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Report (2) 3up2010 -- o7►94 " ,. Adapt Engineering, Inc. 9141frs4 - 10725 SW Barbur Boulevard, Suite 350 Portland, Oregon 97219 4 0111 Tel (503) 892 -2346 Fax (503) 892 -2348 www.adaptengr.com ADAPT June 28, 2010 Adapt Project No. OR10 -1 6454 -GEO AUG 19 2010 Clearwire c/o " °'"< s �� fir:' : 1 �.;<a ��M � Powder River Development Services BU W . D■VISIOpj 17400 Upper Boones Ferry Road, Suite 270 Portland, OR 97224 Attention: Mr. Matthew Carroz Subject: Geotechnical Engineering Evaluation Greton OR- POR424 -A 10250 SW North Dakota Street Tigard, Oregon 97223 Dear Mr. Carroz: Adapt Engineering, Inc. (Adapt) is pleased to submit this report describing our recent geotechnical engineering evaluation for the Greton POR424 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, equipment pad and tower foundations, 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 by Powder River Development on behalf of Clearwire prior to our performing the work. This report has been prepared in accordance with general accepted geotechnical engineering practices for the exclusive use of Powder River Development, Clearwire, 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 Engineering, Inc. Adapt appreciates the opportunity to be of service to you on this project. Should you have any questions concerning this report, or if we can assist you further, please contact us at (503) 892 -2346. Respectfully submitted, Adapt Engineering, Inc. � c � PROI�F� � G INF �9 % rLf / / • • -I Go 4N ' FC H. WAS Ekpinelx.. Daniel H. Watkins, P.E., G.E. Geotechnical Engineer . . or / 9- .//11�rce .. . V. Lew, P. Eng. Senior Geotechnical Engineer Senior Reviewer Attachments: Figure 1 Location/Topographic Map Figure 2 Site & Exploration Plan Boring Log B -1 • . • • Clearwire do Powder River Development Services June 28, 2010 Adapt Project No. OR10- 16454 -GEO • Adapt Engineering, Inc. 11* 10725 SW Barbur Boulevard, Suite 350 Portland, Oregon 97219 Tel (503) 892 -2346 Fax (503) 892 -2348 A DAPT www.adaptengr.com Clearwire c/o Powder River Development Geotechnical Engineering Evaluation • Greton OR- POR424 -A Tower Site Tigard, Oregon OR10- 16454 -GEO June 2010 • Clearwire c/a Powder River Development Services June 28, 2010 Adapt Project No. OR10- 16454 -GEO Adapt Engineering, Inc. PROJECT DESCRIPTION We understand that the proposed project will consist of the construction of a new communications tower and associated equipment shelter within the lease area. Current and future access is via the existing parking and gravel road to the site. The site is located at 10250 Southwest North Dakota Street, Tigard, Washington County, Oregon, as shown on the attached Location /Topographic Map (Figure 1). The proposed lease area and 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 Clearwire and Powder River Development. 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. EXPLORATORY METHODS We explored surface and subsurface conditions at the project site on June 24, 2010. Our surface exploration consisted of a visual site reconnaissance. Our subsurface exploration consisted of advancing one hollow stem auger boring (designated B - 1) to a maximum depth of approximately 41.5 feet below existing ground surface (bgs), within an accessible area near the proposed tower location. The procedures used for our 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. 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 truck- mounted, hollow -stem auger drill rig operated by an independent company working under subcontract to Adapt. A geotechnical representative of 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. Clearwire do Powder River Development Services June 28, 2010 Adapt Project No. OR10- 16454 -GEO Page 1 Adapt Engineering, Inc. During drilling, soil samples were obtained on 2.5 -foot and 5 -foot depth intervals using the Standard Penetration Test (SPT) procedure (ASTM: D 1586). This test and sampling method consists of driving a standard 2.0 -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. 