01 November 2014, Volume 31 Issue 11

    

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CHARACTERISTICS AND TESTS OF ROCK MECHANICS
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  Karstic Rock Mass of Dam Foundation and Its Physical and Mechanical Properties in the Red Beds of Central Yunnan Province

  WANG Kun, WANG Zhong, GAO Qiang

  Journal of Changjiang River Scientific Research Institute. 2014, 31(11): 1-6. https://doi.org/10.3969/j.issn.1001-5485.2014.11.0012014,31(11):1-6

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  Guanyinyan hydropower station on the Jinsha River is a double fold mixed dam. Its concrete gravity dam foundation is located in the red beds of central Yunnan Province and mainly contains conglomerate and sandstone of J₂s stratum, in which dissolution affects the stability of foundation rock mass. According to the distribution of red beds in China, we analysed the deposition and distribution features of red beds in Yunnan and systematically researched the features of karst in red beds of clastic rock as well as some small caves, dissolution holes and cracks. We also conducted tests on the physical and mechanical properties of karstic rock mass in red beds. The results show that the distribution characteristics and mechanical parameters of karstic rock mass could reach the quality of Ⅲa, Ⅲb classes, and meet the dam foundation requirement when appropriately treated. The research achievements provide basis for selecting dam foundation and treating geological defects of karstic rock mass.

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  Determination of Shear Strength Parameters of Rock Mass of Jinping Arch Dam

  RAO Hong-ling,ZENG Ji-quan,PANG Ming-liang,LIU Zhong-xu

  Journal of Changjiang River Scientific Research Institute. 2014, 31(11): 7-11. https://doi.org/10.3969/j.issn.1001-5485.2014.11.0022014,31(11):12-16,21

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  Jinping arch dam is the highest arch dam in the world, and is also the highest dam has been built in the world. It has complex topographic and geological conditions. Methods of determining the shear strength parameters of rockmass are researched by shear tests, test feature point selection, parameter statistics, as well as typical block stability analysis. Research results indicate that the selection of standard value of shear strength parameters varies in different specification requirements in China and abroad. Some feature points on the shear test curve can be determined through the feature points obtained easily. The shear strength parameters of the same project obtained by different methods are different, which may lead to different evaluation results of anti-sliding stability of dam abutment. The research results provide reference for similar engineering.

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  Long-term Stability of Tunnel Anchor in Consideration of Rock Rheology

  FU Jian-jun, JIANG Wu-jun, ZHAO Hai-bin, MEI Song-hua

  Journal of Changjiang River Scientific Research Institute. 2014, 31(11): 12-16. https://doi.org/10.3969/j.issn.1001-5485.2014.11.0032014,31(11):12-16

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  Rock rheology is a focus in analysing long-term stability of tunnel anchor. By uniaxial compression creep tests and long-term contact surface shear strength tests, we obtained rock rheological parameters. These parameters together with CVISC model in FLAC^3D were integrated in the numerical simulation model of an engineering example. Results showed that in 100 years after the design, main cable force of tunnel anchor doubles, the anchor plug body, surrounding rock, and the contact surface between rock anchor plug body and surrounding rock has small long-term deformation, which meets the project’s design safety requirements. This research could be a reference for similar engineering studies.
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  Determining the Comprehensive Deformation Modulus of Foundation after High Dam Constructed

  LI Pan-feng, CUI Chang-wu, CHEN Kui, ZhANG Shao-cheng

  Journal of Changjiang River Scientific Research Institute. 2014, 31(11): 17-21. https://doi.org/10.3969/j.issn.1001-5485.2014.11.0042014,31(11):17-21

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  The engineering properties of high arch dam’s foundation rock change inevitably after excavation unloading, consolidation grouting and dam loading. The comprehensive deformation modulus of foundation rock mass is an important index for safety assessment and feedback analysis, but it cannot be obtained by field test. To solve this problem, we conducted researches on the geological condition, deformation test, borehole elastic modulus, and the relation between deformation modulus E₀ and longitudinal wave velocity V_p with Xiluodu hydropower station as an example. On this basis, we put forward a method of determining the comprehensive deformation modulus of foundation rock mass after the completion of high arch dam construction. The comprehensive deformation modulus of Xiluodu high arch dam foundation after construction completed is between 11-14 MPa. This parameter was used for 3-D numerical simulation, and the simulated deformation was in consistency with monitored deformation, which verified this method is appropriate.
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  Initial Damage of Rock and Its Effect on Uniaxial Compressive Strength of Rock

  ZHANG Li-jie,ZHU Jie-bing,LUO Jian-yu,ZENG Ping

  Journal of Changjiang River Scientific Research Institute. 2014, 31(11): 22-25. https://doi.org/10.3969/j.issn.1001-5485.2014.11.0052014,31(11):22-25,37

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  Computerized Tomography (CT) was employed to research the effect of initial damage of soft rock (claystone) and hard rock (marble) on the uniaxial compressive strength. Soft rock samples were damaged in deterioration test area condition; while hard rock was damaged by different sampling methods. There were three test conditions natural test area, wet and dry cycle test area and concrete protection test area. CT scanning results show that the average CT number of soft rock sample is the highest under concrete protection test condition, followed by that in natural test and in wet and dry cycle test conditions. Rock samples with high average CT numbers has correspondingly high uniaxial compressive strength, and vise versa. The CT number of soft rock sample presents certain regularity under different damage conditions. The degree of initial damage of hard rock by using non-destructive sampling is significantly lower than that using conventional sampling method. The compressive strength of hard rock is affected by its initial damage degree, and the CT numbers and uniaxial compressive strength of marble by using non-destructive sampling are higher than those by conventional sampling.
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  Crack Propagation Mechanism of Inhomogeneous Medium under Dynamic Load

