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HomeMy WebLinkAbout03257 - Technical Information Report - Preliminary �„� �'`. � ��,Q� � � .�� � 3 s`l �.Y3 � S� .� _. ._._�; : - -....ti:.-:'. "3 .� v. � � � � - �% � � f:+� t . � Jy�Tf= - AsSo � l �.te � r� �-_� :- - E � rth � £ � Geoter_hnical �ngineering � � � ; � � � � � �� � , � t�._. � � �,,_. __ � � � _.�.. --�-�� �"'"""""'�''�� Subsurface Exploration, Geologic Hazards, and Preliminary Geotechnical Engineering Report Water Resources �� PROPOSED - �:.' MAINTENANCE AND CLASSROOM � BLTILDING RE-SITE � � RENTON TECHNICAL COLLEGE ;� -: ,'_ Y��. � Renton, Washington Solid and Hazardous Waste 11�1 Prepared for - �__ ���"j Renton Technical College � ,�� � ^�:�; c/o S.M. Stemper Architects, PLLC — z �, -,��,_ _. 'P:c���-�c,,� �c�_ ._�� _sv Project No. KE05606A � � October 13, 2005 �`�_ =�. ,;� ,. :� ,� � �� i -�.�i.. - j-` . ti-. CITYOFRE��y �`� �ECE �� Geologic Assessments � MAR ti 5 2� �� �i�S3lRG�?tt����`�^' Associated Earth Sciences, Inc. ', �:� � � '�i � _� .� 1 : October 13, 2005 Project No. KE05606A Renton Technical College c/o S.M. Stemper Architects, PLLC 4000 Delridge Way SW, Suite 200 Seattle, Washington 98106 ' Attention: Ms. Sally MacGregor Subject: Subsurface Exploration, Geologic Hazards, and Preliminary Geotechnical Engineering Report Proposed Maintenance and Classroom Building Re-site Renton Technical College 3000 NE 4`� Street Renton, Washington Dear Ms. MacGregor: We are pleased to present the enclosed copies of the above-referenced report. This report summarizes the results of our subsurface exploration, geologic hazards, and preliminary geotechnical engineering study and offers recommendations for the preliminary design and development of the proposed project. Our recommendations are preliminary in that site grading, structural plans, and construction methods have not been finalized at the time of this report. We have enjoyed working with you on this study and are confident that the recommendations presented in this report will aid in the successful completion of your project. If you should have any questions or if we can be of additional help to you, please do not hesitate to call. Sincerely, ASSOCIATED EARTH SCIENCES, INC. Kirkland, Washington � ` 7 Kurt D. Merriman, P.E. Principal Engineer KDMiId-KEOi606A3-Projeccs�2005606iKE1WP � � � _ i i . � ��f- � �. � , SUBSURFACE EXPLORATION, GEOLOGIC HAZARDS, AND PRELIlVIINARY GEOTECHIVICAL ENGINEERING REPORT PROPOSED MAINTENANCE AND CLASSROOM BUILDING RE-SITE RENTON TEC�INICAL COLLEGE I Renton, Washington I Prepared for: Renton Technical College c/o S.M. Stemper Arclutects, PLLC 4000 Delridge Way SW, Suite 200 Renton, Washington 98106 Prepared by: Associated Earth Sciences, Inc. 911 5`� Avenue, Suite 100 Kirkland, Washington 98033 425-827-7701 Fax: 425-827-5424 October 13, 2005 Project No. KE05606A Proposed Maintenance/Classroan Building (Building N) Subsurface Exploration, Geologic Ha<.ards, Renton Technical College and Preliminary Geotechnical Engineering Report Renton, Washington Project and Site Conditions I. PROJECT AND SITE CONDITIONS 1.0 INTRODUCTION This report presents the results of our subsurface exploration, geologic hazards, and preliminary geotechnical engineering study for the proposed Maintenance/Classroom Building (Building N) within the Renton Technical College campus located at 3000 NE 4�' Street, Renton, Washington. The general location of the site is depicted on the Vicinity Map, Figure l. The proposed building location and approximate locations of the explorations accomplished for this study are presented on the Site and Exploration Plan, Figure 2. Our recommendations are preliminary in that site grading, structural plans, and construction methods have not been finalized at the time of this report. In the event that any changes in the nature, design, or location of the structure are planned, the conclusions and recommendations contained in this report should be reviewed and modified, or verified, as necessary. 1.1 Purpose and Scope The purpose of this study was to provide subsurface data to be utilized in the preliminary design and development of the subject project. Our study included a review of available geologic literature, excavating an exploration pit, drilling an exploration boring, and performing geologic studies to assess the type, thickness, distribution, and physical properties of the subsurface sediments and shallow ground water conditions. Infiltration testing was conducted within the exploration pit. Geologic hazard evaluations and geotechnical engineering studies were also conducted to deternune suitable geologic hazard mitigation techniques, the type of suitable foundation, allowable foundation soil bearing pressures, anticipated settlements, temporary slope/shoring recommendations, basement/retaining wall lateral pressures, floor support recommendations, and drainage considerations. This report summarizes our current fieldwork and offers hazard mitigation, development, and infiltration recommendations based on our present understanding of the project. 1.2 Authorization Authorization to proceed with this study was granted by Ms. Sally MacGregor of S.M. Stemper Architects, PLLC. Our study was accomplished in general ac�ordance with our proposal letter dated August 25, 2005. This report has been prepared for the exclusive use of Renton Technical College, S.M. Stemper Architects, PLLC, and their a��nts for specific application to this project. Within the limitations of scope, schedule, and bud�et, 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, express or implied, is made. It must be understood that no recommendations October 10, 2005 ASSOCIATED EARTH SCIENCES, INC. .i1T/(d-KE05606A2-Projects120056061KE1WP Page 1 Proposed Maintenance/Classroom Building (Building 1� Subsurface Fxploration, Geologic Hazards, Renton Technical College and Preliminary Geotechnical Engineering Report Renton, Washington Project and Site Conditions or engineering design can yield a guarantee of stable slopes. 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 information provided in a letter dated August 22, 2005 by S.M. Stemper Architects, PLLC, and an attached copy of a portion of the Renton Technical College campus map showing the proposed location of the maintenancelclassroom building. Present plans call for a two-story structure with daylight basement with slab-on-grade floors planned for the basement area of the building. The lowest level will be set at approximately the same elevation as the westerly adjacent parking area. The second floor of the proposed new building will be at approximately the same elevation as the easterly adjacent Building M. The property is situated at 3000 NE 4`� Street in Renton, Washington and is the site of Renton Technical College. The proposed new building will be situated within the northern portion of the school campus. An asphalt concrete parking area extends along the western edge of the proposed building area. A retaining wall, ranging in height to approximately 6 feet, extends generally north-south within the eastern portion of the site to be developed. The retaining wall retains an easterly adjacent play area for the child care Building M located east of the proposed building. A moderate, 15- to 20-foot-high, grass-covered slope descends across the proposed building area from the east retaining wall to the west parking area. A rockery wall extends along the toe of the slope within the southern portion of the proposed building area. !, The existing site slope is considered by the City of Renton Code to be a "Medium Landslide Hazard," which is defined in the Renton Municipal Code, Chapter 3, Section 4-3-050, paragraph 4.c.ii as "Areas with slopes between fifteen percent (I S%) and forty percent (40%) and underlain by soils that consist largely of sand, gravel or glacial till." Based on topographic information provided to us, the overall slope gradient measured from top to toe of slope is approximately 20 to 40 percent (SH:1V [Horizontal:Vertical] to 2.SH:1V). As proposed, site development will require temporary cuts to a height of approximately ?0 feet along the eastern perimeter of the development. Where space limitations result in temporary , excavations steeper or higher than recommended herein, shoring will be required. The actual location and configuration of the temporary cut will factor into the determination regarding how much and where shoring will be required. Ocrober 10, ?�S ASSOCIATED EARTH SCIE:b'CES, I�ti'C. II MT/!d-KE05606A2-Projects120iD56061KE1WP Page 2 Proposed Maintenance/Classroom Building (Building N) Subsurface Exploration, Geologic Hazards, Renton Technical College and Preliminary Geotechnical Engineering Report Renton, Washington Project and Site Conditions 3.0 SUBSURFACE EXPLORATION Our field study included drilling one exploration boring, excavating one exploration pit, perfornung infiltration testing, and conducting a geologic and geologic hazard reconnaissance to gain information about the site. The various types of sed'unents, as well as the depths where � characteristics of the sed'unents 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. If changes occurred between sample intervals, they were interpreted. Our explorations were approximately located in the field by estimation from known site features shown on the site plan provided to us. The conclusions and recommendations presented in this report are based on subsurface conditions revealed in the exploration boring and exploration pit completed for this study. The number, locations, and depths 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 vaziations are observed at that time, it may be necessary to re-evaluate specific recommendations in this report and make appropriate changes. 