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Report (62) GeoPI_. Engineering,Inc. Real-World Geotechnical Solutions Investigation•Design•Construction Support September 13, 2016 ' Project No. 16-4211 RECEIVE. ment ' Spectrum Development Mrr.. Kurt Dalbey JUL 18 /01-; PO Box 1689 Lake Oswego, Oregon 97035 CITY OF TIGARD ' Email: kdalbey@gmail.com BUILDING.Qivisit1N CC: Shad Haney (slhaney©westlakeconsultants.com) ' Via email with hard copies mailed upon request ' SUBJECT: GEOTECHNICAL ENGINEERING REPORT DURHAM SQUARE I SOUTHWEST OF THE INTERSECTION OF SW 74TH AVENUE AND SW DURHAM ROAD TIGARD, OREGON This report presents the results of a geotechnical engineering study conducted by GeoPacific Engineering, Inc. (GeoPacific) for the above-referenced project. The purpose of our ' investigation was to evaluate subsurface conditions at the site and to provide geotechnical recommendations for site development. This geotechnical study was performed in accordance with GeoPacific Proposal No. P-5625, dated April 26, 2016 and your subsequent authorization of our proposal and General Conditions for Geotechnical Services. SITE AND PROJECT DESCRIPTION The subject site is located to the southwest of the intersection of SW 74th Avenue and SW Durham Road in the City of Tigard, Washington County, Oregon. Topography on the site is generally gently sloping at grades of 10 percent or less. However, along the western property boundary, topography slopes down at grades of approximately 50 percent down to Fanno Creek. These steeper slopes are up to about 10 feet tall and are evidence of past grading activity on the site. ' In the central and northern portions of the site, vegetation generally consists of9 rass and small brush, as the ground surface is covered with gravel fill material. The southern portion of the site ' is heavily vegetated, with brush and small to large trees. Preliminary plans indicate the proposed development will consist of the construction of two to Ithree new concrete tilt-up structures, parking areas, and associated underground utilities. We also understand that a retaining wall is proposed in the northern portion of the site, with an exposed height of up to 7 feet. I 14835 SW 72nd Avenue Tel(503)598-8445 Portland, Oregon 97224 Fax(503)941-9281 September 13, 2016 ' Project No. 16-4211 REGIONAL AND LOCAL GEOLOGIC SETTING '� I Regionally, the subject site lies within the Willamette Valley/Puget Sound lowland, a broad structural depression situated between the Coast Range on the west and the Cascade Range on the east. A series of discontinuous faults subdivide the Willamette Valley into a mosaic of fault-bounded, structural blocks (Yeats et al., 1996). Uplifted structural blocks form bedrock highlands, while down-warped structural blocks form sedimentary basins. The subject site is underlain by Quaternary age (last 1.6 million years)Willamette Formation, a catastrophic flood deposit associated with repeated glacial outburst flooding of the Willamette Valley river system (Madin, 1990). In the Willamette River Valley, these deposits consist of horizontally layered, micaceous, fine silt to coarse sand forming poorly-defined to distinct beds less than 3 feet thick. Underlying the Willamette Formation is Miocene (about 14.5 to 16.5 million years ago) Columbia River Basalt, a thick sequence of lava flows which forms the basement of the basin. REGIONAL SEISMIC SETTING At least three major fault zones capable of generating damaging earthquakes are thought to exist in the vicinity of the subject site. These include the Portland Hills Fault Zone, the Gales Creek- Newberg-Mt. Angel Structural Zone, and the Cascadia Subduction Zone. Portland Hills Fault Zone I The Portland Hills Fault Zone is a series of NW-trending faults that include the central Portland Hills Fault, the western Oatfield Fault, and the eastern East Bank Fault. These faults occur in a northwest-trending zone that varies in width between 3.5 and 5.0 miles. The combined three faults vertically displace the Columbia River Basalt by 1,130 feet and appear to control thickness changes in late Pleistocene (approx. 780,000 years) sediment (Madin, 1990). The Portland Hills Fault occurs along the Willamette River at the base of the Portland Hills, and is about 7.0 miles northeast of the site. The Oatfield Fault occurs along the western side of the Portland Hills, and is about 4.8 miles northeast of the site. The accuracy of the fault mapping is stated to be within 500 meters (Wong, et al., 2000). No historical seismicity is correlated with the mapped portion of the Portland Hills Fault Zone, but in 1991 a M3.5 earthquake occurred on a NW-trending shear plane located 1.3 miles east of the fault (Yelin, 1992). Although there is no definitive evidence of recent activity, the Portland Hills Fault Zone is assumed to be potentially active (Geomatrix Consultants, 1995). Gales Creek-Newberg-Mt. Angel Structural Zone ' The Gales Creek-Newberg-Mt. Angel Structural Zone is a 50-mile-long zone of discontinuous, NW-trending faults that lies about 12.8 miles southwest of the subject site. These faults are recognized in the subsurface by vertical separation of the Columbia River Basalt and offset seismic reflectors in the overlying basin sediment (Yeats et al., 1996; Werner et al., 1992). A geologic reconnaissance and photogeologic analysis study conducted for the Scoggins Dam site in the Tualatin Basin revealed no evidence of deformed geomorphic surfaces along the structural zone (Unruh et al., 1994). No seismicity has been recorded on the Gales Creek Fault(the fault closest to the subject site); however, these faults are considered to be potentially active because they may connect with the seismically active Mount Angel Fault and the rupture plane of the 1993 M5.6 Scotts Mills earthquake (Werner et al. 1992; Geomatrix Consultants, 1995). - 1 16-4211 -Durham Square GR 2 GEOPACIFIC ENGINEERING,INC. ISeptember 13, 2016 Project No. 16-4211 ICascadia Subduction Zone The Cascadia Subduction Zone is a 680-mile-long zone of active tectonic convergence where I oceanic crust of the Juan de Fuca Plate is subducting beneath the North American continent at a rate of 4 cm per year(Goldfinger et al., 1996). A growing body of geologic evidence suggests that prehistoric subduction zone earthquakes have occurred (Atwater, 1992; Carver, 1992; I Peterson et al., 1993; Geomatrix Consultants, 1995). This evidence includes: (1) buried tidal marshes recording episodic, sudden subsidence along the coast of northern California, Oregon, and Washington, (2) burial of subsided tidal marshes by tsunami wave deposits, (3) I paleoliquefaction features, and (4)geodetic uplift patterns on the Oregon coast. Radiocarbon dates on buried tidal marshes indicate a recurrence interval for major subduction zone earthquakes of 250 to 650 years with the last event occurring 300 years ago (Atwater, 1992; I Carver, 1992; Peterson et al., 1993; Geomatrix Consultants, 1995). The inferred seismogenic portion of the plate interface lies approximately along the Oregon Coast at depths of between 20 and 40 kilometers below the surface. I SUBSURFACE CONDITIONS Our site-specific explorations for this report were conducted on June 8. A total of five I exploratory borings (designated B-1 through B-5)were drilled. The borings were drilled to depths of 10.5 to 35 feet. The approximate locations of our excavations are shown on Figure 2. Exploration locations were located in the field by pacing or taping distances from apparent I property corners and other site features shown on the plans provided. As such, the locations of the explorations should be considered approximate. I - The boreholes conducted for this study were drilled using a trailer-mounted drill rig and solid stem auger methods. At each boring location, SPT(Standard Penetration Test) sampling was performed in general accordance with ASTM D1586 using a 2-inch outside diameter split-spoon I sampler and a 140-pound hammer equipped with an automatic hammer mechanism. During the test, a sample is obtained by driving the sampler 18 inches into the soil with the hammer free- falling 30 inches. The number of blows for each 6 inches of penetration is recorded. The Standard Penetration Resistance ("N-value") of the soil is calculated as the number of blows Irequired for the final 12 inches of penetration. If 50 or more blows are recorded within a single 6-inch interval, the test is terminated, and the blow count is recorded as 50 blows for the number of inches driven. This resistance, or N-value, provides a measure of the relative density I