Select

2010, 29 (2): 0-0 doi:

[PDF] 141 KB (889)

[HTML]

+

Show Abstract

Select

MECHANISM OF APPARENT DIP SLIDE OF INCLINED BEDDING ROCKSLIDE—A CASE STUDY OF JIWEISHAN ROCKSLIDE IN WULONG，CHONGQING

YIN Yueping

2010, 29 (2): 217-226 doi:

[PDF] 1234 KB (2400)

[HTML]

+

Show Abstract

Taking Jiweishan rockslide in Wulong for example，based on analyzing of geological conditions and mining exploitation，the new failure pattern of inclined thick bedding slope under gravity，karst and mining processing is simulated with the fast Lagrangian analysis of continua in 3-dunebsion(FLAC3D). The results show that the apparent dip slide of inclined thick bedding slope has 5 principal characters：(1) Bedding block-broken body，rock mass is split into obvious distinct blocks with several groups of joints，similar to toy bricks；(2) Incline rock mass support，the sliding rock mass along dip angle is supported by inclined stable rock mass，then sliding direction is changed from dip angle to apparent dip angle；(3) Apparent dip exiting，the valley and cliff provide a free space in the apparent dip exiting；(4) Driving-rock mass sliding，the toy brick rock mass is long-term creeping with the shear strength decreasing from peak to residual value and the sliding force increasing；(5) Key-block resisting，the pressure on the key-block is increasing by driving-rock mass and inner strength is decreasing due to karstlization；the key block is suddenly broken with shear rupture that triggers rockslide. The mining activity of iron-layer 100 m underneath sliding belt induces stress field change and different subsidences between bedding blocks.

Select

IN-SITU STRESS MEASUREMENT AT DEEP POSITION OF LINGLONG GOLD MINE AND DISTRIBUTION LAW OF IN-SITU STRESS FIELD IN MINE AREA

CAI Meifeng，LIU Weidong，LI Yuan

2010, 29 (2): 227-233 doi:

[PDF] 229 KB (1404)

[HTML]

+

Show Abstract

To ensure mining safety，in-situ stress measurement in Linglong gold mine is carried out in two periods. The first period measurement is performed in the shallow position and the second period measurement is performed in the deep position. The measurement process and results are introduced. In order to increase reliability and accuracy of the measurement，a series of new techniques including complete temperature compensation technique and improved hollow inclusion strain devices are used in the measurement. Through in-situ measurement，3D geostresses at 18 points，which are distributed in 7 levels，are determined. Based on the measuring results，comprehensive study of distributing law of the in-situ stress field in the mine is completed. Some conclusions are drawn as fallows：(1) The in-situ stress in Linglong gold mine is dominated by horizontal tectonic stress field rather than the gravity stress field. The magnitude ratio of maximum horizontal principal stress to gravity stress in the mine is 2.26 in average. (2) The maximum horizontal principal stress is oriented in NW direction which is approximately coincided with the orientation of the maximum principal stress of tectonic stress field. (3) The vertical principal stress is basically equal to or a little larger than the gravity. (4) Despite the rock nature in deep position is changed；and the distribution law of in-situ stress state is not remarkably changed in deep position compared with that in shallow position. (5) The maximum horizontal principal stress，minor horizontal principal stress and vertical principal stress are almost linearly increased with depth.

Select

MECHANISM OF SPLITTING AND UNLOADING FAILURE OF ROCK

WANG Mingyang，FAN Pengxian，LI Wenpei

2010, 29 (2): 234-241 doi:

[PDF] 333 KB (1609)

[HTML]

+

Show Abstract

After the introducing of rock structure model with nonuniformities，the influence of stress concentration on the failure mode of rock are analyzed based on stress concentrates during deformation on nonuniformities. In order to investigate the behavior of rock in depth，three cases of stress conditions are studied. They are unconfined uniaxial compression，the loading and unloading of hydrostatic stressed rock in axial direction. Analysis shows that both in loading and unloading process，tension stresses appear in rock. In the loading case，the tension stress may result in splitting which is parallel to the loading direction. In the unloading case，the tension stress is parallel to the unloading direction. The main influential factors of tension stress are physical parameters of nonuniformities，initial stress of rock and unloading speed. The influence of unloading duration and initial stress on the stress concentrations of nonuniformities is analyzed in detail. Results show that the shorter the unloading duration is，the greater the stress concentration is. And if the scale of nonuniformities is large enough，the local tension stress will be approximately proportional to the initial stress. According to the expressions of local tension stress，rock mass will be destructed by tension during rapid unloading in deep rock engineering.

