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HomeMy WebLinkAboutGeoTech Report for Shallow Foundation - BLD Engineering / Geo-tech Reports - 11/30/2007 N.L. OLSON & ASSOCIATES, INC. 4e!, ENGINEERING, PLANNING AND SURVEYING Nov 30, 2007 Project Number: 6786-07 Attn: Mr. Norris Suder 13035 15th Avenue SE Seattle, WA 98125 Phone: (206) 3117-6251 3V? Phone: (360) 275-5310 Subject: Shallow Foundation 11031 NE North Shore Road Belfair, WA 98528-8716 Tax Parcel Number: 32224500031 Reference: GeoResources, LLC Geotechnical Report Proposed Residential Remodel 11031 North Shore Road (Lot 17; Div 4) Mason County, WA Job No: suderN.01 R; Dated May 14, 2004 Dear Mr. Suder; NLO has been requested by the client to determine a method of foundation support proposed between the existing structure and new addition. Presently, the north side of the existing structure has been supported on a seawall that has fell into a state of disrepair and requires replacement with a new strip foundation. SITE LOCATION AND SITE CONDITIONS The property is located at the address of 11031 North Shore Road, Belfair WA, and Mason County's Parcel Number: 322245000031. For a full description of the site and slope area please review GeoResources, LLC., Geotechnical Report presented in Appendix A of this report. PROPOSED DEVELOPMENT Based on conversations with the client and the provided Cabin Revision Plan for Norris Suder, 11031 North Shore Road, Belfair, Wa. 98528; prepared by Clarence Suder Architect, we understand a new addition has been proposed. The proposed structures will be one story and of light wood frame construction with building footprint of roughly 350 square feet (sf). At this time, we anticipate the proposed new addition will be supported on a standard shallow foundation system. Prior to placing the shallow foundation, the existing seawall foundation that GEOTECHNICAL ENGINEERING SERVICES N.L. Olson & Associates, INC. 2453 Bethel Avenue, Port Orchard, Washington 98366 Phone (360) 876-2284 • Fax (360) 876-1487 Project No. 6786-07 December 4,2007 Page No. 2 provides support for the existing structure will need to be removed and a new strip footing installed. Cuts in the range of 5 feet are anticipated to remove the existing seawall and construct the new strip foundation. The proposed new addition, existing building and proposed new strip foundation have been illustrated on the Site Sketch- Figure 1. SEISMIC NLO has reviewed the IBC for seismic design criteria for the proposed construction. The site's ground acceleration was determined from the 2002 USGS Earthquake Hazard Program for the Conterminous 48 States. The PGA was based on the following location 47.38006 Latitude and —123.01457 Longitude. NLO has reviewed the 2006 International Building Code (IBC) for seismic design criteria for the proposed construction in regards to soil only. The IBC seismic design parameters for this site include a seismic zone soil profile type D. The recommended seismic design ground shaking parameters are the values in Seismic Parameter (2006 IBC) Table presented below for Site Class D soils. The spectral accelerations are as provided in the following table. Recommended Seismic Design Ground Shaking Parameters IBC - 2006 Seismic Parameters (2006 IBC) Values Mapped Spectral Acceleration Short Period (Ss) 1.243 Mapped Spectral Acceleration For One Second (S,) 0.484 Site Class D Short period Site Coefficient (Fa) 1.006 1-second Site Coefficient (F„) 1.516 MCE Spectral Response Acceleration for short period (SMs=SsxFa) 1.243 MCE Spectral Response Acceleration for one second (SM1=S,xFv) 0.734 Design Spectral Response Acceleration for Short Period (SDs=2/3xSMs) 0.829 Design Spectral Response Acceleration for one second (SD1=2/3xSM1) 0.489 Design Peak Ground Acceleration (PGA=SDS x 0.4) 0.332 CONCLUSIONS & RECOMMENDATIONS NLO has looked at various methods of foundation support that would allow the existing seawall to remain. In our opinion, removing the seawall is the only viable