of granular soils and the relative consistency of cohesive soils. At the completion of the borings, the holes were backfilled with bentonite and patched with cold-patch asphalt pavement. I Explorations were conducted under the full-time observation of GeoPacific personnel. Soil samples obtained from the borings were classified in the field and representative portions were placed in relatively air-tight plastic bags. These soil samples were then returned to the I laboratory for further examination. Pertinent information including soil sample depths, stratigraphy, soil engineering characteristics, and groundwater occurrence was recorded. Soils were classified in general accordance with the Unified Soil Classification System. ISummary exploration logs are attached. The stratigraphic contacts shown on the individual borehole logs represent the approximate boundaries between soil types. The actual transitions may be more gradual. The soil and groundwater conditions depicted are only for the specific dates and locations reported, and therefore, are not necessarily representative of other locations and times. I I - 16-4211 -Durham Square GR 3 GEOPACIFIC ENGINEERING,INC. September 13, 2016 Project No. 16-4211 The following discussion is a summary of subsurface conditions encountered in our explorations. For more detailed information regarding subsurface conditions at specific exploration locations, refer to the attached boring logs. Also, please note that subsurface conditions can vary between exploration locations, as discussed in the Uncertainty and ' Limitations section below. Undocumented Fill: Underlying the ground surface in all exploration locates, we encountered undocumented fill material. We observed a thin layer of gravel base rock at all exploration locations, which generally consisted of%"-0 crushed aggregate. Underneath the existing base rock, the consistency of the fill material was highly variable. The fill material generally consisted of very soft to medium stiff SILT(ML) with SPT N-values of N=2 to N=6. However, the upper portion of undocumented fill material in boring B-5, located in the existing driveway alignment consisted of medium dense silt GRAVEL (GM)with an N-value of N=17. We observed some charred organic material in the fill, and encountered fine roots and pieces of wood in boring B-4. The depths of undocumented fill material encountered in our explorations are summarized on Table 1. Table 1 —Depths of Undocumented Fill and Buried Topsoil Exploration Depth of DUndocumented Designation Fill (ft) B-1 7.5 - B-2 1 B-3 2.5 B-4 14 B-5 7.5 Catastrophic Flood Deposits—Underlying the undocumented fill material in all exploration locations, we encountered Catastrophic Flood Deposits. The upper two to three feet of these soils generally consisted of sandy SILT (ML)to silty SAND (SM), which graded to sandy GRAVEL (GP). The upper portion of these soils was stiff or loose to medium dense, but graded to dense and very dense. Practical auger refusal was observed at depths of 16, and 10.5 feet in borings B-1 and B-2, respectively. Catastrophic Flood Deposits extended beyond the maximum depths of our explorations in all borings. Soil Moisture and Groundwater On June 8, 2016, groundwater seepage was encountered below depths of 7.5 and 13.5 feet in borings B-1 and B-3, respectively. No seepage or groundwater was encountered in the other borings. However, experience has shown that temporary storm related perched groundwater within surface soils often occur over native deposits such as those beneath the site, particularly during the wet season. It is anticipated that groundwater conditions will vary depending on the season, local subsurface conditions, changes in site utilization, and other factors. 16-4211 -Durham Square GR 4 GEOPACIFIC ENGINEERING,INC. ISeptember 13, 2016 Project No. 16-4211 ICONCLUSIONS AND RECOMMENDATIONS y Our investigation indicates that the proposed development is geotechnically feasible, provided I that the recommendations of this report are incorporated into the design and construction phases of the project. In our opinion, there are three main geotechnical issues for project completion. The first main issue is the presence of undocumented fill materials, which may I complicate site preparation and retaining wall construction. Undocumented fill material with highly variable consistency was encountered in all exploration locations to depths of up to 14 feet, as summarized on Table 1. The second main issue is the presence of groundwater I seepage at relatively shallow depths. On June 8, 2016, groundwater seepage was encountered at depths of 7.5 and 13.5 feet in borings B-1 and B-3, respectively. The third main issue for project construction is the potential for seismically induced settlement, currently estimated to Irange from 2 to 3 inches. A Cone Penetrometer Test (CPT)would help refine this range. The proposed retaining wall in the northern portion of the site should incorporated soldier piles, Ilightweight backfill, and drainage measures in order to improve slope stability. The following report sections provide recommendations for site development and construction in accordance with the current applicable codes and local standards of practice. ISite Preparation Areas of proposed buildings, streets, and areas to receive fill should be cleared of vegetation and any organic and inorganic debris. Existing structures should be demolished and any cavities structurally backfilled. Inorganic debris should be removed from the site. Organic-rich topsoil should then be stripped from construction areas of the site or where engineered fill is to l be placed. The estimated average necessary depth of removal in undisturbed, vegetated areas for moderately to highly organic soils is currently unknown, but is typically on the order of 8 to 12 inches. Deeper stripping may be necessary in localized areas, such as forested parts of the I site. The final depth of soil removal will be determined on the basis of a site inspection after the stripping/excavation has been performed. Stripped topsoil should be stockpiled only in designated areas and stripping operations should be observed and documented by the Igeotechnical engineer or his representative. Organic materials from clearing should either be removed from the site or placed as landscape fill in areas not planned for structures. Undocumented fill material may remain in place in the alignment of the proposed retaining wall 1 in the northern portion of the site, provided that the retaining wall is designed and constructed as described in the soldier pile retaining wall section of this report. I In building areas and areas to receive fill, remaining undocumented fills, buried topsoil, and subsurface structures (tile drains, basements, driveway and landscaping fill, old utility lines, septic leach fields, etc.) should be removed and the excavations backfilled with engineered fill. I Undocumented fill material was encountered in all exploration locations to depths of up to 14 feet, as summarized on Table 1 and shown on the attached Site Plan (Figure 2). Undocumented fill material should be removed from the influence zones of proposed structures, Iassumed at a line of 1.5H:1V from footings. In parking areas, the undocumented fill material may be evaluated by proofrolling. The I undocumented fill materials are likely suitable for reuse as engineered fill provided they are free of highly organic material and debris. We recommend full-time monitoring by GeoPacific during the removal period to assist in identifying materials suitable for re-use as engineered fill, and to verify that these soils are not mixed with organics or debris. I 16-4211 -Durham Square GR 5 GEOPACIFIC ENGINEERING,INC. September 13, 2016 ' Project No. 16-4211 Once stripping of a particular area is approved, the area must be ripped or tilled to a depth of 12 inches, moisture conditioned, root-picked, and compacted in-place prior to the placement of engineered fill or crushed aggregate base for pavement. Exposed subgrade soils should be ' evaluated by the geotechnical engineer. For large areas, this evaluation is normally performed by proof-rolling the exposed subgrade with a fully loaded scraper or dump truck. For smaller areas where access is restricted, the subgrade should be evaluated by probing the soil with a I steel probe. Soft/loose soils identified during subgrade preparation should be compacted to a firm and unyielding condition, over-excavated and replaced with engineered fill (as described below), or stabilized with rock prior to placement of