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2004, 23 (23): -0 doi:
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NEW APPROACH TO MEASURE GOESTRESS——LOCAL BOREHOLE-WALL COMPLETE STRESS RELIEF METHOD

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2004, 23 (23): -3923 doi:
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[PDF 190 KB] (1300)

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Several methods of borehole stress measurement are briefly reviewed. A new goestress measurement method，called local borehole-wall complete stress relief method(LBWCSRM)，is proposed in this paper. This method has marked advantages of no need of overcoring and no other assumption when calculating the crust stress tensor. Theoretically，the application of this method is free from the limitation of borehole depth and versatile for any deep boreholes. So it offers an innovative approach to stress measurement at great depths.

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STUDY ON INTEGRATED IN-SITU MEASUREMENT TECHNIQUE OF MECHANICAL PARAMETERS FOR ROCK MASS AND ITS APPLICATION

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2004, 23 (23): -3928 doi:
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[PDF 182 KB] (1091)

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Along with the construction of various pressure tunnels，the new measurement requirement of mechanical parameters for rock mass has been brought forward. Based on the innovation of test system，the integrated in-situ measurement technique is discussed for mechanical parameters of rock mass，such as crustal stress，ability of resisting split for surrounding rocks，tensile strength as well as permeability of rock mass under high pressure. The application to various projects indicate that the integrated measurement of mechanical parameters for rock mass is quite necessary，and the test results are the sound basis for scientific design of engineers.

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FUNCTION OF CONFINING PRESSURE TEST
ON HOLLOW INCLUSION TRIAXIAL STRAIN GAUGE FOR GEOSTRESS MEASUREMENT

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2004, 23 (23): -3932 doi:
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[PDF 200 KB] (986)

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The confining pressure test is an important and essential test to geostress measurement with hollow inclusion triaxial strain gauge. The calculation formulas of elastic modulus to participate processing of measured data are derived minutely based on the test data. The release strains are corrected to achieve greater reliability of measured geostress results by using the results of confining pressure test. A practical example is presented to show the availability of the study result.

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MEASUREMENT AND CHARACTERISTICS ANALYSIS OF IN-SITU
STRESSES OF YANBEI COAL MINE

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2004, 23 (23): -3938 doi:
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[PDF 456 KB] (1210)

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In order to reveal the mechanism and characteristics of the dynamic phenomena，large deformation and failure of the tunnel at Yanbei mine，Huating mining area，the in-situ stresses of Yanbei coal mine is measured by the hollow inclusion stress-relief method. The result shows that the horizontal in-situ stress is the major principal stress in this area，and the stress has obvious character of the tectonic stress. The major principal stress is between 14.1～16.88 MPa，and its direction is basically according with the tectonic conformation at the survey point， which is the direction basically normal to the strike of the coal seam and strata. The magnitude of in-situ stress is not high，but the difference between the major and minor principal stresses is great，which is 9.85～10.5 MPa. The in-situ stress field shows obvious inhomogeneity，which results from the affection of some factors，such as geological environment and its evolution，tectonic character，properties of coal and strata，and so on.

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RESEARCH ON IN-SITU STRESS MEASUREMENT AND ITS DISTRIBUTION LAW IN HONGTOUSHAN COPPER MINE

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2004, 23 (23): -3943 doi:
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[PDF 386 KB] (1197)

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Hongtoushan copper mine is a deeper metal mine with typical rock burst. For understanding the state and distribution of stresses in the mine，in-situ stress measurement is carried out by means of hollow inclusion gauge method. Three dimensional stress state is obtained for five levels and eight sites through in-situ stress measurement. The measurement results indicate that the orientation of the major principal stress is NNW～NW，and the value of it is linerally increased with depth. The in-situ stresses are varied with different positions at –767 m level，and the value of the major principal stress reaches around 50 MPa.

