Key issues in rock mechanics of the Three Gorges Project in China

The Three Gorges Project is one of the essential key projects for flood controlling and water resources regulation in the Yangtze River.The project includes a river-crossing dam,underground powerhouses,and navigation structures.Because of the huge size and complicated construction technologies,the project faced a series of challenging engineering issues.In terms of rock mechanics,there are many key technical issues,including the sliding resistance and stability of the dam section along the foundations of powerhouses No.1-5,the slope stability of the double-line five-stage shiplock,excavation of large-scale underground powerhouses,and curtain grouting under the dam.With decades of scientific research and 16 years of practical construction experiences and reservoir operations,these key technical issues in construction of the Three Gorges Project are successfully resolved,which will attribute to the development of hydropower technology.On the basis of the monitoring data during construction and normal operation periods of the Three Gorges Project,this paper presents a systematic analysis of these key rock mechanical issues in terms of behaviors,solutions,dynamic controlling,monitoring arrangement and integrated assessment.     

Underground water biological field＇s variation and geoenvironmental safety in city

In the process of city construction, as a comprised factor of city geological environment, underground water takes the most active part, and its dynamic change is fiercest. The city construction unceasingly disturbs underground water chemical, dynamical, physical and biological field. In return, the four fields＇ changes also can affect the geological environment that city lived by, in other words they affect safety and stability of geological environment. Interaction of underground water and the geoenvironment directly displays in the following two ways： The first is that the underground water and the geological body transfer the energy each other; the second is that the strength balance of geological body is broken. Underground water variation brought about by city construction is the factor which cannot be neglected. Underground water variation on the one hand changes soils or rocks＇ physical, biological, chemical and mechanical properties, then influences the deformation and strength of geological body. On the other hand it changes its own physical, chemical properties and biochemical component. At present, from mechanics aspect, interaction between chemical field and biological field variation of the underground water and the geological body lacks research. Although interaction between them is long-term, slow, but when it compared with water-soil or water-rock interaction in the entire process of formation of rocks or soils or geologic evolution history, the qualitative change of the biological and chemical action of rocks or soils brought about by city construction is remarkable, in this paper, aiming at underground water biological field factor which is easily neglected by people, it analyzes that underground water biological field affects possible mechanism and approach of properties variation of rocks or soils in city construction, brings forward further research method and development direction have been also proposed.     

Underground space planning in Helsinki

This paper gives insight into the use of underground space in Helsinki,Finland.The city has an underground master plan(UMP) for its whole municipal area,not only for certain parts of the city.Further,the decision-making history of the UMP is described step-by-step.Some examples of underground space use in other cities are also given.The focus of this paper is on the sustainability issues related to urban underground space use,including its contribution to an environmentally sustainable and aesthetically acceptable landscape,anticipated structural longevity and maintaining the opportunity for urban development by future generations.Underground planning enhances overall safety and economy efficiency.The need for underground space use in city areas has grown rapidly since the 21 st century;at the same time,the necessity to control construction work has also increased.The UMP of Helsinki reserves designated space for public and private utilities in various underground areas of bedrock over the long term.The plan also provides the framework for managing and controlling the city's underground construction work and allows suitable locations to be allocated for underground facilities.Tampere,the third most populated city in Finland and the biggest inland city in the Nordic countries,is also a good example of a city that is taking steps to utilise underground resources.Oulu,the capital city of northern Finland,has also started to ‘go underground'.An example of the possibility to combine two cities by an 80-km subsea tunnel is also discussed.A new fixed link would generate huge potential for the capital areas of Finland and Estonia to become a real Helsinki-Tallinn twin city.     

Safety risk management of underground engineering in China:Progress,challenges and strategies

Underground construction in China is featured by large scale, high speed, long construction period,complex operation and frustrating situations regarding project safety. Various accidents have been reported from time to time, resulting in serious social impact and huge economic loss. This paper presents the main progress in the safety risk management of underground engineering in China over the last decade, i.e.(1) establishment of laws and regulations for safety risk management of underground engineering,(2) implementation of the safety risk management plan,(3) establishment of decision support system for risk management and early-warning based on information technology, and(4) strengthening the study on safety risk management, prediction and prevention. Based on the analysis of the typical accidents in China in the last decade, the new challenges in the safety risk management for underground engineering are identified as follows:(1) control of unsafe human behaviors;(2) technological innovation in safety risk management; and(3) design of safety risk management regulations. Finally, the strategies for safety risk management of underground engineering in China are proposed in six aspects, i.e. the safety risk management system and policy, law, administration, economy, education and technology.     