3.1 Exploration Boring The exploration boring was completed by advancing a 33/s-inch, inside-diameter, hollow-stem auger with a track-mounted drill rig. During the drilling process, samples were obtained at generally 2.5- or 5.0-foot-depth intervals. The boring was continuously observed and logged by a geotechnical engineer from our firm. The exploration log presented in the Appendix is based on the field log, drilling action, and inspection of the samples secured. Disturbed but representative samples were obtained by using the Standard Penetration Test (SPT) procedure in accordance with American Society for Testing and Materials (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 a total of 50 is recorded within one 6-inch interval, the blow count is recorded as the number of blows for the corresponding 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 ��n the attached boring log. October 10, ?00� ASSOCIATED EARTH SCIENCES, 1.�'C. MT/Id-KE05606A2-Projectsl?0p560C�KEiWP Page 3 i� Proposed Maintenance/Classroom Building (Building 1� Subsurface Exploration, Geologic Hazards, Renton Technical College and Preliminary Geotechnical Engineering Report Renton, Washington Project and Site Conditions ' 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. 3.2 Exploration Pit The exploration pit completed for this study was excavated with a rubber-tired backhoe. The exploration pit permitted direct, visual observation of subsurface conditions. Materials encountered in the exploration pit were studied and classified in the field by a geotechnical i engineer from our firm. The exploration pit was backfilled immediately after examination and � logging. Selected samples recovered from the exploration were transported to our laboratory for further visual classification and testing, as necessary. 3.3 Infiltration Testing An infiltration test was conducted at a depth of approximately 5 feet below existing ground surface in infiltration pit IP-1 in the vicinity of the proposed storm water management structure adjacent to the southwest corner of the proposed maintenance/classroom building. The infiltration testing was conducted using a method generally corresponding to the procedure � described for the Pilot Infiltration Test (PIT) in the Washington State Department of Ecology 2001 Stormwater 1l�anagement Manual for Western Washington (Ecology Manual). This test is conducted by discharging water into a flat-bottomed pit of known dimensions for a 4-hour "soai�ing period" to allow the receptor soils in the immediate vicinity of the pit to become saturated. After completion of the soaking period, water is discharged into the pit at a rate sufficient to maintain a constant head in the pit. This is continued until the discharge rate required to maintain a constant head remains fairly consistent over a period of 1 hour. Ground water infiltration was conducted inside a large-diameter (72-inch-diameter) iron ring embedded into the unweathered advance outwash soil. The large-diameter ring was used in lieu of the open pit described in the Ecology Manual to avoid or reduce testing errors due to such factors as sidewall collapse, inaccurate measurement of open pit areas, and sidewall infiltration. The water source used for the test consisted of a fire hydrant located near the northwest corner of the Renton Technical College campus. Water was discharged into the pit through a fabric diffuser to minimize turbulence and scouring of the pit bottom. A flow meter/totalizer was 'i used to monitor the water discharge rate and total flow. A staff gauge with 0.01-foot divisions ' was installed to monitor the depth of water during testing. For the constant head test, a head � of approximately 0.53 feet was maintained in the pit. Following completion of the constant head test, the flow of water into the pit was discontinued, and the rate of water level decline (falling head) in the pit was monitored. Upon completion of the test, the pit was excavated to a depth of 10 feet to allow observation of soil conditions below the elevation of the test. The infiltration pit was backfilled immediately after examination and logging. Selected samples October 10, 2005 ASSOCIATED EARTH SCIENCES, INC. MT/ld-KE05606A2-Projects12005G06iKEIWP Page 4 _ __ _ _ _ _ __. _—�1 Proposed Maintenance/Classroom Building (Building N) Subsurface Fxploration, Geologic Hazards, Renton Technical College and Preliminary Geotechnical Engineering Report Renton, Washington Project and Site Conditions , recovered from the exploration were transported to our laboratory for further visual classification and testing, as necessary. All infiltration test data was recorded by hand in the field and subsequently transferred to an electronic spreadsheet to allow more accurate and consistent infiltration rate calculations. The ' infiltration testing results are summarized below in Table 1. The infiltration rate measured during the constant head test was equal to or slightly greater than the rate measured during the falling head test. This is typical and is reflective of the decreasing head in the pit below that maintained during the constant head test. Table 1 Summary of Infiltration Testing Results Infiltration Rate Constant Head Test Falling Head Test Test No. (in/hr)cn (in/hr)�'� ' IP-1 14.6 12 �'� in/hr = inches per hour 3.4 Laboratory Testing ' In order to provide a prelirninary infiltration rate estimate based on published correlation to soil grain size, samples were submitted for mechanical grain size analysis testing in accordance with ASTM:D 1140. A summary of preliminary testing results is provided below in Table 2. Table 2 Summary of Laboratory Testing Results Percent Silt Infiltration Pit Sample Depth (% passing No. (feet) Soil Type No. 200 sieve) IP-1 0 - 5 SAND, trace silt 2.9 IP-1 5 - 7 SAND, trace silt 2.8 IP-1 7 - 10 SAND, trace silt 4.3 October 10, 2005 ASSaCIATED EARTH SCIENCES, INC. ,r;.:,i-�eos�h,a=-Pr�;P�_�;�.00;�,��xe�wP Page 5 ' Proposed Maintenance/Classroom Building (Building N) Subsurface Fzploration, Geologic Hazards, Renton Technical College and Preliminary Geotechnical Engineering Report Renton, Washington Project and Site Conditions 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. Exploration boring EB-1 was drilled within the higher elevation, eastern portion of the site; � exploration pit EP-1 and infiltration pit IP-1 were excavated near the toe of the slope within the southerly portion of the proposed structure. As shown on the field logs, exploration boring EB-1 encountered approximately 2 feet of relatively loose, sandy fill overlying medium dense, stratified, fine to coarse sand and limited silt to the bottom of the exploration boring at 21.5 feet. Infiltration pit IP-1 encountered approximately 2.5 to 3 inches of asphalt concrete surfacing underlain by a 1-inch thickness of fine crushed gravel over medium dense, stratified, fine to medium sand with a trace of silt to the bottom of the pit at 10 feet. A silty fine sand lens was encountered at a depth of 7 feet within the infiltration pit. Exploration pit EP-1 encountered approxunately 1 foot of loose sand fill over medium dense, stratified, fine to medium sand with a trace of silt to the bottom of the pit at 10 feet. The following sections present more detailed subsurface information. 4.1 Stratigraphy Fill Fill soils (those not naturally placed) were encountered to a depth of approxirnately 2 feet in exploration boring EB-1 and in exploration pit EP-1. With the exception of the asphalt � surfacing and underlying crushed rock base, no fill was encountered in infiltration pit IP-1. Based on the classification of the native soils encountered on-site, it is considered likely that the fill soil was derived from on-site sources and placed during one of the phases of earlier site I development. The fill generally consisted of a loose mixture of silt and sand. The fill soils, as observed, are considered unsuitable for support of the proposed structure. Existing fill soil may be considered for use as structural fill where moisture-conditioned and compacted as recommended in the Structural Fill section of this report. Fill depth may vary across the proposed building area. Fill is also anticipated along the east side of the retaining wall along the eastern portion of the area to he developed. Vashon Recessiorial Ounvash Below the fill, a medium dense, stratified mixture of fine to coarse sand with a trace of silt interpreted as Vashon recessional outwash was encountered. The Vashon recessional outwash was deposited by meltwater streams that emanated from the retreating glacial ice during the latter portion of the Vashon Stade of the Fraser Glaciation approximately 13,000 years ago. The upper portion of the recessional outwash sediments encountered during our exploration typically contained substantial quantities of silt. The weathered recessional outwash horizon was typically limited to the portion of this unit located within approximately 4 feet of the October 1 D, 2005 ASSOCIATED EARTH SCIENCES, INC. ,41T.