Numerical analysis of deformation and failure characteristics of deep roadway surrounding rock under static-dynamic coupling stress

In actual production,deep coal mine roadways are often under typical static-dynamic coupling stress(SDCS)conditions with high ground stress and strong dynamic disturbances.With the increasing number of disasters and accidents induced by SDCS conditions,the safe and efficient production of coal mines is seriously threatened.Therefore,it is of great practical significance to study the deformation and failure characteristics of the roadway surrounding rock under SDCS.In this paper,the effects of different in-situ stress fields and dynamic load conditions on the surrounding rock are studied by numerical simulations,and the deformation and failure characteristics are obtained.According to the simulation results,the horizontal stress,vertical stress and dynamic disturbance have a positive correlation with the plastic failure of the surrounding rock.Among these factors,the influence of the dynamic disturbance is the most substantial.Under the same stress conditions,the extents of deformation and plastic failure of the roof and ribs are always greater than those of the floor.The effect of horizontal stresses on the roadway deformation is more notable than that of vertical stresses.The results indicate that for the roadway under high-stress conditions,the in-situ stress test must be strengthened first.After determining the magnitude of the in-situ stress,the location of the roadway should be reasonably arranged in the design to optimize the mining sequence.For roadways that are strongly disturbed by dynamic loads,rock supports(rebar/cable bolts,steel set etc.)that are capable of maintaining their effectiveness without failure after certain dynamic loads are required.The results of this study contribute to understanding the characteristics of the roadway deformation and failure under SDCS,and can be used to provide a basis for the support design and optimization under similar geological and geotechnical circumstances.

Resist-decreasing effects of rock bolts on strength of rock mass around roadway——insight from numerical modeling

To investigate the resist-decreasing effects of rock bolts on the strength of the rock mass around a roadway, a compara- tive study has been carded out using the numerical analysis code FLAC3D. An unsupported and a rock bolt supported model have been built for comparison. Two types of rock mass strength, the uniaxial compressive strength （UCS） and the wiaxial compressive strength （TCS） of rock mass have been obtained from each model, using a prepared Fish based on the Mohr-Coulomb criterion. The results indicate that when a roadway is excavated, both the UCS and TCS in a definite local rock mass around the roadway would inevitably decrease, no matter whether the roadway is supported or not. The major decreasing region did not settle in the middle of the roadway surface, but within a deeper horizon into the rock mass. The resist-decreasing effects of rock bolts both on the UCS and the TCS of rock mass around roadway are significant.

Application of a combined supporting technology with U-shaped steel support and anchor-grouting to surrounding soft rock reinforcement in roadway

Soft rock surrounding deep roadway has poor stability and long-term rheological effect. More and larger deformation problems of surrounding rock occur due to adverse supporting measures for such roadways, which not only affects the engineering safety critically but also improves the maintenance costs. This paper takes the main rail roadway with severely deformation in China＇s Zaoquan coal mine as an example to study the long-term deformation tendency and damage zone by means of in-situ deformation monitoring and acoustic wave testing technique. A three-dimensional finite element model reflecting the engineering geological condition and initial design scheme is established by ABAQUS. Then, on the basis of field monitoring deformation data, the surrounding rock geotechnical and theological parameters of the roadway are obtained by back analysis. A combined supporting technology with U-shaped steel support and anchor-grouting is proposed for the surrounding soft rock. The numerical simulation of the combined supporting technology and in-situ deformation monitoring results show that the soft rock surrounding the roadway has been held effectively.

Deformation characteristics of surrounding rock of broken and soft rock roadway

A similar material model and a numerical simulation were constructed and are described herein. The deformation and failure of surrounding rock of broken and soft roadway are studied by using these models. The deformation of the roof and floor, the relative deformation of the two sides and the deformation of the deep surrounding rock are predicted using the model. Measurements in a working mine are compared to the results of the models. The results show that the surrounding rock shows clear theological features under high stress conditions. Deformation is unequally distributed across the whole section. The surrounding rock exhibited three deformation stages： displacement caused by stress concentration, theological displacement after the digging effects had stabilized and displacement caused by supporting pressure of the roadway. Floor heave was serious, accounting for 65% of the total deformation of the roof and floor. Floor heave is the main reason for failure of the surrounding rock. The reasons for deformation of the surrounding rock are discussed based on the similar material and numerical simulations.

Numerical simulation and analysis of moisture-heat coupling of soft rock tunnels in the cold regions

With the western development in China, more problems with rock and soil engineering in cold regions will be encountered. To study the stability of rock mass under the frost and thaw condition is of far significance. We attempt to simulate and analyze the temperature and moisture field in the surrounding rock of Dabanshan tunnel at its exit KI06＋025 in the cold region by software Femlab. First, introduced the common numerical solution to the moisture and heat coupled about the soft rock in tunnels of cold region. Then gave emphasis on simulation of the law of temperature distribution coupled temperature-moisture field and draw a parallel between temperature fields with different coefficient of percolation. In the course of simulation we considered the problem of caloric receptivity, thermal conductivity and critical heat varying with temperature.

THE ANALYSIS OF ROCKBURST IN COALMINE

This paper has put forward energy criteria and disturbance-response criteria for rockburst. The coal pillar rockburst or rockburst at roadway and working face have been analyzed. An equation is given to calculate the critical load when a rockburst occurs. The ratio E/A of the elastic modulus E and softening descending modulus A is believed to be an important parameter of rockburst. The concept of resistance zone is put forward and the critical depth of resistance zone can be used in the forecast and prevention of rockburst. The value of dupporting stress of roadway has much effect on the critical load.

