Research And Analysis Of Main Structural Supporting Design And Construction Methods In The Dark Base Hole Project Of Line 3rd Of Tianjin Subway

Base hollow project is the geotechnical engineering focus point that all verymuch pay attention to now, is also technical complex comprehensive very strongdifficulty,and is to raise the project quality focal point that reduces accident. Thiswill inevitably put forward higher requirement for construction technology andthe design of base hollow project. Currently deep base hollow supporting projectsare generally facing the problems: firstly surrounding environment is becomingincreasingly more complex, and there are often high buildings around theconstruction sites;secondly construction costs are lowered, while the constructionhas becomes much more difficult;thirdly excavation depth of the base hollow isgrowing increasing. This requires deep base hollow design and constructionpeople can choices supporting structure not only that is viable, safe and reliable,but also whose cost is reasonable, ensuring deep base hollow supporting systemand the surrounding buildings safe.Bored piles are a new type structure of underground continuous wall, duringthe construction the piles and piles grab and become pile wall configuration, Ithas three functions: loading, supporting and impervious, and suits for the higherlevel water coastal soft areas. Based on the deep base hollow project example ofHuayuan subway station of 3rd line in Tianjin, the major research says:Firstly, choices of base hollow supporting programs, Engineeringenvironment in Tianjin is in vicinity of Bohai sea, has rich buried-shallowlygroundwater, and its rock quality is complex filling soil, red clay, powder clay andsilt red clay. After base hollow supporting programs options, the paper uses boredpiles as the main protecting structure of subway station, and analysis bored pilesbasic principles and their advantages and disadvantages.Secondly, the design calculating of supporting structures internal force. Asthe depth of deep base hollow reaches 16.72 meters and it has four pieces ofsteel supporting. The paper has on the calculating of supporting structure byadopting the classical method (equivalent beam method), analyzed method(Shanjianbangnan method) and finite element method (ANSYS method),andgets the drilling depth of bored piles and the internal calculated results ofsupporting structures. After the comprehensive compare, the internal designvalue of supporting structures is confirmed, and has on the design ofcross-section reinforcing of bored piles.Thirdly, deformation forecast of supporting structure during base hollowexcavation construction process. When base hollow is constructing, because ofsteps, the force of supporting structure is in the dynamics. The paper use"Qimingxing" calculation software of Tongji University to dynamic simulationof every step force during the construction, considering various periods forcesituation, and testing base hollow engineering design.Fourth, the construction of bored pile supporting structure. The paperintroduces bored pile-controlled wall construction in detail, bored pile wallconstruction and key technical quality control of bored piles, including orificepositioning error control, control of bored piles vertical shaft, control of B-pillarconcrete congeal time, construction control of overcoming piping, approach ofaccident piles and so on.Construction practice shows :It is feasible that bored piles act as deep basehollow supporting wall structure and it is scientific and rational of internal forcecalculation of supporting structure. From the point of view of security andstability, it does not appear larger deformation and displacement throughout theconstruction process and surrounding buildings and settlement ,which meetspecifications;From an economic point of view, bored piles is lower aroundfifteen percents at project costs than underground continuous wall at the samecondition, and the steel supporting has higher recovery rate and can use moretimes;From the time benefit, bored piles could carry out a number of controlledoperation faces, bored piles construction speed more rapid, steel supportingconstruction also more convenient, and much shorter than anchor rod.Through the paper research, some important conclusions are gained:Firstly, when bored piles are looked as main supporting wall structures ofthe deep base hollow in 3rd line of Huayuan subway station in Tianjin, theproject practice has shown that bored piles have many features, such as fastconstruction speed, efficiency, low noise, no slurry operations, good imperviousperformance, high quality piles, etc. and under the same conditions, its costs islower about fifteen percents than the underground continuous wall, thus it has alarger promotional value.Secondly, the paper has on the calculating of main supporting wallstructures by the classical method (equivalent beam method), the analyzedmethod (Shanjianbangnan method) and the finite element method (ANSYSmethod),steel supporting axle force design value of supporting wall structureadopts calculations of Shanjianbangnan method, the moment and shearing forcedesign value adopts the calculations of equivalent beam method. Compared withthe design value of the design institute, the third supporting design value islargest in the design institute, and the excavation depth is 13.79 meters;but thefourth supporting design value is largest in the paper, and the excavation depthis 16.72 meters, and it can be seen from the calculations that the position of thelargest value accords more with the actual practice of deep base hollow projectand engineering mechanics.Thirdly, through the simulation analysis of ANASYS method, the resultsare similar with the results of shanjianbangnan method, and accord with theactual condition of dynamic simulation when base hollow is excavated step bystep, which fits the practice and has relatively high precision.Fourthly, by computer software dynamic simulating the base hollowexcavation process, the results can be seen that the force in the supportingposition is in a state of variation, and the same with the moment and shearingforce of the supporting wall structure. The largest level displacement, the largestmoment and the largest shearing force all occur in the seventh piece ofconstruction. At the time the base hollow depth reaches -13.29 meters, and thefourth piece of supporting has not been set up well. Works in the constructionshould focus on strengthening the monitoring and taking technical measures toensure construction safety and smooth operation.Fifthly, in the bored piles construction process, controlling of the time ofthe super-congeal concrete and piles vertical shaft is the key process. Thecongeal time in the project is more than sixty hours, and should strictly controlthe concrete slump constant and concrete perfusion temperature, and should alsostrictly control bored piles vertical shaft to prevent gearing quantity failure.The innovation in the paper mainly embodies the followings: by computersoftware comprehensively simulating base hollow excavation process, the paperanalyses supporting structure stress manner and deformation characteristics ineach process, can master the security and stability of supporting structure at anymoment, and provide effective and timely construction guidance.