Study On Action Mechanism And Design Methodology Of Tunnel Single Shell Lining

The dissertation, proceeding with researching stability of surrounding rock, expounds the rationale of rock bolt,shotcrete and interact with surrounding rock when single shell lining operating , by the means of numerical simulation and in-situ test, in the same time, presents mechanical property guideposts of shotcrete used for single shell lining by laboratory experiments, based on which detailed design philosophy and design cycle were brought forward and applied to engineering practice, and a set of design methodology of single shell lining with theoretical support was first formed too. The main conclusions and achievements are as follows:1,The impact that corrugation,dislocation and other geologic structures and terrains act on stability of surrounding rock was researched, and the paper presents introducing corrugation,dislocation and terrain influence coefficient to rock assessment coefficient Q of N.Barton to reflect the degree of such impact; Yield approach degree was introduced to evaluate tunnel stability, and by which to give a four-grade classification: very stable,stable,critical stable and unstable.2,Design methodology of single shell lining whose thought was to accomplish pre-design by estimating the stability of rock with yield approach degree and to amend design with supporting theory of broken rock zone, was brought forward to improve the level of quasi-quantitative design and to increase the accuracy of design.3,The all process characteristic curve of pressure and deformation of surrounding rock was first gotten by numerical simulation, and the paper indicates that the support object is the expansion deformation or force during rock breaking.4,Based on support theory of broken zone, action mechanism of single shell lining that made up of single shotcrete and bolt was researched and relevant support measure was given too. Stress mechanism of shotcrete support can be divided into two kinds: the part stress and the whole one; Action mechanism of single bolt mainly behaves as suspension and dowel action in discrete rock, while, bolt pressure is mainly the interactional result of expansion deformation and bolt in continuous rock.5,Contact mechanics was introduced to research the action mechanism of single shell lining that made up of multilayer shotcrete, which was compared with that of composite lining. The inner force produced by single shell lining was less 20%-50% than that produced by composite one in the case of same thickness and load, else if produced approximately equal force, single shell lining needed 1/5-1/4 less thickness and 5%-8% less excavation. So it can save project cost for reducing excavation and lining masonry to adopt single shell lining. The distribution of inner force in single shell lining that made up of multilayer shotcrete followed the principle of "first time, then rigidity" which means that "early construct, early stress" and "bigger rigidity, bigger force" when loading together.6,Based on experiences both in and out nations, mechanical property guideposts of shotcrete used for single shell lining was presented by the research to reference compressive strength,initial strength,bond strength and impermeability of shotcrete.7,All factors that influence the area of broken rock zone were studied by orthogonal experimental design, and collated by importance as: Height-to-span ratio,the strength ratio of surrounding rock and lateral pressure coefficient; Support theory of broken zone was applied to rock classification of railway tunnel, presenting rock classification table,support parameter table,detailed design philosophy and design cycle of single shell lining, which were suitable for double-way high-speed railway tunnel with a speed of 200km/h.