Select

FORMATION CONDITION，GENETIC MECHANISM AND TREATMENT MEASURES OF PLATE-SHAPED LANDSLIDE

XU Qiang，FAN Xuanmei，LI Yuan，ZHAHG Shuai

2010, 29 (2): 242-250 doi:

[PDF] 934 KB (1287)

[HTML]

+

Show Abstract

Taking two new and old landslides，located at Xingma Middle School and Dahe Middle School in Nanjiang County，Sichuan Province，as topical cases，a new translational landslide named plate-shaped landslide is presented analyzed through these two cases. The characteristics of such landslides are thin rectangular plate，with the length of the longitudinal axis of the plane shorter than the lateral axis. And it is like a thin plate in section. The main geological setting of this kind of landslide is thick sandstone rock bed inter-bedded with a mudstone rock bed on the bottom，in which there is a long discontinuity developed inside the slope which parallels to the slope angle. The discontinuity will develop into a tension crack when the heavy rainfall occurs and it will be infilled with water quickly till the water table reaches to a certain critical level. The hydrostatic pressure will push the block on the free side out and such movement will stop when the water table in the crack drops with the crack being large enough. A systematic study of the lithology background，tension crack contain water as well as the rainfall triggering factor condition is carried out. Based on the study，in light of the deformation pattern of the plate-shaped landslide，some measures to treat the landslide are provided，which include operating the drainage project to make sure the water can be drained in the crack，setting a short pile or anti-sliding block outside in the toe of slope to prevent the sliding movement，and setting beams or anchorage cables between the blocks on the top of slope to control the deformation which is caused by tension cracks.

Select

TEST STUDY OF IMPACT FAILURE OF ROCK SUBJECTED TO ONE- DIMENSIONAL COUPLED STATIC AND DYNAMIC LOADS

LI Xibing1，GONG Fengqiang1，2，ZHAO J2，GAO Ke1，YIN Tubing1

2010, 29 (2): 251-260 doi:

[PDF] 392 KB (1373)

[HTML]

+

Show Abstract

The impact failure characteristics of rock subjected to one-dimensional coupled static and dynamic loads are conducted with a modified split Hopkinson pressure bar(SHPB). Firstly，the testing principle with axial precompression stress is re-examined based on one-dimensional wave theory. The axial precompression stress(in accordance with the static load strength of 20%，30%，40%，70%，80% and 90% in six series) is loaded on rock specimen before the axial impact loading is carried on，and the critical dynamic strength is obtained and studied respectively. The results show that in the case of critical damage，the total strain on all stress-strain curves (including the conventional impact testing and impact testing with coupled loads) will reduce finally. The reason for this phenomenon can be explained by the release of stored elastic energy of rock in the process of impact. When axial precompression stress is smaller，the stress-strain curves of impact testing are similar. When axial precompression stress is larger，there is no initial linear elastic part in the curves of impact testing with coupled loads. The dynamic strength increases with the increase of axial precompression stress and the maximum impact strength can be obtained when 60% static strength is precompressed. The absorption of energy increases slowly when the incident energy is smaller and will increase quickly when incident energy is larger. Rock specimen will break with shear failure model subjected to one-dimensional coupled static and dynamics loads，while failure mode will be splitting faulting for conventional impact testing.

Select

EXPERIMENTAL RESEARCH ON DEFORMATION PROPERTITIES OF RED-BED SOFT ROCK

CHEN Congxin，LU Haifeng，YUAN Conghua，TONG Zhiyi，SHEN Qiang，LU Zude

2010, 29 (2): 261-270 doi:

[PDF] 524 KB (1368)

[HTML]

+

Show Abstract

Taking the red-bed soft rock as investigative subject，which has caused many deformation failures during the West-section of Shanghai-Chengdu construction，the deformation characteristics of red-bed soft rock are analyzed through indoor triaxial test，field load-bearing plate test and rheological test. With the triaxial test on natural and saturated red-bed soft rocks，the elastic constitutive equations of red-bed soft rock，considering the closing of structural surface，are established；and the deformation characteristics of water-bearning influence is analyzed. By performing load- bearing plate test，the deformation characteristics of two kinds of red-bed soft rocks with different argillaceous contents are analyzed. Meanwhile，the rock characteristics under cyclic load，and the stress and displacement distribution and the influential range and depth are studied. With the rheological test，the rheological constitutive equation considering the closing of structural surface is also established. Through the tests，the deformation characteristics of red-bed soft rock are further understanded，and it can provide the basis for further research. The results can give some advices to the design of counter-inclined red-bed soft rock slope，and can also offer references to the research on the reinforcement effect of prestressed cables.

