DETERMINATION OF EXTENT AND STIFFNESS OF FROZEN GROUND USING SURFACE WAVES

AN INNOVATIVE NEW SEISMIC TECHNIQUE, THE SPECTRAL ANALYSIS OF SURFACE WAVES (SASW) METHOD, HAS OUTSTANDING POTENTIAL FOR LOCATING FROZEN AND UNFROZEN GROUND RAPIDLY AND ACCURATELY THROUGH MEASUREMENT OF THE SEISMIC WAVE VELOCITY PROFILE. THE VELOCITY OF SEISMIC WAVES IS MUCH FASTER IN FROZEN GROUND THAN UNFROZEN GROUND. WAVE VELOCITIES ALSO CAN BE USED TO PREDICT MODULI OR "STIFFNESS". THE SASW METHOD HAS ALREADY BEEN USED TO PREDICT THE SHEAR WAVE VELOCITY AND THICKNESS PROFILES FOR PAVEMENTS, LIQUEFACTION INVESTIGATIONS OF SOIL SITES, EARTH DAMS, CONCRETE DAMS, AND FILLS. THE METHOD IS BASED ON ELASTIC WAVE PROPAGATION THEORY AND SPECTRAL ANALYSIS METHODS FOR EVALUATING DISPERSION CURVES FOR SURFACE WAVES. ONE OF THE MOST EXCITING ASPECTS OF THE METHOD IS ITS CAPABILITY TO DETECT LOW VELOCITY LAYERS UNDERLYING HIGHER VELOCITY LAYERS WITH MEASUREMENTS MADE ON THE GROUND SURFACE. THIS CAPABILITY OF THE SASW METHOD OVERCOMES THE TRADITIONAL LIMITATION ON THE USE OF THE SEISMIC REFRACTION METHOD. THUS, THE SASW METHOD SHOWS STRONG POTENTIAL FOR LOCATING FROZEN AND UNFROZEN GROUND LAYERS, EVEN WHEN THE GROUND SURFACE IS FROZEN AND THE UNDERLYING SOILS ARE THAWED. RESEARCH WILL BE PERFORMED AT TWO SITES IN ALASKA WITH VARYING FROZEN AND UNFROZEN GROUND CONDITIONSTO DEVELOP MEASUREMENT AND ANALYSIS TECHNIQUES FOR USING THESASW METHOD AT ARCTIC SITES. AS THE RESEARCH PROGRESSES, THE SASW METHODS CAPABILITIES FOR DETECTING OTHER SUBSURFACE ARCTIC CONDITIONS SUCH AS FROZEN ROADS, MASSIVE ICE LENSES, AND LATERAL PROPAGATION OF PERMAFROST WILL BE RESEARCHED. THE POTENTIAL BENEFITS OF ACCURATE KNOWLEDGE OF FROZEN GROUND CONDITIONS TO ENGINEERS, CONTRACTORS AND THE PUBLIC ARE TREMENDOUS FOR IMPROVED PERFORMANCE AND ECONOMY OF CONSTRUCTION AND MAINTENANCE OF ROADS, BUILDINGS, RUNWAYS, AND PIPELINE FACILITIES.