1209 MADRONA AVE 2016-10-05 - Laserfiche WebLink

Retaining Wall Installation Final Letter NGA File No.87 1013 13 Packer Retaining Wall February 17,2015 Everett,Washington Page 3 After the installation of the pin piles and grouted anchors, we observed that a foundation drain consisting of a 4-inch perforated PVC pipe was placed behind the base of the retaining wall and covered with drain rock and filter fabric. The wall drain was daylighted through the retaining wall within the central portion of the retaining wall. We observed that the foundation drain was tightlined via a 4-inch corrugated drain pipe to the toe of the steep slope. We recommend that all drainage pipes be inspected periodically to verify they are working properly and any repairs, if needed,be performed promptly. After the wall was constructed, 7.75-inch square metal plates were placed at each anchor location and each anchor was locked off to the specified lock-off load. We returned to the site on December 23, 2015 and February 6, 2015 to observe the finished wall and erosion control measures. We observed that the gap behind the wall were completely backfilled with 2- to 4-inch crushed rock from the top of the retaining wall up to the base of the block retaining wall above the new retaining wall. We also observed that the soils and slope below and to the west of the wall had been covered with heavy-duty erosion control matting, and plants had been placed. The matting had been secured to the ground surface using 24-inch metal stakes. In our opinion, these measures appear to be adequate at this time. We understand that grass will be established within these areas in the spring time. We recommend that this area be continually monitored through the wetter winter months for any indications of instability and corrective actions promptly implemented should any signs of distress be observed. Closure Based on our understanding of the site conditions and our part-time observations during the implementation of the recommended repairs, it is our opinion that the retaining wall and stabilization measures have been installed successfully and in accordance to our recommendations. It is also our opinion that the implemented erosion control efforts are reasonable with site constraints and budget. Though the erosion control measures are expected to perform well, they are not considered permanent, and we therefore recommend that you monitor the slope and stabilization systems from time to time, especially during and after significant rain events. If any signs of distress are observed, we should be contacted. At that time,we would provide recommendations for further repairs to the slope, as warranted. We should stress that the steep slope below the wall will always be prone to sloughing and shallow sliding events due to the steepness of the slope, the nature of the near surface soils, and the wet weather NELSON GEOTECHNICAL ASSOCIATES, INC.oq7:