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2008, 27 (1): 0-0 doi:

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RESEARCH AND DEVELOPMENT OF 20 MN SERVO-CONTROLLED ROCK TRIAXIAL TESTING SYSTEM WITH HIGH TEMPERATURE AND HIGH PRESSURE

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2008, 27 (1): 1-1 doi:

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A 20 MN servo-controlled rock triaxial testing system with high temperature and high pressure developed by the authors is introduced. The system is constituted with main loading sub-system，high temperature control sub-system，sample assembling sub-system，and measuring system. The maximum axial pressure and confining pressure are both 10 000 kN. The maximum sizes of tested cylinder sample can be set as large as f 200 mm×400 mm. The heating temperature can reach as high as 600 ℃. Some related key issues and corresponding solving methods in the test system are also introduced. Compared with high temperature and high pressure test machine of geophysics，the developed test system has some advantages as follows：(1) Larger size sample can be tested，and the volume of the largest sample is 64 times larger than ordinary one and some properties of rock mass can be discovered thoroughly. (2) The servo-controlled system can measure the deformation of sample under different temperatures easily. (3) The thermo-physico-mechanical process of heated rock samples can be measured. (4) Drilling process in deep underground with high temperature can be simulated and investigated. (5) It can be used to study engineering characteristics of rock mass. Certain experimental investigations on coal samples with high temperature and high pressure in the system demonstrated that the plastic properties of the coal sample were enhanced and the Young¢s modulus decreased with temperature. The relationship of the Young¢s modulus with temperature is found with exponential rule. The testing system can be used to investigate certain scientific natures of deep mining process，direct liquefaction and gasification of coal，geothermal excavation，mine safety，construction safety，etc..

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STUDY ON PHYSICAL AND NUMERICAL SIMULATION OF WATER INRUSH PREDICTION THEORY FOR COAL MINING ABOVE CONFINED AQUIFER

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2008, 27 (1): 9-9 doi:

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Based on the method of 3D similitude and numerical simulation，the variety law of aquifer of coal mining above confined aquifer is studied. In most cases，if the distance of coal floor and aquifer is larger than 20 m without tectonic belt，the influence of mining on the aquifer can be ignored. But if the tectonic belt is included，the tectonic belt will be active and the aquifer will connect with the confined water，so water inrush from coal floor may be taken place. The safe distance of mining will be decided with in-situ cases. At the same time，the rationality of the predicting theory of water inrush from coal floor was verified based on the mechanism of water inrush theory with two methods. The conclusions show that in most cases，the confined water is always approaching to the nearest aquifer and than rises to higher aquifer，i.e. the confined water flows from Benxi group aquifer to Taiyuan group aquifer. Finally，water inrush happened. The conclusion indicates that the predicting system is correct and can be used by other similar mines.

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IDENTIFICATION OF NON-STATIONARY CREEP CONSTITUTIVE MODELS OF ROCK

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2008, 27 (1): 16-16 doi:

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Based on the creep experimental data of shale，the relationship among stress level，time and viscoelastic deformation disciplines of rock is analyzed. One-dimensional viscoelastic creep equation of rock is given by back analysis method. According to theoretical and experimental data，large errors will be encountered without considering time-dependent behaviors of the parameters. Therefore，a non-stationary viscoelastic constitutive model can more accurately reflect the deformation behaviors of rock than those of stationary mode. The necessity of non-stationary parameters is testified. In practical cases，the surrounding rocks in a certain tunnel are supposed to be viscoelastic and visco-elastoplastic bodies，respectively；and certain parameters of rocks are regarded as time-dependent variables. By using back analysis of displacement，two-dimensional non-stationary creep constitutive model of the surrounding rock is identified based on measured displacements. The result indicates that the visco-elastoplastic model with non-stationary parameters can reflect the characteristics of rock mass objectively.

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PHYSICO-MECHANICAL PROPERTIES AND LIMIT OPERATION PRESSURE OF GAS DEPOSIT IN BEDDED SALT ROCK

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2008, 27 (1): 22-22 doi:

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Bedded salt deposit is originated from cyclical sedimentation of salt rock and mudstone，anhydrite，or other non-salt rock interlayers；and the physico-mechanical properties determine limit operation pressure of gas deposit to some degree. The authors investigated the penetrability of salt rock and the interlayers；and it was pointed out that the naturally compacted salt rock and interlayers would not affect the safety of the gas storage，provided that they were not damaged. Then，some experimental investigations and theoretical analyses of mechanical and rheological properties of salt rock and the interlayers were carried out. It was concluded that the difference of mechanical properties between salt rock and interlayers could be found with some deformation variances of different lithologies and even shear damage on their interfaces. On the basis of the above studies，a set of laws were proposed for determining the minimum and the maximum operation pressures in bedded salt rock gas storage，including roof stability law，creep control law，cavern wall and naked well tightness law. Finally，an in-situ example for determining the limit operation pressure was analyzed with the given laws. The results are able to guide the construction and operation of the oil and gas deposits in bedded salt rock in China.