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RESEARCH ON COUPLING LAWS BETWEEN EME AND STRESS FIELDS DURING DEFORMATION AND FRACTURE OF COAL AND ROCK IN UNIAXIAL COMPRESSION

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2004, 23 (23): -3948 doi:
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[PDF 232 KB] (933)

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Based on the laboratory experiment，theoretical analysis and numerical simulation，the coupling laws between electromagnetic emission (EME) intensity and stress fields during the deformation and fracture of coal and rock in uniaxial compression are researched in this paper. On the basis of damage characteristics and statistical strength theory of the brittle material like coal and rock，the three dimensional coupling relationship between EME intensity and stress is researched. The relations among the EME intensity，pulse numbers and stress are analyzed theoretically. The theoretical analysis shows that the coupling relationship can be expressed by multinomial approximately. The testing results show that the EME signal increases with stress approximately with the relation of cubic multinomial，the signal of EME emitted in the course of deformation and fracture of coal or rock in compression is relevant to the stress basically，and the intensity and pulse of EME increase with the stress，deformation and fracture. The results of coupling calculation show that the EME signal first increases to a summit value，then decreases suddenly，and it increases also with loading rate and strength of coal and rock，which is consistent with the experimental results.

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MEASUREMENT AND CHARACTERISTICS OF IN-SITU
STRESS IN DEEP ROCK SALT MINE

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2004, 23 (23): -3954 doi:
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[PDF 243 KB] (857)

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According to the requirement of stability analysis for karst cavity and in-situ stress analysis，conditions of drilling-dissolving mining for deep rock salt mine，and practical experience of research on in-situ stress measurement in deep rock salt mine，the selection principle of measurement methods，measured points and samples are determined. The method of building up the coordinate direction of non-directional drilling cores in sediment strata is proposed. Based on the principle of in-situ stress measurement by the Kaiser effect of acoustic emission，the multidirectional sampling and the ellipsoid regression analysis of in-situ stresses are made. Multivariable nonlinear fitting is made to determine a general form of in-situ stress ellipsoid，and then a quadratic orthogonal transformation is made to determine the standard equation of in-situ stress ellipsoid，so that the magnitude and direction of three principal stresses can be obtained. The presented method can avoid more effect of testing errors and get reliable measurement results. According to the testing and analysis results from Changshan Salt Mine，there is horizontal tectonic stress in deep strata，and the direction of major principal stress turns to vertical direction from horizontal direction at the depth of 800 m，and at the depth of 1 000 m the major principal stress is about 30 MPa.

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IN-SITU DEFORMATION OBSERVATION OF ROCK MASS AND FOUNDATION AND STABILITY EVALUATION

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2004, 23 (23): -3959 doi:
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[PDF 247 KB] (1051)

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The technique characteristics and demand of in-situ deformation observation of rock mass and foundation are presented for stability evaluation. The type，function and usage of MD series instrument are described. The deformation results of rock mass and foundation observed with MD series instrument for four large hydropower projects are summed up. Based on the observed deformation results，the stability of the rock mass and foundation is evaluated for the projects.

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VARIATION OF IN-SITU STRESSES BEFORE AND AFTER
OCCURRENCE OF GEOLOGIC FAULT STRUCTURE

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2004, 23 (23): -3964 doi:
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[PDF 174 KB] (1413)

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Literatures always introduce the relationships between different fault structures and principal stresses. But it was not emphasized that these relationships exist only before occurrence of these faults. No literature introduces the relationships between different fault structures and principal stresses after occurrence of these faults. It makes people always think that the directions of principal stresses keep unchanging after occurrence of the faults. In the area of normal and reversed faults，about thousand tests of in-situ stress measurements by hydrofracture in oil wells were conducted in 86 oil fault fields of 13 big oil regions in China. The results of stress measurements indicate that the directions of cracks by hydrofracture are basically perpendicular to fault strike in normal and reversed fault area，which means that the minor principal stress is always horizontal stress parallel to fault strike. This conclusion is different from that of existing literatures. The methods to calculate the in-situ stresses after fault occurrence are introduced，and the above questions are answered quite well.

