4003 NASSAU PL 2016-01-01 MF Import

t ' ' ' �. �. Geqtechnical Engineering Report Kvcrnmo Single-Family Residence 4003 Nessau Place, Everctt September 17, 2002 NGA File No. 356102 Page 9 ground water flowing on tF�e surface of the fill and native materiel. 'Ii�e drain should wnsist of a 4-inch- diameter, rigid, slotted or perforated, PVC pipe surrounded by free-draining material wrapped in a filter fabric. We rccommend that the free-draining material consist of clean (less than 3 percent fines), granular material such as pea gravel or washed rock. The filter fabric could be omitted if pea gravel is used for the backfill. The drein should discharge into a tightline leading to an appropriate collection and discharge point with convenient cleanouis to prolc .�g the uuful life of the drain. The cut-off drain should extend at least 2 feet into tMe underlying native silts, and a minimum of 6 feet of free draining material be used in the backfill. We estimate that an excavation approximately up to 8 feet deep will be necessary to proPerly install the drain. The drain should be located at least 10 feet uphill of the residence. A cut-off drain dehil is shown in Figure 9. Site Preparstion aod Gndiag � It is our understanding that you desire to leave the majority of the existing fill on site and support Iresidence slabs-on-grade and pavement on the existing fill, accepting some risk of future settlement and long tertn maintenance. At the very least, the material exposed in the slab and pavement subgrades ( should be compacted to a non-yielding condition. Areas observed to pump or weave during compaction 1 or areas of high organics content should be overexcavated and repaired prior to placement of structural fill Ior hard surfaces. The subgrade should also benched by creating 4- to 8-foot wide level benches prior to placing new swctural fill. We should be retained to observe subgrade preparation and structural fill placement. The on-site soils are considered highly moisture sensitive. Earthwork should be performed during the drier summer months and suspended during periods of rainfall. Earthwork may be attempted during the wetter times of the year, but will likely be more difficult and expensive. Additionel expenses may include additional overexcavation of wet soils and the import of all-weather granular material for fill. Structural Fill General: Fill placed beneath slabs, pavements, or other settlement-sensitive features should be placed as structural fill. Structural fill, by definition, is placed in accordance with prescribed methods and standards, and is monitored by an experienced geotechnical professional or soils technician. Field NELSON GEOTECHNICAL ASSOC/ATES, INC. (D