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Ralston Quarry Slope Stability <br /> 2) The free-draining gravel should have a maximum particle size of 2 inches, 50 <br /> percent or more retained on the No. 4 Sieve, and 5 percent or less passing the <br /> No. 200 Sieve. <br /> 3) Each collection pipe should be surrounded on the sides and top (only) with 12 or <br /> more inches of free-draining gravel. <br /> The gravel surrounding the collection pipe(s) should be wrapped with filter fabric <br /> (Mirafi 140NO or the equivalent) to reduce the migration of fines into the drain <br /> system. <br /> 4) Each back drain array should be designed to discharge at least 25 gallons per <br /> minute of collected water. <br /> 5) The flow lines of the collection pipes should be placed at a gradient of at least 1 <br /> percent. <br /> The flow lines of the discharge pipes should be placed at gradients as <br /> determined by the civil engineer but presumably generally will follow the descent <br /> of the overall slope. <br /> 6) The underdrain discharge pipes should be routed to outlet(s) for gravity <br /> discharge at appropriate locations and/or drainage structures. <br /> 7) Back drain `clean-outs' should be provided at appropriate intervals and locations <br /> to facilitate maintenance. <br /> 8) Regular maintenance of the back drain systems should be performed to insure <br /> that they continue to work properly. <br /> CLOSURE <br /> Materials Testing Asphalt Paving Company or the contractor should consider retaining <br /> a geotechnical engineer to perform materials testing during construction. The <br /> performance of such testing or lack thereof, however, in no way alleviates the burden of <br /> the contractor or subcontractor from constructing in a manner that conforms to <br /> applicable project documents and industry standards. The contractor or pertinent <br /> Job No. 18-3046 GROUND Engineering Consultants, Inc. Page 29 <br />