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P. 04 <br />Harding Lawson/West Elk Gob Pile Rock Testing <br />RESULTS <br />Page 3 of 4 <br />Results of the uncon5ned compressive strength tests are listed below, along with the as-tested <br />density for each specimen. <br />SAMPLE <br />DEPTH <br />(ft) AS-TESTED I <br />DENSITY <br />~~) ~ LrNCONFINED <br />STRENGTH <br />(Psi) <br />67 2.32 5.520 <br />72 2.42 13,600 <br />74 2.55 1 !6,900 <br />Shear stress vs shear displacement plots are appended for each of the tested direct shear <br />specimens following the body of this report. <br />DISCUSSION <br />Because of the high intact strengths of the umveathered and partially weathered sandstone, failure <br />is unlikely to involve large amounu of intact sandstone. The shalt' units observed in the 20' of <br />core were very thin, and could not be tested for high angle failure strength, but they certainly <br />would be suitable for bedding plane failure. Failure would therefore be constrained principally by <br />joints, faults, bedding in shalt' units, very highly weathered horizons, soil horizons, and,'or <br />sandstone bedding planes. <br />Although some of the direct shear tests indicate initial peak strengths somewhat higher than the <br />residual strengths, the peak strengths are overcome with less than a tenth of an inch of movement. <br />They are therefore not reliable for design. <br />Direct shear strength of the clean, slightly weathered, high angle sandstone joint at 73' appears to <br />be consistently about 38° and purely frictional in nature. <br />Shear strength of a parting along a bedding plane ofthin-bedded sandstone at 63 ~ appears to be <br />about 31°, probably this low because of the presence of a small amount of clay minerals, which <br />also probably caused the formation of the thin-bedded partings in the first place. The sandstone <br />increases slightly in strength (2°) at higher normal stresses. This effect is ascribed to the wearing <br />away of the softer, more argillaceous layer along the bedding plane parting due to repeated <br />shearing, and the worn material being removed between runs. This material would remain in <br />place irr situ, decreasing the magnitude of any inapse in strength with travel. <br /> <br />ROCKTLCt I 7444 Platimrtn Circle, Wal Jordan, t17' 840tH i 8U 11233-3222 <br />