Measures for controlling large deformations of underground caverns under high in-situ stress condition——A case study of Jinping Ⅰ hydropower station

The Jinping Ⅰ hydropower station is a huge water conservancy project consisting of the highest concrete arch dam to date in the world and a highly complex and large underground powerhouse cavern.It is located on the right bank with extremely high in-situ stress and a few discontinuities observed in surrounding rock masses.The problems of rock mass deformation and failure result in considerable challenges related to project design and construction and have raised a wide range of concerns in the fields of rock mechanics and engineering.During the excavation of underground caverns,high in-situ stress and relatively low rock mass strength in combination with large excavation dimensions lead to large deformation of the surrounding rock mass and support.Existing experiences in excavation and support cannot deal with the large deformation of rock mass effectively,and further studies are needed.In this paper,the geological conditions,layout of caverns,and design of excavation and support are first introduced,and then detailed analyses of deformation and failure characteristics of rocks are presented.Based on this,the mechanisms of deformation and failure are discussed,and the support adjustments for controlling rock large deformation and subsequent excavation procedures are proposed.Finally,the effectiveness of support and excavation adjustments to maintain the stability of the rock mass is verified.The measures for controlling the large deformation of surrounding rocks enrich the practical experiences related to the design and construction of large underground openings,and the construction of caverns in the Jinping Ⅰ hydropower station provides a good case study of large-scale excavation in highly stressed ground with complex geological structures,as well as a reference case for research on rock mechanics.     

Experimental study of water curtain performance for gas storage in an underground cavern

An artificial water curtain system is composed of a network of underground galleries and horizontal boreholes drilled from these galleries.Pre-grouting measures are introduced to keep the bedrock saturated all the time.This system is deployed over an artificial or natural underground cavern used for the storage of gas（or some other fluids） to prevent the gas from escaping through leakage paths in the rock mass.An experimental physical modeling system has been constructed to evaluate the performance of artificial water curtain systems under various conditions.These conditions include different spacings of caverns and cavern radii located below the natural groundwater level.The principles of the experiment,devices,design of the physical model,calculation of gas leakage,and evaluation of the critical gas pressure are presented in this paper.Experimental result shows that gas leakage is strongly affected by the spacing of water curtain boreholes,the critical gas pressure,and the number and proximity of storage caverns.The hydraulic connection between boreholes is observed to vary with depth or location,which suggests that the distribution of water-conducting joint sets along the boreholes is also variable.When designing the drainage system for a cavern,drainage holes should be orientated to maximize the frequency at which they encounter major joint sets and permeable intervals studying in order to maintain the seal on the cavern through water pressure.Our experimental results provide a significant contribution to the theoretical controls on water curtains,and they can be used to guide the design and construction of practical storage caverns.     

4^th Intemational Conference on DAM ENGINEERING（CALL FOR PAPERS AND EARLY REGISTRATION）

Organised by: Hohai University, Nanjing, China; China Society for Hydraulic Engineering;China Society for Hydropower Engineering. Introduction: With the rapid economic and industrial growth of many regions in Asia,the development of water resources is a vital element of the infrastructure to satisfy the ever-increasing demand for power, irrigation and drinking water supply. This development includes both the construction of new facilities and the rehabilitation of existing older plants. Dams are usually the key element in such facilities and their economic construction and safety are of paramount importance.     

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.     

隧道掘进机在中国地下工程中的应用现状及前景展望

The application of tunneling machine to Chinese underground engineering construction is outlined, and its future prospect is forecasted in the light of the requirements for Chinese underground engineering construction in the 21^st century， Further suggestion is put forward on the effective use of tunneling machine.     

Latest progress of soft rock mechanics and engineering in China

The progress of soft rock mechanics and associated technology in China is basically accompanied by the development of mining engineering and the increasing disasters of large rock deformation during construction of underground engineering.In this regard,Chinese scholars proposed various concepts and classification methods for soft rocks in terms of engineering practices.The large deformation mechanism of engineering soft rocks is to be understood through numerous experiments;and thus a coupled support theory for soft rock roadways is established,followed by the development of a new support material,i.e.the constant resistance and large deformation bolt/anchor with negative Poisson’s ratio effect,and associated control technology.Field results show that large deformation problems related to numbers of engineering cases can be well addressed with this new technology,an effective way for similar soft rock deformation control.     

