Deformation Control Research Of Pile Retaining Foundation Pit In Soil-Rock Stratum

With the development of underground space and the grand infrastructure of highbuildings in cities, environmental conditions of foundation pit engineering becomemore and more complex. Effect of deep foundation pits safety factor is numerous,leading to frequent accidents of foundation pits at home and abroad. To carry outassessment and research of construction risk, strengthening safety control andmanagement of foundation pit excavation are pressing matter of the moment, and thesafety requirements of subway deep foundation pit construction is higher. Based onthe existing theories and practice results, the difficulty of foundation pit engineeringdesign is already changed from intensity control to deformation, and what’s moreimportant, the key of deformation control is to determine the reasonable deformationcontrol criteria, including the ground settlement around deep foundation pit and thehorizontal displacement of retaining structure, and so on.At present, the deformation studies of foundation pit excavation mainly focus ondeep foundation pit project in soft soil distribution areas. But the deformation of deepexcavation pit in soil and rock composite formation just like Qingdao (covered soillayer upper and rock lower) is less researched. Vertical properties of layers insoil-rock stratum change drastically, causing lateral displacement and peripheralsurface subsidence characteristics different from the foundation pit excavation in softsoil area. There must be deviation by directly applying the standard of retainingstructure displacement and ground surface settlement control in soft soil, resulting ininaccurate assessment and unnecessary waste.Therefore, this research is orientated in deformation control of deep foundationpit excavation in Qingdao’s soil-rock stratum, and focuses on the most common type,row pile retaining. This thesis obtains the following conclusions and results. First,based on engineering geological and hydrogeological conditions of Huiquan Square Metro Station foundation pit, as well as the design and construction scheme of theexcavation, the thesis developed a detailed monitoring programme, including theground settlement around the pit, pipeline settlement, pile body displacement,underground water level, axial force and soil pressure. Monitoring is carried outintegrated continuous integrally and continuously, by which reading the basic relatedlaws of pit deformation and stress. Second, soil-rock layers and foundation pitsupporting structure are established as calculation model. The results of numericalsimulation show that the numerical simulation curve and measured value curve havethe consistent trend and close of maximum value position. Third, the researchdiscusses the foundation pit failure types and judgment standard. And then takingfoundation pit deformation control standard in soft soil for reference, combiningmonitoring data of other pile retaining foundation pits in Qingdao Metro I (Line3)and other completed foundation pit in Qingdao soil-rock area, the thesis reorganizelateral displacement and ground settlement control initial schemes of piles retainingfoundation pit in soil rock stratum according to statistics. At the same time, the initialcriteria of yellow, orange and red warning system is drawn up, too. Finally,rationalization proposals are given in surveying, designing, constructing, monitoringand other aspects. The standard should be inspected and consummated in engineeringpractice to establish a scientific and effective safety evaluation and early warningsystem.