option. If the seawall remains, concrete piles or pin piles will be needed to provide building support, which will prove more expensive than a convention shallow foundation system. In the following, NLO has provided recommendations based on the encountered soil conditions and the soil criteria presented in the referenced GeoResources, LLC., Geotechnical Report. Note: The report has provided recommendations for the strip foundation identified on the Site Sketch- Figure 1. This report does not cover any other geotechnical matters or concerns in regards to this site. N.L. Olson & Associates, INC. 2453 Bethel Avenue, Port Orchard, Washington 98366 Phone (360) 876-2284 9 Fax (360) 876-1487 Project No. 6786-07 December 4, 2007 Page No. 3 FOUNDATION SUPPORT For the building's continuous and column footing system bearing on properly compacted structural fill or dense undisturbed native soil an allowable bearing pressure of 2,000 pounds per square foot (psf) can be used. For frost protections, footings should have a minimum embedment depth of 12 inches below adjacent grade. A base friction coefficient of 0.25 is considered appropriate for the expected dense site foundation support soils. An ultimate passive equivalent fluid earth pressure for retaining structures, considering a horizontal ground surface, of 250 pcf is available to develop additional resistance to lateral pressures. Passive pressures should be ignored or appropriately reduced in areas where the ground slopes downward on the resisting side of the wall within 4 times the footing embedment depth of the wall. The upper two feet of soil should be neglected when calculating the passive resistance. A 1/3 increase in the above value may be used for short duration, wind, and seismic loads. NLO recommends the inspection of all footing subgrade areas to verify if additional overexcavation is required or adequate foundation subgrade soils have been achieved. NLO may require additional overexcavation below the proposed bottom of footing level if soft, loose, or organic laden soils are encountered. Fill material considered for structural fill needs prior approval by a representative of our firm. Structural fill placement should be done in accordance to the structural fill section presented in this letter. SETTLEMENT Based on an allowable soil bearing pressure of 2,000 psf, total settlement in the range of one inch is anticipated with differential settlement of about '/2 inch over a span distance of roughly 50 feet. Most of the anticipated settlement should occur during construction as dead loads are applied. SUBSURFACE DRAINAGE To preclude groundwater build-up adjacent to the building's footing system, we recommended a perforated four-inch diameter pipe - SDR 35 (ASTM 3034). The pipe's perforations must be placed down at the footing subgrade elevation around the bottom of footing level around the foundation perimeter. The footing drainage system should be bedded in sand and gravel and designed to carry any accumulated water away from the structure to an appropriate discharge area. Roof drainage shall not be connected to the footing drains but may use the same outfall piping if connected well away from the building such that roof water will not backup into the footing drains. STRUCTURAL FILL Structural fill is defined as compacted fill placed on slopes or under buildings or pavements that consist of free draining gravelly sand having a maximum size of 1-1/2 inches and with not more than 5.0% fines, material passing a U.S. No. 200 sieve. All imported fill material should conform to the above recommendation regardless of current weather conditions. All structural fill should be placed on a firm, properly prepared subgrade. Fill materials should be placed in layers approximately 8 inches in thickness, moisture conditioned, and compacted to 95% of the maximum dry density as determined by ASTM D-1557. N.L. Olson & Associates, INC. 2453 Bethel Avenue, Port Orchard, Washington 98366 Phone (360) 876-2284 9 