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Home My WebLink AboutBLD2005-00431 Geotechnical Report COUNTY COPY ALKAA LK AI CONSULTANTS, LLC . Environmental Engineering • Geotechnical Engineering • Wetland Consulting 26 June 2005 Project No. ACL05-06-G057 Aquaculture Systems,Inc. P.O. Box 417 Sequim, Washington 98382 Attention: Mr. Steve Fager al leS Subject: Retaining Wall Assessment + , Lot 33,Discovery Bay Village Tax Parcel#947400033 Jefferson County, Washington . Mr. Fager, At your request,ALKAI Consultants, LLC (ALKAI)has performed a geotechnical assessment of the constructed retaining wall at the subject lot. ALKAI understands that this assessment is being required for building permit approval on the subject lot. The retaining wall is located on the eastern portion of the lot where it traverses the hillslope. The wall is part of a cut and fill on the lot to develop a level building area. A schematic cross section of the wall is shown in Figure 1. The wall serves to retain fill on the downhill portion of the developed area. ALKAI understands that the fill is a maximum of 4 feet thick and extends approximately 20 feet back behind the wall. The wall runs north to south and measures approximately 4 feet high and 100 feet long. The wall consists of two rows of ecology blocks manufactured by Fred Hill Materials. With the exception of tapering blocks at each end, each block measures 6 feet wide by 2 feet high by 2 feet thick and weighs 4,400 pounds. The wall is battered back into the hillside at approximately 1:6(horizontal to vertical)ratio. The wall has been backfilled to a relatively flat level to the full height of the wall. The wall and the backfill slope gradually to the north. ALKAI understands that the design of the wall adopted engineering design recommendations prepared by Krazan& Associates for similar walls within the Discovery Bay Village Development. ALKAI understands that the wall was keyed into the very dense native soils. These subgrade soils were inspected by an ALKAI representative on 11 October 2004 and were found to be acceptable as subgrade for the wall. (see attached Field Report No. 1) ALKAI understands that drainage was installed at the base of the walls to prevent the buildup of groundwater behind the walls. The drainage system consisted of approximately 0.5 feet of pea gravel placed at the bottom of the wall,with a geotextile fabric that was placed flat over the pea gravel. Then, 4-inch wrapped ADS drain pipe was placed on the geotextile and then another sheet of the geotextile fabric was place above the pipe. An additional 1 feet of pea gravel was placed above the pipe. The remaining backfill behind the wall consisted of native granular soils,consisting of well-graded gravel with silt and sand. Backfill was compacted construction equipment traffic from a D-7 dozer. The drain pipe is sloped to discharge at the north end of the wall. The constructed retaining wall and associated backfill was inspected by an ALKAI geotechnical engineer on 24 June 2005. Observations indicate that the wall was adequately designed and constructed to function as a 4 foot high retaining structure. Backfill soils were probed and were determined to be dense in the area of the proposed structure near the south end of the wall. Backfill soils were determined to be loose to medium dense behind the north end of the wall. 9465 PROVOST ROAD NW,SUITE 204B•SILVERDALE,WASHINGTON 98383 PHONE:(360)613-2407 FAX:(360)613-2408 • Retaining Vossessment,LotProj 33ect DiscoveryNo.ACLO5-06-G057 Bay Village 26 June 2005 Page No.2 ALKAI understands that Aquaculture Systems, Inc. intends to construct a single family residence on the pad and that the east end of the residence will be located approximately 10 feet from the top of the constructed retaining wall, as shown in Figure 1. Based on ALKAI's understanding of the constructed wall and observations made during and after construction,the proposed residence location appears to be feasible using a shallow foundation system adjacent to this retaining wall,provided that the recommendations provided in our previous report(Preliminary Geological Assessment, Discovery Bay Development, Discovery Bay Village,Jefferson County, Washington, dated 13 September 2004)are implemented, specifically pertaining to minimum footing depth(18 inches)and discharge of drainage systems(away from slopes and disturbed soils). Should you have any questions or concerns,which have not been addressed,or if we may be of additional assistance, please call our office at(360)613-2407. Sincerely, y C. DAVENp cd r - M Jay C. Davenport,P.E. 1 No. r' �� Senior Geotechnical EngineerSS/O1y��G\� Attachments 'wows /2 i eL 20 Figure 1 Field Report 1 c:\documents and settings\all users\documents\projects\ac105-06-g057 discovery bay development\retaining wall assessment.doc JUL • 1 ALKAI Consultants, LLC 9465 • Provost Road NW, Suite 204 B • Silverdale, Washington 98383 • Ph.: (360) 613-2407 • Fax: (360) 613-2408 • • _J v J J CD vi Z �o Z gz Q co z -) -I-• w>2 O to 0 �' Z ' Nm3 ,o O w w o 8 U moo b 3v�iS a ,na L., 1W —I ��zo 0 g &* 23. i� I. a, 0 0 N w 0 1 Z ,S a et ;'� 0 J ;�� Lti i,� N ►•►. w ►••► H cc ►.4,' , 0 cn a x CO :':4 ►' . a J ce . a . ° v. a O 4 • o v Z ~17. / If(1 o 0 8y N 6N m dW a W W 0 N • • • sz ALKAI CONSULTANTS, LLC. FIELD REPORT 14:04"`" Environmental Engineering • Geotechnical Engineering • Wetland Consulting No: _1 DATE: 10/11/04 CONTRACTOR: Aquaculture Systems, LLC. PROJECT #:ACL 04-G102 LOCATION: Discovery Bay, WA PROJECT: Discovery Bay Development JURISDICTION: Jefferson County, WA The undersigned arrived at 12:00 p.m. to monitor site work. Ecology block retaining walls were being constructed on lots 33, 34, and 35. Observed subgrade for 3 out of the 5 block walls. The remaining two walls will be observed at a later date. The walls observed this date were the 75 foot, 80 foot, and 150 foot long retaining walls. Subgrade probed firm and unyielding with approximately 3 to 4 inches penetration with 1\2 inch T-probe. One localized area of the 80 foot retaining wall probed approximately 1.5 feet near the cut for the drain pipe. This area does not appear to pose a significant threat to the wall due to the relatively short height of the wall. The wall is proposed to be 1 to 2 blocks high with drain rock and pipe behind the wall in this area. JUL - 1 20r,5 Staff Geologist: Senior Geologist: 9465 Provost Road NW, Suite 2048 • Silverdale, Washington 98383 • (360) 613-2407 • Fax: (360) 613-2408