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• E~~ • <br />TECHNOLOGIES INC <br />October 17, 1996 <br />Mr. Peter A. Stauch <br />Morrison Knudsen Corporation <br />7100 East Belleview Avenue, Suite 300 <br />Englewood, Colorado 80111 <br />ufh Zuni Street <br />ier, Coleredo 80223-1292 <br />Telephone: 13031744-7105 <br />Facsimile: 13031 744-0210 <br />Subject: Addendum to Preliminary Geotechnical Engineering Study, Bowie No. 2 Mine <br />Surface Facilities, Bowie, Delta County, Colorado <br />Job No. 5002-60-2655.01 <br />Dear Mr. Stauch: <br />V/e have reviewed the recommendations presented in our Preliminary Geotechnical Engineering <br />Study dated July 10, 1996 regarding the use of a filter fabric placed above boulder rubble fill <br />used as a starter material at the toe of major fills. In our report we indicated that boulder rubble <br />was an excellent material at the toe of fills because of its strength and drainage capability. <br />Where boulder nibble is used as a drainage feature beneath a fill, it should be protected from <br />fines migration by either a filter fabric or a suitable filter course. If boulder rubble is placed <br />in areas not intended for drainage, it is important the rock be incorporated into a soil matrix to <br />insure that any voids between rock are filled to prevent migration of fines. In tflis latter case <br />a filter course or fabric would not be required. <br />)f we can provide further information, please call. <br />Respectfully submitted, <br />bIAX111~f <br />~) / <br />~ ~ /: <br />David H. Adams, P.E. <br />Rev. By: AJL <br />/DHA <br />INC. °'+,i,;t~,~ <br />`~~y~~ ' r <br />/,, ,¢' ` - <br />-` • ` ~/1 ti <br />~`. <br />' y::, <br />:w,;. .,. .. , <br />Asfeco • Austin Research Engineers •Chen-Northern • Empire Sails Investigations • Kansas City Testing <br />Maxim Engineers • Nebraska Testing • Patzig Testing • Southwestern Laboratories • Thomas-Hartig • Twin City Testing <br />x~ <br />~! <br />w <br />