Analysis on AE characteristic and its confining pressure effect of outburst coal containing gas

Briquette samples made of outburst coal are taken as study objects to study AE characteristic and its confining pressure effect by using self-developed equipment, Shimazu servo test machine and AE monitor system, and the characteristic of AE parameters are analyzed, too. The results show that in the process of outburst coal containing gas triaxial compression, there is no serious dense or sparse area of AE events, but three relative dense appear in compression phase, middle area of linear elastic stage and near peaking phase area so that the characteristic of AE events look like three peaks. But the amplitude of AE events is small and the good consistency between energy change and amplitude change is showed. Microstructure change caused by external stress field change, fracture and fragmentation of particle of samples, movement besides particle of samples and microstructure change caused by dissipation of gas are the sources of AE events. The number of AE events is reduced as the confining pressure is increased, but the influence on total number of AE events caused by confining pressure show nonlinear, expressed by quadratic function. The number of larger amplitude of AE events show decreasing tendency as the confining pressure is increased, the relation between numbers of AE events whose amplitude is more than certain value and confining pressure is expressed by quadratic function.     

THE STUDY ON CHARACTERISTICS OF ELASTIC WAVE PROPAGATION IN ROCKS UNDER COMPLICATED STRESS STATES

This paper is aimed at investigating the acoustic properties of rock mass under the three-dimentional different stress states, and is presented to discuss emphatically the characteristics of the acoustic wave propagation and the stress-velocity relation in both rocks (sandstone and limestone) under uniaxial and true triaxial compression. The results indicate three regions in which the acoustic velocities and the strains change with the stresses are approximately similar under different stress states; and the acoustic velocity-stress relations for elastic rocks may be represented by different interdependence coefficients under uniaxial compression. At a time, The acoustic measurement method of rock mass stresses and the horizontal tectonic stress are discussed.     

Experimental Analysis on Crack Initiation Stress and Rupture Energy of Marble Failure

Based on the marble conventional triaxial test data, the crack initiation stress and rupture energy under different confining pressures are analyzed. Results showed that the crack initiation position is gradually close to the peak strength point with the increase of the confining pressure. The location of the crack initiation occurs in 50% ~70% peak strength. The rupture energy and confining pressure are in positive linear relationship as well as the rupture energy and peak axial stress. And sudden increase of AE energy count corresponds with the crack initiation stress. AE energy count and cumulative energy increase quickly after the crack initiation position, which increase significantly in the crack initiation point. The crack initiation point of theoretical calculation is in good agreement with acoustic emission monitoring. Mogi-Coulomb criterion is in keeping with experimental results.     

Experiments on triaxial mechanical properties of soft coal containing gas

Taking briquette specimens composed by soft coal with outbursting trends as research object, systematic research of the influence on triaxial mechanical properties of soft coal containing gas caused by confining pressure and gas pressure is done. The results show that confining pressure can significantly affect mechanical properties of soft coal containing gas, the compression phase of soft coal containing gas is obvious and the triaxial strength is increased gradually as confining pressure is increased; the influence on elastic modulus and shape of stress-strain curve is not obvious. The triaxial strength of soft coal containing gas shows decrease trend as gas pressure is increased; the influence on strength of soft coal containing gas caused by gas pressure is obvious when the confining pressure is smaller, but it is not obvious when the confining pressure is bigger. the influence caused by gas pressure on elastic modulus and deformation of yield step is not obvious; gas pressure has not only obvious mechanical effects,but also have chemical action on soft coal containing gas; stress-strain curve of soft coal containing gas can be expressed by conic, the influence caused by gas pressure can be considered as equivalent confining pressure effects.     

A Fracture Mechanics Solution for Control Fissures in Perilous Rock under Seepage Stress

Crack propagation of control fissures in perilous rock under loads is a key process in the failure of perilous rock. Based on the loading mechanism, the control fissures are classified into compression shear and tension shear types. By introducing a model of seepage stress, the calculating principle of the stress intensity factor and the propagation orientation of control fissure under seepage stress are put forward using fracture mechanics methods. Using Shoulishan perilous rock in the Wanzhou district of Chongqing, P. R. China, as an example, the calculated results show that there is an obvious increase of the stress intensity factor. The influence of hydrostatic pressure and hydrodynamic pressure also are analyzed.     

A Determination Method of Anchorage Length of Compression Anchor

The distribution of the axial stress and shear stress on the anchorage segment and the formulation for calculating the anchorage length were derived based on the stress analysis of the anchorage segment of compression anchor. And the effects of parameters, including the elastic modulus, poisson ratio, cohesion, and internal fiction angle of rock mass, on the anchorage length were studied. The results show that the anchorage length decreases with the increase of the elastic modulus, cohesion and internal friction angle of rock mass; and the anchorage length increases linearly but limited with increasing of poisson ratio of rock mass; and it also increases with increasing load.     