-:d-KE05606A2-Projec�s12005606�KE144`P Page 6 Proposed Maintenance/Classroom Building (Building N) Subsurface�rploration, Geologic Hazards, Renton Technical College and Preliminary Geotechnical Engineering Report Reraon, Washington Project and Site Condirions ground surface. Where encountered during our exploration, the Vashon recessional outwash sediments extended to depths in excess of the maximum depth explored. ', 4.2 Hydrology No ground water/seepage was encountered in our explorations. It should be noted that fluctuations in the level of the ground water may occur due to the tune of the year, variations in rainfall, irrigation, on- and off-site land usage, and other factors. 4.3 Site Inf'iltration The Ecology Manual defines three methods for detemuning long-term infiltration rate. The methods are identified in the following paragraphs and results, as related to the project site, are presented. Method 1 The results of grain size analyses conducted on soil samples obtained from IP-1 excavated in the vicinity of the proposed storm water facility indicate a silt content ranging between 0.6 and 4.7 percent. Using the United States Department of Agriculture (USDA) Textural Triangle presented as Figure 7.1 in the Ecology Manual, the texture of the samples tested is determined to be sand. Using this texture classification in conjunction with Table 7.1 in the Ecology Manual, an estimated long-term (design) infiltration rate of 2 inches per hour, whieh includes a correction factor (CF) of 4, is considered appropriate for site soils. Method 2 The second method, Method 2, presented in the Ecology Manual, allows estunation of long- term (design) infiltration rate directly from soil gradation data. This method requires a determination of the effective size of the grains comprising tbe soil. The effective size (D�o) is defined as the size corresponding to 10 percent on the grain size curve. The effective size of soil within samples obtained from the site ranges from approximately 0.15 millimeter (mm} (IP-1 at 7 to 10 feet) to 0.25 mm (IP-1 at 5 to 7 feet). Using the effective size determined for samples tested and Table 7.2 presented in the Ecology Manual, the corresponding estimated long-term (design) infiltration rate for site soil ranges from 2 to 3.5 inches per hour. Method 3 As described in Section 3.3 Infiltration Testing, a PIT was conducted in general conformance with Method 3 presented in the Ecology Manual. The results of the test indicated an infiltration rate of 14.6 inches per hour. October 1 D, 2005 ASSOCIATED EARTH SCIENCES, INC. ,�Lf771d-KE05606A2-Projects120056061KEIWP Page 7 Proposed Mainrenance/Classroom Building (Building N) Subsurface Exploration, Geologic Hazards, Renton Technical College and Preliminary Geotechnical Engineering Report Renton. Washington Project and Site Conditions Infiltration Design (Long-Term) Rate Subsurface conditions encountered during site exploration indicated soil stratification and relatively minor fine soil lenses within the soil underlying the site. Based on observations during site exploration in combination with the results of the PIT and the long-term infiltration " rate determined by the two methods described above, we recommend a maximum design infiltration rate of 2 inches per hour. To enhance the performance of the proposed infiltration system so that a design rate of 2 inches per hour can be used without additional reduction factors, we recommend construction of vertical gravel drains to extend beneath the base of the system through any silty soil layer to allow for a vertical hydraulic connection between the system and the underlying sand stratum. It is our understanding that Stormtech chambers will be used for the site infiltration system. Typical gravel drains for the proposed system would consist of trenches measuring 10 feet deep, 2 feet wide, and 4 feet long filled with pea gravel and covered with filter fabric. For preliminary planning, approximately one gravel drain is recommended beneath each Stormtech SC-740 chamber group (nominal chamber dimensions: 48 inches deep, 51 inches wide, and 90.7 inches long). Placement of recommended drains effectively doubles the storage capacity of the system, provides greater surface area for infiltration to occur, and significantly improves vertical infiltration preventing adverse ground water mounding effects. October 10, 2005 ASSOCIATED EARTH SCIENCES, INC. MT/!d-KE05606A2-Projects12Q056061KE1WP Page 8 Proposed Maintenance/Classroom Building (Building N) Subsurface Exploration, Geologic Hazards, Renton Technical College and Preliminary Geotechnical Engineering Report Renton, Washington Geologic Hazards and Mitigarions II. GEOLOGIC HAZARDS AND MITIGATIONS The following discussion of potential geologic hazards is based on the geologic, slope, and ground water conditions as observed and discussed herein. The discussion will be limited to seismic, landslide or mass wasting, and erosion, including sed'unent transport. 5.0 SEISMIC HAZARDS AND RECOMMENDED MITIGATION � Earthquakes occur in the Puget Lowland with great regularity. The vast majority of these ', events are small and are usually not felt by people. However, large earthquakes do occur as evidenced by the 1949, 7.2-magnitude event; the 1965, 6.5-magnitude event; and the 2001 6.9- magnitude event. The 1949 earthquake appears to have been the largest in this area during recorded history. Evaluation of earthquake return rates indicates that an earthquake of the magnitude between 5.5 and 6.0 is likely within a given approximate 20-year period. Generally, there are four types of potential geologic hazards associated with large seismic events: 1) surficial ground rupture; 2) liquefaction; 3) ground motion; and 4) seismically induced landslides. The potential for each of these hazards to adversely impact the proposed project is discussed below. 5.1 Surficial Ground Rupture Generally, the largest earthquakes that have occurred in the Puget Sound area are sub-crustal events with epicenters ranging from 50 to 70 kilometers in depth. For this reason, no surficial faulting or earth rupture as a result of seismic activity has been documented to date within at least 5 miles of the site. Therefore, it is our opinion, based on existing geologic data, that the risk of surface rupture impacting the proposed project is low, and no mitigations are necessary. 5.2 Liquefaction Liquefaction is a process through which unconsoli�iated soil loses strength as a result of vibratory shaking, such as that which occurs during a seismic event. During normal conditions, the weight of the soil is supported by both grain-to-grain contacts and by the pressure within the pore spaces of the soil below the water table. Extreme vibratory shaking can disrupt the grain-to-grain contact, increase the pore pressure, and result in a decrease in soil shear strength. The soil is said to be liquefied when nearly all of the weight of the soil is supported by pore pressure alone. Liquefaction can result in deformation of the sediment and settlement of overlying structures. Areas most susceptible to liquefaction include those areas underlain by coarse silt and sand with low relative densities accompanied by a shallow water table. ' October 10, 2005 ASSOCIATED EARTH SCIENCES, INC. �t1T'!d-KE05606A2-Projects12Q056061KEIW'P Page 9 Proposed Maintenance/Classroom Building (Building N) Subsurface Fxploration, Geologic Hazards, I Renton Technical College and Preliminary Geotechnical Engineering Report Renton, Washington Geologic Hazards and Mitigations The majority of the soils encountered in our explorations were in a medium dense to dense ; condition and therefore do not present a significant liquefaction hazard. Based on soil density ', and the absence of ground water, site soils are considered to have a low potential for ,, liquefaction. 