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2.4 BUILDING AND STRUCTURES Criteria For Evaluating Impacts to Buildings and Structures There are no known structures within the present mine plan area at the Bowie #2 Mine which could be affected. But, we have addressed the potential impacts to structures in this section in the event that the Bowie #2 Mine is expanded to areas where vulnerable structures exist. Horizontal strain is a measure of the change in length of a piece of ground or structure. Damage to surface structures is frequently a function of horizontal stains. Most relevant codes specify maximum allowable horizontal strains in order to prevent damage to various structures. The complete strain profile at ground surface above an extraction area can be developed using methods detailed in SEH. However, for the current study, it is considered sufficient to estimate maximum strains, since the maximum damage to any structure which could develop can be estimated from these values. Strain is proportional to subsidence (S) and inversely proportional to depth (h), so the maximum strain (E) over and excavation is proportional to S/h. Using the graph presented in SEH, which is reproduced as Figure 15-4, enables an estimate of maximum strains. Fora 860 foot wide panel, where the w/h ratio will be in excess of 1.0 at all overburden depths of less than 860 feet, maximum compressive and tensile strains will be on the order of 0.55 S/h and 0.65 S/h respectively. Fora 9.5 foot mining height, which is the most severe case which will exist at the Bowie #2 Mine, the fo{lowing maximum strains are predicted, assuming a maximum subsidence from Figure 15-3, for the profile which exists after the completion of mining. Overburden W/h Depth(Feet) 200 4.30 500 1.72 1,000 0.86 1,500 0.57 2,000 0.43 Maximum Tensile Stain (u-in/in) 28710 11120 4740 2540 1380 Maximum Compressive Strain (u-in/in) 22530 8720 4370 3690 2770 - 24 - 10!00 PR-~ y • •