To avoid the damage of surrounding rock, pre-stressed anchor cables are installed in high side-wall and cavern intersection area to control the large deformation of surrounding rock. However, research is seldom performed on estimating the pre-load of cables in underground powerhouse with high geo-stress and low strength-stress ratio in the previous literature. Jinping-I hydro-power station is recognised as a typical high geo-stress underground powerhouse. Its cavern exhibits remarkable time-dependent deformation during excavation, which may result in the continuous increase of the inner force of the anchor cable and bars, even the strength failure. To determine an appropriate pre-load, a procedure is proposed for calculating the time-dependent released load of surrounding rock, based on their deformation characteristics. At the same time, a formula is deduced to calculate the pre-load factor of pre-stressed anchor cable. This established formula considers the influences of geo-stress, anchorage force and installation time on the pre-load factor. Comparing the actual values with the theoretical values of pre-load factor of Jinping-I underground powerhouse, the result indicates that the established calculation formula for the pre-load factor is reasonable and can be referenced in practical underground engineering.

The deformation and failure of deep soft rock roadways become more prominent. In this paper, two true triaxial model tests were carried out to investigate the deformation and failure law of deep soft rock roadway excavation and the stability characteristics of the surrounding rock after the support. The surrounding rock stress and roadway deformation characteristics can be divided into three stages: advance influence, rapid change and stability. The deformation and failure sequence during the excavation process of the model roadway is “vault → sidewalls → arch springing → roof collapse”. Roof stability is the top priority. After the supporting structure is applied, the surrounding rock stress increases obviously and the roadway deformation decreases. The model test results are verified through field monitoring, and the key deformation parts of the deep soft rock roadway and the characteristics of the supporting structure force are clarified, which can provide reference for later research.

Xiluodu arch dam valley contraction deformation phenomenon is more obvious during initial impound-ment, and the measured value is far more than similar engineering projects.It is necessary to study the influence of valley contraction on the deformation and stress state of high arch dam.For the three full cycles of water storage and water discharge, the measured contraction of valley width was fitted to each survey line.On this basis, dam dis-placement and stress are calculated for normal and dead water level of each impoundment cycle.Dam displace-ment, stress distribution in consideration of progressive valley contraction are compared and analyzed.The results show that the deformation caused by water and sand pressure can be partially offset by a certain range of valley de-formation under normal water level condition.A certain range of valley contraction deformation will reduce the ten-sile stress of upstream dam heel and downstream compressive stress, thus improve the stress state of the dam under the normal water condition.Under dead water level, with the increase of the valley contraction, the principal com-pressive stress of upstream dam face continues to increase, the principal compressive stress of the downstream dam surface decreases firstly, then increases, and tensile stress occurs at the downstream face.The results show that the dam has a large safety margin under the deformation of the current valley contraction.The stress and strain of Xilu-odu high arch dam are in a safe state under the limit valley contraction deformation state ( VDL04 survey line showed the valley contraction would be 70.04 mm on convergence).

The valley shrink deformation phenomenon of Xiluodu arch dam is more obvious during initial impoundment. By the end of May 19, 2017, the VDL04 line of Valley width deformation reached 62.45mm in dam crest, far exceeding the value of similar projects. It is necessary to study the trend of Valley shrink deformation and its influence on arch dam safety. On the basis of the function fitting and convergence prediction of valley deformation, nonlinear finite element boundary displacement overloading method is applied to simulate developing valley deformation. A method of applying incremental shrinkage valley deformation is adopted to study the stress, deformation and plastic zone change of arch dam and foundation and to analyze the weak parts and failure modes of dam and foundation. The safety evaluation of dam under the condition of valley shrinkage deformation limit is carried out. The results show that with the valley width deformation overload multiple increases, downstream dam surface under 420m constraint region produces tensile and shear failure zone under dead water level condition and generate the left and right two plastic branches in the downstream surface of dam above 420m, which expand along near the left and right side of the arch abutment to the upper elevation and expand to the interior of dam and arch crown beam. At the same time, the upstream dam surface has developed the upstream shear and tensile failure zone at the 550m elevation of the arch crown beam, and the symmetrical extension is presented. Research shows that the valley displacement results in a significant increase in the plastic volume of the dam body under the normal water condition when the valley width overload multiple reaches Kcz=3.0 (VDL04 Valley width line displacement is -22.436cm), the valley displacement results in a significant increase in the plastic volume of the dam body under the dead water condition when the valley width overload multiple reaches Kcz=2.0 (VDL04 Valley width line displacement is -14.972cm).

