Railway tunnel construction is on the unprecedented development. On the basis of analyzing lots of successful and failing engineering projects, the basic idea for railway tunnel construction was put forward, i.e., railway tunnels must be durable; its risk evaluation should be estimated scientifically; the construction time, cost, contract, scheme and design principle should be reasonable; and railway tunnels must be constructed under information management. The design principles were put forward, such as, the selection of single-line or double-track tunnel, the setting of longitudinal slope and aided pilot tunnel, the design of supporting structure, and fast construction, etc. The construction idea and design principle of railway tunnels would provide guideline for tunnel design and construction.
Yichang-Wanzhou Railway which locates in complicated and dangerous mountain areas has complicated geologic conditions and extremely bad geologic phenomena. The article aims to provide some references for similar investigation and route selection by briefly introducing the geologic characteristics, the integrated methods for geologic survey and route selection.
Filling solution cavity of high pressure and rich water have the characteristics features of abundant water, high pressure,large scale and complicated filling medium. Its engineering construction risk is extremely high. The conventional grouting method is affected by inhomogeneity stratum, the choices of material and technique level, so the grouting blind area is difficult to avoid. Once the grouting blind area is breakdown by high pressure water during the process of construction, It will generate large-scale water and mud outburst which cause a disaster. By tackling key problems in science and technology, adopting the energesis and depressurization technology is advanced to father filling solution cavity of high pressure and rich water on Yichang-Wanzhou Railway.It is safe, economical, credible and successful by local practice. The energesis and depressurization technology is adopting arranged and purposeful cccurate–blasting to open out solution cavity, to release storaged energy, to reduce tunnel's influence by water pressure during the process of construction and to finish farthering solution cavity by related measures.
Yichang-Wanzhou Railway is the most complicated project in southwest of China. The conditions of construction are the toughest, the most dangerous in the history of China railways. As to reduce the chance of gushing water and projecting mud soil, the theory of risk management have been introduced and applied in practice for first time. At the same time, the conception of high risks has been put forward and the systemic measures for risk management have been established. Some of the measures are studied and applied for the first time in railway projects including supervisor of geometry survey, advance geometric forecast, safe management at different grades, water monitoring and alarm system. All of these can provide experiences for other karst tunnel's risk management.
Qiyue Mountain Tunnel F11 fault on Yichang-Wuanzhou Railway is formed by breccia, broken rocks and fault gouge composition. It is rich in high-pressure water, with the biggest single whole water inflow of 1 800 m3/h and water pressure of 2.5 MPa. In earlier stage, F11 fault followed the principle of "mainly blocking up and limiting discharge" and grouted the whole cross-section, the construction quantity was huge and the progress was slow. To overcome F11 fault early, the construction technology of "grouting to make solid, using water segrating, excavating and sealing quickly, strengthening monitoring and managing comprehensively" was proposed and whole cross-section grouting was changed into "outside block and inside strengthen grouting" . The common design for high-pressure water-rich fault is thicker reinforced ring and stronger reinforced body. While "outside block and inside solid grouting" assumes the distribution of surrounding rock, water quantity and pressures is uneven, then finds out weak water area and strong water area through advanced prospecting holes, and adopts normal grouting for weak water area and strengthened grouting for strong water area, following the principle of "blocking cracks to reduce water quantity, strengthening supporting rock and improving strata" . Firstly, unconstrained grouting is used through area location holes to effectively control water quantity in strata, then grouting is adopted abiding by the principle of "appropriate drawing pace, blocking water flow, from outside to inside, finding water source by interval holes, and adding holes in necessary areas" . Engineering practices show that "outside block and inside solid grouting" can effectively blocking water and strengthen. The grouting holes and grouting quantity of "outside block and inside solid grouting" are 50 % less than those of whole cross section grouting, and the grouting speed is 80 % higher when water quantity is large, at least 50 % higher in usual condition.
Longlin Temple Tunnel is one of the 26 risk II tunnels on Yichang-Wanzhou Railway. The whole tunnel locates in limestone strata, and the standard height of the whole tunnel is through a vertical seepage zone. In construction process, several large caverns were revealed, whose karst and development characteristics were introduced, and the processing methods of two super-large karsts were discussed. DK232+467 is the biggest cavern in the construction history of China railways, and cavern protection and construction are extremely difficult. Subgrade filling and opencut tunnel were adopted. The large span roof of DK231+796 cavern is very difficult to process and its construction risk is high. Supporting columns were creatively used to support cavern roof. The successfully processing experience of the two super-large caverns will provide reference for similar projects.
When tunnel is constructed in karst cave zone, all kinds of filled caverns will be inevitably meet.The construction method and tunnel structure's stability becomes the key problem for the design and construction. The range of DK255+925~+976, filled with crushed rock and silt, forⅠline of Maluqing tunnel on Yichang-Wanzhou Railway is taken as an example. The mechanical responses of excavation and support are studied by using the three-dimensional fast Lagrangian analysis of continua method. The numerical simulation reveals the distribution characteristics of displacement for surrounding rock and displacement and interial stress for the shotcrete and the maximum axis force for locking anchor pipe under the condition of dynamic step excavation and support. The obtained conclusions offer a guideline for the design and construction of tunnels in similar underground projects.
