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2009, 28 (08): -0 doi:
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SAFETY CRITERIA OF BLASTING VIBRATION IN HYDROPOWER ENGINEERING AND SEVERAL KEY PROBLEMS IN THEIR APPLICATION

LU Wenbo1，LI Haibo2，CHEN Ming1，ZHOU Chuangbing1，WU Xinxia3

2009, 28 (08): -1520 doi:
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[PDF 223 KB] (1329)

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The status and progress of the mechanism of blasting vibration-induced failure or damage，the evaluation method of dynamic stability for rock slope and surrounding rock mass of underground caverns under blasting vibration，and the influence of blasting vibration on early-aged concrete，etc.，are introduced and analyzed. The domestic safety criteria of blasting vibration and permitted standard of blasting velocity for high rock slope，underground caverns，foundation rock mass and early-aged concrete adopted in field of hydropower engineering are presented，which are compared with those employed in fields of mining. Main problems existing in the study of the damage mechanism induced by blasting vibration and deficiencies of currently adopted safety criteria are analyzed and discussed such as no distinction between different damage mechanisms induced by propagation of blasting seismic wave in rock mass and by dynamic response of rock slope and no consideration of influence of vibration frequency and duration on the adopted safety criteria. Finally，some proposals are given to further study in the fields of damage mechanism of blasting vibration，comprehensive safety criteria expressing blasting vibration incorporating factors of vibration amplitude，frequency and duration，allowable vibration standard for early-aged concrete considering the influence of thermal stress，etc..

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CLASSIFICATION AND RESEARCH METHODS OF ROCKBURST EXPERIMENTAL FRAGMENTS

HE Manchao1，2，YANG Guoxing2，3，MIAO Jinli1，2，JIA Xuena1，2，JIANG Tingting2

2009, 28 (08): -1529 doi:
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[PDF 465 KB] (1438)

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A serial of rockburst samples are tested under rockburst simulating system of China University of Mining and Technology，Beijing. Different methods may be used to obtain information of fragments，including scanning medium fragments with area about 100 mm2 by SEM(scanning electronic microscope) and the large fragments by 3D laser scan technology and measuring fragments size. The measuring parameters include mass，length，width and thickness. In order to analyze fragments of different scales conveniently，fragments are divided into four classes including coarse，medium，fine and micro grains and corresponding research methods are defined. The calculated process and results of fractal dimensions with different methods are introduced with an instance of rockburst granite sample. The linear correlation is obvious when fractal dimensions are calculated by methods of double divided interval for measuring data，image process of binary and small island for 3D laser scan data calculation. The fractal dimensions are different when using different methods. Based on the fractal dimensions of different groups of fragments，the degree of crushing of every group of fragments can be analyzed and base data may be provided to further investigate characteristics of energy changing during rockburst.

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RESEARCH ON UNLOADING CONFINING PRESSURE TESTS AND ROCKBURST CRITERION BASED ON ENERGY THEORY

CHEN Weizhong1，LU Senpeng1，GUO Xiaohong2，QIAO Chunjiang2

2009, 28 (08): -1540 doi:
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[PDF 474 KB] (1654)

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As one of the geological hazards，rockburst is often generated in underground engineering under excavation unloading conditions in high geostress areas. According to actual stress state of surrounding rock during excavation，conventional triaxial and unloading confining pressure tests have been conducted for brittle granite under pre- and post-peak strength using different controlling methods and unloading rates. The rock failure process has been studied；the accumulation-release of energy during unloading，characteristics of deformation，failure and accumulation-dissipation-release and rockburst criterion based on energy theory are also discussed. The test results show that granite is in brittle failure both in pre- and post-peak unloading confining tests；and the brittle characteristic in pre-peak test is more stronger than that in post-peak test. The maximum strain energy stored in rock before failure is controlled by confining pressure and unloading rate both in loading and unloading confining pressure processes using different controlling methods. A new discriminant index is defined that the ratio of energy storage to limited energy storage U/U0 for the same stress in the viewpoint of energy and engineering practice. The index can reflect the change of energy，degree of energy accumulation and rockburst in underground engineering under excavation reasonablely；and the grade and position of rockburst can be determined from numerical results.

