Study On Highway Neighbourhood Tunnel By Similar Model Test

Due to complicated topographical and geological conditions in China, during constructing super-highway would unavoidably face with lots of tunnel works. Because of special geological and topographical limitations, special structure shapes such as neighbourhood tunnel and multi-arch tunnel have to been applied.Whereas many critical technical problems have not been solved in both design and construction, such as possible destruction modes of neighbourhood tunnel, definition of smallest reasonable spacing, critical factors that influence stability of surrounding rocks, the function of primary lining and secondary lining, the optimal construction method for secondary tunnel, the best strengthening method of middle rock pillar, design proposal and construction technique concerning neighbourhood tunnel which is at unsymmetrical pressure, and so on.The paper used the laboratory similar model tests which was called "Thescientific research of western traffic construction-research of key techniqueabout design and construction of neighbourhood tunnel " as the primary method and researched in allusion to above mentioned problems. The paper done 43 groups model experiments in rock mass level of III IV and V, then obtained a series of research production.Firstly, the paper experimented on the tunnel destruction modes through the symmetrical pressure model which has no support and compared rock fall and cracking during construction of Dong Jia Shan Tunnel with destruction modes during laboratory similar model, then illustrates the destruction rules of neighborhood tunnel and expatiate the destruction process of middle rock pillars particularly. The paper also educes the important conclusion that the destruction of middle rock pillars appears in the side which is close to first tunnel and it has valuable guidance and reference for construction and survey of neighborhood tunnel.Secondly, this paper took the destruction of unsupported middle rock pillar as the criterion and found the reasonable minimum spacing for different rock mass levels. "For III rock mass level, the reasonable minimum spacing is 0.25B (B is the breadth of a single tunnel), for IV level, it is 0.5B;for V level it is 0.75B". The minimum spacing value is largely less than the spacing value which is prescribed by "the criterion of highway tunnel". By model test and in-site test, this paper also discussed the influence to rock mass stability by rock mass level, spacing and depth. It draws the important conclusions that rock mass level and spacing is the criticalfactors which influence the stability of surrounding rocks.Thirdly, this paper studied the functions of primary lining and secondary lining by model test which were in different rock mass levels. By comparison, this paper confirmed the reasonable construction method for the second tunnel and found the optimal reinforced method for middle rock pillar. It suggested that reverse multiple drift method was better than others for the excavation of the second tunnel. It also advised that the best reinforced method for middle rock pillar is large area grouting.Lastly, this paper discussed the influence of variety of grade, spacing, the smallest depth and grouting for middle rock pillar to the tunnel structure and displacement of ground surface by supported tunnels tests which are in rock mass level V and at unsymmetrical pressure site.The conclusion of the paper is valuable for the design and construction of neighbourhood tunnel.