1020 NORTH PARK DR 2022-02-23 - Laserfiche WebLink

Geotechnical Engineering Evaluation NGA File No. 961916 Mason Residence Addition and Deck August 24,2016 Everett,Washington Page 10 2� development on the slope and allow for normal slope recession and shallow failures during a reasonable life span of the structure. Any proposed development within the setback area, including decks or patios, should be the subject of a specific geotechnical evaluation. Under no circumstances should water be allowed to concentrate on the slopes during or after construction. Site Preparation and Grading After erosion control measures are implemented, site preparation should consist removing the existing deck and slabs-on-grade and stripping any loose soils and undocumented fill to the proposed foundation subgrade elevations. The stripped materials should be removed from the site. If the ground surface, after site stripping, should appear to be loose, it should be compacted to a non- yielding condition. Areas observed to pump or weave during compaction should be over-excavated and replaced with properly compacted structural fill or rock spalls. If loose soils are encountered in the slab areas, the loose soils should be removed and replaced with rock spalls or granular structural fill. If significant surface water flow is encountered during construction, this flow should be diverted around areas to be developed,and the exposed subgrades should be maintained in a semi-dry condition. This site is underlain by moisture-sensitive soils. Due to these conditions, special site stripping and grading techniques might be necessary, especially if grading is attempted in wet weather. These could include using large excavators equipped with wide tracks and a smooth bucket to complete site grading and promptly covering exposed subgrades with a layer of crushed rock for protection. If wet conditions are encountered or construction is attempted in wet weather,the subgrade should not be compacted as this could cause further subgrade disturbance. In wet conditions it may be necessary to cover the exposed subgrade with a layer of crushed rock as soon as it is exposed to protect the moisture sensitive soils from disturbance by machine or foot traffic during construction. The prepared subgrade should be protected from construction traffic and surface water should be diverted around prepared subgrade. Shallow groundwater, if encountered, should be intercepted with cut-off drains and routed around the planned grading area, or the groundwater should be controlled with sump-pumps or dewatering systems. Failure to follow these recommendations could cause erosion and failures on the slopes, as well as result in inadequate subgrades. Temporary Slopes Temporary cut slope stability is a function of many factors, including the type and consistency of soils, depth of the cut, surcharge loads adjacent to the excavation, length of time a cut remains open, and the presence of surface water or groundwater. It is exceedingly difficult under these variable conditions to NELSON GEOTECHNICAL ASSOCIATES, INC.