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2007, 26 (11): -0 doi:
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DEFORMATION CONTROL TECHNIQUES OF
UNFAVORABLE GEOLOGIC BODIES AND DISCONTINUOUS SURFACES IN SUBSEA TUNNEL

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2007, 26 (11): -2161 doi:
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Passing through unfavorable geologic bodies and strata interface is the one of the most difficult problems during subsea tunnel construction. So tunnel geological forecast ahead，grouting reinforcement schemes and construction method optimization are important issues to guarantee the safety of subsea tunnel construction. The control of strata settlement induced by tunnel construction especially for some unfavorable geologic bodies is one of the key techniques during tunnel construction. How to control strata settlement is not only important to the safety during construction period，but also is crucial to long-period safe tunnel operation. According to the characteristics of subsea tunnel，the essence of the inrush of water during subsea tunnel construction is disclosed from the view of the connectivity of strata interface，strata settlement and cave-in，etc.. By using in-situ measured data，numerical simulation and theoretical analysis method，the mechanism of integral deformation of upper strata due to tunnel excavation is then expounded；and subsequently settlement control standard and its determination method for different strata are proposed. The relation between surface crack space and strata displacement is presented to offer guidelines to water inflow prediction. The relation between the thickness of grouting circle and strata settlement is also given to determine the optimal grouting circle thickness for unfavorable geologic bodies. Besides，combined with the characteristics of large-span cross-section of subsea tunnel，tunnel construction technology and monitoring schemes are therein shown. Finally，construction techniques that are used for tunnel passing through unfavorable geology bodies are indicated. The application of above-mentioned technological schemes and measured data are proven to be successful in passing through the weathered slot F1 of Xiamen Xiang¢an subsea tunnel.

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STUDY ON ABNORMAL DEFORMATION CONTROLLING MEASURES FOR LARGE CROSS-SECTION SUBSEA TUNNEL

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2007, 26 (11): -2170 doi:
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Xiamen East Passage subsea tunnel is the first subsea tunnel in China；and its geological conditions are complex and unfavorable with enriched groundwater. During the tunnel construction，the deformation of tunnel support is great. It is important to seek for a reasonable countermeasure to restrict the large deformation to ensure safety construction. Focused on Xiamen East Passage subsea tunnel，field monitoring data are analyzed and numerical calculation is employed. Some measures against abnormal deformation，including setting locking anchor bar，enhancing stiffness and intensity of temporary support，grouting in inverted arch，constructing continuous wall for groundwater proof，changing construction method，are taken. Finally，the countermeasure for abnormal deformation is offered. The analytical results indicate that，to some extent，each countermeasure can decrease the displacements of the tunnel support and all these countermeasures will also reduce plastic area in surrounding rock and increase structure safety to a certain extent. For example，after setting locking anchor bars，arch crown settlement will be reduced about 17%；and level convergence will be reduced 12% and after grouting in inverted arch；arch crown settlement will be reduced about 18%. The analytical method and result can provide references to the latter construction of Xiamen subsea tunnel and the other similar engineering cases.

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SUBSEA TUNNEL PROJECTS IN HARD ROCK ENVIRONMENT IN SCANDINAVIA

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2007, 26 (11): -2176 doi:
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The paper reviews the experiences from Nordic subsea tunnel benchmark projects，with emphasis on subsea road tunnels excavated in bedrock. More than 25 such tunnels have been built in the Nordic countries，representing a total length of more than 100 km，and with the majority of the projects located in Norway. The completed projects include tunnels with length up to 7.9 km and depth below the sea level down to 264 m. All these tunnels have been excavated by methods of drilling and blasting. Important issues concerning investigation，planning，design and construction are described；and important lessons learned from these projects are discussed. Finally，plans for potential future subsea tunnel projects are presented，representing tunnel lengths of up to 24 km and depths below sea level down to 400 m. Also subsea tunnel projects in other Nordic countries will be presented as they have been designed and constructed according to Norwegian subsea tunnel principles.