High stress concentrations near an arch dam–foundation interface may cause cracking and failure, particularly in super-high arch dams. Appropriate reinforcement measures are usually needed at the dam toe to increase the shear strength and bearing capacity of the rock mass foundation. In this paper, the criteria and procedure for reinforcement design of dam toe are first given, as priority issues in the overall safety assessment of super-high arch dams. A complete reinforcement analysis method covering the calculation of reinforcement force, effect evaluation and monitoring validation is proposed. With the Xiluodu super-high arch dam as an example, the reinforcement analysis under the numerical simulation and physical model tests performed are described in detail. The results show that the reinforcement measures adopted, such as the toe block and pre-stressed anchor cables, contribute to decrease the local high stresses at the dam toe, as well as increase the cracking initiation factor and the overall safety factor of the dam–foundation system. The reinforcement force loss of anchor cables during the subsequent construction stage has a limited effect on the dam performance. In terms of improving the stability at dam toe, the reinforcement of anchor cables is suggested to be implemented as early as possible. The reinforced dam is finally verified by field monitoring during the operation period. No anomalies in deformation, stress and seepage response near the dam are identified, and the arch dam is shown to perform as desired.

The 285.5 m-high Xiluodu Arch Dam is located in a seismic region along the Jinsha River in China, where the horizontal components of peak ground accelerations for design and checking earthquakes have been estimated to be 0.355 g and 0.423 g, respectively（ g is the gravitational acceleration）. The ground motion parameters of design and checking earthquakes are defined by exceedance probabilities of 2% over 100 years and 1% over 100 years, respectively. The dam shape was first selected and optimized through static analysis of the basic load combinations, and then adjusted after taking into account the seismic loads. The dam should be operational during and after the design earthquake with or without minor repairs, and maintain local and global stabilities during an extreme earthquake. Both linear elastic dynamic analysis and nonlinear dynamic analysis considering radiation damping, contraction joints, and material nonlinearity were conducted to assess the stress in the arch dam.The dynamic analysis shows that the maximum dynamic compressive stresses are less than the allowable levels, while the area with tensile stress over the limit is less than 15% of the dam surface and the maximum contraction openings range from 10 mm to 25 mm. The arch dam has sufficient earthquake-resistance capacity and meets the safety requirements. Nevertheless, steel reinforcement has been provided at the dam toe and in the zones of high tensile stress on the dam surface out of extra precaution.

As the basic principle used in modem underground engineering,the New Austrian Tunneling Method focuses on providing timely and optimized safe support to develop the maximum self-supporting capacity of the rock or soil itself for the stability of the underground opening.But up to now,no reliable formula and theoretical guidance for timely support have been established.The support time can only be empirically determined based on the in-situ monitoring measurements.The timely and optimized support which uses adequate self-bearing capability of surrounding rock means that the rock stress is in the final stage of elastic deformation,but before brittle failure occurs when reaching the critical elastic strain limit.Based on this idea and the characteristics of time-dependent deformation of underground engineering,an approximation formula to calculate the optimum support time is proposed.The study shows that the optimum support time is related to the deformation convergence time,ratio of rock strength to geo-stress,stress after excavation and anchorage pressure.The optimum support time for top arch and side walls can be determined according to the stresses of surrounding rock from point to point.This study may provide a theoretical method to determine the optimum support time which is a critical problem of underground engineering for a long time.

拱坝坝肩地震动力稳定性一直是工程界关注的一大热点,然而对坝肩动力稳定性的评判方法和标准的研究还不成熟.为完善坝肩动力稳定分析方法,将有限元法与刚体极限平衡法的优势相结合,提出了地震动力超载方法以及极限累积位移评判标准.首先,基于有限元法开展实时动力分析,对坝肩可能的滑移块体采用多重网格应力插值求任意时刻的阻滑力和下滑力,确定其主滑方向,而后采用刚体极限平衡法计算每个滑块的动安全系数;同时,对瞬时动安全系数小于1.0的时段,进行加速度积分,求出滑块累积失稳位移.结合滑块尺寸及滑动面强度参数提出极限累积位移计算公式作为失稳判据,通过比较累积位移与极限累积位移判定滑块的稳定性.基于以上思路开发了一套坝肩动力稳定分析系统SAFEDAM.以沙牌拱坝经受反映5.12地震的人工波为例,开展了沙牌拱坝坝肩动力超载稳定分析,验证了极限累积位移判据的合理性.研究表明,沙牌左岸坝肩超载稳定安全倍数Kpo =3.2,右岸坝肩超载稳定安全倍数Kpo =4.2.工程实例计算表明,该方法计算坝肩动力稳定性使用较为方便可靠,具有较大的工程实用价值,为坝肩动力稳定性分析和评价提供了一条新路径.

