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HomeMy WebLinkAboutRS_Draft_Geotech_Report_180426_v1.pdfJob No. 1801 S&EE S&EE REPORT OF GEOTECHNICAL INVESTIGATION PROPOSED MITIGATION HANGAR BOEING RENTON PLANT S&EE JOB NO. 1801 APRIL 23, 2018 (DRAFT) RECEIVED 05/02/2018 amorganroth PLANNING DIVISION 1801rpt S&EE TABLE OF CONTENTS Section Page 1.0 INTRODUCTION ................................................................................................................................................. 1 2.0 SCOPE OF WORK ............................................................................................................................................... 2 3.0 SITE CONDITIONS ............................................................................................................................................. 3 3.1 SITE HISTORY & GEOLOGY .......................................................................................................................... 3 3.2 SURFACE CONDITIONS ................................................................................................................................. 3 3.3 SUBSURFACE CONDITIONS ......................................................................................................................... 4 3.4 GROUNDWATER CONDITIONS ................................................................................................................. 4 4.0 ENGINEERING EVALUATIONS AND RECOMMENDATIONS ................................................................. 5 4.1 GENERAL .......................................................................................................................................................... 5 4.2 PRELOAD ........................................................................................................................................................... 5 4.3 PILE FOUNDATION ......................................................................................................................................... 6 4.4 LATERAL EARTH PRESSURES ...................................................................................................................... 8 4.5 STRUCTURAL FILL .......................................................................................................................................... 9 4.6 PAVEMENT DESIGN RECOMMENDATIONS ............................................................................................ 10 4.7 UNDERGROUND UTILITY CONSTRUCTION AND ABANDONMENT .................................................... 11 4.8 DEWATERING ................................................................................................................................................. 13 4.9 SEISMIC CONSIDERATIONS ........................................................................................................................ 14 4.10 ADDITIONAL SERVICES ............................................................................................................................ 15 5.0 CLOSURE ............................................................................................................................................................. 16 FIGURE 1: SITE LOCATION MAP FIGURE 2: SITE & BORING LOCAITON PLAN FIGURE 3: LIQUIFACTION MAP FIGURE 4: RESULT OF LIQUEFACTION ANALYSIS PLATE 1: PRELOAD CONFIGRATION PLATE 2: SETTLEMENT MARKER DETAILS APPENDIX A: FIELD EXPLORATION AND LOGS OF BORINGS 1801rpt S&EE DRAFT REPORT OF GEOTECHNICAL INVESTIGATION PROPOSED MITIGATION HANGAR For The Boeing Company 1.0 INTRODUCTION A new mitigation-hangar building is proposed at the northwest corner of the existing 4-81 Building. A Site Location Map is shown in Figure 1, and a Site & Boring Location Plan is shown in Figure 2; both are included at the end of this report. The proposed hangar structure measures approximately 338ft x 173ft in plan on Apron R as an extension to their existing final assembly building 4-81/82. The building is proposed to be 88ft in height. This new hangar will house two 737 aircrafts for the purpose of performing manufacturing activities currently performed in the final assembly building 4-81/82. The new hangar will consist of high bay and low bay buildings. High bay will be located on the northern portion of the building and will house two 737 MAX (Unfueled aircraft). The low bay which is located on the south and will house airplane equipment service and storage area on the first floor and work area function on the second floor. There will be a 10ft separation between the existing building 04-81 and the new hangar structure. Existing utilities within the footprint of the proposed hangar will be relocated, or the system reconfigured and existing lines abandoned in place. The project will require a comprehensive re-evaluation and revision of the existing storm water conveyance system including installation of new storm water tank along with associated treatment system. The project will install a new electrical unit substation dedicated to this building. Mechanical system includes new air handling system located at roof of the hangar. 