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HomeMy WebLinkAboutSWP272282 ,J�'U�`n ., � �J / p . � FOR DISTRIBUTION TO: �- Water Utility ® Building Division trf Wastewater Utility Public Works Constr Inspector J Surface Water Utility Fire Prevention Maintenance Services Transportation Systems Project: Ir) r, l Location: Attached please find copies of: ® PERMIT BILLS OF SALE RECEIPT ® COST DATA INVENTORY LETTER OF SPECIAL BILLING EASEMENTS) ® STUB SERVICE AGREEMENT ® COPY OF AS-BUILT PRECON NOTES FA ® PRECON ATTENDEES DRAINAGE REPORT ® MEMO - WATER BREAKDOWN MAP WITH NEW MAINS AND VALVES /* OTHER From: .Er' Date: I /_ 961 C:TO:➢RECON:DISTFRM TERRA ASSOCIATES, Inc. Mid z�- ��G I n�irruun� nt.11 I ,iilli ',� i� n< < ��• July 10, 1996 Project No.T-3260 Mr. Greg Schoen Griffin-Schoen Properties 24800 Pacific Highway South Kent,Washington 98032 Subject: Geotechnical Report Burger King SW 41st Street and East Valley Highway Renton, Washington Dear Mr. Schoen: As requested, we have conducted a geotechnical engineering study for the subject project. This letter report presents our findings and recommendations for the geotechnical aspects of project design and construction. PROJECT DESCRIPTION The project will consist of the construction of a single-story Burger King restaurant located at SW 41st Street and East Valley Highway in Renton, Washington. We understand that the building will be approximately 96 feet long and 42 feet wide. The foundation supporting the structure will consist of a four-inch thick slab, a 16-inch wide spread footing,and five interior columns. The finish floor grade will be at Elev. 19.5. SCOPE OF WORK Our scope of work on this project included reviewing existing data from our previous study of the site as summarized in our Geotechnical Report dated January 30, 1996 (Project No. T-3062). We also reviewed data from a study of the site performed by RZA-AGRA Engineering and Environmental Services as summarized in their report dated December 1991 (Project No. W-8011). Using this information, we developed project-specific geotechnical recommendations for design and construction. Specifically, this report addresses the following: • Site conditions • Site preparation and grading, including recommendations for design and construction of the building preloading program • Foundation design parameters • Slab-on-grade construction I .' ,:� \\ •. 16)1 I11. - I ) 1'-.Uld.it1,1 Phone (06) 8 1-i i i- Mr. Greg Schoen July 10, 1996 SITE CONDITIONS Surface The project site is level at approximate Elev. 18.0. It is moderately vegetated with tall grass. Surface conditions allowed for standing water in some isolated areas. The area was used for farming in the past. Subsurface Three major geologic units were encountered during the previous explorations. These are artificial fill, alluvium, and estuarine deposits. All are common to the Duwamish River valley floor. The upper five to six feet of soil across the site is fill consisting of medium dense, silty, gravelly sand. Alluvial soils underlie the fill to a depth of about 32 feet. The upper portion of the alluvium deposit, to a depth of nine to ten feet below existing grade, is soft organic silt and peat. The organic silt includes partially decomposed organic matter (peat) in varying amounts. In several of the test borings, fibrous peat was found as a separate soil unit, either within or immediately below the organic silt. The organic silt and/or peat is underlain by medium dense to very dense, gray to black alluvial sand. Occasional silt layers were encountered within the sand unit. The alluvial soils are underlain by estuarine deposits which typically vary in composition from clayey silt to sand and gravel. Shells are typical within these deposits. Gray silt with shell fragments was found in four of the borings underlying the black sand. The Geologic Map of the Renton Quadrangle, King County, Washington by D.R. Mullineaux (1965) shows that the soils are mapped as peat (Qlp). While some peaty soils were observed at the site, the native organic silt and clay underlying the fill at the site correlates better with the description of the nearby mapped alluvium (Qaw). Groundwater Groundwater was encountered in all of the test borings at a depth of about ten feet. Wet fill soils and wet organic soils were also observed above this level. Groundwater levels can vary seasonally with rainfall and other factors. DISCUSSION AND RECOMMENDATIONS Site Preparation and Grading Building and pavement areas should be stripped of vegetation and any other deleterious material. The stripping depth to remove vegetation is expected to be limited, in the range of two to six inches. Following clearing, the fill surface should be proofrolled with heavy construction equipment prior to placement of additional fill. Soft, yielding areas should be overexcavated to firm bearing soil and replaced with structural fill. Where excavations to achieve firm conditions are excessive, the use of a geotextile fabric such as Mirafi 50OX in conjunction with limited overexcavation and replacement with a structural fill can be considered. Typically, 18 inches of clean granular structural fill over the fabric will achieve a stable subgrade. Project No.T-3260 Page No. 2 Mr.Greg Schoen July 10, 1996 Existing fill soils excavated on the site, excluding those containing excessive vegetation debris and organic matter,could be used as structural fill. However, the ability to use these soils as structural fill will depend on their moisture content and the prevailing weather conditions at the time of construction. It will be difficult to achieve proper compaction of these soils when their moisture content is above optimum. When the moisture is excessive, the soil can be dried by aeration to a moisture content which will allow for proper compaction. Alternatively, an additive such as lime or cement can be used to accelerate the drying process to provide a more stable and workable soil. We recommend that the structural fill imported to the site to achieve site grades consist of inorganic free-draining granular soil meeting the following grading requirements: Size Percent Passing 3 inches 100 No.4 Sieve 25 to 75 percent No. 200 Sieve (Based on the 25 percent Minus 3/4-inch Fraction) (see following narrative) For fill placement during wet weather or conditions where the moisture content of fill containing fines can not be controlled,we recommend importing