本文对溪洛渡拱坝蓄水阶段原型监测成果进行归纳总结,论术了监测数据的同步性、连续性、规律性和收敛性特征,初步评价了大坝的运行状态,基于数值仿真反馈分析,研究了大坝受力变形特性的机理,重点阐述了拱坝库盆沉降、上部谷幅收缩效应,分析了坝踵压应力的合理性.结果表明:溪洛渡拱坝初期蓄水期拱坝变形与水库水位变化过程一致,连续变化且符合客观规律,整体时效变形呈现收敛态势;由于溪洛渡特殊的地质条件,库盆压力对大坝变形影响较大,但不影响整体安全稳定;拱坝应力分布良好,坝肩推力在坝基内扩散明显,处于可控状态.综合分析认为,溪洛渡拱坝蓄水过程安全可靠.

通过三维有限元方法进行了溪洛渡拱坝渗流场分析,并采用增量荷载法研究考虑了渗流场通过地基变形作用于高拱坝结构的影响.结合溪洛渡工程,研究了渗流场对高拱坝地基变形的影响,包括横河向和顺河向两方面.对比蓄水前后,采用增量荷载法,研究地基变形增量对高拱坝结构应力和变形的影响及大小.研究成果初步表明渗流场是影响溪洛渡拱坝监测资料反映的径向往上游变形的影响因素之一,后续将深入研究岩石与水力学作用,分析和掌握因水库蓄水而产生的各类荷载以及岩石力学性质的变化,最终明晰高拱坝结构变形机理和真实工作状态.

Starting with the Ertan arch dam (240m high, 3300MW) in 2000, China successfully built a total of seven ultra-high arch dams over 200m tall by the end of 2014. Among these, the Jinping I (305m), Xiaowan (294.5m), and Xiluodu (285.5m) arch dams have reached the 300m height level (i.e., near or over 300m), making them the tallest arch dams in the world. The design and construction of these 300m ultra-high arch dams posed significant challenges, due to high water pressures, high seismic design criteria, and complex geological conditions. The engineering team successfully tackled these challenges and made critical breakthroughs, especially in the area of safety control. In this paper, the author summarizes various key technological aspects involved in the design and construction of 300m ultra-high arch dams, including the strength and stability of foundation rock, excavation of the dam base and surface treatment, dam shape optimization, safety design guidelines, seismic analysis and design, treatment of a complex foundation, concrete temperature control, and crack prevention. The experience gained from these projects should be valuable for future practitioners.

我国水电站地下厂房历经60年的建设发展,数量、规模、技术难度、建设水平等稳居世界前列,形成了具有世界领先水平的超大地下洞室群建设技术体系.本文从建设成就、洞群布置、围岩稳定分析、洞群开挖与支护、监测与反馈技术等方面介绍了我国水电站超大地下洞室群的主要建设技术,并展望了未来的发展方向.

The primary aim of this research is to analyze the hazards and seismic performance of reservoirs and typical large dams based on a field investigation following the Wenchuan 8.0 earthquake. The current seismic performance standards being achieved are discussed and further suggestions are given for super high dams. Based on field investigations, statistics are also given on damaged small reservoirs and damage severities, due to the many various types of earthquake threat. It is of interest to note that the major structures of the medium-sized hydropower stations on the Minjiang river did withstand the Wenchuan earthquake, despite earthquake intensity exceeding engineering design expectations. All the dams remained overall stable. The Shapai roller-compacted concrete (RCC) arch dam and the Zipingpu concrete-faced rockfill (CFR) dam suffered damage. The main earthquake-induced hazards to the dam structures and to both abutments are detailed. Case study analyses of the hazards and reinforcement provision revealed that: 1) The Wenchuan earthquake proved very dangerous for small reservoirs, with destroyed reservoirs widely distributed. The risk of failure of small dams can be classified into three levels based on field investigation. 2) The damage to and behavior of the large dams in the area affected by the earthquake prove that the Chinese codes relating to the seismic design of large dams are appropriate. 3) Appropriate reinforcement can increase the overall stiffness of abutments, riverbed foundation and the adjacent slopes, further improving the seismic performance of dams. 4) The design and management of emergency responses, to cope with extreme conditions, should be improved, and a unified response platform, covering all hydropower engineering projects in each valley should be established. The effects to be expected and the seismic design measures to be taken still pose great challenges for engineers in respect of large dams.

Based on construction and operation of a series of super-high arch dams in China, such as the Ertan Arch Dam, Xiluodu Arch Dam, Jinping-I Arch Dam, Dagangshan Arch Dam, and Xiaowan Arch Dam, construction achievements of super-high arch dams are summarized, and advances in key technologies for super-high arch dam construction are described, including determination of arch dam foundation, shape optimization design, stress analysis and strength design, techniques for stability of dam foundation against sliding, techniques for dam body stability, anti-seismic design, concrete material study, and temperature control and crack prevention of concrete, foundation treatment, and construction technology. It is suggested that construction technology of concrete arch dams in China has reached an internationally leading level. It is pointed out that four issues in construction of super-high arch dams should be further studied:construction of dam safety evaluation systems, dam risk design, anti-seismic measures, and dam health diagnosis technology.

