GENERAL55366 - Laserfiche WebLink

Home Browse Search

DEPARTMENTOFNATURALRESOURCES D. taonte Pascoe E.ecuiive D~rectur III IIIIIIIIIIIII III MINED LAND RECLAMATION DIVISION DAVID C. SHELTON Director Ric h3~C D Lapin Go.=: no, TO: Carol Russell FP.Orl: Jim Pendleton RE: Geote chni cal GEC I•tinerals, Pia rch 17, 1982 ~ • `~C~.. A e of the Supnlernental Submittals Inc.'s Permit Application to the Pursuant to your request, I have reviewed the geotechnical aspects of the supplemental permit application submittals completed by GEC Minerals, Znc. I fo rv~ard the following comments for your consideration. Overburden-Swell Factors In response to the Division's Preliminary Adequacy Review, the applicant has prepared a set of mathematical predictions of projected overburden swell factors for the various areas to be mined. The applicant has utilized over- burden and interburden augerino data and Caterpillar Handbook estimated values for rock and soil material bulking. These tables are presented in the amended application. The first table "Overburden Swell Factor Deter- mination", presents an estimate for average bulking of 6.6?0, which toould be encountered if the entire five seam section Caere to be mined. The second table, "Swell Factor to be Used in 1981 and 1982", presents an estimate of bulking of 10.3% to be encountered within the areas to be mined during 1981 and 1982, c~~hich will extract seams No. I through 9. The third table, "Swell Factors *_o be Used in East Area and North Area", appears to evidence one oversight. This table purports to project an estimate of bulking of 7.60 for the areas to be mined in the "East Pit" and "lJOrth Pit", in which seams No. 2 through lap. 5 are to be extracted. However, in completing the calculations the applicant failed to include the 3.J foot thickness of the No. S coal seam in the calculation of the estimated extracted pit thickness. Appropriate inclusion of the seam No. 5 thic/mess results in a total excavated depth of 98.0 feet, rather than the 94.7 feet reported. This arr~ndment, in turn, results in a projected overburden bulking calculation of 4.0`;', rather than the 7.60 projected within the table. In light of these amended overburden sr:e11 projections, c,'ith the above-discussed correction, the applicant is projecting overburden bulking of approximately 4.0`e to I0.3'.;, which should result in post-mining topographic rises of approximately 5 feet on the ac-erage. This is a considerable arrendment of the applicant's original projection of bulking of approximately 17.0-s. I believe that these projections, including the correction discussed above, represent a prudent projection in keeping with current state-of-the-art. 423 Centennial Building, 1313 Sherman Street Denver, Colorado 80203 Tel. (3031 P,Sfi