11731 AIRPORT RD Geotech Report 2018-01-02 MF Import

08/18/2005 15:27 4257478561 GEOTECH PAGE B8 Lucia Devebpment, LLC JN 05233 August 18,2005 Page 7 should not be placed direetly behind retaining walls due to their Silt content. For increased protection, drainage composkes should be placed along eut slope faces, and the walis should ba backfilled entirely wRh free-draining soil. The later section entRled Drainage Considerations should also be reviewed for recommendations related to subsurface drainage behind foundation and retaining walls. The purpose of these backfill requirements is to ensure that the design criteria for a retaining vrall are not exeeeded because of a build-up af hydrostatic pressure behind the wall. The top 12 to 18 inches of the ba�ll should eonsist of a compacted, relatively impertneable soil or topsoil, or the surtace shouid be paved. The graund surface must also slope away from backfilled walls to reduee the potential for surface water to percolate into the bac�ll. The seciion ent�tled (deneral Eaethwork and Structuraf Fi!l contains recpmmendations regarding the placement and compact:on of structural fill behind retaining and foundation walls. The above recommendations are not intended to waterproof below-grade walls, or to prevent the fortnation of mold, mildew or fungi in interior spacas. Over time, the perfortnance of subsurNace drainage systems can degrade, subsurface groundwater flow pattems can change, and utilities can break or develop leaks. Therefore, waterproofing should be provided where futura seepage through the wdlls is not acceptable. This typieally includes Gmiting cold-joints and wall penetrations, and using 6entonite panels or membrenes on the autside oi the walls. There are a variety of different waterproofing materials and systams, which should be installed by an experienced contractor familiar with ihe anticipated eonsVuction and subsurface eonditions, Applyi�g a thin coat of asphaft emulsion to the outside faee of a wall is not considered waterproofing, and will only help to reduce moisture generated from water vapor or capillary aetian irom seeping through the eoncrete. As with any project, adequate ventilation of baseme�t and erawl spaee areas is important to prevent a build up of water vapor that is commonly transmitted through concrete walis from the surrounding soil, even when seepage is not present. This is appropriate even when waterproofing is applied to the autside of foundation and retaining walls. We recommend that you eontact a specialty consultant if detailed recommendations or speoifications related to waterproofing design, or minimizi�tg the potential for infestations of mdd and mildew are desired. SLABS-ON-C,RADE Due to potemial differential seklement, we recommend that the building floors be structurally supparted on the deep foundation system, either through the use of a struCturel slab or a crawl space. Even where the exposed soils appear dry, water vapor will tend to naturally migrete upwarcl through the soii to the new constructed space above it. All interior slabs-on�rade must be underfain by a capillary break or dreinage Iayer consisting � a minimum 4-inch thickness of gravel or crushed rack that has a fines content (percent passing the No. 200 sieve)of less than 3 percent and a sand conteM (percertt passing the No. 4 sieve) of no more than 10 percent. As noted by the American Concrete Institute (ACI) in the Gufdes for Conaete Floor and Slab Structuies, proper moisture protection is desirable immediately below any on-grade slab that will be covered by tile, wood, carpet, impertneable Floo� coverings, or any moistufe-sensitive equipment or produCts. ACI also notes that vapor retarc/ers, such as 6-mil plastic sheeting, are typically used. A vapor retarder is defined as a material with a permeance of less than 0.3 US perms per square foot (ps� pe� hour, GEOTECH CONSULTANTS, INC. J