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The Use Of Dielectric And Electrical Conductivity Measurements And Ground Penetrating Radar For Frost Susceptibility Evaluations Of Subgrade Soils
- Publisher: European Association of Geoscientists & Engineers
- Source: Conference Proceedings, 8th EEGS Symposium on the Application of Geophysics to Engineering and Environmental Problems, Apr 1995, cp-206-00008
Abstract
In this study several tests have been made to evaluate, if in situ dielectric value and electrical conductivity<br>measurements together with ground penetrating radar survey (GPR) results could be used to estimate frost<br>susceptibility of subgrade soils in Finnish Lapland. Dielectric value and electrical conductivity were measured in<br>situ from the soil beside the road with a Dielectric Constant & Conductivity Meter made by Adek Ltd, Estonia<br>and GPR surveys were performed with 500 MHz ground coupled antenna. GPR measurements were performed<br>both in winter when the ground was frozen and in summer when it was totally thawed. The test site on highway<br>21 at Pello was selected as it exhibited variations of frost heave damages and a section with no frost heave was<br>also surveyed. The measurement results were compared with the frost heave measurements and the visual frost<br>damage mapping on the road surface.<br>The study results showed good correlation between frost heave and dielectric constant. If the dielectric value was<br>less than 8, no frost heave could been found. The highest frost heave values were achieved with the dielectric<br>constant between 15 and 22 in the case of glacial till and 20 and 30 in the case of silt. With higher dielectric<br>values frost heave started to decrease. Electric conductivity measurements gave information about the soil type<br>and compressibility.<br>With Ground Penetrating Radar it is possible to measure the frost depth and estimate the presence of unfrozen<br>water in road structures and subgrade soils. This is based on the fact that the dielectric value of ice is 3.6-4.0<br>and the presence of unfrozen water can be seen as major reflectors in GPR data. GPR results gave also the total<br>thickness of road structures, which is needed for dimensioning road structures against frost heave. Other<br>valuable information gained from the radar results were the presence of bedrock, presence of boulders and<br>information about the quality of the existing road structure.<br>As a result of this study a method of classifying the frost susceptibility of subgrade soils was proposed. This<br>classification is based upon the in situ measurements of dielectric value and electrical conductivity.