Experimental Study On Electrical Resistivity Characteristics Of Silty Clay Under Uniaxial Compression And Frozen-thaw Cycles

In China,more and more constructions in cold regions appear,Strength and deformationof frozen soil,characteristics of frost heave and thaw collapse have become the major task forcold regional construction.But researches on mechanism of frost heaving are still not maturedowing to complexity of frozen soil,and the current study,thinking little of the freezing andthawing process,mostly focuses on the different physical and mechanical properties betweenfrozen soil and thawed soil.It is funded by"research on the submacroscopic deformation mechanism and structuralcharacteristics of silty clay under freeze-thaw cycles"(an open fund of State Key Laboratoryof Frozen Soil Engineering).Using uniaxial compression and freeze-thaw cycle apparatuscombined with electrical resistivity observation for whole process,tests are performed for thesilty clay in Beilu River.Based on the experimental results,changes of electrical resistivity offrozen silty clay under uniaxial compression as well as the relationship between resistivityand mechanical properties have been studied systemically,and an Preliminary study onresistivity characteristics has been carried out for freezing and thawing soil.The main resultsof this paper are in detail listed in the following:(1)Orthogonal tests have been performed under different types of power(DC voltage,AC power),different circuit(voltammetry,reference resistor method)and different testvoltages.Through these experiments,the author introduces a new practical device forlaboratory measurement of frozen soil electrical resistivity,which uses two electrodes,10VDC regulated power and voltammetry circuit.Contact resistance between soil sample andelectrodes is obtained,and modified method of real resistance is proposed.Pilot test resultsshow that the equipment is effect and feasible in measuring electrical resistivity of frozen soil.(2)The test results under different dry density,water content and different temperatureshow that stress-strain curve can be separated into compression stage,elastic stage,plasticflow stage,break-up stage corresponding to decreasing fast stage,decreasing to minimumstage,steady increasing stage,unsteady increasing stage in resistivity-strain curve,themechanism of soil conductivity in every stage has been explained separately.The relationshipbetween resistivity and uniaxial strength is established.(3)This paper analyzes on the similarities and differences of resistivity characteristicsunder freeze-thaw cycle in closed system and in open system.The deformation in wholeprocess of freeze-thaw cycle can be divided into five stages:Cold-contraction,Dramaticincreasing,steady increasing,Dramatic decreasing owing to thawing,stability stage after complete thawing.The author analyzes electrical resistivity properties in differentdeformation stage separately.(4)The resistivity of saturated silty clay in closed system under repeated freeze-thawcycles is studied.The resistivity of frozen soil decreases and that of thawed soil increasesexponentially with increasing of freezing-thawing times.The amount of frost heave,thawcollapse and average dry density in every freeze-thaw cycle rise with increasing offreezing-thawing times,and they are trend to stability after 5 freeze-thaw cycles.(5)Researches show that changes of resistivity,temperature,pressure and deformationduring freezing-thawing cycles are real-time and synchronical,which proves that it is feasibleto study the changes of soil structure during freezing-thawing and problem of strength-deformation under external load by using electrical resistivity method.