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• -16- • <br />I SIT F. GRADING <br />Posed on ttie general soil conditions encountered, slopes <br />graded to 1.75 horizontal to 1 vertical and flatter which are <br />properly compacted anri drained should be relatively stable <br />against massive failure. Steeper slopes such as that proposed <br />near Portal No. 1 will have a higher potential for instability. <br />Seepage and wet surface conditions will be adverse to slope <br />stability and could cause slopr: failure. If wet conditions <br />develop in 1 to 1 graded slopes near Portal No. 1, significant <br />slope movement could occur. lJe assume that some slope movement <br />can be tolerated. <br />Fill section areas should be properly prepared before embank- <br />ments construction. Pefore fill placement, the subgrade should <br />be prepared by removing topsoil and vegetation, scarifying to a <br />depth of about 8 i:~ches, adjusting the moisture ccntent to near <br />optimum and compacting to at least 95p of standard Proctor <br />density (ASTM 6698). Compaction of fill embankments to at least <br />95p standard Proctor density within 2 percentage points of <br />optimum moisture as specified appears adecuate. To reduce <br />problems associated with settlem?nt of deep fill sections, com- <br />paction may be increased to at least 100 of standard Proctor <br />density. The fill should be spread in thin horizontal layers and <br />compacted to the job specifications. The fill should be benched <br />into hillsides steeper than 20°. Non-structural (miscellaneous <br />landscaped areas) backfi]1 may be compacted to at least 90% of <br />standard Proctor density. <br />Chen & Associates <br />