Study On The Safety Of A Deep Foundation Pit With Pile-Anchor Supporting Through Winter In Harbin

Harbin is located in northern latitude 44°04’～46°40’, there are up to six months of winter each year. The average temperature at -15℃ to -30℃ in January, the lowest temperature in the country’s northernmost large city. The duration of deep pit project is generally about one year, construction pit inevitable through winter period. Frost heave and freeze thawing are inevitably complex physical processes, the role of the structure of excavation can not be ignored.Taking Harbin Xiangfang Area Foundation project as the basis. The foundation pit engineering was designed. The on-site real-time monitoring data of construction process in the excavation pit were recorded,. Analysis of field data through the Foundation and Support deformation characteristics and force structures, and explore the deformation Foundation and frost heave on the supporting structure and the anchors’ force. Consider the impact of temperature domain, using ABAQUS finite element software to simulate dynamic construction pit. And then, the comparative analysis of in-situ records, the simulation results without considering temperature influence and the results taking into account temperature influence were carried out. The depth of winter Foundation deformation due to frost heaving and the force structure of the foundation pit were analysed. The results can provide a reference for subsequent similar projects.Through this study, we can get the following conclusions:(1) retaining structure displacement process can be divided into four stages, linear increase in excavation stage; Foundation vacant winter phase steel sheet pile with top horizontal stabilization phase, indicating that winter maintenance and technical measures taken by the Foundation to be effective, the rheology of winter soil is not obvious; Spring after the foundation pit excavation and continue the construction phase, the steel sheet pile top horizontal displacement into linear growth, and the growth rate was higher than the first phase, the reason for the rheology of freeze-thaw cycles of soil; the foundation construction phase is completed, the horizontal displacement at this stage does not change, mainly because this time the foundation, raft construction has been completed, and the underground part of the building is about to complete construction.(2) The excavation space effect was not obvious, the maximum horizontal displacement on the ground floor at lm KB8 measuring points, the maximum displacement was 13.73mm, the maximum displacement is far more less than the warning value 45mm, deformation of the foundation pit structure belonging composite deformation; Increase.the value of excavation phase of the horizontal displacement of more than 50% of the total displacement of the pit after the winter, early spring at large diurnal temperature changes, growth in the total value of the pit horizontal displacement displacement more than 10%. When this stage should be considered excavation design.(3) Numerical simulation foundation pit deformation in the Bottom of the above composite was deformed, the following inverted triangle deformation space played significant effect, and the experimental results showed that the excavation space was not obvious, and the beam waist explained crown to reduce group spatial effects.(4) When foundation experience the winter low temperature on enclosed structure can not be ignored, by comparison of the data, the Foundation insulation measures played a good role.