Practices on rockburst prevention and control in headrace tunnels of Jinping II hydropower station

Rockburst problems induced by high in-situ stresses were prominent during construction of the headrace tunnels of Jinping II hydropower station. The rockbursts occurred in various forms, and it is necessary to take pertinent measures for integrated prevention and control of rockbursts. In view of the rockburst characteristics during tunnel construction of Jinping II hydropower station, the engineering geological conditions were presented, and the features, mechanisms and forms of rockbursts observed during construction were analyzed in detail. A large number of scientific researches, experiments and applications were conducted. Multiple measures were adopted to prevent and control rockbursts, including the prediction and early warning measures, stress relief by blasting in advance, optimized blasting design and optimized tunnel support in the tunnel sections prone to strong rockbursts. The effectiveness of these prevention and control measures was evaluated. Experiences have been accumulated through a great number of helpful explorations and practices for rockburst prevention and control. A comprehensive rockburst prevention and control system has been gradually established.

Rock mechanical problems and optimization for the long and deep diversion tunnels at Jinping Ⅱ hydropower station

According to site-specific environments such as high water pressures, high in-situ stresses and strong rockbursts, the design scheme of the long and deep diversion tunnels at Jinping II hydropower station was optimized to ensure construction safety. New drainage tunnels were considered. Furthermore, lining structures and grouting pressures were modified during the excavation of tunnels. The construction scheme was updated dynamically based on the complex geological conditions. For instances, the diversion tunnels were first excavated by drilling and blasting method at the first stage of construction, and then by the combination method of tunnel boring machine （TBM） and drilling and blasting, and finally by drilling and blasting method. Through optimized scheme and updated construction scheme, the excavation of diversion tunnel #1 was successfully completed in June, 2011. This paper summarizes the key issues in rock mechanics associated with the construction of the long and deep diversion tunnels at Jinping II hydropower station. The experiences of design and construction obtained from this project could provide reference to similar projects.

Laboratory creep tests for time-dependent properties of a marble in Jinping Ⅱ hydropower station

In order to investigate the time-dependent behaviors of deep hard rocks in the diversion tunnel of Jinping II hydropower station, uniaxial creep tests were carried out by using the triaxial testing machine RC-2000. The axial compressive load was applied step by step and each creep stage was kept for over several days. Test results show that： （1） The lateral deformation of rock specimens is 2-3 times the axial compressive deformation and accelerates drastically before damage, which may be employed as an indicator to predict the excavation-induced instability of rocks. （2） The resultant deformation changes from compression to expansion when the Poisson＇s ratio is larger than 0.5, indicating the starting point of damage. （3） In the step-loading stages, the Poisson＇s ratio approximately remains constant; under constantly imposed load, the Poisson＇s ratio changes with elapsed time, growing continuously before the specimen is damaged. （4） When the applied load reaches a certain threshold value, the rock deteriorates with time, and the strength of rocks approximately has a negative exponent relation with time. （5） The failure modes of the deep marble are different in long- and short-term loading conditions. Under the condition of short-term loading, the specimen presents a mode of tensile failure; while under the condition of long-term loading, the specimen presents a mode of shear failure, followed by tensile failure.

Study of International Coordination of Chinese Monetary Policy under Open Economy

Preliminary study is made to the international coordination of national monetary policy under economic globalization and informationalization. This paper uses Game Theory to analyze the operation effect of Chinese monetary policy. It suggests that the maximum effect of Chinese monetary policy can only be achieved by cooperation and coordination with international society.

Preliminary engineering application of microseismic monitoring technique to rockburst prediction in tunneling of Jinping Ⅱ project

Monitoring and prediction of rockburst remain to be worldwide challenges in geotechnical engineering.In hydropower,transportation and other engineering fields in China,more deep,long and large tunnels have been under construction in recent years and underground caverns are more evidently featured by ＂long,large,deep and in group＂,which bring in many problems associated with rock mechanics problems at great depth,especially rockburst.Rockbursts lead to damages to not only underground structures and equipments but also personnel safety.It has been a major technical bottleneck in future deep underground engineering in China.In this paper,compared with earthquake prediction,the feasibility in principle of monitoring and prediction of rockbursts is discussed,considering the source zones,development cycle and scale.The authors think the feasibility of rockburst prediction can be understood in three aspects：（1） the heterogeneity of rock is the main reason for the existence of rockburst precursors;（2） deformation localization is the intrinsic cause of rockburst;and（3） the interaction between target rock mass and its surrounding rock mass is the external cause of rockburst.As an engineering practice,the application of microseismic monitoring techniques during tunnel construction of Jinping II Hydropower Station was reported.It is found that precursory microcracking exists prior to most rockbursts,which could be captured by the microseismic monitoring system.The stress concentration is evident near structural discontinuities（such as faults or joints）,which shall be the focus of rockburst monitoring.It is concluded that,by integrating the microseismic monitoring and the rock failure process simulation,the feasibility of rockburst prediction is expected to be enhanced.