engineered fill. The depth of overexcavation, if required, should be evaluated by the geotechnical engineer at the time of construction. Engineered Fill ' All grading for the proposed development should be performed as engineered grading in accordance with the applicable building code at time of construction with the exceptions and additions noted herein. Proper test frequency and earthwork documentation usually requires daily observation and testing during stripping, rough grading, and placement of engineered fill. Imported fill material must be approved by the geotechnical engineer prior to being imported to the site. Oversize material greater than 6 inches in size should not be used within 3 feet of foundation footings, and material greater than 12 inches in diameter should not be used in engineered fill. In general, we anticipate that soils from planned cuts and utility trench excavations will be suitable for use as engineered fill provided they are adequately moisture conditioned prior to compacting. Engineered fill should be compacted in horizontal lifts not exceeding 8 inches using standard .. I compaction equipment. We recommend that engineered fill be compacted to at least 95% of the maximum dry density determined by ASTM D698 (Standard Proctor) or equivalent. Field density testing should conform to ASTM D2922 and D3017, or D1556. All engineered fill should be observed and tested by the project geotechnical engineer or his representative. Typically, one density test is performed for at least every 2 vertical feet of fill placed or every 500 yd3, whichever requires more testing. Because testing is performed on an on-call basis, we recommend that the earthwork contractor be held contractually responsible for test scheduling and frequency. Site earthwork will be impacted by soil moisture. Earthwork in wet weather would likely require extensive use of cement or lime treatment, or other special measures, at considerable additional cost compared to earthwork performed under dry-weather conditions. I Excavating Conditions and Utility Trenches We anticipate that on-site soils can be excavated using conventional heavy equipment such as ' scrapers and trackhoes. All temporary cuts in excess of 4 feet in height should be sloped in accordance with U.S. Occupational Safety and Heath Administration (OSHA) regulations (29 CFR Part 1926), or be shored. The existing undocumented fill soils generally classify as Type B Soil and temporary excavation side slope inclinations as steep as 1H:1V may be assumed for planning purposes. The existing native soils classify as Type C Soil and temporary excavation side slope inclinations as steep as 1.5H:1 V may be assumed for planning purposes. These cut slope inclinations are applicable to excavations above the water table only. Maintenance of safe working conditions, including temporary excavation stability, is the responsibility of the I 16-4211 -Durham Square GR 6 GEOPACIFIC ENGINEERING,INC. September 13, 2016 Project No. 16-4211 ' contractor. Actual slope inclinations at the time of construction should be determined based on safety requirements and actual soil and groundwater conditions. ' Saturated soils and groundwater may be encountered in utility trenches, particularly during the wet season. Groundwater was encountered at relatively shallow depths in our test pit explorations. We anticipate that dewatering systems consisting of ditches, sumps and pumps ' would be adequate for control of perched groundwater, above the water table. Regardless of the dewatering system used, it should be installed and operated such that in-place soils are prevented from being removed along with the groundwater. ' Vibrations created by traffic and construction equipment may cause some caving and raveling of excavation walls. In such an event, lateral support for the excavation walls should be provided ' by the contractor to prevent loss of ground support and possible distress to existing or previously constructed structural improvements. ' PVC pipe should be installed in accordance with the procedures specified in ASTM D2321. We recommend that trench backfill be compacted to at least 95% of the maximum dry density obtained by Standard Proctor ASTM D698 or equivalent. Initial backfill lift thickness for a%"-0 crushed aggregate base may need to be as great as 4 feet to reduce the risk of flattening underlying flexible pipe. Subsequent lift thickness should not exceed 1 foot. If imported granular fill material is used, then the lifts for large vibrating plate-compaction equipment (e.g. hoe compactor attachments) may be up to 2 feet, provided that proper compaction is being I achieved and each lift is tested. Use of large vibrating compaction equipment should be carefully monitored near existing structures and improvements due to the potential for vibration- induced damage. Adequate density testing should be performed during construction to verify that the recommended relative compaction is achieved. Typically, one density test is taken for every 4 ' vertical feet of backfill on each 200-lineal-foot section of trench. Structural Foundations ' At the time of this report, specific structural loadings have not yet been developed. The proposed concrete tilt-up structures may be supported on shallow foundations bearing on competent undisturbed, native soils and/or engineered fill, appropriately designed and constructed as recommended in this report. Based on our understanding of the proposed building locations and the results of our exploration program, excavation depths of 1 to 7.5 feet may be required to reach competent native soils. Undocumented fill material was encountered ' in all of our exploration, to depths ranging from 1 to 14 feet. The depths of undocumented fill material encountered in our explorations are summarized on Table 1. Native soils consist of medium dense to very dense granular soils and should provide adequate support of structural ' loads. For footing subgrade soils prepared as recommended above, we recommend maximum allowable bearing pressures of 2,000 pounds per square foot (psf) in design of the below-grade portions of the structure. The recommended maximum allowable bearing pressures may be increased by 1/3 the above-recommended value, for short term transient conditions such as wind and seismic loading. All exterior and interior footings should be founded at least 18 inches Ibelow the lowest adjacent finished grade or below top of slab. Minimum footing widths should be determined by the project engineer/architect in accordance with applicable design codes. I 16-4211 -Durham Square GR 7 GEOPACIFIC ENGINEERING,INC. September 13, 2016 Project No. 16-4211 Assuming construction is accomplished as recommended herein, and for the foundation loads , anticipated, we estimate total static settlement of spread foundations of less than about 1 inch and differential settlement between two adjacent load-bearing components supported on competent soil of less than about�/ inch. We anticipate that the majority of the estimated ' settlement will occur during construction, as loads are applied. Wind, earthquakes, and unbalanced earth loads will subject the proposed structure to lateral forces. Lateral forces on a structure will be resisted by a combination of sliding resistance of its base or footing on the underlying soil and passive earth pressure against the buried portions of the structure. For use in design, a coefficient of friction of 0.42 may be assumed along the interface between the base of the footing and subgrade soils. Passive earth pressure for buried portions of structures may be calculated using an equivalent fluid weight of 320 pounds per cubic foot (pcf), assuming footings are cast against native soils or engineered fill. The recommended coefficient of friction and passive earth pressure values do not include a safety factor. The upper 12 inches of soil should be neglected in passive pressure computations unless it is protected by pavement or slabs on grade. Footing excavations should be trimmed neat and the bottom of the excavation should be carefully prepared. Loose, wet or otherwise softened soil should be removed from the footing excavation prior to placing reinforcing steel bars. GeoPacific should observe foundation ' excavations prior to placement of reinforcing steel and formwork, to verify that an appropriate bearing stratum has been reached and that the actual exposed soils are suitable to support the planned foundation loads. I The above foundation recommendations are for dry weather conditions. Due to the high moisture sensitivity