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Home My WebLink AboutGEO2022-00048 for COM2022-00045 - GEO Geological Review - 4/22/2021 r E� ZDZZ- OOO�I� Adapt Consulting 615 8"'Avenue South Seattle,Washington 98104 Tel(206)654-7045 Fax(206)654-7048 www.adaptengr.com April 22,2021 Adapt Project No.WA20-22029-GEO Verizon Wireless c/o New Wave Architecture 1133 164th St. SW, Suite 202 Lynnwood, WA 98087 Attention: Jay Seo Subject: Geotechnical Engineering Evaluation WA4 Rainbow Lake E. McEwan Prairie Road Shelton,Washington 98584 Dear Mr. Seo: Adapt Consulting(Adapt) is pleased to submit this report describing our recent geotechnical engineering evaluation for the above referenced tower site. The purpose of this study was to interpret general surface and subsurface site conditions, from which we could evaluate the feasibility of the project and formulate design recommendations concerning site preparation, tower foundations, access road, structural fill, and other considerations. Our scope of services consisted of a surface reconnaissance, a subsurface exploration, geotechnical analyses, and report preparation. Authorization to proceed with our study was given in the form of a Verizon Wireless purchase order(Number:NNWR442182). This report has been prepared in accordance with general accepted geotechnical engineering practices for the exclusive use of Verizon Wireless, and their agents, for specific application to this project. Use or reliance upon this report by a third party is at their own risk. Adapt does not make any representation or warranty, express or implied, to such other parties as to the accuracy or completeness of this report or the suitability of its use by such other parties for any purpose whatever, known or unknown,to Adapt. Adapt Consulting We appreciate the opportunity to be of service to you. If you have any questions, or if we can be of further assistance to you,please contact us at(206)654-7045. Respectfully Submitted, Adapt Consulting, S:Z 6 2 —_ X V&*4N.) John Frazier,G.I.T. K. V.Lew,P.Longo Staff Geologist Senior Geotechnical Engineer JAMS' �O G SrONAI.� Timothy J.North,P.E. Geotechnical Engineer Senior Reviewer Attachments: Figure 1 Location/Topographic Map Figure 2 Site&Exploration Plan Boring Log B-1 Verizon Wireless April 22,2021 Adapt Project No.WA20-22029-GEO Adapt Consulting Verizon Wireless Geotechnical Engineering Evaluation WA4 Rainbow Lake Shelton, Washington WA20-22029-GEO April, 2021 Adapt Consulting PROJECT DESCRIPTION We understand that current development plans call for construction of a new self-supported telecommunications tower, equipment shelter, access road, and associated utilities. The site is located within a forested area, on commercial forestry land, south off E McEwan Prairie Road in Shelton, Washington; as shown on the attached Location/Topographic Map(Figure 1). The site may be accessed from the existing logging road. The existing and proposed site features, in relation to our exploration,are shown on the attached Site&Exploration Plan(Figure 2). It should be emphasized that the conclusions and recommendations contained in this report are based on our understanding of the currently proposed utilization of the project site, as derived from written and verbal information supplied to us by Verizon. Consequently, if any changes are made to the project, we recommend that we review the changes and modify our recommendations, if appropriate,to reflect those changes. DOCUMENT REVIEW As a part of our study, we reviewed the following maps and documents pertaining to the subject property and vicinity: United States. Department of Agriculture, Natural Resource Conservation Service. Soil Survey of Mason County Area, Washington. 1960. Washington State Department of Natural Resources, Washington Geologic Information Portal, Retrieved January 8,2021, https:Hgeologyportal.dnr.wa.gov/. Our conclusions and recommendations are based in part or wholly on the information contained in these documents. Our geotechnical recommendations are based in part on the accuracy of these documents; Adapt assumes no responsibility for errors or omissions resulting from possible inaccuracies on these documents prepared by others. EXPLORATORY METHODS We explored surface and subsurface conditions at the project site on April 15, 2021. Our surface exploration consisted of a visual site reconnaissance. Our subsurface exploration consisted of advancing one test boring (designated B-1) to a maximum depth of approximately 50-feet below existing ground surface(bgs)near the center of the lease area. The procedures used for subsurface exploration during our site visit are presented in the subsequent sections of this report. The location of the exploration advanced for this study is shown on the attached Figure 2. The specific