2702 59TH ST SW 2023-07-31 - Laserfiche WebLink

Emergency Foundation Under.g Memorandum • NGA File No. 13333B22 Miller Residence Landslide January 18,2023 Everett,Washington Page 2 approximately 1/8-inch of downslope soil movement within the upper 5-to 6-feet of soil. We visited the site again on January 11, 2023. We noted additional soil movement along the planter strip adjoining the southern face of the southeastern portion of the residence.The soils in this area were separating from the foundation stem wall by approximately 1- to 2-inches. At this time, we also exposed the house foundation in one location along the southeast corner of the house and observed that the footing was undermined by approximately 2-inches. CONCLUSIONS AND RECOMMENDATIONS We have been monitoring slope stability conditions at the site on a monthly basis since November 2022. Based on our recent observations, it is our opinion that the slide mass is mobilizing at a significant rate and that the house foundations along the southeastern house extension are at serious risk of being adversely impacted by slope movement.This portion of the residence should be temporarily underpinned on an emergency basis to mitigate adverse impacts to the residence as a result of further ground movement,while permanent landslide stabilization plans are completed. For the underpinning,we recommend 2-inch diameter steel piles driven along the southern perimeter of the southeastern portion of the house and structurally attached to the residence foundation. Each pin pile should be driven to refusal utilizing a 140-pound pneumatic post driver. Refusal criteria is defined as 1-inch or less of vertical movement within 60 seconds of continuous driving.The piles should be attached and vertically restrained to the house foundations utilizing structural brackets. For piles successfully driven to refusal we recommend a design axial compression capacity of 3 tons per pile.The underpinning repairs should be performed by an experienced contractor licensed in the state of Washington. Additionally, we recommend the pile installation and refusal criteria is performed under continuous supervision of NGA. In support of the emergency underpinning,we have discussed plans with the project structural engineer who has provided a schematic pile layout of the areas to be stabilized, as shown on Figure 1. Given the site conditions, it is our opinion the proposed work should be considered for emergency permitting and carried out as soon as possible. CLOSURE We trust this memorandum should satisfy your needs at this time. Please contact us if you have any questions or require additional services. o-o-o r) NELSON GEOTECHNICAL ASSOCIATES, INC.