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CHARACTERISTICS OF EXPONENTIAL STRENGTH CRITERION OF ROCK IN PRINCIPAL STRESS SPACE

YOU Mingqing

2009, 28 (08): -1551 doi:
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[PDF 288 KB] (1420)

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The exponential strength criterion with direct form denotes influences of the minor principal stress and intermediate principal stress on strength. The parameters in the strength criterion have definite mechanical background. Based on the conventional compression strength，the shear strength tends to be constant as normal stress increases；and the crack angle predicted by Mohr circle is closed to 45°. However，the practical crack angle may not agree with the theoretical value because of small difference between envelope and Mohr circle near the tangent point and the heterogeneity of rock. The parameters in strength criteria are not sensitive to fitting errors because of dispersion of test data in the true triaxial compression；the best fitting solution determined by the minimum fitting error may not be able to describe the strength property of rock correctly. The characteristics of exponential strength criterion in principal stress space are studied. It is suggested that the parameters in strength criterion should be determined based on the fact that the influential index of the minor principal stress is equal to that when the intermediate principal stress is equal to the minor principas stress under the condition that the stress tends to be infinite. And the misfit of test data does not significantly increase.

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DETECTING AND STUDY OF BLASTING EXCAVATION-INDUCED DAMAGE OF DEEP TUNNEL AND ITS CHARACTERS

YAN Peng1，2，LU Wenbo2，SHAN Zhigang1，CHEN Xiangrong1，ZHOU Yong1，ZHOU Chunhong1

2009, 28 (08): -1561 doi:
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[PDF 461 KB] (1406)

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Through detecting and numerical simulation of the blasting excavation-induced damage zone(BEDZ) in Jinping II service tunnel，the damage zones induced by dynamic excavation process including blasting load and in-situ stress transient unloading and static excavation process(redistribution of in-situ stress) respectively are compared and discussed. Damage mechanism of in-situ stress transient unloading to rock mass is also studied using numerical simulation technique. The result indicates that the depth of BEDZ is determined by the existence of in-situ stress. When the direction of tunnel axis is vertical to the maximum principal stress，the depth of BEDZ is larger than that of which the direction of tunnel axis is parallel to the maximum principal stress. The BEDZ of Jinping II service tunnel could be divided into two parts：inner damage zone(IDZ) and outer damage zone(ODZ). The IDZ is mainly induced by the coupling effect of blasting loading and transient unloading of geostress，and it is characterized by a sharp reduction of acoustic velocity of rock mass；while the ODZ is caused by redistribution of in-situ stress and characterized by a gradual reduction of acoustic velocity. In addition，the monitored depth of IDZ in Jinping II service tunnel is significantly larger than that of ODZ，and its distribution on tunnel section is strongly controlled by redistribution stress field after excavation. It is indicated that the effect of in-situ stress transient unloading during blasting is one of the direct causes of the formation of IDZ，which is confirmed by both detecting results and theoretical analysis.

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STABILITY ANALYSIS OF DAGANGSHAN DAM ABUTMENT SLOPE UNDER EARTHQUAKE BASED ON PSEUDO-STATIC METHOD

LIU Jie1，LI Jianlin1，2，ZHANG Yudeng3，QU Jianjun2，LI Jianwu2，LI Yingxia2

2009, 28 (08): -1570 doi:
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[PDF 439 KB] (1623)

