Side Pressure Coefficient Research Articles

Stability evaluation of rock pillar between twin tunnels using the YAI

The stability of rock pillar is crucial for ensuring the construction safety of twin tunnels with small clearance, especially when transitioning from the traditional left–right tunnel layouts to the up-down configurations due to complex and variable site constraints. However, there are limited researches on the evaluation and comparative study of the stability of these two types of rock pillars in twin tunnels. This paper introduces the yield approach index (YAI) as a measure to assess the stability of rock pillar in twin tunnels with small clearance, and various influencing factors including side pressure coefficient (SPC), stress release rate (SRR), and the thickness of rock pillar (characterised by the ratio of rock pillar thickness to tunnel diameter, RPT/TD) are considered in the analysis. The study compares and analyzes the stability differences of the rock pillar in different situations. It is observed that the two sides of up-down tunnels pose a higher risk while the rock pillar in the left–right configuration being the most vulnerable. The stability of the rock pillar between the up-down tunnels is significantly higher than that of the left–right tunnels under similar conditions. Moreover, the up-down tunnels exhibit greater sensitivity to SPC, whereas the left–right tunnels are more sensitive to SRR. Additionally, the study reveals that increasing the RPT/TD can effectively improve the stability of the rock pillar within a specific range (1/4 to 2/3). The research method and obtained results of this paper can provide some important references for the stability evaluation and design of twin tunnels with small clearance.

Characteristics of Stress-Displacement-Fracture Multi-Field Evolution around Gas Extraction Borehole

To ensure the effectiveness of the gas extraction borehole, it is necessary to investigate the stress-displacement-fracture evolution of the coal around the borehole. In this study, by constructing a numerical model of a gas extraction borehole, the burial depth and side pressure coefficient are used to characterize the overall stress level of the borehole and the difference in stress distribution caused by complex stress conditions. First, the stress time-varying pattern and force chain distribution of coal around the borehole were revealed. Then, the displacement time-varying pattern and displacement distribution of coal around the borehole were elucidated. Then, the microfracture distribution of coal around the borehole, which characterizes the microfractures, was analyzed. Finally, the validity of the numerical results was verified. The results showed that, after the stress field of the coal around the borehole was adjusted, the force chain of the borehole was unevenly distributed and the stress concentration phenomenon appeared. With the increase in burial depth, the stress around the borehole gradually increased, while the range of stress concentration zone in the borehole kept increasing, and the borehole changed from unilateral instability to bilateral instability. Moreover, the displacement field around the borehole was distributed in the shape of a ”disk leaf”. With the increase in burial depth, the deformation of coal around the borehole increased. With the increase in the side pressure coefficient, the vertical and horizontal displacement also increased gradually. Furthermore, there was a certain correspondence between the development of fracture and the deformation around the coal. With the increase in burial depth, the development of fractures was gradually obvious, and the distribution characteristics were concentrated in the middle and dispersed around. This study provides a theoretical reference for the stability of gas extraction boreholes, aiming to improve the gas extraction effect.

Failure mechanism and stability analysis of an open-pit slope under excavation unloading conditions

Excavation unloading significantly contributes to rock slope failure in an open-pit mine. At present, there is no relevant theoretical study on the failure mechanism of the rock slope under excavation unloading. Therefore, in this study, based on the theory of fracture mechanics, the expression of the stress intensity factor at the crack tip on the rock mass at the vertical distance, h, from the slope top under excavation unloading is derived, the calculation method of the crack initiation angle is given, the expression of the ultimate safe height of the slope under unloading is obtained, and the ratio of the fracture toughness of the slope rock mass to the composite stress intensity factor at the crack tip on the rock mass is defined as the slope stability factor, which is verified by an engineering example. The results show that the crack initiation angle decreased when crack inclination was increased, and the crack initiation angle increased when the side-pressure coefficient, slope angle, and friction coefficient were increased. The ultimate safety height of the slope decreased first and then increased with the increase in the crack angle, and it was approximately linear with the crack length and inversely proportional with the slope angle. The stability coefficient calculated by this method is the same as that calculated by the limit equilibrium method and is small, which indicates the accuracy and rationality of this method. Results in this study can provide a theoretical basis for understanding and controlling the slope collapse disaster induced by excavation unloading.