location and depth of the exploration performed was selected in relation to the proposed site features, under the constraints of budget and site access. The boring location and other features shown on Figure 2 were obtained by hand taping from existing site features; as such,the exploration location shown should be considered accurate only to the degree implied by the measuring methods used. Verizon Wireless April 22,2021 Adapt Project No.WA20-22029-GEO Pagel Adapt Consulting It should be noted that the exploration performed for this evaluation revealed subsurface conditions only at a discrete location across the project site and that actual conditions in other areas could vary. Furthermore, the nature and extent of any such variations would not become evident until additional explorations are performed or until construction activities have commenced. If significant variations are observed at the time of construction, we may need to modify our conclusions and recommendations contained in this report to reflect the actual site conditions. Auger Boring Procedures The boring was advanced using a track-mounted, hollow-stem auger drill rig operated by an independent company working under subcontract to Adapt. A geotechnical representative from Adapt was on-site to observe the boring,obtain representative soil samples,and log the subsurface conditions.After the boring was completed,the borehole was backfilled with bentonite chips. During drilling, soil samples were obtained on 5-foot depth intervals using the Standard Penetration Test (SPT) procedure (ASTM: D 1586). This test and sampling method consists of driving a standard 2-inch outside diameter(OD)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 required to drive the sampler through each of the three, 6-inch intervals is noted. The total number of blows struck during the final 12 inches of penetration is considered the Standard Penetration Resistance, or"blow count". If 50 or more blows are struck within one 6-inch interval,the driving is ceased and the blow count is recorded as 50 blows for the actual number of inches of penetration. The resulting Standard Penetration Resistance values provide a measure of the relative density of granular soils or the relative consistency of cohesive soils. The Boring Log attached to this report describes the various types of soils encountered in the boring, based primarily on visual interpretations made in the field and supported by our subsequent laboratory examination and testing. The log indicates the approximate depth of the contacts between different soil layers, although these contacts may be gradational or undulating. Where a change in soil type occurred between sampling intervals, we inferred the depth of contact. Our log also graphically indicates the blow count,sample type, sample number,and approximate depth of each soil sample obtained from the boring, along with any laboratory tests performed on the soil samples. If any groundwater was encountered in the boreholes, the approximate groundwater depths are depicted on the boring log. Groundwater depth estimates are typically based on the moisture content of soil samples, the wetted height on the drilling rods, and the water level measured in the borehole after the auger has been extracted. Subsurface materials encountered were logged and classified in general accordance with the Manual Visual Classification Method(ASTM D 2488)by the geotechnical representative. SITE CONDITIONS The following sections describe our observations, measurements, and interpretations concerning surface, soil,groundwater,and seismic conditions at the project site: Verizon Wireless April 22,2021 Adapt Project No.WA20-22029-GEO Page 2 Adapt Consulting Surface Conditions Our surface exploration consisted of a visual site reconnaissance. The site is located in a forested area, approximately 300-feet south of E McEwan Prairie Road. The lease area was flagged at the time of our site visit. The ground was covered with immature trees and shrubs. The lease area and vicinity was characterized by flat topography. Subsurface Conditions At the exploration location designated B-1, the near surface soil conditions beneath a foot of surficial gravelly topsoil consists of approximately 9-feet of medium dense silty sand with gravel, overlying medium dense silty sandy gravel. The silty sandy gravel extended to about 25-feet bgs and was underlain by very dense silty sandy gravel from approximately 25-feet bgs to 40-feet bgs. At 40-feet bgs, our test boring encountered very dense coarse sand with silt and gravel. The coarse sand with silt and gravel extended to about 50 feet,the maximum depth of our boring. Groundwater was encountered in the test boring at the time of drilling,at ab out 34-feet bgs. Please note, throughout the