Field Monitoring Of Deformation Of High-Speed Railway Subgrade Overlying Mined-Out Area

This dissertation is based on the piled-slab structure foundation reinforcement engineering of subgrade above mined-out area of Wufushan station of Hefei-Fuzhou high-speed railway. Field monitoring test is carried out in both DK499+920and DK499+940section to research the mechanism of the piled-slab structure. The main contents and achievements of the research are showed as follows:1)Make a systematical summary about the present situation of the research on the mining area, composite foundation of piled-slab structure and deformation monitoring and prediction of subgrade.2)Make an analysis about engineering geological conditions and engineering structure of Wufushan station subgrade reinforcement project.3)Based on the research purposes, design field monitoring test scheme including monitoring sections, monitoring contents, monitoring instruments layout and monitoring methods. According to the designed scheme, install the monitoring instruments, and make monitoring to get the original data.4)Make handling and relevant calculation on the original data, and use the handling data to draw the deformation and stress curves to analyze the monitoring results. Some main conclusions are achieved as follows:(1)The analysis of the results of subgrade settlement deformation and lateral deformation shows it gets a remarkable result that use the pile-slab-stabilizing pile composite structure to strengthen the high-speed railway subgrade above mined-out area on a slope. The settlement of the foundation soil of two sections is between5.00and6.00mm with a little difference; the settlement of the slab has a relatively uniform settlement deformation of about6.00mm; the subgrade embankment and goaf roof has little deformation. The maximum lateral displacement of stabilizing pile and subgrade is no more than7mm, which indicates the whole subgrade is stable. The result of subgrade settlement assessment based on exponential curve shows the post-construction settlement meets the demand of5mm.(2)The analysis of the results of stress monitoring shows pile and soil have similar mechanics characteristics, when the top load actions to the piled-slab structure.The soil stress, pile top stress and pile bottom stress all keep increasing along with the continually increasing load until the filling is finished. The pile top stress is apparently higher than the soil stress; both the pile-soil stress ratio and pile bearing ratio keep increasing along with the continually increasing load. Along with the load increases, the axial force and the skin friction of pile increases, and, on the whole, they decreases with the depth increases. In terms of piles acrossing mined-out area, there is no skin friction, and the axial force keeps unchanged. The pile top load is beared by both the skin friction and the tip resistance. According to the percentage of the tip resistance, most of piles are resistance-friction pile, while a minority of relatively short piles are friction-resistance pile.