  ZHONG Bo-bo,ZHANG Yong-bin,BAI Xiang-yuan,LI Hong

  Journal of Changjiang River Scientific Research Institute. 2014, 31(11): 26-30. https://doi.org/10.3969/j.issn.1001-5485.2014.11.0062014,31(11):26-30

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  The influences of crack inclination angle, rock bridge’s inclination angle and biaxial load on rock crack propagation mode were studied by using Rock Failure Process Analysis(RFPA-dynamic) on rock samples with pre-existing cracks. The results show that 1) under uniaxial dynamic load, crack inclination angle and rock bridge's inclination angle have little effect on crack propagation , and the crack expands in the direction perpendicular to load; 2) the release of accumulated energy of acoustic emission can be divided into four stages under axial dynamic load; 3) under biaxial load, along with the decrease of load ratio, the bending radian of crack increase and the crack is gradually perpendicular to the horizontal load; 4) when the inclination angle of rock bridge is constant with the increase of crack inclination angle, crack tends to the vertical direction under biaxial dynamic load; 5) under uniaxial static load, crack inclination angle and rock bridge’s inclination angle have significant effect on crack propagation mode but have little effect under uniaxial dynamic load.
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  Research on Shear Characteristics and the Evolution Mechanism of Bedding Planes Between Two Different Rock Types Based on Particle Flow Code

  FANG Kun, WU Qiong, WANG Jiao, TAN Fu-li

  Journal of Changjiang River Scientific Research Institute. 2014, 31(11): 31-37. https://doi.org/10.3969/j.issn.1001-5485.2014.11.0072014,31(11):31-37

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  To research the influencing factors of shearing properties and the micro-evolution mechanism of shear failure, we carried out direct shearing numerical experiments. On the bedding planes between silty mudstone and marlite in Badong formation using particle flow software based on wall rock’s micro-parameters determined by laboratory experiment results. The research results are as follows the shearing curve of bedding planes between two different rock types in Badong formation is between silty mudstone and marlite isotropic planes; the shearing mechanical properties of bedding planes between two different rock types are influenced by the surface morphology, normal stress and the wall rock combination. In addition, the shear failure evolution process of bedding planes between two different rock types is influenced by the surface morphology. The shear failure of zigzag bedding planes between two different rock types develops mainly along the weak wall rock gradually from both sides to the middle. The shear failure of flat bedding planes between two different rock types evolves evenly along one side of the weak wall rock. Based on the results, an expression is given to describe the relationship among the ratio of shearing strength of bedding planes of two different rock types to that of normal joint in soft rock, the rock combination coefficient, and the normal stress. It’s concluded that inter formational sliding of bedding planes between two different rock types in Badong formation is an important factor that leads to the rock mass failure of this stratum.
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  Estimating Equivalent Mohr-Coulomb Strength Parameters Based on the Sheorey Rock Mass Strength Criterion

  ZHENG Xing,ZHANG Sheng

  Journal of Changjiang River Scientific Research Institute. 2014, 31(11): 38-41. https://doi.org/10.3969/j.issn.1001-5485.2014.11.0082014,31(11):38-41,46

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  According to the principle of fitting non-linear strength criterion with linear M-C criterion in σ₁-σ₃ plane, we derived the equivalent M-C strength parameters of the Sheorey strength criterion which is based on the RMR system by use of the least square method. We also present the general formulas of the equivalent M-C strength parameters to be used in the evaluation of strength and stability of rock mass. A calculation example is given to compare the M-C strength parameters between Sheorey criterion and Hoek-Brown criterion. Results reveal that the strength parameters of both criteria are well consistent.
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  Correlation between a Tunnel Stress and the Regional Stress Field in North Xinjiang

  YIN Jian-min,ZHOU Chun-hua,LI Yun-an,CUI Dong,WANG Yang

  Journal of Changjiang River Scientific Research Institute. 2014, 31(11): 42-46. https://doi.org/10.3969/j.issn.1001-5485.2014.11.0092014,31(11):42-46

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  Stress measurement data is in lack in Northern Xinjiang’s Altai region. We tested the stress field of a deep water diversion tunnel in this region by using hydraulic fracturing method. Test result and analysis reveal that the tested stress field is tectonic stress type and the maximum horizontal principal stress orientation is NNE, which is in consistency with the focal mechanism solution. Moreover, it reveals that the ratio of average horizontal stress to vertical stress changes no smaller (close to 1.0)in the depth of more than 300 m. We should strengthen the research on tectonic stress field in deep area and pay attention to the application of in-situ measurement means to improve the macroscopic understanding of regional stress field.
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  Quality Classification and Tests on Mechanical Parameters of Dam Foundation Rock Mass

  GUO Xi-feng, YAN E-chuan, WU Xiang-chao, LIU Chuan-zhong

  Journal of Changjiang River Scientific Research Institute. 2014, 31(11): 47-50. https://doi.org/10.3969/j.issn.1001-5485.2014.11.0102014,31(11):47-50

