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2007, 26 (12): 0-0 doi:

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STUDY ON IN-SITU TESTS OF MECHANICAL CHARACTERISTICS
ON SOIL-ROCK AGGREGATE

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2007, 26 (12): 2377-2377 doi:

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Soil-rock aggregate(RSA) is a special kind of geomaterial composed of soils and irregular rock blocks. The mechanical properties of RSA are rarely known although RSA distributes here and there in the mountainous area in China. In-situ large-scale test can explore the mechanical properties of RSA effectively since RSA is described as a kind of heterogeneous and nonuniform material. Here，the method of in-situ test for soils and rocks is referred；and a practical procedure of in-situ test for RSA is proposed and normalized including the method of push-shear test and press-shear test，equipments，steps，and some key points. Combined with the typical RSA at the Baiyian Landslide in the Three Gorges Reservoir area，23 large-scale in-situ tests(including push-shear and press-shear) are carried out. The curves of shear stress-displacement，curves of shear strength，failure mode，and shear strength parameters for RSA with different rock contents，sample sizes and stress states are obtained from tests. The results show that RSA has typical complete curves of stress-strain，strain softening，and high internal friction angle，which are caused by the special structure of RSA. It is also indicated that rock content is an important factor for strength and failure mode of RSA and that dimension effect is observed in the in-situ tests of RSA. The procedure of in-situ tests and results obtained from the tests can provide scientific data for further study of RSA.

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FACTOR OF SAFETY ANALYSIS OF BEDDING ROCK SLOPE
UNDER SEISMIC LOAD

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2007, 26 (12): 2385-2385 doi:

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Based on the strength reduction method，a new method to determine the factor of safety of bedding rock slope under seismic load is proposed. The equilibrium condition is estimated based on the trend of the key points¢ displacements or velocities. The slide surface is also determined by the velocity or displacement vectors of the unstable condition. Based on the new method，the factor of safety of Zhongjiawan bedding slope is calculated by UDEC and compared with the results obtained by limit equilibrium method(LEM). It is revealed that the value calculated by UDEC is close to that by LEM，which indicates that the new method is feasible and reasonable. The influences of height and angle of bedding slope，inclination of interface as well as seismic parameters including amplitudes and frequency on the factor of safety of bedding rock slope under seismic load are analyzed.

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STUDY ON THERMO-HYDRO-MECHANICAL COUPLING MODEL FOR UNSATURATED ROCK

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2007, 26 (12): 2395-2395 doi:

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Considering the effects of temperature on the coefficient of viscosity and void ratio of liquid，liquid flow caused by temperature gradient，heat flow on water potential gradient and heat flow due to thermal convection，based on Darcy¢s law，Fourier¢s law，the equations of equilibrium，the conservation equations of mass and energy are derived using two basic variables for unsaturated porous media，i.e. void ratio and volumetric liquid water content . And then the thermo-hydro-mechanical coupling model is applied to simulate the evolution law of unsaturated water flow in surrounding rock and concrete support of a claystone shaft with considering excavation and ventilation，by which the variations of pore pressure，temperature and saturation degree in claystone and concrete after tunnel excavation and ventilation are obtained. The study has significant effects for underground oil， nuclear waste disposal，design and construction for tunnel in cold regions.

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RETROSPECTIVE ANALYSIS OF TBM ACCIDENTS FROM ITS POOR FLEXIBILITY TO COMPLICATED GEOLOGICAL CONDITIONS

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2007, 26 (12): 2404-2404 doi:

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Tunneling by tunnel boring machine(TBM) in unfavorable engineering geological conditions often incurs accidents from engineering geological problems when the lectotype and collocation of TBM are ignored. These problems reflect the inherently poor flexibility of TBM to complicated geological conditions. Three cases of TBM accidents occurred respectively in Kashmir of India，Yunnan Province and Taiwan of China，deserve retrospective analysis. They are unique examples where TBM encountered huge amounts of accidents and resulted in disasters，which were replaced by the drilling and blasting method(DBM) in the end. The occurrence of these problems implies the unreasonable decision-makings，which are based on scare considerations of the risks but on blind believes of the TBM advantages to a certain extent. As a result，the disadvantages of TBM are obviously exposed，which bucks its advantage as fast advancement rate. Therefore，the construction time is delayed for 1–8 years. From the three cases，it is known that，in regions with active tectonic movements，intensively fractured rock mass and enriched groundwater flows，the selection of tunneling method must face the problems of uncertainty and unpredictability of complicated geological conditions. Approaches purely based on technical innovation and engineering experiences cannot solve all of these problems very well. Therefore，risk analyses should be carefully made，instead of the wishes to obtain one mixed TBM with multiple functions and feasible to various complicated geological conditions. In a word，the selection of TBM should be based on argumentation and demonstration of multi-disciplinary experts to support scientific decision-makings.