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EXPERIMENTAL STUDY ON FLOW RESISTANCE DUE TO MULTI-PIER OF TUNNEL DRAINAGE SYSTEM

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2007, 26 (11): -2193 doi:
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Hydraulic experiments are conducted to investigate the Manning roughness coefficient of the tunnel drainage system. Multi-pier with a rectangular cross-section is used for obstacles. Various uniform flows are achieved by adjusting the discharge and the bottom slope for each experiment to evaluate the Manning roughness coefficient easily and accurately. The Manning roughness coefficients for the multi-pier are evaluated for the various cases of longitudinal and lateral pier spacing and water depth. The results show that the Manning roughness coefficient increases with increasing water depth. It is also found that，when the water depth is fixed，the Manning roughness coefficient increases as the longitudinal pier spacing increases up to approximately the pier width. However，it decreases as the longitudinal pier spacing increases further beyond the pier width. On the other hand，when the lateral pier spacing increases，the Manning roughness coefficient decreases. The major findings in this study can be used for the derivation of an empirical formula to estimate the flow capacity of the tunnel drainage system if further experiments are conducted for various shapes and alignments of multi-pier.

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A DECADE′S HYDROFRACTURING EXPERIENCES OF IN-SITU STRESS MEASUREMENT FOR TUNNEL CONSTRUCTION IN KOREA

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2007, 26 (11): -2200 doi:
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Since the hydrofracturing field testing method was first introduced to Korean geotechnical engineers in 1994，there have been lots of progresses in a hardware system as well as an interpretation tool. The hydrofracturing system of first generation was the pipe-line type，so it was not easy to handle with. It had been modified to a wire-line system at its second generation. It is more compact one but it also needs an additional air-compressor. The currently developed system is much more compact and operated by all-in-one system，so it doesn¢t need an additional air-compressor. With a progress in a hardware system，the software for analyzing the in-situ stress regime has also been programmed. For example，the shut-in pressure，which is the most ambiguous parameter to be obtained from hydrofracturing pressure curves，can now be automatically acquired from the various methods. While the hardware and software for hydrofracturing tests are being developed during the last decade，the paper could accumulate the field test results which can cover the almost whole area of South Korea. Currently these field data are used widely in a feasibility study or a preliminary design step for tunnel construction in Korea. Regarding the difficulties in a site selection and a test performance for the in-situ stress measurement at an off-shore area，the in-situ stress regime obtained from the field experiences in the land area can be used indirectly for the design of a subsea tunnel. From the hydrofracturing stress measurements，the trends of magnitude and direction of in-situ stress field are shown identically with the geological information in Korea.

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TIME-DEPENDENT STRENGTH BEHAVIORS OF PRE-GROUTED ZONES IN HAN RIVER- CROSSING TUNNEL

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2007, 26 (11): -2207 doi:
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Grouting technology is used in subsea and river-crossing tunnels for various purposes such as waterproofing，pre-reinforcement and corrosion protection. Cement is a general grouting material that has strong time-dependent behaviors. A method to characterize the time-dependent behaviors of pre-grouted zones around a river-crossing tunnel using elastic waves is suggested，and a method for the analysis of time-dependent effects on river-crossing tunnels based on numerical simulation is proposed. First，an experimental analysis was performed to characterize the time-dependent behaviors of the grouted material. Then，the obtained results from laboratory tests were applied to the numerical simulation of a tunnel taking into account its construction sequences. From the result，it can be concluded that the stiffness and strength of pre-grouted zones with 2–7 days are appropriate to model the time-dependent behaviors of a river-crossing tunnel. Finally，the suggested analytical method of combining experimental and numerical simulations that consider the time-dependent effects on the pre-grouted zone on the tunnel behaviors can provide reliable and practical design and analysis for a river-crossing tunnel.

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HYDROGEOLOGICAL DESCRIPTIVE MODEL USING DISCRETE FRACTURE NETWORK(DFN) IN A SITE CHARACTERIZATION FOR SUBSEA TUNNELS CONSTRUCTION

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2007, 26 (11): -2217 doi:
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[PDF 278 KB] (1946)

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It was aimed to enhance core methodologies required in establishing a hydrogeological site descriptive model using discrete fracture network(DFN). Well-constructed site-specific hydrogeological model should be essentially required in designing and constructing a water-drainage as well as a waterproof system of subsea tunnels. In the present work，based on the borehole investigation results in a crystalline rock，HydroDFN model was constructed by identifying water conducting features(WCF) from the observed fractures and through an intensive conditioning work for WCF parameters. Equivalent block permeability was calculated from the HydroDFN；and the calculated block permeability was compared and analyzed with the in-situ measured data of permeability in the borehole.

