<br />25 <br /> <br />certerra.com 4660 Main Street, Suite 100, Springfield, Oregon 97478 T: 541.393.6340 <br />clays is not acceptable, the clay should be removed and pavements supported on properly compacted structural fill <br />overlying the hard undisturbed Eugene Formation. <br /> <br />We understand from the project Civil Engineer, KPFF, that the proposed public roadway section will comply with the <br />City of Eugene’s current PIDS (i.e. 6-inch-thick layer of asphaltic concrete or 7 inch thick layer of Portland Cement <br />concrete, overlying 12 inches of properly compacted structural fill base rock), however due to the presence of <br />potentially highly expansive clay on the site we recommend a minimum 18-inch-thick layer of properly compacted <br />base rock (as outlined in Section 3.3 above). We recommend the structural fill be underlain by a geotextile fabric <br />such as Mirafi 500X or equivalent. <br /> <br />After the site has been stripped and prepared in accordance with Section 3.2 of this report, the pavement subgrade <br />should be proofrolled with a fully loaded dual axle dump truck. Areas found to be soft or yielding under the weight <br />of a dump truck should be overexcavated as recommended by the Geotechnical Engineer’s representative and <br />replaced with additional base course. Using the AASHTO method of flexible pavement design, the following design <br />parameters have been assumed: <br /> <br />• An assumed California Bearing Ratio (CBR) value of 5 for the clay that underlies the proposed pavement <br />areas. <br />• A pavement life of 20 years. <br />• A terminal serviceability (Pt) of 2 (poor condition). <br />• A regional factor (R) of 3.0. <br />• An assumed 18,000-pound equivalent axle load (EAL) of: <br />- 100 per day for passenger vehicle parking, and 300 per day for vehicle drive lanes. <br />- 40 per day for delivery truck parking, and 80 per day for delivery truck drive lanes. <br />• An average weight of 4,000 pounds per car and 15,000 pounds per truck was used in our calculations. <br />• Additionally, the drive lanes must be designed to support an 80,000-pound fire truck. <br /> <br />Our assumed traffic loading is based on the site plans we were provided, referenced above, and our past experience <br />on similar projects. The project Civil Engineer should review our assumptions to confirm they are appropriate for the <br />anticipated traffic loading. See Tables 3 through 8 below for recommended pavement section thicknesses based on <br />the above assumptions. <br /> <br />Table 3: Asphaltic Concrete - Recommended Minimum Thicknesses (inches) <br />Private roads overlying firm CLAY subgrade. <br />Pavement Materials Parking <br />Areas <br />Drive Lane <br />Areas <br />Asphaltic Concrete 4 4 <br />Crushed Aggregate Base Course <br />(underlain by Mirafi 500X geotextile fabric or equivalent) 18 18 <br />