Stress Field Of Surrounding Rock Research Articles

Research on mechanical response and time-space distribution of supporting structure of deep-buried tunnel in naturally water-rich loess

When the water content is small, the strength and stiffness of loess is considerably high. But with the increasing of water content, the shear strength of loess decreases since the matric suction of unsaturated loess decrease. If loess is soaked in water for long time after reaching the saturated state and the linking intensity weakened, the loess would be prone to softening deformation, so as to the stress of the tunnel supporting structure, which will cause the decreasing of the stability and durability of the tunnel. Therefore, the in-situ monitoring of surrounding rock deformation and stress characteristics of supporting structure is very important and was carried out in the deep-buried tunnel in naturally water-rich loess in this paper. The time–space effect of tunnel surrounding rock deformation, mechanical response of primary support, and secondary lining were monitored and analyzed. The results indicated that the deformation of surrounding rock was quite large, and the reserved settlement was insufficient. The analysis and calculation of the surrounding rock pressure and the stress of the steel arch indicated that the primary supporting structure of the upper bench was unsafe, the arch-foot had a trend of bending deformation to the side of the tunnel′s inner contour, and the inverted arch had a trend of uplift. Through the analysis of the contact pressure and the stress of the secondary lining reinforced concrete, the sidewall had a trend to deform to a side of the tunnel′s inner contour due to squeezing of the surrounding rock. The inverted arch had a trend to uplift, indicating the significant change and redistribution of the groundwater and surrounding rock stress field. The stress and deformation of supporting structure were highly complex both in space distribution and time development. The research results could provide specific reference and guidance for the design and construction of deep-buried tunnels in naturally water-rich loess.

Theoretical analysis of the surrounding rock stress field and energy field in shallow rectangular chambers during excavation

The mechanical analysis of surrounding rock after chamber excavation is of great significance for revealing the essence of stratum disturbances. Based on the Schwarz alternating method, a shallow rectangular chamber model was decomposed into a rectangular hole problem in an infinite plane and a half-plane problem. The general iterative expression and the explicit stress solution in shallow rectangular chambers when the mapping coefficient takes three terms were established by processing the boundary conditions with a mapping function and Fourier series. Then the analytical solution of the energy density accumulation of the surrounding rock was deduced, and the reliability of the theoretical solutions of the stress field and energy field were verified by numerical simulations. The disturbance laws of the lateral pressure coefficient, burial depth and chamber shape on the two fields were also analysed. The results show that the horizontal stress at the sidewall increases with increasing lateral pressure coefficient and burial depth. The peak of the vertical stress moves away from the wall with increasing lateral pressure coefficient. The energy accumulation at the corner increases with increasing chamber height and decreases with increasing burial depth and chamber width, forming a high stress area at the sidewall. With increasing Poisson's ratio, the corner energy distribution gradually flattens, and the energy decays more rapidly with distance.

Negative Poisson’s ratio cable compensation support for 32 m super-large-span highway tunnel: A case study

Although super-large-span tunnels ensure convenient transportation, they face many support challenges. The lack of normative construction guidance and the limited number of reference engineering cases pose a significant challenge to the stability control of super-large-span tunnels. Based on the geological conditions of a super-large-span tunnel (span = 32.17 m) at the bifurcation section of the Shenzhen interchange, this study determined support parameters via theoretical calculation, numerical simulation, and engineering analogy. The support effects of negative Poisson’s ratio (NPR) anchor cables and ordinary anchor cables on super-long-span tunnels were simulated and studied. Further, based on FLAC3D simulations, the surrounding rock stress field of NPR anchor cables was analyzed under different prestressing conditions, and the mechanism of a long-short combination, high-prestress compensation NPR anchor cable support was revealed. On the basis of numerical simulations, to our knowledge, the three-dimensional (3D) geomechanical model test of the NPR anchor cable and ordinary anchor cable support for super-large-span tunnel excavation is conducted for the first time, revealing the stress evolution law of super-large-span tunnels, deformation and failure characteristics of the surrounding rock, and the changing trend of the anchor cable’s axial force, and verifies that NPR anchor cables with high preloads are suitable for super-large-span tunnel support and have advantages over ordinary anchor cables. This study can provide a reliable theoretical reference for the support design and stability control of the surrounding rock of similar shallow-buried super-large-span tunnels.

Fracture evolution and fracture mechanism of tunnel surrounding rock: A case study based on laboratory tests and theoretical analysis

AbstractTo explore the fracture characteristics and fracture mechanism of the surrounding rock of straight‐walled arched tunnels, this study first carried out biaxial compression tests on rock samples and analyzed the disaster evolution characteristics under loading. Then, a stress distribution function was established using a complex function, and the distribution characteristics of the surrounding rock stress field were determined. Finally, combining the stress field with results obtained by computational tomography and acoustic emission measurements, the dynamic evolution of the main fracture mechanism of the tunnel surrounding rock was comprehensively analyzed, and the fracture mechanism of the surrounding rock of the straight‐walled arched tunnel was elucidated. The research results strengthen the understanding of rock fracture evolution during tunnel construction and operation and provide a basis for tunnel construction and surrounding rock stability analysis.