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The general engineering situation of an abutment slope located in the complex area of Dagangshan Hydropower Station with the maximum design and check seismic intensity at present in China is introduced. According to relative regulations，the pseudo-static method is selected to analyze the stability of Dagangshan dam abutment slope under earthquake；and the method has been improved correspondingly. Based on reasonable rock mass parameters，anchoring parameters and seismic parameters of slope，the stress，strain，plastic zone of the slope under different earthquake accelerations and the cable¢s stress are studied. Then the variation laws of displacement of critical points changing with slope height under different geological conditions and seismic intensities are pointed out；and the main affected area(sensitive area) of different sections under earthquake，the evolutionary laws of plastic zone in the process of earthquake and the corresponding slip modes are obtained，which could offer references for supports. It is considered that，under the earthquake acceleration with 5% exceeding probability in the next 50 years，large plastic area appears in the rock grade V，accumulation body and the areas with rock dikes γL5，γL6，XL316–1，XL9–15 and β6. The plastic areas become larger and show a tendency of transfixion. It is shown that layers in the rock grade V and rock dikes XL316–1，XL9–15 are important for stability of rock slope. It is also suggested that parameters of rock grade V needs to be adjusted so as to further ascertain the distribution and connectivity rate of rock dikes XL316–1，XL9–15.

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STUDY OF SAFETY CONTROL OF FOUNDATION PIT EXCAVATION BY BLASTING IN NINGDE NUCLEAR POWER PLANT

XIE Bing1，2，LI Haibo1，LIU Yaqun1，XIA Xiang1，YU Chong1

2009, 28 (08): -1578 doi:
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[PDF 440 KB] (1321)

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The rock mass around blasting hole will be damaged when foundation pit is excavated by blasting. Therefore，it is very important to control safety of blasting excavation in order to ensure the bedrock quality. Based on bedrock blasting excavation in Ningde Nuclear Power Plant，the attenuation laws of site blasting vibration is obtained through in-situ test；and the relationship between damage depth caused by blasting and peak particle vibration(PPV) of rock mass 30 m away from the blasting center is established through the site monitoring and numerical simulation. Accordingly，velocity threshold is determined based on different allowable damage depths of foundation pit excavation by blasting. It is shown that controlling method and velocity thresholds effectively ensure safety of the bedrock under blasting excavation.

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AN EXPERIMENTAL STUDY OF MIXED-MODE I-II DYNAMIC FRACTURE OF MARBLE

FENG Feng，WANG Qizhi

2009, 28 (08): -1586 doi:
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A diametrical impact experiment with three loading angles(the angles between loading direction and crack line are 0°，10° and 19°respectively) was performed for the geometrically similar cracked straight through flattened Brazilian disc specimens of three sizes(f50 mm，f130 mm，f200 mm) by split Hopkinson pressure bar system. Time-history curves of stress intensity factors(KI(t) and KII(t)) of mixed-mode I-II dynamic fracture，as well as the mode mixture ratio(KI(tf)/KII(tf)) at the initial time of fracture，were determined by experimental numerical method. Within loading time of 100 μs，the mode mixture ratio is affected by the size of specimen：when loading angle is 10°，in which the static condition is mixed-mode loading，the specimen of f50 mm is still in the state of mixed-mode loading，and so is under the dynamic loading condition；however，the f130 mm and f200 mm specimens are in the state of mode II loading. The difference is caused by the disturbance of interaction of stress wave and crack surfaces. Rock fracture toughness of both modes I and II(KId and KIId) has size effect；and the size effect of KIId is much more remarkable than that of KId，which can be explained from the viewpoint of energy. Considering the first nonsingular constant term in Williams series expansion of stresses near the crack tip，T stress has no effect on the computation of dynamic stress intensity factor，however it affects the crack initiation angle for the mixed-mode dynamic fracture.

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PORE DISTRIBUTION REGULARITY AND ABSORPTION-DESORPTION CHARACTERISTICS OF GAS COAL AND COKING COAL

LIU Gaofeng，ZHANG Zixu，ZHANG Xiaodong，LU Runsheng

2009, 28 (08): -1592 doi:
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[PDF 201 KB] (1388)