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EXPERIENCES WITH SUBSEA ROAD TUNNELS IN NORWAY—CONSTRUCTION，OPERATION，COSTS AND MAINTENANCE

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2007, 26 (11): -2226 doi:
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This paper is based on a publication about subsea road tunnels in Norway from year 2002. The title of the publication is “Publication no. 98，Subsea road tunnels in Norway” of Directorate of Public Roads，Road Technology Department. The first Norwegian subsea tunnel was opened in 1983. Subsequently，24 other subsea tunnels have been built. As a result，in the 2007，a total of 25 subsea tunnels with a total length more than 100 km are open to traffic. Some new are under construction and several other subsea tunnels are also in the process of being planned，including tunnels of up to 24 km length. Most of the tunnels have one tube with two lanes，but some tunnels have an extra lane when the gradient is more than 6 %. The subsea road tunnel projects are located on the trunk roads along the coast，replacing often congested ferry connections，and establishing ferry-free connection from the main land to the communities. Experiences from these tunnels are the theme for this presentation. Generally speaking，building costs for subsea tunnels have been reduced over the years. However，costs vary a great deal from project to project. Operation and maintenance costs also vary considerably. Costs for reinvestment and equipment are particularly high. Water ingress has diminished over time，so that the need for pumping leakage water has been reduced. This study of accidents and fires in Norwegian subsea tunnels covers 17 tunnels opened before 1996. 19 personal injury accidents covering the five years from 1995 including 1999 were analyzed. The accident rate was as low as 0.09(injury accidents per mill vehicle kilometer per year). The rate was highest in tunnels with steep gradients and where annual average daily traffic(AADT) was lower than 1 500. Only three fires have been recorded in Norwegian subsea tunnels. This amounts to a rate less than 10% of the accident rate. As the study covers only 17 tunnels and 19 accidents，the results must be interpreted with this in mind.

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APPLICATION OF NORWEGIAN SUBSEA TUNNEL EXPERIENCES TO CONSTRUCTION OF XIAMEN XIANG¢AN SUBSEA TUNNEL

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2007, 26 (11): -2236 doi:
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Norway has the largest number of subsea tunnels in the world. During the last 30 years，more than 40 subsea tunnels have been constructed，totaling more than 240 km. Though most of these tunnels are located in fair to good ground conditions，some challenging ground conditions have been encountered in connection with faults. A main feature during planning and construction of the Norwegian subsea tunnels is sealing the potential inflowing water. A systematic method for detecting such water in time and to seal it has been developed and refined over the years，and has been used in all Norwegian subsea tunnels. This is presented together with few of the more problematic construction experiences to prevent a cave-in to further develop and that involving ground freezing. Further，the application and implementation of the Norwegian experiences are discussed in the planning and during construction of the Xiamen Xiang¢an subsea tunnel，located in partly problematic and challenging ground conditions. The application of the Norwegian experiences is assisted through the consulting services provided by Norconsult experts during the tendering and the ongoing construction of the Xiang¢an subsea tunnel.

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PRIMARY APPLICATION EXPERIENCES OF WATERPROOF TECHNIQUE IN XIAMEN XIANG¢AN SUBSEA TUNNEL