The Transient Unloading Response of a Deep-Buried Single Fracture Tunnel Based on the Particle Flow Method

Particle flow numerical simulation was used to reproduce the transient unloading process of a deep-buried single fracture tunnel. The influence of fracture characteristics on the transient unloading effect was analyzed from the aspects of stress state, deformation characteristics, fracture propagation, and energy conversion. The results shows that the surrounding rock stress field of the deep-buried tunnel is divided into four areas: weak stress area I, strong stress area II, stress adjustment area III, and initial stress area IV. The fracture has an important impact on the stress adjustment process of transient unloading of the deep-buried tunnel, and the stress concentration area will be transferred from the bottom corner of the chamber and the vault to the fracture tip. With the increase in the fracture length, the distance from the stress concentration area at the fracture tip to the free surface gradually increases, and the damage area of the surrounding rock gradually migrates to the deep area of the rock mass. At this time, the release amount of strain energy gradually decreases and tends to be stable, while the dissipation energy shows a near ‘U’ shape change trend of decreasing first and then increasing. Under different fracture angles, the number of mesocracks is significantly different. Among them, the number of mesocracks in the 60° and 30° fractured surrounding rocks is greater followed by the 0° fractured surrounding rock, and the number of mesocracks in the 45° and 90° fractured surrounding rocks is relatively less. In addition, the proportion of compression-shear cracks shows a change trend of increasing first and then decreasing with the increase in the fracture angle, and it reaches the maximum value in the 45° fractured surrounding rock.

Instability Mechanism and Control Method of Surrounding Rock of Water-Rich Roadway Roof

Surrounding rock properties and occurrence stability of a coal seam roof are prerequisites for ensuring the safe and efficient operation of mines. In this study, the mechanisms and control of weakened water-rich roadway roof slabs were investigated regarding the engineering background of water-rich roadway roof slab destabilization in a coal mine in the western Qingyang mining area. The spatial and temporal evolution law of rock deformation and damage of such roadways during excavation were determined through field measurements. First, we tested the strength of the roof slab surrounding rock in water-rich roadways with different water contents and concluded that the primary and excavation-disturbing fissures of the coal-sedimentary rock body are the external conditions for the occurrence of water–rock interaction in water-rich coal seam roadways. Moreover, the rock mechanical damage phenomenon exhibited by clay minerals in contact with water is the key factor leading to the destabilization of the water-rich roof slab’s surrounding rock. Second, a technical approach for controlling the stability of the surrounding rock by adjusting the form of the roadway section and optimizing the support parameters was proposed, and the distribution law of the surrounding rock stress field and displacement field of each section was revealed via numerical calculation. It is considered that adjustment of the stress and displacement control of the surrounding rock of the roadway is more favorable for the straight wall circular arch section. Based on the results of the sensitive orthogonal numerical simulation test, the technical parameters and scheme of the roadway support optimization were proposed. Finally, the research results were applied in the field, and the deformations of the top and bottom slab and the two ribs of the roadway after optimizing the section and support parameters were calculated as 61% and 34% lower, respectively, than those before optimization, indicating that the proposed approach can effectively control the deformation of the water-rich roadway’s surrounding rock and achieve more economic and effective stability control of this type of roadway. The research results provide new ideas and methods for controlling the surrounding rock of water-rich soft rock roadways in the western mining areas of China, which has broad application value and prospects.

A fully coupled hydraulic-mechanical model of deep tunnel considering permeability variation

When the buried depth of underground engineering exceeds 1000 m, the deep surrounding rock will show typical nonlinear deformation characteristics due to the coupling effect of high in-situ stress, and high seepage pressure. The stress field of surrounding rock will change the distribution characteristics of seepage field, and in turn, the change of seepage field will affect the distribution of surrounding rock stress field, which is a process of mutual influence and interaction. Considering the variation of permeability coefficient of deep surrounding rock and non-Darcy flow movement of fluid, a fully coupled hydraulic-mechanical analytical model of deep tunnel was proposed based on Hoek-Brown criterion and effective stress principle, and the detailed application method of the model was also given. Through the triaxial compression test under hydro-mechanical coupling, the nonlinear softening model considering seepage pressure and permeability variation equation were established, which solved two key problems of the model. The corresponding numerical calculation program was compiled based on ABAQUS finite element platform, and the reliability of the calculation program was verified by comparing with the model test results. The influence of the thickness of the grouting layer, the permeability coefficient of the grouting layer, the number of drainage holes and the depth of drainage holes on tunnel surrounding rock seepage pressure and lining seepage pressure were calculated and analyzed, and the anti-seepage optimization design of Xianglushan tunnel was carried out.