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RESEARCH ON TECTONIC STRESS PLANE

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2004, 23 (23): -3970 doi:
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[PDF 322 KB] (1121)

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The concept of tectonic stress plane (TSP) is defined as an ideal curved plane drawn by the locations with different depths where the influence of non-tectonic stress disappears. Therefore，to U-like valleys，three-dimensional model with consideration of different factors，such as valley width，mountain slope，mountain height，gravity loading，and horizontal lateral compression，respectively，is made to conduct 3D finite element modeling research on the spatial variation law of the maximum horizontal principal compressive stress in crust. By mathematical statistics and analysis，the empirical formula is given to show the TSP depth changed with the above factors. The research shows that horizontal lateral compression and mountain height are the major factors to affect the TSP depth，and that when the ratio of the gradient of horizontal lateral compression varied with depth to the gravity gradient is obtained as one，the TSP depth is approxinatelly equal to mountain height.

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DETERMINATION OF MAGNITUDE OF PALAEO-TECTONIC STRESS
AND APPLICATION TO TECTONIC GEOLOGICAL MODELING

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2004, 23 (23): -3979 doi:
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[PDF 211 KB] (1148)

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In the process of numerical modeling of tectonic and the palaeo-tectonic stress field，it is key problem to determine the stress magnitude as the boundary condition of model. The model construction process of Tazhong I# fracture zone in the center of Tarim basin，Xinjiang province，China，is taken as an example to show how to determine the palaeo-tectonic stresses of different beds with different tectonic movement ages. The tectonic geological model is successfully established by using Kaiser effect of the rock and testing result of dislocation in crystal lattice of conchite. The characteristics and resolution of the tectonic evolution are compensatively analyzed.

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SIMPLIFIED TECTONIC STRESS MODEL AND ANALYTICAL SOLUTION FOR CONCAVE-CIRCULAR-ARC FAULT

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2004, 23 (23): -3984 doi:
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[PDF 340 KB] (974)

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In the light of the distribution rule of coal and gas outburst and the tectonic characteristics of neighboring dominant faults in Panyi mine，a simplified two-dimensional mechanics model is set up to obtain the tectonic stresses around the concave-circular-arc fault. Then，the analytical solutions of horizontal and vertical tectonic stresses of the top wall of fault are derived. These analytical solutions show that there is an area where the vertical stress is increased to 2～3 times more than the rock weight induced stress，which is identical with the numerical simulation result. The study result can be applied to explain why the coal and gas outburst occurs in the top wall of fault and shallow lithosphere.

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STUDY ON INFLUENCE OF TOPOGRAPHY ON IN-SITU STRESS BY INTERPRETATION OF MEASUREMENT DATA OF IN-SITU STRESS

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2004, 23 (23): -3990 doi:
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[PDF 536 KB] (1178)

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The measurement results of in-situ stress by hydraulic fracturing in two boreholes are described in detail，including the depth of test section，the maximum and minimum horizontal principal stresses，and the test results of induced fracture impression. In addition，the characteristics of tectonics and topography of study area as well as the relevant rock mass properties are presented. According to the interpretation of test data，it is found that there exist considerable differences between the in-situ stress states of two boreholes which are only 280 m apart. With the aid of three dimensional finite element simulation technique，analysis on the distribution of in-situ stress in study area is carried out，and the influence of topography on in-situ stress state is studied.

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RELATION ANALYSIS BETWEEN IN-SITU STRESS FIELD AND GEOLOGICAL TECTONISM IN SANSHANDAO GOLD MINE

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2004, 23 (23): -3996 doi:
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[PDF 260 KB] (1205)

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Based on in-situ stress measurement，the geological tectonism of Sanshandao Gold Mine is analyzed in detail. The regularity of in-situ stress distribution in the mine and the relationship between in-situ stress field and geological tectonism are studied. The measured 3D in-situ stress state shows a good accordance with the regional tectonic stress field， which strongly proves the correctness of the measured results and has great importance to the design of the gold mine.

