Study On The Thermal And Mechanical Properties Of Fiber-reinforced Soil

Understanding effect of freezing phenomenon in a soil structure is essential to foundation technology,road construction and earthwork application in a cold region.The main purpose of this work is to understand physical,mechanical and thermal properties of fiber-reinforced soil subjected to multiple freeze-thaw cycles and to predict the frost depths in eastern Turkey with the Stefan equation and a modified Berggren(ModBerg)equation.For this purpose,the physical properties including mass losses,changes of water content and height were determined on randomly distributed glass,basalt,steel and flyash-lignin fibers-reinforced soil after a number of freeze-thaw cycles.Further,the thermal characteristics of the fiber-reinforced soil were evaluated and summarized as a function of freeze-thaw cycles,fiber volume fraction,and temperature.To validate the experimental thermal results,a statistical-physical model was employed on the fiber-reinforced soil under different conditions.Besides,the experimental investigation relative to the unconsolidated-undrained triaxial compression behavior of clay soil reinforced with 3 different fiber contents(0,0.5 and 1%)of glass and basalt fibers subjected to 5 different numbers of freeze-thaw cycles(0,2,5,10,and 15)and 2 flyash contents(4 and 8%)and 5 different fiber contents(0,0.25,0.5,0.75 and 1%)of lignin fiber under 2 different numbers of freeze-thaw cycles(0 and 15)were presented with different confining(100,200 and 300kPa).Also,hyperbolic model parameters were predicted to determine the static stress-strain behaviors of fiber-reinforced soil subjected to freeze-thaw cycles.Moreover,a large number of dynamic triaxial tests were carried out with various fiber contents(0,0.5 and 1%)of glass and basalt fibers,confining pressure(300,400 and 500 kPa)and 5 different numbers of freeze-thaw cycles(0,2,5,10 and 15).To validate experimental results on the dynamic parameters of fiber-reinforced soil subjected to freeze-thaw cycles,the Hardin-Drnevich model and the modified Kondner-Zelasko hyperbolic model parameters were predicted and the dynamic shear modulus was expressed by using a nonlinear model as a function of freeze-thaw cycles,volume fractions of fiber,confining pressure,and initial water content.The results showed that different fiber fractions and their mixtures could be employed as supplement additive to improve mechanical,thermal and freeze-thaw performance of subgrade soil for road construction and earthworks.Further,a close match were observed between the results of predicted and experimental for different kinds of fiber in a wide range of fiber ratios and freeze-thaw cycles.