Study On Construction Method Of 2 Expanded 4 On Ultra-soft Rock In The Large Section Neighborhood Tunnel

With the rapid development of tunnel construction, small interval tunnel of large span will increase, and new Austrian tunneling method which applied to small interval and large Tunnel's design and construction especially 2 expanded 4 is still in the exploration and validation phase.Because structure type of small interval tunnel of large span has specificity and novelty,and it's construction process and the existing tunnel interaction is difficult to grasp, Also,because of it's construction side of the opening of the tunnel,the large flat rate, complicated construction process ,the middle pillar of the complex stress and so on, however, construction of the tunnel is an important factor in stability of surrounding rock, Reasonable construction method can take full advantage of the self-supporting effect of rock, rock stability requirements are met in the smallest support condition. Therefore, the study of various construction methods 2 expand 4 in the expansion of stability and mechanical response of rock, which help reasonably tunnel design and construction of the similar to the tunnel 2 extend 4,provide valuable safety information.In this thesis,base on the expansion of Da Mao Shan Tunnel and the basic principles of rock mechanics as well as the thought of new Austrian tunneling method, six different excavation conditions execute numerical simulation in CD construction method of different sizes, different sequence and different footage , combined with on-site monitoring and measurement, the distribution of the dynamic evolution such as various stages of tunnel stress field, displacement field, mechanical characteristics of shotcrete support,also, the distribution of plastic zone and the impact on the existing tunnel aboat have studied,made the following major achievements:1.Settlement curve on the soft rock entrance of the surface appear two side small, big in the middle and has a tiny settlement trough above the existing tunnel,the total displacement of the surface was mainly due to the half section excavation,deformation of the surrounding convergence and crown settlement have oscillation, also,not the wall rock has been moving towards the clearance.2.The shape of rock strength to play was similar to butterfly wings region, The shape of rock strength to play is Interconnected with the adjacent tunnel,rock stress mainly in the area close to the tunnel structure; plastic depth of rock tunnel is 0-5m, the divisions plastic zone and the tunnel face connected with each other, and connected region may be formed with the tunnel 45°vertical plastic sliding surface. the right position of the middle pillar of the displacement has Great changes ,which are the most unstable failure point3.Initial support is in the compressive stress state, the right waist has stress concentration which the corresponding stress is 1.61MPa, but not exceeding the value of concrete compressive strength allows 16.7Mpa; characteristics of Anchor axial force is constantly changing,Distribution of bolt axial force around Rock is very uneven,the position of the foot is in compression, the maximum pressure 43.46KN, the remaining parts is in tension, the maximum pulling force of 167.98KN. 4.Excavation of the new tunnel will impact on the existing tunnel which produce differential settlement and varying degrees of deformation,the final settlement on Arch, arch back, vault is not equal and in turn reduce, the deformation on right side is larger than left, therefore,the entire section shown clear bias state.The increments of maximum tensile stress which new tunnel excavation impact on the existing tunnel is 0.25MPa, slightly less than the tensile stress of weak value of shut (0.3MPa) by the minor impact of the new tunnel; the maximum compressive stressis -0.82MPa , less than the incremental value of the weak impact of stress (1.0MPa), so both the tunnel is safe.5.Merits of 6 different construction method of surface settlement and crown displacement and the force distribution of support structure as well as the distribution of the plastic zone are analysid and compared,and draw CD method of ACBD sequence and footage 1m excavation is the most suitable for Da Mao Shan construction plan on soft rock...