2701 ROCKEFELLER AVE NIMBUS Geotech Report 2023-12-29

Opportunity Zane Development LLC JN 19152 June 6, 2019 Page 15 Even where the exposed soils appear dry, water vapor will tend to naturally migrate upward through the soil to the new constructed space above it. This can affect moisture -sensitive flooring, cause Imperfections or damage to the slab, or simply allow excessive water vapor into the space above the slab. All Interior slabs -on -grade should be underlain by a Capillary break drainage layer consisting of a minimum 4-Inch thickness of dean gravel or crushed rock that has a fines content (percent passing the No. 200 sieve) of less than 3 percent and a sand content (percent passing the No. 4 sieve) of no more than 10 percent. Pea gravel or crushed rock are typically used for this layer. As noted by the American Concrete Institute (ACI) in the Guides for Concrete Floor and Slab Structures, proper moisture protection is desirable immediately below any on -grade slab that will be covered by file, wood, carpet, Impermeable floor coverings, or any moisture -sensitive equipment or products. ACI recommends a minimum 10-mil thickness vapor retarder for better durability and long term performance than is provided by 6-mil plastic sheeting that has historically been used. A vapor retarder is defined as a material with a permeance of less than 0.3 perms, as determined by ASTM E 96. It Is possible that concrete admixtures may meet this specification, although the manufacturers of the admixtures should be Consulted. Where vapor retarders are used under slabs, their edges should overlap by at least 6 inches and be sealed with adhesive tape. The sheeting should extend to the foundation walls for maximum vapor protection. If no potential for vapor passage through the slab is desired, a vapor barrier should be used. A vapor harder, as defined by ACI, Is a product with a water transmission rate of 0.01 perms when tested in accordance with ASTM E 96. Reinforced membranes having sealed overlaps can meet this requirement. We recommend that the contractor, the project materials engineer, and the owner discuss these issues and review recent ACI literature and ASTM E-1643 for installation guidelines and guidance on the use of the prolectiorvblotter material. The General, Permanent Foundation and Retaining Walls, and Drainage Consideretions sections should be reviewed for additional recommendations related to the control of groundwater and excess water vapor for the anticipated construction. EXCAVA77014S AND SLOPES Temporary excavation slopes should not exceed the limits specified in local, state, and national government safety regulations. Also, temporary cuts should be planned to provide a minimum 2 to 3 feet of space for construction of foundations, walls, and drainage. Temporary cuts to a maximum overall depth of about 4 feet may be attempted vertically in unsaturated soil, if there are no indications of slope instability. However, vertical cuts should not be made near property boundaries, or existing utilities and structures. Unless approved by the geotechnical engineer of record, It is Important that vertical cuts not be made at the base of sloped cuts. Based upon Washington Administrative Code (WAC) 296, Part N, the loose to medium -dens near -surface soils at the subject site would generally be classified as Type B. Therefore, temporary cut slopes greater than 4 feet In height should not be excavated at an inclination steeper than 1:1 (Horizontal:Vertical), extending continuously between the top and the bottom of a cut. The underlying dense to very dense glacial till and send soil would be classified as Type A; thus, temporary cut sopes could be steepened to 0.76:1 (Horizontal:Vertical) in the dense underlying glacial till. GEOTECH CONSULTANTS, INC.