| Loess is a type of special soil widely distributed in northwest China.Qinghai Province has a continental plateau climate,with cold winters and cool summers,long sunshine hours,low annual precipitation,and strong solar radiation.The unique climate characteristics determine the special structure of loess.With the promotion of "One Belt And One Road" strategy,under the guidance of starting a new journey of building a socialist modern country in an all-round way,how to deal with engineering geological disasters hinder the development of engineering construction in the loess region has become the focus of many scholars.In this paper,taking the typical undisturbed loess in Haidong area as the research object,the static and dynamic triaxial tests are carried out through GDS standard stress path test system and GDS bidirectional dynamic triaxial test system,and the strength and deformation characteristics of undisturbed loess under static and dynamic loads are tested and studied by combining with PLAXIS 3D finite element numerical simulation software.The research contents mainly include:(1)By controlling factors such as different initial consolidation confining pressure,different initial moisture content and sampling at different angles from natural sedimentation direction,the strength characteristics and deformation characteristics of undisturbed loess under static load were investigated.(2)By controlling different initial consolidation confining pressure,different initial water content,different angle sampling with natural sedimentation direction,different consolidation ratio,different loading frequency and other factors,the strength characteristics and deformation characteristics of undisturbed loess under dynamic load were investigated.(3)According to the laboratory test results,PLAXIS 3D finite element numerical simulation software was used for comparative analysis.The conclusions of the study mainly include:(1)The loess in this region mainly consists of powder particles,which are small and have a large specific surface area,and have a strong sensitivity to water content.Deviatoric stress decreases with the increase of water content,while strain increases with the increase of water content.The strengthes of intact loess at different depths have certain differences.Under the condition of reaching the same strain,the stress of the intact loess increases with the increase of the embedding depth.The increase of the depth improves the anti-vibration and shear strain resistance of the intact loess.Has higher strength.(2)Under the stress control and strain control loading mode step by step,the inflection point occurred when the dynamic straindε =0.5%.The dynamic stress increased with the increase of confining pressure,sampling depth,consolidation stress ratio and vibration frequency,while the dynamic elastic modulus of intact loess increased with the increase of sampling depth,consolidation stress ratio and vibration frequency.The damping ratio of intact loess increases with the increase of dynamic strain and consolidation stress ratio,but decreases with the increase of confining pressure and vibration frequency.Under the single-stage loading mode of stress control,the increase of moisture content promotes the occurrence of dynamic strain.When the number of cycles reaches 400,the curve of dynamic strain cycle number appears inflection point.The dynamic shear modulus of undisturbed loess decreases first,then increases and then decreases with the increase of cycle times,and decreases with the increase of water content.The damping ratio of undisturbed loess increases first and then decreases with the increase of cycle times,and increases with the increase of water content.(3)The modified H-D hyperbolic model more precise description of intact loess of the backbone curve,the fitting degree were greater than 0.97,according to the modified H-D hyperbolic model of the initial elastic modulus with the sampling depth,consolidation stress ratio and vibration frequency increases,the static elastic modulus increases with the increase of sampling depth,confining pressure and decreases with the increase of moisture content,the sampling point is different,the initial static and dynamic modulus of elasticity from big to small in turn is: 0°,30°/60°,45°,90°,intact loess anisotropy is more significant.(4)The increase of confining pressure,consolidation stress ratio and vibration frequency delayed the occurrence of vibration compaction stage to vibration shear stage,vibration shear stage to vibration failure stage,and improved the resistance of intact loess to vibration deformation.Under the same dynamic strain loading,the dynamic stress of intact loess decreases with the increase of cycle times,and the stress relaxation process can be divided into rapid relaxation stage,attenuation relaxation stage and stable relaxation stage.The dynamic stress relaxation of intact loess in this region is relatively slow.(5)By using the soil hardening model to simulate the undisturbed loess under static load,it can be seen that the laboratory test results are in good agreement with the numerical simulation results.The small strain soil hardening model is not suitable for describing the dynamic strength and deformation characteristics of undisturbed loess under large dynamic strain. |
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