1010 NORTH PARK DR 2016-01-01 MF Import

Churehill Residcnce 1-1501 1010 North Park Drive April 10.'_OU3 C•verett, �Vashington P��S- � weiehts, are based on the assump[ion of a uniform level backfill �vith no uuildup of hydrostatic pressure bchind ttte walf. To minimize lateral earth pressures and. prevent the buildup of hydrostatic pressures, the backfill within 18 inche� ci the wsll should contain less than � percent fines, based on that portion passing the U.S. No. �3 sieve. We a(so recommend constructine a perforated footina drain placed at the base of the footing and �veep lioles on 3-foot centers diat extend through the base of the wall. The footing drain should consist of a minimum 4-inch diameter perforated pipe be surrounded in at least 4 inches of clean, &ee-draining granular material, such as pea gravcl or washed rock. A non-woven fil[cr fabric such as Mirafi 140N, or equivalent, should envelop tl�e free-draining granular material. We rccommend that die diameter of the drainage materiaf be greater than the diameter of [he pipe perforations. Footing drains should be directed toward appropriate storm water drainage £acilities or to a suitable discliarge location (with quarry spall erosion protection) near the base of the ravine. Roof or patio deck drains should not be connected to the footing drains. If the backfilled wall is structurally restrained from lateral movemcnt at the top, we recommend that i[ be desigrted for an "a[-resP' equivalent fluid weight of» pounds per cubic foot (pc fl. If the top of the wall is free to move laterally in an amount equal to at least 0.1 percent of the wall heiglit during placement of backfill soils, it may be desi,;,�ed for an "activc" equivalent (luid �veight of �0 pcf. Surcharges due to sloping ground, adjacent foor'n�s, conswction equipment, etc., must be added to these values. The above equivalent � uid pressures assume d�at the bac�ll is compacted to approximately 90 to 92 percent of the modified Proctor maximum dry density. Additional compaction adjacent to the ��rail will increase the earth pressure, whi:e c lesscr degree of compaction could result in post construction settlements. The fill nlaced upslope o£tl�e wall must be placed as strucrural lill th�[ is compacted to a minimum of 90 percent of the modified Proctor maximum dry density. If d�e permanent fill is placed on a slope that is stceper than SH:iV (20% or 1I degrees), it should be benched into native soils of the underlying slope. We recommend that the hiilside 6enci�es wt into tl�e native soil be at least one £oot in widtl�. Construction Considerations The preliminary plans provided by Chopelas & Associates, Inc indicates that die face of the concrete retaining wall will Ue located on the order of 2 to 11 feet from the exisring home and patio foundations. Based on our expiorations, �ve anticipate that a subgrnde adequate to support the proposed retaining wall to be on the order of 10 to 16 feet belo�v the [op of the existing timber pile wall patio grade. The depth o: the existing foundations and the nature of the soils supporting these foundations are currently unlmown. Based on the exploration data, it is our opinion that the existing �vall backfill soils aad underlying colluvium represent a Type C soil, as defined in the Washington Administration Code, that corresponds to a maximum temporary cut 18905 37itl Avenue \Va4 Suim 117 1-I501 7inoer Zem�n 4ssaciates. Inc. Lynnwood, R'uhington 98016 (Jzs) 771 —]lW � �. � G� �