Model Test Study On Synergistic Effect Between Expanded Bolt And Underground Structure

With the rapid development of China ’s economy,the process of urbanization is accelerating,land resources are becoming increasingly tense,and the use of underground space is receiving more and more attention.However,due to the concealment of underground engineering,there are many problems in the design of underground structures.The anti-floating design of underground structures is one of the more important ones.The Tertiary weathered red sandstone widely distributed in Lanzhou area has the characteristics of easy softening and disintegration in water and reduced strength,which makes the anti-floating problem of underground structure more prominent.Aiming at the problem that the underground structure is prone to antifloating failure,this paper first studied the physical and mechanical properties of red sandstone in this area,and obtained the relevant physical and mechanical parameters of red sandstone in this area.The indoor model of the expansion bolt and the underground structure was designed independently,and the force and deformation law of the expansion bolt and the underground structure under different water levels were studied.The main research contents are as follows :(1)The anti-floating technology and underground anti-floating model test at home and abroad are summarized.By consulting the literature and engineering data,the common anti-floating problems in underground engineering are analyzed,and the shortcomings in the anti-floating design of underground structures are put forward.(2)Based on the special geological environment in Lanzhou area,the physical and mechanical properties of red sandstone samples were studied through indoor geotechnical tests.According to the ring knife method,the density of the red sandstone soil sample was 1.95 g / cm3,the water content was 12.28 %,and the dry density was1.73 g / cm3.Through permeability test,particle size screening test and direct shear test of soil samples under different water contents,the permeability coefficient of red sandstone is 0.34 m / d.The particle size is mostly concentrated at 0.075 mm,and all the particle sizes of the soil samples are below 2 mm.The non-uniformity coefficient is 3.26 and the curvature coefficient is 0.79.The non-uniformity coefficient of the red sandstone soil sample is low and not easy to be compacted.The cohesion c of the test soil sample with water content is 25.25 k Pa and the internal friction angle is 40.49 °,which lays a foundation for the anti-floating model test of underground structure.(3)Through the analysis and summary of the existing underground structure antifloating test indoor model,combined with the overall anti-floating characteristics of the expansion bolt and the underground structure,a complete set of underground structure anti-floating test model is designed: including the expansion bolt,complete underground structure,water injection device and water level measurement device.Set two working conditions with or without backfill soil to study the stress and deformation law of the expansion bolt and the components of the underground structure and the synergistic effect of the two when the water level rises.Among them,the expansion bolt in the middle of the floor is the most stressed,and the expansion bolt in the corner is less stressed.The overall deformation of the floor is in the shape of ’ inverted pot cover.Basing on the analysis of the two,it can be found that the two have synergistic deformation under the action of water buoyancy.At the same time,due to the action of the expansion bolt and the column,the ’ inverted pot cover ’ shows a multi-peak trend.The influence of backfill on the middle column is small and the influence of backfill on the side column is the same.The bending moment of the beam without backfill is larger than that with backfill.The backfill plays a protective role in the anti-floating stage of the underground structure.