Study On The Excavation Of Middle-hole CD Method By Numerical

The paper comes from the actual project Tiantan East-station of Beijing No.5 Subway. Inthe paper, the situation of displacement, stresses and plastic regions are studied. At the sametime, through comparing the different excavation-support methods of the middle-hole CDmethod, the best method is chosen. In the paper, four excavation-support methods of middle hole CD method are modeledwith the numerical modeling soft FLAC, in them, three are partial-arcsupport method, they are:A: Half vertical and half symmetrical excavation-support method, B: Vertical excavation-support method, C: Symmetrical excavation-support method and D: Half vertical and halfsymmetrical with vertical support excavation-support method. On the base of the modeling of Amethod, the regularity of the stress caused by the excavation of the station is gained, the twomain results about the plastic region and the displacement are put forward: One is that theplastic regions mainly exist in the two sides of the station and the ground surface outside the linewhich presents 45° with the both sides of the station, the other is that horizontal expansion ofthe section of the station will cause bigger downward displacement on the ground surface. Atlast, the conclusion that the single vertical excavation or horizontal excavation both havedisadvantages to the downward displacement of the ground surface, the combination of the twoexcavation ways can cause the better effect is put forward. In order to get the better excavation-support method, the displacement results came fromthe numerical modeling with the same support parameters and different excavation-supportorder are analyzed. Through the analysis, the conclusion that the Half vertical and halfsymmetrical with partial-arc support excavation-support method which causes the leastdownward displacement is best method is drawn. Through the comparison between the modeling results and the actual results, theconclusion that the modeling results can reflect the actual action truly is got. So, it is reasonableto choose the optimal method with numerical modeling method.