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 borehole, the approximate groundwater depth is 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. SITE CONDITIONS The following sections describe our observations, measurements, and interpretations concerning surface, soil, groundwater, and seismic conditions at the project site. Surface conditions The proposed lease area is located to the north of an existing building and is level and covered with gravel, blackberries, and grass. There was no standing water present during our site visit. Subsurface Conditions Our subsurface exploration indicates the soil conditions in Boring B -1 (below the gravel surfacing) consist of medium stiff silty sand and/or loose sandy silt extending to approximately 13.0 feet bgs. Between approximately 13 feet and 20 feet bgs we encountered very loose silty fine sand grading to dense sand with varying amounts of silt between approximately 20 and 30 feet bgs. At 30 feet bgs we encountered interlayered medium dense silty fine sand and stiff fine sandy silt that extended to the maximum explored depth of 41.5 feet bgs. Groundwater and was encountered at approximately 16 feet bgs, in the boring, at the time of drilling. Throughout the year, groundwater levels would likely fluctuate in response to changing precipitation patterns, off -site construction activities, and changes in site utilization. Clearwire do Powder River Development Services June 28, 2010 Adapt Project No. OR10- 16454 -GEO Page 2 Adapt Engineering, Inc. Seismic Conditions Based on our analysis of the subsurface exploration logs and a review of published geologic maps, we interpret the on -site soil conditions to correspond to Site Class E, as defined by Table 1613.5.2 of the • 2006 International Building Code. The soil profile type for this site classification is characterized by soils with an average blowcount of less than 15 blows - per -foot within the upper 100 feet bgs. Current (2003) National Seismic Hazard Maps prepared by the U.S. Geological Survey indicate that peak bedrock site acceleration coefficients of about 0.187 and 0.398 are appropriate for an earthquake having a 10- percent and 2- percent probability of exceedance in 50 years (corresponding to return intervals of 475 and 2,475 years, respectively). The IBC mapped spectral accelerations for short periods at the subject site (S and S Site Class B) are 94.1 and 33.9 (expressed in percent of gravity) at 0.2 and 1.0- second periods, respectively with 2 percent probability of exceedance in 50 years. In accordance with Tables 1613.5.3(1) and 1613.5.3(2), Site Coefficients F and F„ are 0.971 and 2.645, respectively for a Site Class E. Therefore the adjusted MCE ground motions are S 0.914g and S 0.896g. For purposes of seismic site characterization, the observed soil conditions were extrapolated below the exploration termination depth, based on a review of geologic maps and our knowledge of regional geology. Site Liquefaction Risk Evaluation Given the seismic site classification "E ", we performed an engineering evaluation (per 2007 OSSC 1802.2.7) to assess the site - specific liquefaction risk. In our opinion, the combination of interlayered silty sand and sandy silt, as well as greater than three meters of non - liquefiable soil above the water table presents a low to moderate probability of liquefaction at this site. • CONCLUSIONS AND RECOMMENDATIONS Current development plans call for the construction of a new communications tower and associated } equipment shelter within the lease area. Current and future access is via the existing gravel driveway /storage area. Based on the subsurface conditions revealed by our subsurface exploration, the close proximity of the tower to an existing building, and the limited lease area space, we recommend the proposed telecommunication tower be supported on a concrete drilled pier foundation. Our specific recommendations concerning site preparation, equipment building/propane pad foundations, tower foundation, access driveway, and structural fill are presented in the following sections of this report. 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. Clearwire do Powder River Development Services June 28, 2010 Adapt Project No. OR10- 16454 -GEO Page 3 • Adapt Engineering, Inc. Clearing and Stripping: After surface and near - surface water sources have been controlled; the construction areas should be cleared and stripped of all vegetation, sod, topsoil, and debris. Our site exploration . indicates gravel, blackberries, and grass - will be - encountered within the lease area. • . Additionally, according to Pasquale Pascuzzi (property owner), a French drain that connects the roof down spouts runs somewhere through the lease area. 