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TECHNOLOGIES INC • January 7, 1997 Mr. Peter A. Stauch Morrison Knudsen Corporation 7100 East Belleview Avenue, Suite 300 Englewood, Colorado 80111 96 South Zuni Street Denver, Colorado 80223-1292 Telephone: (3031 7447105 Feceimile: 1303) 744-0210 Subject: Geotechnical Laboratory Testing, Proposed Gob Pile, Bowie No. 2 Mine, Bowie, Delta County, Colorado Job No. 5002 60 2655.04 Dear Mr. Stauch: During subsurface exploration in August, 1996 in the upper portal bench and silo areas, two additional shallow exploratory borings were drilled in the gob pile area in order to obtain samples of the typical subsoil materials. Borings 27 and 28 were drilled at the approximate locations shown on Fig. 1. Boring 27, drilled in the lower portion of the gob pile area, encountered 9'/z feet of man-made fill overlying Mancos shale extending to the maximum depth • drilled, 20 feet. Boring 28, drilled near the center of the gob pile, found colluvium for the full 25-foot boring depth. Relatively undisturbed samples of the subsoil types were obtained using a lined, modified California spoon (2.0-inch I.D.) sampler. The laboratory testing program included consolidated, undrained triaxial shear (ASTM D 4767) and consolidated, drained direct shear tests (ASTM D 3080) run on samples of the fill, colluvium and shale. A direct strear test was performed on a sample of colluvium from Boring 28 at a depth of 19 feet. In general our borings found the colluvium to consist of clayey sand and sandy clay with gravel sized sandstone fragments. The sample tested was a finer grained sandy clay. Test results, presented on Fig. 2, indicate an angle of internal friction (~) of 32' and a cohesion of 900 psf. A triaxial shear test was performed on samples of the Mancos shale from Boring 27. The shale was medium hard to hard. The intent was to conduct tests on samples from depths of 14 and 19 feet at varying confining pressures to develop the failure envelope. During the saturation portion of the test, a fracture in the specimen became evident, yielding a low shear strength. To avoid this situation, amulti-stage test had to be conducted on the sample at the 14-foot depth. Test results, shown on Figs. 3 and 4, indicate a ¢ angle of 12' and a cohesion of 1,100 psf. The fill consisted of clayey, gravelly sand with frequent coal fragments. The samples of fill were insufficient to provide enough undisturbed material to run a test. The in-place moisture • and density of a fill sample at a depth of 4 feet was determined. During drilling a disturbed bulk sample of the fill was obtained. The disturbed material was then remolded into three Asleco • Austin Research Engineers •Chen-Northern • Empire Soils Investigations • Kansas Cily Testing Maxim Engineers • Nebraska Testing • Patzig Testing • Southwestern Laboratories • Thomas-Hartig • Twin City Testing ~; ~~'