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MICRO-CT EXPERIMENTAL TECHNOLOGY AND MESO-INVESTIGATION ON THERMAL FRACTURING CHARACTERISTICS OF GRANITE

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2008, 27 (1): 28-28 doi:

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The constitution and the mechanism of the μCT225kVFCB micro-CT experimental system，which was co-designed by Taiyuan University of Technology，and Applied Electronics Institute，Academy of Engineering Physics of China，is firstly introduced. The maximum power and amplified factor of the system are 320 W and 400 times，respectively. It can perceive distinctly pores and fissures in rock specimens with size as small as 1–2 μm. It is a precise experimental system for intensive investigations on the meso-structure of either metallic or non-metallic materials. Series of dimensional triaxial meso-structure investigations on granite thermal fracturing under temperatures ranging from 20 ℃ to 500 ℃ were carried out with the system. It was demonstrated that the crystal grain size of the granite specimen is 100–300 μm with irregular shapes. The fracturing was developing with heating temperature increase. It was observed that certain micro-fissures in the specimens propagated under 200 ℃，and the micro-fissures developed and even connected to form larger fissures under 300 ℃. The length of the fissure could reach as long as 10 times against that under 200 ℃. A fissure net around each granite crystal grain was formed and made the polygonal grains be isolated with each other when the heating temperature reached 500 ℃. It was found that 90% of the thermo-fracturing happened along the weak boundaries between the crystal grains and the surrounding cement，with less than 10% of the fracturing fissures crossing the grains.

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ROCK SUPPORT DESIGN FOR SPECIAL LIGHTING CAVERNS IN HIGH IN-SITU STRESS ROCK MASS

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2008, 27 (1): 35-35 doi:

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Six caverns are designed in the world¢s longest twin-tube road tunnel，the Qinling Zhongnanshan tunnel，for the special lighting and driving safety purpose. The tunnel is excavated through the Qinling Mountain Range of Shaanxi Province，China，where the maximum rock overburden is about 1 800 m. In-situ rock stress was measured by overcoring method in two boreholes close to the cavern sites，where overburden is 400 and 1 600 m，respectively. The measurement result indicates very high rock geostresses. To meet the lighting requirements，the spindle-shaped caverns are designed to have a length of 200 m and a maximum span of 22 m. However，restricted by the distance between the two existing tunnels，the minimum width of the pillar between the caverns is left to be only 8 m. The main features of the caverns include：(1) high in-situ stress；(2) generally good rock；and (3) small pillar in comparison to the cavern size，which imposes great challenges to the rock support design. The support design is based on empirical approach from rock mass classification Q-system；and it is then verified by the numerical analysis. The supporting system，including both temporary support and permanent support，consists of bolting and shotcreting. In order to ensure the cavern stability during construction and in operation，a complete construction procedure，including sequence of excavation，bolting and shotcreting，is specially defined. Monitoring measures are also proposed. For the caverns located in the extremely high stress region，a flexible support system is designed，allowing the rock mass to partially deform before the permanent support is installed，thus ensuring cavern stability and the well-functioning of the rock bolts and shotcrete as permanent support. Commercial codes FLAC3D and Phase 2 are used in 3D and 2D analyses，respectively. The purpose of the three-dimensional analysis is to demonstrate the 3D effect and variations of stress and deformation along the tunnel axis；while the two-dimensional analysis is to study the functioning of support elements in each excavation stage. Numerical analysis verified the support design with controlled deformation and well functioning of the permanent support elements of both rock bolt and shotcrete.

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THERMOELASTOPLASTIC DAMAGE MODEL OF HETEROGENEOUS MEDIUM AND ITS APPLICATION TO THERMAL CRACKING ANALYSIS OF OIL SHALE IN UNDERGROUND MINING

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2008, 27 (1): 42-42 doi:

