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HomeMy WebLinkAboutSWP272329 ' SUBSURFACE EXPLORATION AND PRELIMINARY GEOTECHNICAL ENGINEERING REPORT 1 HUMBLE AND ASSOCIATES 1 OFFICE BUILDING RENTON, WASHINGTON ' PREPARED FOR The Keimig Associates 1 PROJECT NO. G97159A DULY 1997 1 v S CORPORATE OFFICE 911' (20 )Fifth2 Avenue,safe 100 ��ASSOCIATED Kirkland,Washington 98033 EARTH (20687-7701 FAX (206)827.5424 SCIENCES, INC ' BAINBRIDGE ISLAND OFFICE 179 Madrone Lane North Bainbridge Island,WA 98110 (206)780-9370 FAX(206)780-9438 SUBSURFACE EXPLORATION AND ' PRELIMINARY GEOTECHNICAL ENGINEERING REPORT HUMBLE AND ASSOCIATES OFFICE BUILDING RENTON, WASHINGTON July 3, 1996 Project No. G97159A ' I. PROJECT AND SITE CONDITIONS ' 1.0INTRODUCTION ' This report presents the results of our subsurface exploration and geotechnical engineering study for the proposed Humble and Associates office building in Renton, Washington. A site sketch and approximate locations of the explorations accomplished for this study are presented ' on the Site and Exploration Sketch, Figure 1. In the event that any changes in the nature, design or location of the project are planned, the conclusions and recommendations contained ' in this report should be reviewed and modified, or verified, as necessary. 1.1 Purpose and Scove ' The purpose of this study was to provide subsurface data and geotechnical recommendations to be used in the design and development of the above-mentioned project. Our study included a ' review of available geologic literature, drilling a series of exploration borings and performing geologic studies to assess the type, thickness, distribution and physical properties of the subsurface sediments and shallow ground water conditions. Geotechnical engineering studies ' were also conducted to determine the type of suitable foundation, depth to suitable foundation bearing sediments, anticipated foundation settlements, floor support recommendations, and drainage considerations. This report summarizes our current fieldwork and offers development ' recommendations based on our present understanding of the project. 1.2 Authorization ' Written authorization to proceed with this study was granted by the architect, Mr. Alan ' Keimig, of The Keimig Associates on June 3, 1997. This report has been prepared for the exclusive use of Humble and Associates and their agents, for specific application to this project. Within the limitations of scope, schedule and budget, our services have been ' performed in accordance with generally accepted geotechnical engineering and engineering geology practices in effect in this area at the time our report was prepared. No other warranty, expressed or implied is made. Our observations, findings, and opinions are a means to ' identify and reduce the inherent risks to the owner. 2.0 PROJECT AND SITE DESCRIPTION This report was completed with an understanding of the project based on a fax memo prepared by Mr. Alan Keimig. Present plans call for a wood-frame structure with associated driveways, parking areas and utilities to be built on the subject property. The proposed structure will be predominately 1-story, however, a portion of the structure will be two-stories. We understand ' that the first level will have slab-on-grade floors. The property was situated in the eastern portion of incorporated Renton, Washington in the ' northeast quadrant of the intersection of State Route 169 and Maplewood Place. The approximately 120 feet, southwest-northeast, by 85 feet, southeast-northwest, property was void of structures (with the exception of a concrete noise wall within the SR 169 right-of-way) ' and trees. The nearly level parcel was completely covered in tall field grass. Surrounding land use consisted of undeveloped property to the northeast, northwest, single family homes to the southeast and SR 169 to the southwest. ' 3.0 SUBSURFACE EXPLORATION ' Our field study included excavating a series of exploration pits and drilling exploration borings to gain subsurface information about the site. The various types of sediments as well as the depths where characteristics of the sediments changed are indicated on the exploration logs ' presented in the Appendix. The depths indicated on the logs where conditions changed may represent gradational variations between sediment types in the field. Our explorations were approximately located in the field by estimating distances from site features shown on The ' Keimig Associates' sketch. The conclusions and recommendations presented