Research On Double Ring Truss Support System For Deep Foundation In Soft Soil

With the size of the urban construction develops rapidly in these years, the height of building is gradually increasing as well as the size of city foundation pit project. In:his case the construction becomes more difficult, because of the growing tension in:he grim situation of urban land. Especially in the southeast coastal areas, soft soil is widely distributed in naturepoor, foundation pit design is difficult, due to poor physical and mechanical properties of soft soil, and the widening and deepening of the pit area and the pit depth. Therefore consider the supporting soilbody condition of geotechnical engineering and hydrogeological conditions, how to support the pit, effective use the construction space and reducing the project amount at the same time become the main research directions of the foundation pit in recent years. Dual circular support system is a development of the ring beam support system, also:arried out in recent years for lack of rigidity of the ring beam system in the large diameter pit optimization, it is suitable for use in the complex geometry of the large-scale deep foundation.In this paper, the research is based on a foundation pit support projects in Fuzhou, the pit depth of15m, the side length of44～66m, the main soil distribution as follows:silt, silty clay, silty soil and granite. Analysis and compare the multiple support structure system set the dual ring truss support system in the soft soil of the deep foundation pit support program for the first time. After the simulation by the two-dimensional and three-dimensional numericalsimulation software to the pit, and the comparison of monitoring data of deep foundation in the foundation construction brocess, to simulate different diameter, with similar geotechnical engineering conditions and hydrogeological conditions, obtained the following results:1.Use the calculated results of the two-dimensional, FLAC3D three-dimensional and three-dimensional MIDAS/GTS software to optimize the pit design which will supp (?)rt cross-section optimization for more than10%, and compare the actual monitorin g data and simulation data, concluded that three-dimensional software in the displac ement analysis is more realistic, reliable.2. Analysing the modeling process through the support system within a double ring simplify the process of modeling of pit support piece. The preparation of independent computer program quickly builds the rod parts and envelope, provides an effective support for the rapid modeling of the ring support system in the three-dimensional software.3. By simulation, obtained the mechanical characteristics of the dual circular support system, the deformation characteristics around foundation retaining structure, as well as the effect of the pit on the surrounding environment.4.Simulate the excavation deformation of a single ringpit and double ring foundation support system, confirmed the advantages of the dual circular support system in terms of safety.5.Simulate the diameter100m deep pit and diameter150m deep excavation, by comparing the the axial forces of the support system and the displacement of Pit Support Structure to determine the best match of these two inside and outside the bicyclic diameter of the deep foundation and draw the conclusions of the optimal diameter of the dual circular support system within and outside the bicyclic difference increased with the increase in pit diameter.