of engineered fill and native soils, construction during wet weather is likely to I require overexcavation of footings and backfill with compacted, crushed aggregate. As a result of this condition, we recommend foundation excavations be observed to verify subgrade strength_ Soldier Pile Retaining Wall We understand that a retaining wall is proposed in the northern portion of the site, with a ' maximum exposed height of 7 feet. The proposed retaining wall is located in the middle of a slope, which consists of soft, undocumented fill soils. The construction of a conventional retaining wall at this location would cause excessive settlement and increase the risk of slope ' failure. Slope stability analyses performed on the existing slope show that the slope currently has factors of safety of 1.5 for static conditions and 1.0 for seismic conditions. In order to construct the proposed retaining wall without causing excessive settlement and while ' improving slope stability, we recommend that the retaining wall incorporate soldier piles, lightweight backfill, and drainage measures. A typical wall detail is shown on the attached Figure 3. The soldier piles should consist of 5-inch diameter, schedule 80 pipe piles embedded at least 3 feet into competent native soils. Based on subsurface conditions encountered in our explorations, we anticipate that pile lengths of 20 feet will achieve adequate embedment into competent native soils. The piles should be spaced on 6-foot centers. The pipe piles may driven or be installed in pre-drilled holes. Lagging between the piles may consist of galvanized wire mesh. Other lagging alternatives may be considered as well. Backfill behind the soldier pile retaining wall should consist of permeable, lightweight cellular concrete with a unit weight of 30 to 45 pcf. Lightweight cellular concrete should not be placed below an 16-4211 -Durham Square GR 8 GEOPACIFIC ENGINEERING,INC. ' September 13, 2016 Project No. 16-4211 ' elevation of 130 feet amsl. The lightweight cellular concrete should be benched into the existing soils on the slope, as shown on the attached wall detail (Figure 3). A chimney of drain rock at least 12 inches thick should be maintained behind the retaining wall. ' In order to develop sufficient passive resistance in the undocumented fill material, the upper 4 feet of soil at each pile location should be either excavated with a bucket at least 18 inches wide ' or drilled with a 18-inch diameter auger. After installation of the piles, this excavated section should be backfilled with concrete having a compressive strength of 2,500 psi. ' Slope stability analyses performed for the proposed configuration show that the slope has factors of safety of 2.2 for static conditions and 1.4 for seismic conditions. Based on the results of our analyses, the proposed configuration will have adequate factors of safety for global stability. Some static settlement may occur due to the placement of lightweight fill, traffic surcharge loads, and decomposition of organic material contained in the undocumented fill. It is our understanding that no structures are planned within the influence zone of the proposed ' retaining wall. The roadway planned above the retaining wall will be surfaced with asphalt pavement, which is flexible and should be able to deform sufficiently without distress. Erosion Control Considerations ' During our field exploration program, we did not observe soil types that would be considered highly susceptible to erosion. In our opinion, the primary concern regarding erosion potential I will occur during construction, in areas that have been stripped of vegetation. Erosion at the site during construction can be minimized by implementing the project erosion control plan, which should include judicious use of straw waddles and silt fences. If used, these erosion control devices should be in place and remain in place throughout site preparation and construction. Erosion and sedimentation of exposed soils can also be minimized by quickly re-vegetating ' exposed areas of soil, and by staging construction such that large areas of the project site are not denuded and exposed at the same time. Areas of exposed soil requiring immediate and/or temporary protection against exposure should be covered with either mulch or erosion control ' netting/blankets. Areas of exposed soil requiring permanent stabilization should be seeded with an approved grass seed mixture, or hydroseeded with an approved seed-mulch-fertilizer mixture. ' Wet Weather Earthwork Soils underlying the site are likely to be moisture sensitive and may be difficult to handle or ' traverse with construction equipment during periods of wet weather. Earthwork is typically most economical when performed under dry weather conditions. Earthwork performed during the wet-weather season will probably require expensive measures such as cement treatment or imported granular material to compact fill to the recommended engineering specifications. If earthwork is to be performed or fill is to be placed in wet weather or under wet conditions when soil moisture content is difficult to control, the following recommendations should be incorporated into the contract specifications. > Earthwork should be performed in small areas to minimize exposure to wet weather. ' Excavation or the removal of unsuitable soils should be followed promptly by the placement and compaction of clean engineered fill. The size and type of construction equipment used • may have to be limited to prevent soil disturbance. Under some circumstances, it may be 16-4211 -Durham Square GR 9 GEOPACIFIC ENGINEERING,INC. September 13, 2016 ' Project No. 16-4211 necessary to excavate soils with a backhoe to minimize subgrade disturbance caused by , equipment traffic; D The ground surface within the construction area should be graded to promote run-off of surface water and to prevent the ponding of water; D Material used as engineered fill should consist of clean, granular soil containing less than 5 percent fines. The fines should be non-plastic. Alternatively, cement treatment of on-site soils may be performed to facilitate wet weather placement; > The ground surface within the construction area should be sealed by a smooth drum vibratory roller, or equivalent, and under no circumstances should be left uncompacted and exposed to moisture. Soils which become too wet for compaction should be removed and replaced with clean granular materials; > Excavation and placement of fill should be observed by the geotechnical engineer to verify ' that all unsuitable materials are removed and suitable compaction and site drainage is achieved; and > Straw waddles and/or geotextile silt fences should be strategically located to control erosion. If cement or lime treatment is used to facilitate wet weather construction, GeoPacific should be contacted to provide additional recommendations and field monitoring. Concrete Slabs-on-Grade Preparation of areas beneath concrete slab-on-grade floors should be performed as recommended in the Site Preparation section. Care should be taken during excavation for foundations and floor slabs, to avoid disturbing subgrade soils. If subgrade soils have been adversely impacted by wet weather or otherwise disturbed, the surficial soils should be scarified to a minimum depth of 8 inches, moisture conditioned to within about 3 percent of optimum moisture content, and compacted to engineered fill specifications. Alternatively, disturbed soils may be removed and the removal zone backfilled with additional crushed rock. For evaluation of the concrete slab-on-grade floors using the beam on elastic foundation method, a modulus of subgrade reaction of 150 kcf(87 pci) should be assumed for the medium stiff native silt soils anticipated at subgrade depth. This value assumes the concrete slab system is designed and constructed as recommended herein, with a minimum thickness of crushed rock of 8 inches beneath the slab. Interior slab-on-grade floors should be provided with an adequate moisture break. The capillary break material should consist of ODOT open graded aggregate per ODOT Standard Specifications 02630-2. The minimum recommended thickness of capillary break materials on re-compacted soil subgrade is 8 inches. The total thickness of crushed aggregate will be dependent on the subgrade conditions at the time of construction, and should be verified visually by proof-rolling. Under-slab aggregate should be compacted to at least 90% of its maximum dry density as determined by ASTM D1557 or equivalent. In areas where moisture will be detrimental to floor coverings or equipment inside the proposed I structure, appropriate vapor barrier and damp-proofing measures should be implemented. Appropriate design professionals should be consulted regarding vapor barrier and damp proofing systems, ventilation, building material selection and mold prevention issues, which are outside GeoPacific's area of expertise. 