1801rpt 2 S&EE 2.0 SCOPE OF WORK The purpose of our investigation is to provide geotechnical parameters and recommendations for design and construction. Specifically, the scope of our services includes the following: 1. Review of available geotechnical data. 2. Exploration of the subsurface conditions at the project site by the drilling of one soil test boring. 3. Performance of liquefaction evaluations. 4. Recommendations regarding foundation support. 5. Recommendations regarding the lateral soil pressures for shoring and subsurface retaining wall designs. 6. Recommendation regarding passive soil pressure for the resistance of lateral loads. 7. Recommendation regarding preload and slab design. 8. Recommendations regarding the soil parameters for seismic design. 9. Recommendations regarding underground utility construction; recommendation regarding excavation shoring, angles of temporary slope, suitability of onsite soils for structural fill, and type of suitable imported fill. 10. Recommendations regarding dewatering. 11. Attendance of design meetings. 12. Preparation of a geotechnical report containing a site plan, a description of subsurface conditions, and our findings and recommendations. 1801rpt 3 S&EE 3.0 SITE CONDITIONS 3.1 SITE HISTORY & GEOLOGY Renton Boeing plant is located at the south end of Lake Washington. During WW II, the plant area was leveled by about 3 to 7 feet thick of fill. The native soils immediately under the fill include alluvial deposits that are over 100 feet in thickness. Published geologic information (Geologic Map of The Renton Quadrangle, King County, Washington by D.R. Mullineaux, 1965) indicates that the alluvial soils are underlain by Arkosic sandstone. S&EE performed a few soil test borings in 2012 – 2013 at North Bridge site located at the northwest corner of the plant. These borings found glacially deposited and consolidated soil (hard silt) at depths of about 150 to 170 feet. Boring data from our previous projects at the south side of Renton Airport show that the hard silt is underlain by sandstone. Seismic Hazards Seattle Fault is the prominent active fault closest to the site. The fault is a collective term for a series of four or more east-west-trending, south-dipping fault strands underlying the Seattle area. This thrust fault zone is approximately 2 to 4 miles wide (north-south) and extends from the Kitsap Peninsula near Bremerton on the west to the Sammamish Plateau east of Lake Sammamish on the east. The four fault strands have been interpolated from over-water geophysical surveys (Johnson, et al., 1999) and, consequently, the exact locations on land have yet to be determined or verified. Recent geologic evidence suggests that movement on this fault zone occurred about 1,100 years ago, and the earthquake it produced was on the order of a magnitude 7.5. Due to the close proximity of Seattle Fault, the loose subsoils at the site have high liquefaction potential during strong earthquakes. This high liquefaction susceptibility is shown in Figure 3: Preliminary Liquefaction Susceptibility Map of the Renton Quadrangle, Washington by Stephen Palmer. 3.2 SURFACE CONDITIONS A north-south access road runs through the middle of the proposed building site. The areas adjacent to the road are used primarily for storage. The site surface is flat and paved with asphalt and concrete. Underground utilities including power, water and storm lines are present onsite. A wet vault is present near the northwest corner of the proposed building. The minimum distance between the building and Lake Washington Shoreline is 215 feet. 1801rpt 4 S&EE 3.3 SUBSURFACE CONDITIONS We obtain the subsurface conditions at the site by the review of previous borings, number 1 and 14, and the drilling of a new soil test boring, B-1-2018. The locations of these borings are shown in Figure 2. The boring logs are included in Appendix A of this report. Based on the available boring data, the subsurface conditions at the project area include fill soils over alluvial deposits. The fill is about 5 to 7 feet in thickness and consists of loose sand with gravel. The alluvial soils below the fill include, from top to bottom, the following strata. 1) Loose to medium dense sand, about 15 feet in thickness. 2) Soft, organic silt with peat, about 5 feet in thickness. The materials are very compressible. 3) Loose to medium dense, sand, silty sand and silt. This layer is about 30 to 40 feet in thickness. 4) Medium dense to dense sand and silty sand. This layer is about 30 to 40 feet in thickness. Most of the pile foundations in the plant are embedded in this competent layer. 5) Silty sand and silt. These soils are primarily medium dense or stiff with low compressibility. This is a layer of old alluvium that was deposited over the glacial soils. Based on our 2012 borings at the North Bridge site, we believe that these old alluvial soils are about 40 to 60 feet in thickness. 