| With the continuous development and expansion of city.The underground space of urban isoccupied by a variety of pipelines,structures (Bridges and buildings) foundation,subways and soon. The small spacing of two (or more)tunnels and large cross-section exist in the new planningtunnels, while, with multiple faults, poor stratigraphic conditions, abundant underground waterand other unfavorable factors exist in construction range,increased the difficult of new two lane(multi-line) tunnels construction.Based on the above characteristics of Changsha subway line2, Reference the experience ofdomestic and foreign, through numerical simulation analysis, field monitoring and theoretical, toresearch the key technology of parallel tunnel with small spacing and large cross-section, putforward the improved two side-surrounding pilot tunnel method, and optimized the opportunity ofdemolition of heading support inside and second liner timbering, comparative analysis of the rockpillar stability in two lane tunnel section excavation sequence, rock pillar reinforcement or not,the large cross-section of different excavation methods and the adjacent tunnel under theconditions of different spacing, based on the stability of surrounding rock and the deformationmonitoring results,do the regressing analysis for rock pillar horizontal displacement,strain andinternal force of steel arch,get the more useful forecasting formula. Provide a theoretical basis andpractical experience for construction of urban rail projects, mountain tunnel, undergroundchambers and other buried structures.In this paper, the concretework and research are as follows:1. Research the key technology of two-lane subway tunnel with small spacing and largecross-section(1) According to the actual situation of the project design, analyzed the construction risk andproposed control measures. Based on the determined general construction scheme, use theFLAC3D software do numerical simulation for two lane tunnel excavation construction withsmall spacing and large cross-section, analysis mechanical behavior of two side-surrounding pilottunnel method (nine, six-step), CRD construction methods, proposed six-step twoside-surrounding pilot tunnel method to optimize the construction program.(2) Based on large cross-section excavation construction program In the six-step twoside-surrounding pilot tunnel method, use MIDAS software do simulation analysis for sequenceof two side-surrounding pilot tunnel construction and optimize the opportunity of demolition ofheading support inside and second liner timbering. In the sequence optimization, is proposed an improved six-step method to the pit, compare with the current existing construction methods, thismethod of construction first excavate all the upper section then excavate under section which canincrease the face, there are great advantages in shortening the construction schedule andcoordinating construction process. Provide reference for construction of urban rail projects,mountain tunnel, underground chambers and other buried structures. Within optimized theopportunity of demolition of heading support inside and second liner timbering, by comparingand analysising displacements and internal forces before and after removal of the supportstructure found that when removal of temporary support, the displacements of vault changedgreatly, the moment of initial lining structure changed greatly, increased rapidly. When the secondliner is complete, the internal force rangeability of supporting structure decreases, the basicstructure stabilized. If the removal of temporary supports and second liner can not be applied todo, considering the time effect of releasing the stress, the displacements of vault will increasefurther. When removal of temporary support we can divided into blocks,framing to removed, toreduce the insecurity caused by vault settlement and time effect of releasing the stress. If you canguarantee second liner construct timely, in accordance with the12m long between removal oftemporary support and second liner construction can meet construction safety requirements.2.Analysis the rock pillar stability of two-lane tunnel with small spacing and largecross-section.(1) Through the construction of a variety of conditions simulation analysis, the excavationsequence of the ultra small spacing in two-lane tunnel,is the small section tunnel is first, and lastis the large section tunnel,in order to reduce area of large cross-section tunnel surrounding rockstress changes greatly, thus to affected the single tunnel excavation soil zone. and a small sectiontunnel excavation through a small hole diameter can also be designed to support the excavation todetermine whether it is reasonable, geological survey results are accurate or not, can providereference for large diamete tunnel excavation.(2) On whether to proceed with the rock pillar reinforcement were simulated and analyzed,for rock pillar, when the clear distance of two cavern is small, the stability of rock pillarreinforcement can impact a lot, the general use of reinforcement measures including grouting andused cross anchor on both sides, and through a large number of field examples and numericalanalysis shows that cross anchor is very important for the rock pillar stability.(3) Different excavation methods for two-lane tunnel were simulated and analyzed,according to two side-surrounding pilot tunnel method construction method better than CRDmethod in rock pillar stability, and can guarantee the stability of surrounding rock, the rock pillardeformation and plastic District also within the allowable range of standardize,it can ensure the safety of construction.(4) Simulate and Analysis the different clear distance of parallel tunnel, when theclear distance is less than1.0D, the rock pillar clear distance is smaller, soil displacement, stressand plastic zone of parallel tunnel excavation is larger, so for ultra-small spacing tunnel takemeasures to grout for rock pillar and do cross anchor, the tunnel chamber should be do a numberof excavation, excavating and supporting should be carried out simultaneously, to prevent therelease of the soil stress too much causing rock pillar instability failure3.Rock stability,deformation monitoring and regression analysis in underground excavationof the station interval.Monitored rock stability and deformation in underground excavation of the station interval,analyzed monitoring results. Do regression analysis for monitoring results of settlement,deformation, stress in two-lane tunnel, to get the variation of the horizontal displacement, steelarch strain, internal forces caused by the excavation of rock pillar:(1)CRD construction method, Rock pillar horizontal displacement and time were repeatedlyparabola,the closer distance from single hole, the higher the number of parabola, conversely, thefarther the distance from single hole, the lower the number of parabola.(2) Six-step two side-surrounding pilot tunnel method-B, For underground construction, steelarch vault, the strain of parts of the inverted arch and time meet4times parabola change rule.(3) Steel arch vault, inverted arch moment and time meet2times parabola change rule.(4) Inverted arch Axial force and time meet3times parabola change rule.(5) Vault axial force and time change is linear. |
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