Study On Matrix Suction And Dynamic Resilience Modulus Of Unsaturated Subgrade Soil Improved By Oil Shale Residue And Fly Ash In Seasonal Frozen Regions

Due to the influence of the natural environment,the structure,physical properties,mechanical properties(strength,stability,etc.)of the roadbed in the seasonally frozen area will continue to change due to the influence of the natural environment.The principle of effective stress believes that soil exists in the form of solid-liquid two-phase,and the friction force between the particles of the soil provides the effective stress of the soil.In the study of unsaturated soils,it is believed that the soil is composed of four phases of soil particles,pore water,pore gas,and water-vapor shrinkage film.Unless extremely close to the groundwater level is extremely humid,the filling of the road,road and airport roadbed are unsaturated fourphase soil,so it is necessary to discuss saturated soil and unsaturated soil separately.Soil sees a series of effects brought about by the change of humidity under natural conditions of forming solid,liquid two-phase and ignoring subgrade,which will lead to errors in theoretical research and affect the stability and safety of engineering construction.The matrix suction of soil originates from the surface tension of water-air boundary shrinkage film in soil pores,which is a key variable in geotechnical analysis of unsaturated soil mechanics.For road construction materials,resilient modulus is the embodiment of their ability to resist deformation under load,and it is an important performance index mainly affected by humidity,compaction and other factors.In recent years,many studies have shown that there is a close relationship between resilient modulus and matrix suction,which is mainly affected by soil moisture content,which can provide certain adhesion and anti-deformation ability on soil particles.It can improve the modulus of resilience to a certain extent.The roadbed materials in seasonal permafrost areas are not only affected by the humidity changes caused by rainfall evaporation in nature,but also undergo the weakening of roadbed performance caused by freezing and thawing caused by the huge temperature difference between seasons every year.Therefore,considering the factors such as humidity,freeze-thaw and so on,the research on the relationship between matrix suction and dynamic resilient modulus of unsaturated roadbed fillings is of great significance to ensure the safety and stability of subgrade structure in long-term service under the dual action of load and environment.Taking the change of moisture content as the main factor and freezing and thawing as the additional factor,this paper studies the relationship between matrix suction and dynamic resilient modulus of unsaturated oil shale waste residue-fly ash improved soil.Firstly,the oil shale waste residue-fly ash improved soil and Jilin silty clay with low liquid limit and two kinds of roadbed fillings were compared and analyzed.Under indoor laboratory conditions,filter paper matrix suction experiments,freeze-thaw cycle experiments and SEM electron microscope scanning experiments were carried out.The soil-water characteristic curve and pore structure characteristics after different freeze-thaw cycles were obtained,and the evolution law of matrix suction was analyzed from two angles: the change of moisture and the change of freeze-thaw times.combined with the change of pore structure before and after freeze-thaw,the interaction among freeze-thaw cycle,pore structure and soil-water characteristic curve was analyzed.On this basis,the dynamic resilience modulus experiments of oil shale waste residue-fly ash improved soil with different moisture content,freeze-thaw cycles and stress path were carried out.The influence of the above factors on the dynamic resilient modulus of roadbed is comprehensively analyzed.The relationship between dynamic resilient modulus and matrix suction is established by using water content as the medium,and a matrix suction-dynamic resilient modulus prediction model is proposed,which is compared with the model recommended by the American Highway and Transportation Association.The results show that the matrix suction-dynamic resilient modulus prediction model established in this paper has a higher degree of fit.On this basis,a freeze-thaw reduction coefficient describing the variation of dynamic resilient modulus with freeze-thaw times is proposed and introduced to predict the dynamic resilient modulus of roadbed after freeze-thaw cycle.The study in this paper shows that there is a significant correlation between the predicted results of this method and the measured results.