1331 MADRONA AVE 2016-01-01 MF Import

Construction Criteria Trenches 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 ir.stailation. The cut width must inciude sufficient material to conform to the trench perimeter irregularities and for 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 of ilie trench to keep the lined trench open. When overlaps are required between rolls, the upstream roll should overlap a minimum of two feet over the downstream roll in order to provide a shingled effect. The cverlap insures fabric continuity and allows the fabric to conform tc the excavated surface during aggregate placement and compaction. The washed rock should be placed in lifts and compacted using plate compactors. A maximum loose lift thickness of 12 inches is recom�nended. The compaction process ensures fabric conformity to the excavation sides, thereby reducing potential soil piping, fabric clogging, and settlement problems. Following l'he washed rock piacement, the filter fabric shall be folded over the washed rock to form a 12-inch minimum longitudinaf overiap. The desired fill soii (for roof runoff infiltration systems) or stone aggregate (roof runoff dispersion systems) shail be placed over the lap at sufficient intervals to maintain the lap during subsequent backfilling. Natural or fili soils shall be prevented from intermixing with tfie washed rock. AII contaminated washed rock shall be removed and replaced with uncontaminated washed rock. Voids between the fabric and excavation sides shai! be avoided. Removal of boulders or other obstacles 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 wili be avoided by eliminating voids. Vertically exca�•ated walis may be difficult to maintain in areas where the soil moisture 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 than rectangular cross-sections may result. This is acceptable, but significant changes in the size a�d/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. Roof runoff systems shall be flagged or marked to keep equipment away from the area. In addition, excavated foundation so;ls should not be piaced in the area designated for the roof runoff systems. ��