year groundwater levels may likely fluctuate in response to changing precipitation patterns,off-site construction activities,and changes in site utilization. Seismic Conditions Based on our analysis of subsurface exploration logs and a review of published geologic maps, we interpret the on-site soil conditions to correspond to Site Class C, as defined by Table 20.3-1 within Chapter 20 of ASCE 7 in accordance with the 20181nternational Building Code(IBC). The soil profile type for this site classification is characterized by dense soils with an average blow count greater than 50 blows-per-foot within the upper 100 feet bgs. Our recommended seismic design parameters are summarized in the table below. Table 1 Seismic Design Parameters Short Period 1 Second Maximum Credible Spectral Acceleration Ss=1.53 I S1=0.572 Site Class C Site Coefficient Fa 1.2 F„=1.428 Design Spectral Response Acceleration Parameters SDs=1.224 SDI=0.544 For purposes of seismic site characterization, we extrapolated the soil conditions below the exploration termination depths,based on our knowledge of the regional geology. Verizon Wireless April 22,2021 Adapt Project No.WA20-22029-GEO Page 3 Adapt Consulting CONCLUSIONS AND RECOMMENDATIONS The current development plans call for construction of a new telecommunications tower and compound. Based on the site and subsurface conditions revealed by our field exploration,the proposed tower may be supported on either a drilled pier or concrete mat foundation. A drilled pier can provide a cost-effective foundation for communication tower structures, provided that adequate embedment depths can be achieved with the drilled pier augering equipment that the site is accessible to the drill rig, and that drilled pier contractors are available within a reasonable distance from the site. Alternatively, a reinforced concrete mat foundation may be selected if difficult drilling conditions are anticipated due to the presence of bedrock or boulders, provided that the proposed lease area can accommodate the generally larger excavation plan area required for a mat foundation. As the site is feasible for both foundation options from a geotechnical standpoint, we recommend foundation selection evaluate the economic cost for the foundation alternatives considering mobilization costs and contractor availability. For planning purposes, we have therefore provided design criteria for compressive, uplift and lateral support of both a mat foundation and a drilled pier foundation option below. Our specific recommendations concerning site preparation, equipment building or cabinet foundations, tower foundations,access driveway,and structural fill are presented in the subsequent sections. Site Preparation Preparation of the lease area for construction should involve clearing, grubbing, stripping, cutting, filling, dewatering,and subgrade preparation. We provide the following comments and recommendations relative to site preparation. Temporary Drainage: We recommend intercepting and diverting any potential sources of surface or near-surface water within the construction zones before stripping begins. Because the selection of an appropriate drainage system will depend on the water quantity, season, weather conditions, construction sequence, and contractor's methods, final decisions regarding drainage systems are best made in the field at the time of construction. Nonetheless, we anticipate that curbs, berms, or ditches placed along the uphill side of the work areas will adequately intercept surface water runoff. Clearing and Stripping: After surface and near-surface water sources have been controlled, the construction areas should be cleared and stripped of all vegetation,topsoil,and debris. Any miscellaneous materials stored in this area should be relocated. Our site exploration indicated surface soil conditions below our exploration below the topsoil consists of medium dense silty sand with gravel, but significant variations could exist. It should also be realized that if the stripping operation proceeds during wet weather, a generally greater stripping depth might be necessary to remove disturbed, surficial, moisture-sensitive soils; therefore, stripping is best performed during a period of dry weather. Backfill materials, where required, should be placed and compacted according to the recommendations presented in the Structural Fill section of this report. Verizon Wireless April 22,2021 Adapt Project No.WA20-22029-GEO Page 4 Adapt Consulting Excavations: Based on our exploration, we anticipate that shallow excavations will encounter consists of medium dense silty sand with gravel below a surficial topsoil layer. We anticipate these surficial soils can be cut with conventional earth working equipment such as small dozers and trackhoes. Backfill