3.4 GROUNDWATER CONDITIONS Based on our knowledge of the site conditions and previous groundwater data, we believe the groundwater table at the project site will vary from about 3 to 5 feet below the ground surface. The depth of groundwater is mainly affected by the lake level. The level fluctuates about 2 feet with the lowest level in the wet winter months and highest in the dry summer season. 1801rpt 5 S&EE 4.0 ENGINEERING EVALUATIONS AND RECOMMENDATIONS 4.1 GENERAL 1. The subsurface soils at the site include soft and loose, un-consolidated alluvial soils from the ground surface to depths of about 60 feet. Due to their low shear strength and high compressibility these soils are not suitable for the support of conventional spread footings. Augercast piles are recommended for building support. The piles should be 20-inch in diameter and extend to a depth of 75 feet measuring from the current ground surface. 2. The results of our settlement analyses show maximum settlements of 4 to 6 inches under the proposed floor load. We believe this settlement is excessive and thus recommend preloading the slab area to pre-induce the ground settlement. To avoid down drag forces on piles the preload should be conducted prior to pile installation. 3. The upper 65 feet or so of the subsoils are loose and liquefaction prone. The proposed pile foundation would mitigate the impact of liquefaction on building support. However, liquefaction induced sand boils and uneven ground settlements will threaten the slab-on-grade. As such, reinforcements in slab-on-grade should be considered. Details of our recommendations are presented in the following sections. 4.2 PRELOAD The preload program should begin by breaking the asphalt and concrete pavement into pieces of less than 5 feet by 5 feet in size. This will promote uniform ground settlement and avoid bridging effect over non- uniform subgrade reaction. The preload should consist of non-structural fill soil that is at least 7 feet in thickness. The fill should be placed to have a minimum in-place density of 120 pcf (pounds per cubic feet), and be compacted to the extent that the fill can support the construction equipment. The surface should be graded for surface drainage. Except for the east side, northwestern portion and southeastern portion of the building, there should be 2H:1V side slopes and the edge/top of the slope should extend 7 feet beyond the building lines. A preload configuration is shown in Plate 1. 1801rpt 6 S&EE Based on our evaluations, the maximum ground settlement under the preload will be on the order of 6 inches and will take about 8 to 10 week to reach maturity. A total of 3 ground settlement monitoring markers in the preload area and a total of 3 building settlement monitoring points on the 4-81 building wall should be installed prior to the placement of preload fill. The approximate locations of these monitoring locations are shown on Plate 1. A sketch showing the settlement marker is included in Plate 2. The movement of these monitoring stations should be surveyed initially (prior to the placement of preload), once every day for the first 5 days, and once every week thereafter. The survey results should be transmitted to our office within 24 hours. We will determine the termination of the preload period upon theoretical (about 90%) maturity is reached. Subgrade Preparation for Slab-On-Grade: Upon preload completion the preload soil and broken pavement should be removed. The subgrade should then be excavated to allow for a 12-inch-thick slab base course. The excavated subgrade should then be thoroughly compacted by at least 6 passes of a vibratory roller weighing at least 10 tons. Any soft, wet or organic soils should be over-excavated. This over-excavation should be backfilled with the base course material stated below. The subgrade preparation should be monitored by a site inspector from our office. Base course material should consist of well-graded crushed rock or a blend of commercial rock products conforming to WSDOT specifications for Crushed Surfacing, Specification 9-03.9(3). The base course should have adequate moisture content at the time of placement and should be compacted to a firm and unyielding condition or at least 95 percent of the maximum dry density, as determined by the modified Proctor compaction test (ASTM D 1557). Slab-On-Grade Design: Concrete slab-on-grade can be designed using a subgrade reaction modulus of 200 pounds per cubic inch (pci). If thickened edges are to be installed, the slope at the thickened edges should be 2H:1V or flatter. 