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TBA METHOD OF DISPLACEMENT BACK-ANALYSIS USED TO DETERMINE HORIZONTAL IN-SITU STRESS COMPONENT AND ELASTIC MODULUS OF SURROUNDING ROCKS

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2004, 23 (23): -4000 doi:
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[PDF 286 KB] (896)

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For rock mechanics and engineering geology，it is very important to determine in-situ stress and elastic modulus of surrounding rocks. Some existing methods are effective，but majority of them are inadequate for the demand of engineering designs. For this reason，a new displacement back-analysis method，TBA method，is developed，which is different from conventional in-situ stress measurement methods. The principles and procedures of TBA method are described in detail，and two example cases are provided to demonstrate the practicality of TBA method.

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BACK ANALYSIS OF 3D IN-SITU STRESS FIELD OF UNDERGROUND POWERHOUSE AREA OF LONGTAN HYDROPOWER STATION

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2004, 23 (23): -4006 doi:
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[PDF 335 KB] (1067)

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Based on the comprehensive analysis of geological conditions and deformation monitoring，the simplified geological model and excavation model of the experimental cavity are set up. The assumption of linear distribution of in-situ stresses of rock masses along depth is adopted，and based on the in-situ stress measurement，the interval of in-situ stresses is decided for back analysis. Then，the uniform design method and FLAC3D are used to make back-analysis on in-situ stress field of the underground powerhouse area of Longtan Hydropower Station through simulating the excavation of the experimental cavity by steps. 12 excavation cases are selected for simulation. The displacement object function values are calculated for each case by steps. The minimization of object function is made，and the distribution regularity of in-situ stresses of rock masses along depth is obtained. By comparison of measured and calculated displacements and in-situ stresses of rock masses，it is shown that the obtained results are satisfactory and the presented back analysis is reasonable and effective.

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RANDOM IDENTIFICATION APPROACH FOR INITIAL STRESS FIELD
OF ROCK MASS WITH OPTIMAL ALGORITHM

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2004, 23 (23): -4012 doi:
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[PDF 203 KB] (930)

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The optimal algorithm is applied to determine the initial stress field of rock mass according to the stress changes around tunnel after excavation. The inverse problem of parameter identification is formulated as optimal problem，which is solved with BFGS algorithm. The best estimation of stress field is determined by comparing measured and predicted stress changes. The measurement errors are taken into account in the identification of the initial stress parameters of rock mass. The values and direction of the principal stresses can be accurately identified by using proposed inversion algorithm. The computational results show that the proposed identification algorithm is effective for determining the initial stress parameters and has strong ability against the measurement noises.

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NUMERICAL STIMULATION OF TECTONIC STRESS FIELD AT DANJIANGKOU RESERVOIR AREA

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2004, 23 (23): -4017 doi:
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[PDF 582 KB] (1154)

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Finite element model is established according to seismogeological structure of Danjiangkou reservoir area. Then the tectonic stress field and in-situ stress field are calculated by using the software of ANSYS before the reservoir impoundment，and the distribution characteristics of stress field and plastic strain feature in reservoir area are analyzed. The results show that the horizontal deformation is dominant in the reservoir area，with the trends of NWW compression and NEE tension. Faults affect seriously the distribution of stress，and stress concentration occurs in the two sides of faults. Earthquakes easily occur in the places where the horizontal principal tensile stress is bigger or the plastic strain is concentrated. The research achievement can be reference of the induced-earthquake forecast and safety evaluation after the water level of Danjiangkou reservoir rises.

