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Home My WebLink About965300053 Geotech AssessmentSTRATUM GROUP P.O. Box 2546, Bellingham, WA 98227 Phone (360) 714-9409 September 5, 2007 Dennis Shields Kala Bluffs LLC Kala Point Professional Building 260 Kala Point Drive Port Townsend, WA 98368 Re: Geotechnical Report Phase 6, Kala Bluffs Port Townsend, Washington Dear Mr. Shields: ~~~~~ . d~ ~ ~ 2~~~ ~~ It is our understanding that you plan to construct two single-story condominium buildings and a single story home along Bluffs Lane at Kala Point, Port Townsend, WA. We visited the property on September 4, 2007 to evaluate the geology and geotechnical conditions at the site and vicinity. The proposed buildings will not be at risk from landslides, slope. failures or erosion. Soils underlying the site. will provide adequate foundation support. GENERAL GEOLOGY Northwestern Washington has been occupied by continental glaciers at least four times during the Pleistocene Epoch (1.6 million to 10,000 years ago). During these glacial and accompanying interglacial periods, the underlying bedrock was deeply eroded. The Surficial Geolo ig'c Ma~of the Port Townsend 30- by 60-Minute Quadrangle Puget Sound Region Washington (Pessl, Dethier, Booth and Minard, 1989) indicates that the subject property is underlain by glacial till. Site observations on the subject property and in the vicinity are consistent with the above- described mapping. The till underlying the subject property consists of a poorly sorted mixture of rock fragments deposited directly by glacial ice during the last ice., age. `The pebbles, cobbles and boulders are firmly embedded in a matrix of finer material consisting of a variable mixture of clay, silt and sand. Overall, the till at the site is very hard and compact. The till soils at the site consist of sand with gravel with trace silt. SPECIFIC SITE OBSERVATIONS The subject property is located northeast of the intersection of Kala Point Drive and Seaview Drive within Kala Point. The property is relatively level with a gentle slope towards the east. The proposed building sites are grass covered. September. 5, 2007 Phase 6, Kala Bluffs, Kala Point, WA Geotechnical Report ACT 2 6 207 1~ ~ No areas of water seeps or vegetation indicating seasonal water seeps were observed anywhere on the property. Six test holes were excavated using a shovel and hand auger. The soils encountered at the site were consistent. The upper 3 to 4 inches of soil consisted of silty sand and gravel with roots. Below approximately 5 inches the soil consisted of very compact, brown gravelly fine SAND (SP) with trace silt. Theses soils were encountered to the maximum depth of our hand augering at a depth of 5 feet. The soil is a fairly coarse grained glacial till. There is no evidence of surface water flow on the site. A ditch located along the north side of Sailview Drive shows little evidence of surface water flow. The lack of surface water flow is likely the result of the area being underlain by sandy soils. It~ppears .that storm water readily infiltrates into the ground at the site. CONCLUSION AND RECOMMENDATIONS Development on the site as proposed will be feasible with standard building and, foundation construction practices. No geologic hazardous conditions are present on or near the site. Soils underlying the site consist of very compact gravely sand that has been over consolidated from glacial loads. The soil is very compact and is not subject to expansion or shrinkage. Foundation Recommendations We conclude that the site is suitable for development of the type proposed, provided our recommendations are followed. Conventional, shallow column (spread) and continuous footings will provide adequate support for the proposed buildings. The test pit explorations revealed adequate foundation support to the depth of the explorations. Our conclusions and recommendations assume a relatively light structure that will not be particularly settlement sensitive. Should: a heavier structure be proposed in the future (i.e. continuous footings greater than 2-foot wide or column footings greater than 4-foot by 4-foot with bearing pressures exceeding of 2,000 psf), we should be informed so we can reevaluate our recommendations. We recommend that the buildings be supported on isolated column (spread) and continuous footings founded on undisturbed native soils or a minimum of 6-inches of compacted structural fill. If founded on structural fill; the fill should extend beyond the edges of the footings a distance equal the thickness of the structural fill. Bearing soil should be firm and non-yielding and free of standing water prior to pouring concrete. Bearing soil that is disturbed during foundation excavation should be removed. All continuous and isolated column footings should have minimum widths of 18 and 24 inches, respectively, and should be founded a minimum of 18 inches below the lowest adjacent fmal grade to provide adequate frost protection. Each structure should be placed entirely on native soils or entirely on structural fill to minimize differential settlement. Stratum Group File: 9.1.07 2 September 5, 2007 Phase 6, Kala Bluffs, Kala Point,. WA Geotechnical Report ~~~ ~~i~ All shallow footings supported on properly prepared subgrade may be proportioned using a net allowable bearing pressure of 2,000 psf. The term net allowable bearing pressure refers to the pressure which can be imposed on the soil at foundation level due to the total of all dead plus live loads exclusive of the weight of the footing or any backfill placed above the footing. These values may be increased by one-third for transient wind or seismic loads. We recommend that a geotechnical engineer or engineering geologist from our office inspect all excavations and the compaction of structural fill prior to construction of footing forms. Settlement of foundations depends on foundation size, depth, and bearing pressure, as well as the strength and compressibility characteristics of the underlying soil. Assuming construction is accomplished as recommended above and for the loads anticipated, we estimate the total settlement of foundations should be small (less than about one inch). Our estimate assumes a maximum sized footing utilizing a maximum allowable contact pressure and also assumes a typical consolidation coefficient for the foundation soils. This settlement estimate assumes relatively light loads with continuous footing widths not to exceed 2 feet and column footings not exceeding 4-foot by 4-foot. Our test pit exploration revealed that the native gravely sand soils are over consolidated and, as such, much of the settlement should take place relatively rapidly, as the loads are applied. Development of the site can be accomplished with typical foundation work. Roof gutters and the; down spout system should either direct water into an approved storm water system or should be I infiltrated into the ground in a level spreader placed in such a manner as to avoid concentrating surface water discharge. Stratum Group appreciates the opportunity to be of service to you. Should you have any questions regarding our assessment please contact our office at (360) 714-9409. Sincerely yours, Stratum Group ~. Dan McShane, L.E.G., M.Sc. Licensed Engineering Geologist Stratum Group File: 9.1.07 . Fgure 1. Site Location 48°03.576' N, 122°46.718' W WGSB4 122°48.000' W 122°47_~on~ w ,.,,.~~.. , -,.,,,.~ „ c t c c c d C 0 a z 0 0 0 ri 0 0 ~f 6 t~ ~ s. 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