Multi-scale Study On The Influence Of Combined Water On Mechanical Properties Of Undisturbed Loess

Undisturbed loess has the characteristics of small density,low humidity,loose structure,pore development and significant collapsibility.The engineering properties of loess are closely related to its internal structure and water content.The combination of water is an important factor affecting the strength characteristics of loess.The increase of combined water content in loess will destroy the internal structure of undisturbed loess,thus reducing the strength of undisturbed loess.In this paper,the original loess in the Shichuanhe area of Fuping County,Shaanxi Province,the effects of combined water on the mechanical properties and deformation characteristics of loess were systematically studied from the macroscopic,mesoscopic and microscopic perspectives of soil using triaxial compression test,SEM and other laboratory methods,and discrete element numerical simulation.(1)Through the indoor triaxial compression test,the deformation and mechanical properties of the undisturbed samples with different combined water contents and the remolded samples under saturated water content under fixed confining pressure were analyzed.The deformation and mechanical properties of samples with strong combined water content(w(28)10%)and weakly bound water(w(28)25%)were analyzed under variable confining pressure.The effects of different combined water and different confining pressures on the mechanical properties of undisturbed loess were studied.The results showed that weakly bound water was the main factor affecting the deformation of soil samples.With the increase of combined water content,the structurality of undisturbed loess was weaker.The boundary water content of strong and weak combined water was defined as the boundary water content of weak strain hardening and strong strain hardening of undisturbed loess.The structural parameters can show good sensitivity to the compressive properties of undisturbed loess.(2)Qualitative and quantitative analysis of the microstructure of undisturbed loess based on scanning electron microscopy.The results showed that the diameter of the soil-like particles under the strong combined water content was too large.The particles were multi-directionally oblate,and the circularity,shape complexity and orientation of the sample particles(pores)mainly composed of weakly bound water were Loess above the strong combined water content.Strong combination of underwater soil samples was more structural;with the increase of confining pressure,the particles were broken and mainly small diameter;large and medium pores were reduced obviously,and fine pores were increased.(3)Based on the indoor triaxial compression test,a three-dimensional particle flow model was established by using discrete elements.The triaxial compression test of undisturbed loess with 10% and 25% water content was numerically simulated,and the model stress curve,failure mode and contact force distribution were obtained.The variation of the porosity distribution;the calculation results are reasonable and consistent with the macroscopic stress characteristics.