materials, where required, should be placed and compacted according to recommendations presented in the Structural Fill section of this report. Temporary Cut Slopes: All temporary soil cuts (greater than 4-feet in height) associated with site excavations or regrading activities should be adequately sloped back to prevent sloughing and collapse, unless a shoring box or other suitable excavation side wall bracing is provided. We tentatively recommend a maximum cut slope inclination of 1.51-1:1V(Horizontal:Vertical)within the medium dense surficial soils that will likely be exposed within the upper 4-feet below the ground surface across the site. If groundwater seepage is encountered within the excavation slopes,the cut slope inclination may need to be on the order of 2H:1V, or flatter. However, appropriate inclinations will ultimately depend on the actual soil, rock and groundwater seepage conditions exposed in the cuts at the time of construction. It is the responsibility of the contractor to ensure that the excavation is properly sloped or braced for worker safety protection, in accordance with OSHA safety guidelines. In addition to proper sloping, the excavation cuts should be draped with plastic sheeting for the duration of the excavation to minimize surface erosion and ravelling. Dewaterina: Our exploration encountered groundwater at about 34-feet bgs. However, perched groundwater may be encountered depending on the actual excavation depth and the time of year that construction proceeds. If groundwater is encountered, we anticipate that an internal system of ditches, sump holes,and pumps will be adequate to temporarily dewater the excavations. Subaade Preparation: Exposed subgrades for shallow footings, slabs-on-grade, roadway sections and other structures should be compacted to a firm, unyielding state, if required to achieve adequate density and warranted by soil moisture conditions. Any localized zones of loose,granular soils observed within a subgrade area should be compacted to a density commensurate with the surrounding soils. In contrast, any uncontrolled fill material or organic, soft, or pumping soils observed within a subgrade should be overexcavated and replaced with a suitable structural fill material. Frozen Sub rg ades: If earthwork takes place during freezing conditions, we recommend that all exposed subgrades be allowed to thaw and be re-compacted prior to placing foundations or subsequent lifts of structural fill. Tower Mat Foundation If chosen,the base of a mat foundation should be located at a minimum depth of about 4 feet bgs, on the medium dense gravelly silty sand. After excavation to design grade, the subgrade should be cleaned of material loosened by excavation. Irregularities resulting from the excavation should be filled with sand, lean concrete,or other suitable material to produce a level bearing surface for the foundation. Verizon Wireless April 22,2021 Adapt Project No.WA20-22029-GEO Page 5 Adapt Consulting We recommend using an ultimate static bearing capacity of 6,000 pounds per square foot (psf). In accordance with the provisions of the EIAMA 222-G code, this static bearing pressure does not incorporate a factor of safety. We estimate post construction settlements will be less than one inch. We estimate that the differential settlement will be approximately half of the total settlement. Lateral loads acting on the foundations can be resisted by passive earth pressure on one side of the foundation and by friction along the soil-concrete interface at the base of the foundation. We recommend using an ultimate foundation base friction coefficient of 0.60 for the medium dense gravelly silty sand.An ultimate passive earth pressure of 450 pounds per-cubic-foot(pcf), expressed as an equivalent fluid unit weight, may be used for that portion of the foundation embedded more than two foot below finished exterior subgrade elevation. In order to develop this capacity, concrete must be poured neat in excavations, the adjacent grade must be level, and the static ground water level must remain below the base of the footing throughout the year. The passive pressure within the upper two feet of embedment should be neglected. Eccentric loads and moments acting on the foundation produce a skewed bearing pressure distribution to the ground. The mat foundation should be sized so that the resultant load acts within the middle third of the foundation for one-way and two-way eccentric loading to maintain a compressive contact pressure along the base of the foundation. The maximum bearing pressure from the eccentric loading must be less than the ultimate bearing pressure given above. Tower Drilled Pier Foundations The subsurface soil and groundwater conditions observed in our site exploration are considered to be generally