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The low-permeability and impermeability of the stratum are hot issues for oil shale in underground mining，so it is of vital significance to form permeable belts among various mining shafts，while the thermo- chemical functions during oil shale heating are prerequisites of forming the permeable belts. Based on the problems mentioned above，the oil shale thermoelastoplastic damage model of heterogeneous medium is established；and then a systematic method of defining damage variables is given. Further，the material parameters of thermal expansion coefficient，thermal conductivity，specific heat，elastic modulus and tensile and compressive strengths are used as the random variables of satisfying Weibull distribution；and the parameters of numerical calculation is given in Matlab with Monte Carlo method. In addition，numerical simulation of thermal cracking during the process of heating in oil shale in underground mining is performed. The results indicate that the different thermal expansions and elastoplastic properties and distributed randomness of various mineral particles composed of oil shale will lead to the nonuniformity of thermal field，deformation field and stress field in heating process，which makes the particles of oil shale deform incompatibly；and the release of product pyrolysis results in irreversible damages of oil shale material and structure. These are the main reasons for the thermal fracture of oil shale. When oil shale is heated through thermal conduction，temperature transfers slowly，so the spacing between heating well and production well should not be kept too long. When difference exists in oil shale reservoir¢s properties，heating well should be chosen in the high conductivity region. Oil shale¢s stratification is vital for developing permeation zone in in-situ retorting. Oil shale will generate additional expansion force as it reaches its pyrolysis temperature，and stratification will be cracked first，so the oil shale stratification should be utilized to enhance its permeability.

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EXPERIMENTAL STUDY ON EFFECT OF PORE PRESSURE ON FELDSPAR FINE SANDSTONE PERMEABILITY UNDER DIFFERENT TEMPERATURES

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2008, 27 (1): 53-53 doi:

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In order to study the rule of effects of temperature and effective pore pressure on rock permeability，the 20 MN servo-controlled triaxial rock testing machine with high temperature and high pressure is used to research feldspar fine sandstone¢s permeability with time under different temperatures and triaxial compression tests. The rock sample is cylinder-shaped，and the dimensions of rock sample is f 200 mm×400 mm. With the experimental results，there is a temperature threshold of feldspar fine sandstone¢s permeability during the rising course of temperature. Feldspar fine sandstone¢s permeability rises abruptly when feldspar fine sandstone¢s temperature reaches its temperature threshold. The permeability of feldspar fine sandstone is 65 times against that under indoor temperature. Moreover，it exceeds the threshold of pore pressure in the area of temperature threshold of feldspar fine sandstone at the same time. At the threshold of pore pressure，feldspar fine sandstone¢s permeability changes acutely，rising more than that under low pore pressure. The effect of pore pressure on feldspar fine sandstone¢s permeability declines even if raising feldspar fine sandstone temperature over the temperature threshold of feldspar fine sandstone.

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ANALYSIS OF EFFECT OF FISSURES CAUSED BY UNDERGROUND MINING ON GROUND MOVEMENT AND DEFORMATION

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2008, 27 (1): 59-59 doi:

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Based on in-situ data，the four stages of fissures and the mechanism of ground movement and deformation caused by underground mining are analyzed. The results are drawn as follows. (1) Subsidence is shown of discontinuous movement，and it is found in concave region；the ground subsidence decreases，but increases in convex region. (2) The fissure can increase the displacement along with the mountain slope down ramp direction，and the increase is related to slope form，position of gob，and characteristics of surface. (3) The fissure can change the horizontal deformation properties. It can reduce tensile strain or increase the compression strain in the tensile strain region，or reduce compression strain or tensile strain in compression strain region，or increase strain in tensile or compression regions.

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2008, 27 (1): 65-65 doi:

[PDF] 349 KB (1538)

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With the exploitation of the coal resources，many engineering cases show that residual movement distortion in mined-out area would destroy the buildings on the top of the area. Combined with the characteristics of the mined-out area under Lishi—Jundu highway in Shanxi Province，the grouting in mined-out areas，drilling data and the related relationship between the mined-out area span，time，and residual subsidence are put forward；and the distortion anticipation methods and corresponding formulas are also presented. What is more，the grouting volume in the treatment mined-out area is analyzed. The related laws between the mined-out area span，time，and residual subsidence are gained. The effects of treatment mined-out area can be analyzed and estimated by calculating equivalent height of unfilled space of mined-out area and equivalent height of grouting volume.

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EXPERIMENTAL STUDY ON MECHANICAL CHARACTERISTICS OF GRANITE UNDER HIGH TEMPERATURES AND TRIAXIAL STRESSES

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2008, 27 (1): 72-72 doi:

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Extracting heat from hot dry rock(HDR) and nuclear waste disposal both need researches on granite mechanical characteristics at high temperature and high pressure in depth. Utilizing the 20 MN servo-controlled triaxial rock testing machine with high temperature and pressure developed by the authors，the research of thermal deformation and failure characteristics of large size granite samples of f 200 mm×400 mm at high temperature and triaxial stresses through recent half a year is carried out；and the characteristics of thermo-mechanical parameters such as linear thermal expansion coefficient and elastic modulus changing with temperature，are also achieved. The research results indicate that：(1) Under 3D hydrostatic stress，granite¢s thermal deformation course can be divided into slow deformation stage at low temperature，fast deformation stage at medium-high temperature and slow deformation stage at high temperature. Thermal expansion coefficient measured without stress state may excessively magnify the rock¢s thermal expansion or thermal effect and will result in wrong conclusion，so the thermal expansion coefficient measured with stress state can reflect the actual state of rock mass. (2) Granite shows feature of expansion in volume at low stress while shrinkage in volume after exceeding a certain stress under high temperature and triaxial stresses. It is a different feature contrasted with that of normal temperature. (3) The failure shape of granite at high temperature is of shear failure，while granite will transform to ductility under high confining pressure and high temperature. (4) The elastic modulus of granite decreases with the increase of temperature under confining pressure. The variety course can be divided into three stages，i.e. slow decreasing stage，fast decreasing stage and constant stage.