Deformation and Failure Laws of Surrounding Rocks of Coal Roadways under High Dynamic Load and Intelligent Prediction

Under high dynamic load, roadway deformation and failure may occur, posing great challenges. As for now, few studies have been carried out on the impacts of various factors on the deformation of roadway surrounding rocks under high dynamic load, not to mention those on intelligent prediction of the deformation and failure laws. This paper fills these research gaps by studying the deformation and failure characteristics of roadway surrounding rocks and the intelligent prediction method under high dynamic load. The finite difference software Flac3D was used to analyze the influences of roadway buried depth, lithology, and side pressure coefficient on the stability of surrounding rocks and a model was constructed for deformation prediction under high dynamic load. Finally, the influence of various factors on the deformation and their weight was obtained and the deformation can be predicted in line with the BP neural network prediction theory. The results show that the prediction effect is good, with high accuracy.

Experimental Study on Anchoring Physical Properties of Different Anchoring Lengths Coupled with Temperature and Pressure

Aiming at deep roadway anchorage solids, laboratory similar model tests were used to reveal the mechanical properties of anchorage solids with different anchorage lengths under the coupling effect of temperature and pressure, and SPSS statistical analysis software was used to conduct linear regression analysis of the ultimate anchorage force obtained from the tests. The results show that: through multiple linear regression analysis, the influence degree of temperature and pressure coupling on the ultimate anchorage force is arranged in order of anchoring length > surrounding rock strength > temperature > side pressure coefficient, and the linear regression equation of the model is obtained. Compared with the linear regression equation of simulation results, the model has a high explanatory ability.

Computer-Aided Analysis of Small Clear Space Intersection Tunnel and Heavy Load Railway Surrounding Rock Structure Dynamic Response Characteristics Analysis under Intelligent Manufacturing

Among many tunnel construction projects, small clear tunnels have been the focus of urban rail transit construction in recent years. The purpose of this research work is to study the dynamic response characteristics of the surrounding rock structure of a heavy-duty railway with a small clearance crossing tunnel. It is proposed to analyze the dynamic response characteristics of the surrounding rock structure through the frequency response function. The vertical acceleration, tensile force, stress, and internal strength of the pipe section are specifically analyzed. The influence of the pipe joint and the assembly method on the dynamic response is also analyzed. The influencing factors of stability are analyzed from buried depth, clear distance, and surrounding rock grade. Studies have shown that the minimum clear distance of crossing tunnels increases nonlinearly with the increase of tunnel depth and gravity, and decreases nonlinearly with the increase of cohesion, internal friction angle, calculated internal friction angle, and lateral pressure coefficient. When other parameters are the same and when the side pressure coefficient is less than 1, the minimum clear distance is larger than that of the side pressure coefficient when it is equal to 1. When the vibration frequency exceeds 100 Hz, the coherence coefficient is basically close to 1, indicating that the frequency response function response result of this section is the most reliable. It is hoped that it can provide a reference for the dynamic stability analysis of the surrounding rock structure of the heavy-duty railway surrounding rock structure and the surrounding stratum and the research of structural vibration reduction technology for the small clearance crossing tunnel in the future.