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RESEARCH ON PREDICTION METHOD OF CONCRETE FREEZE-THAW DURABILITY UNDER FIELD ENVIRONMENTS

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2007, 26 (12): 2412-2412 doi:

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Lots of standard freeze-thaw experimental data cannot be directly used to predict freeze-thaw durability of concrete in field because of difference between laboratory and field environments. How to simulate the damage development process of concrete under freeze-thaw cycles in field by the standard freeze-thaw experimental data in laboratory and then to obtain a prediction of concrete freeze-thaw durability is necessary for engineering. The difference between laboratory environment and field environment is analyzed firstly，and then it is assumed that concrete pore distribution is relative constant and concrete in field is placed in saturated environments. On the base of mechanism of fatigue damage，the Miner¢s damage cumulative principle and equivalent principle are used to simulate freeze-thaw damage process of concrete in field by climatological data. The obtained formula can be used to calculate equivalent numbers of freeze-thaw cycles in laboratory by the numbers of freeze-thaw cycles in field，which can connect different freeze-thaw environments in laboratory and field. Using standard freeze-thaw experimental data and equivalent laboratory freeze-thaw cycle number，the freeze-thaw life of concrete in field can be predicted. The prediction results comparing with field data of concrete structures in Shisanling Reservoir and some ports in North China are satisfied.

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EXPERIMENTAL STUDY ON STRENGTH AND DEFORMATION PROPERTIES OF HOLLOW CYLINDRICAL SPECIMENS OF MARBLES

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2007, 26 (12): 2420-2420 doi:

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A series of pseudo-triaxial compression tests on hollow specimens of marble with fine and medium crystals without considering inner pressure were carried out to study the effects of nonuniform stresses on the bearing capacity and deformation. There are no essential differences in the deformation behavior between solid and hollow specimens when the axial deformation is small. With the deformation increasing，failure in the hollow specimen starts from the hole wall for the minor principal stress；and the bearing capacity drops off. According to the stress state based on the analysis of linear elastic mechanics and the assumption of failure synchronization in the whole specimen，the strength provided by Coulomb criterion is a smaller estimated one. The strength property of hollow cylinder specimen is influenced by following factors. On the shear failure surface of specimen，normal force and shear force provided by confining pressure and axial load respectively are determined by the balance of the total forces and have no relation with hole. The hole just induces the nonuniform distribution of stresses. The bearing area becomes small for the hole；and the strength provided by confining pressure will increase. On the other hand， the failure in the specimen happens step by step；the bearing capacity of the whole specimen provided by cohesion or material strength will be less than that of the solid specimen，and decreases with confining pressure and inner diameter increasing. The experimental results provide a reference to understand the strength criteria，numerical calculation and failure of tunnel and well.

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STUDY ON SEALABILITY OF UNDERGROUND ENERGY STORAGE IN DEEP SALT FORMATION IN YUNYING AREA，HUBEI PROVINCE

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2007, 26 (12): 2430-2430 doi:

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For the feasibility analysis of the energy storages in deep salt formation in China，a comprehensive analysis of the sealability of salt caverns as oil/gas storages in the Yunying salt mine in Hubei Province is proposed. In the salt mine，the salt layers are usually intersected by many indissoluble or slightly soluble interlayers. Considering these sedimentary characteristics，a series of experiments concerning the sealability of the salt storages are carried out. The experiments，i.e. direct shear test，Brazilian test and microscopic test，on the mechanical properties of the interfaces between salt and anhydrite layers show that the salt and anhydrite layers have been bonded perfectly，and the salt/anhydrite interfaces are actually not weak as expected. This unique feature benefits definitely the stability and sealability of the salt storage caverns. To further investigate the permeability，the sealability and the loading capacity of the bedded salt rocks，an in-situ high water pressure test on a borehole in the bedded salt formation is performed recently. From the in-door and in-situ experiments，a conclusion can be drawn that the bedded salt formation in the Yunying salt mine satisfies completely the sealability requirement of the energy storage caverns.