fill soil that has a maximum of five percent passing the No. 200 sieve. Up to Elev. 19.5, structural fill materials should be placed in uniform loose layers not exceeding 12 inches and compacted to a minimum of 95 percent of the soils' maximum density, as determined by ASTM Test Designation D-698 (Standard Proctor). The moisture content of the soil at the time of compaction should be within about two percent of its optimum, as determined by this same ASTM method. Preloading Program We recommend preloading the building area to minimize long-term settlement. To accomplish this, we recommend placing an additional three feet of surcharge material (to Elev. 22.5) above the proposed finish floor level at Elev. 19.5. The surcharge should extend at least five feet beyond the building perimeter. The soil used for the surcharge has no requirement other than being placed in a uniform manner with a final unit weight no less than 120 pounds per cubic foot (pco- The estimated total preconstruction settlement is about three inches provided the surcharge material stays in place for four to five weeks after placement. Due to variation in subsurface conditions, the preloading may take longer or shorter than estimated. The post-construction settlement is estimated to be about 1.0 to 1.5 inch with a differential settlement of 0.5 to 0.75 inch. Project No.T-3260 Page No. 3 Mr. Greg Schoen . July 10, 1996 The progress of settlements should be monitored to verify the magnitude and rate settlement is actually occurring. For this purpose, we recommend installing settlement markers prior to placement of the structural fill and the preload fill. The settlements should be monitored every other day during placement and then weekly thereafter. The settlement readings should be obtained by a registered land surveyor and should be based on an established benchmark well away from the building area. The settlement markers should be clearly flagged and protected from potential damage by equipment during grading work and placement of the preload fill. It is imperative that the earthwork contractor recognize the importance of the settlement markers and that all efforts are taken to prevent them from disturbance and damage. It is extremely difficult to evaluate the settlement progress with markers that have been hit and displaced or completely destroyed during grading activities. Spread Footinp-s Assuming a finish floor at Elev. 19.5 and a footing depth of 18 inches,footing bottoms will be at Elev. 18.0 which roughly corresponds to existing grade. At this level, uniformly compacted fill materials will not be present below footings. To provide appropriate support, we recommend placement of at least 2.5 feet of structural fill below all footings (to Elev. 15.5). This may be accomplished by excavating trenches along footing lines extending at least one foot outside each side of the footings. Foundations can then be supported on this structural fill. Foundations should bear at a minimum depth of 18 inches below final exterior grades. Spread footings supported as described should be designed for an allowable bearing capacity of 2,000 pounds per square foot (psf). A 1/3 increase in this capacity can be used when considering short-term transitory loading such as wind or seismic. For resisting lateral loading, a friction coefficient of 0.4 can be used. In addition, passive resistance developing in the opposite direction of the lateral thrust on the sides of the footing and foundation stem wall can be considered. We recommend computing the passive resistance using an equivalent fluid weight of 350 pcf. This value assumes that the foundation will be constructed neat against the excavation or backfilled with a structural fill. This value is provided with a safety factor of 1.5. Floor Slab Construction New structural fills will be suitable for supporting slab-on-grade construction. Immediately below the floor slabs, we recommend making an allowance for placing a four inch layer of clean free-draining sand or gravel that has less than two percent fines passing the No. 200 sieve. This free-draining material will work as a capillary break. Where moisture via vapor transmission is not desired, a 10 to 12 mil thick plastic membrane should be placed above the capillary break material. The membrane should then be covered with one to two inches of moist sand to help protect it during construction and to aid in uniform curing of the concrete floor slab. The subgrade modulus for slab and foundation design is estimated to be 300 to 400 pounds per cubic inch(pci). Project No.T-3260 Page No. 4 Mr.-Greg Schoen 'July 10, 1996 ADDITIONAL SERVICES Terra Associates, Inc. should review the final design and specifications in order to verify that earthwork and foundation recommendations have been properly interpreted and implemented in project design. We should also provide geotechnical services during construction in order to observe compliance with the design concepts, specifications, and recommendations. This will also allow for design changes if subsurface conditions differ from those anticipated prior to the start of construction. LIMITATIONS We prepared this report in accordance with generally accepted geotechnical engineering practices. This report is the property of Terra Associates, Inc. and is intended for specific application to the Burger King project in Renton, Washington. This report is for the exclusive use of Burger King, Griffin-Schoen Properties, and their authorized representatives. No other warranty,expressed or implied, is made. The analyses and recommendations presented in this report are based upon data obtained from test borings summarized in our Geotechnical Report dated January 30, 1996 and in the Subsurface Exploration and Geotechnical Report dated December 1991 by RZA-AGRA Engineering and Environmental Services. Variations in soil conditions can occur, the nature and extent of which may not become evident until construction. If variations appear evident, Terra Associates, Inc. should be requested to reevaluate the recommendations in this report prior to proceeding with construction. We trust this information is sufficient for your present needs. Please call if you have any questions or need additional information. Sincerely yours, TERRA ASSOCIATES,INC. Maher A. Shebl, Ph.D. � og�,, `9j� Staff Engineer Anil Butail, P.E. ?030C President MAS/AB:tm EXM-Es 12!9/ � Project No.T-3260 Page No. 5