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. • • •Excavations: Site excavations ranging up to about 2 -feet deep are anticipated to accommodate the proposed equipment shelter foundation. Based on our explorations, we anticipate that this excavation will encounter medium stiff fine sandy silt. The surficial soils can be cut with conventional earth working equipment such as small dozers and trackhoes. We recommend the use of a smooth edge bucket to accomplish . foundation excavations to avoid unnecessary disturbance of the foundation subgrades. • Backfill materials, where required, should be placed and compacted according to recommendations presented in the Structural Fill section of this report. Dewatering: Based on our site reconnaissance investigation, we do not anticipate groundwater seepage within the upper 2.0 -feet. However, groundwater may fluctuate within the upper soils, as such, pumping • of accumulated groundwater, or surface runoff may be necessary depending on the actual excavation depth and the time of year that construction proceeds. If water is encountered, we anticipate that an internal system of ditches, sump holes, and pumps will be adequate to temporarily dewater the excavations. • Subgrade Preparation: Exposed subgrades for shallow footings, mat foundations, 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 Subgrades: If earthwork takes place during freezing conditions; we • recommend that all exposed subgrades be allowed to thaw and be.recompacted prior to placing foundations or subsequent lifts of structural fill. If soils are to wet to be compacted they should be removed and replaced with structural fill. • Equipment Building or Cabinet Foundations - • • It is our understanding that the. support 'pad for the proposed 'equipment building or cabinet pad will ' • consist of a poured -in- place, concrete' slab -on -grade with thickened edges; we recommend that these thickened slab edges be designed as spread footings. 'Alternatively, the equipment support pad may be designed as a structural slab -on -grade with a uniform thickness and a reduced bearing pressure. • In either case, we anticipate that the support pad bearing pressure will be relatively light. The following sections provide our recommendations and comments for equipment pad design and construction. • • Clearwire do Powder River Development Services June 28, 2010 - Adapt Project No. OR10- 16454 -GEO Page 4 • • Adapt Engineering, Inc. Subgrade Conditions: The prepared bearing subgrade soils should consist of firm and unyielding native fine sandy silt or. compacted structural_ fill. Exposed slab -on- grade, footing or overexcavation subgrades should be compacted to a firm, unyielding state, in accordance with the recommendations provided in the • • • Site Preparation section of this report. • Subgrade Verification: Footings or slabs -on -grade should never be cast atop soft, loose, organic, or frozen soils; nor atop subgrades covered by standing water. A representative from Adapt should be retained' to observe the condition of footing subgrades before concrete is poured to verify that they have been adequately prepared. Footing Overexcavation To limit settlements, we recommend that any loose or soft fill soils or unsuitable native organic soils encountered below the footing subgrade elevation be overexcavated and replaced with structural fill. Any locally deeper zones of organics or soft soils encountered at the base of the overexcavation should be removed and replaced with structural fill.. In consideration of the light loads imposed by the equipment, we recommend the overexcavation extend no deeper than 2 -feet below the thickened slab bearing elevation. Because foundation stresses are transferred outward as well as downward into the bearing soils, all footing overexcavations should also extend horizontally outward from the footing edge a distance equal to the one half the overexcavation depth for the structural backfill. Therefore, an overexcavation that .extends. 2 -feet below the footing base should also extend 1 -foot outward in all directions from the footing edges (a 2V 1 projected line from the bottom of the footing to the bottom of the fill prism). . Footing Dimensions: For a poured -in- place, concrete slab -on -grade with thickened -edge footings, we • recommend that the spread footing elements be constructed to have a minimum width of 12- inches. For frost protection, we recommend that the footings at this site penetrate at least 18- inches below the lowest adjacent exterior grades. • • Bearing Pressure and Lateral Resistance: A maximum allowable static bearing pressure of 1,500 pounds per- square -foot (psf) may be used for perimeter strip footings or thickened -edge pad footings designed as described above. For the alternate equipment support pad design using . a uniform thickness, structural slab -on - grade, we recommend a maximum allowable static soil bearing