Numerical simulation study of the failure evolution process and failure mode of surrounding rock in deep soft rock roadways

Based on the safety coefficient method,which assigns rock failure criteria to calculate the rock mass unit,the safety coefficient contour of surrounding rock is plotted to judge the distribution form of the fractured zone in the roadway.This will provide the basis numerical simulation to calculate the surrounding rock fractured zone in a roadway.Using the single factor and multi-factor orthogonal test method,the evolution law of roadway surrounding rock displacements,plastic zone and stress distribution under different conditions is studied.It reveals the roadway surrounding rock burst evolution process,and obtains five kinds of failure modes in deep soft rock roadway.Using the fuzzy mathematics clustering analysis method,the deep soft surrounding rock failure model in Zhujixi mine can be classified and patterns recognized.Compared to the identification results and the results detected by geological radar of surrounding rock loose circle,the reliability of the results of the pattern recognition is verified and lays the foundations for the support design of deep soft rock roadways.

沁水东大煤矿坚硬顶板水压预裂大巷围岩控制技术研究与应用

沁水东大煤矿中央轨道大巷布置在3号煤层下方的岩层中,两侧采煤工作面回采动压影响下表面出现不同程度的变形,严重影响矿井的安全高效生产。通过数值模拟研究得出更为合理的大巷保护煤柱宽度为70 m;切顶卸压后可降低巷道围岩内的垂直应力,提高围岩稳定性。在3102工作面进行水压致裂技术应用试验后,中央轨道大巷围岩稳定性受回采动压的影响显著降低,围岩变形得到控制。可为类似地质条件下巷道变形控制提供借鉴。

Deformation mechanism and excavation process of large span intersection within deep soft rock roadway

The FLAC3D software was used to simulate and analyze numerically the displacement, stress and plastic zone distribu-tion characteristics of a large span intersection in a deep soft rock roadway after the surrounding rock was excavated. Our simula-tion results show that there are two kinds of dominating factors affecting roadway stability at points of intersection, one is the angle between horizontal stress and axial direction of the roadway and the other are the angles at the points of intersection. These results are based on a study we carried out as follows: first, we analyzed the failure mechanism of a large span intersection and then we built a mechanical model of a rock pillar at one of the points of intersection. At the end of this analysis, we obtained the failure characteristics of the critical parts on the large span intersection. Given these failure characteristics, we proposed a new supporting method, i.e., a Double-Bolt Control Technology (DBCT). By way of numerical simulation, DBCT can effectively control the deformation of the surrounding rock at the points of intersection in roadways.

Frictional contact algorithm study on the numerical simulation of large deformations in deep soft rock tunnels

There exist three types of nonlinear problems in large deformation processes of deep softrock engineering, i.e., nonlin- earity caused by material, geometrical and contact boundary. In this paper, the numerical method to tackle the nonlinear eontact and large deformation problem in A Software on Large Deformation Analysis for Soft Rock Engineering at Great Depth was presented. In the software, based on Lagrange multiplier method and Coulomb friction law, kinematic constraints on contact boundaries were introduced in functional function, and the finite element equations was established for two incremental large deformation analyses models, polar decomposition model and additive decomposition model. For every incremental loading step, by searching for the contact points in the potential contact interfaces （the excavation boundaries）, the Lagrange multipliers, i.e., contact forces are cal- culated iteratively by Gauss-Seidel method, and justified through satisfy the inequalities of static constraint on contact boundaries. With the software, large deformation and frictional contact of a transport roadway were analyzed numerically by the two models. The numerical examples demonstrated the efficiency of the method used in the software.

Numerical simulation of grooving method for floor heave control in soft rock roadway

Grooving method can restrain the deformation and destruction of surrounding rock by transferring the maximum stress to deep rock,bringing about the effective control for floor heave in soft rock roadway. Based on this important effect,and to discuss the relationship between cutting parameters and pressurerelief effect,this paper carried out a numerical simulation of grooving along bottom slab and two sides of gateway with finite difference software FLAC^（2D）.The results show that the control effect on floor heave in soft rock tunnel can be improved by selecting appropriate cutting parameters.Appropriately increasing the crevice depth in the middle of the floor can improve the stress state of bottom slab by stress transfer. So the floor heave can be more effectively controlled.To lengthen the crevice in the corners of roadway can simultaneously transfer the maximum stresses of bottom slab and two sides to deep rock,and promote the pressure-relief effect.Extending the crevice length and crevice width on both sides within a certain range can decrease the stress concentration in the corners of roadway,and reduce the deformation of two sides.The cutting position beneficial to restrain the floor heave is close to the bottom slab.

Roadway failure and support in a coal seam underlying a previously mined coal seam

The influence of an upper,mined coal seam on the stability of rock surrounding a roadway in a lower coal seam is examined.The technical problems of roadway control are discussed based on the geological conditions existing in the Liyazhuang Mine No.2 coal seam.The stress distribution and floor failure in the lower works after mining the upper coal is studied through numerical simulations.The failure mechanism of the roof and walls of a roadway located in the lower coal seam is described.The predicted deformation and failure of the roadway for different distances between the two coal seams are used to design two ways of supporting the lower structure.One is a combined support consisting of anchors with a joist steel tent and a combined anchor truss.A field test of the design was performed to good effect.The results have significance for the design of supports for roadways located in similar conditions.