"The interactions of the chemical, thermal, and mechanical processes occurring during the retorting of oil shale are quite complex . Particularly in the case of modified in-situ retorting of oil shale, the synergistic or combined effects of those various processes may dominate the effects considered independently . The resultant structural and chemical response could vary drastically from what would be predicted by conventional (single effect) analyses . A few examples of such combined effects are : 1 . Exfoliation along bedding planes due to thermal warping , stress gradients, and trapped hot gas pressure, combined with the clamping effects due to compressive stress orthogonal to bedding planes . 2 . Enhanced heat transport by hot gas convection down cracks due to pressure pulses (see Reference 1) . Here again, one must consider clamping effects due to compressive stresses orthogonal to the bedding planes. 3. Removal of material from the surface by spallation, with the retort heat attacking the new surface to continue this process in a propagating damage front . This front may actually propagate faster than a normal pyrolysis front. 4 . Lubrication of cracks and joints by water or liquid hydrocarbons to lower the friction angle . Consider the action of the baseline stress field with respect to squeezing the fluid along a joint and into the interior of the structure."