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Hg-injection experiment was carried out with coal samples in the gas coal from Caiyuan Mine in Weishan City，Shandong Province，and the coking coal from Malan Mine in Gujiao City，Shanxi Province，to find out the distribution regularity of pore volume and specific surface area in various pore sizes. The absorption- desorption experiment on binary-component gas(CH4/CO2) was carried out with equilibrium water coal sample to analyze the influence on coal adsorbing gas in deep coal bed in the aspect of pore configuration. The results indicate that the pore configuration of the coking coal is more complicated than that of gas coal；and there are smaller and micro pores in coking coal rather than in gas coal. The absorption capacity of coal is determined by the distribution of micro pores；and the most effective absorption pore radii are below 10 nm. The absorption capacity of coking coal is stronger than that between gas coal. It is analyzed that the absorption capacity difference of gas coal and coking coal would lead to the phenomenon that absorption in high-pressure stage is less than that in low-pressure stage in the experiment. Based on the research of the pore distribution and absorption-desorption characteristics of coal，the absorption capacity of coal in deep coal bed can be revealed at micro level；and the characteristics and mechanism of absorption-desorption of coal are explored，which enriches the absorption-desorption theory of coal and is of great significance to coal and gas outburst prevention and coal-bed methane exploitation.

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ACOUSTIC EMISSION CHARACTERISTICS OF GRANITE UNDER STRAIN ROCKBURST TEST AND ITS MICRO-FRACTURE MECHANISM

MIAO Jinli1，2，HE Manchao1，2，LI Dejian1，2，ZENG Fanjiang1，2，ZHANG Xi1

2009, 28 (08): -1603 doi:
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[PDF 1086 KB] (1670)

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The frequency-spectrum and time-frequency characteristics of acoustic emission original wave data are analyzed，which are obtained through monitoring strain rockburst test under true triaxial stress state with special characteristics of unloading one side of the specimen suddenly. The micromechanism of rock failure process is analyzed based on the microstructure SEM(scanning electronic microscope) images of Sanya granite samples before and post failure，frequency-spectrum and RA(rise time/amplitude) characteristics of AE waveform obtained during rockburst. When the rock sample is relatively stable，AE waves with the feature of low-amplitude and low-energy are formed，and microcracks slip or split in local zone correspondingly. However，the amplitudes of AE waves increase not only in low-frequency range but also in high-frequency during rockburst，which implies that high energy is releasing and macrocracks in the rock specimen are generated. The RA values increase before rockburst and decrease during rockburst. High RA value is wave generated by tensile cracks and low RA value is wave generated by shear cracks propagation. The test results reveal that many relative high-frequency- low-amplitude waves and low-frequency-high-amplitude waves generated during rockburst are related to transgranulation/cleavage tensile microcracks and intergranular shear macrocracks respectively，which shows the characteristics of high energy releasing and low RA value.

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STUDY OF CT MESO-EXPERIMENT OF ROCK DAMAGE UNDER
CYCLIC LOAD

LI Shuchun1，2，XU Jiang1，YANG Chunhe1，3，PU Yibin2，MA Wei2

2009, 28 (08): -1609 doi:
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[PDF 260 KB] (1424)

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The computerized tomography(CT) real-time tests of fatigue damage meso-propagation law of rock under two-grade cyclic loads have been accomplished using specified loading equipment of CT machine. It is shown that in the first grade of cyclic load equal to the strength of 38% to 76%，the standard deviation of CT number under the maximum stress increases with the increase of the number of cycle；while the density and CT number tend to decrease with relatively small variations. The process shows that the accumulation of damage is slow. In the second grade of cycle load equal to the strength of 45% to 90%，although the number of cycle is less than that in the first grade，the changes of standard deviation of CT number under the maximum stress，density and CT number are larger than those in the first grade；in the cycle before failure，the standard deviations of CT number，density and CT number change greatly.

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NUMERICAL SIMULATION AND EXPERIMENTAL STUDY OF
DAMAGE RANGE OF SURROUNDING ROCK IN LARGE
TUNNEL UNDER BLASTING EXCAVATION

ZHANG Guohua1，CHEN Libiao2，XIA Xiang1，LIU Minggui1，LI Qi1，3

2009, 28 (08): -1619 doi:
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[PDF 1838 KB] (2050)