针对混凝土坝工程建设投资大、周期长,同时混凝土容易开裂的特点,提出了混凝土坝厚浇筑层、短间歇期的快速浇筑新方法,并以陶岔混凝土坝为背景,从温度控制、防裂安全和施工工艺等角度研究了该方法的可行性和实现策略.基于水管冷却大体积混凝土温度和应力高精度仿真计算理论和方法,对快速浇筑条件下坝体的温度与应力特性和裂缝机理进行了深入分析与探讨,剖析应力安全的主要影响因素,在此基础上提出了合理可行的综合温控防裂方法.混凝土坝脱离基础约束区后将浇筑层厚度从3.0m增加至4.5m甚至6.0m,浇筑层间歇期缩短至7d以内,单纯地从温度控制、应力安全和施工工艺等角度分析,是基本可行的,但须采取更加严格的温控措施.研究表明,浇筑层厚越大,早期坝体内部最高温度越高,仓面及坝体表面温度梯度越大;间歇期缩短,坝体内部最高温度增加,但仓面温度梯度减小,坝体表面温度梯度增加,拉应力与温度梯度呈正相关关系.新方法能够在确保坝体应力安全的前提下显著加快混凝土坝建设速度,在混凝土筑坝技术领域应用前景广泛.

By taking the construction of a concrete gravity dam within the South-to North Water Transfer Project as a stufy case，the impacts from different thicknesses of concrete placing layers，different intermitted periods in-between interlayers of concrete placement，different concrete placing temperatures on the temperature and stress at the aerly age of concrete of the dam are analyzed and discussed herein; in which the temperature and stress characteristics of the concrete at the early age as well as the cracking risk are deeply studied，and then the corresponding anti-cracking method to ensure the stress safety concerned is put forward. The study provides a technical support for establishing the concrete temperature control criteria and the relevant temperature control measures for the dam concrete under rapid placement.

The aim of this study is to examine cracking and instability of the high and steep left bank slope with weak rock mass structures, and effectiveness of the reinforcements designed for the slope at the Jinping hydroelectricity power station, southwestern China. A new geomechanical model testing method is first proposed for evaluating slope safety factors. In the proposed geomechanical model test, the slope is constructed on a flat testing bed, which can be rotated by hydraulic lifts. By increasing the rotation angle of the testing bed, the forces tending to induce the sliding of the slope are increased, which may cause crack initiation and propagation in the slope and result in rock mass slippage. Thus, through the proposed geomechanical model test, the slope failure mechanism, progressive failure process and final failure pattern can be studied. Moreover, the stability safety factors can be evaluated according to displacement data monitored by sensors installed in the geomechanical model. The geomechanical model test of the Jinping left-bank slope reveals that the bending and toppling cracks occur simultaneously in the unreinforced zone of the slope together with strong relaxation and tension cracks. It is found that the factor controlling the rock mass failure and instability is the structurally weak rock mass and the dominant failure mode is the integral catastrophic instability mode, in which the slope energy is totally dissipated and the slope destabilizes at a limit state. The reinforcement installed in the large area above the elevation of the dam-slope abutment and the unloading action due to the excavation of rocks lying above the dam platform have effectively improved the anti-slide safety factor of the slope, and thus increased its inherent safety factor. On the basis of the geomechanical model testing results and their comparisons with field monitoring results, it is concluded that the installed rock bolts and long anchor reinforcement measures are very effective in keeping the cracks closed in the rock mass and maintaining the slope stability.

Introducing hierarchical and adaptive technique, increasing the order of hierarchical and expand-ing the space of basis function to improve the numerical precision,the 3D p-version hierarchical finite ele-ment method(FEM) and corresponding finite element program of concrete cooling pipe temperature field are proposed and compiled. For a same calculation model, the different mesh density of the traditional FEM and p-version hierarchical FEM is used for analysis and comparative study of concrete cooling pipe tempera-ture field. The comparison of the calculation results shows that the p-version hierarchical finite element method brings better precision with a coarse grid in unsteady cooling pipe temperature field analysis. At the same time, under the condition of the same computational precision, the element number can be re-duced,so that the time consumption for preprocess and computation is obviously reduced.

In order to have a good understanding of the geotechnical behavior around underground opening excavated in stratified rock mass, numerical simulation of a gate-shaped cavern excavation was conducted by applying a transversely isotropic model base on microstructure tensor method. The simulations were performed under the assumption that both the beddings and the in-situ middle stress vector run parallel with the cavern. Effect of the dip angle of beddings and that of in-situ major stress vector on deformation and failure of rock mass around the cavern was investigated. The mechanism underneath the image of deformation and failure was also discussed. It is found that the dip angle of beddings has less influence than the in-situ stress on deformation while the dip angle of bedding and the direction of in-situ major stress vector are equally important to the failure of surrounding rock mass.