in this report are based on the two exploration ' borings completed for this study. The number, location, and depth of the explorations were completed within site and budgetary constraints. Because of the nature of exploratory work below ground, extrapolation of subsurface conditions between field explorations is necessary. It should be noted that differing subsurface conditions may sometimes be present due to the random nature of deposition and the alteration of topography by past grading and/or filling. ' The nature and extent of any variations between the field explorations may not become fully evident until construction. If variations are observed at that time, it may be necessary to re- evaluate specific recommendations in this report and make appropriate changes. ' 3.1 Exploration Borings The exploration borings were completed by advancing a 4-inch inside-diameter casing with a truck-mounted drill rig. During the drilling process, soil samples were obtained at generally 5- foot depth intervals. The borings were continuously observed and logged by a geotechnical 1 ' 2 engineer from our firm. The exploration logs presented in the Appendix are based on the field logs, drilling action, and inspection of the samples secured. Disturbed but representative samples were obtained by using the Standard Penetration Test procedure in accordance with ASTM:D 1586. This test and sampling method consists of driving a standard 2 inch outside-diameter split barrel sampler a distance of 18 inches into the ' soil with a 140 pound hammer free-falling a distance of 30 inches. The number of blows for each 6 inch interval is recorded and the number of blows required to drive the sampler the final 12 inches is known as the Standard Penetration Resistance ("N") or blow count. If 50 blows ' are recorded within one 6 inch interval, the blow count is recorded as 50 blows for the number of inches of penetration. The resistance, or N-value, provides a measure of the relative density of granular soils or the relative consistency of cohesive soils; these values are plotted on the ' attached boring logs. The samples obtained from the split barrel sampler were classified in the field and ' representative portions placed in watertight containers. The samples were then transported to our laboratory for further visual classification and laboratory testing, as necessary. 4.0 SUBSURFACE CONDITIONS ' Subsurface conditions at the project site were inferred from the field explorations accomplished for this study, visual reconnaissance of the site and review of applicable geologic literature. ' As shown on the field logs, the exploration pits generally encountered a thin layer of fill materials overlying natural sand and silt sediments. The following section presents more detailed subsurface information organized from the upper (youngest) to the lower (oldest) ' sediment types. 4.1 Stratigraphy Alluvium ' Below the topsoil layer, loose sand to medium dense sandy gravel was encountered. This material is interpreted to be postglacial alluvial deposits. Alluvium is sediment deposited in ' streams or rivers and is sorted by the flow energy of the particular event. In a high-energy stream environment, typically coarse-grained sediments, such as gravels and cobbles, are deposited. In a low-energy stream environment, fine-grained sediments, such as silts and ' sands, are deposited. Because this material is generally encountered in river valleys, a high ground water table is also typical. 4.2 Hydrology We found that the shallow ground water table in the vicinity of our explorations was roughly 13 to 15 feet below existing grade. We believe this to be so due to the saturated nature of the ' 3 sediments encountered in our borings from depths of 13 and 15 feet and below. Due to the project's proximity to the Cedar River, it is likely that the ground water level is directly related to the level of the river. It should be noted that fluctuations in the level of the ground water table may occur due to the time of the year and variations in rainfall amounts. No surficial standing water or drainage channels were noted during our site work, however, the Cedar River was located roughly 300 feet to the south of the project. 