Naturally Frozen Soils from the Field to the Laboratory

For designing infrastructure foundations in cold regions, it is essential to evaluate the mechanical properties and characteristics of naturally frozen soils obtained from the field. However, sampling frozen soils is a difficult task, especially when looking for minimally disturbed, naturally frozen soil samples. The less disturbed the samples are, the more reliably one can evaluate the mechanical properties of the frozen soils at its in situ condition. This paper describes the detailed processes used to extract and machine naturally frozen soil samples for mechanical property testing. The extraction process involves a chainsaw with a carbide chain to cut a square into the ground of the desired size, and the isolated block is snapped from the ground using a wedge. The machining process involves cutting the block sample into octagons. During this process, particular attention is paid to the orientation of soil fabric. Once an octagon is made, a lathe is used with a special holding bit to avoid disturbing the octagon ends. Carbide cutting tools are needed as standard cutters dull very quickly and begin heat-affecting the soil. The rate of lathing is carefully controlled to minimize the heat disturbance and roughness of the cylinder surface. A four-jaw chuck is used to face both sides of the specimen with the lathe to ensure the two faces are parallel. This machining process is believed to minimize the thermal and mechanical disturbances to the specimen. The testing equipment and sensors used to measure the stress-strain behavior are described. Testing data obtained from two sets of examples with different orientation angles are presented.