5.3 Ground Motion Based on site stratigraphy and visual reconnaissance of the site, it is our opinion that any earthquake damage to the proposed structure founded on suitable bearing strata would be caused by the intensity and acceleration associated with the event and not any of the impacts discussed in the Seismic Hazards and Recommended Mitigation section of this report. Structural design of the building should take into consideration stress caused by seismically induced earth shaking. Due to the thickness and consistency of the sediments underlying the site, amplification of seismic motion upward through this soil column is possible. The approximate proposed building period should be compared to the estimated soil column period of vibration to check for resonant conditions. It is these conditions that result in our recommendation for the more stringent Site Class D for use with the International Building Code (IBC), as discussed below. Guidelines presented in the 2003 IBC, Section 1615, may be used. Information presented in � Figure 1615(1) indicates a mapped spectral acceleration for short periods of S5 = 1.37. I Information presented in Figure 1615(2) indicates a mapped spectral acceleration for a 1- II second period of S� = 0.47. Based on the results of subsurface exploration and on an !, estimation of soil properties at depth utilizing available geologic data, Site Class D in li conformance with Table 1615.1.1 may be used. Site coeff'icients Fa = 1.0 and F� = 1.5 in ' conformance with IBC Tables 1615.1.2(1) and 1615.1.2(2), respectively, may be used. � 5.4 Seismically Induced Landslides I The existing slope within the building area is to be removed and replaced with a retaining wall as a part of site development. Therefore, the potential risk of seismically induced landslides affecting the proposed structure is eliminated. No mitigations are recommended regarding seismically induced landslides. Slope stability is discussed further in the following section. 6.0 LANDSLIDE HAZARDS AND MITIGATION Generally, there are two rypes of landslides that commonly occur in the Puget Sound region. The first type is termed Earth Slump or Slump-Earth Flow. This type of earth movement is deep-seated and usually involves the regolith (topsoil) and the underlying sedimentary units. Slides of this type can be very large. October 10, 2005 ASSOCIATED EARTN SCIENCES, INC. MT/!d-KE0560fiA2-Projecrs120056061KElWP Page 10 '1 in N Subsu ace Ex loration Geolo ic H r Proposed Maintenance/Classroom Bu�ldcng (But d g ) rf p , g aza ds, Renton Technical College and Preliminary Geotechnical Engineering Repon Renton, Washington Geologic Hazards and Mitigations The second type is termed Debris Slump or Debris Flow and usually involves the upper few feet of the regolith. This type of slide is very dependent on local drainage patterns and the resulting moisture content of the soils. Based on the site stratigraphy and visual geologic reconnaissance, the slope areas appear to be � more susceptible to a shallow debris flow due to the presence of the medium dense outwash soil encountered below the surficially disturbed fill/topsoil horizon. A slope stability analysis was beyond the scope of this study, and therefore the stability risks cannot be quantified by this study. However, it is our opinion, based on previous similar studies and similar slope and soil types, that the seismic and static factors of safety would lie within generally accepted limits and that the deep-seated landslide risks on the site are low under both static and seismic conditions. The proposed development should not increase the risk of deep-seated movements provided the recommendations presented in this report are followed. As discussed earlier in this report, proposed development will eliminate the existing slope within the building area and will eliminate the potential risk of landslides affecting the proposed structure. Slopes will remain north and south of the proposed structure and adjacent to pedestrian walkways. Based on observed evidence of weathering and disturbance due to I burrowing rodents, it is our opinion that shallow movement on the slope areas to remain north I and south of the proposed structure presents a low risk under current site conditions. Since local drainage, slope steepness, slope height, and vegetation cover largely influence the shallow stability and soil erosion, the planned development will require specific mitigation measures to avoid increasing the shallow earth movement risk. These mitigations include controlling runoff, establishing vegetation cover, and following the recommendations as outlined in this report. In our opinion, by following these recommendations, the risk of shallow earth movement on the site or on surrounding properties will not be increased by the proposed construction. 7.0 EROSION HAZARDS AND MITIGATION As defined by the City of Renton, "Erosion hazard areas are identified by the presence of vegetative cover, soil texture, slope, and rainfall patterns, or human-induced changes to such characteristics which create site conditions which are vulnerable to erosion. Erosion hazard areas are classified as having moderate to severe, severe, or very severe erosion potential by the Soil Conservation Service, United States Department of Agriculture (USDA). " Soils in the vicinity of the project are mapped by the USDA as Alderwood gravelly sandy loam on slopes of 6 to 15 percent. Site-specific information from our explorations is in general agreement with the USDA mapping. Some areas of Alderwood soils on slopes of 15 to 30 percent may be encountered, but are not mappable at the USDA map scale. Surface runoff and erosion hazards soil characteristics of these soil types are presented in Table 4. October 10, 2005 ASSOCIATED EARTH SCIENCES, INC. .MT/lQ-K605606A2-P�ojeclsi2Q0560GIKE!RP Page 11 � Proposed Maintenance/Classroom Building (Building N) Subsurface Fxploration, Geologic Hazards, Renlon Technical College and Preliminary Geotechnical Engineering Report Renton, Washington Geologic Hazards and Mitigalions Table 4 Surface Runoff and Erosion Hazard Soil Characteristics Soil Type Percent Slope Surface Runoff Erosion Hazard Alderwood 6 to 15 Medium Moderate Alderwood 15 to 30 Medium to Rapid Moderate to Severe The on-site soils contain a significant amount of fines and are considered moisture-sensitive. Therefore, all permanent and temporary slopes should be protected from erosion. The following general erosion mitigation measures are recommended for use throughout the site. 1. All storm water from impermeable surfaces should be tightlined into approved storm water drainage systems. 2. To reduce the amount of sediment transport from the proposed construction area, silt fencing should be placed along the lower elevations of the cleared areas. 3. Temporary sediment catchment facilities, interceptor drainage swales, and surface conveyance swales should be installed to intercept runoff and eroded sediment prior to site work. Check dams should be installed, as necessary. 4. Earthwork should proceed during the drier summer periods of the year and disturhed areas should be revegetated as soon as possible. Temporary erosion control measures should be maintained until permanent erosion control measures are established. 5. All devices used to collect surface runoff should be directed into a tightline or swale system designed to convey the collected drainage to discharge within an approved storm drain system. 6. Soils that are to �:. reused 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 stockpiles in flat areas, or the use of straw bales/silt fences. 7. Prior to the onset of winter, any exposed subgrade should be hydroseeded, covered with plastic sheeting, or otherwise protected. Seed should be planted soon enough to ', have the grass established by October 31. If suitable ground-cover vegetation is not I ' established prior to the wet season, mulch cover or plastic sheeting should be used. ' October 10, 2005 ASSOCIATED EARTH SCIENCES, INC. �LfT/!d-KE05606A2-Projeas1200560i61KE1 WP Page 12 I Proposed Maintenance/Classroom Building (Building 11� Subsurface Fxploration, Geologic Hazards, I�, Renron Technical College and Preliminary Geotechnical Engineering Repon , Renton, Washington Geologic Hazards and Mitigations ��i 8. At the end of each workday, disturbed areas should be sloped to drain into a storm ' conveyance and seal-rolled to promote surface drainage. 9. A temporary, rock-surfaced construction entrance and staging areas should be I established early in the project sequence. 10. All storm water from impermeable surfaces, including driveways and roofs, should be tightlined into approved facilities and not directed onto or above steeply sloping areas. , 11. As much of the natural vegetation on the slopes as is possible should be left intact i during construction. Sloping areas without sufficient vegetation and areas stripped of vegetation during construction should be planted as soon as possible or otherwise protected. 12. Erosion control measures should be inspected regularly and maintained/improved as necessary to maintain function. 13. The surface of the slopes to remain adjacent to the proposed building and associated hardscape should be scarified, moisture-conditioned as necessary, and compacted. The resulting slope gradient should be as uniform as possible and should match that of the surrounding areas. 14. Regular pest control services should be employed to maintain the site free of burrowing rodents. Associated Earth Sciences, Inc. (AESI) would be available to provide site-specific recommendations upon request. We recommend that an erosion control inspector or the geotechnical engineer make on-site inspections as needed to monitor performance of the erosion control system. In this way, site-specific recommendations, modifications, and construction sequencing decisions can be made during the construction phase. October 10, 200J ASSOCIATED EARTN SCIENCES, INC. 11!