Research On Anisotropy Of Resistance Coefficient And Influenced By Soil Stratification

Resistance coefficient(coefficient of subgrade reaction),which is widely used in design and evaluation of substructure and transportation projects,is the key parameter to characterize the interaction between structure and soil.The stratification,anisotropy and spatial heterogeneity of soil will have an important impact on the resistance coefficient,while the structural form(foundation,beam,plate,shell,cylinder,etc.)and burial depth will also cause the change of resistance coefficient.Therefore,selecting the appropriate resistance coefficient can not only calculate the mechanical response of the structure more simply and accurately,but also ensure the design safety and economic rationality.This paper mainly analyzes the anisotropy of resistance coefficient and influenced by soil stratification.The main content and research achievements are as follows:(1)Structural mechanical response and soil stratificationIn order to analyze the effect of soil stratification on structural mechanical response and the attenuation law of soil layer effect with depth,the interaction between pipeline and isotropic layered soil is studied theoretically and verified by numerical examples.The results of parameter analysis show that the first layer of soil beneath the pipeline has the most obvious effect on its deformation,and the influence of soil layer gradually attenuates with the increase of depth.Computational values obtained by simplified homogeneous treatment without considering the stratification of soils tend to be dangerous(upper soft and lower hard)or conservative(upper hard and lower soft)as compared with stratification,while the homogeneous solution is more accurate when considering the attenuation law of soil layer effect.The attenuation function obtained by weight analysis method conforms to negative exponential distribution,and the influence attenuation of upper soft and lower hard soil layer is faster than that of upper hard and lower soft soil layer.(2)Analysis of vertical resistance coefficient considering structural buried depth and soil stratificationIn terms with the buried beam structure,considering the influence of the buried depth,soil stratification and transverse isotropy on the vertical resistance coefficient,the generalized Vesic solution of the vertical resistance coefficient is derived by analogy method between Winkler model solution and layered elastic theory solution,and the influence of the parameter variation on the value of the vertical resistance coefficient is analyzed in detail.The results show that the vertical resistance coefficient increases to the maximum with the increase of the depth of the beam,which is about 2.05 to 2.25 times as much as that at the surface.The coefficient decreases with the increase of the total thickness of the foundation and increases with the increase of the ratio of horizontal to vertical elastic modulus.In the meantime,the coefficient is related to the soft and hard distribution pattern of the soil layer,furthermore,the weighted average elastic modulus of the soil layer is the same and the harder the first layer of soil is,the larger the value is.(3)Orthotropic anisotropy of soil resistance coefficient around buried pipelinesAs to the buried pipeline,the orthogonal anisotropy of the soil resistance coefficient around the buried beam structure is studied on the basis of the change of the tube-soil stiffness ratio and the pipeline embedding.and the vertical and horizontal resistance coefficients are obtained by the analogy method,while the axial resistance coefficient is solved by the shear displacement method or the mirror method.The rationality of resistance coefficients are verified by examples.The difference of the value of resistance coefficients are analyzed,which show that the axial resistance coefficient is less than the vertical resistance coefficient in homogeneous semi-infinite soil.And the ratio of horizontal resistance coefficient to vertical resistance coefficient is less than 1 when the pipeline is partially buried.However,the ratio is more than 1 when completely buried and tends to be 1 after the buried depth-diameter ratio reaches 20.The finite compressive properties of the soil below the pipeline have significant effects on the vertical and horizontal resistance coefficients,especially the vertical direction.However,the homogenization solution of the resistance coefficient is quite different from the stratified solutions,and the stratified solutions should be used when the stratification characteristics are obvious.(4)Anisotropy of resistance coefficient of surrounding rock(soil)of tunnelThe variation of resistance coefficient in isotropic semi-infinite soils with diverse or identical tunnel buried depth is analyzed by the mirror method.Then the variation of resistance coefficient with rotation angle in the fully infinite soils with transverse isotropy of type 1 or 2 and orthotropic anisotropy is obtained by the stress function method.The results show that the resistance coefficient increases gradually with the increase of tunnel burial depth,and tends to be stable after reaching to a certain depth.When buried depth of tunnel is small,the resistance coefficients show an obvious anisotropy trend.In the second kind of transversely isotropic and orthotropic soil,the resistance coefficients show obvious anisotropic phenomena,and the horizontal resistance coefficient is more sensitive to the variation of soil parameters than the vertical resistance coefficient.However,the degree of anisotropy decreases as the soil parameters or ratios approaching to 1.The rationality of the theoretical calculation method is verified by comparing the actual measured values with the engineering examples of loess tunnels,and the recommended values of soil resistance coefficient of loess tunnels are given.