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SIMULATION STUDY OF INDUCED STRESS FIELD
IN REFRACTURING GAS WELL

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2004, 23 (23): -4022 doi:
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[PDF 302 KB] (1647)

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Refracturing is an important technique for enhancing or stabilizing well productivity in the low-permeability oilfield. The reorientation of refracture is fairly difficult and most important in refracturing. The refracture orientation depends on the stress field in vertically-fractured gas well. The stress field，especially the orientation of horizontal principal stress in vertically-fractured gas well，determines the azimuth of refracture creation and refracture propagation. The stress characteristics of vertically-fractured gas well and the main factors affecting the change of stress value and the stress orientation are studied systematically. It is proved that the induced stress resulting from the initial hydraulic fracture and the variation of pore pressure resulting from production can change the distribution of stress field of the gas well and lead to the reorientation of stress field. Using the theory of elasticity and fluid-solid coupling，the mathematical model of induced stress of refracturing gas well is set up and the software is developed to quantitatively analyze and simulate the stress filed before refracturing for vertically-fractured gas well. The application to Xinchang gas field shows that the initial differential stress and production time are the key factors to determine the stress reorientation in refracturing gas well.

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APPLICATION STUDY OF MOVING LEAST SQUARE
METHOD TO SIMULATION OF IN-SITU STRESSES
WITH LARGE DEPTH

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2004, 23 (23): -4028 doi:
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[PDF 257 KB] (968)

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The application of moving least square method to simulation of in-situ stresses with large depth is presented in this paper. Based on the analysis of the principle and model of calculation for the moving least square method，the measured pore pressure data are used to fit the known data. The number of selected known data and the two adjustment coefficients in the model have influences on simulation result. The impact extents of every factors are analyzed. The main factor is the number of selected known data，the second factor is the two adjustment coefficients，and the third factor is the values of data. In addition，the fitting effect of boundary and numerical stability of the moving least square method are discussed. The results show that the moving least square method has better simulation result with satisfactory stability. In order to improve the fitting precision of calculation model，some suggestions are put forward with a practical example.

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STUDY ON DISTRIBUTION CHARACTERISTICS OF IN-SITU
STRESSES FOR PINGDINGSHAN NO.1 MINE

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2004, 23 (23): -4033 doi:
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[PDF 252 KB] (1195)

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The measurement and calculation are presented to determine the in-situ stresses for Pingdingshan No.1 Mine. Based on the determined in-situ stresses，their distribution characteristics are obtained by using theoretical and statistical analyses. The relationship between in-situ stress and geological tectonism is also studied and some meaniful conclusions are obtained.

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STRESS ANALYSIS OF SURROUNDING ROCKS OF HYDRAULIC HIGH PRESSURE TUNNELS UNDER STEEP ROCK SLOPE

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2004, 23 (23): -4038 doi:
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[PDF 452 KB] (1282)

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The distribution of effective stress induced by the seepage from pressure tunnel into rocks under a rock slope is estimated by using the image well method proposed by Harr(1962) and the assumptions made by Zienkiewicz(1958) and Fernandez(1994). The rocks are treated as a homogeneous，isotropic，porous，elastic medium. When loaded by its own weight only，the stress distribution in the rocks surrounding pressure tunnel after excavation and water filling is studied. When the pressure tunnel is designed with the Norway rule，the minor principal stress is tensile in the vicinity of tunnel. The tensile area is like a butterfly and it will be extended with the increment of the rock slope angle. The potential hydrosplitting of rocks around pressure tunnel is taken into account and it will appear in the extended orientation of butterfly. If the thickness of tunnel overburden is increased with 1/8 of the minimum one，the tensile area will be decreased effectively. For the pressure tunnel under steep rock slope，the highest slope angle should be chosen very carefully.