Select

SIMPLIFIED ANALYSIS OF TUNNEL EARTHQUAKE RESPONSE AND CENTRIFUGE MODELLING CALIBRATION

HUANG Maosong1，2，CAO Jie1，2

2010, 29 (2): 271-280 doi:

[PDF] 551 KB (1263)

[HTML]

+

Show Abstract

Based on plane strain and quasi-static assumption，by using elasticity theory method，the soil-spring coefficient and shear stress expression of stratum around a circular tunnel under dynamic load are derived. These are introduced into the response-displacement method to evaluate tunnel responses；and this method is further simplified and improved. To validate the revised approach，centrifugal tests are performed. The comparison between test result and analysis result by simplified and improved method is made；and it is proved that the revised simplified solution is feasible and practical. Meanwhile，the tunnel strains are observed，and the stress states under different force conditions(static and dynamic) are compared intuitively. The results indicate that the dynamic responses of tunnel are significantly different from those under static condition；and the performance of ground and tunnel depends on earthquake intensity and boundary conditions closely. The study results can provide a reference to earthquake resistance design of tunnel.

Select

RESEARCH AND DEVELOPMENT OF A NEW SIMILAR MATERIAL FOR SOLID-FLUID COUPLING AND ITS APPLICATION

LI Shuchen，FENG Xianda，LI Shucai，LI Liping，LI Guoying

2010, 29 (2): 281-288 doi:

[PDF] 319 KB (1511)

[HTML]

+

Show Abstract

A new similar material(PSTO) for solid-fluid coupling has been developed through hundreds of compounding tests based on the theory of solid-fluid coupling and the experimental study of solid model material. It is mixed with sand，talc powder，paraffin and hydraulic oil. Sand and talc powder are used as aggregated；paraffin is used as a cementing agent；hydraulic oil is used as a regulator. The effect of different mixing ratios and loading temperatures on the properties of the samples has also been studied through large numbers of laboratory tests. The new material is completely non-hydrophilic，thus there is non-occurrence of softening under the action of water. It belongs to brittle materials with a similar nature of rock mass，which can be used to simulate low-strength and medium-strength rock materials with different permeabilities. So it is an ideal similar material for solid-fluid coupling. This material has been used in a tunnel water-inflow model test；and the variation of the multi-field information such as displacement，stress and seepage pressure has been effectively revealed.

Select

CT REAL-TIME SCANNING TESTS ON SINGLE CRACK PROPAGATION
UNDER TRIAXIAL COMPRESSION

LI Tingchun，LU Haibo

2010, 29 (2): 289-296 doi:

[PDF] 367 KB (1368)

[HTML]

+

Show Abstract

The propagation law of the single crack under triaxial compression is systematically studied through the CT real-time scanning tests. In the tests，through comparison of similar physico-mechanical parameters to the real rock，ceram is selected to precut the test specimens. From the comparative analysis of CT values，CT variances and CT images in different manifold areas，the damage evolution processes，such as the courses of compressed crack，self-similar propagation，wings growth，microcracks propagation，accelerated crack growth and the damage evolution of the specimen failure，of the crack is accurately obtained as follows：the test results show that under triaxial compressive stresses，the crack is obviously compressed at first；then，the propagation of wing crack is restricted，and the self-similar propagation is enlarged by comparison with the uniaxial test result and the propagation of wing crack starts from the edge of self-similar propagation. In conclusion，the propagation of initial crack is influenced obviously by the confining pressure，which makes it slower and similar to ductile failure.

Select

APPLICATION OF ELECTRICAL RESISTIVITY TOMOGRAPHY MONITORING SYSTEM TO MINE WATER INRUSH MODEL TEST

LIU Bin，LI Shucai，LI Shuchen，LI Liping

2010, 29 (2): 297-307 doi:

[PDF] 634 KB (1405)

[HTML]

+

Show Abstract

For real-time monitoring of rock fracture and seepage channel formation and capturing of precursory information in process of mine water inrush，3D electrical resistivity tomography(ERT) is applied to real-time monitoring work in mine water inrush model test. ERT monitoring system with automatic-acquisition function is used to implement real-time and dynamic monitoring work for resistivity variation. An optimization scheme for ERT inversion is proposed，in which Cholesky decomposition algorithm is used to solve large linear system in ERT forward modeling and preconditioning conjugate gradient(PCG) algorithm is used for inversion equation. Thus 3D ERT real-time inversion method is set up；to realized quick inversion of originally observed data and real-time output of dynamic images. In addition，a multi-parameter monitoring and analysis method is proposed，in which ERT is considered as a main means combined with analysis of originally apparent resistivity data and time-history curves for key points data. In the test process，dynamic images of crack generation，propagation and transfixion in aquifuge are obtained by ERT. The position and formation process of the major crack and seepage channel are also obtained，which are consistent with actual situation in the test. By comprehensive analysis of the results obtained with multi-parameter monitoring and analysis method，inducement of the fracture and inrush in aquifuge are gained. And the earliest time for capturing precursory information is obtained，which is 998 s ahead of inrush. The model test shows that the formation process of the crack and seepage channel is effectively reflected；and a series of precursory information is captured successfully by using ERT；and this system can give important reference to in-time early warming and prediction of inrush disaster.

