Optimization Design Of Tunnel Support Based On Inverted Arch Numerical Analysis

Necessity of the arch setting for composite lining structure on the three land tunnel hasbeen the focus of academic debate:《Specifications for design of highway tunnel》(JTGD70－2004) think that inverted arch plays the key role in the stability of tunnel for Ⅲgradeof highway tunnel, we should set invert with45cm thickness; however,《Design rules ofhighway tunnel》(JTG/T D70－2010) think we can not set the inverted arch, which is at thebottom of tunnel with better surounding-rock conditions, such as Ⅲ1、Ⅲ2grade. However,Ⅳ1surounding rock should be set inverted arch with45cm thickness. This will not onlybring great difficulties to the design of highway tunnel, and the construction of invertedarch itself high cost, construction difficulty, tunnel bottom is the most serious part of thediseases. So it has an important practical significance that researching on specificconditions to cancel the inverted arch, putting forward to take the bottom supportingmeasures to this problem. Paper analyses the two themes.In this paper, author uses the numerical simulation method of FLAC3Dto analysisevery stages of Ⅳ1and Ⅲ2tunnel support design, especially research on the effect ofinverted arch and even put forward two kinds of new support schemes to instead of it. Forexample, cross-beam and foundation-beam, which are at the bottom of flat tunnel, are usedto replace the inverted arch setting. Therefore, we can select the same field conditions ofⅣ1and Ⅲ2grade rock section as the test section, respectively establishes four models:(1)51m flat tunnel;(2)51m inverted arch tunnel;(3)51m flat tunnel with cross-beam;(4)51mflat tunnel with foundation-beam. Contrast test content including: the verticaldisplacement、surrounding rock stress、plastic zone、the axial force of bolt、second liningstructure etc. Get the following main conclusion.1. Inverted arch will decrease the displacement at the bottom of tunnel by9.225%~10.597%; make plastic zone volume of the tunnel surrounding rock reduce by12.803%~43.478%; but the effects which include inverted arch tunnel bears bolt axial force andinhibites vault deformation force, it is not obvious;2. In the surrounding rock section of three land Ⅳ1tunnel, from the numericalsimulation to consider the abolition of arch is not appropriate. When tunnel bottom has Ⅲ2or higher level of surrounding rock, we can combine with the actual engineering data toconsider the abolition of arch;3. From the numerical simulation, the effect of tunnel with foundation-beam is better.