7105 JUNIPER DR 2025-03-27 - Laserfiche WebLink

April, 14, 2023 G-5844 7105 —Juniper Dr, Everett, WA Page 2 tier is approximately 65.0 feet long. The retaining wall has an average height of 3.0 feet, with a maximum height of approximately 4.25 feet, approximately 30.0 to 48.0 feet south of the wall's northern extent. The backfill immediately behind the retaining wall was observed to consist of an approximately 12.0 inches thick prism of drain rock, followed by native soil with an average grade of approximately 22.5 percent, rising approximately 2.0 to 3.0 feet over a distance of approximately 9.0 to 13.3 feet. The wall cross sections illustrated on Plate 2--W Wall Cross Sections & Elevation View are located where the maximum backslope grade was measured, and where the shortest distance between the retaining wall and existing residences was measured. We measured the dimensions of the segmental concrete blocks used to construct the retaining wall were 16 inches long, by 12 inches wide by 6 inches tall. These dimensions are consistent with the ManorStone concrete block units manufactured by Mutual Materials, and the MiraStone concrete block units manufactured by Cornerstone Wall Solutions. As such, the specifications for MiraStone concrete blocks were utilized for our retaining wall calculations presented in the attached Appendix A --Retaining Wall Calculations. Retaininy, Wall Subsurface Drainage and Backfill Based on our discussion with you and the contractor,New Life Rockeries, the retaining wall was installed with subsurface drainage and backfill that were in general conformance with the subsurface drainage recommendations presented in the wall manufacturer's design and construction documents. We observed an approximately 12 inches wide prism of free draining crushed rock backfill immediately behind the retaining wall that extended from the wall's base to near the top of the wall, and based on our discussions with the contractor, a slotted drain pipe was laid beneath and bedded in the free draining crushed rock to facilitate subsurface drainage. We observed that grades at the base of the retaining wall were sloped to direct surface water away from the retaining wall. WALL DESIGN PARAMETERS We used the methodology (Coulomb earth pressure analysis) described in the National Concrete Masonry Association's (NCMA) Design Manual for Segmental Retaining Wails, Third Edition (Bernardi, et. al, 2009)for the segmental concrete block retaining wall's design. It is our opinion that this methodology recognizes the nuances of segmental retaining wall design and provides the necessary criteria for proper engineering and design evaluation of segmental retaining wall GEO Group Northwest, Inc.