Study On Deformation Control Of Chengdu Subway Deep Foundation Pit

The subway construction brings a great deal geotechnical engineering problems of subway deep foundation pit excavation and support. The deformation control of the deep foundation pit engineering is very important to the peripheral environment. Compared with the coastal soft soil area, although the geologic strata is better in Chengdu area, the surrounding geologic strata deformation caused by deep foundation pit is smaller, if the appropriate control measures are adopted can control the influence to the surroundings environment nicely, but the deformation control still is the key factor to design, construction and observation of Chengdu subway. It is having important theories meaning and apply value to study the deformation control of Chengdu subway deep foundation pit. In addition, the paper studies observation data obtained in the field of other typical deep foundation pit engineerings of Chengdu subway No.1line, and No.2line, the primary contents of the paper is the Chunxi road station deep foundation pit of Chengdu subway No.2line. The paper studies the deformation characters and major influencing factors of deep foundation pit engineerings by regression analysis, statistics analysis and numerical simulation method etc, in the different geological conditions, the different depth of foundation pits, the different pattern of exterior-protected construction, and the different construction parameters. Then the paper studies the method of deformation control of deep foundation pit of Chengdu subway. The main research work and contribution as follows:(1) Chengdu subway No.1line and No.2line cross from north to south and from east to west in Chengdu,14.975kilometer and22.019kilometer long. It is a linear engineering which cross the city center area. The geological environment is complex and multivariate, having a good representation. Based on collecting a lot of investigation data, the thesis analyses the engineering geology character of the rock-soil body of deep foundation pit of Chengdu subway. According to the geological environment of the subway No.1line and the No.2line, puts forward three kinds of typical geological structural models and subtypes of Chengdu subway deep foundation pit, to provide a geological basis reference for the stability and the deformation analysis and evaluation of deep foundation in Chengdu region.(2) Through detailed analysing the observation data of deep foundation pit of typical stations of Chengdu subway No.1line and No.2line, the paper summarizes the interaction between various geological structural models and various patterns of exterior-protected construction, the deformation law and the major influencing factors of deep foundation pit of Chengdu subway station which is deep stripe foundation pit on the basis of sand-pebble layer, in the different foundation pit scale (length, depth), the different construction parameter condition, to provide a reference for the other analogical engineering practices and further studies on deep foundation pit of Chengdu region.(3) By studying and analysing the deformation forecast, the deformation prediction and the deformation control technology of Chunxi road station deep foundation pit of Chengdu subway No.2line, summarizes the space-time effect law of deep foundation pit of Chengdu subway, puts forward the key elements and methods of the deformation control for the deep foundation pit of Chengdu subway, provides the basis for the establishment of the deformation control system of deep foundation pit engineering of Chengdu subway.Research production of numerical simulation method indicates overexcavation will result in a rather large deformation for the deep foundation pit engineering in Chengdu region. The analysis shows that the space-time effect is obvious in the deep foundation pit of Chengdu subway. It is the effective way to control the deformation of deep foundation pit of Chengdu subway that combining design with construction closely, observing strictly construction program of excavation and support and the construction parameters proposed by design department, strengthenning the information feedback of construction and the deformation prediction, implementing dynamic design and information construction.(4)How to determine the deformation warning limit is still lacking in system research on Chengdu subway deep foundation pit engineering, also lacking in unified quantitative index and the discrimination standard. It will limit and weaken to give out warning aginst the possible emergency and accident. The statistic analysis of22deep foundation pit observation data of Chengdu subway No.1line and No.2line is carried out in the paper, and the deformation warning limit is putted forward to the different geological condition, the different foundation pit depth, the different patern of exterior-protected construction of the deep foundation pit.