5910 LARIMER RD 2018-01-02 MF Import

Van Derbeken and Keck Properties Geotechnical Services Report Lorimer Road, Everett, Washington At the time of our site work, on December 14, 2006, the landslide extended from below the toe of the lower rockery to an area 40 to 60 feet beyond the upper rockery. It also extended from just inside the south property line of the Van Derbeken property to the approximate center of the Keck property to the north. The ground surface between the upper and lower rockeries was bulging upward 4 to 6 inches and extended about 8 feet beyond the base of the upper rockery. The ground surface at the toe of the lower rockery was bulging outward and soft silt was oozing from beneath the toe of the rockery. Multiple landslide scarps were observed upslope of the upper rockery. The scarps appear to represent a series of en echelon slides. En echelon slides occur as soils move downslope and remove support for the upper soils. These upper soils then fail and the process repeats. Field Exploration An initial site reconnaissance was performed on December 1, 2006- At that time several landslide scarps were observed on the slope behind the houses. The largest scarp was only about 1 foot high. Several cracks were observed in die ground that ranged from I to 2 inches up to about 6 inches wide. It was decided at that time that subsurface exploration should be performed with a limited access drill rig to determine the depth and extent of the slide and the underlying soil and ground water conditions. On December 14, 2006, following a series of storm events, Mr. Van Derbeken notified our office that the landslide was moving and getting much worse and requested immediate help. According to Mr. Ron Van Derbeken, the landslide was moving downslope at a rate of about 4 to 6 inches a day when it was raining and slower when the rains would stop. This movement was measured from a point on the Van Derbeken residence to a spot on the lower rockery. It was not possible to obtain the services of a limited access drill rig on such short notice, so a small, rubber tracked excavator was secured and a series of exploration pits were excavated on the site in the late afternoon and evening of December 14, 2006. During the field explorations a large storm event struck the area with strong winds, heavy rain, thunder, lightning and very difficult lighting conditions in the late afternoon. These conditions made it difficult to evaluate :ire soil conditions and to obtain information in all areas of the landslide. Therefore, one pit was excavated at the toe of the lower rockery, two pits were excavated on the level area between the two rockeries and one pit was excavated on the slope about 30 feet above the upper rockery. Logs of the exploration pits are attached. CONCLUSIONS AND RECOMMENDATIONS Based on the field data obtained it was determined that the landslide was relatively shallow, on the order of 6 feet thick in the yard area and about 8 feet thick on the slope above the upper Cary A. Flowers, PLLC. 19572 126 Avmue NE Shoreline, Wmhinglon 98155-1106 206-417-7640 2