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STUDY ON ENERGY YIELD CRITERION OF GEOMATERIALS

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2007, 26 (12): 2437-2437 doi:

[PDF] 291 KB (1970)

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After comparing the difference of materials properties and the induced difference of mechanical characteristics between metals and geomaterials，it is concluded that geomaterials are frictional materials with multiphase and have frictional characteristics. By analyzing the mechanical elements of two kinds of materials，it is considered that there are frictional stresses in the mechanical elements of frictional materials. By generalizing the Tresca yield criterion and the Mohr-Coulomb yield criterion，the energy yield criterion considering only simple shear surface is deduced，which proves that the Tresca yield criterion and the Mohr-Coulomb yield criterion are the simple shear energy yield criteria of metals and geomaterials，respectively. The energy yield criterion about three shear surfaces is discussed；then the triple shear energy yield criterion and corresponding Drucker-Prager yield criterion of geomaterials are established. The Mohr-Coulomb yield criterion and the triple shear energy yield criterion are used to validate the true triaxial test data. The errors show that the results of the triple shear energy yield criterion are more close to the test data than those of the Mohr-Coulomb yield criterion，which proves that the energy yield criterion is correct. At last，a simple slope is computed using the Mohr-Coulomb yield criterion and the triple shear energy yield criterion respectively；and the results indicate that the Mohr-Coulomb yield criterion is more conservative than the triple shear energy yield criterion.

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FRACTOGRAPHY OF SANDSTONE FAILURE UNDER TEMPERATURE-TENSILE STRESS COUPLING EFFECTS

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2007, 26 (12): 2444-2444 doi:

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The scanning electron microscope(SEM) is employed to study sandstone fractography under thermo- mechanical coupling effects. Through several fracture morphologies at different temperatures，such as cleavage，quasi-cleavage，fatigue，secondary and fragmentary，local ductile，intercrystalline fracture and some special fractographies，the temperature has been confirmed to influence actually micro fracture mechanism of sandstone. The fracture mechanism will transfer from brittle fracture mechanism to brittle-ductile coupling fracture mechanism with the increasing temperature. At low temperatures，the fractography of sandstone is quite smooth；but at high temperatures，the fractography is rougher，and a great deal of plastic deformation is observed obviously. Therefore，the fractography is more various and complicated after high temperature effects. The reasons can be summarized as follows. The thermal motion of mineral particle，crystals and atom will be strengthened after temperature effects；and sandstone will fracture at more widely positions. Several fracture mechanism models had been used to interpret some failure phenomena. In addition，some novel rock fractographies were reported. At last， it is concluded that any micro fractographies which has been reported in metallic fractography can also be found in rock fractography. Moreover，rock fratography is more various and more complicated because of rock own characteristics and thermal-mechanical coupling effects.

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DETERMINATION AND APPLICATION OF JOINTED ROCK MASS PARAMETERS BASED ON FINE STRUCTURE DESCRIPTION AND NUMERICAL EXPERIMENT

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2007, 26 (12): 2458-2458 doi:

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The effects of fracture，joints and other inter-block gaps on rock mechanical properties can be very significant. A method based on site investigation and numerical test is conducted to determine and optimize the mechanical properties for engineering design. Contrasting with field experiment，it is convenient，fast and cheap. The method makes it possible to develop large sample rock mass in-situ tests，which will make a big push for the parameter risk prediction and reliability analysis of engineering rock masses. The research mainly includes two parts of work，i.e. the in-situ fine structure description and numerical test. Engineering geology information which is the input for numerical test is the base of the analysis. Detailed geological investigation is the soul of the fine structure description. Based on statistical window，geological sketch and digital photography，a new method for rock mass fine structure in-situ mapping is developed. It has already been taken into practice and has received good comments in Jinping First Stage Hydropower Station. After obtaining the basic geological information，the rock mass structure model is established through the in-situ mapping. In order to verify the validity and precision of the numerical analysis，a physical model direct shear test is carried out. According to the comparison，the relative error between the numerical test and the physical test is less than 10%. It is precise enough for rock mass mechanical parameter determination. Taking the Jinping First Stage Hydropower Station for example，large sample numerical experiments are carried out in the dam site. The complete stress-displacement curve，stress distribution，displacement distribution and plastic zone distribution are given by the numerical test. By comparison，the results obtained from numerical experiment and those from rock mass evaluation are marched well.