1 1 1 ' 4 ' July 3, 1997 Project No. G97159A H. DESIGN RECOMMENDATIONS 5.0 INTRODUCTION Our exploration indicates that, from a geotechnical standpoint, the parcel is suitable for the proposed development provided the recommendations contained herein are properly followed. It is our opinion that the subsurface sediments, based on the density of the sediments and the depth to ground water, will not be subject to liquefaction (loss of internal strength) during a ' seismic event. As such, we recommend that the proposed structure be founded on conventional spread footings. However, due to the loose nature of the near surface sediments, compaction of the footing subgrades will be necessary prior to concrete placement. ' 6.0 SITE PREPARATION Site preparation of the planned building and paved areas should include the removal of all ' topsoil, grass and any other deleterious material. Additionally, the remaining roots should be grubbed. ' Due to the loose nature of the upper zone of the alluvial soils, densification of the native sediments will be necessary prior to footing/slab-on-grade construction. Following clearing and grubbing, we recommend that the upper 4 feet of soil be removed from the building envelope. We recommend also that the excavation extend a minimum of 7 feet beyond the edges of all perimeter footings. The material removed from the excavation should be ' stockpiled onsite and protected from rain and erosion. The base of the resultant excavation should be compacted by a minimum 10-Ton vibratory compactor to at least 90 percent of its maximum dry density. Following density testing of the subgrade, the resultant excavation ' should be backfilled to the base of footing elevation with the onsite granular soils following the recommendations presented in the Structural Fill section of this report. ' In our opinion, stable utility trench slopes should be the responsibility of the contractor and should be determined during construction. We recommend that temporary, unsupported cut slopes in the alluvial sediments be made no steeper than 2H:1 V (Horizontal:Vertical) due to ' the loose nature of the soils within the upper zone of the alluvial stratum. As is typical with earthwork operations, some sloughing and raveling may occur and cut slopes may have to be adjusted in the field. In addition, WISHA/OSHA regulations should be followed at all times. The near surface alluvial sediments contain a high percentage of fine-grained material, which makes them moisture-sensitive, and subject to disturbance when wet. The contractor must use care during site preparation and excavation operations so that the underlying soils are not ' softened. If disturbance occurs within proposed paved areas, the softened soils should be either recompacted or removed and the area brought to grade with structural fill. Because the near surface soils are considered moisture sensitive, consideration should be given to protecting construction vehicle access and staging areas with a minimum 1 foot layer of crushed quarry rock. ' 7.0 STRUCTURAL FILL As previously mentioned, structural fill will be necessary to provide a structural pad for the proposed building. All references to structural fill in this report refer to fill type, placement and compaction of materials as discussed in this section. ' Structural fill is defined as non-organic soil, acceptable to the geotechnical engineer, placed in maximum 8 inch loose lifts with each lift being compacted to at least 95 percent of its maximum dry density as determined by ASTM:D 1557. ' The contractor should note that any proposed fill soils must be evaluated by Associated Earth Sciences, Inc. prior to their use as fill. This would require that we have a sample of the material at least 48 hours in advance to perform a Proctor test and determine its field ' compaction standard. Soils in which the amount of fine-grained material (smaller than No. 200 sieve) is greater than approximately 5 percent (measured on the minus No. 4 sieve size) should be considered moisture-sensitive. Use of moisture-sensitive soil in structural fills should be ' limited to favorable dry weather conditions. The onsite soils within the upper 10 feet were near their optimum moisture content at the time of our explorations. We anticipate that the onsite soils will be suitable for use as structural fill during dry season construction. ' Construction equipment traversing the site when the soils are wet can cause considerable disturbance. If fill is placed during wet weather or if proper compaction cannot be obtained, a select import material consisting of a clean, free-draining gravel and/or sand should be used. Free-draining fill consists of non-organic soil with the amount of fine-grained material limited to 5 percent by weight when measured on the minus No. 4 sieve fraction. ' A representative from our firm should be present during placement of structural fill to observe the work and perform a representative number of in-place density tests. In this way, the ' adequacy of the earthwork may be evaluated as filling progresses and any problem areas may be corrected at that time. It is important to understand that taking random compaction tests on a part-time basis will not assure uniformity or acceptable performance of a fill. As such, we are available to aid the owner in developing a suitable monitoring and testing program. 