TWO APPROACHES FOR DETERMINING AREAS OF PLASTIC DEFORMATION IN A HOMOGENEOUS BASE FOUNDATION

The paper presents comparison of results of calculations of position, sizes and shapes of plastic deformation areas carried out on the basis of use of Coulomb plasticity condition and solution of elastic-plastic problem and mixed problem of elasticity theory and ground plasticity theory which resulted, among other things, in graphs of dependence of depth of plastic zones development on value of intensity of external influence. Calculations have been executed at three values of coefficient of side pressure of ground about = 0.37; 0.54; 0.72 for uniform strip load (no die), and for absolutely rigid die under condition of full sticking and under condition of no friction on ground-stamp contact. As a result, it was found that the plastic regions corresponding to the "Coulomb" solution differ essentially from similar regions based on elastic-plastic (mixed) solutions. Their sizes, with the same intensity of loading, are larger, their rate of development into the deepening of the base is higher than that of the alternative ones, and when the load reaches the maximum permissible value, they merge under the punch and form a single sickle-shaped area. In the case of "Coulomb" plastic areas, their shape and rate of development into the foundation in the initial stages of loading are rather strongly dependent on the value of soil side pressure coefficient. In the case of "mixed" solution, the "velocity" of this process is practically independent of the value of coefficient o. If we use the condition of closing of plastic regions in the foundation under load as the criterion for determination of the maximum permissible value of intensity of external action, then in "Coulomb" regions this value will be substantially lower than in alternative ones for all considered values of the coefficient of lateral pressure of soil.

Analysis of Crack Initiation and Propagation Thresholds of Inclined Cracks under High-Pressure Grouting in Ordovician Limestone

Control of the grouting pressure within the critical grouting pressure for crack propagation in Ordovician limestone can not only ensure grout penetration length, but also prevent the risk of creating an artificial water channel. Based on the fracture mechanics theory, a formula was proposed to calculate the critical grouting pressure of mixed mode I-II cracks in Ordovician limestone. The necessary conditions for tilted crack opening, the rationality of the existing empirical value of the maximum allowable grouting pressure was investigated based on the mechanical model. The RFPA2D-Flow numerical simulation software was used to evaluate the deduced theory. The research results show that the deduced theoretical calculation formula of the critical grouting pressure agrees with the numerical simulation results; when the mixed mode I-II fracture initiation occurs, the grouting pressure exceeds the perpendicular stress of the overlying rock; the greater the density of the overlying rock mass, the greater the value of grouting pressure for fracture initiation; when the side pressure coefficient was ≥1, crack dip angle increased and the grouting pressure for fracture initiation tended to decrease; and the empirical grouting pressure at the maximum allowable grouting pressure is 2.0–2.5 pw, which will not cause propagation and failure of the existing crack.

Case Study on Rock Support Technology for Roadways Based on Characteristics of Plastic Area

Rocks surrounding deep, high-stress roadways typically undergo a vicious cycle of destruction → repair → re-destruction → re-repair over a long time. This article uses the roadway restoration project of Pingmei Mine No. 6 (400 m underground) as research object. Starting from the plastic area, the characteristics of the distribution of rock surrounding the circular roadway are analyzed, and the influence of the side pressure coefficient, cohesive force, inside friction angle, support strength, and roadway radius on the plastic area is studied. Four types of distribution patterns were observed in rocks surrounding the plastic area of the roadway: round, oval, rounded rectangle, and butterfly. The side pressure coefficient, cohesive force, and inside friction angle affected the distribution and range of rocks surrounding the plastic area of the roadway. The support radius of the roadway and the support strength of its face did not change the distribution of the plastic area, but only affected its size. Therefore, to maintain the long-term stability of weak and broken roadways, the strength of the surrounding rocks must be increased, and roadway renovation should be avoided as it affects the distribution of the plastic area and reduces its scope. Engineering practice has shown that the “anchor net spray + hollow grouting anchor cable” technology for the combined, step-by-step repair and support of roadways, with a hollow grouting anchor cable as core, can suppress the distribution and scope of the plastic area to guarantee safe and long-term use of the roadway.

Analysis of the distribution characteristics and laws of in situ stress in China’s coal mines