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Based on the in-situ monitoring of acoustic velocity in Damaoshan Tunnel with large section，accumulative damage range of surrounding rock is studied in tunnel with large section excavating with two side-wall pilot tunnel method of the advancing to-and-fro blasting operations. Monitoring results of acoustic velocity show that surrounding rock will cause damage at a certain degree and range in advancing to-and-fro blasting load operations. The accumulative damage range of surrounding rock is mainly determined by the blasting of excavating face of pilot tunnel I which is parallel to it. The range increases with the approaching of excavating face of pilot tunnel I，and reaches the maximum value when the two are flushed. However，when the excavating face of pilot tunnel I gradually moves away and the blasting of pilot tunnel III starts to get through，it only leads to the increase of damage degree；the damage range of surrounding rock does not expand. Therefore，when simulating the damage range of surrounding rock in advancing to-and-fro blasting load operations，single blasting parallel to monitoring section can be simulated as repeated to-and-fro blasting vibrations approximately. The vibration velocity which determines the damage range of surrounding rock can be transformed into explosion pressure through software DYNA；and then the pressure can be transferred to anisotropic damage model of rock realized by UDEC software. Compared with monitoring results，this method can better simulate the accumulative damage range of surrounding rock in advancing to-and-fro blasting load operations so as to provide for reference in similar engineering projects.

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STUDY OF KEY TECHNIQUES OF DYNAMIC LOADING CT TEST DEVICE FOR ROCK-LIKE MATERIAL

DING Weihua1，CHEN Houqun2，YIN Xiaotao3，LIU Shaocong1，ZHANG Jian1，FENG Yu1

2009, 28 (08): -1628 doi:
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[PDF 822 KB] (1216)

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A portable test device based on the conventional medical CT scanner is developed；and a test system of rock-like material is formed. Some key problems in rock-like material test by CT are analyzed. Concrete test procedure of CT and some problems during test，including sample binding，alignment and fixing，are summarized. The preliminary dynamic pressure results of concrete by CT are given. And concrete crack rheological test by CT is carried out as well. The results indicate that this loading device satisfies the design demand. Concrete crack evolvement during dynamic loading process can be detected with a similar real time by CT；and crack rheological effect can be ignored in many cases. It has brought forth some new ideas to the study of dynamic behavior and damage law of rock-like material under dynamic loading.

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MODEL TEST ON METRO STATION CONSTRUCTED BY COMBINATION OF SHIELD METHOD AND SHALLOW-BURIED TUNNELING METHOD

LIU Weining1，LU Meili2，ZHANG Xinjin1，LI Zhaoping1

2009, 28 (08): -1639 doi:
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[PDF 480 KB] (1472)

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In order to solve the contradiction of construction time limit for running tunnel constructed by shield method and station in China，the new-style station construction method，in which the station is constructed by shield method and mining method，is put forward. In the model test study with scale ratio of 1∶10，the simulation of model stratum，excavation scheme and tunnel support scheme are introduced；and the station construction process is reappeared. The variation laws of strain，convergence of the shield segments and displacement of the soil around station tunnel are achieved. The results show that the excavation and tunnel support schemes can ensure the safety of the station under the conditions of model stratum and in-situ stress，by which the feasibility of station construction technology recommended is proved as well.

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INFLUENCE OF PRE-REINFORCEMENT MEASURES ON EXCAVATION STABILITY OF TUNNELLING

CHEN Weitao1，WANG Mingnian2，ZHANG Lei2，WEI Longhai2，HE Yulong2

2009, 28 (08): -1645 doi:
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[PDF 207 KB] (1359)

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RESEARCH ON DEVIATORIC STRESS VARIATION LAWS FOR DEEP FROZEN CLAY AT DIFFERENT TEMPERATURE GRADIENTS

ZHAO Xiaodong1，2，ZHOU Guoqing1，2，LI Shengsheng3

2009, 28 (08): -1651 doi:
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[PDF 261 KB] (1102)