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  The foundation stratum of a concrete hyperbolic arch dam consists of near horizontal layered rockmass having relative soft layers in the upper abutment. There are obvious differences among rockmass behavior at different elevations. In this research, rockmass quality classification is carried out for the main bearing stratum at dam site, and then direct shear tests and deformation tests are conducted for thin limestone and calcareous mudstone interlayer nuddy dolomite. Test results are in agreement with the results of rockmass quality classification. Some engineering recommendations are also given in the light of dam foundation’s rockmass mechanical characteristics.
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  Experimental Study on the Correlation between Mechanical Parameters of Red Mudstone and Acoustic Velocity

  TAN Xin,PU Yu,PENG Wei

  Journal of Changjiang River Scientific Research Institute. 2014, 31(11): 51-55. https://doi.org/10.3969/j.issn.1001-5485.2014.11.0112014,31(11):51-55

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  The velocity of acoustic wave propagation is closely related with rock mass strength and deformation characteristics. Uniaxial compressive strength tests, uniaxial compression tests and sound velocity test were conducted on 169 red mudstone samples from the red-layer region in Chongqing. Relationships between uniaxial compressive strength R, elastic modulus E_e and wave velocity V_P are established by different functional relationships. Comparative analysis results show that their relationship expressed using second-order polynomial is the best. The empirical relationship between R and V_p could be expressed by R=4.7×10^-6×V²_P-0.023 4V_P+33.771, and the relationship between E_e and V_p is E_e=0.003 7×V²_P-19.312V²_P+27 333. The rock mechanics parameters of an engineering example were calculated and analyzed by using the established relationships. It was found that the recommended value of uniaxial compressive strength of the example is 5-6 MPa, and the elastic modulus is 2 000-3 000 MPa.
ANALYSIS OF DAM FOUNDATION AND SLOPE
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  System of Parameter Selection for Reservoir Bank Collapse Prediction

  PENG Shi-xiong, CHEN Wei-dong

  Journal of Changjiang River Scientific Research Institute. 2014, 31(11): 56-59. https://doi.org/10.3969/j.issn.1001-5485.2014.11.0122014,31(11):56-59,65

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  Due to the complex geological structure of soil slope, and the numerous bank collapse modes, the parameters of bank collapse prediction are difficult to obtain accurately. On the basis of field parameters of bank collapse survey and statistics of 10 large reservoirs, we analysed the influence factors of bank collapse parameters, including geological factors like the types, origin, era, structure and composition of the soil, as well as the softening effect of reservoir water, water dynamic effect caused by reservoir water lifting, and the wind (wave) scouring effect. Also we proposed several methods to calculate the parameters of the prediction of bank collapse. These methods include the field survey method, the engineering analogy method, and the underwater stable slope angle analysis based on particle composition analysis of fractal theory. Hence we established the system of parameters selection through field geological naming and laboratory soil test naming combined with the geological formation.
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  Formation Mechanism of Erguxi Toppling Slope at Shiziping Hydropower Station

  ZHANG Shi-shu, PEI Xiang-jun, WANG Ren-kun, RAN Cong-yan, YU Ting, ZHAO Xiao-ping, TIAN Xiong

  Journal of Changjiang River Scientific Research Institute. 2014, 31(11): 60-65. https://doi.org/10.3969/j.issn.1001-5485.2014.11.0132014,31(11):60-65

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  Erguxi toppling slope is located in the reservoir area of Shiziping hydropower station in Sichuan Province. On September 2013 the storage water level was raise up to 2 540 m and the slope deformed strongly and then blocked G317 road. Preliminary analysis shows that during the rapid cutting of valley, the stress release in rock mass leads to displacement towards the free face, and because of hard rock and soft rock, the deformation is uncoordinated. The deformation of soft rock is lager than that of hard rock, resulting in the stress concentration in hard rock, and when the stress is larger than the hard rock strength, hard rock failure happens. The 5.12 Wenchuan earthquake together with highway excavation and rainfall further exacerbated the toppling slope, and then the slope gradually reached a state of stress balance. According to field geological survey, we analyzed the formation mechanism of the toppling slope by means of drilling core and monitoring. Results reveal that the slope is in the early stage of toppling of interbedded soft and hard rocks. The damage of slope rock mass was caused by earthquake and was intensified by water storage and rainfall. At present the slope is in stress adjustment and the deformation will continue for a long period, and also water level rise will no doubt exacerbate its deformation.
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  Argument of Deep Sliding Mode and Resistance Angle of Gravity Dam Foundation in Red Bed Region

  FU Jing, HUANG Shu-ling, WU Yong-jin, ZHI Cheng-jie

  Journal of Changjiang River Scientific Research Institute. 2014, 31(11): 66-70. https://doi.org/10.3969/j.issn.1001-5485.2014.11.0142014,31(11):66-70,88

