2106 120TH PL SE 2016-01-01 MF Import

Construction Criteria T�enches shall be excavated to the design dimensions. Excavated materials shall be placed away from the trench sides to enhance trench wall stability. The filter fabric roll must be cut to the proper width prior to installation. The cut v�idth must include suflicient material to contorm to the trench perimeter irregularities and ior a 12-inch minimum top overlap. The fabric roll must be placed over the trench and unrolled a sufficient length to allow placement of the fabric down into the trench. Stones or other anchoring objects should be placed on the fabric at the edge ot the trench to keep lhe lined trench open. When overlaps aro required between rolls, the upstream roll should overlap a minimum of two feet over the downstream roll in order to provide a shingled efiect. The overlap ir�sures tabric continuity and allo•Ns the fabric to conlorm to the excavated surface during aggregate placement and compaction. The washed rock should be placed in lifts and compacted using plate compactors. A maximum loose li(t thickness of 12 inches is recommended. The compar,tion process ensures fabric conformity to the excavation sides, thereby reducing potential soil piping, fabric clogging, and settlement problems. Following The washed rock placement, ihe filter tauric shali be folded over the washed rock to form a 12-inch minimum longitudinal overlap. � he desired iill soil (for roof runoff in(iltration systems) or stone aggregate (roof runofi dispersion systems) shall be placed over ihe lap at sufficient intervals to maintain the lap during subsequent backfilling. Natural or fiil soils shall be prevented irom intermixing with the washed rock. All contaminated washed rock shall be rerr,oved and replaced with uncontaminated washed rock. Voids between the fabric and excavation sides shall be avoided. Removal of boulders or other cbstacles from the trench walls is one source of voids. Natural soils should be placed in these voids at the most convenient time during construction to ensure fabric conformity to the excavation sides. Soil piping, fabric clogging and possible surface subsidence will be avoided by eliminating voids. Vertically excavated walls may be difiicult to maintain in areas where tho soil mcisture is high or where soft or cohesion less soils predominate. These conditions require laying back of the side slopes to maintain stability and trapezoidal rather ihan rectangular cross-sections may result. This is �+cceptable, but significant changes in the size and/or shape of the trench must be taken into consideration in size calculations. Heavy equipment and traffic shall be restricted from traveling over infiltration areas in order to minimize compaction of the soil. Root runoff systems shall be flagged or marked to keep equipment away from ihe area. In addition, excavated foundation soils should not be placed in the area designated tor the roof runoff systems.