Stability Of Surrounding Rock Research Articles

Reinforcement Analysis of Bifurcated Highway Tunnels with Large Section of Different Surrounding Rock Grades in Tiger Leaping Gorge

In order to analyse the reinforcement effect of tunnels with different surrounding rock grades in Tiger Leaping Gorge, a three-dimensional tunnel model was established. The effects of surrounding rock parameters and bolt supporting on the displacement and tension strain disturbance zone of surrounding rock were explored. The numerical results of tension strain and displacement show that the improvement of surrounding rock stability is limited by reinforcement measures, and the change of tension strain disturbance zone is also small when the rock is intact. However, when the surrounding rock is relatively fragmented, the range of tension-strain disturbance zone and displacement of the cave are very large. After strengthening, the range of tension-strain disturbance zone is reduced by 61.5%. Comparing the displacement of vault and arch waist, it can be seen that the displacement of cave in grade V surrounding rock is larger, the vertical displacement of vault is 3.5 times higher than that of grade IV surrounding rock, and the horizontal displacement of large section in arch waist is 58.63 mm, and it has great influence on the stability of tunnel. The displacement value of vault and arch waist reinforced in grade V rock is similar to that of tunnel without reinforcement in grade IV rock.

Research on the Deformation and Control Technology of Surrounding Rock in Entry Retaining along the Gob Side

This paper studies and introduces the successful case of gob‐side entry retaining technology and the typical mining pressure law in Luan mining area, which is the main mining coal seam in Qinshui coalfield. Qinshui coalfield has an estimated coal reserve of 300 billion tons, accounting for 9.58% of the total national coal reserve in China, especially anthracite, chemical coal, and coking coal. The methods of field investigation, theoretical analysis, physical experiment, and industrial test are adopted. Through the field investigation, theoretical analysis, physical experiments, and industrial test, the following conclusions have been drawn in this study: (1) A thorough engineering geological investigation was conducted on the entry retaining along the gob side on noncoal pillar mining working face, which covers multiple periods of mining process including the roadway excavation period, primary mining period, primary mining stability period, and secondary mining influence period. A series of analysis and tests were conducted such as core sampling, rock mechanics property testing, borehole detection, and flexible formwork support evaluation, which laid a foundation for identifying the mining pressure law of gob‐side entry retaining by using noncoal pillar mining. (2) The mining pressure law was studied through the collection of the field measurements taken from the entry retaining along the gob side on noncoal pillar mining working face. The keys to achieve the roadway surrounding rock stability through noncoal pillar mining are obtained. According to the study, the stability control of retained roadway surrounding rock mainly depends on the stability of top coal, coal side, and shoulder angle coal. (3) In this study, a roadway reinforcement scheme is proposed to improve the surrounding rock control technology for gob‐side entry retaining by noncoal pillar mining, whose effectiveness has been verified by a series of industrial test. Therefore, the wide adoption of the noncoal pillar mining method in Number #3 coal mine can significantly relieve the predicament of coal pressing under a large number of buildings in Luan mining area, which provides insightful guidance to the coal‐free pillar mining in the whole Luan mining area.

Optimization of construction parameters of Highway Tunnel CRD Method

For shallow buried tunnels with poor surrounding rock stability, reasonable construction parameters are of great significance for ensuring tunnel construction safety and controlling construction quality. Taking Huiqing a tunnel as an example, comprehensive analysis of the partition wall R=11.6 ∠ 520, R=5.76 ∠1060, R=5.46 ∠1040, R=+∞∠1800 three different radii of curvature, using FLAC software for four calculations Numerical simulation of working conditions, analysis of plastic zone changes and surrounding rock deformation under different calculation conditions, and the radius of curvature of this project is proposed. The research results show that the middle partition wall adopts R=5.76 and the central angle=1060 can ensure the stability of surrounding rock and the minimum deformation of surrounding rock, which can provide a certain reference for the construction of such highway tunnels.

