7818 LARIMER RD B Geotech Report 2022-10-25

Retaining walls should be designed for seismic loading conditions. We recommend the addition of uniform lateral pressure under seismic conditions of 9H psf, where H is the design height of the retaining wall in feet. The safety factor of 1.25 may be used for retaining wall design under seismic loading conditions. Retaining wall backfill should be placed in strict accordance with our earthwork recommendations given below. Backfill should not be over -compacted to minimize excessive lateral pressures on the walls. As a precautionary measure, a drainage collection system (drains or geosynthetic drains) should be included in the wall design to minimize hydrostatic pressures. A prefabricated drainage composite or drain board such as the MiraDrain 2000 or an engineer -approved equivalent may be installed along the backfilled side of the basement foundation wall. SUBSURFACE DRAINAGE Proper subsurface drainage is critical for long-term performance of the proposed structures. As a minimum, recommendations illustrated in Figure 8 and given below should be strictly followed. • A perimeter drain/dewatering system should be installed to reduce the potential for groundwater entering foundation and slab areas. • The subgrade beneath a structural floor system should be graded so that water does not pond. In addition, drain laterals that span the crawl space are recommended to prevent ponding of water within the crawlspace. • As a minimum, the subsurface drainage system should consist typically of 4-inch minimum diameter perforated rigid PVC pipe surrounded by at least one pipe diameter of free draining gravel. The pipe should be wrapped in a geosynthetic to prevent fine soils from clogging the system in the future. The pipe should drain by gravity to a suitable all-weather outlet or to a properly designed area underdrain system. Surface cleanouts of the perimeter drain should be installed at minimum serviceability distances around the addition. A properly constructed drain system can result in a reduction of moisture infiltration of the subsurface soils. Drains which are improperly installed can introduce settlement or heave of the subsurface soils and could result in improper surface grading only compounding the potential issues. • The entire design and construction team should evaluate, within their respective field of expertise, the current and potential sources of water throughout the life of the structure and provide any design/construction criteria to alleviate the potential for moisture changes. If recommended drain systems are used, the actual design/layout, outlets, and location should be designed by AGS. The construction means, and methods should be observed by a representative of AGS. Proposed Construction Project No: 0470-WA18 January 24, 2019 Page No: 11 of 17