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STUDY ON CHARACTERISTICS OF GROUND MOTION AT PERMAFROST SITES ALONG QINGHAI—TIBET RAILWAY

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2007, 26 (12): 2466-2466 doi:

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Based on the field geological investigation at permafrost regions，geological description and field test of waves velocities at 14 typical boreholes distributing in permafrost areas along the Qinghai—Tibet Railway，elementary characteristics of wave velocities of soils at the permafrost regions are presented. And then，combining the results of dynamic triaxial test，using three time histories of ground motion acceleration with the exceedance probabilities 62.5%，10.0% and 2.0% in 50 years related to the research area，the characteristics of ground motion are analyzed for the 10 permafrost profiles by an equivalent linearization method to estimate the seismic response of frozen soil ground. Moreover，the influence of earth temperature on seismic acceleration response spectrum for permafrost sites is studied. Consequently，the following conclusions can be drawn. (1) Under the similar conditions，the wave velocities of frozen soils along the Qinghai—Tibet Railway are greater than those of other non-frozen soils areas；and the velocity ratio between the shear wave and compression wave does the same. (2) Earthquake intensity is a critical factor to influence the acceleration amplitude of ground motion at permafrost regions，e.g. with the decrease of earthquake intensity，the acceleration amplitude of the ground motion reduces gradually. (3) The proportion of the moderate and the short periods of seismic acceleration response spectrum in permafrost regions is primary. (4) The amplitude of acceleration response spectrum of ground motion decreases distinctly while earth temperature of frozen soils reduces. The research should contribute to earthquake disaster prevention of engineering structures in permafrost areas on Qinghai—Tibet Plateau.

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EVOLUTION PROCESS AND PATTERN OF SLIDING ZONE IN LARGE CONSEQUENT BEDDING ROCK LANDSLIDE

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2007, 26 (12): 2473-2473 doi:

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Large consequent bedding rock landslide is one of the most serious geological disasters. The evolution of landslide is controlled by the characters of sliding zone. And then，evolution process and pattern of sliding zone in the landslide become the key scientific questions. Firstly，the distribution and sliding zone development of large consequent bedding rock landslides in the Three Gorges Reservoir area are analyzed. Secondly，the evolution process of sliding zone of the landslide is divided into three stages，i.e. original soft rock，interbedded shear zone and sliding zone. Thirdly，the evolution of sliding zone characters is studied by comparing the characters in the three stages. By field investigation，grain test，X-ray diffraction(XRD)，differential thermal analysis(DTA)，scanning electronic microscope and energy dispersive X-ray(SEM-EDX)，physicochemical test and physico- mechanical test，the physical property，clay mineral component and content，microstructure and contact feature，physicochemical property and physico-mechanical property are systemically studied. Finally，the evolution pattern of sliding zone in large consequent bedding rock landslide is shown. The following conclusions can be drawn in the evolution of sliding zone. (1) The grains size become finer. (2) The content of clay mine rises，the interbedded shear zone is montmorillonitization；and the sliding zone is illitization and kaolinitization. (3) The microstructural character of interbedded shear zone is most unfavorable. (4) The physicochemical and physico-mechanical characters of the intebedded shear zone are most unfavorable. (5) The characters of the interbedded shear zone are most unfavorable；and the landslide with interbedded shear zone should be paid more attentions to.

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A SUB-REGIONAL EXPLICIT-IMPLICIT RECURSIVE METHOD WITH MIXED STEP-SIZE STRATEGY IN TIME DOMAIN FOR DYNAMIC STRUCTURE-FOUNDATION INTERACTION ANALYSIS

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2007, 26 (12): 2481-2481 doi:

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To satisfy the requirement of large engineering problems，evaluation efficiency and accuracy have played important roles in the application of time-domain numerical solution. Based on the damping solvent extraction method(DSEM)，a new sub-regional explicit-implicit recursive method with mixed step-size strategy in time domain is proposed to cope with the numerical analysis of dynamic structure-foundation interaction，which can alternatively apply implicit and explicit integral algorithms with different time steps to the computations of structure region and soil region. This method is convenient to combine the numerical advantages of big calculated time steps in implicit numerical integration and wide applicability for explicit integration. According to the same displacement interpolation relations in single time step for the explicit prediction-correction and implicit Newmark-b integral arithmetic，the deformation compatibility on the interface between structure and soil region can also be naturally guaranteed. Finally，key influential factors for the implementation，such as integral time step and various displacement interpolations on the interface，are also numerically discussed in the detailed practical application，which shows that the new proposed method can efficiently improve the evaluation efficiency under the condition of satisfying engineering accuracy well.

