Study On Buoyancy Reduction Coefficient Of Subterranean Structures In Different Subsoil

With the development and utilization of underground space,the problem of buoyancy of underground structure becomes more and more prominent.A great deal of engineering practice shows that the buoyancy of underground structure calculated according to Archimedes principle is overestimated.Therefore,the current method of calculating the buoyancy of underground structure is to reduce the Archimedes formula,and then how to scientifically and reasonably value the reduction factor becomes a problem to be solved,which not only relates to the safety of the structure,but also affects the construction period,cost and design scheme.In this context,the method of calculating the buoyancy reduction coefficient of underground structure is systematically studied by combining theoretical analysis,laboratory test and numerical simulation,which provides reference for the calculation of buoyancy of underground structure.The main contents and research results of this paper are as follows:(1)In terms of theoretical analysis:the buoyancy mechanism of underground structure is introduced from micro and macro levels.Buoyancy,discussed the different strata in underground structure analysis of the reduction factor of?and foundation soil structure state parameters(porosity n?permeability coefficient k?dry density?_d),the correlation between provide theoretical basis for the model test and numerical simulation.(2)In terms of laboratory test:a buoyancy measurement system with a complete seepage path is proposed,which can eliminate the lateral wall friction resistance and the negative pressure of the base,and accurately judge the floating moment of the model box.By using the system,the floating moment of the model box in saturated gravel,red sandstone and silty clay is accurately determined,and the actual buoyancy of the model box in these three kinds of foundation is obtained,and the buoyancy reduction coefficients are 0.988,0.470 and 0.744,respectively.In the test,the buoyancy test of saturated gravel was taken as the reference test,and the error of the system was obtained to be 1.2%.The reliability of the system design was verified within the allowable error range.The structural state parameters of red sandstone and silty clay foundation were measured before the buoyancy test.(3)In terms of Numerical simulation:based on the fluid-solid coupling theory,the finite element model is established,and the model tests of red sandstone and silty clay are analyzed by finite element method.The buoyancy reduction factors obtained by the analysis are 0.465 and 0.754 respectively,The simulation results are in good agreement with the experimental results,and the rationality of the finite element model is verified.On this basis,three kinds of foundation samples with different structural state parameters were made for red sandstone and silty clay,respectively,and their finite element analysis was carried out,and the buoyancy reduction factor of red sandstone foundation was 0.499,0.451 and 0.417,respectively,and the silty clay was 0.816,0.742 and 0.705,respectively.The results show that the buoyancy reduction factor of red sandstone and silty clay foundations increase with the increase of porosity and permeability,and decrease with the increase of dry density.(4)In terms of the value of buoyancy reduction factor:the ternary linear regression equations for the reduction coefficient of red sandstone and silty clay were established by using linear regression method,with the dry density,porosity and permeability coefficient of the same soil as independent variables and the reduction factor as dependent variables.On this basis,the collinearity diagnosis of the independent variables in the equation was carried out,and the dry density and porosity in the independent variables were eliminated.The goodness of fit R~2 of both equations is greater than 0.71,and the results can provide reference for the value of buoyancy reduction factor of underground structures in the future.