Laserfiche WebLink
Everett General Hospital R. Medical Center W-5557 <br /> 29 March 1988 Page 9 <br /> 4.6 Drainage Considerations <br /> The glacially consolidated soils present at depth may allow the development of a <br /> perched ground water condition. Wet zones were encountered above the proposed <br /> floor level, which indicates that perched ground water may develop within the sides <br /> of open excavations, and within the backfilled soils adjacent to basement walls. <br /> If areas of spring activity or seepage are encountered in excavations, it would <br /> be necessary to drain this water from the construction area, which appears generally <br /> feasible by ditching and pumping. The site also should be graded for adequate <br /> surface drainage during construction, to direct all surface runoff away from the <br /> construction area. Traffic across the foundation subgrade soils when they are wet <br /> will lead to disturbance of the otherwise firm soils. <br /> We recommend that the building perimeters be provided with a perimeter footing <br /> drain system, with the footing drain invert located at least 1 foot below the top <br /> of the adjacent floor slab. The footing drain should consist of a perforated pipe <br /> within an envelope of pea gravel or washed rock extended at least 6 inches on all <br /> sides of the pipe, surrounded by filter fabric. This foundation drain system <br /> should be discharged by a tight-line to a storm sewer or other suitable discharge. <br /> Roof or surface runoff should not discharge into the footing drain system. Instead, <br /> a separate tight-line drain system should be used. Basement wall backfill above <br /> the footing drain installation should consist of free-draining granular material <br /> as described previously in this report. <br /> We recommend below-slab drains in the medical office building. The below-slab <br /> drains should be constructed as described above for footing drains, with the <br /> perforated pipe invert 12 inches or more below the bottom of floor slab. We <br /> tentatively recommend at least two below-slab drains be placed within the western <br /> half of the medical office building lower floor level. This recommendation should <br /> 1 be confirmed or revised after observation of ground water conditions by RZA in the <br /> j excavation. <br /> 4.7 Excavation Considerations <br /> In our opinion, temporary open-cut excavations can be utilized in order to achieve <br /> design basement slab and foundation subgrade elevation. Based on topographic <br /> I <br />