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<br />Memo to Dave Berry <br />Bowie No. 2 Second Additional Geotech Study <br />page 7 <br /> <br />the Bowie No. 2 Mine site. BRL should commit to the continued collection <br />and presentation of inclinometer data at the Bowie No. 2 mine site. <br />2. Use of Filter Fabrics <br />Maxim Technologies, apparently in response to a request from the <br />applicant, reconsidered and restated its recommendation concerning the <br />use of filter fabric above basal boulder rubble blankets beneath reclaimed <br />fills. Maxim has specified that where used as a drainage blanket coarse <br />boulder rubble should be fabric shielded to prevent invasion of fines into <br />the drainage blanket. In situations were the boulder rubble is being used <br />to increase frictional bond of the basal layer of the fill "it is important <br />that rock be incorporated into a soil matrix to insure that any voids <br />between rock are filled to prevent migration of fines." I agree with these <br />statements. However, in the final design specifications of the permit <br />more detail will be necessary. First, how will the two differing <br />situations be identified and projected under reclaimed conditions? Often, <br />after backfilling, previously well-drained situations develop ground water <br />saturated conditions. <br />Further, specification for fabric installation over coarse boulder rubble <br />materials will require allowances to avoid over stressing the fabric's <br />tear resistance. Repeatedly at coal mine sites, underdrains have been <br />compromised when fabric's failed between coarse underdrain matrix and <br />overlying fine grained soils. The fabric is incapable of bridging the <br />matrix voids in the boulder rubble. At a minimum, properly graded finer <br />grained filter layers should be placed to support the filter fabric. <br />3. Expansive Soils Shear Strength <br />In their original geotechnical engineering report, Maxim Technologies <br />reported that several soils exhibited volumetric expansion (under 500 psf <br />fixed loads) of up to 13 percent, correctly termed "highly expansive. <br />Further, the author appropriately commented; "Clearly, most of the clays <br />