ABSTRACT
The time-dependent deformational behavior of salt makes the task of salt mine pillar design complex. Current methodologies for pillar design that involve numerical modeling require the commitment of significant computer and human resources to develop an acceptable solution. For this method, preliminary pillar characteristics (size and shape) are based on historical pillar designs, observed behavior, and engineering judgment. Then a worst case-best case approach is used in conjunction with a series of numerical simulations to define the appropriate pillar-design limits. However, as salt mines become deeper and mining economics drive pillar-design decisions, our observations database will become ever smaller. A need exists for simple pillar-design tools that help salt mining operations determine acceptable pillar characteristics and bounds the scope of analysis required to establish a formal pillar design.
Van Sambeek (1996) describes such a tool in the previous conference proceedings. The pillar-design equation developed in that paper is suitable for estimating stresses in square pillars, although assumptions were required to extend its use to rectangular salt pillars. Results from a series of two-dimensional finite element simulations using both axisymmetric and plane-strain analyses could not verify the assumptions used in developing the pillar-design equation for rectangular pillars.
Three-dimensional finite difference simulations of rectangular salt pillars were performed to examine the assumptions used in the extension of the pillar-design equation. The three-dimensional modeling results bolster use of the equation for estimating stress conditions in salt pillars of various shapes and sizes. In particular, this paper (1) reviews the initial pillar-design equation, (2) compares two- and three-dimensional numerical modeling results, and (3) presents equation modifications to improve the agreement with three-dimensional numerical modeling results.
