Preliminary Geotechnical Engineering Report <br />Project No. 18-4986, 177 Day Island Road, Eugene, Oregon <br />NO " <br />During placement of pavement section materials, density testing should be performed to verify <br />compliance with project specifications. Generally, one subgrade, one base course, and one <br />asphalt compaction test is performed for every 100 to 200 linear feet of paving. <br />Wet Weather Construction Pavement Section <br />This section presents our recommendations for wet weather pavement section and construction for <br />new pavement sections at the project. These wet weather pavement section recommendations <br />are intended for use in situations where it is not feasible to compact the subgrade soils, due to wet <br />subgrade soil conditions, and/or construction during wet weather. <br />Based on our site review, we recommend a wet weather section with a minimum subgrade <br />deepening of 6 inches to accommodate a working subbase of additional 1Y2"-0 crushed rock. <br />Geotextile fabric, Mirafi 500x or equivalent, should be placed on subgrade soils prior to placement <br />of base rock. <br />In some instances, it may be preferable to use Special Treated Base (STB) in combination with <br />over-excavation and increasing the thickness of the rock section. GeoPacific should be consulted <br />for additional recommendations regarding use of STB in wet weather pavement sections if it is <br />desired to pursue this alternative. Cement treatment of the subgrade may also be considered <br />instead of over-excavation. For planning purposes, we anticipate that treatment of the onsite soils <br />would involve mixing cement powder to approximately 6 percent cement content and a mixing <br />depth on the order of 12 to 18 inches. <br />With implementation of the above recommendations, it is our opinion that the resulting pavement <br />section will provide equivalent or greater structural strength than the dry weather pavement section <br />currently planned. However, it should be noted that construction in wet weather is risky and the <br />performance of pavement subgrades depend on a number of factors including the weather <br />conditions, the contractor's methods, and the amount of traffic the road is subjected to. There is a <br />potential that soft spots may develop even with implementation of the wet weather provisions <br />recommended in this letter. If soft spots in the subgrade are identified during roadway excavation, <br />or develop prior to paving, the soft spots should be over-excavated and backfilled with additional <br />crushed rock. <br />During subgrade excavation, care should be taken to avoid disturbing the subgrade soils. <br />Removals should be performed using an excavator with a smooth-bladed bucket. Truck traffic <br />should be limited until an adequate working surface has been established. We suggest that the <br />crushed rock be spread using bulldozer equipment rather than dump trucks, to reduce the amount <br />of traffic and potential disturbance of subgrade soils. <br />Care should be taken to avoid over-compaction of the base course materials, which could create <br />pumping, unstable subgrade soil conditions. Heavy and/or vibratory compaction efforts should be <br />applied with caution. Following placement and compaction of the crushed rock to project <br />specifications (95 percent of Modified Proctor), a finish proof-roll should be performed before <br />paving. <br />18-4986, 177 Day Island Road GRPT 14 GEOPACIFIC ENGINEERING, INC. <br />Version 1, August 27, 2018 <br />