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DISCUSSION ON STRAIN SOFTENING DAMAGE CONSTITUTIVE MODEL FOR FISSURED ROCK MASS

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2007, 26 (12): 2488-2488 doi:

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Firstly，according to the limitations and deficiencies of the rock damage model based on the Lemaitre¢s hypothesis of strain equivalence，the concept of ratio of voids was applied to describe the volume change of voids or rock mass during the process of deformation of fissured rock mass on the basis of further discussion on the damage mechanism of deformation for fissured rock mass and considering the effect of volume change of fissured rock mass under loading. And a damage model for fissured rock mass was established by analyzing the force upon fissured rock mass on microscopic scale. Secondly，a strain softening damage constitutive model for fissured rock mass was brought forward by thoroughly investigating the relationship between the effective stress and macroscopic nominal stress and introducing the statistical damage theory. Meanwhile，a method to determine the model parameters was developed. This model can fully reflect the property of strain softening of deformation for fissured rock mass；especially it can be used to well simulate the initial phase of compression of voids in the process of fissured rock mass deformation. There is no need for unconventional rock mechanics test to determine the model parameters，moreover，the physical meanings of the model parameters are explicit. Thus，this model is more convenient for use. Finally，the rationality and feasibility of the model are identified by comparative analyses between the existing research results and measured date.

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STUDY ON COMPRESSIVE CREEP TEST ON DIABASIC DIKE AT DAM SITE OF DAGANGSHAN HYDROPOWER STATION

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2007, 26 (12): 2495-2495 doi:

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Compressive creep test is an important means of understanding creep deformation properties of soft rock and is also an important basis of establishing compressive creep constitutive model of soft rock. The process，method and achievements of compressive creep test for large-scale rigid bearing plate of diabasic dike at Dagangshan Hydropower Station are introduced in detail. The changing laws of compressive creep deformation with time under different pressures are analyzed. Compressive creep empirical equations for diabasic dike at dam site have been established by regression fitting method，which provides important experimental and theoretical references to understand the creep characteristics of diabasic dike at dam site of Dagangshan Hydropower Station.

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RESEARCH ON PLANE STRAIN MODEL TEST OF ROCKBURST OF CIRCULAR CAVERN IN HARD BRITTLE ROCKMASS

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2007, 26 (12): 2504-2504 doi:

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In order to discuss rockburst process and mechanism in the surrounding rock of a circular cavern，a physical model，which is 800 mm long，800 mm wide and 200 mm thick with a f 160 mm circular cavern，is produced with hard brittle physical model material from orthogonal experiments by the generalized indexes of uniaxial compressive strength( )，brittleness coefficient(K) and exponential of impact energy( ). The physical model is tested in the large true triaxial model-test machine in geotechnical engineering under the plane strain condition. There are some test results as follows. The peak value of the -( ) curve moves backwards；and the shape of the -( ) curve is not metabolic if the state of the surrounding rock changes from elasticity to plasticity during the process of the horizontal load( ) and the vertical load( ) being kept equal and being loaded in phase. On the other hand，flake like shallot skin comes into being in the cavern wall when and loaded in phase are all 600 kN，then large-scale paroxysmal breakage occurs in the surrounding rock during a short time and a limited loading-zone when and loaded in phase are equal to 630 kN. Subsequently，a relatively steady period appears in a relatively long time and a relatively broad loading-zone，following stress adjustability，if and are loaded in phase sequentially.

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STUDY ON DAMAGE CHARACTERISTICS OF ROCK MASS UNDER BLASTING LOAD IN LING¢AO NUCLEAR POWER STATION，GUANGDONG PROVINCE

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2007, 26 (12): 2510-2510 doi:

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Sonic wave tests have been conducted in the construction site of Ling¢ao Nuclear Power Station(LNPS) in Guangdong Province，China. Based on the change rate of sound wave speed before and after blasting，damage zone size of surrounding rock has been determined. On the other hand，a statistics-based damage variable of rock mass has been proposed based on micromechanics. Damage zone size of rock mass under blasting is thus studied using a hybrid LS-DYNA and FLAC3D scheme. It is reported that the numerical simulation results agree well with the site monitoring results，and the damage threshold for the rock in site of LNPS，，is 0.2. The variation of damage zone size with charge weight has been analyzed by numerical simulations. It is observed that the rock damage zone size increases with charge weight. Damage zone depth of rock mass under blasting is less than damage zone radius. The damage zone radius is approximately 3 times of the damage zone depth.

