LABORATORY STUDY OF HYDRAULIC FRACTURING IN CLAY.

A laboratory test technique was developed to study hydraulic fracture initiation in soils. The soil used for the study was a laboratory compacted low plasticity clay. The samples were tested in a standard laboratory triaxial cell with a hypodermic needle implanted in the center of the sample. The internal fluid pressure was increased via the hypodermic needle until hydraulic fracture was initiated in the sample. Onset of fracture was measured by a pore pressure transducer and flow meter. The tests were conducted at various confining pressures to evaluate the effect of external stress level on fracture initiation. The pressures required to induce fractures in the soil were compared with analytical methods for predicting fracture, and the results are discussed.