Study on Identification of Construction Method for Ultra‐Large‐Span Tunnel

Although the determination of tunnel construction methods is extremely critical for the construction of ultra‐large‐span tunnels, the determination of construction methods is still at a qualitative level, which relies on the engineering experience of on‐site technicians and lacks rigorous and systematic theoretical basis and technical standards. By means of orthogonal test method, the proper construction method was established for the deep‐buried ultra‐large‐span tunnel where the tunnel excavation span, tunnel surrounding rock strength, and rock integrity coefficient were set as the main control factors. The stability of tunnel surrounding rock under various test conditions was quantified according to the plastic zone properties calculated by the three‐factor and five‐level orthogonal test model. Meanwhile, the macro form and quantitative method of test combinations under different levels of various factors were proposed to obtain the influence of each factor on the stability of tunnel surrounding rock, and thus the functional relations between various factors and tunnel stability were obtained. On this basis, the identification and the criterion of the ultra‐large‐span tunnel construction method were established, which can quantitatively reflect the contribution of excavation span of the tunnel, the number of lateral drifts in cross section, surrounding rock strength, and rock integrity coefficient to surrounding rock stability of the tunnel. The construction method calculation results of the Malin tunnel, a practical underground project, are obtained according to the orthogonal test model calculation. Based on the method, Malin tunnel can be constructed safely and efficiently. The research results could provide the theoretical basis for the identification and selection of construction method for ultra‐large‐span tunnel.

Geological Structural Surface Evaluation Model Based on Unascertained Measure

The surrounding rock structure plane survey is the basis for mine geological structure evaluation and stability of surrounding rock. On the basis of the unascertained measurement theory and scanline method, the surrounding rock stability of the underground geological structure plane in Lingbao Luoshan Gold Mine is evaluated. First, according to the structural plane five grading standards, the 9 single-index measure functions are constructed. Second, the information entropy is used to determine the weight of each indicator. Accordingly, a multi-index comprehensive measure evaluation vector is established. Finally, the confidence level is used to determine the structural plane stability level. Results show that surrounding rock grades of middle sections of R1, R2, and R3 are Grades III, IV, and IV in Lingbao Luoshan Gold Mine, respectively. The evaluation grade is consistent with the actual situation of the mine, and strengthening the surrounding rock support for the middle sections of R2 and R3 is necessary. According to engineering practice, the evaluation model of the underground structure of metal mines established in this study has a practical value.

Study on support time in double-shield TBM tunnel based on self-compacting concrete backfilling material

Double-shield tunnel boring machine (TBM) typically supports surrounding rock structures using precast lining segments, pea-gravel backfilling and grouting, which can provide full play for the self-bearing capacity of surrounding rock. However, the risk of TBM jamming is increased by a lack of timely support. We propose a support method using self-compacting concrete backfilling material (SCCBM) instead of pea-gravel backfilling and grouting. In this paper, based on simulations of a TBM construction process, the support time and mechanical properties of the SCCBM are analysed. The deformation characteristics of surrounding rock are simulated using the viscoplastic creep model based on the internal variable thermodynamics theory. Creep parameters are obtained through the inversion analysis of displacement data collected at a construction site. The age-hardening process of SCCBM is simulated using the Mohr–Coulomb criterion, whose mechanical parameters change over time. Surrounding rock deformation, support system stress, yield region, surrounding rock stability, and the effects of the age-hardening rate of SCCBM are analysed. Additionally, the optimal supporting time is determined by comprehensively analysing surrounding rock deformation and supporting system stress. Overall, backfilling SCCBM with an optimal supporting time can not only reduce the deformation of surrounding rock and risk of TBM jamming, but also enhance the stability of surrounding rock.

Risk Analysis and Extension Assessment for the Stability of Surrounding Rock in Deep Coal Roadway.

In order to evaluate the surrounding rock stability of deep roadways, the diversity of accident hazard sources in deep coal mining is statistically analyzed. To conduct an effective evaluation, first, the risk analysis of the factors affecting the rock mass accidents is carried out, and the comprehensive safety index system of rock accidents in deep mine roadway is established. Further, combining the theory of hazard sources with the extension method, a matter–element model for the risk assessment of rock mass accidents in deep roadway is established. Finally, the hazard sources for the surrounding rock stability of deep roadway in the E-Zhuang coal mine of Xinwen Ming area are evaluated. The results show that the risk grade of the surrounding rock for deep roadways in E-Zhuang coal mine is “B”, which is generally safe, the human factors and organizational management factors are relatively safe, and some suggestions for improvement are put forward.