8.0 FOUNDATIONS Spread footings may be used for building support when founded on approved structural fill. ' An allowable bearing pressure of 2,000 pounds per square foot (psf) should be used for design ' 6 purposes, including both dead and live loads. An increase of one-third may be used for short- term wind or seismic loading. Perimeter footings should be buried at least 18 inches into the surrounding soil for frost protection. All footings should have a minimum width of 18 inches. ' It should be noted that the area bounded by lines extending downward at 1H:1V from any footing must not intersect another footing, filled area, or loose native sediments which have not been compacted to at least 95 percent of ASTM:D 1557. Anticipated settlement of footings founded on approved structural fill should be on the order of 1 inch or less. However, disturbed soil not removed from footing excavations prior to footing placement, could result in increased settlements. Perimeter footing drains should be provided as discussed under the section on Drainage Considerations. 9.0 FLOOR SUPPORT ' Slab-on-grade floors may be used over approved structural fill. The floor should be cast atop a minimum of 4 inches of washed pea gravel to provide a capillary break and a polyethylene plastic vapor barrier should be used under the floor to help prevent passage of moisture through the floor. Based on American Concrete Institute recommendations, we suggest placing a two to three inch layer of clean sand over the vapor barrier to protect the barrier and to allow ' some moisture loss through the bottom of the slab to aid in the curing process. 10.0 DRAINAGE CONSIDERATIONS All perimeter footings should be provided with a drain at the bottom of the footing. Drains ' should consist of rigid, perforated, PVC pipe surrounded by washed pea gravel. The level of the perforations in the pipe should be set approximately 2 inches below the bottom of the footing and the drains should be constructed with sufficient gradient to allow gravity discharge away from the building. Roof and surface runoff should not discharge into the foundation drain system but should be handled by a separate, rigid tightline drain. In planning, exterior grades adjacent to walls should be sloped downward away from the structure to achieve surface drainage. ' 11.0 EROSION CONSIDERATIONS ' To mitigate the erosion potential and offsite sediment transport, we recommend the following: 1) Construction should not take place during periods of heavy rains if traffic within ' the site disturbs the underlying soils. Disturbed areas should be re-vegetated as soon as possible. 1 7 ' 2) Soils that are to be used around the site should be stored in such a manner as to reduce erosion. Protective measures may include, but are not necessarily limited to, covering with plastic sheeting, the use of low stock-piles in flat areas, or the use of hay bales/silt fences. ' 12.0 PROJECT DESIGN AND CONSTRUCTION MONITORING We are available to provide additional geotechnical consultation as the project design develops and possibly changes from that upon which this report is based. We recommend that Associated Earth Sciences, Inc. perform a geotechnical review of the plans prior to final design completion. In this way, our earthwork, foundation and pavement recommendations may be properly interpreted and implemented in the design. We are also available to provide geotechnical engineering and monitoring services during construction. The integrity of the foundations and pavements depends on proper site ' preparation and construction procedures. In addition, engineering decisions may have to be made in the field in the event that variations in subsurface conditions become apparent. ' Construction monitoring services are not part of this current scope of work. If these services are desired, please let us know and we will prepare a cost proposal. ' We have enjoyed working with you on this study and are confident that these