4937 SEA BREEZE WAY 2017-01-13 - Laserfiche WebLink

• Geotechnical Engineering Evaluation Pepe Retaining Wall Everett, Washington � NGA File No. 916915 April 27, 2015 Page 5 transitional beds soils. Underlying the undocumented fill soils in Test Pits 2, 3, and 4, we encountered a concrete pile, rebar cables, and a concrete deadman anchor, respectively, all associated with the failing retaii�ing walL Test Pit 1 was completed within the transitional beds soils at a depth of approxitnately 8.0 leet below the existing ground surfiace. Test Pits 2, 3, and 4 were completed on the retaining wall componcnts at depths of 2.0, 5.0, and 3.0 feet bclow the existing ground surface, respectively. Hand Hole 1 was located on the slope below the: wall. We encountered approximately one foot of loose, dark brown, silty tine to medium sand with gravel which we interpreted as topsoil. Underlying the topsoil, we enco�intered approximately 0.2 feet of inediwn stiff brown-gray, silt with fine sand and trace gravel which we interpreted as transitional beds soils. Hand Hole 1 was completed within the transitional beds soils at a depth of approxi��ately 1.2 feei below the existing ground surface. Hydrologic Conditions Gro�mdwater seepage was not encountered in o�ir explorations on April l0, 2015. There is a significant potential for a perched gro�mdwater condition to develop on this site. Perched water occurs when surface water intiltrates through less dense, more permeable soils and acc��mulates on top of relatively low permeability materials and �mdocumented filL The more penneable soils consist of the topsoil/weathered soils. The low penneability soil consists of tl�e siltier transitional beds soils. Perched water does not represent a regional gro�indwater °table" within thc upper soil horizons. Perched water tends to vary spatially and is dependent upon t�he ainount of rainfalL We would �;xpcct the amount of perched groundwater to decrease during drier times oi'the year and increase during wetter periods. SENSITIVE AREA EVALUATION Seismic Hazard We reviewed the 2012 International Building Code (IBC). Since mostly dense soils are interpreted to underlie the site at depth, the site conditions best fit the IBC description for Soil Class D for native soils. Hazards associated with seisinic activity include liquefaction potential and amplificatioi� of ground inotion. Liquefaction is caused by a rise in pore pressures in a loose, tine sand deposit beneath the ��ro�mdwater table. lt is our opinion that the dense or better native deposits interpreted to underlie the site have a low potential for liquefaction or amplification of ground motion. NELSON GEOTECHNICAL ASSOCIATES, INC.