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CONTROL EFFECT OF FISSURE SCALE ON DEFORMATION AND FAILURE OF ROCK MASS

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2008, 27 (1): 78-78 doi:

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Rock mass contains large-scale deficiencies，such as pores，fissures and faults，which are usually referred to rock defects. Faults，cracks and fissures are called high-level defects，micro-cracks, pores are called low-level defects. Rock defects of rock deformation and the damage control will have close relationship with different fissure scales. The relationship of quantity and scale of rock mass fissure is analyzed，including great crack and microcosmic fissure. Then with numerical simulation，it is found that the fractures of rock samples will increase gradually；and the control effects from microcosmic fracture scale to deformation and the rock mass failure are studied. The result indicates that the arrangement defect controls the deformation，stability and rock mass failure when the scales of crack，fissure，cavity，spacing，hole are coexisting in rock masses.

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GAS-LIQUID TWO-PHASE CRITICAL SEEPAGE LAW IN SINGLE FRACTURE AND ITS RANDOM AND COMPOUND MATHEMATICAL MODEL

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2008, 27 (1): 84-84 doi:

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Based on analyzing the micro critical seepage phenomena of gas-liquid two-phase flow in a single fracture，a random and compound mathematical model was constructed to describe this phenomenon. Using this model，the numerical simulations of the probability distribution scope of the occurrence of critical seepage phenomena，the micro characters of gas/water connected clusters in critical seepage district，and the characteristics of the pressure gradient in critical seepage district are all carried out. The mechanism of the gas-water two-phase critical seepage law is revealed；and the critical seepage phenomena could occur when the relative gas saturation is 44%–77%；but the probability of the occurrence of the phenomenon is above 0.8 when the gas relative saturation is 47%–65%. However，when the gas relative saturation is 57%–60%，the probability of the occurrrence of the phenomena is 1.0.

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STUDY ON COUPLED THERMO-MECHANICAL CREEP PROPERTIES OF BEDDED ROCK SALT

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2008, 27 (1): 90-90 doi:

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Through coupled creep experiment and theoretical analysis of thermo-mechanical behaviors of bedded rock salt，the results are obtained as follows. (1) The creep ratios and creep strain of rock salt vary with ingredient and structural distribution. (2) Under normal temperature，the creep strain and creep ratios of bedded rock salt increase when its loading stress increases；and the steady creep ratios are with good power function of deviatoric stress. (3) Under thermo-mechanical coupling，the steady creep ratios are affected by temperature when the loading stress is the same；and the steady creep ratios of bedded rock salt are shown with exponential function of temperature. At the same temperature and stress，the transversal displacement，strain and creep ratios are larger than those of bedded salt-mudstone；the creep ratio in landscape orientation of rock salt is 1.6–1.8 times larger than that of salt-mudstone interlayer. (4) As the ingredient and structure of each interlayer of bedded rock salt are different，the creep strain is not consistent with the action of stress and temperature，and it will result in shearing failure. Finally，the creep constitutive equation of bedded rock salt is established according to fitting experimental data；and the achieved results can provide some references to the stability analysis of oil and gas storage cavern in bedded salt deposits.

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DISCUSSION ON METHOD FOR DETERMINING REASONABLE POSITION OF ROADWAY FOR ULTRA-CLOSE MULTI-SEAM

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2008, 27 (1): 97-97 doi:

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With numerical simulation method，the distribution law of coal pillar support pressure in the floor was studied. The result shows that stress distribution of floor under coal pillar has obvious heterogeneous characteristic in that the highest stress concentration lies under coal pillar and concentration degree decreases quickly away from coal pillar. The reason that roadways were easy to transform and fail under heterogeneous load was analyzed. Under the heterogeneous load，the roadway support structure is subjected to emergent partial overload and produces local failure and will lose its stability. It is pointed out that the influence of the heterogeneity of stress distribution on the bottom plate under the coal pillar should be considered when laying the roadway of ultra-close lower-seams besides avoiding the coal pillar abutment stress concentration area. The heterogeneous degree can be measured by the rates of stress variation. In-situ observation confirmed the method，which indicates that the proposed methods are feasible to the study of reasonable position of the roadway for ultra-close lower-seams. The results have references to the layout of roadway with similar conditions.