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  Tingzikou dam is a concrete gravity dam built in typical red rockbed region. The rock geological characteristics are of gentle dipped strata containing several weak interlayers, unfavourable to the deep anti-slide stability of the dam. At present, equal K value method is still the main method of analysing the deep stability against sliding of gravity dam. In practice, the variation of resistance angle greatly influences the result of the safety factor. The focus of this paper is to analyze Tingzikou gravity dam’s stability safety against deep sliding. The difference of the deep sliding surfaces and their variation law using finite difference based strength reduction method and rigid body limit equilibrium based equal safety coefficient method. The reasonable value of resistance angle in the rigid body limit equilibrium method is discussed. This research provides sound basis for the design of gravity dam’s foundation stability against sliding.
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  Stability Analysis for the Left Bank Slope of Baihetan Hydropower Station Based on Block Element Method

  ZHENG Hui-feng, WU Guan-ye, XU Jian-rong

  Journal of Changjiang River Scientific Research Institute. 2014, 31(11): 71-75. https://doi.org/10.3969/j.issn.1001-5485.2014.11.0152014,31(11):71-75

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  The stability of unloading block on the left bank slope has been a critical issue for Baihetan hydropower station. Study on the geologic condition, failure characteristics and deformation mechanism indicates that the sliding failure of three dimensional rock blocks along discontinuities is the main potential failure mode of the left slope. General limit equilibrium method and continuum mechanics method both have some limitations in analyzing the stability of complex block system. In this paper, the method of automatically identifying block is employed to establish the block system model of the left slope. Three-dimensional elasto-viscoplastic block element method(BEM) is adopted to calculate the strength reserve safety factor of sliding blocks. And the controlling discontinuities and the key blocks are revealed. Research results are consistent with both the general limit equilibrium analysis and geomechanical model test, which supports the reinforcement measures for the left slope. The study in this paper could be a guide for the stability analysis of complicated rock block system.
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  Deformation Mechanism and Engineering Influence on the Stability of Tanggudong Landslide

  XIAO Hua-bo, WANG Gang, ZHENG Han-huai, XIA Wan-hong

  Journal of Changjiang River Scientific Research Institute. 2014, 31(11): 76-80. https://doi.org/10.3969/j.issn.1001-5485.2014.11.0162014,31(11):76-80

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  According to slope structure analysis and simulation using finite difference method, changes of stress and strain in the Tanggudong slope during the down-cutting of Yalong River valley in the history were studied. The deformation mechanism of slope with structural planes dipping outside in the slope foreside can be summarized into three stages (unloading tension crack, sliding tension pressed crack, and tension pressed-shearing). According to the mechanism analysis and simulation, the locked section of rock mass in the upstream residual deformation slope will show strong stress concentration and severe plastic failure under the impounding of downstream dam site of Lenggu hydropower project and earthquake condition. That can lead to high-speed landslide of the whole slope.
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  Rock Mass Weathering and Unloading Characteristics: Case Study on the High and Steep Slope of Yaojiaping Hydropower Project

  ZHOU Li-ming, XIAO Guo-qiang, WANG Fa-gang, FU Dai-guang

  Journal of Changjiang River Scientific Research Institute. 2014, 31(11): 81-86. https://doi.org/10.3969/j.issn.1001-5485.2014.11.0172014,31(11):81-86

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  The study on rock mass weathering and unloading characteristics in the high and steep slope of Yaojiaping hydraulic engineering mainly include two parts partition of unloading zones in the slope and evaluation of unloading rock mass quality. By employing small arrangement of refraction wave method, we effectively eliminated the effect of excavation disturbed zone (after test adit excavation) on the partition of unloading zones. We also obtained the original rock wave velocity which is directly related to the weathering and unloading. According to national standard of rock mass classification, we carried out wave velocity test and indoor rock mechanical test, and obtained the BQ value of unloading rock mass and its distribution rule.
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  Effects of Dense Unloading Fissures on the Stability of High and Steep Slope of Dagangshan Hydropower Station

  WANG Di-kai, WANG Jie-xiong, DONG Yu-fei

  Journal of Changjiang River Scientific Research Institute. 2014, 31(11): 87-91. https://doi.org/10.3969/j.issn.1001-5485.2014.11.0182014,31(11):87-91,107

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  In the light of special geological conditions of high rock slope in southwest China, we propose a new monitoring method which integrates the monitoring of slope surface, shallow-layer, deep-layer and microseismic monitoring based on long-term engineering practice and summary. According to monitoring results and the geological conditions and slope failure mode, we analyze the deformation of area with dense unloading fissures responding to slope excavation, and summarize the deformation characteristics and analyze its influence on slope stability. The area with dense unloading fissures on the right bank slope of Dagangshan hydropower station is taken as a case study. Furthermore, we compare the conventional monitoring results and microseismic monitoring results with the results of numerical simulation by RFPA^3D. The comparison reveals that the influence of dense unloading fissures is mainly reflected in the slope rock mass structure along the surface deformation.
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  Numerical Simulation of Toppling Rock Mass of Xinlong Hydropower Station

  LIU Li-juan, YOU Xiang, GU Cheng-zhuang

  Journal of Changjiang River Scientific Research Institute. 2014, 31(11): 92-96. https://doi.org/10.3969/j.issn.1001-5485.2014.11.0192014,31(11):92-96