Energy Dissipation Method for Surrounding Rock's Stability Analysis and Its Application

Energy Dissipation Method for Surrounding Rock's Stability Analysis and Its Application

Classification and Application of Surrounding Rock Stability of Straight Wall Semi-circular Arch Roadway

The stability of roadway surrounding rock plays an important role in the safety of roadway, so the classification of roadway stability becomes an indispensable part in the safety analysis of coal roadway. Based on the statistical analysis of 25 relevant literatures and the principle of index selection, 12 classification indexes were determined by comprehensive analysis. A genetic neural network model was established. Data of 12 straight wall semi-circular arch roadways were investigated as training samples, and 4 roadways were selected for testing. The prediction accuracy of the model is 100%. Combining with the theory of strong support for coal roadway sidewall and angle, the stability classification model is applied to the classification of surrounding rock stability of straight wall semi-circular arch roadway, and reasonable supporting countermeasures and suggestions for different grades of surrounding rock are given. In order to verify the reliability of the model, the model has been applied in engineering, and achieved good results. It proves that the model has goodfit and strong applicability.

Numerical Researches on the Optimization of Construction Methods in Tunnels with Super Large Section

At present, the selection of construction methods in the tunnels with super large sections often relies on the experience for lack of a definite and feasible method. Based on the design method of formation-structure tunnels, the paper adopts FEM strength reduction to conduct numerical researches on the optimization of construction methods in tunnels with super large section. Taking a tunnel with super large section in a subway station as example, the paper first carries out numerical simulation on arch-wall method and double sidewall pilot tunnel method. Then it compares and analyzes the calculation results of surrounding rock displacement, stress on anchors and surrounding rock stability during construction. Finally, the paper suggests double sidewall pilot tunnel method. The analysis on the calculation examples shows that numerical method can quantitatively and directly display the difference between various construction methods and realize the optimization of construction methods in tunnels with super large section.

Effect of joint characteristics on surrounding rock stability and stress mechanism of bolt under blasting excavation

Joint characteristics of rock mass are the key factors of tunnel surrounding rock failure. This paper relies on the two-lane mountain tunnel project and takes the IV class surrounding rock as the research object. By means of on-site investigation, numerical simulation and on-site monitoring, the effects of different joint development characteristics under blasting vibration on tunnel surrounding rock deformation, instability mode and force mechanism of rock bolts are studied. It is found that the instability mode of tunnel is obviously affected by the larger joint dip angles. When the dip angle of one group of consecutive joints is kept unchanged and the dip angle of another group of joints is changed, the vault settlement decreases first and then increases with the increase of joint dip angles. The influence of horizontal joint spacing on surrounding rock deformation and vault settlement is much greater than that of vertical joint. Under the most disadvantageous working conditions of the two sets of consecutive joints, the effective range of the axial force of rock bolts depends on joint dip angles and has little correlation with joint spacing. The axial force of rock bolts decreases with the increase of horizontal joint spacing, while the influence of vertical joint spacing on bolt is less.

Key Factors Identification and Risk Assessment for the Stability of Deep Surrounding Rock in Coal Roadway.

In order to evaluate the stability of deep surrounding rock, all of the affecting factors should be theoretically identified. However, some factors have slight impacts on the stability of deep surrounding rock compared with others. To conduct an effective risk assessment, key factors should be first extracted. The analytic hierarchy process (AHP) and grey relation analysis (GRA) methods are integrated to determine the key factors. First, the AHP method is applied to sort the factors by calculating the weights of them. Seven out of fifteen factors are extracted as the key factors, which account for 80% of the weights. Further, the GCA method is used to validate the effects of these key factors by analyzing the correlation between the performance of each factor and that of the reference. Considering the influence of these key factors and experts’ judgements, the multilevel fuzzy comprehensive evaluation method is adopted to obtain the risk level of the deep surrounding rock stability. Finally, the risk assessment of the deep surrounding rock in the E-Zhuang coal mine of Chinese Xinwen Mining Area illustrates the operability of the proposed method.