pressure of 500 psf across the pad area. These bearing pressure values can be increased by one -third to accommodate transient wind or seismic loads. An allowable base .friction coefficient of 0.31 and an allowable passive earth pressure of 250 pounds per cubic foot (pcf), expressed as an equivalent fluid unit weight, may be used for that portion • of the foundation embedded more than 1 -foot below finished exterior subgrade elevation. These lateral • resistance values incorporate a minimum safety factor of 1.5. Grading and Capping:. Final site grades should slope downward away from the structure so that runoff water will flow by gravity to suitable collection points, rather than ponding nearr the structure. Ideally, the area surrounding the structure would be capped with concrete, asphalt, or compacted, low - permeability • (silty) soils to reduce surface -water infiltration into the subsoils adjacent to/below the foundation. • Clearwire do Powder River Development Services June 28, 2010 Adapt Project No. OR10- 16454 -GEO • Page 5 Adapt Engineering, Inc. • Settlements: We estimate that total post - construction settlements of properly designed thickened -edge footings bearing on properly prepared subgrades could approach 1 -inch, with differential settlements approaching one -half of the total. For a structural slab -on -grade equipment pad with a uniform thickness (without thickened edges), somewhat greater movements may be experienced. 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 Capacities: We recommend that the drilled pier penetrate at least 25.0 -feet below the ground surface to fully penetrate the relatively soft/loose soils encountered between 13 feet and 20 feet bgs and bear well within the dense fine sand below 20 feet bgs. For vertical compressive soil bearing capacity, we recommend using the unit end bearing capacity presented in Table l below, where B is the diameter of the pier in feet and D is the depth of penetration into the bearing layer in feet. This allowable end bearing capacity includes a minimum safety factor of 1.5. • Table 1 Allowable End Bearing Capacity Depth (feet) Allowable Bearing Capacity (tsf) Limiting Point Resistance (tsf) 25-42 1.3 D/B 2.0 Frictional Capacities: For frictional resistance along the shaft of the drilled piers, acting both downward and in uplift, we recommend using the allowable skin friction value listed in Table 2. We recommend that frictional resistance be neglected in the uppermost 2 -feet below the ground surface. The allowable skin friction values presented includes a minimum safety factor of 1.5. Table 2 Allowable Skin Friction Capacities Depth (feet) Allowable Skin Friction (tsf) 0 -2 0.0 2 -13 0.06 13 -20 0.03 20-42 0.20 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. Clearwire do Powder River Development Services June 28, 2010 Adapt Project No. OR10- 16454 -GEO Page 6 Adapt Engineering, Inc. • 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. Our recommended passive earth pressures for the soil layers encountered at this site are presented in Table 3 and incorporate a safety factor of at least 1.5, which is commonly applied to transient or seismic loading conditions. 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. Table 3 Allowable Passive Pressures Depth (feet) Allowable Passive Pressure (pct) 0 -2 0 2 -13 250 13 -20 120 • 20-42 180 • 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 (k this relationship is expressed as p=k 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 k is also affected by the soil type, as follows: • SAND and Soft CLAY: For cohesionless soils (sand, non - plastic silt) and soft cohesive soils (clay, cohesive silt), the horizontal subgrade modulus (k increases linearly with depth (z). This relationship is expressed as k = n • where n is the coefficient of horizontal subgrade reaction and (zB) is the scaling • factor (B is the pier diameter). Clearwire do Powder River Development Services June 28, 2010 Adapt Project No. OR10- 16454 -GEO Page 7 Adapt Engineering, Inc. • Stiff or Hard CLAY: For stiff or hard cohesive soils (clay, cohesive silts), the horizontal subgrade modulus (k is essentially the same as the vertical subgrade modulus (k,,) and is considered constant with depth. This relationship is expressed as k /1.5[1], where [1(ft) /1.5B] is the scaling factor (B is expressed in feet). Our recommended values for the coefficient of horizontal subgrade reaction (n and the vertical subgrade modulus (k,,) for the soil layers encountered at this site are presented in Table 4 below. These values do not include a factor of safety since they model the relationship between contact pressure and displacement. 