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  Xinlong hydropower station is the fourth station of Ganzi-Xinlong segment of cascade hydropower stations in the upstream of the Yalong River. Toppling rock mass develops widely near the dam on the right bank, with a total volume of about 16 million m³. After the reservoir impoundment, the shear strength of the deformation rock is reduced under the effect of groundwater level rise and soaking, leading to the instability of the toppling rock slope and threatening the safety of dam, flood discharge tunnel and water inlet. By analyzing the engineering geological condition and instability mode, we established discreet element model of the toppling rock slope and obtained the deformation characteristics and failure mechanism of the toppling rock. In seismic condition,the deformation failure of slope mainly happens in strong toppling rockmass,which first inclines towards the free face, and finally breaks off. It has features of landslide because shear failure first happens at the slope toe and top and then penetrates through the whole slope. It also has features of collapse in seismic vibration condition. This research could be a scientific basis for the stability evaluation and slope excavation.
STABILITY OF UNDERGROUND CAVERN SURROUNDING ROCK
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  Stability Analysis for Surrounding Rock Mass of Dagangshan Underground Powerhouse During Construction Excavation

  WANG Jian-hong, HE Ru-ping, WEI Ying-yu

  Journal of Changjiang River Scientific Research Institute. 2014, 31(11): 97-101. https://doi.org/10.3969/j.issn.1001-5485.2014.11.0202014,31(11):97-101

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  Dagangshan hydroelectric power station is a large scale hydropower project developed recently on the Dadu River. In order to analyze the stability of surrounding rock of underground powerhouse caverns during construction excavation, the multiple regression analysis method is employed to inverse the initial geostress field of plant zone, and the functions of initial stress distribution are proposed. The variation regularities of displacement field, stress field and plastic zone of underground powerhouse caverns after excavation are obtained according to the established 3-D numerical computational model. Computing results show that the surrounding rock of Dagangshan underground caverns is stable as a whole after excavation. The weak rock veins are key factors influencing the stability of surrounding rock of underground powerhouse. The soft rock veins and fracture zone must be pre-grouted and reinforced during construction. These computation conclusions have guided the design and construction of the project effectively.
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  Characteristics of Microseismicity of Underground Group Caverns Subjected with Excavation Unloading

  SHA Chun, LI Biao, XU Nu-wen, DAI Feng, HE Gang, LEI Ying-cheng

  Journal of Changjiang River Scientific Research Institute. 2014, 31(11): 102-107. https://doi.org/10.3969/j.issn.1001-5485.2014.11.0212014,31(11):102-107

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  The underground powerhouse of Houziyan hydropower station is a typical deep-buried powerhouse with characteristics such as large scale excavation span, complex structures and stress condition of overlying rock mass. The stability of rock mass in the process of excavation unloading has always been one of the most important and difficult problems during the project construction. So far conventional monitoring methods such as GPS, multiple position extensometers cannot effectively measure and reveal the microfractures inside the surrounding rock mass of underground powerhouse. A high resolution microseismic monitoring system was installed in the underground powerhouse on April 2013, aiming to real-time analyze the deformation and stability of surrounding rock mass subjected with continuous excavation. The real time positioning and investigation of microfractures in deep rock mass is achieved. The monitoring results show that the temporal-spatial evolution distribution regularity of microseismicity can demonstrate the failure mechanism of initiation, propagation, coalescence, interaction and breakthrough till macroscopic deformation of microcracks in deep rock mass of underground powerhouse. Meanwhile, microseismic monitoring can dynamically identify and delineate micro-fracture clustering areas of surrounding rockmass and the potential instability risk areas in the underground powerhouse along with continuous excavation. Finally, assisted with acoustic detection results, a relationship is established between microseismic clusters and rock mass quality. The results could provide guidelines for later excavations and supports in the underground powerhouse of Houziyan hydropower station. Moreover, it’s also a new idea for the stability evaluation of surround rock mass in similar deep-buried underground engineering.
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  Damage Feature and Support Measures of Surrounding Rock of Large-span Cavern under High Intermediate Principal Stress

  ZHANG Luo-bin, CHENG Li-juan, HOU Pan

  Journal of Changjiang River Scientific Research Institute. 2014, 31(11): 108-113. https://doi.org/10.3969/j.issn.1001-5485.2014.11.0222014,31(11):108-113,119

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  The underground powerhouse of Houziyan hydropower station is located in high situ stress (mainly horizontal tectonic stress) region with complex geological conditions and big buried depth. Its first principal stress and intermediate principle stress reaches 36.43 MPa and 29.82 MPa respectively. The adverse impact couldn’t be avoided by adjusting the powerhouse axis, hence posing great challenge to the construction and support design. With this project as an example, we summarize the deformation features oflarge-span underground caverns with high intermediate stress, and discuss the deformation mechanism of surrounding rock mass according to the deformation data, support monitoring data and acoustic detection data during construction.It was found that 1)rockburst is common; 2)the deformation and failure depth are large; 3)the anchor support structure has big load level. The results of fast feedback analysis during construction period, the situ monitoring data and the acoustic detection data are used to verify the effectiveness of the support measures. We also summarized some experiences and lessons in this regard.
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  Active Prevention of Rock Burst by Blasting Technology in Jinping Auxiliary Tunnel

  WANG Ji-min,WU Xin-xia,ZENG Xiong-hui, YAN Peng

  Journal of Changjiang River Scientific Research Institute. 2014, 31(11): 114-119. https://doi.org/10.3969/j.issn.1001-5485.2014.11.0232014,31(11):114-119