Experimental Study on the Interaction between Backfill and Surrounding Rock in the Overhand Cut-and-Fill Method

Backfilling is commonly used in underground mines to improve the stability of overlying strata. The performance of the backfill and its interaction with surrounding rock are the key issues in backfill mining research. In this paper, the displacement and stress field evolution characteristics of the overlying strata in backfill mining were analyzed by a physical model, as well as the interaction between the backfill and surrounding rock. The research results show that when backfill mining is employed, the backfill mass and the unexcavated rock mass jointly bear the loads of the overlying strata. The loads of the overlying strata are transferred to the dense backfill mass and the surrounding rock. The stress in the near-field area of the surrounding rock increases and stabilizes gradually. The backfill mass improves the stress distribution state and reduces the stress concentration of the surrounding rock, which is conducive to preventing the progressive damage of the overlying strata. In addition, the backfill mass excavation has a significant influence on the stability of the overlying strata and the surrounding rock stress field. The backfill mass is a passive force-bearing structure that can effectively manage the deformation of the overlying strata and the phenomenon of underground pressure.

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.

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.

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.

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.

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 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.

Research on gas leakage mechanism and detection technology of coal mine gas drainage

Aiming at the low concentration of gas in the percolation borehole, the paper analyzes the mechanism of gas leakage in the sealing hole of the pumping hole based on the multi-physics coupling theory based on the distribution of the surrounding rock stress field of the mining borehole and the roadway. The drilling hole sealing detection device and the determination method are used to detect gas concentration at different depths in the borehole in the normal extraction state, and analyze the variation law of the gas drainage concentration along the hole depth distribution to achieve fast and accurate judgment of the leak position and sealing test of the pumping hole. The test proves that the method and the device can effectively detect the leaking position and sealing effect of the extraction drilling hole, and can provide a simple and rapid detection method and science for the improvement of the sealing process, the adjustment of the sealing depth and the fine management of the coal mine site.

Mechanical Analysis of Large-span Tunnel Construction in Urban Seaside

Hou, F.-J.; Li, S.-C.; Li, W.-J.; Li, X.-Z., and Han, X.-M.; 2019. Mechanical analysis of large-span tunnel construction in urban seaside. In: Gong, D.; Zhu, H., and Liu, R. (eds.), Selected Topics in Coastal Research: Engineering, Industry, Economy, and Sustainable Development. Journal of Coastal Research, Special Issue No. 94, pp. 255–259. Coconut Creek (Florida), ISSN 0749-0208.A tunnel in urban seaside is designed as a two-way eight-lane with a span of nearly 20 meters. The stratum is a horizontal layered rock mass and a three-level surrounding rock. In order to achieve rapid construction of large-span tunnels, combined with engineering background, horizontal layered rocks. The constitutive calculation model of the body is optimized and analyzed, and the whole time and space analysis of the tunnel construction process is carried out. The results show that for the layered rock mass stratum, the tunnel surrounding rock stress field is also the displacement field and the plastic zone distribution, and the transversely isotropic medium model is adopted. The root can fully reflect the engineering characteristics of the horizontal layered rock mass; The deformation of the tunnel surrounding rock after excavation shows that the horizontal layered rock mass is beneficial to the stability of the tunnel arch and the cavern; The settlement of the surrounding rock dome of the horizontal layered rock mass tunnel .The convergence deformation (6.0 mm) accounts for about 50% of the final deformation. The horizontal layered surrounding rock should actively control the deformation of the front of the face to enhance the stability of the cavity.

Force State of Country Rock and Supporting Structure in Multi-Arch Tunnel under Central Hole + CRD Method

The reason situ stress is very complicated, and it is still not very clear question. In this paper, the construction process through practical engineering analysis on a variety of construction methods and steps arch tunnel to study the effects of different excavation methods and deep anchor support large section tunnel under guard by theoretical analysis of surrounding rock stress field, strain field and variation of the displacement field, analysis of different rock excavation methods, supporting stress state characteristics, in order to optimize the choice of tunneling method provides a theoretical basis. Under the conditions all kinds of rock reasonable steps to secure construction methods put forward and lay the foundation for long-term safety arch tunnel.

Establishment and application of drilling sealing model in the spherical grouting mode based on the loosing-circle theory

There are quite a few studies that have been done on borehole sealing theory both domestically and internationally. The existing researches usually consider drilling of the surroundings as a dense homogeneous elastic body which does not meet the characteristics of real drilling of the fractured body. Based on the loosing-circle theory and analyses of the surrounding rock stress field, cracks and seepage fields, combined with Newtonian fluid spherical grouting model, we deduced the dynamic relationship between the seepage coefficient and rock or grouting parameters of the drilling sealing fluid mode of spherical fissure grouting. In this experiment, mucus was injected in the simulated coal seam and the permeability coefficient of the sealing body was calculated by using the model. To verify the validity of the model, the calculated sealing body number was compared with the extreme negative pressure that the sealing body could withstand. The theoretical model revealed the drilling sealing fluid mechanism, provided a method for the quantitative calculation of the drilling sealing fluid effect by grouting mode and a reference for the subsequent research of sealing mechanism.