Taking the construction geology technology practice of karst tunnels on Yichang-Wuanzhou Railway as an example, construction geology, which is a continuation of engineering geological exploration in construction stage, can be used to solve the problems which do not exist or cannot be solved in exploration stage. Taking advanced geology predication as its subject, aiming at avoiding large-scale construction geological harzards, construction geology refers to the comprehensive engineering geology work for ensuring construction progress, construction safety, engineering benefit and project quality, such as predicting possible displacement of tunnel surrounding rock; forecasting potential salt cavities, faults and underground rivers; finding out potential hydrogeology problems and concealed geological disasters after project completion, etc. Construction geology includes comprehensive advanced geology predication, hydrogeological observation and concealed karst exploration.
This paper mainly introduced Yichang-Wanzhou Railway Dazhiping Tunnel DK133+990 karst excrescent body's hydrogeology characteristics, karst development scale, water inrush and mud burst processes and characteristics of high-pressure water-rich cavern. According to karst cave project, hydrogeology condition and water inrush and mud burst mechanisms, cave processing should comprehensively take many factors, such as construction and operation safety, ect. into consideration, and abide by the principle of "releasing energy to reduce pressure, reinforcing by grouting, supporting in advance and processing comprehensively" .
The revealed karst, karst features and treatment measures are described in detail, and different types of karst-specific countermeasures are put up. At the same time, it is stressed that in the encounter of large-scale high-pressure water-rich cavity filling, macro-scopical analysis and understanding of the geological background governs in determining the treatment schedule. The by-pass schedule pertaining to large-scale karst cavities during construction is put up, and relatively construction organization is modified to ensure the project term target. All these can provide reference for the construction of the long karst tunnels.
Karst disaster is badly endangering the safety of tunnel construction and impedes the construction schedule seriously. In present, it is an important and difficult problem in tunnel construction all over the world. The feature of karst water burst in Maluqing Tunnel is analyzed first, and then advanced geological forecasting technology, hydrological observation, reverse slope drainage technology and water release technology in the treatment for the +978 Karst cave are introduced separately; what is more, disclosure progress and the status after disclosing of the +978 Karst cave are depicted detailedly. Finally, curtain grouting technology for stratum consolidation and pile-cap technology for spanning karst cave after the +978 Karst Cave disclosed are introduced too. Successful experience for the karst treatment in Maluqing Tunnel will provide a reference to the treatment for karst cave with large quantity water during the similar tunnel construction in the future.
Taking collapse treatment of cavity rich-water of the Yesanguan Tunnel for example, the construction processes to treat collapse with the method of grouting solid in the condition of drainage and pressure decreasing were introduced. The machinery and equipment of drilling grouting as well as control measures of grouting process in the boundary conditions were also discussed, with a view to provide a reference for dealing with issues of similar projects.
Karst caves and faults are big challenges in tunnel construction. Water gushing happens in these strata frequently, which affects construction schedule and construction safety. Qiyueshan Tunnel on Yichang-Wanzhou Railway crosses underground rivers, karst caves and fractured faults in high pressure and water gushing strata. Fractured fault F11, which has high water pressure, large volume of water gushing and complicated geological condition, is the key of the whole tunnel. Taking the technologies of grouting, water control and rock collapse prevention adopted for fault F11 as an example, the authors present the new construction scheme, new construction technology and new effect examination method for water control and rock collapse prevention in high pressure and rich water fault F11. This paper can provide reference for similar projects in the future.
Tunnel lining water pressure problem has been bone of contention for a long time. Relying on Yichang-Wanzhou Railway karst tunnels to research on distribution of linning water pressure on different anti-drainage patterns (the whole block, block combined with drainage and drainage mode). The primary research method was model test and field monitoring. Model test scale was 1∶16, and test apparatus could be applied earth pressure and water pressure. Acquiring the distribution of linning water pressure by model test: the lining water pressure can't discounted and reduced by the grouting ring at the condition of whole block; the lining water pressure reduced significantly and linear decreased as the development of drainage discharge at the condition of block combined with drainage, simultaneously, the better the effect of grouting, the more outstanding the water pressure reduce; the lining still bear a certain degree of water pressure at the condition of drainage. A part of conclusion about distribution of linning water pressure from model test has been verified in field monitoring.
Water inrush is often encountered during tunnel excavation in karst region, and it will cause the deformation and failure of surrounding rock. So it is of important significance to study the mechanism of water inrush for the prevention of Karst disasters. In this paper, the characters of stress distribution、displacement field and acoustic emission(AE) during the process of water inrush and surrounding rock failure were studied by using RFPA2D (Rock Failure Process Analysis ) software, developed by Center for Rockburst and Induced Seismisity Research of Northeastern University. The results deepen the understanding of the mechanism of water flush and surrounding rock failure caused by gradually increasing hydraulic stress in Karst caves, and it can provide reliable reference for prevention of Karst disasters.
This Issue
Dec 2009, Volume 11 Issue 12