Based on the measured in situ stress data in China’s coal mines, the relationship among the type of stress field, magnitude of stress, stress value, and the depth of burial was analyzed. The trends in the changes in side pressure coefficient and side pressure ratio were regressed and fitted with the increase in depth. This was compared to the Hoek-Brown curve, and the distribution characteristics and variation laws of underground stress field in China’s coal mines were determined. (1) Generally, in situ stress increases with burial depth, but the geological structure and lithology render horizontal stress considerable. (2) In 87.72% of stress fields, which are considered typical tectonic stress fields, the horizontal stress comes into prominence. (3) About 64% working environment is the middle- and high-stress zones, and low- and ultrahigh-stress zones account for about 18% each. (4) The ratio of horizontal principal stress was distributed within a range of 1.0~2.5, and it was affected very little by burial depth. However, the difference increased continuously with burial depth, causing an obviously growing shear failure of coal and rock. (5) The side pressure coefficient is mostly distributed in 0.9~2.0, and it decreases with burial depth and is gradually close to 1.32. (6) Most side pressure ratio is in 0.5~1.6. When the burial depth is less than 700~750 m, the horizontal principal stress is lower than one in the world. Conversely, the magnitude of horizontal principal stress was more pronounced in deeper areas, but it always plays a leading role in the in situ stress field. (7) The seismic belt has a great influence on coalfield stress fields. Without affecting the stress field, the direction of maximum principal stress is approximately parallel or perpendicular to the trajectories of principal stress in China Continental Plate. However, under the composite effect of geological structure, the direction changed visibly. There is no apparent relationship between the two and no law to follow. The statistics of in situ stress are important reference values for understanding stress distribution in China’s coal mines, and it also has a practical guiding significance for safely and efficiently mining underground.

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.

Weakening effects of hydraulic fracture in hard roof under the influence of stress arch

For the problem of hydraulic fracture propagation when weakening the hard roof in fully mechanized top-coal caving stope of ultra-thick coal seam, based on the stress arch theory and the fracture mechanics, a two-dimensional model for hydraulic fracture of the roof in the stope was established to investigate the propagation laws of hydraulic fracture. The result shows that, after mining, the principal stress direction of overlaying rock deflects to form the stress arch, whose arrow height and arch thickness increase with the increase of the mining width and the side pressure coefficient. Within the influence range of stress arch, the hydraulic fracture in hard roof deflects towards the stope direction in the course of propagation and forms the “arch” fracture, which cuts off the roof below the fracture in a laminated way. The deflection angle of hydraulic fracture increases with the increase of the mining width, but decreases with the increase of the side pressure coefficient and the fractured horizon. This research can provide theoretical basis for the application of hydraulic fracturing method in the stope roof weakening.

The use of computer image analysis in determining material flow in the roller press compacting unit during compacting of fine-grained material

Mechanisms of fine-grained material flow in a roller press are a constant subject of research. The proper transfer of feed in the feeder has a significant influence on the correct course of the compaction and consolidation process, product quality, and the intensity of wear of the forming components. A few mathematical models of compaction process have been put forth, but they are focused mainly on loads in the compacting unit and consolidated material properties. During compaction the loose material properties including the Young module, the external and internal friction coefficient, and the side pressure coefficient change continuously. Therefore visualisation tests were carried out to survey the flow of material in a compaction unit equipped with rollers with a flat working surface and gravity feeder. Using the NI Vision Builder program, the recorded video observations were analyzed and the medium speed distribution of the material in the feeder was determined. The results were presented in the form of graphs and compared with one another, specifying the relationship between the material speed distribution and the press operation parameters.

The calculation of the side pressure coefficient in conditions of the limited stress situation

The calculation of the side pressure coefficient in conditions of the limited stress situation

Influence of Side-Pressure Coefficient on Deformation of Tunnel Surrounding Rock and Bolt Axial Force

Internal force and deformation of surrounding rock and supporting structure of the nonlinear research is the use of finite element software ADINA by ideal elastic-plastic constitutive model.Results show that the lateral pressure coefficient increased from 0 to 1, and even decrease sharply arch sedimentation of surrounding rock, side wall horizontal displacement towards the hole along the radial direction development gradually reduced to 0 and reverse to the hole, when the lateral pressure coefficient is less than 0.5, bolt axial force biggest change is not obvious, when lambda increases gradually, the largest bolt axial force significantly increased.

The Coefficient of Tunnel Broken Zone and Field Test

The coefficient of tunnel broken zone combined with the max thickness is used to descript the loosening zone distribution after excavation, which defined to the ratio of broken zone area to tunnel cross section. With 16 operation modes designed by Orthogonal test, coefficient of the broken zone can be obtained with numerical methods. The findings suggest that the order of each factor is: surrounding rock grades, ratio of depth to span, side pressure coefficient, buried depth, span length. Gonghe tunnel of Yu-Xiang highway is used to introduce the basic flow of tunnel broken zone coefficient test. Results show that the broken zone coefficient is closely related to geological conditions and excavation methods and the scope of broken zone can effectively reduce by selecting suitable ratio of depth to span and excavation method.