Select

NUMERICAL SIMULATION AND ASSESSMENT OF SEEPAGE CONTROL EFFECTS ON SURROUNDING ROCKS OF UNDERGROUND POWERHOUSE IN SHUIBUYA HYDROPOWER PROJECT

CHEN Yifeng1，ZHOU Chuangbing1，MAO Xinying2，HU Ran1

2010, 29 (2): 308-318 doi:

[PDF] 685 KB (1542)

[HTML]

+

Show Abstract

To reduce the seepage of the underground opening in Shuibuya hydropower project and improve the seepage stability of the surrounding rocks，a seepage control system including grouting curtain，drainage hole array and drainage tunnels is designed and deployed. The long-term seepage control effects of the surrounding rocks of the underground powerhouse are performed by a stationary seepage analysis method combining the variational inequality formulation of Signorini¢s type with an adaptive penalty Heaviside function to guarantee the numerical stability and convergence. Meanwhile，the difficulty in finite element mesh generation is reduced and the calculation time and modeling accuracy are balanced with a global model of equivalent modeling and a submodel of accurate modeling for drainage hole array. Intuitive criteria for assessment of the reasonability of the numerical results are established，namely stationary seepage free surface in any homogeneous medium must be continuous，smooth and can not be return-curved，unless it intersects with an interface between two media of distinct permeabilities. By making comparison with the measurements of pore water pressures in the surrounding rocks，the feasibility and effectiveness of the proposed model are demonstrated. The reasonability of the design of the seepage control system and the possibility of its further optimization are illustrated. The research results are helpful for optimization design of the seepage control system in similar projects.

Select

DISCRETE ELEMENT ANALYSIS OF COLLAPSING AND SLIDING RESPONSE OF SLOPE TRIGGERED BY TIME DIFFERENCE COUPLING EFFECTS OF P AND S SEISMIC WAVES——TAKING TANGJIASHAN LANDSLIDE IN BEICHUAN COUNTY FOR EXAMPLE

CUI Fangpeng1，2，HU Ruilin1，YIN Yueping3，XU Qiang2，ZHANG Ming1，2

2010, 29 (2): 319-327 doi:

[PDF] 1440 KB (1580)

[HTML]

+

Show Abstract

Collapsing and sliding responses of Tangjiashan landslide near Beichuan county and its running out process triggered by time difference coupling effects(considering horizontal and vertical seismic force effects all together)，the regionality and spatial heterogeneity of P and S seismic waves generating horizontal and vertical seismic loads are elaborated；and formation mechanism and key controlling factors of collapsing and sliding of the slope are confirmed by applying DEM numerical simulation. The result shows that initial collapsing and sliding of the slope are triggered by combined action of horizontal and vertical tension caused by P seismic wave，and the vertical tension plays a superiority role. Ejecting and flowing of the broken slope mass are triggered by combined action of P and S seismic waves. Secondly，combined action between horizontal and vertical tension of P wave is the key controlling factor inducing the slope collapsing and sliding. At the same time，slope topography is the key controlling factor leading to collision and debris flow of the slope mass fractured in latter process. Finally，amplification effect of parameters in slope dynamic response shows that the amplification coefficient of vertical acceleration is larger than that of horizontal acceleration，and the vertical velocity and horizontal velocity decreasing one by one，and this trend is consistent with key controlling factor inducing slope fracturing，i.e. vertical seismic loads playing a superiority role. It is of great theoretical and practical value for studying collapsing and sliding of slopes triggered by seismic loads.

Select

STUDY OF SCALE EFFECT ON STRESS AND DEFORMATION OF ROCKFILL

HUA Junjie，ZHOU Wei，CHANG Xiaolin，ZHOU Chuangbing

2010, 29 (2): 328-335 doi:

[PDF] 390 KB (1420)

[HTML]

+

Show Abstract

Firstly，scale effect on instantaneous deformation of rockfill is studied by experimental data in former studies and numerical tests base on stochastic granule discontinuous deformation(SGDD) model. It is demonstrated that larger specimen shows higher shear strength and initial modulus of elasticity under the same axial stress and confining pressure without considering creep deformation of rockfill. Secondly，two kinds of specimens with different sizes(f50 cm×100 cm(maximum grain diameter is 10 cm) and f30 cm×60 cm(maximum grain diameter is 6 cm)) are subjected to stress control triaxial creep tests，which aim to study the scale effects on creep deformation of rockfill. It reveals that scale effect has significant influence on creep property of rockfill. Larger specimens give more creep deformation，but no clear law is found about the scale effect on the factor of creep rate . Finally，based on the synthetical analysis of scale effect on total deformation including instantaneous and creep deformations of rockfill，the total deformation of big specimen is larger than that of the small one as a whole.

