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PN: 50663GE <br />November 20, 2006 <br />The requested scope of service of this geotechnical engineering study does not include <br />evaluation of materials for construction of MSE structures. Please contact us if this information <br />is desired. <br />7.0 SUBSURFACE DRAIN SYSTEM <br />A subsurface drain system and/or weep holes should be included in the retaining structure <br />design and may need to be developed along the roadway in the event that subsurface water is <br />encountered at undesirable locations. Exterior retaining structures may be constructed with weep <br />holes to allow subsurface water migration through the retaining structures. A drain system <br />constructed with a free draining aggregate material and a perforated pipe should be constructed <br />adjacent to retaining structures or adjacent to foundation walls on sites with expansive soil <br />conditions. We suggest that the system consist of afabric-wrapped aggregate, or a sand material <br />(some sands may not need fabric, we aze available to discuss this with you) which surrounds a <br />rigid perforated pipe. We typically do not recommend use of flexible corrugated perforated pipe <br />since it is not readily possible to establish a uniform gradient of the flexible pipe throughout the <br />drain system alignment. Corrugated drain the is perforated throughout the entire circumference <br />of the pipe and therefore water can escape from the perforations at undesirable locations after <br />being collected. The nature of the perforations of the corrugated material further decreases its <br />effectiveness as a subsurface drain conduit. <br />The drain system pipe should be graded to surface outlets or a sump vault. Typically a <br />minimum gradient of about two (2) percent is preferred for subsurface drain systems, but site <br />geometry and topography may influence the actual installed pipe gradient. Water must not be <br />allowed to pool along any portion of the subsurface drain system. An improperly constructed <br />subsurface drain system may actually promote water access to undesirable locations. The drain <br />system pipe should be surrounded by about two (2) to four (5) cubic feet per lineal foot of free <br />draining aggregate or sand. If a sump vault and pump aze incorporated into the subsurface drain <br />system, caze should be take so that the water pumped from the vault does not recirculate through <br />pervious soils and obtain access to the basement or crawl space azeas. A generalized subsurface <br />drain system concept is shown below. The concept below will need to be adapted for the <br />retaining structure or reinforced fill as appropriate for this project as the plans grogress. <br />l~ TRAUTNER ~ <br />A DIVISION OF TRIGONHi~ <br />