16-4211 -Durham Square GR 10 GEOPACIFIC ENGINEERING,INC. ' September 13, 2016 Project No. 16-4211 ' r Footing and Roof Drains If the proposed structures will have a raised floors, and no concrete slab-on-grade floors are used, ' perimeter footing drains would not be required based on soil conditions encountered at the site and experience with standard local construction practices. Where it is desired to reduce the potential for moist crawl spaces, footing drains may be installed. If concrete slab-on-grade floors ' are used, perimeter footing drains should be installed as recommended below. Where used, perimeter footing drains should consist of 3 or 4-inch diameter, perforated plastic pipe embedded in a minimum of 1 ft3 per lineal foot of clean, free-draining drain rock. The drain pipe and surrounding drain rock should be wrapped in non-woven geotextile (Mirafi 140N, or approved equivalent)to minimize the potential for clogging and/or ground loss due to piping. ' Water collected from the footing drains should be directed to the local storm drain system or other suitable outlet. A minimum 0.5 percent fall should be maintained throughout the drain and non- perforated pipe outlet. The footing drains should include clean-outs to allow periodic maintenance and inspection. In our opinion, footing drains may outlet at the curb, or on the back sides of lots where sufficient fall is not available to allow drainage to the street. Construction should include typical measures for controlling subsurface water beneath the ' structure, including positive crawlspace drainage to an adequate low-point drain exiting the foundation, visqueen covering the exposed ground in the crawlspace, and crawlspace ventilation (foundation vents). The client should be informed and educated that some slow flowing water in I the crawlspaces is considered normal and not necessarily detrimental to the home given these other design elements incorporated into its construction. Appropriate design professionals should be consulted regarding crawlspace ventilation, building material selection and mold prevention ' issues, which are outside GeoPacific's area of expertise. Down spouts and roof drains should collect roof water in a system separate from the footing drains in order to reduce the potential for clogging. Roof drain water should be directed to an appropriate discharge point well away from structural foundations. Grades should be sloped downward and away from buildings to reduce the potential for ponded water near structures. Pavement Design -On Site Private Driveways and Parking Areas We understand that the proposed new on site automobile driveways and parking areas will be ' surfaced with asphalt concrete pavement. We assume the proposed new automobile driveways will be subjected to an initial two-way ADT(average daily traffic count) of 400 vehicles per day, and that the automobile parking areas will be subjected to an initial ADT of 100 vehicles per ' day. Further, we assumed 3 percent of the vehicles will be heavy trucks (FHWA Class 5 or greater). For design purposes, we assume that the native soils on the site exhibit a resilient modulus of at least 4,500 pci, based on the results of our explorations. Table 2 presents the recommended section thicknesses for the proposed on site automobile driveways and parking areas that are to be completed as part of the project, under dry weather construction conditions. In our opinion, this pavement section is suitable to support the anticipated light levels of traffic. ' The pavement sections recommended in Table 2 are for typical volumes of light automobile traffic. Heavy truck traffic will reduce the design life of the pavements and may lead to inadequate pavement performance. If heavy truck traffic is anticipated, GeoPacific should be 16-4211 -Durham Square GR 11 GEOPACIFIC ENGINEERING,INC. September 13, 2016 Project No. 16-4211 contacted for additional pavement design recommendations based on the traffic volumes ' expected. Table 2 - Recommended Minimum Dry-Weather Pavement Section , Layer Thickness (inches) Material Layer Compaction Standard Driving Lanes Parking Areas Asphaltic Concrete (AC) 4 3 91% of Rice Density AASHTO T-209 Crushed Aggregate Base2 2 95% of Modified Proctor 3/4"-0 (leveling course) ASTM D1557 Crushed Aggregate Base12 8 95% of Modified Proctor 1%"-0 ASTM D1557 Recommended Subgrade 12 12 95% of Standard Proctor or Approved Subgrade ' Any pockets of organic debris or loose fill encountered during subgrade preparation should be removed and replaced with engineered fill (see Site Preparation Section). In order to verify subgrade strength, we recommend proof-rolling directly on subgrade with a loaded dump truck during dry weather and on top of base course in wet weather. Soft areas that pump, rut, or weave should be stabilized prior to paving. If pavement areas are to be constructed during wet I weather, the subgrade and construction plan should be reviewed by the project geotechnical engineer at the time of construction so that condition specific recommendations can be provided. The moisture sensitive subgrade soils make the site a difficult wet weather construction project. General recommendations for wet weather pavement construction are presented below. During placement of pavement section materials, density testing should be performed to verify ' compliance with project specifications. Generally, one subgrade, one base course, and one asphalt compaction test is performed for every 100 to 200 linear feet of paving. Wet Weather Construction Pavement Section This section presents our recommendations for wet weather pavement sections, which are for ' construction of on-site driving lanes and parking areas. These wet weather pavement section recommendations are intended for use in situations where it is not feasible to compact the subgrade soils to Clackamas County requirements, due to wet subgrade soil conditions, and/or construction during wet weather. Based on our site review, we recommend a wet weather section with a minimum subgrade deepening of 6 inches to accommodate a working subbase of additional 1W-0 crushed rock. Geotextile fabric, Mirafi 500x or equivalent, should be placed on subgrade soils prior to placement of base rock. I In some instances it may be preferable to use Special Treated Base (STB) in combination with overexcavation and increasing the thickness of the rock section. GeoPacific should be consulted for additional recommendations regarding use of STB in wet weather pavement sections if it is desired to pursue this alternative. Cement treatment of the subgrade may also be considered instead of overexcavation. For planning purposes, we anticipate that treatment - I 16-4211 -Durham Square GR 12 GEOPACIFIC ENGINEERING,INC. ' September 13, 2016 Project No. 16-4211 of the on-site soils would involve mixing cement powder to approximately 6 percent cement content and a mixing depth on the order of 12 inches. ' With implementation of the above recommendations, it is our opinion that the resulting pavement sections will provide equivalent or greater structural strength than the dry weather pavement section currently planned. However, it should be noted that construction in wet ' weather is challenging, and the performance of pavement subgrade depend on a number of factors including the weather conditions, the contractor's methods, and the amount of traffic the areas are subjected to. There is a potential that soft spots may develop even with ' implementation of the wet weather provisions recommended in this letter. If soft spots in the subgrade are identified during roadway excavation, or develop prior to paving, the soft spots should be over-excavated and backfilled with additional crushed rock. During subgrade excavation, care should be taken to avoid disturbing the subgrade soils. Removals should be performed using an excavator with a smooth-bladed bucket. Truck traffic ' should be limited until an adequate working surface has been established. We suggest that the crushed rock be spread using bulldozer equipment rather than dump trucks, to reduce the amount of traffic and potential disturbance of subgrade soils. ' Care should be taken to avoid