Improvement and Construction of a Biaxial Plane - Strain Apparatus for Rock

A biaxial plane-strain apparatus for investigating the deformation and failure features of rock is improved and constructed on a passive stiff-frame concept;furthermore,a new device inducing confinement on both sides of the prism specimen was designed and built,which can not only impose varying confining pressure on the specimen,but dynamically monitor the change in confinement due to deformation of the specimen during testing.Theoretical analysis and test results show that for rock specimens with Young's modulus below 14.16GPa,the apparatus can provide an acceptable plane-strain condition and be of practical use.     

直墙拱形巷道围岩应力场分析

为得出直墙拱形巷道围岩应力分布规律,应用复变函数弹性理论推导了直墙拱形巷道围岩应力分布的解析表达式。对直墙拱形巷道边界的围岩应力和巷道水平线方向的围岩应力分布规律进行分析,并考虑直墙拱形巷道断面高宽比和侧压系数对其影响规律。研究表明：在不同巷道断面高宽比、侧压系数下,直墙拱形巷道围岩应力集中区域主要集中在直墙底部底角处、拱形顶板中点附近和底板中部3个位置。不同巷道断面高宽比下,直墙拱形巷道沿水平线的应力分布规律基本相同。侧压系数大于1时,采用巷道断面高宽比小于1较有利于巷道稳定;侧压系数小于等于1时,采用巷道断面高宽比大于1较有利于巷道稳定。     

Research on Bifurcation and Chaos Characteristics of Meso-Scopic Fracture Process of Rock

On the basis of test results of meso-scopic fracture process and evolution of microcracks of rock in uniaxial compression,the number and orientation of microcracks at each stress level are obtained.A mathematical model for describing the germination and evolution of microcracks is proposed.The bifurcation and chaos behaviours of the evolution of microcracks and meso-scopic fracture process are studied for the first time with the bifurcation and chaos theory of modern nonlinear science.When the characteristic values which represent the gernimation and closure effect of microcracks take certain values,the evolution of microcracks can be described by the Logistic equation.Therefore,the evolution of microcracks of rock has the bifurcation and chaos characteristics.[WT5HZ]     

A THEORETIC BREAKDOWN CRITERION OF HYDROFRACTURING IN ROCK SALT

Experimental results of the basic mechanical properties and failure mode performed on rock salt demonstrate that rock salt is a typical and peculiar soft rock , whose" Young' s modulus/strength(E/S)"ratio is extremely small,and whose failure follows the deformation failure criterion. With these results,this paper develops a theoretic breakdown criterion of hydraulic fracturing in rock salt,which is based on the greatest tension strain failure theory and includes the vertical stress effects. It has been suggested that the critical tension strain should be determined from uniaxial compression tests. This theoretic criterion exceedingly agrees with experimental results and is applicable for every soft rock with small E/S ratio under various stresses.     

FEM Analysis of Stress Distribution Law in the Rocksalt Cavity''s Surrounding Rock

Basic on the FEM numerical analysis, the contour maps stress of rocksalt cavity's surrounding rock and the major principal stress's law changed with the depth and horizontal direction are analyzed. The influencing factors to the distribution of the stress surrounding rocksalt cavity, such as cavity's span, water pressure and the depth of rocksalt layer is also studied. The results show that major principal stress becomes big with the increase of rocksalt's depth. The cavity's influence to the stress's distribution will be clearer with the nearer to the cavity. The stress's centralization will be weaker with the accretion of water pressure in rocksalt's cavity. But the stress's centralization will be stronger, and the stress's value increases.     

稻谷堆弹性模量的实验测定与研究

利用TSZ-6A型应变控制式三轴仪进行三轴实验,测定围压分别为50 kPa、100 kPa、150 kPa、200 kPa时,稻谷堆（水分为11.89%w.b,13.55%w.b,15.73%w.b,17.62%w.b）的弹性模量,同时研究围压和水分与稻谷堆弹性模量的关系。实验结果表明：对于水分范围为11.89%~17.62%w.b的稻谷堆,在围压为50 kPa~200kPa的范围内,其弹性模量范围为8.69 MPa~37.07 MPa。根据围压与稻谷堆弹性模量的关系可以拟合得到方程：y=Ax＋B,其中,A、B为与水分有关的参数。在相同水分条件下,稻谷堆的弹性模量随着围压的增大而增大;在相同围压条件下,稻谷堆的弹性模量与水分没有显著的相关性。     

Study on Acoustic Emission of Limestone in Uniaxial Compression Test

In order to study the acoustic emission of rock under compression by means of the rock acoustic parameter dynamic testing system (RAPDTS), some uniaxial compression tests on a kind of limestone from Guangxi Province were carried out. It was concluded that the formations of new micro clefts generated in the rock and the enmargements of existing clefts are the principal factors that cause the acoustic emission.     