Select

TEST STUDY OF GAS SEEPAGE CHARACTERISTICS OF GAS-BEARING COAL SPECIMEN DURING PROCESS OF DEFORMATION AND FAILURE IN GEOSTRESS FIELD

YIN Guangzhi1，2，HUANG Qixiang1，2，ZHANG Dongming1，2，WANG Dengke1，2

2010, 29 (2): 336-343 doi:

[PDF] 443 KB (1307)

[HTML]

+

Show Abstract

Based on the briquets of the outburst coal seam of typical coal and gas outburst mine of Datong in Songzao Coal and Electricity Company，by means of self-developed triaxial gas-seepage experimental device，the experimental research of permeability of gas-bearing briquets in the complete stress-strain process is performed. The research results show as follows：if the gas pressure is fixed，the seepage velocity of briquets drops at first and rises later with increasing axial stress，and increases after peak stress. There is significant corresponding relationship between the complete stress-strain process curve and the seepage velocity-strain curve. The seepage velocity in peak stress decreases with the increase of confining pressure，and indicates obvious linear relationship. The comparative experiments in certain confining pressure and gas pressure show that rising confining pressure can decrease permeability of briquets and rising gas pressure can increase permeability of briquette specimens. The results have a referential value for using geostress field draining gas in coal bed and predicting deformations and failure of coal through gas emission.

Select

THREE-DIMENSIONAL ENERGY DISSIPATION LAWS AND REASONABLE MATCHES BETWEEN BACKFILL AND ROCK MASS

LIU Zhixiang，LI Xibing，ZHAO Guoyan，LI Qiyue，WANG Weihua

2010, 29 (2): 344-348 doi:

[PDF] 182 KB (1234)

[HTML]

+

Show Abstract

According to experimental results of four kinds of cemented backfills with the ratios of cements to tailings 1∶4，1∶8，1∶10 and 1∶12，the laws of three-dimensional energy dissipation of backfill are presented during the course of breakage. According to the characters of stress transfer and energy release in rock mass during deposit exploiting，the laws of energy release in excavated rock mass are researched；and the results show that the deeper ore body in underground is，or the bigger the elastic modulus of rock mass is，as well as the lower the Poisson¢s ratio of rock mass is，the higher the energy release in excavated rock mass is. With the characters of energy dissipation in coupling action between backfill and rock mass，their reasonable matches can be explored，and the feasibility，in which the lowest ratio 1∶12 of cement to tailings can be adopted in Anqing Copper Mine，is verified. The results show that the matching coefficient K between backfill and rock mass correlates with three- dimensional geostresses，mechanical parameters of backfill and rock mass；and it is necessary to design reasonable compression strength of backfill and to realize reasonable match between backfill and rock mass under different mining conditions.

Select

TEST STUDY OF CREEP PROPERTIES OF GAS-BEARING COAL SPECIMENS UNDER TRIAXIAL COMPRESSION

WANG Dengke1，LIU Jian1，YIN Guangzhi2，3，WEI Xiaoji4

2010, 29 (2): 349-357 doi:

[PDF] 291 KB (1148)

[HTML]

+

Show Abstract

A self-developed triaxial creep system of gas-bearing coal is introduced firstly. A series of triaxial creep tests on gas- bearing coal specimens are carried out by using the creep system，and results of the creep tests under different creep stresses，confining pressures and gas pressures are obtained. The results show that creep stress，confining pressure and gas pressure are the important factors affecting the creep properties of the coal specimens；the creep behaviors of the specimens can be split into two parts mainly：one is the attenuating creep，the other is the non-attenuating creep. Decelerating creep stage is caused by elastic aftereffect；by the actions of creep stress，confining pressure and gas pressure during creep tests，steady-state creep rate increases with the increasing of confining stress and gas pressure，and decreases with the increasing of confining pressure. Accelerating creep stage marks the starting of the failure of coal specimens. Based on the creep results，the creep rates at decelerating creep stage and steady-state creep stage are analyzed in detail；and in addition，a power function and an exponent function are proposed which can effectively describe the creep rates at transient creep stage and steady-state creep stage respectively. By a normalized method，a mathematical equation is constructed which can model the relationship among the steady-state creep rate，creep stress，confining pressure and gas pressure. And using this equation，the value of steady-state creep rate under various stress conditions can be estimated easily.