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ANALYSIS OF TIME-SERIES CHARACTERISTICS OF STRATA DRILLABILITY OF PILOT DRILLING FOR CHINESE CONTINENTAL SCIENTIFIC DRILLING

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2008, 27 (1): 102-102 doi:

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The analysis and prediction of deep formation drillability are important for drilling and exploring engineering. In general，the formation drillability index is calculated based on well acoustic logging after the well being completed or at some stages. Using the well logging data，some methods can be employed to calculate the stratum drillability. For the sake of improving prediction technique，the characteristics of formation drillability time series(DTS) are needed. Based on the study of strata drillability time-series of pilot drilling of Chinese continental scientific drilling(CCSD)，two typical indices were put forward. They are characteristics of time-series geometrical form and intrinsic change tendency. These two indices are expressed with correlation dimension(D2) and Hurst(H) exponent，respectively. Based on the analysis of 32 actual well formation drillability profile curves of different oil fields in China，a conclusion was drawn that most of the curves show fractal characteristics. For a drillability time-series，its correlation dimension(D2) can describe the degree of variety and it can be used to express the curve¢s outside geometrical characteristic. The Hurst exponent can be used to estimate the time-series¢ development tendency. The application results show that D2 and H can describe the main characteristics of a DTS perfectly. With these two characteristics，a drillability prediction model based on intelligent neural network was developed. This model was used to predict the formation drillability of CCSD，and it was proven to be practicable.

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STUDY ON SEVERAL KEY ISSUES IN NONDESTRUCTIVE DETECTION OF BOLT BONDING INTEGRITY

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2008, 27 (1): 108-108 doi:

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The latest researches on nondestructive detection of rock bolt bonding integrity are summarized. By means of theoretical analysis and laboratory research，several key issues in nondestructive detection，i.e. end reflection，consolidation wave and dynamic response of rock bolt under loading，are discussed. With the variation of free part length of different grouted rock bolts，the fact is found that the end reflection is not very obvious when the grouted length is shorter than 3/4 wave length of input signal. If changing the grout concrete strength，the relationship between consolidation wave speed and bolt bonding integrity is achieved. In addition，the testing rock bolt response under loading and the relationship between basic frequency of dynamic response and loading level are also gained. All of these relationships are valuable in engineering practice.

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STRENGTH CRITERIA OF DEEP ROCK MASS

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2008, 27 (1): 117-117 doi:

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The most distinguished difference between deep and shallow levels is the so-called high geostress. The failure mode of the shallow rock mass is brittle failure. The failure modes of the deep rock mass may be brittle failure or ductile failure that depend on the property of rock mass and the geostress state. Mohr-Coulomb criterion，Hoek-Brown criterion，Druck-Prager criterion and unified strength criterion are suitable for brittle failure of the shallow rock mass. A new strength criterion，which is applicable to deep rock mass，is proposed. The new strength criterion，in which the effect of intermediate principal stress is considered，can consider the brittle failure and ductile failure of the deep rock mass. Moreover，the new strength criterion that is relative to the rock mass rating(RMR) classification can be applied to the research of the tensile failure of deep rock mass. All the parameters have clear physical concept，which can be conveniently determined by experiments or RMR in the presented criterion. Finally，in order to examine the proposed strength criterion，the comparison between the present strength criterion and the experimental data is performed. It is shown that the presented strength criterion is in good agreement with the experimental results.

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A NEW GENERALIZED POLYAXIAL STRAIN ENERGY STRENGTH CRITERION OF BRITTLE ROCK AND POLYAXIAL TEST VALIDATION

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2008, 27 (1): 124-124 doi:

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Based on some principal rules of brittle rocks¢ polyaxial tests and previous researches，three controlling failure types for brittle rock are obtained. The first type represents the brittle failure controlled by extension microcrack under the condition of lower hydrostatic pressure；the second represents the ductile failure controlled by friction sliding action under the condition of higher hydrostatic pressure when microcrack is close；and the third represents brittle-ductile failure type controlled by multiple factors mentioned above under the condition of high hydrostatic pressure when some microcracks are open and others are close. On the basis of the achieved result and the effect of stress such as minor principal stress，intermediate principal stress，hydrostatic pressure，stress Lode degree，a generalized hyperbolic failure function adapted naturally with the envelope form of Mohr-Coulomb criterion is proposed for brittle rocks；and a smooth failure function acquired by Yu Maohong is also presented. Thus，a generalized polyaxial strain energy(GPSE) strength criterion is created. The criterion is similar to hyperbolic strength criterion including uniaxial compression strength and uniaxial tensile strength，which is an extended form of Griffith-Murrell criterion essentially under the condition of polyaxial stress when hydrostatic pressure is lower，and it represents the first failure type. However，the criterion is similar to generalized Mises criterion when hydrostatic pressure is higher，and it represents the second failure type. The transition part between the two criteria represents the third failure type when hydrostatic pressure is high. Finally，the GPSE strength criterion for rock is verified by polyaxial test data of brittle rocks. The strength criterion for rock can be widely used to brittle rocks and allows for a good description of the several effects of stresses mentioned above，nonlinear characteristics of strength and marked difference for tensile strength and compression strength.