over-compaction of the base course materials, which could create pumping, unstable subgrade soil conditions. Heavy and/or vibratory compaction efforts should be applied with caution. Following placement and compaction of the crushed rock to I project specifications (95% of AASHTO T-180), a finish proof-roll should be performed before paving. I The above recommendations are subject to field verification. GeoPacific should be on-site during construction to verify subgrade strength and to take density tests on the engineered fill, base rock and asphaltic pavement materials. Seismic Design Structures should be designed to resist earthquake loading in accordance with the methodology described in the 2012 International Building Code (IBC), ASCE 7, and with applicable Oregon Structural Specialty Code (OSSC) revisions (current 2014). We recommend Site Class D be used for design per the OSSC, Table 1613.5.2 and as defined in ASCE 7, Chapter 20, Table 20.3-1. Design values determined for the site using the USGS (United States Geological Survey) Seismic Design Maps Summary Report, are summarized in Table 3. • 16-4211 -Durham Square GR 13 GEOPACIFIC ENGINEERING,INC. September 13, 2016 , Project No. 16-4211 Table 3 - Recommended Earthquake Ground Motion Parameters (2016 USGS) ' Parameter Value Location (Lat, Long), decimal 45.403, -122.755 Probabilistic Ground Motion Values, 2% Probability of Exceedance in 50 yrs Peak Ground Acceleration 0.419 g Short Period, Ss 0.963 g 1.0 Sec Period, Si 0.419 g Soil Factors for Site Class D: Fa 1.115 FY 1.581 Residential Site Value = 2/3 x Fa x Ss 0.716 g Residential Seismic Design Category D Soil liquefaction is a phenomenon wherein saturated soil deposits temporarily lose strength and ' behave as a liquid in response to earthquake shaking. Soil liquefaction is generally limited to loose, granular soils located below the water table. Following site development, soils on the site will consist of soft to medium stiff silt fill material, medium stiff to stiff silt, loose to medium dense native sand, and medium dense to very dense gravel. A layer of loose silty sand was encountered below a depth of 6 feet and a layer of loose sand interbedded with sandy silt was encountered from 10 to 15 feet in boring B-3. The portions of these layers below the water table are considered potentially liquefiable. According to the Oregon HazVu: Statewide Geohazards Viewer, the subject site is regionally characterized as having a high risk of liquefaction (DOGAMI:HazVu, 2016). A preliminary assessment of liquefaction induced settlement was performed based on the Standard Penetration Test N-values obtained from borings on the site. However, these N-values are considered imprecise due to the solid stem auger/open hole method of drilling and sampling. It is likely that a significant amount of soil heave and disturbance occurred during sampling, particularly below groundwater levels, where the soil density is of most interest in a soil liquefaction evaluation. Soil heave and disturbance during drilling can cause the N-values to be lower than they would be in an undisturbed condition. GeoPacific analyzed soil liquefaction potential using the maximum considered peak ground 1 acceleration, in accordance with Section 1803.5.12 of the 2014 OSSC. The boring log data was analyzed using the SPT-based methodology and the commercial computer program Liquify5. For the purposes of liquefaction analyses, we assumed groundwater at depths of 6 and 8.5 feet below the ground surface. On June 8, 2016 groundwater was encountered at a depth of 8.5 feet. The preliminary assessment of liquefaction hazard indicates that potentially liquefiable zones exist in the depth interval between about 6 and 15 feet. For seismic settlement estimates, see the following report section. More precise estimates of the soil liquefaction hazard can be made by performing a Cone Penetrometer Tests (CPT) on the site. The CPT method is anticipated to provide a more reliable estimate of the soil liquefaction hazard on the site because it provides continuous information regarding stratification of the soils and direct measurements of undisturbed in-situ soil properties. If desired, GeoPacific can be consulted to coordinate CPT testing on the site, analyze the CPT results, and present a refined assessment of soil liquefaction potential. . 1 16-4211 -Durham Square GR 14 GEOPACIFIC ENGINEERING,INC. ' September 13, 2016 Project No. 16-4211 ' Seismically Induced Settlements Settlement of the ground surface may occur as a result of earthquake shaking, particularly ' where soil liquefaction occurs. It has long been recognized that sands tend to settle and densify when subjected to earthquake shaking. Using the methodologies of Ishihara/Yoshime and Idris/Seed, we estimated seismic-induced settlements at the site. For the purpose of this ' evaluation, we used estimated ground motions for the design earthquake. We estimated seismic-induced settlements for both liquefied and non-liquefied soil layers, as well as saturated and unsaturated soil zones. Results of these estimates are considered imprecise due to the solid stem auger/open hole method of drilling and sampling, as previously discussed. Based on the results of our analyses, 2 to 3 inches of seismically induced settlement are estimated on the site. Based on this preliminary evaluation, it is our opinion that the proposed structure may experience settlements on the order of 2 to 3 inches during the assumed seismic event. We anticipate that differential settlement would be approximately one-half of the total estimated settlement, measured between two adjacent building foundation components. The project structural engineer and/or architect should evaluate the existing structure to determine if it can ' accommodate the estimated seismic settlements without risk of structural collapse. It should be noted that under the assumed seismic events, some damage may occur to the structure due to differential settlement. Substantial repair costs and/or loss of use may result from a significant earthquake event near the site. I :, In order to lower the risk of damage to the structure in the event of a seismic event, the proposed structure could be founded on a mat slab, spread footings supported by deep I foundations, or a mat slab supported by deep foundations. If these alternative foundation systems are desired, GeoPacific can be consulted to provide additional recommendations for structural foundations. Rammed aggregate piers, or geopiers, may also be a feasible solution for the site. Geopiers are typically designed and installed by a design-build contractor, but GeoPacific may be consulted to provide the design-build contractor with information and review the proposed foundation plan, if that option is selected. ' Detailed assessment of lateral spreading hazards are beyond the scope of this study. However, Based on the depths of the liquefiable layers, the gentle slope of the native soil, and on ' horizontal distances from slope faces, the risk of lateral spreading is anticipated to be low. As previously discussed, the estimates of seismic induced settlements can be refined by using CPT data instead of SPT N-values. The CPT method is anticipated to provide a more reliable estimate of the seismically induced settlements on the site because it provides continuous information regarding stratification of the soils and direct measurements of undisturbed in-situ soil properties. If desired, GeoPacific can be consulted to coordinate CPT testing on the site, analyze the CPT results, and present a refined assessment of soil liquefaction potential. I II16-4211 -Durham Square GR 15 GEOPACIFIC ENGINEERING,INC. September 13, 2016 , Project No. 16-4211 UNCERTAINTIES AND LIMITATIONS , We have prepared this report for the owner and their consultants for use in design of this project only. This report should be provided in its entirety to prospective contractors for bidding and , estimating purposes; however, the conclusions and interpretations presented in this report should not be construed as a warranty of the subsurface conditions. Experience has shown that soil and groundwater conditions can vary significantly over small distances. Inconsistent conditions can occur between explorations that may not be detected by a geotechnical study. If, during future site operations, subsurface conditions are encountered which vary appreciably from those described herein, GeoPacific should be notified for review of the recommendations of this report, and revision of such if necessary. Sufficient geotechnical monitoring, testing