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• The gradation for the rock material will be as follows: <br />Sieve Size Percent Passing <br />12 inch 100 <br />6 inch 40-80 <br />3 inch 10-30 <br />1-1/2 inch 0-10 <br />Prior to placement of the rock in the trench, a filter fabric <br />such as Mirafi 140N will be laid in the trench to envelop the <br />rock, as shown on Drawing No. MG-R-C-003. Initially the <br />lateral underdrains will be constructed to the backslope <br />limit at Bench 1 (elevation 6710 feet). The lateral rock <br />underdrains will be extended if field observations indicate <br />sufficient infiltration is occurring through the completed <br />pile or the colluvium requires further dewatering. <br />• <br />The temporary collection channel will be converted into a <br />longitudinal underdrain as the pile advances above Rench 1. <br />This longitudinal underdrain will intercept any seepage that <br />may occur from above, and direct the flow towards the lateral <br />underdrains. The rock material and gradation will be the <br />same as the one used for lateral underdrains described pre- <br />viously. <br />Additional longitudinal underdrains up gradient may be re- <br />quired if field conditions indicate sufficient infiltration <br />is occurring in the completed pile or the colluvium requires <br />further dewatering. <br />• <br />10 <br />