A fundamental experimental study of pillar behavior

The split platen technique was used to measure vertical stress as a function of location and total load within model pillars. Stress distributions were measured for four different rock types; salt, coal, limestone and cement with various diameter to height ratios. For the salt, coal and limestone, the formation of a confined core was observed. With the presence of a confined core, the sample after initial failure became stiffer with continued deformation and there was an increase in the overall load bearing capacity. For the cement sample, there was no formation of a confined core and overall load bearing capacity continued to decrease after initial failure. The formation of a confined core for a specific rock type was suggested to be dependent upon the diameter to height ratio. Thus, the split platen technique is capable of determining the critical diameter to height ratio required in the formation of a confined core.