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2007, 26 (11): -2247 doi:
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Xiamen Xiang¢an subsea tunnel is the first subsea tunnel in China. The geological conditions of land parts of this tunnel are mostly backfill soil，sandy soil or complete weathered rock. Moreover，underground water has strong seepage characteristic. Sandy layer is enriched in water and four weathered grooves under sea directly connect with the seawater. The total water head of groundwater and seawater is between 50 m and 70 m；and the hydrostatic pressure acting on the tunnel arch crown is 0.65 MPa. Therefore，the lining waterproof is a very prominent issue. Considering the geological factors，such as water level，gushing water，erosion of framework and formation of framework，composite lining structure is adopted in Xiamen Xiang¢an subsea tunnel，and the long-time waterproof principle is main shutoff，limited discharge，multilayer proofing and rigidity-flexibility combination. Therefore，the waterproof project is set as part total-closure and limited discharge. For example，the total-closure waterproof is adopted in the parts of main tunnel，which is enriched in water；and the limited discharge project is adopted in the other parts of main tunnel where the surrounding rock is favorable. The total-closure waterproof is adopted in the service tunnel because of its little circle section. Waterproof can be reinforced through injecting pulp. Moreover，construction quality can ensure waterproof system of Xiamen Xiang¢an subsea tunnel. In fact，the waterproof design of Xiamen Xiang¢an subsea tunnel and construction effect is very well accepted. The achieved experiences can provide some references to similar projects.

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EXPERIMENTAL STUDY AND ANALYSIS OF SHEAR-FLOW COUPLING BEHAVIORS OF ROCK JOINTS

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2007, 26 (11): -2253 doi:
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Owing to the long-term geological processes，there are all sorts of discontinuities such as joints in the rockmass. In the jointed rock，the fluid flows are dictated mainly through the passage of the discontinuities. Under the current increased environmental and regulatory controls，the accurate prediction of total inflow to the tunnel excavation is significant factors in the design and construction stages of the underwater tunnel. The surface roughness of discontinuities in rock masses is an important factor to analyze the mechanical and hydraulic characteristics of rock joints. The hydro-mechanical behaviors and properties of rock joints are usually determined by laboratory experiments on fracture specimens. Laboratory testing of rock fractures involves a number of technical issues that may have significant impacts on the reliability and applicability of the testing results；for example，the quantitative estimation of the evolutions of hydraulic transmissivity fields of fractures during shear under different normal constraint conditions，and the sealing techniques when fluid flow during shear is involved. In this study，a new hydro-mechanical test apparatus for rock joint is developed. The surfaces of rock joints are measured before shear by using a 3D laser scanning profilometer system．Thus，a number of shear-flow coupling tests were carried out on three kinds of rock fracture specimens under constant normal load(CNL) or constant normal stiffness(CNS) constraint to evaluate the influences of morphological properties of rock fractures on their hydro-mechanical behaviors. Combined with the cubic law for fluid flow，the test results are analyzed and discussed；and some conclusions about the tests are drawn.

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MODEL TEST ON SEGMENTAL LINING OF NANJING YANGTZE RIVER TUNNEL WITH SUPER-LARGE CROSS-SECTION

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2007, 26 (11): -2260 doi:
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The mechanical characteristics of the single segment lining(f 14.5 m) of Nanjing Yangtze River Tunnel under high static water pressure and the interaction between the lining and the stratum are studied by the indoor model test. With the developed water pressure devices，such as uniform water pressure device and nonuniform water pressure device，the actual circumstance of the water pressure on the lining is simulated；and the effects of the actual water pressure on the structural characteristics of the lining of super-large cross-section for subriver shield tunnel are achieved. The effects of different kinds of segment erections on distribution laws of the inner forces of the segmental lining under high water pressure and the differences of the inner forces due to the nonuniform and the uniform water pressures are discussed. Furthermore，the above-mentioned results are studied with the finite element calculation results. The study can provide instructional references to both design and construction of the Nanjing Yangtze River Tunnel；meanwhile，it can also be adopted for similar projects.

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STUDY ON APPROPRIATE PARAMETERS OF GROUTING CIRCLE FOR TUNNELS WITH LIMITING DISCHARGE LINING IN HIGH WATER PRESSURE AND WATER-ENRICHED REGION