and consultation should be provided during construction to confirm that the conditions encountered are consistent with those indicated by explorations, and to verify that the geotechnical aspects of construction comply with the contract plans and specifications. Within the limitations of scope, schedule and budget, GeoPacific attempted to execute these services in accordance with generally accepted professional principles and practices in the fields of geotechnical engineering and engineering geology at the time the report was prepared. No warranty, expressed or implied, is made. The scope of our work did not include environmental assessments or evaluations regarding the presence or absence of wetlands or hazardous or toxic substances in the soil, surface water, or groundwater at this site. I We appreciate this opportunity to be of service. Sincerely, . I GEOPACIFIC ENGINEERING, INC. uSA.4 ,cs,4•\-4 ,17,) 900 4 � - (iikvA 03, 22, 0Y 43' IN G, PNO 47:Ars: 12150/ Benjamin G. Anderson, P.E. Project Engineer 111 Attachments: References Figure 1 —Vicinity Map Figure 2—Site Plan and Exploration Locations Figure 3—Soldier Pile Retaining Wall Typical Detail Boring Logs (B-1 through B-5) Slope/W Plots of Slopes Stability Analyses (4 Pages) LiquifyPro Liquefaction Analyses and Research (4Pages) - 164211 -Durham Square GR 16 GEOPACIFIC ENGINEERING,INC. 1 September 13, 2016 Project No. 16-4211 IREFERENCES I Atwater, B.F., 1992, Geologic evidence for earthquakes during the past 2,000 years along the Copalis River, southern coastal Washington: Journal of Geophysical Research, v. 97, p. 1901-1919. Carver, G.A., 1992, Late Cenozoic tectonics of coastal northern California: American Association of IPetroleum Geologists-SEPM Field Trip Guidebook, May, 1992. Geomatrix Consultants, 1995, Seismic Design Mapping, State of Oregon: unpublished report prepared for IOregon Department of Transportation, Personal Services Contract 11688, January 1995. Goldfinger, C., KuIm, L.D., Yeats, R.S.,Appelgate, B, MacKay, M.E., and Cochrane, G.R., 1996, Active strike-slip faulting and folding of the Cascadia Subduction-Zone plate boundary and forearc in I central and northern Oregon: in Assessing earthquake hazards and reducing risk in the Pacific Northwest, v. 1: U.S. Geological Survey Professional Paper 1560, P. 223-256. I Madin, I.P., 1990, Earthquake hazard geology maps of the Portland metropolitan area, Oregon: Oregon Department of Geology and Mineral Industries Open-File Report 0-90-2, scale 1:24,000, 22 p. Oregon Department of Geology and Mineral Industries, HazVu website I (http://www.oregongeology.org/hazvu) Peterson, C.D., Darioenzo, M.E., Burns, S.F., and Burris, W.K., 1993, Field trip guide to Cascadia I paleoseismic evidence along the northern California coast: evidence of subduction zone seismicity in the central Cascadia margin: Oregon Geology, v. 55, p. 99-144. Unruh, J.R., Wong, I.G., Bott, J.D., Silva, W.J., and Lettis, W.R., 1994, Seismotectonic evaluation: Scoggins Dam, Tualatin Project, Northwest Oregon: unpublished report by William Lettis and Associates and Woodward Clyde Federal Services, Oakland, CA, for U. S. Bureau of Reclamation, Denver CO(in Geomatrix Consultants, 1995). IWerner, K.S., Nabelek, J., Yeats, R.S., Malone, S., 1992, The Mount Angel fault: implications of seismic- reflection data and the Woodburn, Oregon, earthquake sequence of August, 1990: Oregon Geology, v. 54, p. 112-117. IWong, I. Silva, W., Bott, J., Wright, D., Thomas, P., Gregor, N., Li., S., Mabey, M., Sojourner, A., and Wang, Y., 2000, Earthquake Scenario and Probabilistic Ground Shaking Maps for the Portland, I Oregon, Metropolitan Area; State of Oregon Department of Geology and Mineral Industries; Interpretative Map Series IMS-16. Yeats, R.S., Graven, E.P., Werner, K.S., Goldfinger, C., and Popowski, T., 1996, Tectonics of the U Willamette Valley, Oregon: in Assessing earthquake hazards and reducing risk in the Pacific Northwest, v. 1: U.S. Geological Survey Professional Paper 1560, P. 183-222, 5 plates, scale 1:100,000. IYelin, T.S., 1992, An earthquake swarm in the north Portland Hills(Oregon): More speculations on the seismotectonics of the Portland Basin: Geological Society of America, Programs with Abstracts, v. 24, no. 5, p. 92. 111 111 I . 1 16-4211 -Durham Square GR 17 GEOPACIFIC ENGINEERING,INC. I 14835 SW 72nd Avenue GeoP 1 i A_ Portland,Oregon 97224 VICINITY MAP - EnUineer+nil,Inc Tel: (503)598-8445 Fax: (503)941.9281III 5114/ l intnr•,c-r r '+ North SW AM111nrd St R#0111 5,I 's til co SW bona SI 4.0 P-. R. .. SUBJECT SITE 1 t Dliftem Elementary 3 1 CC. Z1 / « 1 I 1 N i n ' I I Du rhar i gtK1 o rt C i!y P + Yill A I �,��:rl7f�rll "i ,� f . ur Curhani At D�utnam yo�14 44" 4V c:141( f in oto-r o. W, ,' I BASE MAP OBTAINED FROM DOGAMI SLIDO STREET VI`W, 2016 ( Date: 09/13/16 , Legend Approximate Scale 1 in=800 ft Drawn by: BGA Project: Durham Square Project No. 16-4211 FIGURE 1 I Tigard, Oregon I — EN MI — MI NE — MO N MN M MI MN MN MI MN MI MO r 14835 SW 72nd Avenue SITE PLAN AND coo' Portland,Oregon 97224 Engineering Inc Tel:(503)59$-8415 Fax:(503)941.9281 EXPLORATION LOCATIONS Approximate Location of j` • `` r `� ` tr,?y ��� Proposed Soldier Pile :`e Retaining Wall with an Exposed "4-ill B-4 ��.. Roo Height of up to 7 Feet .�m R r � i4 ,/ ., ' Ny = ata00' e'a <,..1,4" Oekc" Approximate Site itel- - ~' , S Boundary;, �4 w �,,, .o y; 13-2 .-- ,$'Fc ,.-? 4; / `k o Nim `�` North Legend Date: 07/12/16 Boring Designation,Approximate Location, and 140' Drams by:BGA INF- 7 5, Depth of Undocumented Fill APPROXIMATE SCALE 1"=140' Project: Durham Square Project No. 16-4211 FIGURE 2 Tigard, Oregon 14835 SW 72nd Avenue Soldier Pile Retaining Wall 6eoP Portland,Oregon 97224 Detail Engineering.Inc Tel:(503)598-8445 Fax:(503)941-9281 Typical Pavement Section or Min. 5-Inch Diameter Schedule 80 12-Inch Low Permeability Soil Pipe Piles on 6-Foot Centers Relatively Level Conditions with 250 psf Traffic Surcharge 12-Inch Chimney of .e.. i ' Clean Drain Rock .r �' i : r r 130 ft amsi Min.Elevation for Lightweight Cellular Concrete____.)` Permeable,Lightweight Cellular Concrete Existing Grade 4ftMin. __1 18-Inch Wide Concrete Collar for Passive Resistance, Backfilled with Concrete UNDOCUMENTED FILL MATERIAL 3 ft Min. Embedment into NATIVE SAND AND GRAVEL Competent Native Soils Date: 09/12/16 Legend 0 5, Drawn by:BGA APPROXIMATE SCALE 1"=5' Project: Durham Square Project No. 16-4211 FIGURE 3 Tigard, Oregon In MI NS NS 111111 — MN 11111 - - 11111 11111 - - I MI all EN — I 14835 SW 72nd Avenue . OOP. -Ili, Portland,Oregon 97224 BORING LOG IEnnmeerurp Ini Tel: (503)598.8445 Fax: (503)941-9281 Project: Durham Square Project No. 16-4211 BoringNo. B-1 1 Tigard, Oregon I 1 z15 1 18 i 3.! Material Description N 3 Soft, SILT(ML), brown, with some charred organic material, moist (Undocumented Fill) 111 5— 6 Grades to sandy Grades to medium stiff, with gravel-size pieces of cemented sand below 6.5 feet I and very moist to wet - El 9 pStiff, (Catsandyastrophic SILTFlood D(ML)toepositssilty)SAND(SM), brown, wet I 0 10— 25 Medium dense, silty GRAVEL(GM), gray and reddish brown, wet _ (Catastrophic Flood Deposits) _ ,/Medium dense, SAND(SP), fine-to course-grained, wet (Catastrophic Flood Deposits) I ` 15— M 244 — Boring terminated at 16 feet due to practical auger refusal I Groundwater encountered at 7.5 Hole caved to 9.8 feet 20- I 25- I 30_ 1 ' 35- - LEGEND Date Drilled: 06/08/16 I . room000 ill — 1017 or Logged By: BGA Static Water Table Bag Sample Surface Elevation: Split-Spoon Shelby Tube Sample at Drilling Static Water Table Water Bearing Zone I 1 14835 SW 72nd Avenue Geopl Portland,Oregon 97224 BORING LOG „,, Tel:(503)598-8445 Fax:(503)941-9281 1 Project: Durham Square Project No. 16-4211 Boring No. B-2 Tigard, Oregon ' cc2 ° _ca vi � _ � � ra. = 2 - 3= Material Description z 3N mg !Medium dense, silty GRAVEL(GM)gray, damp(Undocumented Fill) r , 5 Medium stiff, sandy SILT(ML), brown, moist(Catastrophic Flood Deposits) 5 ill 6 Grades to with increased sand content 1 7/23 27 Medium dense, sandy GRAVEL(GM),fine-to coarse-grained, moist 10— (Catastrophic Flood Deposits) Boring terminated at 10.5 feet due to practical auger refusal No seepage or groundwater encountered 1 15— ' i 20- 1 25- 1 30- 35— LEGEND 0- 35—LEGEND Date Drilled: 06/08/16 ,� Logged By: BGA 100 to ' 000. _ Surface Elevation: Static Water Table Static Water Table Water Bearing Zone Bag Sample Split-Spoon Shelby Tube Sample at Drilling I _ 14835 SW 72nd Avenue • eop l( Portland,Oregon 97224 BORING LOG I tntmtteet4.lnc Tel:(503)5984445 Fax:(503)941-9281 s