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<br />I, <br />I <br />I <br />I, <br />I <br /> <br />~ <br /> <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I. <br />I <br />I <br />v <br /> <br />I <br />I <br /> <br />::::-. -A <br /> <br />Woodward.clyde <br />Consultants <br /> <br />Mr. Hal Simpson <br />Colorado State Engineer <br />October 26, 1992 <br />Page 3 <br /> <br />#2 (approximately 10 feet deep) and #3 (approximately 12 feet deep) were in the right <br />abutment contact near the embankment. These sinkholes were excavated as one large <br />excavation. The excavations were completed down to a brown, weathered, closely <br />fractured sandstone. The overlying soil was variable consisting of a combination of <br />previously placed reservoir blanketing material and natural soil.. Sand was encountered <br />in portions of sinkhole #3 excavation, which we understand was placed during previous <br />sinkhole backfill operations. The excavations for sinkholes #4 (approximately 14 feet <br />deep) and #5 (approximately 16 feet deep) were completed as a single large <br />excavation. The excavation was completed through' previously placed reservoir <br />blanketing material and original soil. In portions of sinkhole #4, previously placed <br />plastic sheeting was encountered,.~hich we unilerstand was. placed during previous <br />sinkhole backfill operations. In portignsof-sinkhole #4 in the area of the previous <br />repairs, the excavations were extended down'to..gray, slightly weathered, medium hard <br />to soft sandstone. The remaining portion of the excavations for sinkhole #4 and #5 <br />were terminated within"aclinker (residue of burnt coal) and a reddish brown, closely <br />fractured, medium hard' sandstone, which exhibited baking from the burning of the coal <br />seam. <br /> <br />". <br /> <br />Graded Filter Installation' <br />'" ." <br /> <br />", <br /> <br />--.... <br /> <br />A clean aggregate was used to fill major voids and fractures in the sinkhole <br />fou~dations. A minimum of 6 inches of C33 sand was used to cover the aggregate and <br />provid'e'asi.tpportingJayer for a Mirafi 140N geotextile. The gravel and sand materials <br />" . <br />were accepted. for-use based on visual classification in the field and gradation test <br />results supplied 'by the contractor and supplier. <br /> <br />Backfill Placement <br /> <br />23067/LF.8 10-lO-92 (l:l8plll)/RPTII <br />