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INTERACTION BETWEEN TRANSVERSE ISOTROPY ROCK SLOPE AND PRESTRESSED ANCHOR CABLE WITH FRAME
BEAM SUPPORT

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2008, 27 (1): 135-135 doi:

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The rock mass in natural state is a discontinuous anisotropy mass，therefore，if rock mass is still regarded as isotropy mass，it will not agree with the actual situation. In general analysis of engineering cases，anisotropy material includes orthotropy material and transverse isotropy material. In order to study the interaction between transverse isotropy rock mass and supporting structure，engineering geology of the slope at an expressway project is considered. Then，the laboratory tests for rock samples from field were carried out；and the uniaxial compression tests for rock samples with different stratification planes are performed to determine the indices of describing elasticity characteristics of transverse isotropic rock. Based on the theory of stress-strain relationship of transverse isotropy rock mass，the analytical model of interaction between rock mass transverse isotropy of slope and prestressed anchor cable with frame beam is established；and the notion of the optimum anchorage angle in prestressed anchor cable is presented. The interaction between rock mass transverse isotropy of slope and prestressed anchor cable with frame beam was analyzed with finite element analysis. At the same time，the study on parameters of the interaction between rock mass transverse isotropy of slope and prestressed anchor cable with frame beam and the optimum anchorage angle in prestressed anchor cable is performed. The rules of the influence on directivity of stratification plane of supporting structure are determined. The results show that some reasonable and reliable references and actual engineering experiences on the design of prestressed anchor cable with frame beam supporting for transverse isotropy rock slope can be accepted.

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STUDY ON CONSTITUTIVE MODEL OF HARD ROCK CONSIDERING SURROUNDING ROCK DETERIORATION UNDER HIGH GEOSTRESSES

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2008, 27 (1): 144-144 doi:

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In the practice of tunneling in hard rock stratum under high geostress，mostly，two phenomena can be observed：(1) the rock has the activity of brittle breakage induced by the unloading；and (2) the parameters of surrounding rock in the excavation damage zone(EDZ) have changed，including elastic modulus E，cohesion c and friction angle j. Therefore，a rock mass deterioration model(RDM) is presented. The RDM takes the damage of rock as a process of propagation of microcracks. It means that the microcracks lead to the reduction in deformation modulus and cohesion and the increase of friction angle in the EDZ. The relationship between mechanical parameters and damage degree represented by general plastic strain of EDZ is established. Then，the model defines an equation which is the function of general plastic strain to rule the change trend of parameters. It is implemented by integrating with the FLAC3D. The model has three basic characters，i. e. the stress-strain curve is composed of linear elastic part，stress falling part and plastic flow part；the subsequent yield surface can change its shape and area along with accumulation of general plastic strain；and the mechanical parameters are updated with the deteriorating of surrounding rock in EDZ. This model is verified by fitting stress-strain curve of granite in triaxial compression test and modeling experimental tunnel at Jinping II Hydropower Station in China. The results indicated that the RDM is reasonable.

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EXPERIMENTAL STUDY ON COMPOSITE SHAFT LINING OF INNER STEEL PLATE CYLINDER AND HIGH STRENGTH REINFORCED CONCRETE IN DEEP FROZEN SHAFT

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2008, 27 (1): 153-153 doi:

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Based on the theory of confined concrete，the composite shaft linings of inner steel plate cylinder and high strength reinforced concrete have been adopted to solve the difficult problem of supporting coal frozen shafts penetrating through thick soil cover of 600–800 m. Through model experiments，the mechanical characteristics of such shaft linings are studied. The test results indicate that the concrete¢s deformational capacity and compressive strength increase greatly in triaxial compression stress state in inner steel plate cylinder；and the shaft lining is fairly plastic when it fails，and the brittleness defect of high strength concrete is improved. If the shaft linings of high strength reinforced concrete，which are used in site now，have been changed to the composite shaft linings of inner steel plate cylinder and high strength reinforced concrete，and the load bearing capacity of shaft lining will be increased greatly，and the supporting problem of the frozen shaft in the special deep alluvium will be reasonably solved. The main factors affecting load bearing capacity of this shaft lining are the concrete compression strength，the ratio of lining thickness to inner radius，the thickness of inner steel state and the reinforcement ratio. Increasing concrete compressive strength has a remarkable effect on the load bearing capacity of shaft lining. If concrete compression strength increases 10 MPa，the load bearing capacity of shaft lining will increase about 13.8 percent. Moreover，increasing reinforcement ratio has small effect on the load bearing capacity of shaft lining. Therefore，single outer row steel bar is used in practical engineering to economically and reasonably design shaft lining. Finally，a formula to calculate the load bearing capacity of the composite shaft linings of inner steel plate cylinder and high strength reinforced concrete was obtained according to the theory and experimental results. These results have provided a basis for similar engineering practice when designing this kind of shaft lining structure.

