Experimental Study On Buoyancy Of Underground Granary Considering Side Friction Resistance And Soil Supporting Force

With its unique advantages of constant temperature,humidity,green and environmental protection,the underground granary stands out in the modern storage system,which meets the requirements of the national "resource-saving and environment-friendly" social construction.However,it will be subject to underground water buoyancy when it is promoted and constructed for high water level areas along the coast.At present,the traditional Archimedes law is used in the anti-floating design of large-scale underground structure to calculate the buoyancy at the highest water level of anti-floating fortification,which has less consideration for the anti-floating beneficial effect of soil.Based on this,combined with the national grain public welfare scientific research project(201413007-01),taking the underground granary under construction as the research background,considering the engineering situation of backfilling 2:8lime soil around the underground granary construction,the scale model cylinder of the underground granary is made in the laboratory.The buoyancy tests of three groups of underground granary models with compaction degre of 78.1%?81.7%?89.04% and four groups with buried depth of 5cm?15cm?25cm and 35 cm were carried out by using the idea of water injection floating up.The main research is summarized as follows:(1)This paper puts forward the calculation method of buoyancy,side friction resistance and soil supporting force in the buoyancy calculation system of underground granary,constructs the mechanical model of buoyancy calculation of underground granary,adopts the experimental design idea of water injection floating up,and formulates the buoyancy test scheme of underground granary.(2)The feasibility of the device is verified by comparing the theoretical and actual buoyancy water level of the model cylinder of the pure water buoyancy test of underground granary.The soil physical parameters required for the subsequent buoyancy test are determined by the geotechnical test of the 2:8 lime soil,and the change rule of cohesion and internal friction angle of the shear index between the soil particles is obtained when the compaction degree of the2:8 lime soil changes.(3)The reduction coefficients of buoyancy are 0.72,0.74 and 0.63 by three groups of buoyancy tests of underground granaries with different compaction degre.The test results show that the anti floating effect of soil is more obvious when the compaction degree of 2:8 lime soil is higher;the reduction coefficient of buoyancy is 0.81,0.79,0.78,0.76 through the buoyancy test of four groups of underground granaries with different buried depth,respectively.The test shows that the increase of buried depth(backfill 2:8 lime soil height)can improve the anti floating effect of soil body,and the 2:8 lime soil can resist about 2% buoyancy when the buried depth of model cylinder increases 10 cm.(4)Based on the test calculation results,the side friction resistance increases with the increase of buoyancy,while the supporting force of soil decreases continuously with the increase of buoyancy until it disappears.The increase of compaction degree of 2:8 lime soil will improve the ability of 2:8 lime soil to resist water pressure,the more difficult the soil is to produce subsidence,and the increase of burial depth will reduce the ability of 2:8 lime soil to resist water pressure,and the easier the soil is to consolidate and sink drop.The change of displacement difference in critical state indicates that the floating failure of underground granary is instantaneous and sudden,and the reduction coefficient of buoyancy after the floating failure is slightly smaller than that in critical state.(5)Based on the least square method of MATLAB,the empirical formula for the calculation of the buoyancy of the underground granary under the condition of backfill is derived,and then the formula for the calculation of the reduction coefficient of the buoyancy of the underground granary is derived.The formula can provide theoretical guidance for the anti-floating design of the underground granary.