SOME RESULTS ON THE SWELLING OF SOIL IN THE PRESENCE OF FROST AND APPLICATION OF THESE RESULTS TO SOIL CLASSIFICATION ACCORDING TO THEIR DEGREE OF FROST SENSITIVITY

THE AIM OF THE REPORT, WHICH WAS PRESENTED AT THE OECD SYMPOSIUM ACTION ON PAVEMENTS, OSLO, OCTOBER 1973, IS TO PRESENT: (1) RESULTS OF LABORATORY STUDIES OF THE FROST BEHAVIOUR OF SOILS, IN PARTICULAR SOIL SWELLING; AND (2) AN EXPERIMENTAL METHOD OF CLASSIFICATION OF SOILS ACCORDING TO THEIR DEGREE OF FROST SENSITIVITY, BASED ON SWELLING RESULTS. THE FROST BEHAVIOUR OF SOIL SENSITIVE TO FROST IS BASED ON A HIGHLY COMPLEX RELATION BETWEEN MACROSCOPIC PHENOMENA OF HEAT AND MASS TRANSFER AND MICROSCOPIC PHENOMENA OF INTERFACE IN PORES. THE LATTER PHENOMENA RESULT IN THE FACT THAT THE PRESENCE OF BOUND WATER AND THE DISTURBED GEOMETRY OF THE FROST FRONT CAUSE WATER SUCTION AT THE LEVEL OF THE FROST FRONT, FLOW IN THE NON-FROZEN PART, SEGREGATION OF THE ICE IN THE SHAPE OF LENSES, AND SWELLING IN THE FROZEN PART. LABORATORY STUDIES CONDUCTED AS CYLINDRICAL SAMPLES OF SOIL, WHICH ARE WELTED THROUGH THEIR BASES AND SUBJECTED TO A ONE-DIMENSIONAL THERMAL FLOW BY MEANS OF APPLICATION OF CONSTANT NEGATIVE TEMPERATURE ON THEIR UPPER PART, HAVE SHOWN THE EXISTENCE OF A RELATION BETWEEN FROST SWELLING AND THE SQUARE ROOT OF THE FROST INDEX APPLIED, THE GRADIENT OF THE STRAIGHT LINE DEPENDING ON THE TYPE OF SOIL CONSIDERED. IT WAS ALSO DEMONSTRATED THAT SWELLING APPEARS ONLY WHEN THE SPEED OF PROGRESSION OF THE FROST FRONT BECOMES SLOWER THAN A CRITICAL SPEED. AN EXPERIMENTAL METHOD OF CLASSIFYING SOIL SENSITIVE TO FROST WAS DEVELOPED FROM A COMPARISON OF THE VALUES OBTAINED FOR DIFFERENT SOIL SAMPLES, OF SIMILAR DIMENSIONS AND MOISTURE CONTENT, SUBJECTED TO THE SAME FREEZING PROCESS. THE METHOD PROVED TO BE SATISFACTORY AND WAS FURTHER DEVELOPED IN TWO ROAD LABORATORIES IN FRANCE. A TABLE SHOWS THE CLASSIFICATION SET UP FOR THE SOILS CONSIDERED.