推广应用隧道掘进机促进我国地下空间开发

1　国际发展态势在资源和环境问题日趋严峻的情况下 ,世界各国都日益重视地下空间的开发利用。人们普遍认为 :“19世纪是桥梁的世纪 ,2 0世纪是高层建筑的世纪 ,2 1世纪则是地下空间的世纪”。号召人们“往深处想” ,把地下空间当成一种新型的国土资源 ,并在总体上称之为“地下产业” (ＵｎｄｅｒｇｒｏｕｎｄＩｎｄｕｓｔｒｙ)。地下产业的主要优点在于 :(1)大量节约土地 ;(2 )有利于环境保护 ;(3)有利于生态平衡 ;(4)节约能源 ;(5 )抗震性能及防护性能好 ;(6 )运行费用较低。在岩土工程领域 ,随着地下电站、地下城市、地下铁道、海峡隧道…     

锦屏二级水电站引水隧洞TBM施工工法研究

 锦屏二级水电站引水隧洞是我国目前规模最大的水工隧洞群,特点是洞线长、埋深大、技术难度大,且沿线突水、岩爆、塌方各种地质灾害十分突出,为确保工程施工的安全与按期顺利发电,有必要选择安全快速的掘进方式,为此针对TBM工法,进行大量的调查研究与分析论证,研究结果表明：无论是从岩石的可钻性、耐磨性,还是从岩石的变形、破坏特性,TBM施工都是可行的,对可能遇到的地下水、岩爆、围岩大变形等不良地质条件的处理,较传统的钻爆法有一定的优势,对人员设备的安全具有更好的保护作用。结合地质超前预报和施工中不断改进的施工工艺和支护手段,可以较好地解决施工过程中可能遇到的一些工程难题。     

台灣水利隧道工程TBM開挖首次貫通案例

新武界隧道及栗栖溪引水工程之隧道總長約16.5km,興建完成後將為台灣最長之水利隧道。其中,中游段之引水隧道艮約7.8km,因推估地質均質尚佳且無明顯之剪裂帶或斷層带存在,並為考慮縮短工期、降低對環境之衝擊、減少勞工需求及提昇台灣隧道工程施工技術等因素,決定採用安全且一貫連續快速作業之隧道鑽掘機(TBM)開挖施工。施工期間,於2001年11月份創下659.3m／月之台灣最快鑽掘紀錄,其後雖曾遭遇局部岩盤破碎或異常擠壓等不良地質,以及遭受桃芝颱風之暴雨肆虐成災,然於採取適當應變措施及處理得宜下,TBM終於克服困難並持續順利鑽掘,且於2002年6月7日成功貫通,完成鑽掘工作,為台灣隧道工程首次以TBM貫通案例,且達到最佳平均月進度(315m/月)及最大鑽掘長度(6523m)之新里程碑。     

隧道及地下工程岩溶危害预报的专家系统

在碳酸盐岩类地区修建铁路或公路隧道以及其它各种类型的地下工程时,可能遇到岩溶水突入、涌沙以及洞室坍塌等岩溶地质现象造成的危害。本文根据国内岩溶专家的经验制成专家系统,以便根据具体的水文地质和工程地质勘测资料,对工程所选定的位置和通过的地区的岩溶现象可能对工程发生的危害做出分级预报。本系统可在工程选址、设计以及施工过程中作为一个辅助决策系统为决策者提供信息,以减少工程失误,降低工程造价,保证工期。本系统业经有关专家初步验证,此外,本系统亦可供在水工隧道、地下厂房和矿山坑道的岩溶灾害预报工作中使用。     

Application and development of hard rock TBM and its prospect in China

Compared with the drill and blast method, TBM tunnelling has significant advantages with high construction efficiency, low project cost, conducive to environmental protection, favorable stability control of surrounding rock mass, etc. At present in China, it has become the first choice and development trend in the construction of long and deep buried tunnels and over one thousand meters deep coal mine roadways. Recently, the engineering application and fundamental research of TBM tunnelling in China has made great progresses, also unavoidably with some unsolved problems. In this paper, the application and development of TBM manufacturing and tunnelling technologies in China are reviewed and summarized, and the market demand and application prospect are predicted. The complex geological conditions and technical challenges which will be encountered in China’s future TBM engineering are analyzed. Current progresses in the three aspects of TBM fundamental research, technology development, and engineering application are summarized. The development trend of TBM manufacturing and tunnelling technologies in China are prospected.     

