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June 13,2023 <br />HWA Project No. 2022-188-21 <br />4.6 FoorncDnq,rxs <br />During periods of high rainfall, ponding of water could occur next to building foundations, and <br />we recommend that perimeter footing drains be installed around all building foundations. <br />Footing drains should consist of l00mm (4-inch) minimum diameter slotted plastic pipe bedded <br />in washed drain rock or pea gravel material. At least 8 inches of drain rock should surround the <br />drainpipe. Footing drain inverts should be at least 12 inches deeper than the boffom of floor <br />slabs. Footing drains should discharge into the storm drain system in such away that storm <br />water cannot backup around the footings and gain ingress beneath floor slab areas. Roof drains <br />should not be tied into the perimeter drain system, to prevent potential backup into the perimeter <br />drains during intense storm events. The ground surface around the structures should be graded to <br />direct surface water away from the structures. <br />4.7 Tnq,Nsrnn Sr.c.rroN Rrtarnrnc W.ll-r-s <br />Presently, the transfer station design includes a single-lane tunnel constructed between two CIP <br />reinforced concrete walls. The eastern wall would be a free-standing wall constructed a few feet <br />inside the external building shell, and would not retain any fill. The west wall would retain <br />structural fill placed to support the tipping slab approximately 16 feet above the roadway elevation <br />of the tunnel drive. <br />Design of the west wall of the tunnel drive will need to consider the effects of placing and <br />compacting fill behind the wall as well as how the top of the wall is treated with respect to the <br />tipping floor slab. Details for design are provided in the following sections. <br />4.7.1 Wall Foundations <br />The design of foundations for CIP walls should follow the recommendation provided for spread <br />footings in Section 4.4. <br />4.7.2 Lateral Earth Pressures <br />CIP walls should be designed for the lateral earth pressures associated with their connection <br />condition at the top of the wall. The earth pressures provided assume properly compacted, well- <br />drained, granular fill adjacent to the walls. Retaining walls constrained against rotation should <br />be designed for an at-rest earth pressure equivalent to a fluid weighing 60 pounds per cubic <br />foot (pcf). Retaining walls allowed to rotate may be designed for an active earth pressure <br />equivalent to a fluid weighing 40 pounds per cubic foot (pcf). Retaining walls designed for <br />seismic earth pressures can be designed for active-plus-seismic earth pressures of 55 pcf. This <br />earth pressure was computed using the Mononobe-Okabe method and a design peak ground <br />acceleration (PGA) of 0.18 g or 0.4*Sns. <br />2022-188-21 KCTS - Final Geotechnical Report I2 HWA GEOSCIENCES INC.