9512 EVERGREEN WAY 2022-08-29 - Laserfiche WebLink

May 4, 2017 HWA Project No. 2017-036-21 (WSDOT Standard Specifications Section 9-03.14(1)) in accordance the minimum standards for parking areas outlined in the City of Everett Standard Section 3-5.2. We recommend that the pavement sections are constructed on properly prepared subgrade soils or compacted structural fill as described below. Subgrade stripping for parking should extend down through all loose organic soils and other deleterious materials onto competent native or medium dense fill subgrade comprised of granular silty sandy soils. After stripping and excavating to desired grade, and prior to placing any fill, exposed subgrade soils should be evaluated by HWA. Typically, this will involve evaluation of the subgrade response to several passes with a fully loaded dump truck. All loose/soft soil areas that exhibit yielding or are visibly highly organic should be sub -excavated and replaced with structural fill materials. Thereafter, any disturbed or loosened areas of the exposed subgrade should be scarified to a depth of 8 inches and re -compacted to 95% of maximum dry density, as determined using test method ASTM D 1557, Modified Proctor. Material used to raise site grades, or placed directly under pavement structure is classified as structural fill. Imported structural fill should consist of the materials described in Section 4.6.2. 4.6 CONSTRUCTION CONSIDERATIONS 4.6.1 Subgrade Preparation In the proposed footing areas, subgrade preparation should begin with the removal of all vegetation, topsoil, and any deleterious materials. Following the removal of all unsuitable materials, the bearing soils (glacial till) should be excavated to design grade with a smooth bucket to limit the level of subgrade disturbance. The subgrade should be inspected by a representative of the geotechnical engineer and any soft, yielding, areas should be over -excavated to the depth determined by the geotechnical engineer. If structural fill is required, it should be placed in accordance with the compaction criteria presented in Section 4.6.2. Because of the moisture sensitive nature of glacial till, care should be taken to prevent any water from mixing with the subgrade (i.e. rain or water used in construction). 4.6.2 Structural Fill Materials and Compaction Material used as structural fill should consist of Gravel Borrow, as described in Section 9- 03.14(1) of the 2016 WSDOT Standard Specifications for Road, Bridge and Municipal Construction. We do not recommend the use of onsite fill and weathered till soils as structural fill. The ground surface within the construction area should be graded to promote rapid runoff of precipitation, and to prevent surface water from ponding; Final Geologic Assessment 9 HWA GeoSciences Inc.