Significant Analysis of Soft Rock Tunnel Disaster-Causing Factors Based on Orthogonal Test

The impacting effect of lithological features, tectonic stress, the mechanical parameters, structure surface contrasts were comparative analysis, to explore the effect from mentioned factors to surrounding rock-lining in schist tunnel. In order to make sure the dependence relationship of large deformation with these factors, the significant and interaction on large deformation in rock-mess and lining mechanical mechanism were studied according to the experiment data and statistics theory. The result shows that elastic modulus E, side pressure coefficient λ, and joint spacing S have obvious influence on the mechanical properties of surrounding rock-lining, and there is interaction among them. Furthermore, the influence of the interaction between S and λ to rock-lining is found to be significant, and there is an obviously dependent relationship between anchor failure and joints spacing. Therefore, when discussing the reduction measures to avoid the large deformation, the most appropriate method is to study it in overall factors and with the interaction.

Study of physicomechanical properties of solid domestic waste during compaction by an unbound method into large blocks

Technology is considered for compaction of solid domestic waste into large blocks, excluding subsequent stitching and binding with wire, in order to avoid arbitrary breakage during lifting and transport operations. As a result of calculation and theoretical studies, and laboratory experiments for determining the dependence of side pressure coefficient, static and dynamic coefficients of external friction due to compaction pressure, and also calculation of limiting state parameters, it is shown that the stated aim is achieved with compaction of solid domestic waste with a conical punch. Model blocks are obtained by experiment that have adequate strength during shipment and disposal at a landfill site. In view of the imperfection of existing technology for compacting solid domestic waste (SDW), it is necessary to carry out research for selection of a compaction regime in order to obtain a strong briquette without additional binding. The aim of this work is development of a procedure for determining the physicomechanical parameters of SDW briquettes, establishment of their quantitative values for use in designing compaction, and creation of unbound SDW briquetting technology. During compaction there is a change in the shape and dimensions of a dispersed body, such as SDW, as a result of a reduction in pore volume and deformation of the material structure [1]. The capacity of solid dispersed material to increase its density under the action of pressure and to form a briquette of prescribed shape and dimensions is called “compaction” [2]. These production properties of SDW taking account of dimensions and configuration of finished objects, physiochemical, and mechanical properties of its structural elements, i.e., particles, should be considered in the choice of production parameters for compaction. Several methods exist for SDW compaction [3]. In contemporary enterprises for SDW processing by compaction, pressing devices are used whose operating cycle consists of the following operations:

Propagation Mechanism of Coal Rock Fracture under Gas Pressure

The failure of coal rock under gas pressure and in-situ stress is an inevitable stage of coal and gas outburst. The propagation mechanism of coal rock fracture under gas pressure is studied in this paper using fracture mechanics. The expression of normal stress and shear stress is given first with the simplification that the fracture is elliptical. Then the relationship among critical gas pressure, fracture direction and side pressure coefficient is studied in two branches as tension-shear failure and compression-shear failure. For tension-shear fracture, the fracture will be easy to propagate while the fracture has the same direction as maximum principal stress. For compression-shear fracture, the propagation direction is determined by the difference of compression-shear parameter and friction coefficients.

CHARACTERISTICS OF TUNNELS WITH SHOTCRETE/ROCK-BOLTS AND ITS PRELIMINARY DESIGN METHOD

In the previous paper, the authors proposed the design formula which was based on the distortional strain energy stored at each stage of tunnelling. In this paper, the side pressure coefficient k and elastic constant ER of ground are firstly studied with the displacement data obtained by the tunnel measurement in the past, and then the applicability of the proposed design formula, the efficiency of tunnel support and the safety factor of actual tunnels are discussed. The preliminary design method of tunnel is also presented.