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ANALYSIS ON IN-SITU STRESS FIELD CHANGE DUE TO UNDERGROUND
MINING OF METAL ORE AND ITS INFLUENCE ON RANGE OF ROCK
MASS DISPLACEMENTS

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2004, 23 (23): -4047 doi:
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[PDF 284 KB] (1075)

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The change of in-situ stress field due to underground mining of metal ore has often resulted in major disasters in the metal mines. Stress change not only influences the stability of the deep tunnel，but also changes the range of rock mass displacements due to mining. Based on the results of numerical analysis for a large amount of measured results of in-situ stress in metal mine，the fundamental theoretical formulas of in-situ stress in horizontal and vertical direction are given. The results of the numerical analysis show that the in-situ stress，the range of rock mass displacements and deformations in overlying strata increase with the increment of depth of underground mining. The influence of the tectonic stress in the horizontal direction on range of rock mass displacements is evident，which is very important for deep underground excavation activities，especially for the metal ore mining.

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RELATION AMONG THREE DIMENSIONAL TECTONIC STRESS FIELD，FRACTURE AND MIGRATION OF OIL AND GAS IN OIL FIELD

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2004, 23 (23): -4052 doi:
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[PDF 266 KB] (1198)

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The relation among tectonic stress，migration of oil and gas，and fracture are described. It is pointed out that tectonic stress is an important factor for controlling migration of oil and gas. Formation and development of fracture are closely related to tectonic stress. On the bases of tectonic stress measurement，three dimensional stress field is modeled by using finite element method in Liaohe oil field. It is shown that oil and gas are migrated from high stress area to low stress area，and the low stress area is favorable for the formation of oil field. Fractures are predicted by using criterion of Griffith and criterion of Navier-Coulomb，respectively. Favorable area for oil exploration is pointed out.

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REVIEW AND OUTLOOK FOR WEST CHINA BOREHOLE STRAINMETER NETWORKS

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2004, 23 (23): -4058 doi:
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[PDF 471 KB] (962)

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The West China Borehole Strainmeter Networks are established in the late eighties of the twentieth century. RZB-1 borehole strainmeter with strain sensitivity of 10－10 and strain drift less than 10－7/year were adopted to detect the crustal strain energy built-up from active tectonic processes in order to study earthquake precursors. Strainmeters were installed in 9 observatories in three provinces of west China，Xinjiang，Gansu and Sichuan，and are kept on operating up to the present. This paper summarizes the observation data of strainmeters and their application to monitoring and predicting strong earthquakes occurring round the station. Four kinds of abnormal strain changes before big earthquakes are evident，that is，(1) distortion of strain tides and annual variation form，(2) strain building up of amplitude as much as 10－6 with compressive and tensive jumps，(3) duration of abnormal strain accumulation lasting few months，and (4) axis of the major principal stress turning and pointing to epicentre before the coming shock. At last，three suggestions are brought forward to help developing borehole observation and retative research in China.

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THEORETIC STUDIES ON THE SHORTEST‘QUIET’DISTANCE BETWEEN BOREHOLE STRAIN OBSERVATORY SITE AND SURFICIAL MECHANICAL DISTURBANCE SOURCES

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2004, 23 (23): -4063 doi:
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[PDF 267 KB] (866)

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Rivers，lakes，large storages and railway are some of the main disturbance sources to affect the strain field of borehole strain observatory due to loading and unloading on the surface. In this paper，the corresponding models are established for each of these disturbance sources，respectively，in order to determine the shortest‘quiet’distance between the site of borehole strain observatory and the sources.

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DISTRIBUTED OPTICAL FIBER SENSOR FOR
MONITORING ROCK DEFORMATION

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2004, 23 (23): -4068 doi:
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[PDF 242 KB] (1179)

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Optical fiber sensor is embeded in rock layer of model to find premonitory information of rock deformation and the process of rock damage with mining. Based on optical time domain reflectomter technology，a new type of microbending sensor，named snakelike optical fiber sensor is presented. The sensor can achieve not only microbending，but also macrobending. By using the 2 m-size simulation experiment with analogy material，the feasibility of optical fiber detection of rock deformation is verified.

