

The surrounding rock failure range of floor drainage roadway under the mining influence and its effect on the aquiclude are the key to determine the aquiclude thickness of the floor. This paper studied the distribution characteristics of the surrounding rock plastic zone by the numerical simulation when the floor drainage roadway was located at different positions under the working face and determined the rational position. Results show that (1) when the floor drainage roadway is staggered inward, the floor surrounding rock is prone to appear the butterfly plastic zone under single work face mining. And the butterfly plastic zone increases sharply after being affected by secondary mining of adjacent working face. (2) When the floor drainage roadway is staggered outward, the floor surrounding rock plastic zone extends gently affected by a single working face. And the depth of the plastic zone has no obvious change after being affected by secondary mining of adjacent working face. (3) According to the risk of water inrush, the three layout schemes can be ranked as follows: stagger inward 25 m > stagger inward 80 m > stagger outward 15 m . (4) Considering the floor stress environment, gas extraction efficiency, and water prevention and control, the reasonable location of floor drainage roadway below the No. 11060 working face of Zhaogu No. 2 Coal Mine was finally determined. It was arranged in the sandy mudstone layer on the upper part of L9 limestone under the middle part of coal pillar and was drived along the seam floor.

Surrounding Rock Failure Characteristics and Water Inrush Mechanism of Roadway above the Aquifer in Nonuniform Stress Field

The expansion of the roadway surrounding rock failure zone may connect the floor aquifer and cause the roadway water inrush. In order to reveal the mechanism of the roadway water inrush above confined water, we established the force model of the roadway surrounding rock above confined water in nonuniform stress field and studied the shape characteristics and expansion law of the roadway surrounding rock plastic zone. The results show that the roadway surrounding rock will form three kinds of plastic zone under different lateral pressure coefficients: circular, elliptical, and butterfly; when the shape of plastic zone is circular or elliptic, the maximum radius increases linearly with the increase of regional stress; when the shape is butterfly, the maximum radius increases exponentially with the increase of stress. Under the condition of a larger bidirectional stress ratio, the surrounding rock of the roadway will show butterfly-shaped failure, and small stress change will cause malignant expansion of the plastic zone; when the plastic zone is connected with the underlying aquifer, confined water of floor will enter the rock mass from the water diversion point and eventually flood into the roadway, causing floor water inrush.

Influence of in-situ rock stress on the stability of roadway surrounding rock: a case study

Abstract In-situ rock stress was measured in the development roadway of Gucheng coal mine at +420 m level by using the stress relief method of hollow inclusion. The results show that the first principal stress was the vertical stress, the maximum horizontal principal stresses were distributed in the range of N10°E and N20°E, and the average side pressure coefficient was 0.83. There was a large difference between the maximum horizontal principal stress and the minimum horizontal principal stress, and the calculated average ratio was 2.02. A spatial stress conversion model of the horizontal roadway based on the measured in-situ rock stresses was built, and the distribution laws of stress and displacement of the surrounding rock of the roadway were analyzed in depth along the changing radial direction. According to the Mohr–Coulomb failure criterion, an asymmetric surrounding rock plastic zone was obtained and the plastic failure radius was 5.0 m. Considering the roadway-surrounding rock differential control, the stronger support in the risk areas was practiced and validated. The work in this paper would provide some ideas for the design and optimization of the support parameters for roadway engineering.

Study on distribution law and influencing factors of surrounding rock plastic zone in mining roadway

By analyzing and studying the deduced theory of the surrounding plastic zone in the circular mining roadway, it is found that the radius of the surrounding plastic zone in the roadway considering the influence of mining coefficient can be divided into two stages: In the first stage, when the mining coefficient is small, the radius of the plastic zone is less sensitive to the mining coefficient, and the process increases linearly with the gradual increase of the mining coefficient. In the second stage, when the mining coefficient increases to a certain extent, the sensitivity of the radius of the plastic zone to the mining coefficient increases rapidly, and the non-linearity increases rapidly with the increase of the mining coefficient. With the gradual increase of the mining coefficient, the geometrical distribution morphology of the surrounding plastic zone of the roadway varies from circular to ellipse to round rectangle to butterfly, and the larger the mining coefficient, the more easily the surrounding rock is butterfly plastic zone, and the developmental dimension and range of the butterfly-leaf are larger. The growth of the buried depth of the roadway and the decrease of the cohesion and internal friction angle of the surrounding rock will lead to an increase in the radius of the plastic zone. With the rise of the mining coefficient, the sensitivity of the plastic zone radius to the buried depth of the roadway, cohesion and internal friction angle gradually enhanced. The butterfly plastic zone of the mining roadway has directional, and the butterfly-leaf will rotate to different degrees with the change of the principal stress direction of the surrounding rock of the roadway, When the maximum depth of butterfly-leaf plastic zone is located directly above the roof of roadway, the roof stability is the worst, and roof caving is easy to occur, thus, the support should be strengthened.