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The loading and unloading triaxial tests were carried out on the deep frozen clay at four temperature gradients using the method of freezing before K0 consolidation，and attenuation law for deviatoric stress as well as deviatoric stress increasing rates in the process of loading and unloading was investigated. The results show that the increasing rate of deviatoric stress at different temperature gradients is similar to that in the homogeneous temperature fields，which can be fitted by modified Duncan-Chang hyperbolic model. However，the influence of temperature gradients on the deviatoric stress is larger than that of the temperature. The most obvious regularity observed in the initial stage of loading and unloading process is that both increasing rates of deviatoric stress and attenuation degree are weakened by the temperature gradients. The attenuation law for deviatoric stress under the same axial deformation can be described by the attenuation factor A；and the relationship between A and temperature gradients agrees well with that of the generalized hyperbolic model. The unloading process enhances the attenuation trend of deviatoric stress increasing rates for deep frozen clay at the initial stage both in loading and unloading processes；and the influence of unloading process on the attenuation rates along with the amplitude of the deviatoric stress is obviously larger than that of the loading process as the temperature gradients increase. The strength of deep frozen clay would be overestimated if the effects of non-homogeneous temperature fields and unloading path for the frozen walls are neglected.

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DEVELOPMENT OF RANDOM MESOSTRUCTURE GENERATING SYSTEM OF SOIL-ROCK MIXTURE AND STUDY OF ITS MESOSTRUCTURAL MECHANICS BASED ON NUMERICAL TEST

XU Wenjie1，HU Ruilin2，YUE Z Q3

2009, 28 (08): -1665 doi:
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[PDF 678 KB] (2076)

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The mesostructure characteristics significantly affect meso-failure evolution mechanism and the macro- mechanical characteristics of soil-rock mixture(S-RM) under external forces. It is very important for the improvement of theoretical system of S-RM mechanics to study the mesostructural mechanics of S-RM based on its mesostructural characteristics. Accordingly，the statistics，geometry，random simulation techniques，etc. are used，and the random mesostructure generation system of S-RM based on arbitrary polygonal and elliptic rock blocks(R-SRM2D) has been developed. Based on R-SRM2D，a series of random S-RM samples with different rock block contents，granularity compositions，rock block spatial distributions and soil-rock interfaces are generated，which is used to study the relationship between mesostructure difference and meso-failure mechanics or macro- mechanical characteristics of S-RM by numerical test. Meaningful results have been obtained theoretically. It is indicated that with the increment of rock block content，the elastic modulus and uniaxial compressive strength of S-RM increase；at a certain rock block content，the macro-strength of S-RM decreases with the increment of rock block fractal dimension；the compressive strength of S-RM reaches maximum value when the longer axis of rock blocks is perpendicular or parallel to the principal stress axis；when the angle between the longer axis of rock blocks and the principal stress axis is equal to (45°－φs/2)，the compressive strength of S-RM reaches minimum value；the cementation action of soil-rock interface makes the macro-strength of S-RM increases obviously，whose uniaxial compressive strength increases nearly twice.

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ENERGY EQUIVALENT METHOD FOR CALCULATING PARAMETERS OF M-C AND D-P CRITERIA AND ERROR ANALYSIS

CHU Xihua，XU Yuanjie，KONG Ke

2009, 28 (08): -1673 doi:
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[PDF 516 KB] (1536)

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Based on the description of Mohr-Coulomb(M-C) and Drucker-Prager(D-P) yield criteria with invariant of stress，a formula for error estimation of unit strain energy between the two stress states is established in the deviatoric plane of the principal stress space，which satisfies M-C and D-P yield criteria respectively. A general procedure to transform M-C material parameters to D-P analysis parameters is obtained. The results show that general calculation formula，error estimation for parameters matching from M-C to D-P are provided；and an explanation of mechanics meaning of matching is presented as well. It is also shown that the differences among parameters matching methods are brought by different error control conditions；and the zero error of energy in the deviatoric plane can be expressed by Lode angle or stress path. Furthermore，the multivalue of Lode angle according to zero error of energy and the equivalency of serials of D-P criteria are discussed.

