Materials (under evaluation) - Laserfiche WebLink

It should be assumed ±1 to 2 feet of structural fill (i.e., compacted gravel or rock) will be needed under large footings. If raised floors are planned, we recommend the use of continuously reinforced strip footings in the interior instead of isolated pier pads to reduce the risk of differential settlement. Granular building pads constructed of crushed gravel or crushed rock will be needed under all concrete slabs. The building pads should be elevated above existing grades to provide positive drainage away from the structures. Seasonal Issues The foundation soils are primarily fine-grained and highly moisture-sensitive. That is, if the soil is wet of optimum, it will tend to pump or severely rut when exposed to construction equipment. Care will be needed during site grading to prevent disturbance of the subgrade. Compaction of the near-surface will only be practical during the dry summer months when aeration and moisture-conditioning will be possible. The risk of subgrade disturbance is reduced if construction occurs during sustained dry and warm weather (typically July through September). Site preparation during the early spring, fall or winter when the subgrade is wet is expected to substantially increase earthwork costs and, therefore, is not recommended. Site Stripping It should be assumed that general site grading will require stripping organics and hauling the material offsite or placing it outside the footprint of structures, pavements or other facilities. Stripping depths on the order of ±3 to 6 inches will be required to remove the bulk of the organics, with deeper excavations required in isolated areas to remove larger tree roots. Ground Water No ground water was encountered in the test pits. We expect the ground water levels will fluctuate seasonally and will be significantly higher during the wet winter and spring months. Perched ground water may also be encountered at shallow depths within the low-permeable, fine-grained foundations soils. In general, ground water during dry weather should not be a significant construction issue, but may impact deep utility trenches. Perimeter foundation drains are recommended for all structures, which is typical for similar developments in the area. Pavements The pavement subgrade will consist of low to medium plasticity silt to clayey silt. This material has a relatively low resilient modulus (M value). Therefore, a subgrade R geotextile and a relatively thick base course section will likely be required for new pavements, particularly if the roads will need to support materials delivery and construction equipment during the winter. Typical Asphaltic Concrete (AC) thicknesses for residential developments are 3 to 4 inches. Base course thicknesses of ±10 to 12 inches are typically suitable if the section is not required to support heavy vehicles. A base rock thickness of 24 inches should be anticipated if the section will support equipment during the winter months. River Road Multi-Family Development April 30, 2018 Preliminary Geotechnical Investigation 7. Project 2171066 Eugene, Oregon Evergreen Housing Development Group, LLC