Stress Distribution in Fixed Anchor Length of Compression Type Anchor in Soft Rock Mass

To study stress distribution in fixed anchor length of compression type rock anchor cable, field test was carried out. Strain sensors were placed in the grout paste in fixed anchor length with certain interval. Axial and radial strains of the grout were noted by test. Shear stress distribution curve along the fixed anchor length was obtained by stress-strain relationship and static equilibrium analysis. Analysis results prove that maximal shear stress on the interface can achieve upper level and move forward when the load increases; the transmission length is short; shear stress transfers forward; and three dimensional state is obvious around capacity plates in soft rock mass.     

Stress wave effect in numerical simulation on rock breaking under high pressure water jet

The evolvement of rock damage struck by a high pressure water jet is characterized by nonlinear properties, thus making it a complicated dynamic problem. Based on a nonlinear finite element and elastic plasticity theory, a computational model was established. The dynamic load striking the rock by a high pressure water jet was simulated by the dynamic contact method. Furthermore, the propagation of a stress wave in the same rock was simulated at different impact velocities. The results show that the propagation velocity of a stress wave is proportional to the impact velocity of the high pressure water jet. The effects of a stress wave in sandstone and coal impacted by high pressure water jets of the same velocity were simulated.The effect of a stress wave in coal was stronger than in sandstone, while the region of propagation of stress wave in coal was smaller.     

围压与含水率对小麦堆弹性模量影响的实验研究

使用应变控制式三轴仪,测定了不同围压和含水率条件下的小麦堆弹性模量,并分析了围压与含水率对小麦堆弹性模量的影响.实验结果表明：同一含水率下,小麦堆（含水率为11.88％ w.b、12.91％ w.b、14.40％ w.b、15.40％ w.b、16.85％ w.b）弹性模量随着围压（50 kPa～200 kPa）增大而增大;同一围压下,小麦堆的弹性模量随着水分的增大而减小.     

Construction and Application of a Plane - strain Apparatus for Rock

A plane - strain apparatus for investigating the deformation and failure features of rock was altered and constructed on a passive stiff-frame concept, further, a new device inducing confinement on both sides of the prism specimen was designed and built, which can not only impose varying confining pressure on the specimen, but dynamically monitor the change in confinement due to deformation of the specimen during testing. Theoretical analysis and test results show that for rock specimens with Youngt modulus below 17.4 GPa, the apparatus can provide an acceptable planestrain condition and be of practicability.     

Relationship Between Dynamic and Static Value of Elastic Modulus in Rock

Taking the deposited-layer rock and compacted-layer rock as study target,by elastic wave experiment and uniaxial compression experiment,the physics mechanics parameters and acoustics parameters of these rock are worked out; Based on it, by the correlativity is established between dynamic and static value of elastic modulus in rock of different lithology taking nonlinear fitting,it offers reference for the study of the drill and measuring well in the exploitation of oil. Influenced by the integrality and weathering breakage degree of rock,the biggish different is existed between dynamic elastic modulus gained by dynamical method and static elastic modulus obtained by static method,and the relationship between dynamic and static value of elastic modulus is approximatively expressed as a relationship of quadratic polynomial function.     

Multi-field coupling effect on coalbed methane seepage characteristics and numerical simulation

This paper studies the seepage of coal samples under the influence of each single factor, the axial stress, confining pressure, gas pressure, and temperature by experiments. It uses Ansys12.0 to numerically simulate the law of coalbed methane seepage, coal deformation, pore pressure, the distribution of flow field under the influence of each single field and multi-field coupled. The numerical simulation show that the result of numerical simulation of gas seepage law in the coal under each single fields is basically the same as the experimental result. The curve of gas seepage and average effective stress under the condition of multi-field coupled is negative exponential relationship. Stress influenced the deformation of the specimen is greater than the seepage field. The axial stress on the deformation of the specimen is greater than confining presses The influence on the flow field by confining pressure is greater than axial stress, the influence of axial stress on the pore pressure is greater than confining pressure, pore-pressure under the action of multi-field is bigger than pro-pressure under each single field. To study the seepage law of coalbed methane, it should consider the influence of gas-solid-heat at the same time.     

Elasto-plastic analysis on surrounding rock of roadways based on seepage, strain softening and dilatancy

According to seepage body force, strain softening and rupture expansion of rock mass, elastic-plastic mechanics theory, distribution laws of stress and displacement of surrounding rock in seepage field are derived, and relationships between different zonation range of the surrounding rocks, pore water pressure, strain softening and rupture expansion are established. The results show that the pore water pressure and rupture expansion rock mass have a more obvious impact on the surrounding rock rupture area than the plastic zone. Both the plastic zone and the rupture area are larger when the seepage field is considered. The impact of strain softening on both the plastic zone and the rupture zone of surrounding rock is very significant, and both seepage and strain softening rupture expansion affect deformation of surrounding rock of roadways obviously. It provides certain reference values for the roadway support engineering in seepage field.