DESCRIPTION: Cowlitz County reconstructed a mile-long section of Hazel Dell Road to accommodate two, 12‑foot wide travel lanes with wider shoulders and improved horizontal and vertical curves.
SERVICE: Our work included test pits and geotechnical borings, laboratory testing, engineering analyses, and recommendations for site preparation, embankment construction, slope excavation, and retaining walls. The project challenges included fitting the widened road section between the steep slopes and the riparian zone of Leckler Creek. Retaining walls were recommended to avoid large excavations on the steep natural slopes. Based on preliminary analysis, constructability and costs, soil nail walls were selected to support the slopes. The soil nail wall was designed to fit the naturally variable terrain and variable geologic conditions along the alignment.
Foundation Engineering also provided construction‑phase geotechnical services. Construction of the upper row of soils nails required field adjustment due to slope irregularity. During construction of soil nail walls, Foundation Engineering tracked and documented geological conditions to document that the encountered conditions are consistent with the design assumptions. We also documented the soil nail verification and proof tests.
At the beginning of construction, several proof tests failed to reach the design capacity. Documentation of the installation provided the evidence needed to demonstrate the failed tests were due to the contractors drilling method and not the geologic conditions. Therefore, changed conditions were avoided and the contractor was able to modify their drilling and installation methods so that no more test nails failed.