Borehole mining. Improved technology expands horizon consolidation and thermoelasticity

Borehole mining, as a viable concept for recovery deep sedimentary mineral resourcees, historically has been long on promise but short on results. Application of the technology seems best suited for recovery of Miocene phosphate resources on the East Coast of the US. These deposits are potentially enormous in scope and underlie sections of the coastal plain and the near offshore continental shelf. A borehole mining test program, using an existing prototype borehole system, successfully extracted Miocene phosphate in northeast Florida in 1984-1985. The top of the main mineral zone was 80 m (261ft) below the surface. A new prototype borehole mining system designed in 1986 incorporated several innovations offering potentially higher productivity and lower power consumption than was achieved with the previous test unit. Economic restraints at that time prevented the construction and testing of this design. three-dimensional Biot consolidation theory is developed which operates directly in the time domain and requires only boundary discretization. Consequently, the dimensionality of the problem is reduced by one and the method becomes quite attractive for geotechnical analyses, particularly those that involve extensive or infinite domains. Furthermore, as a result of a well-known analogy fully elaborated here, the new BEM formulation is equally applicable for quasi-static thermoelasticity. Several detailed examples are presented to illustrate the accuracy and suitability of this boundary element approach for both consolidation and thermomechanical analyses.