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2007, 26 (11): -2270 doi:
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Subsea tunnels are located deeply under sea with high groundwater pressure. Therefore，external water pressure on lining should be considered when designing tunnel structure. With the idea of blocking groundwater and limiting discharge，external water pressure on tunnel lining can be reduced remarkably with low discharge，so tunnel structure design will be more economical. To find the appropriate parameters of grouting circle is the key issue to perfectly blocking groundwater and limiting discharge. Based on the case of Yuanliangshan tunnel located at high water pressure and water-enriched karst region，the basic regulations of the effects of grouting circle on tunnel gushing water and external water pressure on lining are studied by theoretical calculation and analysis. The concept of tunnel discharge ratio is put forward；and the relation between tunnel and external water pressure on lining is analyzed. Based on the above-mentioned research results，the method and program for choosing appropriate parameters of grouting circle are proposed；and the appropriate parameters of grouting circle for Yuanliangshan tunnel are given. The parameters of grouting circle are adopted；and satisfactory effects are achieved. The monitoring amount of gushing water after grouting is basically identical with theoretically calculated value. Research results indicate that the reduction coefficient of external water pressure on lining is decided by tunnel discharge ratio；it will be zero only when water seepage behind tunnel lining can be discharged absolutely，or there is external water pressure on lining. The effects of grouting circle will not share the external water pressure with tunnel lining，but block groundwater and reduce the external water pressure on lining remarkably with low discharge. The research results will provide references to tunnel waterproofing and drainage system design in high water pressure and water-enriched regions including subsea regions.

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DIGITAL UNDERGROUND SPACE AND ENGINEERING

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2007, 26 (11): -2277 doi:
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After a comprehensive review on the exploitation of information technology in geotechnical engineering and underground engineering，a concept of digital underground space and engineering(DUSE) is proposed. The objectives of DUSE are strategically targeted to provide a way to obtain and organize information about underground space and engineering as follows：(1) a framework in which to publish information；(2) a set of standards about data；(2) new software and services to process useful information out of these data；and (4) new visualization tools to display all relevant information. Then，a theoretical framework of DUSE，which describes the system architecture of DUSE from the viewpoint of engineering，information，services and software system，are put forward. Thus，a taxonomy of all the data in the system is defined. Modeling of 3D space geometrical objects is divided into three categories，which are geological modeling，pipeline modeling and underground structure modeling. Accordingly，the modeling methods of each category are discussed；and spatial query tools and spatial analysis methods are examined. Some basic principles that should be followed in the process of employing visualization and virtual reality technology are also given. Finally，a case study of Shanghai Yangtze River tunnel project is provided. Research results show that DUSE is an innovative new information platform for the whole cycle life of underground space and engineering. DUSE is also a digital museum of the underground space and engineering. By employing the concept，the method and the techniques provided in DUSE，a more realistic and transparent underground space and engineering could be built；huge amount of data could be easily managed and effectively visualized. Therefore，useful information of these data can be processed，improving working efficiency and promoting the implementation of intelligent decision about the engineering project. In addition，some research topics that need to be further addressed are also discussed.

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STUDY ON DETERMINATION METHOD FOR MINIMUM ROCK COVER OF SUBSEA TUNNEL

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2007, 26 (11): -2289 doi:
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At present，many subsea tunnels are under construction or design in China，and the minimum rock cover is one of main issues in subsea tunnel vertical cross-section lining design；and the subsea tunnel cost and safety are directly governed by the minimum rock cover. The determination method and criterion for the minimum rock cover depth is studied. Different methods determining the minimum rock cover depth are analyzed；and the factors of the different methods for the minimum rock cover are researched. The idea and method to determine the minimum rock cover depth of the subsea tunnel by the weight factors are also obtained. At last，combining with practical subsea tunnel engineering，the minimum rock cover of the Ningbo Xiangshan Harbour subsea tunnel by the above methods is analyzed.

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STUDY ON SLURRY-WATER GUSHING DURING UNDERWATER SHIELD
TUNNEL CONSTRUCTION

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2007, 26 (11): -2296 doi:
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The slurry type shield method is the first choice for submarine soft-soil shield tunnel. If the slurry pressure is too high，it may lead to hydraulic fracturing of stratum in front of open face and cause accident of water gushing. The phenomena described as above，including mechanism of fracturing and the influence of slurry pressure on stratum fracturing，are studied. The achieved results show that，as slurry type shield is driven in submarine stratum，it is inevitable for some tiny cracks to exist in the strata，but the phenomena with/without water gushing has close relation with driving parameter，slurry characteristics，stratum characteristics and overburden thickness. Through theoretical analysis and shield model test，a semi-empirical formula of slurry gushing and anti-gushing method is put forward.