Project: Durham Square Project No. 16-4211 BoringNo. B-3 ITigard, Oregon e A g o ` a -g I z Fig I t 141 SI 3 2 I Material Description — Soft to medium stiff, SILT(ML), brown, with occasional gravel, moist _(Undocumented Fill) — i 8 Medium stiff, SILT(ML), brown, moist(Catastrophic Flood Deposits) 5— — 111 9 Loose, silty SAND (SM), gray and brown, fine-to coarse-grained, with I — occasional rounded gravel, moist(Catastrophic Flood Deposits) 10 Grades to medium dense and without gravel Grades to wet below 8.5 feet I 10— _ 7 Loose, SAND(SP), gray, fine-to medium-grained,wet, with 6" layer of sandy silt at 10.5 feet,wet(Catastrophic Flood Deposits) t — j 15— e _ _ 0 15 Medium dense, sandy GRAVEL(GP), gray, subangular to w 7 subrounded, wet(Catastrophic Flood Deposits) II Very dense gravel 17 to 20 feet based on drilling conditions 20— , 17 I _ 4 25—M l)/ Very dense gravel 26 to 28 feet based on drilling conditions — / 30— ✓, — f Boring terminated at 35 feet — Hole caving below 15 feet, so no samples taken below 20 feet Wet below 8.5 feet, groundwater measured at 10.5 feet 35 " LEGEND I A/ [11 Date Drilled: 06/08/16 - , H s 1 04040 Logged By: BGA Bag Sample Split-Spoon Shelby Tube Sample Static Water Table Surface Elevation: I at Drilling Static Water Table Water Bearing Zone I 14835 SW 72nd Avenue LOG"a Geer "a BORING Portland,Oregon 97224 V - rnpmeennp.inr. Tel: (503)598-8445 Fax: (503)941-9281 1 Project: Durham Square Project No. 16-4211 Boring No. B-4 Tigard, Oregon a, C C e o.s a'� i. a " i °' Material Description I 9t W � e � c - I 3 Soft, SILT to sandy SILT(ML), brown, with disturbed texture, very moist (Undocumented Fill) 5— [1 I 6 Grades to medium stiff, gray,with trace amounts of charred organic material and fine roots, and moist 3 Grades to soft,with 1-inch chunk of wood at 8.25 feet 10— I 4 •- - • ' • Medium dense, sandy GRAVEL(GP), gray, moist I — � (Catastrophic Flood Deposits) 15— Ill 12 Medium dense, silty SAND(SM), brown, fine-to medium-grained, moist — \ (Catastrophic Flood Deposits) — Boring terminated at 15.5 feet No seepage or groundwater encounteredI 20_ I - I 25- - I 30- - 35I— LEGEND Date Drilled: 06/08/16 - I Logged By: BGA100 to M 7:4 - I ,,000 _, Surface Elevation: Static Water Table Bag Sample Split-Spoon Shelby Tube Sample at Drilling Static Water Table Water Bearing Zone 1 I 14835 SW 72nd Avenue . GeoP /!I i Portland,Oregon 97224 BORING LOG IEimmecnnl,.ln, Tel:(503)598-8445 Fax:(503)941-9281 Project: Durham Square Project No. 16-4211 j Boring No. B-5 Tigard, Oregon £ 9!1. m 8iita 0 3 0 3 8 Material Description U - - I 17 Medium dense, silty GRAVEL(GM), brown, with some organic debris I (Undocumented Fill) 5' - 2 Very soft, SILT(ML), brown, moist(Undocumented Fill) —- M 12 Stiff, sandy SILT(ML), brown, with occasional gravel, moist (Catastrophic_ Flood Deposits) 10- 11 ' 121edwm derise,'sar�dy��AVErL( P), gray, moist — £Catastrophic Flood Depositsl . Medium dense, silty SAND(SM), brown, fine-to medium-grained, moist (Catastrophic Flood Deposits) — Boring terminated at 11.5 feet 15- No seepage or groundwater encountered - 20- 1 — 25— I - 30— Ii I 35— - LEGEND Date Drilled: 06/08/16 I M 1� or Logged By: BGA 1,000 g ' Static Water Table Surface Elevation: Bag Sample SW-Spoon Shelby Tube Sample at Driting Static Water Table Water Bearing Zone 16-4211 -Durham Square-Existing Conditions-Static Name:Silty SAND and Poorly Graded SAND(SM-SP) Model: Mohr-Coulomb Unit Weight: 125 pcf Cohesion':0 psf Phi' Name: Poorly Graded SAND(SP),Fine to Medium Model:Mohr-Coulomb Unit Weight: 120 pcf Cohesion':50 psf Phi':2 Static Factor of Safety: 1.5 150 15 • 140 130 C 171.3 O 120 a) W 110 100 90 0 10 20 30 40 50 60 70 80 90 Distance J I I I I 16-4211 -Durham Square-Existing Conditions-Seismic Name:Silty SAND and Poorly Graded SAND(SM-SP) Model:Mohr-Coulomb Unit Weight: 125 pcf Cohesion':0 psf Phi':38 Name:Poorly Graded SAND(SP),Fine to Medium Model: Mohr-Coulomb Unit Weight: 120 pcf Cohesion':50 psf Phi':25° Pseudostatic Factor of Safety: 1.0 150 10 • 140 130 C 0 - 120 N W 110 100 90 0 10 20 30 40 50 60 70 80 90 Distance 16-4211 -Durham Square-Proposed Conditions-Static Name:Silty SAND and Poorly Graded SAND(SM-SP) Model:Mohr-Coulomb Unit Weight: 125 pcf Cohesion':0 psf Phi':38 Name:Poorly Graded SAND(SP),Fine to Medium Model: Mohr-Coulomb Unit Weight: 120 pcf Cohesion': 50 psf Phi':25° Name:Lightweight Concrete Model: Mohr-Coulomb Unit Weight:30 pcf Cohesion':0 psf Phi':45° Name:Concrete Model:Mohr-Coulomb Unit Weight: 150 pcf Cohesion':2,000 psf Phi':50° Static Factor of Safety:2.2 150 22 • 140 Lighr ,,r- 130 • C O (13 120 a) W 110 100 90 0 10 20 30 40 50 60 70 80 90 Distance I I I I i I 1 I 1 16-4211 -Durham Square-Proposed Conditions-Seismic Name:Silty SAND and Poorly Graded SAND(SM-SP) Model: Mohr-Coulomb Unit Weight: 125 pcf Cohesion':0 psf Phi':3 Name:Poorly Graded SAND(SP), Fine to Medium Model.Mohr-Coulomb Unit Weight: 120 pcf Cohesion':50 psf Phi':25 Name:Lightweight Concrete Model: Mohr-Coulomb Unit Weight 30 pcf Cohesion':0 psf Phi':45° Name:Concrete Model: Mohr-Coulomb Unit Weight: 150 pcf Cohesion':2,000 psf Phi':50° Pseudostatic Factor of Safety: 1.4 150 -- 14 140 — .•.•.'..•6 ;no.•.•T:.•...••0•• s646&6.•:❖.•m:•:•. Lighwoo i , 130 — C 0 > 120 W 110 100 90 0 10 20 30 40 50 60 70 80 90 Distance I LIQUEFACTION ANALYSIS Durham Square I Hole No.=B-3 Water Depth=8.5 ft Magnitude=7.67 ii Ground Improvement of F1ll=1 ft Acceleration=0.56g N-Value Unit Weight-pcf Fines % Soil Description (ft) 0 100 0 200 0 100 0 IIIIIIIII IIIIIIIII I I 1 T 1 T 1 T I Soft to meduim stiff SILT(ML)MI I g ;4; Loose silty SAND(SM) I 1 a'1 dpi —i0 •::.r;: Interbedded layers of loose SAND(SP) and sandy SILT(ML) i:::;: _ < .z;�::: —15 "' Medium dense sandy GRAVEL(GP) I-- b ;.y I —20 I ?..,- —25 '• rs 11 P. 0 _ I ea. —35 I' SPT or BPT test I J WIPlate A-1* LIQUEFACTION ANALYSIS I Durham Square • Hole No.=B-3 Water Depth=8.5 ft Magnitude=7.67 Ground Improvement of Fill=1 ft Acceleration=0.56g Shear Stress Ratio Factor of Safety Settlement Soil Description Raw Unit Fines I (R)0 0 1 0 1 5 0(in.) 10 SPT Weight % 111111111 11111111 111111111 Soft to meduim stiff SILT(ML)fill I .._.__ r._____..�— 8 120 NoLq I I , Lo ___ 9 120 30 Loose silty SAND(SM) � ' I .'`.v. 10 120 50 «. —10 • '.,.=f Interbedded layers of loose SAND(SP) 7 120 75 I •:,,.:1.;.;•,.:::...:...!:,.....1.:':,;.;:::: .<i. �'"��� and sandy SILT(ML) 7 120 40 {:�:�r 7 120 :50 71205I 7 120 -._._., .. 4 120 75 15 Medium dense sandy—GRAVEL(GP) 7 120 NoLq q 'a: -20 II ' ` 6 120 NoLq r,r t _ =� 6 120 NoLq t':, I —25 .. 11 120 NoLq I •S .1: MED —30 61 120 NoLq •.y 8 fs1-1 S=2.17 in. 'w a —35 CRR — CSR fs1�-- Saturated — �i~ Shaded Zone has Liquefaction Potential Unsaturat. -- t alePlate A-1 I LIQUEFACTION ANALYSIS Durham Square Hole No.=B-3 Water Depth=6 ft Magnitude=7.67. Ground Improvement of Fi11=1 ft Acceleration=0.56g Shear Stress Ratio Factor of Safety Settlement Soil Description Raw Unit Fines (ft)0 0 1 0 1 5 0(in.) 10 SPT Weight % 1 i I I T 1 1 i t i I II ill I I i I 1 I i I I i 1 Soft to meduim stiff SILT(ML)fill r 8 120 NoLq 1 —5Loose silty SAND(SM)5 ____ 9 120 30 10 120 50 - -10 , r=; Interbedded layers of loose SAND(SP) 7 120 75 ` :r:i and sandy SILT(ML) 7 120 75 I 1 7 120 75 7 120 40 — t t` 4 120 75 —15Medium dense sandy GRAVEL(GP) _ 7 120 NgLq -t s. t� . —20 :,:; 6 120 NoLq a ,;;% 6 120 NoLq .w - -25 11 120 NoLq ',; :▪ ? — ,..' 61 120 NoLq i — --,..1" m � S 7' U r - fs1=1 S=2.65 in. '-; —35 CRR — CSR 1— Saturated z Shaded Zone has Liquefaction Potential Unsaturat. Plate A-1 - I MIS UR UN NM En MIN Inn 111111 MN 11111 NM 111111 EMI NM MS NMI NM NM INN , , . PSH Deaggregation on NEHRP D soil Unnamed 122.755° W, 45.403 N. Peak Horiz. Ground Accel.>=0.5631 g Ann. Exceedance Rate .404E-03. Mean Return Time 2475 year si, Mean(R,M,E0) 66.8 km, 7.67, 1.25 - Modal (R,M,E0) = 84.0 km, 9.00, 0.97 (from peak R,M bin) .0.: Modal (R,M,E*) = 84.0 km, 9.00, 1 to 2 sigma (from peak R,M,E bin) Rt Binning: DeltaR 10. km, deltaM=0.2, DeltaE=1.0 N ' to a c . o a c o (.) . o Azs.`' 42 c?.....- ;-......----- ,,„„ og 4 , , 1 -......e , .c.t,, 4P ,..b. _ NglIk - lig -....- %M4i 411, .„,--4-7t- Prob.SA, PGA .5-4, _,..,,f,„ ,00-,... srAt (5. e? 401** <median(R,M) >median -r‘ Z eib O.° 40 ...,..z, 0 0<E0<0Nztt --,?... ---- .a• III -2<E0<-1 n 0.5 <E0< I -•"-,,,,,,--, .0-,,, -...` •.,..411-- 111 -1 <E0<-0.5 • 1 <E0<2 b. .... TIT:, c.:,. II -0.5 <E0<0 II 2<E0<3 200910 UPDATE maw 2016 Sep 13 19:11:52 Distance(R),magnitude(M),epsilon(E0,E)deaggregation for a site on soil with average vs=250.Ws top 30 m.USGS CGHT PSHA200$UPDATE Bins with It 0.05%contrib.omitted