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RESPONSES OF SATURATED ROCKS TO MEAN STRESS AND DYNAMIC STRESS AMPLITUDE

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2008, 27 (1): 161-161 doi:

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By shifting the mean stress and the sine wave stress amplitude，uniaxial cyclic experiments were performed to study the dynamic response of fluid-saturated sandstones and marbles. The experimental results show that the modulus increases as the mean stress increases. As the mean stress increases，the Poisson¢s ratio increases at first，and then decreases. The area of hysteresis loop decreases，and the attenuation decreases too. When shifting both the mean stress and the dynamic stress amplitude，the influence on dynamic response is the most intensive. The influence on dynamic response by shifting only the dynamic stress amplitude and remaining the mean stress unchanged is also very intensive. The influence on dynamic response by shifting only the mean stress is not much intensive. Stress corrosion on surrounding media has been discussed. Because of the stress corrosion of water，the attenuation of water-saturated sandstones is twice as that of oil-saturated sandstones；and the dynamic response of water-saturated sandstones is clearer than that of oil-saturated sandstones. Because marbles are more compacted than sandstones and the porosity is only about 1%，the stress corrosion is more serious in sandstones than that in marble. This research is very significant to the alleviation and control of seismic and geological disasters.

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STUDY ON GEOMETRICAL INFORMATION OF OBTAINING ROCK MASS DISCONTINUITIES BASED ON VIRTUOZO

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2008, 27 (1): 169-169 doi:

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In light of the present situation of obtaining discontinuity information with conventional artificial measurement of heavy labor and low efficiency，the method of rapid obtaining rock mass discontinuity information based on digital photogrammetric workstation—VirtuoZo was put forward firstly. The study opened up a new path for rapid obtaining discontinuity information to promote the development of rock mass mechanics. The study closely combines geometrical information with engineering geology；and rock slope was regarded as research object. The method of space front intersection was adopted to do the control survey with Topcon total station instrument(2¢¢). The common digital camera was used to take photographs of the slope. On the basis of this，VirtuoZo was used to establish the model between images and objects，obtaining three-dimensional images and the spatial coordinates of characteristic points of discontinuities. This was coupled with the study of models of trace line displaying and orientation calculating based on spatial coordinates of rock mass discontinuities. Therefore，the geometrical information of rock mass discontinuities can be obtained，including trace lines and orientations. Compared with orientations that are measured artificially with compass，the precision of obtaining orientation information based on VirtuoZo was analyzed. The method of rapidly obtaining rock mass discontinuity information based on VirtuoZo was verified to be feasible and had extensive application prospect through discontinuity information acquisition and its application to practice in the lithologic slope strengthening engineering of Baolilinyu village in Guangzhou.

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STUDY ON SHEAR BEHAVIORS OF ROCKFILL IN LARGE-SCALE TRIAXIAL TESTS UNDER DIFFERENT STRESS PATHS

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2008, 27 (1): 176-176 doi:

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According to the original gradation of the upstream main rockfill in the Yixing Pumped-storage Power Station，the rockfill samples are conducted with combining the similar gradation and equivalent weight modeling techniques. Some large-scale triaxial tests are performed on the samples with YS–30 large-scale triaxial test machine to investigate their shear behaviors under the different stress paths. It is shown that the stress paths together with the consolidation stress sc are the main external influential factors on the shear behaviors of the rockfill. The shear strength of the rockfill is of high nonlinearity，but the stress path almost does not influence the shear strength. With the increases of sc and the stress ratio k，the relationship of stress and strain changes from strain-softening(when sc is low) and the strain-hardening(when sc is high) to entire strain-hardening，but the relationship of volumetric strain and axial strain changes from the shear dilatancy(when sc is low) and shear shrinkage(when sc is high) to entire shear shrinkage. With the increase of stress ratio k，most of the plastic deformation of the rockfill changes from shear plastic deformation to compression plastic deformation；and the failure mode also changes from shear failure to compression failure. The transformation between shear dilatancy and shear shrinkage depends upon a critical stress ratio kcrit and consolidation stress(sc)crit.