Optimization Construction Scheme of Single-Sided Shallow Tunnel Enlarging

At present, the construction schemes of tunnel enlarging are analogized by creating a new tunnel through a traditional method. However, the traditional excavation method ignores the advantage of long-term support and stability of the original tunnel lining to the surrounding rock, and the construction efficiency is also reduced. The optimized construction plan was theoretically analyzed using the case of the Chongqing Yuzhou tunnel enlarging. The optimization construction schemes of single-sided shallow tunnel enlarging were extracted in accordance with the foundation of the study on the construction mechanics of a shallow tunnel, that is, the way of the rational arch axis enlarging in the crosswise direction and the jump-driving method in the lengthwise direction. The construction analysis was compared with the field monitoring measurement results and ANSYS simulation of the 3D finite element calculation of the entire tunnel enlarging process. By optimizing the construction scheme, the calculation value of the compressive stress of the original tunnel lining was increased by excavation face advancing. The original tunnel lining that had not been dismantled can play the role of the column and bear the surrounding rock pressure caused by the jet-hopping excavation. This lining could effectively improve the safety and stability for tunnel enlarging. The adopted rational arch axis excavation in the transverse direction could reasonably and significantly transfer the surrounding rock pressure. This process could reduce the tensile stress and increase the compressive stress of the initial support structure. Results of the numerical calculation and field monitoring data showed that the excavation scheme of the shallow tunnel is optimized after unilateral expansion. The optimization construction schemes can change the original rock stress path and play a role in the surrounding rock stability. The displacement of the tunnel vault can be reduced by 16%-20%, and the tunnel vault does not appear in the tension zone. The optimization of construction scheme can reduce the arch subsidence and tensile stress of the lining, ensure the safety of construction, and shorten the construction period. These obtained beneficial conclusions can be supplied to the next similar tunnel enlarging projects.

Stability Control for Gob-Side Entry Retaining with Supercritical Retained Entry Width in Thick Coal Seam Longwall Mining

Taking gob-side entry retaining with large mining height (GER-LMH) of the 4211 panel in the Liujiazhuang coal mine as the engineering background, a numerical simulation was conducted to study the surrounding rock deformation, stress, and plastic zone distribution of GER-LMH with respect to retained entry width. The concept of critical retained entry width of GER-LMH was proposed. In view of the deformation characteristics of surrounding rock, an innovative approach to determine the critical width of GER-LMH based on the cusp catastrophe theory was proposed. The cusp catastrophe functions were set up by approximate roadside backfill body rib convergence and roof subsidence series with respect to different retained entry widths. The critical retained entry width of GER-LMH was 4.0 m according to bifurcation set equations. Surrounding rock stability control principle and technique of GER-LMH was proposed, including “rib strengthening and roof control”: road-in support with high pre-stress rockbolts and anchor cables, roadside backfill body construction technology with high-water quick consolidated filling materials and counter-pulled rockbolt, road-in reinforced support technology with hydraulic prop support and roof master. Field test and field monitoring results show that GER-LMH with supercritical retained entry width in the 4211 panel could meet the requirements for ventilation when the 4211 panel was retreating.

Stability Analysis of Surrounding Rock in Paste Backfill Recovery of Residual Room Pillars

A method of paste backfill recovery for residual room coal pillars is hereby proposed. The principles and processes of this method are systemically explained to address issues such as mining-induced earthquakes from spontaneous destabilization, surface subsidence, and low recovery rates. These are caused by the instability of residual coal pillars due to their spontaneous combustion in room-and-pillar mining in medium-to-small coalmines in the northern Shaanxi area. This method is based on the local abundance of surface aeolian sand and solid wastes to be used as paste-backfilling materials in coalmines in the northern Shaanxi area. Uniaxial compressive strength, bleeding rate, and slump tests were performed on paste-backfilled samples constituted at different ratios based on the types of materials involved in paste backfilling in the northern Shaanxi region, thereby helping to confirm the optimal ratios for paste-backfilling materials for the Ershike coal mine. A simulation was conducted to investigate the failure, goaf vertical stress distribution, and surface deformation properties of paste-backfilled pillars and coal pillars, where paste backfilling was used with paste-backfilling materials constituted at different compressive strengths. This was to verify the experimental results that would be obtained with paste-backfilling materials constituted at different ratios, and reveal the mechanism by which paste backfilling of residual room pillars can maintain the mine’s surrounding rock stability. These study results are of great instructive significance to the safe recovery of residual room pillars in China’s western mining areas.