recommendations will aid in the successful completion of your project. If you should have any questions, or require further assistance, please do not hesitate to call. ' Sincerely, ASSOCIATED EARTH SCIENCES, INC. ' Kirkland, Washington ' D. K w�F WA '] 3 ti • a ' OVA 325855 V� ICI 44 `� ssIO1VALE�G EXPIRES � Z5Ronald A. Parker, P.G. Stephen D. Kunzweiler, P.E. Principal Senior Staff Engineer SDK/ld-G97159A1-6/10197 Id-W W 8 �■ M M ooa E.1 eer LEGEND EB-1 0Approximate location of exploration boring IT NORTH REFERENCE: BASE MAP PROVIDED BY CLIENT. SITE AND EXPLORATION PLAN o ioo zoo ASSOCIATED O & ASSOCIATES BUILDING SCALE IN FEET EARTHRENT RENTON, WASHINGTON '�ZMSCIENCES, INC G97159A 6/97 FIGURE 1 EXPLORATION BORING LOG ' Number EB-1 Page 1 of 2 STANDARD PENETRATION ' SEDIMENT DESCRIPTION ~ d Z w RESISTANCE W 2 0 Q Blows/Foot U) 0 U 110 20 30 40 I 1 I i I Dry, brown, medium SAND. (Alluvium) 5 -4 Moist, brown, fine SAND, gravel at 12'. (Alluvium) 10 1 1 ' --- No sample. 15 WD I I i 20 21 Saturated, gray, gravelly, fine to coarse SAND with silt. (Alluvium) — — 25 I ' Saturated, gray, sandy, fine to coarse GRAVEL with silt. 84 (Alluvium) 30 T — ' % 40 I Subsurface conditions depicted represent our observations at the time and location of this exploratory hole,modified by geologic interpretations,engineering analysis,and judgment. They are not necessarily representative of other times and locations. We will not ' accept responsibility,for the use or Interpretation by others of Information presented on this log. Reviewed By ' Associated Earth Sciences, Inc. Humbolt and Associates Building 911 Fifth Avenue, Suite 100 Renton, Washington ' Kirkland, Washington 98033 Project No. G97159A Phone: 206-827-7701 June 1997 Fax: 206-827-5424 EXPLORATION BORING LOG ' Number EB-1 Page 2 of 2 STANDARD PENETRATION F d Z w RESISTANCE ' SEDIMENT DESCRIPTION o ¢ 0 Blows/Foot 10 20 30 40 Saturated, gray, fine to coarse SAND. (Alluvium) i A 22 I 40 — 54 45 — ' 48 BOH @ 46-1/2' 1 50 _ I ' 55 I ' -- 60 - I I --- 65 ------------------- I Subsurface conditions depicted represent our observations at the time and location of this exploratory hole,modified by geologic interpretations,engineering anatysis,and judgment. They are not necessarily representative of other tines and locations. We will not ' accept responsibility for the use or interpretation by others of Information presented on this log. Reviewed By L-5D� ' Associated Earth Sciences, Inc. Humbolt and Associates Building 911 Fifth Avenue, Suite 100 Renton, Washington Kirkland, Washington 98033 Project No. G97159A Phone: 206-827-7701 June 1997 Fax: 206-827-5424 EXPLORATION BORING LOG ' Number EB-2 Page 1 of 2 STANDARD PENETRATION ' F- d Z W RESISTANCE SEDIMENT DESCRIPTION Q Q 0 Blows/Foot m ' 110 20 30 40 I ' Dry, brown, fine SAND with a 2" lens of silt at 6'. 5 (Alluvium) ♦3 I Dry, brown, sandy, fine to coarse GRAVEL with silt. 10 (Alluvium) I 1 35 i saturated at 13' and below - ' 15 — _. Saturated, gray, sandy, fine to coarse GRAVEL with silt. j WD ♦14 ' (Alluvium) I 1 20 1 1 ♦ j 25 I ' - 25 1 2♦ i I - 30 r 1 11 I♦4 Subsurface condltions depicted represent our observations at the time and location of this exploratory hole,modified by geologic ' Interpretations,engineering analysis,and judgment. They are not necessadly representative of other times and locations. We will not accept responsibility for the use or Interpretation by others of Information presented on this log. Reviewed By 5D y- Associated Earth Sciences, Inc. Humbolt and Associates Building 911 Fifth Avenue, Suite 100 Renton, Washington t Kirkland, Washington 98033 Project No. G97159A Phone: 206-827-7701 June 1997 Fax: 206-827-5424 EXPLORATION BORING LOG Number EB-2 Page 2 of 2 STANDARD PENETRATION SEDIMENT DESCRIPTION a- a Z w RESISTANCE LU O= Q Blows/Foot 0 ' 10 20 30 40 Saturated, gray, fine to coarse GRAVEL with silt. 38♦' (Alluvium) I ' 40 r -- 39 i 1 45 I 35 BOH @ 46-1/2' I 1 - 50 - i 1 60 i -- 65 — 1 _ 1 subsurface conditions depicted represent our observations at the time and location of this exploratory hole,modifled by geologic 1 interpretations,englneenng analysis,and Judgment. They are not necessarily representative of other tines and locations. We vdll not accept responsibility for the use or interpretation by others of Information presented on this log. Reviewed By 1 Associated Earth Sciences, Inc. Humbolt and Associates Building 911 Fifth Avenue, Suite 100 Renton, Washington 1 Kirkland, Washington 98033 Project No. G97159A Phone: 206-827-7701 June 1997 Fax: 206-827-5424