Select

CONSTITUTIVE MODEL FOR ELASTO-BRITTLE-PLASTIC DAMAGE OF COAL ROCK MASS DUE TO MINING AND ITS APPLICATION

LIU Hongyong1，CHENG Yuanping1，ZHAO Changchun2，WANG Haifeng1，CHEN Haidong1

2010, 29 (2): 358-365 doi:

[PDF] 355 KB (1425)

[HTML]

+

Show Abstract

The exploitation of the protective layer and pressure-relief gas drainage is an effective primary method to eliminate coal and gas outburst and it is widely used in many mineral fields. In order to improve the effectiveness，safety and economy of the protective layer mining，a set of numerical equations of elasto-brittle- plastic constitutive model of coal rock mass damage due to mining are set up based on the plastic flow format of Drucker-Prager constitutive model in fast Lagrangian analysis of Continua in 3-dimension continua(FLAC3D). And the model is modified by using the inscribed circle criterion and the ideal brittle-plastic model. The model is developed into DLL file in VC++2005 programming environment for FLAC3D；and the correctness and rationality of this model used to study the brittle strain-softening characteristics of coal rock mass due to mining are validated by comparing with uniaxial and triaxial compression numerical tests. This model is used to simulate the super-remote protected seams exploitation of Xinjing coal mine in Yangquan coal field. The results show that the protected layer lies in the top edge of fractured zone 125 m away from the protected layer；and the relieved gas in the super-remote protected layers could be better drained utilizing the mining influence of the protective layer. And the conclusions agree with that of the similar experiment，which indicates that the elasto-brittle-plastic constitutive model of coal rock mass damage due to mining could be used to preliminary evaluation of protective layer mining and relief-pressure gas drainage. Simulation results may bring forward reasonable suggestions for the design of protective layer mining and relief-pressure gas drainage.

Select

EXPERIMENTAL STUDY OF SEEPAGE IN YICHANG FRACTURED SANDSTONE WITH TIGHT ORIGINAL ROCK FILLINGS

LIU Jie1，LI Jianlin1，2，WANG Ruihong2，ZHU Ting2，QU Jianjun2，ZHAO Zongyong2

2010, 29 (2): 366-374 doi:

[PDF] 299 KB (1088)

[HTML]

+

Show Abstract

In view of the great differences of the seepage law of the fractured rock with or without filling materials，and that most of the seepage fractures in the engineering rock mass are the shear sliding fractures filled with the original rock broken materials，the research of the influence on seepage discharge caused by the factors such as loading paths，axial compression，confining pressure，fracture depth，particle size of original rock fillings etc.，has important reference value to the selection of the seepage parameters and the stability discrimination of the rock slope. With the experimental study of the fracture seepage aiming at the sandstone with artificial cutting fractures in Yichang area，some conclusions are drawn as follows：(1) The metrical data of seepage discharge do not have the repeatability before filling sand grains are tightly. It is not only under the influence of the axial pressure loading path，but also under the influence of the confining pressure way. The seepage velocity tends to be stable with repeatability after more than four times of loading and unloading cycles under axial pressure and confining pressure. (2) There is a linear relationship between the axial pressure and the seepage discharge of large opening fracture with solid fillings when the fracture depth is less than 2.5 cm，then after the fracture depth reaches 2.5 cm，the relationship becomes nonlinear. And it is mainly because that the increasing fracture depth induces the increment of the change possibility of the sand position and structure. (3) To the fractured rock mass with fillings，the influence of the confining pressure is significant，but to the big opening fracture without fillings，the influence of the confining pressure on the seepage discharge is little，it is because the order of the shape variable of rock mass caused by the confining pressure is too small compared to the wetted cross-section of the fracture with big opening. (4) When axial pressure is less than 0.03 MPa or confining pressure is bigger than 1 MPa，the effect of filling granularity on seepage discharge has the nature of randomness. When axial pressure is more than 0.03 MPa and confining pressure is bigger than 1 MPa，the bigger the sand particle size is，the bigger the corresponding seepage velocity is. At the moment，the bigger the axial pressure is，the more the effect of filling granularity on seepage discharge is. Size relationships and proportions of three different granularity corresponding velocities are stable with the growth of confining pressure.

Select

RESEARCH ON DYNAMIC FRACTURE BEHAVIORS OF STANSTEAD GRANITE

CHEN Rong1，2，GUO Xian1，3，LU Fangyun1，XIA Kaiwen2

2010, 29 (2): 375-380 doi:

[PDF] 306 KB (1687)

[HTML]

+

Show Abstract

A recently proposed method is used to measure dynamic fracture parameters of Stanstead granite(SG)，such as fracture initiation toughness，fracture energy，fracture propagation toughness，and fracture propagation velocity. With the method，a notched semicircular bend specimen is loaded by the split Hopkinson pressure bar(SHPB) system；and a laser gap gauge system is employed to monitor the crack surface opening displacement (CSOD) of the specimen. The dynamic initiation toughness is subsequently calculated by using a quasi-static formula，for the dynamic force balance is achieved in the test. Based on the CSOD data，residual kinetic energies of the two fragments are estimated. The average propagation fracture energy and thus the propagation toughness are calculated. The average fracture propagation velocity is estimated with a series of crack gauges glued on the specimen. It is shown from the results of the experiments that both the initiation and propagation toughnesses of this brittle solid are loading- dependent. The propagation toughness is larger than the initiation toughness. The propagation fracture toughness is shown to increase with the fracture propagation velocity. The fracture arrest toughness and the limiting fracture propagation velocity are obtained by a literature model of this relationship. The results of SG in this work are compared with the ones of Laurentian granite(LG). The grain size of SG is much larger than the one of LG，so that the fracture is easy to be generated and arrested but difficult to propagate. On the contract，the LG has smaller dynamic propagation toughness and the larger limit fracture propagation velocity.