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EXPERIMENTAL STUDY OF SIMULATION OF COAL AND GAS OUTBURST

YIN Guangzhi1，2，ZHAO Hongbao1，2，XU Jiang1，2，WANG Weizhong1，2

2009, 28 (08): -1680 doi:
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[PDF 576 KB] (1400)

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Based on self-developed large-scale simulation test system of coal and gas outburst，experimental verification of its reliability is carried out；and experimental study of simulation of variation laws of intensity of coal and gas outburst is done under different water contents of coal as well. It is shown that：(1) the simulation results obtained by the large scale simulation test system of coal and gas outburst are fairly consistent with actual results of coal and gas outburst；(2) the reliability is satisfactory；(3) both possibility and intensity of coal and gas outburst decrease with the increase of water contents of coal；and (4) under the test conditions，the relationship between the water contents and intensity of coal and gas outburst is conic.

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RESEARCH AND DEVELOPMENT OF TESTING APPARATUS OF COAL SOLID-GAS COUPLED MESO-MECHANICS

CAO Shugang，LIU Yanbao，LI Yong，ZHANG Liqiang，WANG Jun

2009, 28 (08): -1690 doi:
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[PDF 898 KB] (1488)

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A coal solid-gas coupled meso-mechanical testing apparatus has been developed，which can be used to study the law of deformation and destruction of gas-bearing coal. Some key technical issues，such as sealing method，light transmitting mirror technique，etc.，have been further analyzed. The apparatus is comprised of loading system，gas charging system，microscopic observation system and acoustic emission monitoring system. Compared with the current meso-mechanics apparatus，it has the following advantages. Firstly，three types of force state are provided including uniaxial compression，plane strain and triaxial compression(s2 = s3). Secondly， several measuring methods are offered，and the real-time observation of the micro-structural images and the collection of stress-strain and acoustic emission signals are realized during experimental process. Thirdly，it is gas-tight and exploding endurable，which makes it similar to actual testing environment. Fourthly，the structure is very simple，low-cost and high reliability. The meso-mechanics experiments have been carried out using this apparatus under gas pressure of 1.0 MPa and confining pressure of 1.0 MPa(s2 = s3). And the apparent images and acoustic emission characteristics in failure process of coal specimens have been obtained. The formation process of tension cracks and their propagation in regional areas before and after failure have been analyzed. It is shown that the testing apparatus can provide a new and practical test method for solid-gas coupled experiments.

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RESEARCH ON INFLUENCE OF CRACK LENGTH ON TEST VALUES OF ROCK DYNAMIC FRACTURE TOUGHNESS

ZHANG Sheng1，WANG Qizhi2，LIANG Yalei1

2009, 28 (08): -1696 doi:
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[PDF 352 KB] (1407)

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In order to study the influence of crack length on test values of rock fracture toughness，one-size holed-cracked flattened Brazilian disc of marble specimen with diameter of 80 mm and specimens of different cracks lengths were performed with split Hopkinson pressure bar system. The strain waves in elastic bar and fracture mode of specimens with different crack lengths were obtained；and the dynamic fracture toughness of marble were determined by experiment-numerical analysis. It is shown that the average dynamic fracture toughness is 2.6 times larger than the average static one under average loading rate of 2.96×104 MPa·m1/2·s－1；and the dynamic fracture toughness test values do not vary with crack lengths significantly compared to the static one. Moreover，the method to determine dynamic fracture toughness independent of size and configuration is discussed.

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EXPERIMENTAL STUDY OF MOTION CHARACTERISTICS OF WEAK INTERCALATION IN ROCK MASS BLASTING

ZHANG Jichun1，XIAO Zhengxue2，ZHENG Shuangying3，GUO Xuebin2，OUYANG Ji1，XIAO Dingjun2

2009, 28 (08): -1703 doi:
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[PDF 387 KB] (1056)

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Taking one-hole bench blasting as prototype，the blasting experiment of concrete models with a weak intercalation is carried out. The motion state of intercalation in blasting process can be observed using high-speed digital camera，and the motion characteristics of intercalation and variation laws under the conditions of different charges，moisture contents and the minimum burdens are analyzed. The research results show that the clear motion images of intercalation more than 2–4 cm away from blast-hole center can be obtained by high-speed digital camera，which confirms the pushing action of blasting upon the weak intercalation adjacent to blast-hole；the maximum motion velocity of intercalation in concrete model blasting can reach 450 m/s；and with the increase of the distance from the blast-hole center，the motion velocity linearly decreases approximately and its decrease range is mainly affected by the moisture content and charge；the motion velocity of intercalation and the maximum motion distance increase with the increase of charge，moisture contents and the minimum burden；moreover，the charge plays an important role in the final motion distance of intercalation.

