Research On The Construction Methods And Ground Response In The Excavation Progress Of Loess Tunnels

Zhengzhou-Xi'an special railway line for passenger transport is one of domestic high speed railways which planed to be constructed and located on the heartland of Chinese bess distributing. The mileage of all the tunnels those crossed loess belt is as much as 65km. All the tunnels on the special railway line are twin-track tunnels, their excavation area reached 174m~2 which is the biggest in our county's loess tunnels at present.Based on the analysis of relevant literature, it is found that although domestic and overseas scholars have done a mass of study on loess, most of them studied on the universality characters of bess such as the form, growth rule, characteristic, conditions of form, etc. The study which aimed at practical projects is not systemic and in-depth enough. The research on the technique of loess tunnel construction, especially the technique of superhuge tunnel construction under the complicated conditions is not enough, and there're lacking for the mature construction experiences which can be used for reference, so existing progenies are difficult to supervise the design and construction of Zheng-Xi railway effectively.In the thesis, based on the worldwide research achievements, the 3D mechanical capabilities of primary support in different construction ways are analyzed by numerical simulation method, the advantages and disadvantages in different construction ways are estimated. Furthermore, the ground mechanical response in the construction process of Gongyi tunnel which designed by the author is analyzed practically. The main achievements are as follows:(1) The construction process of arc-drift, CD and CRD methods are simulated by 3D elastopiastical numerical computation software. The statics of bess ground and support in each phase of construction process is calculated, the stress and displacement field of surrounding rock and support system are analyzed, the intensity of support is verified and the design of support is optimized for choosing the best project and giving directive advices to design and construction.(2) The measure of construction control which will be used inthe segment where the tunnel crossed below 310 national highway is studied practically. Based on fmite element method, the incidence of tunnel excavation, the response of loess ground and the effect of heterotaxy control by different engineering measures(such as the part and the range of grouting, the length of excavation and the thickness of shotcrete, etc.) are analyzed precisely, and the appraisement of the effect of heterotaxy control is given.