Select

RESREACH ON MECHANICAL CHARACTERISTICS OF STRONGLY WEATHERED GRANITE FOR XIAMEN SUBSEA TUNNEL

YU Hongdan1，CHEN Weizhong1，GUO Xiaohong2，JIA Shanpo1，CAO Junjie1，LIANG Wei2

2010, 29 (2): 381-387 doi:

[PDF] 364 KB (1357)

[HTML]

+

Show Abstract

The underwater section of the Xiamen subsea tunnel will encounter many weathered strata，and the main rock of the weathered strata is fully or strongly weathered granite. The main mechanical characteristics of this kind of rock is low strength，high compressibility；its self-stability，and its bearing capacity is low；and it brings many unexpected problems to the liner design and the tunnel construction technology. A series of laboratory tests for the strongly weathered granite have been performed to study the hydro-mechanical coupled behavior；and a new mechanical model has been suggested；and corresponding parameters have been identified by back analysis. The results obtained from the research work are useful for soft rock engineering especially for weathered granite engineering；it has guiding effect on the tunnels¢ design and construction in this kind of rocks.

Select

DETERMINATION OF REASONABLE FORCED CAVING INTERVAL IN SHALLOW-BURIED SEAM WITH HARD AND THIN BEDROCK

FANG Xinqiu1，2，HAO Xianjie1，LAN Yiwen1

2010, 29 (2): 388-393 doi:

[PDF] 200 KB (1075)

[HTML]

+

Show Abstract

During mining of shallow-buried seam with loose topsoil and hard and thin bedrock，in order to avoid support break-off and sand inrush happening，forced caving is often adopted in practical engineering in order to avoid support break-off and sand inrush happening. But how to determine the reasonable forced caving interval lacks rational basis. Combining the practical condition of Liangshuijing coal mine，according to rock strata control theory，the reasonable forced caving interval is studied by using methods of theoretical analysis，numerical simulation and in-situ measuring. The results indicate that when the working face advances 20 m far away from cut-hole，namely，between the periodic weighting step distance and first weighting step distance of basic roof，forced roof caving can successfully avoid first weighting，which has less influence on supports and can also avoid support break-off. The conclusions have been proved successfully by in-situ experiment.

Select

EXPERIMENTAL RESEARCH ON ANCHORAGE PERFORMANCE OF FULL-THREAD GFRP BONDING ANCHOR BOLTS

LIU Yinghao1，YUAN Yong2

2010, 29 (2): 394-400 doi:

[PDF] 287 KB (1605)

[HTML]

+

Show Abstract

Through the experiments on the improved pull-out tests of full-thread glass fiber reinforced plastic (GFRP) anchor bolts，the bonding behavior between the bolts and rock mass is studied. By studying the anchorage force of different GFRP anchor bolts，the parameters for application of GFRP anchor bolts to engineering practice are proposed. The testing results indicate that the anchorage force of the bolts increases with the increases of bolt diameter，anchorage length and mortar strength；the bonding strength of bolts in creases with the increase of mortar strength，but decreases with the increases of bonding length and bolt diameter. And the results are explained with the bonding stress distribution of the GFRP anchor bolts. By the results，several conclusions are drawn：(1) the recommend diameter of the GFRP anchor bolts in engineering is 12–32 mm；(2) the anchorage length of the GFRP bolt should be larger than 20 times of its diameter；and (3) the compressive strength of the mortar used as anchor agent should be more than 15 MPa.

Select

ANALYTICAL METHOD FOR PILE COMPOSITE GROUND UNDER FLEXIBLE FOUNDATION

LU Wenzhi1，2，YU Jianlin1，GONG Xiaonan1

2010, 29 (2): 401-408 doi:

[PDF] 302 KB (1347)

[HTML]

+

Show Abstract

Interactions among flexible foundation，cushion，composite ground，and underlying soils have not been well researched. A simplified analytical model is presented considering the above four parts as an interactive system. The method allows the relative movement between piles and soils，and assumes different settlements of foundation soil at the same level plane. The force equilibriums of a typical element are established. And then，according to the compatibility of stress and deformation on the interfaces between these four components，the formulas for settlement and stress ratio of pile-soil，which are used to characterize the behaviors of the composite ground，are derived. Comparisons demonstrate that the results from this solution are in accordance with the measured ones of a project in China¢s Zhejiang Province，and they are closer than those obtained using the recommended method of the current codes in China. The pile-soil load ratio and the load transfer law of pile composite ground under flexible foundation are different from those of rigid foundations. More attentions should be paid to the concepts of equal settlement plane and neutral point plane for the engineering designs. Finally，same suggestions are proposed for further study of analytical method of pile composite grounds under flexible foundation.