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. Table 4 Recommended Horizontal Subgrade Reaction Values Depth Interval nh k. (feet) (Pci) (pci) 0 -2 N/A 0 2 -13 8 N/A 13 -20 2 N/A 20-42 16 N/A Coefficient of Horizontal k n k =k J(1.5B) Subgrade Reaction (pci) (Sand & Soft Clay) (Stiff Clay) Construction Considerations: Our exploration revealed the site soils consist of medium stiff silty sand and/or loose sandy silt extending to approximately 13.0 feet bgs. Between approximately 13 feet and 20 feet bgs we encountered very loose silty fine sand grading to dense sand with varying amounts of silt between approximately 20 and 30 feet bgs. At 30 feet bgs we encountered interlayered medium dense silty fine sand and stiff fine sandy silt that extended to the maximum explored depth of 41.5 feet bgs. Groundwater and was encountered at approximately 16 feet bgs, in the boring, at the time of drilling. The foundation - drilling contractor should be prepared to case the excavation to prevent caving and raveling of the pier shaft sidewall due to the presence of soft/loose soils and the presence of granular soils below the groundwater table. 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 slurry 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 Clearwire c/o Powder River Development Services June 28, 2010 Adapt Project No. OR10- 16454 -GEO Page 8 .Adapt Engineering, Inc. • . remove loose soils and/or mud from the bottom of the pier. 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. Structural Fill We do not anticipate that site grading will include significant fills; however, the following recommendations for structural fill are provided for design and construction purposes, if required. Materials: Structural fill includes any fill materials placed under footings, pavements, or driveways. • Typical materials used for structural fill include: clean, well - graded sand and gravel; 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. Use of the on -site soils as structural fill is also feasible. Placement and Compaction: When used as structural fill, the upper gravelly on -site fill soils may be reused and should be placed in lifts with a maximum thickness of 8 inches and compacted to not less than 95 percent of the material's maximum dry density, as determined by ASTM D -1557. If the on -site fill soils cannot be properly moisture - conditioned, we recommend using imported granular material for structural fill. • Imported granular structural fill should consist of angular pit or quarry run rock, crushed rock, or crushed • gravel and sand that is fairly well graded between coarse and fine particle sizes. The fill should contain no organic matter or other deleterious materials, have a maximum particle size of one inch, and have less than 5 percent passing the U.S. No. 200 Sieve. In deep excavations, or where subgrade soils require stabilization, the particle size may be increased to four inches. The percentage of fines can be increased to 12 percent of the material passing the U.S. No. 200 Sieve if placed during dry weather and provided the fill material is moisture- conditioned, as necessary, for proper compaction. The material should be placed in lifts with a maximum uncompacted thickness of 12 inches and be compacted to less than 95 percent of the maximum dry density, as determined by ASTM D -1557. During the wet season or when wet subgrade conditions exist, the initial lift thickness should be increased to 24 inches and should be compacted by rolling with a smooth -drum, nonvibratory roller. CDF and lean-mix concrete do not require . special placement or compaction procedures. • Subgrades and Testing: Regardless of location or material, all structural fill should be placed over firm, unyielding subgrade soils. A representative from Adapt should be retained to observe the condition of • subgrade soils before fill placement begins, and that a material testing firm 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. • Clearwire do Powder River Development Services • June 28, 2010 Adapt Project No. OR10- 16454 -GEO "Page 9 Adapt Engineering, Inc. CLOSURE The conclusions and recommendations presented in this report are based, in part, on the explorations that we performed for this study. If variations in subsurface conditions are discovered during earthwork, we may need to modify this report. The future performance and integrity of the tower foundations will depend largely on proper initial site