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Lei M.,Central South University | Peng L.,Central South University | Shi C.,Central South University | Wang L.,Chengdu Electric Power Bureau | Liu Z.,Design and Research Institute Co. of CREEC
Zhongnan Daxue Xuebao (Ziran Kexue Ban)/Journal of Central South University (Science and Technology) | Year: 2013

Using the similarity theory and fundamental equations of elasticity mechanics, the similarity criterion of model experiments was deduced, and the experimental program was designed concretely. Through digging simulating tests of model tunnel with three different bias angles (15°, 30° and 45°), the dynamic change law and distribution forms of surrounding rock pressure and lining stress, and the failure mechanism of lining and surrounding rock of shallow buried tunnel under unsymmetrical loading were studied. The results show that during tunnel excavation process, surrounding rock pressure and lining stress change sequentially with excavation, around excavation face, the earth stress releases significantly and shows conspicuous bias characteristics and time-space effect phenomenon. With the increase of bias angle, surrounding rock pressure at shallow buried side decreases gradually, but increases at depth buried side.compared to Code method, the calculation method of surrounding rock pressure on shallow buried tunnel under unsymmetrical pressure underestimates the bias characteristics, it is unsafe. The existence of unsymmetrical loading changes the stress condition of lining structure, the failure forms and types at different positions differ very much, and it is affected by the bias angle, so in practical construction process, the apparent developing characteristics of lining structure should be monitored closely in order to adopt nichetargeting measurements. The failure procedure of surrounding rock in whole construction stage can be described as: Displacement and deformation at locality positions of ground surface → cracking in surface ground at depth buried side under tension → shear slip at depth ground, and its failure forms are an inverse cone-shaped body composed with tunnel at its top and side-entrance slope line at its bottom. Moreover, the rupture angle is affected by the bias angle, being smaller than the code value at shallow buried side, but larger at depth buried side, so the failure form also indicates that the code underestimates the bias characteristicss. Source


Yang X.,Design and Research Institute Co. of CREEC | Chen S.,Chengdu Geological Prospecting and Geotechnical Engineering Co. of CREEC | Li Y.,The No 1 Civil Construction Design And Research Institute Of Creec
Modern Tunnelling Technology | Year: 2013

Geotherms are one of the major hazards to underground structure construction. As a severe geothermal phenomenon has not yet been encountered during tunnel construction, there are barely any systematic theoretical guidelines or treatment experiences to turn to. Based on the survey, design, and construction of the section of the Jiuzhai Tunnel on the Yumeng Railway affected by high-temperature groundwater, this paper presents the difficulties encountered during construction under geothermal conditions, summarizes the types of geothermal hazards to tunnel construction, and puts forward some suggestions regarding revisions to the evaluation standards for geothermal hazards. By means of surveying the thermal (hot) springs near the tunnel, sampling the geothermal water inside and outside the tunnel, analyzing the composition characteristics of hydrogen and oxygen isotopes, and evaluating the tritium radioactive isotopes, the main causes of high-temperature groundwater are analyzed. Moreover, the treatment concept of "ventilation cooling + heat sources reduction + individual protection + partial mechanical refrigeration + construction organization adjustment" is put forward based on site tests, testing, scheme design, and construction verification, and some suggestions on tunnel alignment in geothermal areas are given. Source


Yang H.,Kunming University of Science and Technology | Yang Y.,Design and Research Institute Co. of CREEC | Fu B.,Kunming University of Science and Technology | Wang X.,Kunming University of Science and Technology | And 2 more authors.
Yanshilixue Yu Gongcheng Xuebao/Chinese Journal of Rock Mechanics and Engineering | Year: 2015

Geomembrane with optical fibers is a new type of anti-seepage material, which provides a function of determining the cleft places itself. To study the stability of slope of the laterite dam embedded with the geomembrane with optical fibers, shear strength tests and anti-slide model tests were performed, so that test data about the membrane-soil interface, for example, the cohesion, the friction angle, the slip gradient and the frictional coefficient, were obtained. The data were compared with the ones of the pure laterite and of the laterite with the built-in composite geomembrane. The interface between the geomembrane with optical fiber and the laterite was found to have enough affinity to resist shearing. The anti-slide stability of the dam slope met the specified requirement if the geomembrane with optical fiber was used in earth dam. ©, 2015, Academia Sinica. All right reserved. Source


Li H.,Southwest Jiaotong University | Zhang Z.,Southwest Jiaotong University | Zhang Y.,Southwest Jiaotong University | Chen L.,Southwest Jiaotong University | And 2 more authors.
Modern Tunnelling Technology | Year: 2014

The swelling tendency of expansive rock not only results in the obvious manifestation of supporting structure stress and deformation at the construction stage, but also has a long-term "post-loading effect" during the operation stage, which is different from general tunnels. Based on the principle of elastic mechanics, this paper derives the analytical solution of tunnel support structure stress and deformation under different swelling conditions of surrounding rock. It also analyzes the theoretical relationship between the tunnel support structure stress and deformation and their distribution law regarding the variations of the rock swelling rate, structure support rigidity, and rock swelling pressure. Using a project as an example, the finite element method is adopted for verification, and the results prove that this analytical solution has a certain degree of reliability and can provide a basis for tunnel design and construction as well as a long-term safety evaluation for completed structures. Source


Liu W.,Design and Research Institute Co. of CREEC | Yang W.-H.,Design and Research Institute Co. of CREEC | Zhao F.-Y.,Design and Research Institute Co. of CREEC | Su H.-Y.,Design and Research Institute Co. of CREEC
Journal of Railway Engineering Society | Year: 2014

Research purposes: Caohai is an important part of Dianchi lake, Caohai and transportation construction in the southwest of Kunming city have a close relationship. It has a representability to the engineering geological conditions of Dianchi lake. Studying Caohai main engineering geological problems is advantageous to the Caohai area engineering construction, has great significance to recognize the engineering geological conditions of Dianchi lake, and has very good guidance function to engineering schemes and measures of Dianchi lake area. Research conclusions: (1)Caohai engineering geology condition of Dianchi lake is complex, the main engineering geological problems are peat soil, regional major fault and earthquake, the area with high seismic intensity of sand liquefaction and soft soil subsidence, the shallow natural gas and so on .They have a large influence on engineering. (2)The engineering through Caohai can use tunnel and bridge scheme, the tunnel scheme is better by comprehensive comparison. Tunnel construction can use two process of cut and cover method and shield tunnelling method, cut and cover method can use two kind of construction methods of cofferdam cut and build island cut, shield tunnelling method has minimum impact to natural ecological environmental. (3)The geological conditions of Caohai and Dianchi lake area are similar, have the same engineering geological problem. The road engineering through the Dianchi lake should use shield tunnel scheme. (4)The research results can provide references for underground engineering of soft soil area. Source

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