4.3 PILE FOUNDATION During the course of the project design, a few pile options were discussed and considered. We believe that augercast piles are best suited for the building support. The piles should be 20-inches in diameter and have a length of 75 feet, measuring from the existing ground surface. Pile Capacities: The pile will develop a downward capacity of 175 kips and upward capacity of 70 kips. These values include a safety factor of 2 and have considered the effect of liquefaction. The capacities 1801rpt 7 S&EE can be increased by 1/4 when considering the transient loads such as wind but not seismic forces. We recommend that all piles are spaced at least 3 pile diameters ON CENTER. Resistance to Lateral Load: Assuming that the top of pile is 3 feet below the ground surface and for a free/pin head condition, the pile will have a lateral capacity of 10 kips for a lateral pile top deflection of about 0.4 inches. We recommend that the pile be designed with a point of fixity at a depth of 25 feet below the ground surface. Additional lateral resistance can be obtained from the passive earth pressure against pile caps and grade beams, as well as friction at the bottom of slab-on-grade. The former can be obtained using an equivalent fluid density of 250 pounds per cubic feet, and the latter using a coefficient of friction of 0.5. These values include a safety factor of 1.5. Pile Settlements: Pile settlement will result from elastic compression of the piles and the supporting soils. The settlement is estimated to be about ½ to ¾ inches, and will occur within 8 weeks upon loading. Pile Installation: Cement grout must be pumped continuously during withdrawal of the auger, the rate of which should not exceed about 5 to 8 feet per minute. Also, at least 8 feet of grout head must be maintained during the entire withdrawal. We anticipate that the grout volume discharged from the pump to be about 1.2 to 1.5 times the theoretical volume of the drilled hole. The grout volume is usually obtained by counting the number of pump strokes. The grout pressure at the pump should be maintained in the range of 150 to 350 psi, depending on the length of the feeder hose used. The drilling contractor should provide pressure gages at the pump prior to drilling. For adjacent piles that are less than 5 feet clear space, the minimum waiting period is 12 hours. Quality Control: The following quality control measures must be implemented by the piling contractor. 1) Prior to pile installation, the contractor should calibrate the grout pump by filling a 55-gallon drum. This calibration should be performed three times and approved by the onsite geotechnical engineer. 2) The rebar cage should be equipped with centralizers and the cage should be plumb before inserting into the drilled-hole. Single cable hooked on one side of the cage, or any other mean resulting in tilting of the cage is not allowed. 3) The cage should sink to the design depth by its own weight. Pushing the cage down by machine is not allowed. If grout de-hydration or any other reason preventing cage installation, the hole should be re-drilled and re-grouted. 1801rpt 8 S&EE 4) Pile installation should be monitored by an engineer from our office. Our field representative will evaluate the adequacy of the construction methods and procedures. Any problems which might arise, or deviations from the specifications, will be considered during our evaluations and approval of each pile installed. 4.4 LATERAL EARTH PRESSURES Lateral earth pressures on retaining walls or permanent subsurface walls, and resistance to lateral loads may be estimated using the following recommended soil parameters: Soil Density (PCF) Equivalent Fluid Unit Weight (PCF) Coefficient of Friction Active At-rest Passive 125 40 50 200 0.4 Note: 1) Hydrostatic pressures are not included in the above lateral earth pressures. 2) Lateral earth pressures are appropriate for level structural fill placed behind and in front of walls. The active case applies to walls that are permitted to rotate or translate away from the retained soil by approximately 0.002H, where H is the height of the wall. This would be appropriate for a cantilever retaining wall. The at-rest case applies to unyielding walls, and would be appropriate for walls that are structurally restrained from lateral deflection such as basement walls, utility trenches or pits. SURCHARGE INDUCED LATERAL LOADS Additional lateral earth pressures will result from surcharge loads from floor slabs or pavements for parking that are located immediately adjacent to the walls. The surcharge-induced lateral earth pressures are uniform over the depth of the wall. Surcharge-induced lateral pressures for the "active" case may be calculated by multiplying the applied vertical pressure (in psf) by the active earth pressure coefficient (Ka). The value of Ka may be taken as 0.4. The surcharge-induced lateral pressures for the "at-rest" case are similarly calculated using an at-rest earth pressure coefficient (Ko) of 0.6. 