Monitoring And Numerical Analysis On Soil Deep Foundation Pit Engineering Under Heaving Conditions

On the foundation pit engineering of the northern seasonal frozen area, it may go through winter, which could affect the retaining structure of deep foundation pit by frost heaving. The volume of the soil affected by frost heaving will be enlarging. The retaining structure of deep foundation pit will be deformed by the influence of frost heaving. The extent of deformation may be gigantic, which could cause damage eventually, even causing collapsing accident. The soil frost deformation could also bring the safety hidden danger to the surrounding constructions as well as pipelines. It may lead to the deformation of the underground structures, the cracking of pipelines, and even the destruction. Therefore, a research on the frost soil’s force features and deformation regulations of the foundation pit engineering has a strong guiding and realistic significance to the design and construction of the foundation pit engineering in frost region.Based on the frost-heave theories at home and abroad and finite element simulation, this paper has analyzed the influenced mechanism of the retaining structure of deep foundation pit caused by soil frost heaving. Besides, it also summarizes the affecting factors of soil frost heaving, and has analyzed three frost heaving mechanism in proper order. Furthermore, the formulas are given. This paper takes a foundation pit engineering of Qinghai Province as an example, and introduces its engineering geological conditions and support scheme. The monitoring operation is of great importance due to more surrounding constructions of the foundation pit engineering and the close distance to the pit wall. During the construction period, the temperature, the horizon displacement of retaining structures and the axis force of anchor has been monitored. ANSYS is used to analyze the retaining structure of the foundation pit engineering and the surrounding area. The results show that the temperature simulation meets the actual situation basically, and the coupling of heat stress is quiet accurate. The simulated results can basically reflect the frost soil’s force features and deformation regulations of the foundation pit. This paper has simulated and analyzed the horizontal displacement of pile and anchor axial force both within and without frost heaving. The results show that the value is bigger under the condition of frost heaving, which gives the fact that frost heaving has significant effect on the retaining structure of foundation pit. And then, the simulation results and monitoring data have been compared. By comparing the two graphs, conclusion can be drawn that the curves of the simulation results and monitoring data are basically in coincidence, while the results of numerical simulation are generally larger. The selection of the soil thermodynamic parameters different with the actual situation could be one probable reason. Moreover, there could be some operating mistakes that affect the results during the engineering construction.In brief, applying ANSYS to analyze the heat coupling on the retaining structure of foundation pit engineering, the simulation results are basically consistent with actual situation no matter in temperature field, displacement field, or stress field. It shows that the simulation results are good, and it could reflect the frost soil’s force features and deformation regulations of the foundation pit. The method is feasible and reasonable. In the design of foundation pit engineering in future, the effect of frost heaving should be taken into consideration. Furthermore, measures should also be taken to decrease the frost heaving and deformation of foundation pit in engineering. Based on these factors, engineering quality and safety can be ensured.