`Id-KE0560h4°-Prqie�-ts'?OO�h06iX.E'li�P P$ge ]3 Proposed Maintenance/Classroom Building (Building 1� Subsurface Exploration, Geologic Hazards, Renton Technical College and Preliminary Geotechnical Engineering Report Renton, Washington Preliminary Design Recommendations III. PRELIMINARY DESIGN RECOMMENDATIONS 8.0 INTRODUCTION � : Our exploration indicates that, from a geotechnical standpoint, the project azea is suitable for the proposed development provided that the recommendations contained herein are properly followed. It is our understanding that column loads will be on the order of 100 to 150 kips. Subsurface conditions disclosed by our explorations revealed medium dense to dense advance outwash sediments at a depth of approximately 1 to 2 feet below existing ground surface. , Given the loose nature of the fill and disturbed advance outwash soil, it is not recommended for support of building foundations. The existing fill and disturbed advance outwash materials may be suitable for reuse as structural fill provided the moisture content is maintained within the compactable range. Site development will require temporary cuts to a height of 20 feet (maximum) along the eastern, northern, and southern perimeters of the proposed structure. Where space limitations result in temporary excavations steeper or higher than recommended herein, shoring will be required. The actual location and configuration of the temporary cut will be factors in how much and where shoring will be required. Recommendations are presented in the Shoring - Soldier Pile Walls section of this report. 9.0 SITE PREPARATION Site preparation within the planned building area should include removal of all trees, landscape structures, pavements, brush, debris, and any other deleterious material. Additionally, any organic topsoil should be removed and the remaining roots grubbed. Any buried structures and/or utilities should be removed or relocated if they are encountered under/within the area to be developed. The resulting depressions that extend below or outside the plann�d excavation envelope should be backfilled with structural fill, as discussed under the Structural Fill section of this report. 9.1 Temporary Cut Slopes In our opinion, stable construction slopes should be the responsibility of the contractor and should be determined during construction based on the conditions encountered at a particular location and time. For estimating purposes, however, we anticipate that temporary, unsupported cut slopes in the sandy fill and advance deposit soil can be planned at a maximum slope of 1.SH:1V. To provide additional protection, the top of a cut slope should begin no October 10, 2005 ASSOCIATED EARTH SCIENCES, INC. M19T.�:d-K£05606A2-Pro,�ects'�_'(�5606iK£�A'P Page 14 Proposed Maintenance/Classroom Building (Building N) Subsurface Exploration, Geologic Hazards, Renton Technical College and Preliminary Geotechnical Engineering Report Renton, Washington Preliminary Design Recommendations closer than 5 feet from existing structures such as light poles/hardscape to remain. To reduce the potential for loose, unstable zones on the cut face, we recommend that the surface be recompacted using a backhoe-mounted plate compactor ("hoepac") as the excavation proceeds. Compaction should be performed under the observation of a representative of AESI. As is typical with earthwork operations, some sloughing and raveling may occur and cut slope ' gradient may have to be adjusted in the field. In addition, WISHA/OSHA regulations should ' be followed at all times. Where space limitations result in temporary cuts steeper or higher than recommended herein, shoring will be required. The actual location and configuration of the temporary cut will . factor into determination of how much and where shoring will be required. Recommendations ' are presented in the Shoring - Soldier Pile Walls section of this report. 9.2 Erosion/Piping Protection for Temporary Cuts � Cuts in sandy advance outwash sediments may be prone to localized erosion due to seepage if I encountered. During earthwork, areas determined by the project geotechnical engineer ar geologist to be potentially unstable due to seepage/erosion may require removal of the unstable/saturated soil and placement of a stabilizing rock blanket. If necessary, a rock blanket would typically consist of a minunum, 2-foot-thick prism of 2- to 4-inch-sized crushed quarry , rock embedded in the seepage zone. A layer of filter fabric (Mirafi 140N, or equivalent) should be provided between the rock and the subgrade soil to prevent the migration of fines � through the rock. The requirement for and extent of rock protection for seepage zones can be determined in the field during site earthwork as seepage areas are exposed. In general, late, dry season construction is anticipated to minimize the seepage quantities and the requirements ! for erosion/piping protection. 9.3 Site Disturbance A portion of the on-site soils contains a high percentage of fine-grained material, which makes �, them moisture-sensitive and subject to disturbance when wet. The contractor must use care !,I during site preparation and excavation operations so that the underlying soils are not softened. If disturbance occurs, the softened soils should be removed and the area brought to grade with structural fill. Consideration should be given to protecting any unpaved access and staging areas with an appropriate section of crushed rock or asphalt treated base (ATB). , , If crushed rock is used for the access and staging areas, it should be underlain by engineering I� � stabilization fabric to reduce the potential of fine-grained materials pumping up through the ;� rock and turning the area to mud. The fabric will also aid in supporting construction equipment, thus reducing the amount of crushed rock required. We recommend that at least 10 inches of rock be placed over the fabric; however, due to the variable nature of the near- October 10, 2005 ASSOCIATED EARTH SCIE�ti'CES, Ir�'C. !�fTiTd-KE05606.92-Projects120056061KF_IWP Page 15 Proposed Mainlenance/Classroom Building (Building 1� Subsurface Exploration, Geologic Hazards, Renton Technical College and Preliminary Geotechnical Engineering Report Renton, Washington Preliminary Design Recommendations surface soils and differences in wheel loads, this thickness may have to be adjusted by the contractor in the field. , No information regarding the pavement section existing along the east, west, and south sides of the proposed building area was available to AESI as of the date of this report. It is considered likely that repetitive heavy loading, such as that anticipated by construction traffic, including loaded dump trucks, could cause damage to existing pavement. Repair of these areas as necessary should be included in construction scope and budgets. 10.0 SHORING - SOLDIER PILE WALLS To achieve design daylight basement elevation, an excavation ranging in depth to 20 feet is currently anticipated for this project. Some form of temporary shoring will be required to support the temporary excavation where open cuts in conformance with recommended gradients are not feasible. This section of the report presents preliminary design considerations and criteria that should be considered in the design of the shoring for the excavation. With this information and other pertinent data, it should be the responsibility of the shoring subcontractor(s) to determine the appropriate design, construction methods, and procedures for installation of the shoring system. ', The most common method of shoring used in the area consists of a conventional soldier I pile/waler shoring system utilizing steel soldier piles, sometunes in conjunction with an internally braced or tieback system. Soldier piles, which are wide-flange beams, are placed in pre-drilled holes that extend beyond the bottom of the excavation. The portion of each soldier pile extending below the bottom of the excavation is grouted in place with sufficient-strength concrete to transmit the vertical loads of the soldier beams to the soil below the excavation level. The upper portion of the soldier pile is then backfilled with a relatively weak grout so that it may be removed for placement of lagging. We recommend that lagging be backfilled with sand slurry pumped into place behind shoring walls to minimize the potential for movement of the cut soil. 10.1 Shoring Wall Retained Earth Pressures For cantilever walls, we recommend that the shoring system be designed to withstand lateral soil pressures based on "active" conditions. This design pressure, based on a level back�ll, is in the form of an equivalent fluid equal to 35 pounds per cubic foot (pc fl triangular distribution acting over the pile spacing above the excavation level. Below the level of excavation, the 35 pcf may be considered to act only over the diameter of the grouted soldier pile section. Any applicable surcharges from adjacent structures, stockpiled materials, construction equipment, or sloping ground must be added to the above values. Where supporting a backslope of 1.SH:1V, an equivalent fluid equal to 60 pcf triangular distribution may be used. Again, October 10, 2005 ASSOCIATED EARTH SCIENCES, INC. MT/!d-K60560Cv12-Pro�ec15120p560GIKEIWP Page 16 Proposed Maintenance/Classroom Building (Building l� Subsurface Exploration, Geologic Hazards, Renton Technical College and Preliminary Geotechnical Engineering Repon � Renton, Washington Preliminary Design Recommendations � below the level of excavation, the 60 pcf may be considered to act only over the diameter of the grouted soldier pile section. The use of active pressure for the shoring system assumes sufficient deformation if the soil occurs to develop an active condition-- typically on the order of 0.001 to 0.002 times the height of the excavation. Any settlement-sensitive structures should be set back a minimum horizontal distance equal to the shoring wall height so that wall ` deflections/soil movement do not impact adjacent foundations. A combination of temporary 1.SH:1 V slopes and shoring may be utilized to reduce the overall height of shoring. Once the shoring/slope configuration is developed, AESI should be I� consulted to review the design parameters, as necessary. 