1215 W MUKILTEO BLVD 2017-07-28 - Laserfiche WebLink

April 29,2015 HWA Project No.2014-162-21 Geotextile A geotextile separator should be placed between the drainage filter material and the native exposed soils. The geotextile should meet the requirements of Table 3 of WSDOT Standard Specifications Section 9-33.2(1) (WSDOT, 2014). Subsurface Drain Pipe Wall drainage should be provided by installing a 4 inch (minimum) diameter, perforated drain pipe behind the base of each proposed wall. This drain pipe should be installed just behind the base of the bottom rock of each wall. The perforated drain pipes should be connected to a 4 inch diameter tight line that is routed to a suitable outlet or stormwater collection structure. Perforated drain pipes should be encapsulated in at least 1 foot of material meeting the gradation requirements for Gravel Backfill for Drains as specified in Section 9-03.12(4) of the WSDOT Standard Specifications (WDOT, 2014). Subgrade Preparation After clearing, grubbing and general site preparation has taken place; a keyway to accommodate the base course of rock facing should be excavated to expose suitable bearing soils but not less than the depth indicated in Table 2. The keyway should extend the entire length of the facing and decline towards the embankment at the approximate final slope (batter) of the wall. The keyway excavation should extend to relatively undisturbed native soils. If loose compressible soils are encountered in the rockery foundation area, it may be necessary to remove and replace such soils to depths determined by the geotechnical engineer in the field. Rock Facing Construction The first course of rocks should be placed on firm, unyielding soil at the depths prescribed in Table 2. There must be full contact between the rock and the soil, which may require shaping the ground surface or slamming or dropping the rocks into place so that the soil foundation conforms to the rock face bearing on it. As an alternative, it is satisfactory to use lean concrete in which to seat the first row of rocks or to use 3/4-inch minus crushed rock into which the foundation rocks are seated. The Contractor should use rock sizes specified in Table 2, using the largest rocks at the bottom and progressively smaller rocks toward the top. Each rock must bear solidly on two or more rocks below it and so there is no sign of instability such as "rocking" or "tipping" of individual rocks. The intermediate axis of each rock should be placed perpendicular to the slope. The rock surfaces between individual courses should be relatively flat, and should never slope downward toward the face of the wall. The rocks should be placed so that there are no continuous joint planes over three or more rocks in the vertical or horizontal direction. The rocks should fit so 2014-162 Letter Report 7 HWA GEOSCIENCES INC.