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STRATUM DEFORMATION MONITORING AND MECHANISM
ANALYSIS OF XIAMEN SUBSEA TUNNEL

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2007, 26 (11): -2302 doi:
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Xiamen subsea tunnel is the first subsea tunnel in China. During its excavation process，engineers are faced with many technical difficulties，especially the large deformation of stratum，the controlling methods of sand layer and complete weathered granite. In addition，the issues that how to go through the weak structure interface， complete weathered deep valley or capsule during construction are specially considered；all these issues urgently need the understanding of the deformation law of tunnel for upper strata；and the controlling measures of the large deformation should be taken. Combining the three-dimensional numerical modeling of fluid-solid coupling，it is shown by the in-situ deformation monitoring that how the stratum subsidence is distributed and developed with time and space，and that how groundwater transports and works. Meanwhile，mutual influences and interaction of surrounding rock-lining-presupporting-pregrouting-water structure system can be well modeled and explained. The research results agree well with the results of field test of weak deep-sea valley. It is also further verified that surrounding rock，lining，as well as construction controlling techniques are the key factors in subsea tunneling.

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PRACTICE ON SYNTHETIC GEOLOGICAL PREDICTION AHEAD OF CONSTRUCTION OF XIAMEN SUBSEA TUNNEL

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2007, 26 (11): -2309 doi:
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In view of the actual situation that there is still not any systematic theory of geological prediction for the tunnel construction，the concept of geological prediction ahead of construction for the tunnel and technical scheme of geological prediction have been constructed on the basis of the previous research results；and a complete set of geological forecasting techniques including the macro forecast，the long-term prediction，the short-term prediction and the alarm of the disaster approach，have been proposed based on the theory of geomechanics. According to the practical test of the prediction in Xiamen subsea tunnel，the accuracy of the prediction can meet the requirements of the construction standards. It shows the rationality and feasibility of the related theory and the technical method；and the proposed technical method can provide some references to the tunnel constructions.

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HIGH PRESSURE PERMEABILITY TEST ON HYDRAULIC TUNNEL WITH STEEP OBLIQUITY FAULTS UNDER HIGH PRESSURE

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2007, 26 (11): -2318 doi:
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The high pressure permeability test(HPPT) of in-situ test is an effective method to investigate the deformation and permeability of rock mass due to high pressure. During the process of full-scale experiment of a pumped storage power station，an approach for HPPT with steep obliquity faults and the experiments are studied to observe the variation of pore water pressure and deformation of the rock mass due to high water pressure. A wave-like theory of hydraulic fracture for description of fractured area spreading is also developed to understand the experimental results. The failure characteristics due to seepage under high pressure are presented on the basis of combining experimental results and knowledge of hydraulic fracture；also，different forms of seepage failure between rock mass and soil are presented. To investigate the characteristics of seepage deformation due to high pore water pressure in rock mass，pore pressure and deformation of the rock mass are measured simultaneously during the experiment. The deformation law due to the variation of pore water pressure in rock mass indicates that the coupled hydro-mechanical effect cannot be ignored during the analysis of the stress state and stability of surrounding rock mass. It is suggested that the theory of coupling analysis would be helpful to reduce the failure risk of surrounding rock mass located in high pore water pressure environments.

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EXPERIMENTAL STUDY ON INFLUENCES OF GROUNDWATER AND CONFINING PRESSURE ON MECHANICAL BEHAVIORS OF SOFT ROCKS