suitable for the use of a drilled pier foundation to support the proposed tower. The following recommendations and comments are provided for purposes of drilled pier design and construction. End Bearing Ca acp ities: We recommend that the drilled pier be founded on soils disclosed below 7.5-feet bgs. For vertical compressive soil bearing capacity, we recommend using the unit end bearing capacity presented in Table 2 below, where B is the diameter of the pier in feet and D is the depth into the bearing layer in feet,in accordance with the EIAMA G-code. This ultimate end bearing capacity does not include a safety factor. Table 2 Ultimate End Bearing Capacity Depth(feet) Ultimate Bearing Capacity(tsf) Limiting Point Resistance(tsf) 7.5-15 6.0 DB 10 15-25 12.0 DB 15 25-50 20.0 DB 20 Verizon Wireless April 22,2021 Adapt Project No.WA20-22029-GEO Page 6 Adapt Consulting 9 Frictional Capacities: For frictional resistance along the shaft of the drilled piers, acting both downward and in uplift, we recommend using the ultimate skin friction value listed in Table 3. We recommend that frictional resistance be neglected in the uppermost 2-feet below the ground surface. The ultimate skin friction values presented do not include a safety factor, in accordance with the provisions of the EIA/TIA 222-G code. Table 3 Ultimate Skin Friction Capacities Depth (feet) Ultimate Skin Friction(tsf) 0-2 0.00 � 2-10 0.60 10-15 0.25 15-25 0.75 25-50 0.90 Lateral Capacities: Drilled pier foundations for communication monopole towers are typically rigid and act as a pole, which rotates around a fixed point at depth. Although more complex and detailed analyses are available, either the simplified passive earth pressure method or the subgrade reaction method is typically used to determine the pier diameter and depth required to resist groundline reaction forces and moments. These methods are described below. • Passive Earth Pressure Method: The passive earth pressure method is a simplified approach that is generally used to estimate an allowable lateral load capacity based on soil wedge failure theory. Although the lateral deflection associated with the soil wedge failure may be estimated, design lateral deflections using the passive earth pressure method should be considered approximate, due to the simplified nature of the method. According to the NAVFAC Design Manual 7.02 (1986), a lateral deflection equal to about 0.001 times the pier length would be required to mobilize the allowable passive pressure presented below; higher deflections would mobilize higher passive pressures. The ultimate passive pressure may be taken as the product of the allowable pressure and factor of safety. Our recommended passive earth pressures for the soil layers encountered at this site are presented in Table 4 and do not incorporate a safety factor. These values are expressed as equivalent fluid unit weights, which are to be multiplied by the depth (bgs) to reflect the linear increase within the depth interval of the corresponding soil layer.The passive earth pressures may be assumed to act over an area measuring two pier diameters wide by up to eight pier diameters deep. Verizon Wireless April 22,2021 Adapt Project No.WA20-22029-GEO Page 7 Adapt Consulting Table 4 Ultimate Passive Pressures Depth (feet) Ultimate Passive Pressure(pen 0-2 0 2-10 450 10-15 500 15-25 600 25-34 750 34-50 600 • Subgrade Reaction Method: The subgrade reaction method is typically used to compute lateral design loads based on allowable lateral deflections. Using this method, the soil reaction pressure(p)on the face of the pier is related to the lateral displacement(y)of the pier by the horizontal subgrade modulus(kh); this relationship is expressed as p=khy- Because soil modulus values are based on small scale, beam load test data, and are usually reported as a vertical subgrade modulus (k,,), they must be converted to horizontal subgrade modulus values representative for larger scale applications (such as large pier diameters)by means of various scaling factors,as discussed below. In addition to the scaling and loading orientation, the soil-pier interaction governing kh is also affected by the soil type,as follows: • SAND and Soft CLAY: For cohesion-less soils (sand, non-plastic silt) and soft cohesive soils (clay, cohesive silt), the horizontal subgrade modulus (kh) increases linearly with depth(z). This relationship is expressed as kh=nhz(1B), where nh is the coefficient of horizontal subgrade reaction and (1B) is the scaling factor. • Stiff or Hard CLAY: For stiff or hard cohesive soils (clay, cohesive silts), the horizontal subgrade modulus(kh) is essentially the same as the vertical subgrade modulus (k,,) and is considered constant with depth. This relationship is expressed as kh=kJl(ft)/l.5B], where [1(ft)/1.5B] is the scaling factor (B is expressed in feet). Our recommended values for the coefficient of horizontal subgrade reaction(nh)and the vertical subgrade modulus (kv) for the soil layers encountered at this site are presented in Table 5 below. These values do not include a factor of safety since they model the relationship between contact pressure and displacement and are ultimate values. Therefore, the structural engineer or monopole manufacturer should select an appropriate allowable displacement for design, based on the specific requirements of the communication equipment mounted on the tower. Verizon Wireless April 22,2021 Adapt Project No.WA20-22029-GEO Page 8 Adapt Consulting Table 5 Recommended Horizontal Subgrade Reaction Values Depth Interval nh k, (feet) (pci) (pci) 0-2 0 N/A 2-10 20 N/A 10-25 50 N/A 25-34 125 N/A 34-50 90 N/A Coefficient of Horizontal kh=nh(z/B) kh=k„/(1.5B) Subgrade Reaction(pci) (Sand&Soft Clay) (Stiff Clay) Construction Considerations: Our explorations disclosed soil conditions beneath a foot of surficial gravelly topsoil consists of approximately 9-feet of medium dense silty sand with gravel, overlying medium dense silty sandy gravel. The silty sandy gravel extended to about 25-feet bgs and was underlain by very dense silty sandy gravel from approximately 25-feet bgs to 40-feet bgs. At 40-feet bgs, our test boring encountered very dense coarse sand with silt and gravel. The coarse sand with silt and gravel extended to about 50 feet,the maximum depth of our boring. Based the subsurface conditions disclosed in our exploration, knowledge of regional geology and reviewed geologic maps,the lease area is underlain by glacial deposits. Glacially derived soils commonly contain oversized soil particles, such as cobbles or "erratic" boulders. Drilling action indicated the presence of oversized particles, and difficult drilling conditions should be anticipated during operations through a glacial till deposit. It may be necessary to drill a small diameter pilot hole to initially penetrate the soils and reaming operations may prove difficult. Groundwater was encountered in the test boring at the time of drilling, at about 34-feet bgs. Please note, throughout the year groundwater levels may likely fluctuate in response to changing precipitation patterns, off-site construction activities, and changes in site utilization. Thus dewatering may be required depending on the actual depth and time of year of drilled pier construction. The foundation-drilling contractor should be prepared to case the excavation to prevent caving and raveling of the pier shaft sidewall, if necessary due to unexpected soil or excessive groundwater seepage conditions. Should heavy groundwater inflow be encountered in the drilled pier excavation, it may be necessary to pump out the accumulated groundwater prior to concrete placement, or to use a tremie tube to place the concrete from the bottom of the drilled pier excavation, thereby displacing the accumulated water during concrete placement. Alternatively, the use of bentonite slung could be utilized to stabilize the drilled pier excavation. Drilled Pier Excavation Conditions: The drilling contractor should be prepared to clean out the bottom of the pier excavation if loose soil is observed or suspected, with or without the presence of slurry or groundwater. As a minimum,we recommend that the drilling contractor have a cleanout bucket on site to Verizon Wireless April 22,2021 Adapt Project No.WA20-22029-GEO Page 9 Adapt Consulting remove loose soils and/or mud from the bottom of the pier. It may be necessary to drill a small diameter pilot hole to initially penetrate the soils and reaming operations may prove difficult. If groundwater is present and abundant within the pier hole, we recommend that the foundation concrete be tremied from the bottom of the hole to displace the water and minimize the risk of contaminating the concrete mix. The Drilled Shaft Manual published by the Federal Highway Administration recommends that concrete be placed by tremie methods if more than 3 inches of water has accumulated in the excavation. Dewatering may be required depending on the actual depth and time of year of drilled pier construction. The foundation-drilling contractor should be prepared to case the excavation to prevent caving and raveling of the pier shaft sidewall, if necessary due to unexpected soil conditions or excessive groundwater seepage. As the site soils were very dense at depth, and research indicates potential for the presence of oversized particles, the drilled pier contractor should be prepared for difficult drilling conditions. Foundation Construction Considerations A geotechnical engineer from Adapt (or their representative) should confirm suitable bearing conditions and evaluate