The Reduction Analysis Of Lining Vertical Soil Pressure In Phase Transition Layer Of Sandy Pebble For Beijing Region

Based on statistical induction of geological data from the survey of typical phase transition layer of sandy pebble in Beijing Subway, theoretical analysis and numerical simulation of soil pressure in the lining structure was studied.And combined with the geological survey data of some Beijing Subway Stations and tunels, the soil pressure and stress of the lining supporting structure under different deepness were also investigated. The main contents are as following:(1) By summarizing the depth distribution for thirty-two subway stations,three shield tunnels,fifteen mining method tunnels of4th subway line,5th subway line,10th subway line and14th subway Line in Beijing, a preliminary analysis about properties of phase transition layer in sandy gravel had been reached. The properties of phase transition layer in sandy gravel includes loose granule silty soil and pebbles constitute the main frame structure of layer, and the layer can easily collapse, slip failure.(2)Combined with step one, the geological conditions and the typical parameters in Beijing area were reached. Based on the calculation of the classical earth pressure theory and numerical simulation, the adaptability of earth pressure theory under different deepness is analyzed and compared,therefore the reduction factor in vertical earth pressure of supporting structure was developed. Examples show:①Theoretical calculation shows that vertical earth pressure decreases with the increase of soil depth.②Reduction factor of vertical earth pressure varies under different deepness.Reduction factor changes from0.92to1within the range of0～6m;Reduction factor of pressure decreases nonlinearly within the range of6～12m and the reduction factor changes from0.84to0.92, while the reduction factor changes from0.74to0.84within the range of12～18m;When the deepness is greater than the18m, the vertical earth pressure tends to the loose earth pressure of2.5times hole diameter.(3) With simulation analysis of FLAC3D,the elastic-plastic theory and based on the related tunnels in Beijing Subway14th Line,preliminary simulation results show that:when the tunnel depth is4m or6m (depth less than1times the hole diameter),there is a slight reduction for the vertical earth pressure, approximately equal to the pressure of whole soil column;within the deepness of6～18m, the vertical earth pressure increases nonlinearly as the depth increases, and the reduction factor of vertical earth pressure fluctuates between0.6and0.9;When the deepness is greater than18m, the vertical earth pressure tends to the loose earth pressure of2times hole diameter.