1801rpt 9 S&EE SEISMIC INDUCED LATERAL LOADS For seismic induced lateral loads, the dynamic force can be assumed to act at 0.6 H above the wall base and the magnitude can be calculated using the following equation: Pe = 14H Where Pe = seismic-induced lateral load H = wall height BACKFILL IN FRONT OF RETAINING WALLS Backfill in front of the wall should be structural fill. The material and compaction requirements are presented in Section 4.5. The density of the structural fill can be assumed to be 130 pounds per cubic feet. BACKFILL BEHIND RETAINING WALLS Backfill behind the wall should be free-draining materials which are typically granular soils containing less than 5 percent fines (silt and clay particles) and no particles greater than 4 inches in diameter. The backfill material should be placed in 6 to 8-inch thick horizontal lifts and compacted to a firm and non-yielding condition or at least 90 percent of the maximum density in accordance with ASTM D-1557 test procedures. In the areas where the fill will support pavement, sidewalk or slabs, the top two feet of the backfill should be compacted to at least 95 percent of the maximum density. Care must be taken when compacting backfill adjacent to retaining walls, to avoid creating excessive pressure on the wall. DRAINAGE BEHIND RETAINING WALLS Unless the wall is designed to support hydrostatic pressure, rigid, perforated drainpipes should be installed behind retaining walls. Drainpipes should be at least 4 inches in diameter, covered by a layer of uniform size drain gravel of at least 12 inches in thickness, and be connected to a suitable discharge location. An adequate number of cleanouts should be installed along the drain line for future maintenance. 4.5 STRUCTURAL FILL Structural fill should be used for wet vault, utility trenches, and in areas that will support loads such as slab, pavement, walkway, etc. Structural fill materials should meet both the material and compaction requirements presented below. 1801rpt 10 S&EE Material Requirements: Structural fill should be free of organic and frozen material and should consist of hard durable particles, such as sand, gravel, or quarry-processed stone. Due to their silty nature the on-site soils are not suitable for structural fill. Suitable imported structural fill materials include silty sand, sand, mixture of sand and gravel (pitrun), and crushed rock. All structural fill material should be approved by an engineer from our office prior to use. Please note that: 1) Flowable CDF (Control Density Fill) is considered an acceptable structural fill. The material should have a minimum compressive strength of 150 psi; 2) Recycled concrete often has a fines content exceeding 20%, making the material sensitive to moisture. As such, the material may be difficult to use in wet winter months. Placement and Compaction Requirements: Structural fill should be placed in loose horizontal lifts not exceeding a thickness of 6 to 12 inches, depending on the material type, compaction equipment, and number of passes made by the equipment. Structural fill should be compacted to a firm and non-yielding condition or at least 95% of the maximum dry density as determined using the ASTM D-1557 test procedures. 4.6 PAVEMENT DESIGN RECOMMENDATIONS We recommend that all pavement subgrades be proof-rolled to identify areas of soft, wet, organic, or unstable soils. Proof-rolling should be accomplished with a heavy (10-ton) vibratory roller, front-end- loader, or loaded dump truck (or equivalent) making systematic passes over the subgrade while being observed by a site inspector from our office. In areas where unstable and/or unsuitable subgrade soils are observed, these soils should be over-excavated a minimum 12 inches. Additional over-excavation depth may be required to remove buried debris, organic or very soft soil. Woven geotextile having a minimum 200 to 400 pounds grab tensile strength may be necessary for additional subgrade stabilization. The geotextile should be placed with 12-inch overlaps and all wrinkles removed. The over-excavation should be monitored by an inspector from our office. Our inspector will provide recommendations regarding the final depth of over-excavation and the preparation of the over-excavated subgrade. The over-excavation should then be backfilled with 1-1/4” minus crushed rock. The material should have adequate moisture content, and be compacted to a firm and non-yielding condition by a compactor approved by our site inspector. 1801rpt 11 S&EE After proof-rolling, the top 12 inches of the entire subgrade should be thoroughly compacted to a firm and non-yielding condition or at least 95 percent of the maximum dry density, as determined by the modified Proctor compaction test (ASTM D 1557). The subgrade soil should have adequate moisture content (within +/-2% from optimum) at the time of compaction. Asphalt pavements constructed over proof-rolled and compacted subgrades, as specified above, can be designed with a CBR (California Bearing Ratio) value of 12; concrete pavement can be designed with a subgrade reaction modulus of 100 pci (pounds per cubic inches). A typical standard-duty (lightweight) pavement section that was used on similar projects at the plant consists of 3 inches of Class B asphalt over 6 inches of base course. A heavy-duty pavement section could consist of 6 inches of Class B asphalt over 12 inches of base course. A concrete pavement section could consist of 8 inches of reinforced concrete over 6 inches of base course. Base course under pavements should consist of well-graded crushed rock; well-graded recycle concrete; or a blend of commercial rock products conforming to WSDOT specifications for Crushed Surfacing, Specification 9-03.9(3). The base course layer should be compacted to a firm and unyielding condition or at least 95 percent of the maximum dry density, as determined by the modified Proctor compaction test (ASTM D 1557). 