Study on Surrounding Rock Stability of Long-Span Coal Roadway under Influence of Mining and Support Technology Optimization

Taking stoping safety of large-span working face in a coal mine in Shanxi as the background, the damage and movement law of overlying strata structure in coal roadways under the influence of mining are studied. Combined with the actual production of the mine, the mining pressure characteristics of the working face and the influence range of mining in the working face are mastered. Main research contents and conclusions are that: (1) Numerical simulation of roadway stability is carried out using UDEC software, stimulating the stress and strain variation of surrounding rock under unsupported state. Based on this, the roadway support parameters are simulated and optimized, which provides valuable reference for practical engineering. (2) Study the simplified design process of bolt support parameters, improve the accuracy of bolt support parameters and reduce the cost of coal mine support to increase the incidence of coal mine roof accidents, providing a basis for coal mine safety production.

交通–电力共建隧道横通道与检修道交叉段围岩稳定性研究

交通–电力共建隧道横通道与检修道交叉段围岩稳定性研究

Study on instability failure mode and monitoring early warning standard of surrounding rock in fully weathered argillaceous sandstone section of large section tunnel

Based on the special geological conditions of a tunnel in Qingyuan section of Huizhou-Zhanzhou Expressway, FLAC3d numerical simulation software is used to simulate the rheological properties and instability of surrounding rock in large-section fully weathered sandstone section, and the stability and loss of surrounding rock are analyzed. The deformation of the dome and the face at steady state is analyzed. It is found that: 1) when the surrounding rock is in a stable state, the deformation curve of the dome is smooth. When the surrounding rock of the face is unstable, the front of the face appears ahead. Deformation should be first strengthened on the surrounding rock in front of the face. 2) The arched foot is an important part of the instability of the surrounding rock. In order to prevent the expansion of the collapsed part, the arched part should be reinforced. 3) In order to obtain the limit state of surrounding rock stability, the strength of surrounding rock is reduced, and the strength reduction coefficient corresponding to the displacement sudden point is taken as the safety factor of rock stability around the hole, and the stability safety coefficients of surrounding rock of each construction step are greater than 1.2. 4) The dynamic standard values of deformation control in the whole construction stage are obtained by analyzing the deformation curves of each data monitoring point with time in the corresponding time period of each construction step.

Influence of Fault on the Surrounding Rock Stability for a Mining Tunnel: Distance and Tectonic Stress

Stability of surrounding rock mass and safety of supporting system in mining tunnel are always dominated by fault near excavation limit. The influence degree of the fault varies significantly under different fault distances to mining tunnel and initial stresses condition. In this paper, a series of numerical experiments are conducted to study the displacement, stress, and plastic region in surrounding rock mass. The stress characteristics in sprayed concrete layer are analyzed to study the influence of the fault distance on excavation limit and the initial stress in ground. The fault distance is defined geometrically by a mutual perpendicular line between the excavation limit and fault line nearest to the mining tunnel to quantify the influence. In order to simulate fault specialty reasonably, an interface model based on the theory of cohesive joint element is proposed in the numerical experiment model. Some other disciplinary and quantificational regularities about the influence of the fault distance and tectonic stress are summarized based on the numerical results. The results show that there is a critical distance to judge whether a fault has a prominent influence to mining tunnel. The critical distance depends on the quality of mining tunnel surrounding rock mass, initial stress, and the degree of excavation limit curvature. With the increase of lateral stress coefficient, the vertical displacement at crown decreases, but the horizontal displacement increases in the both right and left sidewalls.

Stability Prediction Model of Roadway Surrounding Rock Based on Concept Lattice Reduction and a Symmetric Alpha Stable Distribution Probability Neural Network

To combat the uncertainty of the multiple factors affecting roadway surrounding rock stability, five initial indexes are selected for reduction according to concept lattice theory: rock quality designation (RQD), uniaxial compressive strength (Rc), the integrity coefficient of rock mass, groundwater seepage, and joint condition. The aim of this study is to compute correlation coefficients among various indexes and verify the effectiveness of lattice reduction. Alpha stable distribution is used to replace the commonly used Gauss distribution in probabilistic neural networks. A prediction model for the stability of roadway surrounding rock is then established based on a concept lattice and improved probabilistic neural network. 100 groups of training sample data are plugged into this model one by one to examine its rationality. The established model is employed for engineering application prediction with ten indiscriminate sample groups from the Jianlinshan mining area of the Daye iron mine, revealing accuracy of up to 90%. This demonstrates that our prediction model based on a concept lattice and improved probabilistic neural network has high reliability and applicability.