Fax (360) 876-1487 Project No. 6786-07 December 4, 2007 Page No. 4 REPORT LIMITATIONS This report has been prepared for the client regarding the subject project. Information presented in this report has been collected and interpreted in a manner consistent with the level of care and skill ordinarily exercised by members of the profession currently practicing under similar conditions, and in accordance with sound and generally accepted principles consistent with normal consulting practice. No other warranty, expressed or implied, including (but not limited to) any warranty or merchantability or fitness for a particular use has been made. In the event that change in the nature, design, or location of the proposed construction is made, or any physical changes to the site occur, recommendations are not be considered valid unless the changes are reviewed by NLO and conclusions of this report are modified or verified in writing. NLO should be retained to provide geotechnical services during construction. This is to observe compliance with the design concepts, specifications or recommendations and to allow design changes in the event subsurface conditions differ from anticipated prior to the start of construction. We do not accept responsibility for the performance of the foundation or earthwork unless we are retained to review the construction drawings and specifications, and to provide construction observation. Should you have any questions or concerns, which have not been addressed, or if we may be of additional assistance, please call our office. Sincerely, 'i IR.. J O � 'A Wesley . Johnson, P.E. 59" t Project gineer $°oNAt F Attachments: Site Sketch Exrs�:s sni�' N.L. Olson &Associates, INC. 2453 Bethel Avenue, Port Orchard, Washington 98366 Phone (360) 876-2284 9 Fax (360) 876-1487 3/"x3" LAGS TOE NAIL EXIST 32" O.0 ,J JOISTS TO 44 BEAM 2x10 RIM (SHIM W/ (3) 10d NAILS TO MATCH FL00 HEIGHT) /— EX 2x6 JOIST 27 -0" —�' 5'6" DOUBLE JOINT UNDER 4x4 BEAM, TOE MAIL TO INTER BRACED WALL SILL W/ 16d @3" O.C. 6x12 VENT (TYP) 2x8 TREATED SILL Y2"0 oz 8 ; _ z ANCHORS © 4" O.C. - - - - - - - - - - — Ln • j DEPTH TO BE FIELD VERIFIED A BY GEOTECHNICAL ENGINEER, 18'> MAY EXTEND BEYOND 5 FT CV n SECTION B-B ,$ FOOTING = o I I CD SCALE: 1/2"= 1' 2x10 JOISTS HANG I N ( i FROM RIM W/ LB210 30" CRAWLSPACE I TOP FLANGE HANGERS ACCESS B 2x10 RIM JOIST 2x10 JOIST 26 TREATED SILL ! X BATHROOMI REMOVE EXIST SEAWALL & I REPLACE W CONTINUOUS Y"0 ANCHORS - / z 6" @ 6' O.C. FOOTING 4 BEAM AS SHIM TO 4 CONT. #4 VERT ©24" O.C. 4x B \ ALTERNATE HOOKS EXIST JOISTS REVISED FOUNDATION PLAN AREA OFCALCS 351 SF z 18" SCALE: 1/4"= 1' AREA OF VENT REQ'D= 351/150= 2.34 SF 6x12 VENT= 0.5 SF `V 5 VENTS REQ'D SECTION A-A SCALE: 1/2"= 1' �`2�aMuaZ9 REVISIONS rBYDATE A 2 CABIN ADDITION FOUNDATION FOR: NORRIS SLIDER N0. DATE BY DESCRIPTION DESIGNED 11/0 /A\ SCALE: AS ber 2J DRAWN 11/0 � J N.L.OIsonBtAssociates,nC. T T DATENovanbx 29, 2007 Engineering, Plannin and Surve n +Dole $ SUDER ADDITION 13035 15TH AVENUEDRAWING NUMBER CHECKED 11/0 69 r 9 ° A�°. ' SEATTLE, WA 98125 076786A- (360) B76-22B4 11031 NORTH SHORE RD xxxxxx APPROVED ACCEPTED 2453 Bethel Avenue,P.O.Box 637,Port Orchard,WA 9M f —�o:21 BELFAIR, WA 98528 SHEET 7 Of 7 WA L- pm 2 r � = AP R.R o X,. L4�CAT�t 0 4\0 I^LO CIC 6 r~c eK wa�.L `i 4 \ \ SkIOR,TAG� \ \ \ \ \ NEW FREE ZF-PROD F y' g W0sF- 51P, MEW f ZEEZEPR00P � �.\ �;� FTT 1 ` 0 FJe4AuS7r - 13,F" i� -, Q `J ;Roar: m I Ar S ROor- "TRUSSF-s V-0"O.c. � ds i� ''• SMav{,� � RaMOVE DROP DOWN ATTICIIESS CXISrINC r � LADDER IN CEILII44- � Y SLip1yG, w DOUR Bit- -Sr P:WKL L oQ O Dr=cK ri w x Y CLL v x 1055'.94 sq.FT 4 DECK -70-o50 Q 4— C,JIvJf�401v1_ �P_�1( L� Exterior Braced Wall Panel shall be wood structural panel sheathing not less than 5/16"thick for studs at 16"o.c. Nail w/8d @ 6"o.c. at all edges and 12"o.c. in field. Interior Braced Wall Panel shall be 1/2"thick gypsum wall board sheathing Nail w/6d cooler nails or wall board nails @ 7"o.c. at all edges and 12" in field.