4.7 UNDERGROUND UTILITY CONSTRUCTION AND ABANDONMENT Existing underground utilities inside the footprint of the proposed building should be rerouted or abandoned onsite. For the existing wet vault that is located at the northwest corner of the building, the vault walls should be cut to at least 2 feet below the final grade; water and loose sediments inside the vault should be removed; and then the vault be filled with structural fill. Structural fill materials should meet the material and compaction requirements presented in Section 4.5 of this report. 1801rpt 12 S&EE 4.7.1 Open-Cut When temporary excavations are required during construction, the contractor should be responsible for the safety of their personnel and equipment. The followings cut angles are provided only as a general reference: Open cuts above groundwater table may be sloped at 1H:1V. Open cuts below groundwater table may need to be 1.5H:1V or flatter. For a combination of open cut and shoring, benching in the upper 2 to 4 feet works well in the past as it lessens the overburden pressure and facilitates backfill. The benches should have a 1:1 ratio between height and horizontal run, and the height of each bench should be limited to 2 feet. 4.7.2 Shoring Design Since the soil conditions varies horizontally, one set of soil pressure diagrams for shoring design may not be adequate. As a starting point, we recommend the following soil parameters for the design. We should review the design and provide recommendations for necessary adjustments. Soil’s total unit weight: 115 to 130 pcf (pounds per cubic feet) Soil’s buoyant unit weight: 45 to 70 pcf Active soil pressure: 45 pcf, equivalent fluid density, above groundwater table Active soil pressure: 20 pcf, equivalent fluid density, below groundwater table Passive soil pressure: 240 pcf, equivalent fluid density, above groundwater table (include 1.5 safety factor) Passive soil pressure: 80 to 100 pcf, equivalent fluid density, below groundwater table (include 1.5 safety factor) Imbalanced hydrostatic pressure should be added to the active side. The pressure will depend on the type of dewatering method. A 2 feet over-excavation at the passive side should be considered in the design. 4.7.3 Subgrade Preparation All loose soil cuttings should be removed prior to the placement of bedding materials. Wet and loose subgrades should be anticipated. The contractor should make efforts to minimize subgrade disturbance, especially during the last foot of excavation. Note that subgrade disturbance in wet and loose soil is inevitable, and subgrade stabilization is necessary in order to avoid re-compression of the disturbed zone. Depending on the degrees of disturbance, the stabilization may require a layer of quarry spalls (2 to 4 inches or 4 to 6 inches size crushed rock). Based on our experience at the plant, when compacted by a hoepac or the dynamic force of the excavator’s bucket, a 12 to 18 inches thick layer of spalls would sink 1801rpt 13 S&EE into the loose and soft soils, interlock and eventually form a stable subbase. A chocker stone such as 5/8” x 1-1/4” clean crushed rock should be installed over the quarry spalls. This stone should be at least 6 inches in thickness and should be compacted to a firm and non-yielding condition by a mechanical compactor that weighs at least 1,000 pounds. In the event that soft silty soils above groundwater table are encountered at subgrades, the subgrade should be over-excavated for a minimum of 6 inches. A non-woven geotextile having a minimum grab tensile strength of 200 pounds should be installed at the bottom of the over- excavation and the over-excavation backfilled with 1-1/4” minus crushed rock. The material should have adequate moisture and be compacted to a firm a non-yielding condition using the same compactor. 4.7.4 Bearing Capacity and Subgrade Modulus Subgrade so prepared should have an allowable bearing capacity of 1,500 psf (pounds per square feet), and a subgrade modulus of 50 pci (pounds per cubic inches). The bearing capacity includes a safety factor of 3, and can be increased by 1/3 for transient loads. Total settlement under these loads should be on the order of 1/4 to 1/2 inch. 4.7.5 Backfill Structural fill materials should be used for backfill. Structural fill materials should meet the material and compaction requirements presented in Section 4.5 of this report. 