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  The regularities of rock burst distribution along auxiliary tunnel during excavation are presented, and the measures of controlling rock burst by technology of destressing blasting and controlled blasting are discussed. The practice of rock burst controlling during the excavation of Jinping auxiliary tunnel which crosses the Jinping mountain with an average buried depth of 1 500-2 000 m is taken as a research background. The regularities of rock burst distribution along the auxiliary tunnel indicate that the rock burst should be prevented in two ways the stress concentration in surrounding rock and also the energy storage capability of surrounding rock should be reduced. Particular attention should be paid to relieve the stress in the areas in front of and both sides of tunnel face when destressing blasting methods are adopted during excavation of tunnel sections with strong and extremely strong rock burst proneness, and the distance between blast holes should be within 1-2 m, which should not be too large, or the efficiency and effectiveness of stress relieving would be reduced. In addition, the controlled blasting measures, such as improving the shape of cavern contour, adjusting drilling procedures and controlling blasting footage below 2 m, could be used to improve the stress state and reduce blasting disturbance, and they are proved to have positive effect on reducing the frequency and grade of strong and extremely strong rock burst.
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  Mechanism of Rock Burst Caused by Excavation Unloading Effect

  WANG Yang,YIN Jian-min,LI Yong-song, ZHOU Chun-hua,AI Kai

  Journal of Changjiang River Scientific Research Institute. 2014, 31(11): 120-124. https://doi.org/10.3969/j.issn.1001-5485.2014.11.0242014,31(11):120-124

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  In view of the rock bursts caused by excavation unloading in the deep diversion tunnel of JinpingⅡhydropower station, we carried out numerical simulation to research the effects of unloading range and unloading degree of surrounding rock on rock burst. Research indicates that the potential power source zone of rock burst gradually transfers to the deep and the probability of rock burst is further reduced when the unloading range and unloading degree increase. Moreover, the impact of unloading degree on rock burst is more significant than that of unloading range. The research provides theoretical foundation for preventing rock burst in deep underground projects.
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  Rapid Analysis Method for the Stability of Underground Chambers with Double Faults

  LI Ning, LIU Nai-fei, JIAN Qiang

  Journal of Changjiang River Scientific Research Institute. 2014, 31(11): 125-130. https://doi.org/10.3969/j.issn.1001-5485.2014.11.0252014,31(11):125-130

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  The analysis speed of commercial softwares cannot meet the timeliness requirements of information construction. In view of this, an entirely new idea is proposed in this paper. Firstly, 4 groups including 15 parameters which have significant impacts on the stability of tunnel are generalized and test plan is drawn up. Subsequently the relational database of numerical analysis results and the main influences is established, and the rapid analysis and evaluation system for underground chamber with double faults is built up with the help of BP neural network. This system is employed to analyze the stability of the powerhouse of Laxiwa hydropower station. The error of peripheral deformation is less than 20%, which meets the engineering requirements and shows a good reliability of this system.
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  Analysis of the Excavation and Support Process of Large Underground Caverns in Jointed Rock Masses by Discrete Element Method

  WANG Shuai,TANG Ai-song,XIONG Shi-hu,HUANG Shu-ling

  Journal of Changjiang River Scientific Research Institute. 2014, 31(11): 131-135. https://doi.org/10.3969/j.issn.1001-5485.2014.11.0262014,31(11):131-135

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  With the underground caverns of Dagangshan hydropower project as background, discrete element program is adopted to simulate the excavation and support processes of underground caverns cut by different geological structures. The research focuses on the effect of bolt on the deformation, stress state and damage zone of different rock structures, and the mechanism of bolt support in jointed rock mass is discussed. The results reveal that the rock bolt gradually takes effect with the relative dislocation of joints and stress adjustment of ground rock. Limited to this interaction mechanism, bolts cannot improve rock stress state effectively. Therefore, the role of bolt strengthening is to enhance the shear strength and tensile strength of joint, improve safety factor of key blocks, and prevent the blocks from collapsing. Comparison with monitoring data manifests that the discrete element model could reflect the effect of rock bolt support in practical engineering.
ENGINEERNG DESIGN AND CONSTRUCTION MONITORING
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  Reassessment of Structural Safety of Super High Arch Dam

  WANG Ren-kun, ZHANG Chong, CHEN Li-ping, ZHONG Yi-hui

  Journal of Changjiang River Scientific Research Institute. 2014, 31(11): 136-142. https://doi.org/10.3969/j.issn.1001-5485.2014.11.0272014,31(11):136-142

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  The safety factor of arch dam, which is an important standard of dam safety evaluation, shows a great disparity between design value and actual value. In order to rationally identify the ral safety condition of arch dam, a large number of high arch dam projects are discussed. An estimation formula of the actual possible safety factor of arch dam is derived by correcting the actual strength of concrete and the maximum possible stress of dam structure by using multi-arch beam method. Results demonstrates that the actual safety factor could be guaranteed to be larger than 1.0, which indicates a rational safety margin. The design safety factor could achieve the real security requirements.
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  Combinatorial Method of Deformation Prediction Based on Multipoint Monitoring for Large Slope and Its Engineering Application

  TAN Xiao-long

  Journal of Changjiang River Scientific Research Institute. 2014, 31(11): 143-148. https://doi.org/10.3969/j.issn.1001-5485.2014.11.0282014,31(11):143-148