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INVERSION OF VISCOELASTO-PLASTIC PARAMETERS BASED ON FAST LAGRANGIAN ANALYSIS OF CONTINUUM-PARALLEL PARTICLE SWARM ALGORITHM AND ITS APPLICATION

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2007, 26 (12): 2517-2517 doi:

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An algorithm for back analysis of displacement is proposed. The method，regarding the monitoring displacement as a goal，estimates rheological mechanical parameters inversely in terms of residual sum of squares of the behavior predicted by the model and the actual behavior of rock mass under certain conditions using the improved parallel particle swarm algorithm hybridized with FLAC3D. Both EBE method and domain decomposition technology are not used to deal with the calculated zone，while optimization algorithm which designs calculating schemes is parallel in the methodology. The difficulties of sub-domains division and exchange of a great deal of data among personal computers are avoided，so efficiency and velocity must be improved well for back analysis of large-scale geotechnical engineering using numerical method. These are proven by analysis of capacity of the algorithm based on the example of section BK14+599 at assistant tunnel B of Jinping second stage hydropower station. The viscoelasto-plastic parameters of assistant tunnel B of Jinping second stage hydropower station covered by about 1 538 m-thick rock mass，as an example，are obtained inversely using the proposed method and the obtained parameters are used for estimation of mechanical and deformation characteristics of assistant tunnel. The results indicate that：(1) the maximum deformation arises at vault and two side walls，mainly distributes along the two side walls；and (2) the phenomenon of floor heave comes up，and stress concentration comes into being at basement and spandrel of assistant tunnel B. These all agree with field investigation. So attentions must be paid to the occurrence of the above phenomena during the design and excavation of diversion tunnels.

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ANALYSIS OF ENERGY DISSIPATION AND DAMAGE EVOLUTION OF SANDSTONE DURING TENSILE PROCESS

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2007, 26 (12): 2526-2526 doi:

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As a kind of complex inhomogeneous geological material，the mechanical response of rock behaviors distinct nonlinear and anisotropical characteristics. Direct tensile test of rock can be conducted by means of the advanced test system，accordingly the basic mechanical behavior of rock can be further studied in addition to the current numerous compression tests. It is observed during the cyclic tensile test of sandstone that the whole work of external applied load results in not only the increase of elastic deformation energy but also the irreversible damage because it is partly dissipated. Based on the analysis of such energy dissipation，a damage evolution equation of rock can be constructed；and the corresponding parameters can be determined through tests. Experimental study and theoretical research demonstrate that the damage evolution equation of rock based on the analysis of energy dissipation can well characterize the damage evolution process of rock.

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MT SIMULATION OF COUPLED THM PROCESSES BY NEAR FIELD MODEL IN EXCAVATION DAMAGE ZONE

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2007, 26 (12): 2532-2532 doi:

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The results of benchmark test(BMT) from the study on coupled thermo-hydro-mechanical(THM) processes in the excavation damage zone(EDZ) around nuclear waste repository in fractured rocks are presented. This is an important part of international cooperation project DECOVALEX-THMC TASK B. The results focus on the influence of fractures on the evolution of EDZ over 1×106 years after disposal of high-level radioactive waste. The numerical study is conducted for two model domains，homogeneous and heterogeneous near-field models，surrounding a repository. The heterogeneous near-field model domain includes a realistic fracture network derived by detailed fracture mappings at the Äspö hard rock laboratory，Sweden. In this study，fractures are represented discretely，but softening and weakening effects of fractures intersecting a continuum element are simulated using continuum elements by a reduction in modulus. Using this approach for fracture representation，numerical analyses are conducted using elastoplastic cellular automata(EPCA) code. Elastic and elastoplastic analyses are performed to study the evolution of stress and deformations in EDZ adopting time-dependent thermal，mechanical and fluid pressure boundary conditions. The analysis shows a strong impact of fractures on the distribution of rock stress and deformation as well as the failure process. The numerical results are consistent with those obtained by other international research teams，indicating the validity of EPCA code. The results also indicate that the EPCA code can be used to perform next step analysis of DECOVALEX-THMC project.