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STATISTICAL CHARACTER OF STEPING CHANGE ANOMALITY OF COMPONENT-TYPE BOREHOLE STRAIN AND ITS APPLICATION TO EARTHQUAKE PREDICTION IN XINJIANG

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2004, 23 (23): -4072 doi:
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[PDF 353 KB] (953)

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There are five abnormity types of component-type borehole strain in Xinjiang，among which the more important is the stepping change type. The relation is systematically studied between the statistical character of anormality of steping change and the earthquake in Xinjiang. It is shown that the anomality of steping change is of short-impending priority. The abnormality with duration less than 90 days is more than 97% of the recorded data. After three months of anomality appearance，the possibility for earthqake to occur is 55%. The magnitude of strain steping change is between 10－6 and 10－4，which consists of elastic deformation and plastic one，and plastic deformation is the main deformation taking 77% of the recorded steping change anormality. The mirror effect of steping change anormality on earthquake is quite good with mirror effect rate of 85%.

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STRESS STATE AND FRICTIONAL STRENGTH OBTAINED WITH
FRICTIONAL EXPERIMENTS OF FAULT

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2004, 23 (23): -4079 doi:
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[PDF 303 KB] (1034)

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Triaxial frictional experiment is made in laboratory on gabbro. The different stress-displacement curves are obtained from the experiment，and it is shown that the deformation is divided into three stages，elastic deformation stage，elasto-plastic flow-transitional stage，and steady strain-hardening stage. The stress state outside the fault gouge is ascertained by the experiment，while in the fault gouge，different stress states exist in different stages. By analyzing the stress state and strength variation，the change process of the orientation of maximum compressive stress within the fault gouge is illustrated.

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STUDY ON DEFORMATION AND RUPTURE FEATURES OF MODEL III SHEAR FAULTS USING FOCAL MECHANISM SOLUTION OF
ACOUSTIC EMISSION

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2004, 23 (23): -4084 doi:
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[PDF 652 KB] (919)

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The microfracture activity during the deformation of the sample containing two intersecting model Ⅲ shear faults under biaxial load is experimentally studied using acoustic emission technique. Generally，the microfractures tend to migrate from the cut side to the uncut side of the sample and occur alternately between the two faults. The statistics of focal mechanisms of microfractures shows that the faults with smaller and larger angles to the major principal stress dominate the deformation in the earlier and later stages，respectively. The interaction of the two faults controls the instability of the whole sample.

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FORMAT AND STANDARD OF DATA IN CRUSTAL STRESS DATABASE
IN CHINA AND ADJACENT AREA

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2004, 23 (23): -4090 doi:
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[PDF 214 KB] (951)

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The in-situ stress information of crustal stress database in China is grouped into seven categories，earthquake focal mechanisms，well bore breakouts，hydraulic fracturing，overcoring，fault slip，stress and strain in series and orders. The data overlay China and adjacent area. The type of stress indicators，data quality assignment and the format and standard of input data in the stress database are put forward，and consistent with international standard. Up to date，more than 4 700 items of in-situ stress data have been compiled in database. There are 3 320 items for earthquake focal mechanisms，454 items for well bore breakouts，192 items for hydraulic fracturing，340 items for overcoring，420 items for fault slip，as well as many items of relative information of stress and strain from 23 stations. Among the data，over 4 200 items are considered reliable items，with standard deviation of horizontal stress orientations less than 25°.

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DISCUSSION OF TWO ELEMENTARY PROBLEMS
IN ROCK MECHANICS

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2004, 23 (23): -4095 doi:
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[PDF 166 KB] (1052)

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Two important elementary problems of rock (mass) mechanics are put forward，residual stress in rock mass and rock mechanics theory that embodies unloading characteristics，which needs to be established urgently. The main reason and mechanism about forming residual stress are analyzed，and several examples are presented. The theoretical disadvantage resulting from using the loading theory to calculate unloading problem is demonstrated by a simple example. In the past，the influence of initial stress on calculation result is not considered，and the excavation-induced displacement calculated according to existing theory is much smaller than real one. The smaller the Young¢s modulus is and the bigger the in-situ stress is，the bigger the error of calculated displacement for rock (mass) is.