4.8 DEWATERING Dewatering will be required for excavations deeper than the groundwater table. Based on our experience with the similar subsoils at the plant, we believe that for excavation shallower than 4 to 5 feet, dewatering can be successful using local sumps. The contractor should install sumps at locations and spacing that are best fitted for the situation. To facilitate drainage, the sump holes should be at least 2 feet below the excavation subgrade. If possible, the granular backfill around the sump should make hydraulic connection with the crushed rock or quarry spalls placed for subgrade stabilization. For dewatering deeper than 5 to 7 feet, our experience at Boeing Renton Plant has shown that wellpoints installed to a depth of about 25 feet and spaced at 5 to 8 feet will dewater to a depth of about 15 feet below ground surface. We suggest that the contractor retain a dewatering specialist for a detailed dewatering design. 1801rpt 14 S&EE 4.9 SEISMIC CONSIDERATIONS 4.9.1 Design Parameters We have evaluated the geotechnical-related parameters for seismic design in accordance with 2015 IBC. The spectral responses were obtained from USGS website using a latitude of 47.501 degrees and a longitude of -122.206 degrees. The values for Site Class B (rock) are: SS = 1.455 g (short period, or 0.2 second spectral response) S1 = 0.545 g (long period, or 1.0 second spectral response) Using the boring data, we determined that the subsoils correspond to Site Class E (“Soft Clay Soil”). The site coefficient values are used to adjust the mapped spectral response acceleration values to get the adjusted spectral response acceleration values for the site. The recommended Site Coefficient values for Site Class E are: Fa = 0.9 (short period, or 0.2 second spectral response) Fv = 2.4 (1.0 second spectral response) 4.9.2 Seismic Hazards Liquefaction during strong seismic events is the primary geotechnical hazard at the site. This is a condition when vibration or shaking of the ground results in the excess pore pressures in saturated soils and subsequent loss of strength. Liquefaction can result in ground settlement or heaving. In general, soils that are susceptible to liquefaction include saturated, loose to medium dense sands and soft to medium stiff, low-plasticity silt. The evaluation of liquefaction potential is complex and is dependent on many parameters including soil’s grain size, density, and ground shake intensity, i.e., Peak Ground Acceleration (PGA). We have performed liquefaction analyses using a computer program, Lique-Pro. Figure 4 shows the results of the analysis. These results indicate that a ground settlement on the order of 10 inches may occur and the liquefaction zone may extend to a depth of 65 feet. We believe that the proposed preload may reduce the ground settlement to about 5 to 7 inches. This settlement may result in severe damage to slab-on-grade. As the piling penetrates the liquefaction zone, impacts to the building support should be minimal. The site is flat and at least 215 feet away from Lake Washington shoreline. As such, there is no hazard associated with slope stability or lateral spread. 1801rpt 15 S&EE 4.10 ADDITIONAL SERVICES We recommend the following additional services during the construction of the project: 1. Review design plans to confirm that our geotechnical recommendations are properly implemented in the design. 2. Review contractor’s submittals. 3. Response to contractor’s RFI. 4. Construction monitoring services. The tasks of our monitoring service will include the followings: 4.1 Monitoring preload construction; review preload progress and determination the maturity of preloading. 4.2 Monitoring the installation of augercast piles. Our representative will evaluate the capacity of each pile and provide recommendations as needed. 4.3 Monitoring the installation of underground utilities; observation of subgrade preparation and recommendations regarding subgrade stabilization. 4.4 Observation and approval of structural fill material, its placement and compaction. Our representative will confirm the suitability of the fill materials, perform field density tests, and assist the contractor in meeting the compaction requirements. 4.5 Monitoring subgrade preparation for slab-on-grade. 4.6 Recommendation regarding construction dewatering. 5. Preparation and distribution of field reports. 6. Other geotechnical issues deemed necessary. 1801rpt 16 S&EE 5.0 CLOSURE The recommendations presented in this report are provided for design purposes and are based on soil conditions disclosed by the available geotechnical boring data. Subsurface information presented herein does not constitute a direct or implied warranty that the soil conditions between exploration locations can be directly interpolated or extrapolated or that subsurface conditions and soil variations different from those disclosed by the explorations will not be revealed. The recommendations outlined in this report are based on the assumption that the development plan is consistent with the description provided in this report. If the development plan is changed or subsurface conditions different from those disclosed by the exploration are observed during construction, we should be advised at once so that we can review these conditions, and if necessary, reconsider our design recommendations. LOGAN AVEEXIT 5 900 515 900 EXIT 4 EXIT 4A 405 405 167 EXIT 4B 405 169 167 D9 D40 D35 D30 EXIT 2B From Issaquah From