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I ® J CTL/THOMPSON, INC. CONSULTING GEOTECHNICAL ANU MATERIALS ENGINEERS January 16, 1981 Empire Energy Corporation P.0. Box 66913 AMF O'Hare, Illinois 60666 Subject: Confirming Lab Testing and Analysis Coal Waste Disposal Area Empire Energy Mines No. 5 and No. 9 Near Craig, Colorado Job No. 6918 Gentlemen: As requested, we have completed laboratory testing and analyses of the sub- ject coal waste disposal structure. This investigation was conducted to confirm strength assumptions used for preliminary recommendations reported on October 12, 1979 (Job No. 5843). The purpose of this letter is to pre- sent confirming laboratory and analyses results. On December 16, 1980, our engineer visited the coal waste disposal site to obtain samples of the waste product. At the time of our visit, processing wastes were being stockpiled in an area measuring 100 feet by 300 feet. The thickness of waste ranged from 1 to 6 feet. Samples obtained contained clay, sand, gravel and coal with natural moisture contents ranging from 10 to 15 percent. Testing. indicates the waste contains 15 to 20 percent coal. Obser- vation indicates some isolated areas may contain higher percentages of coal. Bulk samples of the waste product were returned to our laboratory and tested to determine moisture-density relationships and strength characteristics. A standard Proctor compaction test, conducted in accordance with AASHTO Method T-99 indicated a maximum dry density of 108 pcf at an optimum moisture content of 11.0 percent, as shown on Fig. 1. Samples of the coal waste were prepared near optimum moisture and compacted to approximately 95 percent of maximum standard Proctor density to simulate field conditions. These samples were tested in direct shear to determine strength characteristics as illustrated on Figs. 2 and 3. These test results suggest that under dry conditions the angle of internal friction (¢) is approximately 42o and the cohesion (C) is approximately 1500 psf. The second test series illustrated on Fig. 3 was conducted on samples which had been soaked prior to testing. These results indicate a 0 angle of 42° with 300 psf cohesion. These laboratory test results confirm the initial strength assumption of 0 equal 25° with no cohesion was conservative. As part of this investigation, a series of slope stability analyses were conducted using both the Method of Slices and the Janbu calculation techni- ques. The proposed 4:1 (horizontal to vertical) slope configuration with an 1Q]1 WFCT 17TH AVFNI IF PIFNVFIJ t"nl (IC,cM tln]M /~n~. o~c n~-.~