The Choice of Basic Pillar Design Theory for Locked Sand Condition

Because of unique properties of locked sand (very high friction angle and very low cohesion), a new pillar design method based on present basic pillar design theories must be developed. Wilson theory puts its focus on confining pressure, which is related to friction angle and cohesion. Triaxial tests results show that locked sand at Pattison mine has an average friction angle of 57°, which means the strength of the material increases rapidly with the confining pressure, and average cohesion of 2.6 MPa. Results show that choosing Wilson theory as basic pillar design theory not only considers the high friction angle of locked sand, but also minimizes the effects of Wilson’s hypothesis of neglecting the unconfined strength.