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2007, 26 (11): -2324 doi:
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Baozhen tunnel is the only soft rock tunnel and the key project in the Yichang—Wanzhou Railway. The very complex geological environments，such as high earth stress，deep-buried rich groundwater，very weak and cracked rock masses and asymmetric pressure along the rock strata，make self-stability of the tunnel unfavorable. During tunnel construction，the high deformation rate，intense and long-time deformation are the basic characteristics. At the same time，the deformation shows asymmetrical features and uniformities. Through analyzing the causes of large deformation，it is deemed that groundwater and high earth stress are the critical factors causing large deformation. So using XTR01–01 microcomputer electro-hydraulic servo-controlled triaxial test instrument to study the change law of soft rock strength under different saturated time and confining pressure is significant to assure the design, construction and operation safety of tunnel. The mechanical behaviors of black macker that is widely distributed in Baozhen tunnel are discussed by designing a series of triaxial compressive tests under different saturated times；and research on variation laws of mechanical properties under different confining pressures and saturated times is carried out，describing complete stress-strain curve of macker(saturated time is 1 month) with different confining pressures. The variation laws along with confining pressure and saturated time are analyzed. In addition，the mechanism and relationship between confining pressure，saturated time and strength are researched. Finally，according to dynamic evolution law of adjacent rock，the supporting principles for large deformation in weak rock and high earth stress are put forward.

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STUDY ON DURABILITY PARAMETER DESIGN OF SUBSEA TUNNEL REINFORCED CONCRETE BASED ON CHLORIDE CORROSION

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2007, 26 (11): -2333 doi:
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Kiaochow Bay subsea tunnel is the second self-building tunnel in China with the designed service life over 100 years. On the basis of service environment of subsea tunnel concrete，the durability experiments of concretes are conducted and concretes are compared with those of other major engineering cases. The prediction modeling of service life considering concrete carbonation，initial chloride contents and chloride diffusion in concretes is proposed. Considering the requirement of 100 years service life of subsea tunnel，the modeling parameters are calculated according to prediction modeling of service life. The results show that cover thickness of lining concrete，which faces to atmosphere，should be more than 70 mm and those of other sides should be more than 60 mm. The initial chloride concentration in concrete should be less than 0.15% of binding materials；and chloride diffusion coefficient of lining concrete must be less than 4×10－12 m2/s. Moreover，the water to binder ratio w/b of lining concrete should be less than 0.34 and strength grade higher than C50. Based on quantitative relationship between durability of concrete and mixture proportion，raw materials and the principle of mixture proportion designed as well as raw materials choice are given based on 100 years service life of subsea tunnel.

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DEVELOPMENT AND PROPERTIES STUDY ON FUNCTIONALLY GRADED CONCRETE SEGMENT USED IN SHIELD TUNNELING

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2007, 26 (11): -2341 doi:
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For the environments with high pressure and enriched water of Wuhan Yangtze River Tunnel，the properties of high-durability and long-life are necessary for the segments used in shield tunneling lining structure. By means of the principle of functionally graded materials(FGM)，the FGM design and optimization for reinforced concrete segment were proceeded，and the multifunction，which consists of higher impermeability of covering，higher strength of structure layer；and fire-resistant inner layer of the segments，were realized. Furthermore，the proper interface producing technology is adopted to assure the homogeneous transition of properties of different material layers，and the integrated design effects of function and structure are achieved. According to a series of tests in structure layer concrete and layer covering materials，it can be seen that the permeability of layer covering is much lower than that of the ordinary concrete and the chloride diffusion coefficient of layer covering was decreased with one order of magnitude，while the service life was increased more than ten times. It was better than the reported greatest value(6×10－13 m2/s). The mechanical properties of structure layer and layer covering are excellent and can satisfy the requirements of design. The compressive strength of layer covering concrete is C70 or above，and that of structure layer concrete is C50. The volumetric stability of layer covering and structure layer are good and the corrosion resistance is improved greatly；and the neutralization deepness of functionally graded concrete segment(FGCS) concrete is less than 1 mm. Furthermore，the fire- resistant inner layer was improved effectively by brushing fire resistance and antiknock materials，and the fire-resistant limit was 4.72 times against that of untreated samples. Finally，the service properties of FGCS were proven to be well by means of the producing and testing in factory for prefabrication.