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  Time series analysis model based on single monitoring point is independent which doesn’t fully consider the space correlation of similar monitoring points, and couldn’t reflect the overall trend and pattern of slope deformation. On the basis of single point grey forecasting model, we applied fuzzy clustering method to the time series relationship analysis of slope monitoring points and established a deformation prediction model in consideration of multipoint space relevance. The model is applied to slope engineering of Jinping hydropower station and the results show that the reliability and accuracy of this method are obviously higher than those of single point prediction model.
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  Safety Forecasting Based on Microseismic Monitoring and Its Application to Rock Slope

  ZHOU Zhong,CAI De-wen,SHA Chun,XU Nu-wen

  Journal of Changjiang River Scientific Research Institute. 2014, 31(11): 149-154. https://doi.org/10.3969/j.issn.1001-5485.2014.11.0292014,31(11):149-154

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  The stability problem of the left bank slope at Jinping-I hydropower station is very prominent. On the basis of microseismic (MS) monitoring technique, the forecasting frames, MS forecasting function and multiple information integration criteria are researched, and a safety early warning system for rock slope stability is set up. The forecasting idea for the left bank slope of Jinping-I hydropower station is built. Thus a comprehensive forecasting system of high slope stability is put forward. This system involves local forecasting based on MS monitoring, global forecasting in consideration of MS damage effect, and multiple information integration criteria. Furthermore, it is applied to the engineering problem at the left bank slope. Results suggest this comprehensive forecasting method could predict the deformation instability risk of rock slope. This research provides basis for the safety warning of the left bank slope of Jinping-I hydropower station during its construction and operation.
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  Dynamic Design of the Intake Slope on the Right Bank of Jinping-I Hydropower Station

  YOU Xiang,YANG Tao,ZHANG Min,YANG Peng-fei

  Journal of Changjiang River Scientific Research Institute. 2014, 31(11): 155-159. https://doi.org/10.3969/j.issn.1001-5485.2014.11.0302014,31(11):155-159,171

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  The slope of approach channel for the inlet of Jinping-I Hydropower Station on the right bank is steep and complex. The engineering geological conditions cannot be confirmed accurately before the slope is excavated. Dynamic design of the slope is necessary according to the new geological conditions revealed during the slope excavation. During the initial excavation, the bottom sliding surface g_yj3 is revealed as controlling structural surface of the slope. The method of determining its parameters and the stability calculation of the block are discussed in this paper. When the slope is excavated to 1 860 m, the controlling structural surface g_8sz-1 is revealed. The method of determining its attitude is discussed. In order to avoid the surface g_8sz-1 being exposed in construction, the size of the platform at 1827m is redesigned. Moreover, three-dimensional numerical model is established to analyze the deformation characteristics of the block after the platform is optimized to determine the scope of controlling block. The safety factor of the bottom sliding surface point is used to study the slide mechanism of block and the support layout scheme. Finally, the stability of the supported block is evaluated by inversion analysis of the slope body’s monitoring data. This research provides reference for the dynamic construction design of steep slope in hydropower projects.

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  Optimization of Construction Schemes for River-crossing Tunnel of Qingdao Metro

  WANG Wei-ming, CAO Zheng-long, LI Qiang

  Journal of Changjiang River Scientific Research Institute. 2014, 31(11): 160-165. https://doi.org/10.3969/j.issn.1001-5485.2014.11.0312014,31(11):160-165

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  The tunnel between Zaoshan station and Licun station of Qingdao metro line 2 is constructed under the Licun-river. The top of the tunnel which is located in the strongly weathered granite layer is covered by sand layer of high permeability and silt clay layer of impermeability. The construction safety must be ensured so that it would not destroy the upper natural aquifer. Five schemes of construction were put forward based on the geological conditions and construction experience. The tunnel excavation process was numerically simulated. Almost all of the factors that influence the deformation and the development of plastic zone of the surrounding rock were taken into account, including construction speed, excavation step distance, excavation method and supporting structures. The most suitable construction scheme was selected by analyzing the deformation regularity of the surrounding rock and comparing the curves of deformation at key locations and settlement at the top of the tunnel in each scheme. Furthermore, the construction parameters of the optimal scheme were secondly optimized according to the control indexes of the range of plastic zone of overlying rock, the settlement of the top and the convergence value of the sides. In the precondition of ensuring the water resisting effect of silt clay layer, the construction speed was greatly increased. Moreover, the construction method provides scientific basis and technical guidance for safe and rapid construction.
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  Treatment by Areas and Stages for the Cracking Deformation Slope on the Right Bank of Pubugou Reservoir Head

  RAN Cong-yong, HE Lan, YU Xue-ming, YE Fa-ming

  Journal of Changjiang River Scientific Research Institute. 2014, 31(11): 166-171. https://doi.org/10.3969/j.issn.1001-5485.2014.11.0322014,31(11):166-171

