Surrounding Rock Stability Control Theory And Technique Of Deep Buried Weak Rock Tunnel Constructed With Double Shield TBM

With the development of national economy and the advance of science and technology,the utilization of underground space is paid attention to more and more. As the tunnel scale become longer, larger, and deeper, the advantages of full face rock tunnel boring machine (TBM) have grown all the more obvious. Because of the main features of security and adaptation to complex stratum, the double shield TBM (DSTBM) has been widely applied to the the fields of underground projects,and can provide advanced technical method for more and more large-scale water transfer projects in the foreseeable future. This dissertation focuses on the surrounding rock stability control theory and technique of deep buried weak rock tunnel constructed with DSTBM method and will provide the key technical solution. The main contents include: stability analysis of surrounding rock with high geostress, calculation and design of segment lining structure, deformation properties of weak rock and the effect factors, rapidly identification and prediction of surrounding rock types, construction plan decision of weak rock tunnel sections, and so on.The responding laws of surrounding rock stress and deformation to different deepth,lithology and geostress field are researched and obtained by elasto-plastic finite element method. The conclusion shows that the deformation, the maximum tensile stress, the maximum compressive stress, and the shear failure scope increase with the increase of bury deepth of the surrounding rock, and hard rock and weak rock have different responding laws of stress and deformation to gravity geostress field and entire geostress field. The results provide calculational basis to the calculation and design of segment lining structure, and the Yin-da-ji-huang project is demonstrated as an examples.Based on the demand analysis of surrounding rock types identification and prediction during construction of DSTBM, using the multi-variables linear regression methods, the relational expression between in surrounding rock quality index BQTBM and the related DSTBM boring parameters is put forward by utilizating the field records of the Yin-da-ji-huang headrace tunnel, which can be expressed as BQTBM=18.406F0.373/P0.127 (correlation coefficient R2=0.865). This research result provide empirical method of rapidly identification and prediction of surrounding rock types in isolation environment according with the domestic design system, which will help to reach the aim of feeding back information in time, designing based on informations, constructing rapidly, safely and economically.Using the three dimensional viscoelastic plastic model, the rheological properties and the deformation properties deponding on age of weak rock in the unloading process are analyzed and studied. Because of the uncertainty of rock mechanical parameters and geostress field, many different computational schemes including advanced adit schemes are carried out and compared. Main results have been obtained as follows:the weak rock with higher geostress has evident rheological behavior of greater momentary deformation and initial strain rate, strain with decay creep; of all the rock mechanical parameters, the momentary deformation modulus has more prominent effect on the deformation of weak rock; the initial geostress field has prominent effect on the excavation deformation, and the higher the initial geostress, the greater the deformation and the plastic zone scope; the greater the size of the advanced adit, the more prominent the stress release efficiency, except undersized advanced adit. The raditions between weak rock deformation and geostress field,rock mechanical parameters are founded, which will provide academic basis for deciding the stability control plan in large deformation section of deep buried weak rock tunnel constructed with DSTBM.Based on the relation of rock deformation and support, the support structure characteristics of weak rock tunnel are analyzed. The concept of coupling between in surrounding rock and support according to the New Austrian Tunneling Method (NATM) is applied to study the support opportunity and procedure of the tunnel constructed by DSTBM, in which the precast reinforcing bar concrete segment lining and the layer formed by pea gravel backfilling and grouting have different deformation characteristics. The post-treatment reinforcing measures of weak surrounding rock and support structure are put forward. DSTBM Method has special mechanical structure and construction surroundings which is different from Opening TBM Method or Drilling Dlasting Method, and various advance geological predictation methods have different principles and application conditions. The advance geological predictation plan, suitable for DSTBM Method, is put forward as fellows:macroscopically forecasting by geological analysis techniqueâ†'daily geological predictating by Bore-Tunneling Electrical Ahead Monitoring Method (BEAM)â†'identificating surrounding rock types in real time by analyzing the DSTBM tunnelling parameters and rock mucksâ†'exceptionally geological predictating by advanced drilling,TSP method, etc. The concept, computational method and guarantee measures of critical jamming avoidance speed are put forward based on weak rock deformation law. Taking the Yin-da-ji-huang project as an examples, this part researchs the several key technical issues in weak surrounding rock: DSTBM mechanical transformation, advanced grouting in normal working state, and DSTBM equipment jamming relief, advanced adit in abnormal jamming state. This part is a complex application combined with the forementioned parts, and provide the decision threads and methods of control technique of stability and deformation during DSTBM construction in weak rock tunnel section with greater deformation.