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FIELD TEST STUDY OF BLAST-RESISTING OF A NEW COMPOSITE ANCHORAGE TYPE OF STRUCTURE IN ROCK——
ANALYSIS OF MACRO EFFECT AND MEASUREMENT RESULT

LU Weiguo1，GAO Qian1，ZENG Xianming1，2，LI Shimin2，LIN Dalu2，HOU Fengze3

2009, 28 (08): -1713 doi:
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[PDF 430 KB] (1086)

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In order to research whether the new composite anchorage type of structure can improve the blast-resisting behavior for rock cavities，comparative field blast-resisting tests of new composite anchorage type of structure and single anchorage type of structure have been carried out. It is shown that critical damage load of cavity of new composite anchorage type of structure is 143% against that of the single anchorage type of structure. For the damage extent，the cavity of single anchorage type of structure is 2.5 times larger than that of new composite one. Under the lower blast load，the value of the vibration acceleration of the single anchorage type of structure is 1.6 to 12.3 times larger than that of the new composite one. The average displacement of the new composite anchorage type of structure is 65% compared with that of the single one. The time stress wave time acting on new composite anchorage type of structure is 2.5 to 5.0 times larger than that of the single one. The maximum strain of single anchor bolts is 2 to 4 times and even 6.9 times larger than that of the new composite one. The maximum surface strain of single anchorage structure is 2 times larger than that of the new composite anchorage structure. The new composite anchorage type of structure has an obvious reducing effect. So it is feasible to adopt the new composite anchorage type of structure to reinforce the rock cavity，which has great technical and economic benefits.

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ANALYSIS AND DISCUSSION OF FAILURE MECHANISM AND FRACTURE SURFACE OF SLOPE UNDER EARTHQUAKE

ZHENG Yingren1，2，YE Hailin1，3，HUANG Runqiu3

2009, 28 (08): -1723 doi:
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[PDF 1712 KB] (2185)

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The failure mechanism of slope under earthquake is the premise of slope¢s dynamic stability analysis. Presently，pseudo-static method and dynamic time-history analysis method are commonly used，which regard the failure mechanism of slope under earthquake as shear failure，and take the shear sliding surface obtained by limit equilibrium method as failure surface under dynamic effect of earthquake without considering the tension failure under seismic load. It may lead to inaccuracy in the stability analysis of slope under earthquake. Investigation of the slopes during Wenchuan earthquake shows that tension failures mostly appear in the upper part of the landslides，and even some rock and soil masses are thrown out，which is an obvious enlightenment. So the FLAC dynamic strength reduction and program of FLAC3D with the function of tensile and shear failure analysis are adopted to study failure mechanism of slope under earthquake numerically. The study shows that the failure of slope under earthquake is made up of the tension failure in the upper part of the fracture zone and the shear failure in the lower part instead of shear sliding failure. A method of locating the fracture surface of slope under earthquake through several ways is provided，which is an accurate foundation for dynamic stability analysis of slopes.

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DISCUSSION ON “RESEARCH ON GREY-CUSP-CATASTROPHIC DESTABILIZATION PREDICTION MODEL OF TUNNEL SURROUNDING ROCK AND PRIMARY SUPPORT SYSTEM”

2009, 28 (08): -1726 doi:
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[PDF 202 KB] (978)

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REPLY TO “DISCUSSION ON ‘RESEARCH ON GREY-CUSP-CATASTROPHIC DESTABILIZATION PREDICTION MODEL OF TUNNEL SURROUNDING ROCK AND PRIMARY SUPPORT SYSTEM’”

XU Jiancong1，2

2009, 28 (08): -1728 doi:
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[PDF 151 KB] (1016)

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