Experimental Study Of Nano-silica On The Mechanical Properties Of Frozen (Thawing)-Soil

According to the design requirements and technical specifications,soil strength is often needed to be improved so that it meets the requirement of the subgrade in construction process of the road.Lime,cement are commonly used soil improvement materials for road construction,while for the road construction in frozen soil region,the heating can affect the ground temperature,and freezing phenomenon makes the improved soil structure destroyed in the roadbed maintenance period,thus affecting the final strength.Therefore it is necessary to find a new modified material.This paper will try to use nano silica as a new modified material infrozen soil region geotechnical engineering,and the physical and mechanical properties of the nano silica-soilis studied.When the amount of nanosilica added to silty clay is 5%(w/w),the strength of clay can increase by approximately 8 times in the case of nanosilica.When the nanosilica concentration was increased to 2%,the quantity of water supplied increased by 53%,while the amount of frost heave produced decreased by 26% at the same time.TheSilty clay forms aggregates with nanosilica particles as the nuclei.These aggregates fill the interparticle gaps in the clay samples,resulting in an increase in strength and a decrease in the amount of frost heave produced.A concentration of 1% is the threshold at which changes in the compressive resistance of silty clay and its frost heave rate can be observed.A method for accurately determining the optimum water content of soil and the corresponding maximum dry density has beendeveloped using a small number of soil samples,based on the physical parameters of the confined compression modulus of soil.Thepeak value of the compression modulus on the force-compression modulus curve is used to determine the optimum moisture contentand maximum dry density.The proposed method is validated using four different types of soils: Qinghai-Tibet clay,nano SiO2-clay,Lanzhou loess,and Qinghai-Tibet sand soil.The results show that as opposed to conventional compaction methods,the new methodallows for accurate determination of the optimum water content and the maximum dry density for various types of soil.Additionally,for certain moisture contents,when the compaction of soil is the greatest,clay and nano SiO2-clay attain the theoretical saturation status,whereas sand soil and loess do not.A series of conventional triaxial tests on Tibetan silty sandy soil and nanosilicaTibetan silty sandy soil samples(1% in weight)are carried out to investigate the influence of nanosilica on Tibetan silty sandy soil's property.At-2degreesCelsius the Tibetan silty sandstrength increases by a factor of 1 time at allco nfining.A new strength criterion was developed,which is not only able to describe strength characteristics of common frozen sand soil,but also can describe the freezing nano-silica silty sand and frozen Lanzhou loess' s strength characteristics.