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STUDY ON REINFORCEMENT TECHNOLOGY OF DEEP UNLOADED FISSURES IN LEFT BANK OF JINPING FIRST STAGE HYDROPOWER STATION AND ITS NUMERICAL SIMULATION

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2007, 26 (12): 2541-2541 doi:

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There are many unloaded fissures in elevation more than 1 650 m in the deep left bank of Jinping First Stage Hydropower Station. These fissures occur in the depth from 50 m to 300 m，with large quantity，large scale and long extension，and strike basically parallel with the waterway. The elevation of the dam crest is 1 885 m，and its normal impounded level is 1 880 m. Therefore，these fissures possess adverse impact on safety of the dam after water impound and must be reinforced. The usual grouting or anchor cable technology can not reinforce it better. By the aid of existing geologic exploratory tunnel，anchor tunnel technology and prestressed anchor beam technology maybe have good reinforcement effects. Anchor tunnel technology is a new kind of technology which makes use of existing geologic exploratory tunnels，lays steel and fills concrete in the tunnels to form reinforced concrete columns in order to prevent side slopes from sliding by tensile strength and shear strength of reinforced concrete. Prestressed anchor beam technology is one that is improved from anchor tunnel technology，which divides the anchor tunnel into key reinforcement section and common reinforcement section. The key reinforcement section is often the position where faults or fissures occur while the common reinforcement section is the position where rock mass is good. IV–IV section in the foggy region of left bank is selected for numerical simulation of anchor tunnel and prestressed anchor beam. After comparison of the reinforcement effect of both technologies，it is found that the reinforcement effect of prestressed anchor beam is better than that of anchor tunnel.

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EXPERIMENTAL RESEARCH ON RULES OF ROCKBURST TENDENCY EVOLUTION AND ACOUSTIC-ELECTROMAGNETIC EFFECTS OF COMPOUND COAL-ROCK SAMPLES

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2007, 26 (12): 2549-2549 doi:

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In the mining(drifting) faces and roadways，the roof，coal seam and floor all together compose a mechanical equilibrium system. When the system is disturbed by mining effect，the elastic energy accumulated in coal or rock materials can be induced to release through weak structure suddenly and rockburst will be formed. So，to monitor and forecast rockburst，and to deal with strength weakening，the rules of rockburst tendency evolution of different types of compound samples composed of roof，coal seam and floor and acoustic-electromagnetic effect will have a very important practical function. Based on a great number of experimental researches on rockburst tendency and acoustic-electromagnetic effect of compound samples，it is found that the higher the strengths of coal seam and roof samples are，the stronger the rockburst liability is；and the rockburst liability indexes increase with the height ratio of roof to coal. The higher the strength，roof height ratio and rockburst liability indexes of compound samples are，the stronger the intensity of electromagnetic emission(EME) and acoustic emission(AE) signals is. The experimental results also show that the intensity of EME and AE signals rise up slowly before rockburst failure，and increase to the maximum when rockburst precursor，and suddenly decline after rockburst. Above conclusions will have an important directive significance to weaken the strength of rockburst in field and to check the effect of relieve-shot.

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RESEARCH ON LIMIT ANALYSIS UPPER BOUND METHOD FOR STABILITY EVALUATION OF ANCHORED ROCK SLOPE

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2007, 26 (12): 2556-2556 doi:

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A new computational model for stability analysis of anchored rock slope is presented based on the theory of limit analysis upper bound method after taking the supporting effect of rock-bolts，the influences of seismic force and fissure water pressure into consideration. A kinematically admissible velocity field for the model can be obtained when the rock slope is divided into different sliding block elements along the slip surface and structural planes. According to the conditions of associated flow rule and displacement compatibility，the move of the two adjoining elements can not cause overlap or indentation. Moreover，the mathematical formulas of strain velocity field can be derived. By using the model，not only the external power done by dead weight，seismic force，fissure water pressure and anchorage force but also the internal energy dissipation produced in the slip surface and structural planes can be totally calculated. According to the condition of virtual work rate equation in limit state，the formula of stability factor for limit analysis upper bound method can be deduced. In order to evaluate the validity of the proposed method，a typical case is calculated. Results show that the stability factor of rock slope will decrease when the fissure water pressure and seismic force are considered. However，the safety factor of rock slope stability will increase after the slope is reinforced.

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GENERATION AND VISUALIZATION TECHNOLOGIES OF THREE-DIMENSIONAL NETWORK OF ROCKMASS STOCHASTIC STRUCTURAL PLANE

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2007, 26 (12): 2564-2564 doi:

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Based on the research work on generation and visualization of three-dimensional stochastic fracture network simulation，a new three-dimensional stochastic fracture network model is established. It is assumed that the fracture shape of the model is a Baecher disc，the distribution is stochastic，and the correlativity of dimension，location，orientation and aperture of all fractures is independent. Based on these，a sample element of a three-dimensional structural plane network is generated separately by Poisson stochastic process. The spatial geometrical intersection information of the fractures and the boundary sides is discussed in detail. As a result，a program named FRCGEN-3D for three-dimensional stochastic fracture network of flow is developed by the FORTRAN90. To visualize the three-dimensional network model and check the data conveniently，a new specialized visualization system called V-FNW is developed with OPEN GL tools in Visual C++，which is powerful and famous for graph process. The system V-FNW shows interactive interface with three-dimensional graph rendering，rotation and intersection. Finally，an example of a stochastic model with a set of specific data is given；and the result is reasonable. It provides a visual platform of fracture network simulation for rock mechanics and rock hydromechanics，which is very important and valuable in the further research.