10.2 Shoring Wall Passive Earth Pressure The soldier piles must be located a sufficient depth below the base of the excavation to provide adequate lateral resistance to horizontal loads. The lateral resistance may be computed on the basis of passive pressure in the form of an equivalent fluid equal to 300 pcf. The upper 2 feet of passive soil resistance should be ignored due to disturbance. This pressure may be considered to be acting against twice the diameter of the grouted soldier pile section. Piles � should extend at least 10 feet below the excavation level. 'i 10.3 Shoring Inspections � Shoring installation should be observed by a representative of AESI to verify that subsurface conditions are as anticipated and that the shoring elements are installed in conformance with the shoring plan. Inspections should include pile installation, excavation and lagging placement, lagging backfill, and drainage. Survey monitoring of the piling and adjacent structures may also be required. 10.4 Tiebacks Tieback anchors may be used to aid in resisting lateral loading on the shoring system. A tieback system consists of drilling behind the soldier pile wall at an angle to the horizontal and installing rods or cables with a grout anchor. The anchor loads are transmitted to the surrounding soil by side friction or adhesion with the soil. If requested, recommendations for design and testing of tieback anchors can be provided. 11.0 STRUCTURAL FILL Structural fill will be necessary for wall backfill, utility backfill, and beneath hardscape. All references to structural fill in this report refer to subgrade preparation, fill type, placement, October 10, 2005 ASSOCIATED EARTH SCIEA�CES, INC. 41T/id-KEOS606A?-Projects120056061KEiWP Page 17 Proposed Maintenance/Classroom Building (Building NJ Subsurface Fxploration, Geologic Hazards, Renton Technical College and Preliminary Geotechnical Engineering Report Renton, Washington Preliminary Design Recommendations and compaction of materials, as discussed in this section. If a percentage of compaction is specified under another section of this report, the value given in that section should be used. If fill is to be placed on slopes steeper than SH:1V, the base of the fill should be tied to firm, stable subsoil by appropriate keying and benching, which would be established in the field to � suit the particular soil conditions at the time of grading. The keyway will act to embed the toe of the new fill into the hillside. Generally, the keyway for hillside fills should be at least 4 feet wide and cut into medium dense sand or stiff silt. Level benches would then be cut ' horizontally across the hill following the contours of the slope. No specific width is required for the benches, although they are usually at least 4 feet wide. All fills proposed over a slope should be reviewed by our office prior to construction. After stripping, planned excavation, and any required overexcavation have been performed to -- the satisfaction of the geotechnical engineer/engineering geologist, the exposed ground should be recompacted to 90 percent of the modified Proctor maximum density using ASTM:D 1557 as the standard. If the subgrade contains too much moisture, adequate recompaction may be difficult or impossible to obtain and should probably not be attempted. In lieu of ' recompaction, the area to receive fill should be blanketed with washed rock or quarry spalls to act as a capillary break between the new fill and the wet subgrade. Where the exposed ground remains soft and further overexcavation is impractical, placement of an engineering stabilization fabric may be necessary to prevent contamination of the free-draining layer by silt migration from below. After recompaction of the exposed ground is tested and approved or a free-draining rock course is laid, structural fill may be placed to attain desired grades. 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 95 percent of the modified Proctor maximum density using ASTM:D 1557 as the standard. The top of the compacted fill should extend horizontally ' outward a minimum distance of 3 feet beyond the location of footings ar pavement edges before sloping down at an angle of 2H:1V. The contractor should note that any proposed fill soils must be evaluated by AESI prior to their use in fills. This would require that we have a sample of the material 72 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 the 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 1'united to favorable dry weather conditions. The on-site soils generally contained significant amounts of silt and are considered moisture-sensitive. In addition, 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 ' OCIobeY 10, 2005 ASSOCIATED EARTH SCIENCES, INC. � ' MT/!d-KE05606A2-Projects12005606�xEiwP Page 18 � Proposed Maintenance/Classroom Building (Building 1� Subsurface Exploration, Geologic Hazards, Renton Technical College and Preliminary Geotechnical Engineering Report Renton, Washington Preliminary Design Recommendations amount of fine-grained material limited to 5 percent by weight when measured on the minus No. 4 sieve fraction with at least 25 percent retained on the No. 4 sieve. An AESI representative should inspect the stripped subgrade and 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 I monitoring and testing frequency. � I i I 12.0 FOUNDATIONS i �I Spread footings may be used for building support when founded directly on suitable outwash soil or on structural fill placed as previously discussed. Footings founded on suitable outwash sand or on structural fill above the outwash sand may be designed for an allowable foundation ; soil bearing pressure of 2,500 pounds per square foot (ps�, including both dead and live loads. ', An increase of one-third may be used for short-term wind or seismic loading. Based on the � anticipated dense condition of the granular soils at the base of the excavation along the east perimeter of the proposed structure, a higher allowable bearing capacity of 6,000 psf may be used in design of the footing for the eastern retaining wall. All foundations must penetrate to the prescribed bearing stratum and no foundations should be constructed in or above loose, organic, or existing fill soils. In addition, all footings must have a minimum width of 18 inches. Perirneter footings should be buried at least 18 inches below lowest adjacent grade for frost protection; interior footings require only 12 inches burial. Considering the granular nature of the site soils, settlements are expected to be small and occur rapidly during the initial application of dead load. Anticipated settlement of footings founded as described above should be on the order of 3/a inch with differential movement about half of that total. However, disturbed soil not removed from footing excavations prior to footing placement could result in increased settlements. Installation of settlement-sensitive surfaces should be delayed as long as practical. All footing areas should be inspected by AESI prior to placing concrete to verify that the design bearing capacity of the soils has been attained and that construction conforms to the recommendations contained in this report. The City of Renton may require such inspections. Perimeter footing drains should be provided, as discussed under the section on Drainage Considerations. It should be noted that the area bounded by lines extending downward at 1H:1V from any footing must not intersect another footing or intersect a filled area that has not been compacted October 1 D, 2005 ASSOCIATED EARTH SCIENCES, INC. �,r:,;r„-f;i�us�oh��:-P��,���rs��zoos�ixeiwP Page 19 Proposed Maintenance/Classroom Building (Building NJ Subsurface Fxploration, Geologic Hazards, Renton Technical College and Preliminary Geotechnical Engineering Report Renlon, Washington Preliminary Design Recommendations to at least 95 percent of ASTM:D 1557. In addition, a 1.SH:1V line extending down from any footing must not daylight because sloughing or raveling may eventually undermine the footing. Thus, footings should not be placed near the edge of steps or cuts in the bearing soils. 