Ground movements due to the construction of cut-and-cover structures and slurry shield tunnel of the Cairo Metro

This paper presents an evaluation of the settlement prediction techniques used to estimate the surface settlements associated with the construction of the Greater Cairo Metro Line 2. The construction of the Cairo Metro involved the construction of cut-and-cover underground stations and bored tunneling. A typical underground station was executed using top-down construction technique. The twenty two meters excavation was carried inside a watertight box with 50-m-deep diaphragm walls to form the sides and a 7-m thick grouted plug at the bottom. Tunneling was performed using a slurry shield tunnel boring machine, TBM, having an internal diameter of 9.48 m. This analysis is the first step in view of enhancing the procedures of settlement prediction and appraising potential damages to overlying structures and utilities for the future construction of the twin road tunnels in the historical urban environment of Al Azhar area and Khan El Khalily market in Cairo.     

重庆地铁六号线一期工程TBM法施工技术

重庆轨道交通六号线一期工程是国内首次采用TBM法施工的城市地铁工程.本文通过重庆轨道交通六号线一期工程的施工,对TBM施工适应性进行了分析、比较详细地介绍了TBM设备选型及其关键施工技术.     

Detecting and monitoring of water inrush in tunnels and coal mines using direct current resistivity method:A review

Detecting, real-time monitoring and early warning of underground water-bearing structures are critically important issues in prevention and mitigation of water inrush hazards in underground engineering.Direct current(DC) resistivity method is a widely used method for routine detection, advanced detection and real-time monitoring of water-bearing structures, due to its high sensitivity to groundwater. In this study, the DC resistivity method applied to underground engineering is reviewed and discussed,including the observation mode, multiple inversions, and real-time monitoring. It is shown that a priori information constrained inversion is desirable to reduce the non-uniqueness of inversion, with which the accuracy of detection can be significantly improved. The focused resistivity method is prospective for advanced detection; with this method, the flanking interference can be reduced and the detection distance is increased subsequently. The time-lapse resistivity inversion method is suitable for the regions with continuous conductivity changes, and it can be used to monitor water inrush in those regions. Based on above-mentioned features of various methods in terms of benefits and limitations, we propose a three-dimensional(3D) induced polarization method characterized with multi-electrode array, and introduce it into tunnels and mines combining with real-time monitoring with time-lapse inversion and cross-hole resistivity method. At last, the prospective applications of DC resistivity method are discussed as follows:(1) available advanced detection technology and instrument in tunnel excavated by tunnel boring machine(TBM),(2) high-resolution detection method in holes,(3) four-dimensional(4D)monitoring technology for water inrush sources, and(4) estimation of water volume in water-bearing structures.     

特长隧道TBM掘进施工技术研究

针对秦岭隧道复杂地质情况 ,采用TBM施工方法 ,对秦岭Ⅰ线隧道出口段的TBM掘进速度与地质、设备维护及管理的关系进行了分析 ,并提出提高工时利用率的方法 ,为敞开式TBM在我国隧道工程施工中的应用积累了经验。     

管片衬砌承担高内水压力的可行性分析

 双护盾掘进机掘进与管片衬砌几乎同时进行,具有快速施工的特点,但管片衬砌能否承受电站引水隧洞高内水压力作用,是决定引水隧洞能否采用管片衬砌及TBM施工的关键之一。结合青松电站引水隧洞,对管片衬砌在承受高内水压力作用下的应力与变形特性进行三维有限元计算,对影响管片接缝张开的主要因素进行分析,获得在高内水压力作用下的管片应力、变形分布,深化对高内水压力作用下的管片衬砌特性的认识。计算发现在内水压力作用下,管片衬砌具有柔性变形特征,就青松电站而言,在现有的接缝止水技术条件下,管片衬砌可承受高水头内水压力作用,这对推动管片衬砌及TBM在引水隧洞中的应用具有重要意义。