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STUDY ON CRACK INITIATION MECHANISM OF THREE GORGES GRANITE

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2007, 26 (12): 2570-2570 doi:

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Based on the conventional triaxial compression test of Three Gorges granites，the crack initiation stress under different confining pressures can be obtained by studying the crack strain curves. The result shows that the crack initiation stress changes at the same extent with confining pressure；compared with the peak strength，the crack initiation stress is generally located between 25% and 50% of the peak strength. Through experimental and theoretical analyses，it is found that the microcosmic failure of Three Gorges granites is mainly induced by tensile cracks under uniaxial and triaxial compressive conditions；and the cracks inside the granite belong to I-mode fracture in stable crack growth stage. Furthermore，the fracture mechanical model of Three Gorges granite is established in order to study the relationship between crack initiation stress，crack initiation angle and confining pressure. Some beneficial conclusions are drawn.

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EXPERIMENTAL STUDY ON SILTY MUDSTONE STRENGTH ATTENUATION AND ENVIRONMENTAL EFFECT

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2007, 26 (12): 2576-2576 doi:

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Aimed to understand how rocks get deteriorated under different conditions，accelerated simulations of water-rock interaction for silty mudstone have been carried out continuously in static water surroundings with two acid solutions(H2SO4 and HNO3)，a sodium hydroxide solution(NaOH)，a sodium humate solution，and a inorganic saltsolution(KCl) with different mass contents(1%，5% and 10%) for 120 days. The unconfined compressive strength(UCS)，microscopic characteristic changes，oxides component changes of silty mudstone are monitored during the simulation. And then the sensitivities of the UCS to solutions types and deterioration mechanism are analyzed. The results show that strength attenuation and eroded rate will nonlinearly increase with the concentration of H+，acid atom，concentration of inorganic salt and soak period；the change of UCS is direct proportional to the change of rock mass. It is verified that dissolution and precipitation，oxidation and reduction present simultaneously in the course of water-rock interaction；and the rule of strength attenuation is effected by all of them；the main reason of strength attenuation is different in different water-rock interaction stages. UCS is closely related to the change of divalent iron ion and calcium ion under chemical weathering. Water quality will be deteriorated because of the much metal stripping during water-rock interaction. However，the results show that long-term water-rock interaction also has its beneficial aspect to the rock UCS；and the environmental effects of water-rock interaction have dual characters.

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ANALYSIS OF SURROUNDING ROCK DEFORMATION CHARACTERISTICS IN UNDERGROUND POWERHOUSE

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2007, 26 (12): 2583-2583 doi:

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As a discontinuous medium，the deformation behaviour of rockmasses is quite different from that depicted by continuous media. Based on the monitored deformation date during excavation，the deformation characteristics and mechanism are analyzed for an underground powerhouse considering its geological data and excavation process. The spatial distribution of rockmass deformation is greatly controlled by geological structural planes. Whether in horizontal direction，vertical direction or along the monitoring borehole depth，the deformation difference may exist if a structural plane is encountered；the influence of the adjacent excavations on rockmass deformation is complex，and the general rule that “the nearer the distance is，the greater the influence is” may not exist；rockmass deformation is mainly composed of the “opening displacement” of major structural planes，which constitutes 84%–93% of the monitored deformation. The characteristics mentioned above suggest the limitation of numerical methods based on mechanics of continuous media for modeling the deformation of rockmass. Therefore，application of discontinuous numerical methods such as DDA is a subject being worthy of further investigation.

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DISCUSSION ON “STUDY ON PHYSICAL MODEL OF COMPLETE FAILURE PROCESS OF QUASI-BRITTLE MATERIALS IN TENSION”

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2007, 26 (12): 2588-2588 doi:

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REPLY TO “DISCUSSION ON ‘STUDY ON PHYSICAL MODEL OF COMPLETE FAILURE PROCESS OF QUASI-BRITTLE MATERIALS IN TENSION’”

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2007, 26 (12): 2589-2589 doi: