9512 EVERGREEN WAY 2022-08-29 - Laserfiche WebLink

May 4, 2017 HWA Project No. 2017-036-21 protection considerations, all footings should be buried at least 18 inches, measured from finished grade to footing base level. If footings are supported by structural fill, this fill should extend horizontally beyond the outer edges of the footings a minimum distance equal to the fill thickness below the footing, measured at the level of the excavation base. If adjacent individual footings are located at different elevations, it is recommended that the horizontal distance between them be at least 1.5 times the elevation difference between their bases. Where adjoining continuous footings are at different elevations, the upper footing should be stepped down to the lower footing. It is recommended that the footing steps be proportioned such that the horizontal run is not less than twice the vertical step height, and no less than 4 feet in length. Because of the potential long-term occurrence of shallow perched water over till soils, we recommend that perimeter foundation drains be provided around all exterior footings at a level slightly below the base of the footings. Footing and roof drains should not be inter -connected to prevent the potential clogging and flooding of the foundation drains. Floor slabs may be supported at grade on structural fill compacted to the requirements indicated above. If grade -supported slabs are employed, they must be underlain by a capillary break layer comprised of clean, uniform, open -graded, washed rock or pea gravel, to prevent future slab dampness which could be detrimental to floor coverings. This capillary break layer should be at least 6 inches thick and should be in contact with, or be provided with suitable drainage outlets to, the perimeter foundation drain system. A plastic vapor barrier should be placed on top of the capillary break layer to isolate the slab concrete from this layer, and should consist of plastic sheathing such as Visqueen. We anticipate that foundations cast on glacial till will settle very little, and what settlement there is should occur during and shortly after construction. The largest potential for both overall settlement and differential settlement is due to inadequate preparation and cleaning of the foundation subgrade, or poor compaction of structural fill, supporting the foundations. 4.3 SEISMIC CONSIDERATIONS Table 1 below presents recommended seismic coefficients for use with the General Procedure described in Section 1613 of the 2015 International Building Code (IBC) (ICC, 2014). The seismic ground motion procedure contained in 2015 IBC is based upon a Maximum Considered Earthquake (MCE) with a 2 percent probability of exceedance in 50 years (i.e., return period of approximately 2,475 years). The relevant probabilistic spectral response parameters were developed using the United States Geological Survey's website. The IBC accounts for the effects of site -specific subsurface ground conditions on the response of structures in terms of site classes. Site classes are defined by the average density and stiffness of Final Geologic Assessment 7 HWA GeoSciences Inc.