preparation, drainage, and construction procedures. Monitoring by experienced geotechnical personnel should be considered an integral part of the construction process. We are available to provide geotechnical inspection and testing services during the earthwork and foundation construction phases of the project. If variations in the subgrade conditions are observed at that time, we would be able to provide additional geotechnical engineering recommendations, thus minimizing delays as the project develops. We are also available to review preliminary plans and specifications before construction begins. p Clearwire do Powder River Development Services June 28, 2010 Adapt Project No. OR10- 16454 -GEO Page 10 • .....„... ...T.7.......s...,e-- ..... .,- .‘r.*:::717.1:::::T..-: .1: "-:. T7: • : ...-1' _ 2,4 ' ,s,,"..71;; ,..' " 0414. -- , za... , , -- . • . '. - • • .. I • ) ' ' Z . c ` (47 :. - 1' - •- • ,• -,._.....- --,,,.:._, -- „,10 ,....,, ....t ... . • ._-,.. . :.- , c77.&.• .. . -.,.., --:„. ,.. , •),,-,,,,,, iv,*---:.-:,, 6 .., ..,. . Ipi ,.. ) , ... • ,• it : . • ti,.• .1.-,.• •.• ki ) ✓ ji b! . •e.,.:• • ' . is-7 � J , . a - 1 : I ' . 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Location : Greton OR_POR424 -A 10725 SW Barbur Blvd., Suite 350 10250 SW North Dakota Street Tigard, Oregon 97223 Oregon 97219 Portland, Client : Clearwire do Powder River Development Tel: (503) 892 -2346 Fax: (503) 892 -2348 Date : 6/28/10 Job # : OR10- 16454 -GEO • GRASS AND TREES RAILROAD SW NORTH DAKOTA STREET GRASS FENCE I A* BLACK BERRIES GATE BORING • , B -1 ; — JERSEY BARRIER • • PROPOSED PROPOSED TOWER LEASE AREA PAVED PARKING • EXISTING BUILDING • N • Not to Scale Adapt Engineering, Inc. FIGURE 2 - Site & Exploration Plan p 9 9� Location : Greton OR- POR424 -A 10725 SW Barbur Blvd., Suite 350 10250 SW North Dakota Street • Portland, Oregon 97219 Tigard, Oregon 97223 Tel: (503) 892 -2346 Fax: (503) 892 -2348 Client : Clearwire do Powder River Development Date : 6/28/10 Job # : OR10-16454-GEO • Adapt Engineering, Inc. • r BORING LOG 10725 SW Barbur Blvd., Suite 350 Portland, Oregon 97219 TEL:503.892.2346 FAX: 503.892.2348 PROJECT : Greton OR- POR424 -A 10250 SW North Dakota Street Job Number: OR10 - 16454 Boring No.: B -1 Tigard, Oregon 97223 • Elevation R .r... nee : Woul Compl.t.d : N A TESTING mound So,(.,. El.otion: mpto D.,.u NA OBSERVATIONS th m Y O � EE -0 Gravel Surfacing ML - Medium stiff, light brown, fine sandy SILT, damp 3 .I 2 4 5 ML - Medium stiff, light brown, fine sandy SILT, damp, 2 (very little sample) I 2 3 5 • SM -ML - Loose /Stiff, brown and gray, silty fine SAND /fine sandy SILT, moist, mottled 3 3 4 1.5 5 10- SM -ML - Loose /Stiff, brown and gray, silty fine SAND /fine 1 sandy SILT, moist, mottled 4 3 1.0 3 15 SM - Very Loose, brown, silty fine SAND, saturated T 2 I 5 1 V 2 8/24/10 20- SM - Dense, brown, fine SAND, trace silt, saturated 6 I 6 9 13 • 25- SM - Dense, brown then gray, fine SAND, some silt, wet to 5 saturated 7 8 16 • p LEGEND I 2.Inch G.D. spin -Spoon Sample Static Water Level at MN; i Grab Sample DATE i 1' Geoprobe . Static Water Level Type of Analytical Testing Used DATE Page: X Sample not Recovered . t Perched Groundwater NR No Recovery 1 of 2 ATD At Tone of Mang Drilling Start Date: 6/24/10 Drilling Completion Date: 6/24/10 Logged By: DHW • • Adapt Engineering, Inc. BORING LOG 10725 SW Barbur Blvd., Suite 350 Portland, Oregon 97219 TEL:503.8922346 FAX: 503.892.2348 • PROJECT : Greton OR- POR424 -A 10250 SW North Dakota Street Job Number: OR10 -16454 Boring No.: B -1 Tigard, Oregon 97223 e Elevation 0.fu.nee : Well Completed : NA TESTING d.ound a ,,?... Elevation : Casino EN.aeon: NA OBSERVATIONS _ ¢ f 0 _ c. Ig V NF 47 Jo 8E OF y2 00 f 03 30 SM -ML - Medium dense /very stiff, gray, interlayered silty 1 4 . - fine SAND /fine sandy SILT, trace clay, wet to saturated 8 5 1.0 13 35 SM - Very Stiff, gray, fine sandy SILT, some clay, moist 7 9 7 0.5 10 40- SM -ML - Medium dense /very stiff, gray, interlayered silty T 6 _ fine SAND /fine sandy SILT, trace clay, wet to saturated , _ 10 16 1.0 • 17 • - Boring terminated at approximately 41•.5 feet bgs. Groundwater encountered at approximately 16 feet bgs - at time of drilling. - . - -- 45- • . - -- - 50 • • 55- a - - - - LEGEND I 2 -Inch G D Split -Spoon Sample s Static Water Level at DrlWg Grab Semple DATE i t' Geoprobe . Static Water Level iiii Type of Analytical Testing Used DATE Page: X Sample rot Recovered � Parched Groundwater NR No Recovery 2 of 2 ATD Al Time of Drilling Drilling Start Date: 6/24/10 Drilling Completion Date: 6/24/10 Logged By: DHW