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TECHNICAL PRINCIPLE OF TOP-COAL CAVING WITH VIBRATION AND ITS PRACTICE

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2008, 27 (1): 187-187 doi:

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Low recovery ratio of top-coal in the fully-mechanized coal mining is a hot technical problem. A series of investigation methods and results of mechanical design，laboratory experiments，DEM numerical simulation，and in-situ practice of the vibration top-coal caving are described. The experimental results demonstrated that the vibration effect range can reach 0.65 m far from the roof of mining space；and it is also found that vibration frequency 1.0 Hz is the optimum choice. The numerical simulation results illustrated that the top coal could be caved layer by layer，with the effect of vertical weighty and horizontal vibration forces working together. Consequently，the waste stone ratio in mined coal was decreased and the recovery ratio of top coal was increased. The results of 6 months in-situ practice in Wangzhuang mine，Lu¢an Coal Industry Company，demonstrated that the recovery ratio of top coal was increased by 3% in average with the vibration mechanism. The systematical investigations have demonstrated that the vibration top-coal caving is an advantageous and profitable technique，which can greatly increase the recovery of top-coal and decrease the waste stone ratio.

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MECHANICAL MODEL STUDY ON ROOF CONTROL FOR FULLY-MECHANIZED COAL FACE WITH LARGE MINING HEIGHT

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2008, 27 (1): 193-193 doi:

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By using in-situ measured data and the physical simulation technique，the structural characteristics of roof control with large mining height are studied. The mechanical model of roof control for the coal face with large mining height was put forward. According to different strata structures of the immediate roof，the immediate roof of the large mining height is divided into three types：type I，type II，and type III. Immediate roof type I will be calculated according to the given loading method and multiplying mining height method. Immediate roof type II is not suitable for large mining-height technique. The roof control of immediate roof type III should consider the thickness，location and engineering mechanical characteristics of the key layer of immediate roof. When the key layer of the immediate roof is closer to support load，the influence of shock loading should be considered.

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EXPERIMENTAL STUDY ON MECHANICAL BEHAVIORS
OF COAL GANGUE MIXED WITH SOIL UNDER CYCLICAL LOADINGS

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2008, 27 (1): 199-199 doi:

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In order to analyze the technical feasibility of coal gangue mixed with soil as fillings of road embankment，the mechanical behaviors of coal gangue samples mixed with soil were studied by the consolidated undrained triaxial dynamic tests. For coal gangue with mixed soil samples，ratios of dry weight of coal gangue to that of soil are prepared with 4∶1，3∶1，and 2∶1，respectively. The results of dynamic strength tests indicate that dynamic stress sd of gangues mixed with soil increases with the proportion of soil；and there exists an optimum ratio between 3∶1 and 4∶1. The dynamic stress-strain curves can be fitted by hyperbolic curve；the dynamic hyperbolic model and its parameters are also obtained. The maximum dynamic modulus increases with the increase of confining pressure in the relation of exponential function through regression. All of these results can be used to analyze the stability of the coal gangue embankment under traffic load and its deformation. To further verify the results of indoor tests，an in-situ experiment was performed in actual road；and its ground deflections were determined. It is found that the strength of coal gangue mixed with soil as filling can meet the requirements of road embankment.

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LI Runde，ZHANG Hongru，LIU Weining

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2008, 27 (1): 206-206 doi:

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Precision instrument is very sensitive to environmental ground vibrations，which may not be felt by human being but can cause malfunction of precision instrument. Four measure sections were chosen along metro line，where in-situ tests of metro and ground traffic induced vertical ground vibrations were carried out by using high sensitive accelerometers. The 350 ground vibration time-history curves of 94 records were transformed into 1/3 octave band frequency spectrum. Based on the transformation，the characteristics of ground vibrations induced by the normal operation of metro and ground traffic were investigated. Finally，the law of impacts of ground vibrations on precision instrument was discussed with reference to an electron microscope Tecnai30 for analyzing environmental vibration impacts on precision instrument. It is found that there exists an “equal vibration frequency” for ground vibrations. When the frequencies of ground vibrations are smaller than the “equal vibration frequency”，ground vibrations are mainly dominated by background vibrations，while the effect of distance is very weak；however，when bigger than the “equal vibration frequency”，it is mainly governed by distance，but the effect of background vibration is only inferior to the distance. Ground vibrations with frequency smaller than “equal vibration frequency” have higher impacts on precision instrument affected by background vibrations. When vibration frequency is bigger than “equal vibration frequency”，impacts on precision instrument decrease with increasing distance form line center. Superposition of metro induced ground vibrations and ground traffic causes the response within 6–30 Hz is found to be prone to affect precision instrument. “Equal vibration frequency” is first found in this experiment and its implication needs to be further studied.

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闫志刚博士论文

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2008, 27 (1): 215-215 doi:

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周葆春博士论文

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2008, 27 (1): 216-216 doi:

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