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STABILITY ANALYSIS OF ROCK COVER OF QINGDAO KIAOCHOW BAY SUBSEA TUNNEL UNDER EXPLOSIVE LOADS

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2007, 26 (11): -2348 doi:
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In order to analyze the effects of the explosive load on the rock cover of Qingdao Kiaoshow Bay subsea tunnel，a calculating model is used；and the explosive load is imposed on surrounding simultaneous blast holes with equivalent stress. Left and right typical segments are chosen according to different surrounding rock types and rock cover thickness；and 3D finite element analysis is performed by ABAQUS. By means of analysis of velocities and accelerations at survey points，it is easy to draw the conclusion that each velocity-time curve and acceleration-time curve can satisfy the subsea distortion rule，and the level and vertical rapidity peak values satisfy those of subsea tunnel failure criterion. The influence scope under explosive load is much less than design rock cover. Then，the design rock cover is steady under such explosive load. At the same time，the referenced rock cover is offered in view of the economical factors，and the value is testified finally.

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ANALYSIS AND PREDICTION OF EFFECT OF CONTROLLING GROUND SETTLEMENT AT XIAMEN SUBSEA TUNNEL

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2007, 26 (11): -2356 doi:
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Xiamen Xiang¢an subsea tunnel is the first subsea tunnel in China. The ground settlement became large when the CRD method was adopted on the right line in Wutong side. So it is determined to change the excavation method，i.e. the both-side drift method. Combined with the construction site and ground settlement，the CRD method is then adopted. The main purpose is to find the possible reasons that cause the large settlement. First，it is focused on the influence of the excavation，and it is seen that the displacement of the tunnel is the main reason that causes the ground settlement. Second，the decreases of the cohesion and friction of soils that are caused by continuous rainfall are contributed to the large settlement. Third，the ground surface of soils is changed into artificial landfill compared with the completed parts. At the same time，the controlling effects of ground settlement when the excavation way is changed to adopt the both-side drift method are obvious. The development of ground settlement with this method is different from that with CRD method，though the maximal settlement is all located at the top of the subsea tunnel. Finally，the difference between the two methods on the controlling effects of ground settlement and the regularity of the surface deformation are summarized. It can provide references to the construction of the project，and it can be adopted for similar projects.

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STUDY ON INFLUENCES OF CHANNEL DREDGING ON LONGITUDINAL STABILITY OF SUBSEA SHIELD TUNNEL

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2007, 26 (11): -2363 doi:
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[PDF 419 KB] (1177)

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The characteristics and influence factors of the longitudinal stability of subsea tunnel with long-distance，high water pressure and large diameter are analyzed；and taking a certain project for example，a study on channel dredging as a new and important influence factor is carried out. Combined with the characteristics，techniques and working procedure of channel dredging，numerical simulation method with a large-scale model with 2.4 km long tunnel structure and seabed stratum is performed. The relations and influences of the channel dredging depth，the dredging working procedure，the alluvium thickness，etc. are presented on structure longitudinal stability，such as deformation and stress. Then，some conclusions of the control function from channel dredging depth to tunnel structure stability are drawn；and a nonlinear relation between dredging depth and structure transmutation and stress is achieved. It can be seen that tunnel longitudinal transmutation is obvious when channel-dredging depth is larger than 7 m. Also，it is pointed out that the control index of channel dredging depth and the layout project of channel dredging should be optimized. Finally，the reinforcing method of the shield tunnel structure and the surrounding stratum is given to guarantee the structure stability. The primary research results have some references to the proper layout and design of the subsea tunnel；meanwhile，more detailed research is also needed in the future.

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NEW MODEL AND METHOD FOR FORECASTING POST-CONSTRUCTION SETTLEMENT OF LOESS-FILL EMBANKMENTS

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2007, 26 (11): -2370 doi:
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[PDF 274 KB] (1332)

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Post-construction settlement is one of the main issues in high grade railway construction in loess areas. The effective solution to the problem is to find the post-construction settlement law for the guidance to the design and construction based on the field monitored data. After analyzing the large quantities of monitored data from the second line of Lanzhou—Wuwei Railway in loess areas，a new model is put forward. The hyperbolic and exponential models usually used as prediction were also applied to the forecasting settlements based on the same monitored data with the presented new model. The results show that the prediction error is smaller than that with usual models；and the forecasting data agree well with the monitored data. The new model presents a new method for analysis and prediction of settlement and it is found to be a good reference to post-construction settlement of embankment in loess areas.