13.0 LATERAL WALL PRESSURES All backfill behind walls or around foundation units should be placed as per our recommendations for structural fill and as described in this section of the report. Horizontally backfilled walls, which are free to yield laterally at least 0.1 percent of their height, may be designed using an equivalent fluid equal to 35 pcf. Fully restrained, horizontally backfilled rigid walls that cannot yield should be designed for an equivalent fluid of 55 pcf. An incremental dynamic lateral load of 6H and 8H psf for the active and at-rest loading cases, respectively, may be used where determining seismic earth pressure in conformance with the 2003 IBC. Where driveway or parking areas are adjacent to walls, a surcharge equivalent to 2 feet of soil should be added to the wall height in determining lateral design forces. The lateral pressures presented above are based on the conditions of a uniform, level backfill consisting of free-draining soil compacted to 90 percent of ASTM:D 1557. A higher degree of compaction is not recommended as this will increase the pressure acting on the wall. A lower compaction may result in settlement of any slab-on-grade or other structures above the walls. Thus, the compaction level is critical and must be tested by our firm during placement. Surcharges from adjacent footings, heavy construction equipment, or sloping ground must be added to the above values. Footing drains should be provided for all retaining walls, as discussed under the section on Drainage Considerations. It is irnperative that proper drainage be provided so that hydrostatic pressures do not develop against the walls. This would involve installation of a minimum, 1-foot-wide blanket drain to within 1 foot of the top of the wall using imported, washed gravel against the walls. Less permeable on-site soil may be used as a cap over the gravel. Filter fabric (Mirafi 140N, or equivalent) should be placed over the gravel drain prior to soil cap placement to reduce the potential for migration of fines. 13.1 Passive Resistance and Friction Factors Retaining wall footings/keyways cast directly against undisturbed, dense outwash sediments in a trench may be designed for passive resistance against lateral translation using an equivalent fluid equal to 300 pcf. The passive equivalent fluid pressure diagram begins at the top of the footing; however, total lateral resistance should be summed only over the ciepth of the actual key (truncated triangular diagram). These values apply only to footings/keyways where concrete is placed directly against the trench sidewalls without the use of forms. Octoher 10, 2005 ASSOCIATED F_ARTH SCIE,'�'CES, LtiC. ,l?7��id F,I:l�cN75.A_'-Pr�i�er�si��Kl5tiflF�f�F_IWP Pa�Qe 20 Proposed Maintenance/Classroom Building (Building NJ Subsurface Fxploration, Geologic Hazards, Renton Technical College and Preliminary Geotechnical Engineering Report Renton, Washington Preliminary Design Recommendations If footings are placed on suitable advance outwash sediments and then backfilled, the top of the compacted backfill must be horizontal and extend outward from the footing for a minimum lateral distance equal to three times the height of the backfill before tapering down to grade. ' With backfill placed as discussed, footings may be designed for passive resistance against lateral translation using an equivalent fluid equal to 250 pcf and the truncated pressure diagram E discussed above. Passive resistance values include a factor of safery equal to 3 in order to � reduce the amount of movement necessary to generate passive resistance. The friction coefficient for footings cast directly on undisturbed, dense outwash sediments or structural fill may be taken as 0.35. This value includes a safety factor of at least 1.5. 14.0 FLOOR SUPPORT The slab-on-grade floor may be founded on structural fill or unweathered outwash sediments. The floor should be cast atop a minimum of 4 inches of washed pea gravel to act as a capillary break. It should also be protected from dampness by a minimum 10-mil-thick vapor retarder membrane. 15.0 DRAINAGE CONSIDERATIONS All retaining and perimeter footing walls should be provided with a drain at the footing elevation. Drains should consist of minimum, 6-inch-diameter, rigid, perforated, polyvinyl chloride (PVC) pipe surrounded by washed pea gravel. The level of the perforations in the pipe should be at least 12 inches below the bottom of the floor slab, and the drains should be constructed with sufficient gradient to allow gravity discharge away from the building. � Footing drains should be provided with cleanouts to allow periodic future '� cleaning/maintenance. ' All retaining walls should be lined with a minimum, 12-inch-thick, washed gravel blanket to within 1 foot of the top of the wall and which ties into the footing drain. Less permeable on- site soil may be used as a cap over the gravel. Filter fabric should be placed over the gravel prior to soil cap placement to reduce the potential for migration of fines into the wall drain. Roof and surface runoff should not discharge into the footing 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 (minimum 2 percent slope) to achieve surface draina�e. October]0, 2005 ASSOCIATED EARTH SCIENCES, INC. MT/!d-KE05606A2-Projects�20056061KEIWP Page 21 Proposed Maintenance/Classroom Building (Building NJ Subsurface Explorarion, Geologic Hazards, Renton Technical College and Preliminary Geotechnical Engineering Report I Renton, Washington Preliminary Design Recommendations 16.0 PROJECT DESIGN AND CONSTRUCTION MONITORING j At the time of this report, site grading, structural plans, and construction methods have not �I, ; � been fmalized, and the recommendations contained herein are preliminary. We are available to i � provide additional geotechnical consultation as the project design develops and possibly '' changes from that upon which this report is based. We recommend that AESI perform a �I geotechnical review of the plans prior to final design completion. In this way, our earthwork ''� � and foundation recommendations may be properly interpreted and implemented in the design. ' I , We are also available to provide geotechnical engineering and monitoring services during ; construction. The integrity of the foundation 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 �. M E j� ��,���ti wwsy��I,� `,J yt• �' �O '�7' x '� ; � � 1 � �23580�� � �SiER �NAI,�' ��� ���-�, EXPIRES 11�2���(p Maire Thornton, P.E. Kurt D. Merrirnan, P.E. 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E ec�X��,ii� v �;� � � \ Q c_ m.�-.�: � /_.i// . ��i ii // // ///%//• '.! /i i/` i/ mve'e `--� �\ � }`,_�. � � � � ra-% o�.wi w rr. �l J�J�Y- � 0 20 10 � � / Ll 019i�Mi � �[6��a<s�— OIYMG '� \ I 1 \\\ �b �� II I �� A.fd1 Erv��su �ax1� W���_/�,i� \ \ � Reference: PACE �, ,-�„Y„�8�,�� � ���, � � �-��c��\: � U C � C m � Associated Earth Sciences, (f1C. FIGURE 2 � SITE AND EXPLORATION PLAN ' Q � � � � � PROPOSED MAINTENANCE AND CLASSROOM BUILDING DATE 10/05 o RENTON, WASHINGTON PROJECT N�. KE05606A I � H W � a � � 'o� Well-graded gravei and Terms Describing Relative Density and Consisfency " o'o' GW 9ravel with sand,little to Densi SPTmblowsJfoot �. ^ y LL 'o � no fines Very l.00se 0 ro 4 ` m Coarse- �se 4 to 10 m i0 ' ='o�o° Poorly-graded gravel Grained Soils m � � �a D o D o Gp t�edium Dense �o to 3o Test Symbals and gravel with sand, Dense 3o to 50 o � a °'°'� Very Dense >50 G =Grain Size ,o,o, fittle lo no fines Z o � ����o Consisten SP T��blows/foot M=Moisture Content ,� o �1/ A=Aflerberg Limits Silry gravel and silty � c � Very Soil 0 to 2 C=Chemical o L � � • �M gravel with sand Fine- Sott 2 to a DD = Ory Density � d !fl � - Grained Sats t�tedium Slif( 4 to 8 K =Permeability C N jy � g � : $liti 8101$ � � � Clayey gravel and very St�rt 15 l0 30 � � � Gc Uayey gravel with sand Hard >"a0 „� � Componenf Defcnitions ' L o Well-graded sand 2nd Descriptive Term Size Range and Sieve Number � � --: Syy sand with gravel,6ttle Bou�ders Larger than 12' 1O " '�'�'�''� to no fines Cobbles 3'to 17 `o � d . � c .•_•:•:-:• � m " """'�" Grave! 3'to No.4(4.75 mm) y ` ='�'���'•" Poor - raded sand � > � •- �g Coarse Gravel 3'to 3/4' in U� •. SP and Sand with g�2vel, Fine Grave! 3/4'fo No.4(4.75 mm) m a v little to no fines c d Sand No.4(4.75 mm)to No.200(0.075 mm) � � z Coarse Sand No.4(4.75 mm)to No.10(2.00 mm) '" Silly Sand and Medium Sand No.70(2.00 mm)lo No.40(0.425 mm) m � � N • S M Sllly Sand with Fine Sand No.40(0.425 mm)to No.200(0.075 mm) co m .� U � a �- o LL :. g�ave� Silt and Clay Smaper Ihan No.200(0.075 mm) � � � sc Clayey sand and �3�Estimated Percentage Moisture Content � ^' : clayey sand with gravel Percentage by Dry-Absence of masture, `n Component dusty,dry to the touch We�ght Silt,sandy silt,gravelly silt, Trace <5 Slighty Moist-PercepUble m o ML silt with sand or gravel Fe`"' S to�o masture m � Little 1 S l0 25 Moist-Damp but no visible v� H � With -Nm-primary coarse water o `D � Clay of low to medium constituents: > 15% Very Moist-Water visible but `�' v � -Fines conterri between not(ree draining o � � plasticity; silty,sandy,or I Z �= CL 5%and 15% Wet-Vsible tree water,usua gravelty clay,lean clay �Y o °=� irom below water�able N (n � — — a � =— Organic clay or silt of low Symbols � � _— o� plastiCity etows/6'or � Sam lef � = P poAlOn of G Cement grwt o — TYpe / surface seal Elastic silt,clayey silt,siit { Sampler Type 2.0'OD Brstonile e with micaceous or : � DescripGon o „ MH SpGt-Spoon , (•) seal � o diatomaceous fine sand or S�P�� 3.0'OD S lit-S Sam Ier H �� Silt S P P� P - - '_Fdter padc wi�h o m o � � 3.25'OO Spfit-Spoon Ring Sampler �.