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  Pubugou dam is a gravel-soil-core rock-fill dam, if the upstream slope fails, the surge wave would pose great danger to the dam and block the intakes. Given those factors, the deformation and fracture mass is designed as a B1 slope. The slope is divided into 3 zones surface loose zone with small scale slip from the surface to inner layer, off-load deformation zone with relaxed-tension crack and sound rock zone. After detailed exploration, we analysed the slope structure, failure pattern and stability zoning according to the geological conditions. In line with the deformation and failure features and the construction progress of pubugou hydropower station, we took reinforcement measures which contain no excavation, strong support (deep anchorage and surface support), support at different periods and areas, and integral control. Those measures are dynamically adjusted and designed with real time monitoring results. Analysis on the monitoring result after the first stage and preliminary treatment of second stage shows that the deformation trend is becoming slower and no abnormal deformation or sliding layer occurs. In order to provide basis for optimization and make sure the slope is stable in the future, the analysis on the monitoring result is highlighted. This paper provides design idea, reinforcement measures, calculation method, monitoring apporoaches and evaluation process for other similar conditions.
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  Method of Fine Blasting and Mining of Hard-rock Transition Material for High Gravelly Soil Core Rockfill Dams

  WANG Xiao-dong, WU Xiao-yu, WU Xin-xia, ZHANG Dan

  Journal of Changjiang River Scientific Research Institute. 2014, 31(11): 172-176. https://doi.org/10.3969/j.issn.1001-5485.2014.11.0332014,31(11):172-176

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  Transition material is crucial to the deformation compatibility of high gravelly soil core rockfill dam. The gradation of transition material is required to be continuous, and the maximum particle size should be less than 300 mm according to specification. Blasting excavation is quite difficult because the average block size (d₅₀) is small (only 15 mm-55 mm), especially when the source material is granite or other hard rocks. By appropriately increasing the unit explosive consumption, arranging reasonable hole distance between gun holes, and adopting tinny difference sequence blasting network, the transition material of Changheba hydropower station could be directly obtained by blasting excavation method. According to the test results, a method is proposed to correct the uneveness index of Kuz-Ram model. To control the block size of the transition material blasting excavated from sound rock, the blasting area should be well chosen, and high power emulsion explosive, high-precision detonator and optimized blasting parameters could be adopted. This research provides reference for blasting excavation of rockfill dam material which is strictly required in particle size distribution.
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  Monitoring and Analysis of Tension-Displaced Rock Mass during the Construction of Jinping Hydropower Station

  DENG Jian-hua,QIU Shan-ming,YANG Hong

  Journal of Changjiang River Scientific Research Institute. 2014, 31(11): 177-181. https://doi.org/10.3969/j.issn.1001-5485.2014.11.0342014,31(11):177-181,188

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  The left bank excavation slope of Jinping first stage hydropower station is remarkable of its height, scale and bad stability condition. The tension-displaced rock mass is comprised of several structural tectonic structural planes and is critical to the stability of the whole excavation slope. The safety monitoring for the tension-displaced rock mass is introduced. Overall analysis on the time evolution and spatial distribution of the tension-displaced rock mass is conducted by using correlation, factors analysis, and eigenvalues statistics according to geological conditions and construction information. The monitoring data of surface, shallow and deep deformation suggest that the tension-displaced mass is consistent with the overall slope deformation characteristics after excavation and support, and after six years of tests, it has gradually stabilized.
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  Influence of Blast Source Parameters on Spectral Characteristics of Vibration Induced by Blast of Rock Mass

  LI Peng,LU Wen-bo,WU Xin-xia,CHEN Ming,YAN Peng

  Journal of Changjiang River Scientific Research Institute. 2014, 31(11): 182-188. https://doi.org/10.3969/j.issn.1001-5485.2014.11.0352014,31(11):182-188

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  This research is conducted in the aim of better controlling the impact of blasting vibration. The spectral expression of triangle blast load and the spectral solution of vibrations induced by the blast sources of sphere charge and cylinder charge are derived through theoretical analysis. The regularity of main frequency attenuation of vibration induced by single hole blast is investigated by the dynamic finite element method based on the equivalent simulation of blast load. On this basis, the influence of blast source parameters on spectral characteristics of vibration induced by blast of rock mass is discussed. The results indicate that the spectral composition and main frequency attenuation law of blasting vibration are dependent on the parameters of the blast source. The time of blast load buile-up mainly affects the spectral range, while factors such as the time of blast load reduction, the charge weight and the charge structure mainly affect the high and low frequency proportions and the frequency attenuation rate of blasting vibrations.
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  Summary on the Monitoring of Vibration Caused by Blasting Excavation of Force-resisting Mass on the Left Bank of Jinping First Stage Hydropower Project

  ZHAN Xue-jun, WU Cong-qing, LEI Ji-fei, ZHENG Yuan-fu

  Journal of Changjiang River Scientific Research Institute. 2014, 31(11): 189-194. https://doi.org/10.3969/j.issn.1001-5485.2014.11.0362014,31(11):189-194

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  On the basis of measuring particle vibration velocity and macroscopic investigation of the force-resisting mass on the left bank of Jinping first stage hydropower project, we proposed the empirical formula of vibration spread regularity and the measures of controlling blasting vibration of the adjacent tunnel’s newly casted concrete. Testing results show that vibration control for the drainage hole of dam foundation is crucial. If the maximum explosive quantity of single shot as well as the angle included between cut hole’s axial direction and tunnel’s axial direction are suitable, and if the excavation and supporting time is rationally arranged, the safety controlling standard can be met. But for the sake of safety, the maximum explosive quantity of single shot should be strictly controlled. Furthermore, blasting vibration control and factors affecting the peak vibration velocity are analyzed. This research is a reference for similar engineering excavation.