the foundation subgrades. Localized deepening of footing excavations may be required to penetrate any deleterious materials. Because foundation stresses are transferred outward as well as downward into the bearing soils, all footing over-excavations should extend horizontally outward from the footing edge a distance equal to the one half the over-excavation depth for the structural backfill. Access Driveway Based on available site plans and our site reconnaissance visit, it may be necessary to construct a new access road. Should it be necessary to provide an extension to the existing roadways or to improve the existing access roads, we recommend that the subgrade be prepared in accordance with the Site Preparation section of this report. For planning purposes, we anticipate that 6 to 12-inches of"clean" sand and gravel subbase material and a minimum 3-inches of crushed rock surfacing will be required to create a stable gravel roadway surface at this site. Adapt can provide additional subgrade stabilization or gravel road section recommendations based on observed field conditions at the time of construction. Where cuts and fills are required,they should be accomplished in accordance with the recommendations provided in the Site Preparation and Structural Fill sections of this report. Structural Fill The following comments, recommendations, and conclusions regarding structural fill are provided for design and construction purposes. Materials: Structural fill includes any fill materials placed under footings, pavements, driveways, and other such structures.Typical materials used for structural fill include:clean,well-graded sand and gravel (pit-run); clean sand; crushed rock; controlled-density fill (CDF); lean-mix concrete; and various soil mixtures of silt, sand, and gravel. Recycled concrete, asphalt, and glass, derived from pulverized parent materials may also be used as structural fill. Verizon Wireless April 22,2021 Adapt Project No.WA20-22029-GEO Page 10 Adapt Consulting Placement and Compaction: Generally, CDF,and lean-mix concrete do not require special placement and compaction procedures. In contrast, pit-run, sand, crushed rock, soil mixtures, and recycled materials should be placed in horizontal lifts not exceeding 8 inches in loose thickness, and each lift should be thoroughly compacted with a mechanical compactor. Using the modified Proctor maximum dry density (ASTM: D-1557)as a standard,we recommend that structural fill used for various on-site applications be compacted to the following minimum densities: Fill Application Minimum Compaction Stab/Footing subgrade 90 percent Gravel drive subgrade(upper 1 foot) 95 percent Gravel drive subgrade(below 1 foot) 90 percent Subgrades and Testing: Regardless of location or material, all structural fill should be placed over firm, unyielding subgrade soils. We recommend that a representative from Adapt be retained to observe the condition of subgrade soils before fill placement begins, and to perform a series of in-place density tests during soil fill placement. In this way, the adequacy of soil compaction efforts may be evaluated as earthwork progresses. Fines Content: Soils used for structural fill should not contain individual particles greater than about 6 inches in diameter and should be free of organics, debris, and other deleterious materials. Given these prerequisites,the suitability of soils used for structural fill depends primarily on the grain-size distribution and moisture content of the soils when they are placed. When the "fines" content (that soil fraction passing the U.S. No. 200 Sieve) increases, soils become more sensitive to small changes in moisture content. Soils containing more than about 5 percent fines(by weight)cannot be consistently compacted to a firm, unyielding condition when the moisture content is more than about 2 percentage points above optimum. The sites near surface silty soils should be considered extremely moisture sensitive. The use of "clean"soil is necessary for fill placement during wet-weather site work,or if the in-situ moisture content of the sandy site soils is too high to allow adequate compaction. Clean soils are defined as granular soils that have a fines content of less than 5 percent(by weight)based on the soil fraction passing the U.S. 3/4- inch Sieve. CLOSURE We have prepared this report for use by the owner/developer, and other members of the design and construction team for the proposed WA4 Rainbow Lake tower site. The opinions and recommendations contained within this report are not intended to be, nor should they be, construed as a warranty of subsurface conditions,but are forwarded to assist in the planning and design process. We have made observations based on our explorations that indicate the soil conditions at only