Select

EXPERIMENTAL RESEARCH ON IN-SITU MECHANICAL PROPERTIES OF SILT IN YELLOW RIVER DELTA

XU Dongsheng，WANG Ren，MENG Qingshan，WANG Zhibing，YANG Chao

2010, 29 (2): 409-416 doi:

[PDF] 634 KB (1638)

[HTML]

+

Show Abstract

The silt in the Yellow River Delta mainly belongs to the quaternary deposits. Based on the in-situ drilling test，pressuremeter test(PMT)，dilatometer test(DMT) and laboratory test，the mechanical properties of silt are studied. Laboratory test results show that there are many special characteristics of silt soil，such as the homogeneous particle size(grain sizes of silt centralized in 0.075–0.005 mm)，poor gradation and little clay content in the silt，therefore，it is hard in compaction. In addition，the porosity of the silt is very high，which leads to large compressibility. The results of PMT demonstrate that the allowable bearing capacity of foundation in the Yellow River Delta is 300 kPa. In addition，the critical edge pressure of silt increases with the depth，and decreases in the depth greater than 13.0 m. The quantitative relationship between modulus of lateral pressure test and depth is also presented. Moreover，the suggested value of modulus of lateral pressure test is 1 800 kPa in the Yellow River Delta. As for DMT，the results reveal that most strata in the area belong to silt ones except for some rock flour or silt clay in some layers. Then，the changes of static lateral pressure coefficient K0 and horizontal stress index KD with depth are studied. Finally，the relationship between dilatational modulus ED and compression modulus Es is discussed；meanwhile，the variations of ED and Es with depth are analyzed.

Select

RESEARCH ON SOIL DEFORMATION DURING SHIELD CONSTRUCTION PROCESS

TANG Xiaowu1，2，ZHU Ji1，2，LIU Wei1，2，CHEN Renpeng1，2

2010, 29 (2): 417-422 doi:

[PDF] 342 KB (1755)

[HTML]

+

Show Abstract

Derived from Mindlin solution，the deformation formula induced by torque between cutterhead and soil is obtained by integration and coordinate transformation，which leads to the total deformation formula induced by shield tunneling. The deformation characteristics and complicated interactions between shield and soil are analyzed based on the Line No.1 of Hangzhou Metro with sandy silt. It is shown that the friction force and bulkhead thrust are the main factors of shield thrust setting，while the friction between the cutterhead and soil is the main factors of cutterhead torque setting. Friction force between shield and soil would make front soil of shield upheave，and subsidence of surface soil is induced by ground loss when the friction force between the cutterhead and soil results in the surface settlement asymmetrical distribution. Compared with the field measurements，the formula is suitable for the distance within the shield cutterhead(±2L)，which can help guiding actual tunnel construction.

Select

EXPERIMENTAL RESEARCH ON CHANGING RULES OF DYNAMIC MODULUS AND DAMPING RATIO OF SATURATED SOFT CLAY UNDER BIDIRECTIONAL EXCITING CYCLIC LOADING

WANG Jun1，CAI Yuanqiang1，2，DING Guangya1，PAN Xiaodong3

2010, 29 (2): 423-432 doi:

[PDF] 510 KB (1256)

[HTML]

+

Show Abstract

Dynamic modulus and damping ratio of saturated soft clay under bidirectional cyclic loading are investigated by GDS dynamic triaxial system. It is observed that the pore water pressure ratio increases significantly with the increase of radial cyclic stress ratio. Radial cyclic stress has great effect on initial pore water pressure；and the increase of initial pore water pressure is approximately equal to the radial cyclic stress. The threshold of cyclic stress ratio changes little under bidirectional cyclic loading. The dynamic modulus and damping ratio are affected by radial cyclic stress significantly. By increasing the radial cyclic stress，the damping ratio increases while the dynamic modulus decreases. Small strain elastic modulus decreases as the radial cyclic stress increases and there is a linear relation between the small strain elastic modulus and the radial cyclic stress ratio. An empirical model for the small strain elastic modulus is obtained based on the modification of Hardin equation. The radial cyclic stress and confining pressure have little effect on the curves of - and - . By modifying hyperbolic model，the empirical models for describing the change of dynamic modulus and damping with dynamic strain are obtained.

Select

2010, 29 (2): 433-433 doi:

[PDF] 103 KB (1266)

[HTML]

+

Show Abstract