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J III IIIIIIIIIIIII III 999 .~ . I ROCKY MOUNTAIN GEOTECHNICAL, INC. Achieving Harmony with Earth December 13, 1984 Blue Ribbon Coal Company P.O. Box 939 Paonia, CO 81428 Attn: Larry Reschke Re: Laboratory Testing Select Material Dear Mr. Reschke: Direct Shear testing was performed on the select material delivered to Rocky Mountain Geotechnical by Blue Ribbon Coal Company. The moisture-density relationship of the material was also determined for use in field density testing. The Direct Shear test was performed to determine the suitability of this material for the mine bench stabilization. The material is to be • placed in the areas indicated as "Select Material" on the construction drawings prepared by Rocky Mountain Geotechnical. Prior to performing the Direct Shear test, a sieve analysis and Proctor test were run on the sample. The results of these tests are indicated on Figures 1 and 2. Due to the large percentage of large material, the Direct Shear test was performed on the portion of the sample passing the #4 sieve. The angle of internal friction (H) measured from the test can then be adjusted to account for the larger material. A phi of 36 degrees is required for the design presented by Rocky Mountain Geotechnical. The results of the Direct Shear test are presented on Figure 3. The results indicate a cohesion (c) = 0 and phi = 35 degrees. This value is determined from the portion of the material passing the 54 sieve compacted to 908 of maximum Proctor density. The material passing the #4 sieve was utilized in the test due to the size of the Direct Shear box. The larger sized particles, if used in the Shear test, would result in an artificially high phi angle due to the forced shearing plane in the Shear box. Due to the large percentage of material retained on the A4 sieve, an increase of phi would be expected. An increase in phi would also be expected due to the angularity of the coarse material. An increase from 35 degrees to 36 degrees or more, as required to • meet the design requirements is anticipated for this material. The Railroad Station • 555E Pities Peak Avenues Swbe 107 • Culnrniln S~u~in{~s. Culnrnrlo E30003 • 011131 63 1 1999