those specific locations and only to the depths penetrated. These observations do not necessarily reflect soil types,strata thickness,or water level variations that may exist in other locations. If subsurface conditions Verizon Wireless April 22,2021 Adapt Project No.WA20-22029-GEO Page 11 Adapt Consulting vary from those encountered in our site exploration, Adapt should be alerted to the change in conditions so that we may provide additional geotechnical recommendations, if necessary. The future performance and integrity of the improvements will depend largely on proper initial site preparation, drainage, and construction procedures. Observation by experienced geotechnical personnel should be considered an integral part of the construction process. The conclusions and recommendations contained in this report are based on our understanding of the currently proposed project, as derived from written and verbal information supplied to us by Verizon. When the design has been finalized, we recommend that we review the design and specifications to see that our recommendations have been interpreted and implemented as intended. If design changes are made, we request that we be retained to review our conclusions and recommendations and to provide a written modification or verification. The scope of our services does not include services related to construction safety precautions, and our recommendations are not intended to direct the contractor's methods, techniques, sequences, or procedures, except as specifically described in our report for consideration in design. Within the limitations of scope, schedule, and budget, our services have been executed in accordance with the generally accepted practices in this area at the time this report was prepared. No warranty or other conditions,express or implied, should be understood. Verizon Wireless April 22,2021 Adapt Project No.WA20-22029-GEO Page 12 7 SUBJECT SITE wigAdapt Inc. FIGURE 1 - Location & Topographic Map 615 8th Avenue South Location :WA4 Rainbow Lake Seattle, WashingtonE. McEwan Prairie Road Tel(206) 654-7045 Shelton, Washington 98584 Fax (206) 654-7048 Client :Verizon Date :04/22/21 .lob# : WA20-22029-GEO C FOREST—� (AVERAGE CANOPY HE IGH7 IS 47'AOL) OF 050A PROPOSED LATTICE TOWER Of 1224 PROPOSED LEASE AREA \ / ♦\ ',y; i / // T LEGEND: ' 1�--B-1 - BORING NUMBER AND APPROXIMATE LOCATION NOTES: n IMAGE BASED ON DRAWINGS PROVIDED BY VERIZON ' �J NOT TO SCALE Adapt Inc. FIGURE 2 - Site & Exploration Plan 615 8th Avenue South Location :WA4 Rainbow Lake Seattle, Washington E. McEwan Frairie Road Tel(206) 654-7045 Shelton,Washington 98584 ' Fax (206) 654-7048 Client :Verizon Date :04122121 Job# : WA20-22029-GEO Adapt Inc. BORING LOG ow 61s 8th Avenue South Seattle, Washington 99104 TEL 206 654 7045 FAX 206 554 2049 PROJECT :Rainbow Lake E.McEwan Prairie Rd Job Number, WA20-22029-GEO BoringNo.: B-1 Shelton,Washington 98584 64104e 4 0.1.... W.H C40er140d ... m..,.t.0...n..w.e C"'46- 1.. OBSERVATIONS resnrfc ' r 0 � 0 Organic rich, silty SAND with gravel. Grey, medium dense, grevelly silty SAND (SW-SM); dry 16 S-1 23 31 Limited recovery in 3-1 5 13 S-2 12 12 11 S-3 16 16 10 — — — — — — — — — — — — a Medium dense to dense, silty sandy GRAVEL S-4 8 (GW-GM); moist 6 15 12 S-5 17 19 20 16 S-6 20 24 255 — — — — — — — — — — — — S-7 50/3 Very dense, silty sandy GRAVEL (GW-GM); moist LEGEND: T 2—h O D SPI.-Spoon Same. Stec W.I.L.1.1.1 Dr.unq G,+6 S—Pi. 1 DATE 2-ndr O 0 Gaoprap. —V- Siano W.I.L—I Typ.of An.ly—I T.*,N UM4 DATE X S—pl.nol Recrnera4 71L P—rc.4 Grau d-W NR No Row—y 1 0(2 ATD Al Tim.of OnI.g Drilling Company:Boretec Drilling Start Date:4/15/21 Logged ByJBF Drilling Method:HSA Drilling Completion Date:4/15/21 Adapt Inc. BORING LOG im 615 8th Avenue South Seattle. Washington 98104 T E L 206 654 7045 FAX 206 6"7048 PROJECT :Rainbow Lake E.McEwan Prairie Rd Job Number: WA20-22029-GEO BoringNo.: B-1 Shelton,Washington 98584 u..a•e aN.•x•• ww c•.n•u. 4r•uN.whn fu••U•e C•Pq pn•x... Tf lTING OBSERVATIONS 30 Very dense, silty sandy GRAVEL (GW-GM); S-8 50/1 moist Groundwater encountered at about 34-feet bgs 35 Becomes Wet S-9 50/6 40 — — — — — — — — — — — S-10 50/4 Very dense, coarse SAND with gravel and silt Drillers noted heave action in (SP); wet boring at about 42-feet bgs 45 29 S-10 50/3 50 1-10 50/4 Boring terminated at approximately 50 ft bgs. Groundwater was encountered at about 34-feet bgs, at the time of drilling. Boring was backfilled with bentonite clay. LEGEND: I 2 rx6 0 D SPI.-Spoon Swpl. _ Sleec W.I.L•.N D.•xng G SwIi DATE 2-nv.O D G.oii n Sl.i W.I.L—I Tyi or A-1y6uW Toping Uwd ' DATE Page X S-91.not Rocrnx•O �_ Pad.ea r ouna.v w NR No R—Iry 2 Of 2 ATD At Time of Ding Drilling Company:Boretec Drilling Start Date:4/15/21 Logged By.JBF Drilling Method:HSA Drilling Completion Date:4/15/21