Bellevue 4-04 Medical Clinic Safety LK WASHINGTON BLVD N From Seattle LAKE WASHINGTON Boeing Employees Flying Association RA I N I E R A V E N 4-41 4-20 4-21 4-69 4-402 4-78 4-77 4-79 4-71 4-42 4-45 Apron D 5-27 5-403 5-288 9 7 1 16 17 15 12 13A 14 10-18 GARDEN AVE N N EVA NEDRAGEVA KRAPN 8TH ST 11 10-16 10-13 4-89 4-88Badge Office 10-20 10-80 Hub 4-17 4-90 4-75 4-81 4-82 4-83 4-86 Renton Airport From I-5 From Longacres Park From Kent and Auburn From Enumclaw Apron A Apron BRAINIER AVE N AIRPORT WAY RE N T O N A V E S S 3RD ST S 2ND ST Renton Stadium 5-09 5-02 S U N S E T B L V D W BENSON RD S M. L . K I N G J R W A Y S SW 10TH S T OAKESDALE AVE SW SW 19TH ST SW 16TH ST DNOMYAR WS EVA WS EVA DNILTALBOT RD S EVA NIAM HOUSER WAY N LOGAN AVE N CEDAR RIVER N 1 S T S T BRONSON W AY N S 4TH ST N 3RD ST N 4TH ST N NEDRAG S EVA TTENRUBLOGAN AVE S SW 7TH ST GRADY WA Y S W N EVA YROTCAFMONSTER RD 5-50 5-51 N EVA SMAILLIW7-206 Triton Tower Two 7-207 Triton Tower Three From Seattle 5-08 Washington – Renton North 8th and Park Avenue North, Renton, WA 98055 N 5TH ST N 6TH ST N 8TH ST 5-45 Revised 03-09 Boeing North Bridge Boeing South Bridge 7-244 Rivertech Corporate Center HOUSER WAY BYPASS Copyright 2009© The Boeing Company. All rights reserved.PARK AVE N WELLS AVE N POWELL AVE SW NACHES AVE 4-95Shed 4-96GuardShack Employee gates AMS Turnstile gates Fence lines Boeing property General parking Restricted parking Bus stop Helistop 51 52 53 54 55 51 52 53 54 55 A B C D E F A B D E F C D44 D41 D4 D32SITE FIGURE 1 - Site Location Map Figure 2 Site & Boring Location PlanBoring 1Boring 14Boring B-1-2018 Figure 3 SITE LiquefyPro CivilTech Software USA www.civiltech.comCivilTech Corporation LIQUEFACTION ANALYSIS Boeing Mitigation Hangar S&EE Job No. 1801 Hole No.=B-1-2018 Water Depth=3 ft Magnitude=7.5 Acceleration=0.35gGround Improvement of Fill=1 ft (ft)0 15 30 45 60 75 90 105 10 110 5 10 115 5 0 100 90 5 107 50 12 117 5 0 91 100 4 105 50 15 119 5 4 106 100 7 112 50 1 90 100 27 122 5 9 126.5100 Medium dense fine sand Very soft silt and loose silty fine sand Medium dense fine sand Very soft silt and loose silty fine sand Medium dense fine sand Very sofrt silt and loose silty fine sand Medium dense fine sand Medium stiff silt Raw Unit FinesSPT Weight %Shear Stress Ratio CRR CSR fs1 Shaded Zone has Liquefaction Potential 02 Soil DescriptionFactor of Safety 051 Settlement Saturated Unsaturat. S = 9.83 in. 0 (in.) 10 fs1=1.00 Figure 4 Last Saved by: Brook.emry on: Apr 20, 2018 7:47 AM File: Q:\FederalWay\2018\A18.0200\00\CADD\Dwgs\Pre-app\01_4-Mitigation-Hangar-C01.dwgSTEV E N P. T R UESTATE O F WASHIN GTON31271R EGIST E R E DPROF E SSIONA L E N G INEERPRELIMI N A R Y LANELANEC01C1 PRELOAD GRADING AND ELEVATION PLAN RENTON SITE Plate 1 Building Settlement Monitoring Points (3) Ground Settlement Markers (3) Preload soil, 7 feet (Broken pavement) Plate 2 Settlement Marker 1801rpt S&EE APPENDIX A FIELD EXPLORATION AND LOGS OF BORINGS The subsurface conditions at the project site were explored with the drilling of one soil test boring, B-1- 2018 from March 26 to 27, 2018. The location s of this boring is shown on Figures 2, and the boring logs are included in this appendix. Our knowledge of the subsurface conditions are augmented by previous borings drilled in the site vicinity. These borings are Borings 1 and 14, and their logs are included in this appendix. The test boring B-1-2018 was advanced using mud-rotary technique. A representative from S&EE was present throughout the exploration to observe the drilling operations, log subsurface soil conditions, obtain soil samples, and to prepare descriptive geologic logs of the exploration. Soil samples were taken at 2.5-,5.0-, and 10-foot intervals in general accordance with ASTM D-1586, "Standard Method for Penetration Test and Split-Barrel Sampling of Soils" (1.4” I.D. sampler). The penetration test involves driving the samplers 18 inches into the ground at the bottom of the borehole with a 140 pounds hammer dropping 30 inches. The numbers of blows needed for the samplers to penetrate each 6 inches are recorded and are presented on the boring logs. The sum of the number of blows required for the second and third 6 inches of penetration is termed "standard penetration resistance" or the "N-value". In cases where 50 blows are insufficient to advance it through a 6 inches interval the penetration after 50 blows is recorded. The blow count provides an indication of the density of the subsoil, and it is used in many empirical geotechnical engineering formulae. The following table provides a general correlation of blow count with density and consistency. DENSITY (GRANULAR SOILS) CONSISTENCY (FINE-GRAINED SOILS) N-value < 4 very loose N-value < 2 very soft 5-10 loose 3-4 soft 11-30 medium dense 5-8 medium stiff 31-50 dense 9-15 stiff >50 very dense 16-30 very stiff >30 hard After drilling, the test borings were backfilled with bentonite chips. The ground surface was patched with concrete. A chart showing the Unified Soil Classification System is included at the end of this appendix.