A Multi-Gap Multi-Channel Gas Switch for the Linear Transformer Driver

A multi-gap and multi-channel gas switch with convexo-convex discal planet electrodes was designed and investigated. Eight gaps are formed in series by a trigger electrode, six intermediate electrodes and two high voltage electrodes with a uniform gap length of 5 ram. The self breakdown and triggered breakdown performance of the switch are reported. Both the delay time and jitter decrease with the increase in the trigger voltage, switching coefficient and the decrease in the trigger isolating resistor. The delay time of the switch is about 40 ns, and the jitter is less than 2 ns when charged with 4-85 kV and triggered by a voltage pule of -75 kV. The inductance of the switch is about 30 nH.

Visual Dynamic Simulation and Optimization of Zhangjiuhe Diversion Project

With the aim of visualizing the real-time simulation calculation of water delivery system (WDS), a structural drawing-oriented (SDO) simulation technique was presented, and applied to Zhangjiuhe Diversion Project, which is a long-distance water delivery system constructed for draw- ing water from the Zhangjiuhe River to Kunming city. Taking SIMULINK software as simulating plat-form, the technique established a visual dynamic simulation model for the system. The simulation procedure of the system was simplified,and the efficiency of modeling was also enhanced according to the modularization and reutilization of the simulation program. Furthermore, a self-optimization model was presented. Based on the digital simulation models, the on line controlled optimization link was added, and the input data can be continually optimized according to the feedback information of simulating output. The system was thus optimized automatically. Built upon MATLAB software, simulation optimization of the Zhangjiuhe Diversion Project was achieved, which provides a new way for the research of optimal operation of WDS.

The world's largest tunnel group is broken through

On December 8,2011, the last diversion tunnel in the world＇s largest tunnel group is broken through at the site of Jinping II Hydropower Station on Yalong River, Sichuan, China. The project has great significances in the great plan of West China Development and the power transmission from west to east. The tunnel group contains four diversion tunnels, one drainage tunnel and two traffic tunnels. The overall length is about 120 km. The other three diversion tunnels were drilled through on June 6, August 16, and October 20, 2011, respectively.

Experimental Field Study of Movement Charateristics of Rock Blocks Falling down a Slope

The downslope movement of detached rock blocks along steep slopes is an important process endangering the safety of infrastructure along the foot of a slope and on the valley bottom,but only limited knowledge is available on the influence of various factors on the velocity and distance of movement of such blocks.We discuss the influence of the mass and shape of the rock blocks,the steepness of the slope,and the thickness of the overburden on the slope,on the distance of movement of rock blocks which was observed in 256 field experiments with differently shaped blocks from 3 different positions on the slope with a height of 176 m.The statistical evaluation of the results of the field tests shows that the slope condition of gradient and overburden is the main factor,the form of rock masses is the second factor,and the mass is the third of the influencing factors.It is the maximum average acceleration for movement of rock masses when the mass of rock masses is 15≤m27 kg,the form of rock masses is flake,the condition of gradient is on average 59.6° and the overburden is basic exposed bedrock and a small quantity of gravel-soil in the experiment condition.It is the minimum average acceleration for movement of rock masses when the mass of rock masses is 9.5≤m15 kg,the form of rock masses is rectangular,the condition of gradient is on average 39° and the overburden is gravel-soil and cinder.Then,the foundation for impact energy is provided and the new feasible methods to prevent potential unstable rock masses are put forward.

Study on the performance of arch dam influenced by relaxation of the foundations following excavation

This paper studies the influence of a stress relaxation zone caused by foundation excavation on the performance of Jinping-I arch dam, using the orthogonal experiment method. Firstly, by adopting the characteristic stress of the dam as an index and coupling it with range analysis, the most significant factors and the degree of relaxation influence on the arch dam performance are found. This is then combined with monitoring data from the dam, and the extent of influence on the arch dam performance caused by the relaxation is evaluated through numerical analysis. The results show that the relaxation of foundation excavation has a negative impact on the performance of the arch dam in general, the extent of elastic modulus degradation in the relaxation zone being the main factor affecting stresses in the dam. The relaxation of the rock mass leads to an increase in dam stress in local areas near the relaxation zone, but has little effect on more distant areas.