> : _= blank casing � � o Clay oi high plasticity, � �� sand or ravell cla fa[ Bulksample _ '-• seciion m c= CH Y 9 y y' 3.0"OD Thin-Wall Tube Sampler - =' Screened casing � y J clay with sand or gravel ' (ncluding She�by tube) �� °f�`o�'� �j — � Grab Sample ':w+th filtel pack m �� �iii� -• End cap c � �i��i� Organic cfay or silt of o Portion not recwered "- J %;;:; aH medium to high �» , ������ Percentage hy dry weight �� Depth of ground water ����� plasticity �1 (gp7�5tandard Penetration Test (ASTM 0-1586) 1 ATD=At time af drilfmg >. `—' Peat, muck and other �� Q StaGc water level(date) c � In Genera!Accordance with =o�o p'� highly ofganiC sOils Standard Practice for Description �� Combined USCS symhols used for and Identificalion of Soils(/ISTM D-2488) fines belween S%and 15% Cfassifications of soils in this repoA are based on visual field and/or laboratory o�servations,which indude density/consistency,masture condiGon,grain size,and ptasticity eslimales and should not be construed to imply field or laboratory lesting unless presented herein.VisuaRmanual and/or laboralory dassificalion a methods of ASTM 0-2487 and 0-2488 were used as an idenlificalion guide for lhe Unified Soil Classificalion System. 0 _ p 3 > Associated Earth Sciences, Inc. F�cuRe � � � � � � IExploration Log Key A-,� �a I - �Associated Earth Sciences, Inc. Ge010 ic & Monitorin Well Construction Lo Project Number Weil Number Sheet ; � � � � � KE05606A EB-1 1 of 1 ' ' Project Name Renton Technical College Location Renton, WA Elevation(Top of Well Casing) Surface Elevation(ft) Water Level Elevation Date StaNFinish /��,g/�3/�5 DrillinglEquipment Davies Driiling Hole Diameter(in) Hammer WeighUDrop 140#/30�� ; V O - m.� � � m E � o� � � � WELL CONSTRUCTION 'T� m �� DESCRIPTION , � Surface Monument 15 Fill ' i 14 Moist,dark brown to light brown,silty SAND,roothairs. Cement 14 ------------ -- - ------ - Outwash Bentonite 5 , � Moist,gray,fine SAND/coarse SAND,stratified. � 12 � ' �2 �� Well Screen � Moist,gray,fine SAND/coarse SAND, stratified. s �s , 15 ; I � y Moist,gray,fine SAND/coarse SAND,stratified. 12 15 I Zp End Cap i 7 Moist,gray,fine SAND/coarse SAND,stratfied. 24 � ; 30 ! goring terminated at 21.5 feet on 9/13/05 � No ground water. I 25 I 30 I � ! 0 35 �, o� �I � 0 � t7 2 � I m � I a' � ¢ Sampler Type(ST): � � 2"OD Split Spoon Sampler(SPT) � No Recovery M - Moisture Logged by: MT � � J �j 3"OD Split Spoon Sampler(D&M) � Ring Sample � Water Level Q Approved by: �� � Grab Sample � Shelby Tube Sample 1 Water Level at time of drilling(ATD) i _ -� I LOG OF EXPLORATION PIT NO. EP-1 � This log is part of the report prepared by Associated Earth Sciences, Inc.(AESI)for the named project and should be � read together with that report for complete interpretation.This summary applies oniy to the location of this trench at the � time of excavation.Subsurface conditions may change at this location with the passage of time.The data presented are o � a simpification of actual conditions encountered. � ;; DESCRIPTION Topsoil � Loose, damp, light brown, silty fine SAND. r... 1 � ---------------------- --------------------- Outwash Medium dense, damp, light brown, silty fine SAND, slight stratification. 2 � 3 4 � Medium dense, damp to moist, light brown, fine to medium SAND, coarser with depth. , 5 I 6 7 � � 8 � 9 I , � 10 Bottom of exploration pit at depth 10 feet 11 No ground water/seepage. No caving. 12 � 13 -t i 14 , 15 16 ' E ! 17 18 19 � , �� N LV _ - O O N m Renton Technical College Maintenance/Classroom Building a o Renton, WA a < Associated Earth Sciences, Inc. � Logged by: MT Project No. KE05606A N � � � � � -� � Approved by � 9/26105 a J Y LOG OF INFILTRATION PIT NO. IP-1 � This log is part of the report prepared by Associated Earth Sciences, Inc. (AESp for the named project and should be I � read together with that report for com�lete interpretation.This summary applies only to the locafion of this trench at the � time of excavation.Subsurface conditions may change at this location with the passage of time.The data presented are o a simplfication of actual conditions encountered. I � DESCRIPTION , -' _ _____ 2 112"to 3"Asphalt Concrete on surface over 1"thick Fine Crushed Gravel _ � _ , � Outwash �'� , � � I � ' ! '� 2 Medium dense, damp, light brown, silty fine SAND, slight stratification. ', I� 3 I � ---- ------- -------- ------ ----- 4 Medium dense, damp, light brown, fine to medium SAND, slight stratification. I 5 6 7 ----------------------- -- -------- --- Medium dense, moist, I�ht brown, silty fine SAND._ � ------------ ------------------------ 8 � � Medium dense, damp, light brown, fine to medium SAND, slight stratification. 9 � I , , 10 I � Bottom of exploration pit at depth 10 feet I� � 1 1 No ground water/seepage. No caving. 12 , 13 �: 14 , J 15 ; ' 16 - 17 — 18 19 � � �� � L 0 0 N m Renton Technical College Maintenance/Classroom Building n o Renton, WA a a Associated Earth Sciences, ItIC. pro ect No. KE05606A N Logged by: MT 1 � Approved by: � � � � � 9/26/05 U Y Associated Earth Sciences, Inc. � � � � � Ce�r,�y�r�fi��2��eav��of S'eyvice February 28, 2006 Project No. KE05606A Renton Technical College clo S.M. Stemper Architects, PLLC 4000 Delridge Way SW, Suite 200 Seattle, Washington 98106 Attention: Ms. Sally MacGregor-Crone Subject: Protected Slope Area Within Proposed Building Area Maintenance and Classroom Building Re-Site Renton Technical College 3000 NE 4'" Street Renton, Washington Dear Ms. MacGregor-Crone: It is our understanding that the location for the proposed maintenance and classroom building has been revised since the date of our referenced report and letter. Based on information presented on the "Maintenance and Classroom Re-Bid" dated February 2, 2006 by S.M. Stemper Architects, PLLC (Stemper Architects), the currently proposed building location is situated farther north and east than originally planned. The currently proposed location removes most of the protected slope azea, as defined by the Renton Municipal Code (slopes higher than 15 feet and over 40 percent grade), in the vicinity of the proposed building. As requested, this letter presents our geotechnical recommendations for the proposed revised building location and addresses the impact of the revised building location on the protected slope area mapped on the site. Figure 2, attached to this letter, depicts the revised location of the proposed maintenance and classroom building based on information presented on the , "Maintenance and Classroom Re-Bid" dated February 2, 2006 by Stemper Architects. A�s � proposed, the excavation for the proposed building will remove the protected slope within the � building footprint and retain resulting cuts by permanent, drained retaining walls. ' Recommendations presented in our referenced report and letter remain applicable and should be incorporated into site development plans. It is our opinion that by eliminating the protected slope, the intent of the geologic hazard requirements (Renton Municipal Code Section 4-3-050) is satisfied. i ICirl:land Office•911 Eifth Avenue,Suite 100•ICirldand,V(�A 98033°P�(425)827-7?01•F�(42>)82%-5424 � E��erett Office•2911 1/2 He�ti�tt Aveiiue,Suite 2•Everett,Wt1 98201�P�(425)259 05?2•F�(�251252-3�i08 ' �titiv�vaesgeo.com ; i ; The proposed exterior stairway to be located along the south side of the new building is anticipated to protect underlying soil from surface weathering and resulting surficial slope deterioration. An interceptor drain is recommended along the southern edge of the stairway to reduce the potential for erosion due to concentrated flow along the unpermeable concrete stairway. Figure 3 presents a typical detail for use in designing the interceptor drain. We have enjoyed our continued work with you on this project. If you have questions or require any additional information, please do not hesitate to call. Sincerely, , ( ASSOCIATED EARTH SCIENCFS, INC. � Kirkland, Washington , � ME � ,�,�.���w�s R ,� '' � � c� � ' x � i - 2 G' I f i . :��,�235'�80�� faNAL� EXPIRES �1�ZOI (p � ' ' Kurt D. Meniman, P.E. � Principal Engineer I I ', I ', Attachments: List of References ' Figure 1: Vicinity Map i Figure 2: Revised Site and Exploration Plan ', Figure 3: Typical Interceptor Trench Detail , � I � KDMlsn � ' KFA5606A6 i Projcctsl?00506061KE\N P - 2 i � ' List of References Subsurface Exploration, Geologic Hazards, and Preliminazy Geotechnical Engineering Report Proposed Maintenance and Classroom Building Re-Site Renton Technical College 3000 NE 4'� Street Renton, Washington Report Date: October 13, 2005 , Recommendations for Temporary Shoring Proposed Maintenance and Classroom Building Re-Site Renton Technical College 3000 NE 4'� Street Renton, Washington Letter Date: January 13, 2006 I KDMlsn KE05606A6 Proj ects��0U50G06'�K E�.w'P 1� - _ ..... _... . .w.,., ^,.^;^n+n.. �.oe �r. �y. .;.�. 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