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OFFICE COPY • 1 � G EODESIGN z ( ,,:9:11-)or I ' REPORT OF GEOTECHNICAL ENGINEERING SERVICES Proposed Twality Middle School Additions Tigard, Oregon For Tigard - Tualatin School District 23J September 17, 2003 GeoDesign Project: TigardTual -12 -01 1 City of Tigard Approved Plans By /3SP Date / ® 4' s/ iL 0 03 - 0003 - RE 1 DEC 2 4 20G3 CITY OF TIGAHD Engineers I Geologists I Environmental Consultants BUILDING DIVISION 1 CEO DESIGNz 14945 SW Sequoia Pkwy - Suite 170 I Portland OR 97224 ' Off 503.968 8787 I Fax 503 968.3068 September 17, 2003 Tigard - Tualatin School District 23J ' 6960 SW Sandburg Street Tigard, Oregon 97223 ' Attention: Mr. Stephen Poage Report of Geotechnical Engineering Services ' Proposed Twality Middle School Additions Tigard, Oregon ' GeoDesign Project: TigardTual -1 2 -01 GeoDesign, Inc. is pleased to submit our report of geotechnical engineering services for the ' proposed building additions and parking improvements to the Twality Middle School. The school is located at 14650 SW 97th Avenue in Tigard, Oregon. This report includes a site - specific seismic evaluation for both the Twality Middle School and the adjacent Templeton Elementary School ' parcel. A copy of this site - specific seismic evaluation is presented in Appendix C as part of this report. Our services for this project were conducted in accordance with our proposal dated July 10, 2003. ' We appreciate the opportunity to be of continued service to you. Please call if you have questions regarding this report. Sincerely, ' Geo esil; Inc. t Geor 9 '0 nders, P.E. Princip I Geotechnical Engineer cc: Mr. Keith Johnson, Dull Olson Weekes Architects, P.C. (four copies) Mr. Nick Harris, Cornerstone Management (two copies) ' Mr. Matt Johnson, SJO Consulting Engineers, Inc. (one copy) PDR:TCM:GPS:kt ' Attachments Four copies submitted Document ID: TigardTual -1 2 -01- 091 703- geor.doc I I TABLE OF CONTENTS PAGE NO. I 1.0 INTRODUCTION 1 2.0 PURPOSE AND SCOPE 1 ' 3.0 SITE CONDITIONS 2 3.1 Surface Conditions 2 3.2 Subsurface Conditions 2 I 4.0 CONCLUSIONS AND RECOMMENDATIONS 3 4.1 General 3 4.2 Erosion Control 3 I 4.3 Site Preparation 4 4.4 Construction Considerations 4 4.5 Groundwater Considerations 5 I 4.6 Structural Fill 5 4.7 Shallow Foundations 6 4.8 Floor Slabs 7 4.9 Retaining Structures 7 4.10 Trench Excavation 8 4.11 Pavements 9 I 4.12 Seismic Considerations 1 1 5.0 OBSERVATION OF CONSTRUCTION 1 1 I 6.0 LIMITATIONS 1 FIGURES Vicinity Map Figure 1 I Site Map Figure 2 APPENDICES I APPENDIX A Field Explorations A -1 I Laboratory Testing A -1 Key to Test Pit and Boring Log Symbols Table A -1 Soil Classification System and Guidelines Table A -2 I Rock Classification Guidelines Table A -3 Boring Logs Figure A -1 APPENDIX B I Cone Penetrometer Results B -1 Cone Penetrometer (C-1) Figure B -1 APPENDIX C I Site - specific Seismic Hazard Report C -1 Historical Seismicity Figure C -1 Site - specific Spectra - Crustal Earthquake Figure C -2 1 Site - specific Spectra - Subduction Earthquake Figure C -3 I I GEODESIGN? i TigardTual -12 -01 :091 703 1.0 INTRODUCTION This report presents the results of GeoDesign's geotechnical engineering evaluation for the proposed building addition and parking improvements to the Twality Middle School. The school ' is located at 14650 SW 97th Avenue in Tigard, Oregon. This report also includes a site - specific seismic evaluation for both the Twality Middle School and Templeton Elementary School parcel. A copy of this site specific seismic evaluation is presented in Appendix C as part of this report. The site location relative to surrounding physical features is shown in Figure 1. Mr. Keith Johnson of Dull Olson Weekes Architects, P.C. provided us with a preliminary site plan as well as a proposed grading plan for the project. In addition, Mr. Matt Johnson of SJO Consulting Engineers, Inc. provided us with preliminary grading information. Based on preliminary information provided by Mr. Keith Johnson, the project consists of constructing classroom additions southwest of the existing building along with an additional parking area in the northwest corner of the site. The addition will be approximately 60 by 90 feet in plan dimension and will be located at the southwest corner of the existing building. Additionally, we understand that 16 new parking spaces are to be constructed in the northwest portion of the site. Based on information provided by Mr. Matt Johnson, we understand that the ' finished floor grades of the proposed building addition will match those of the existing building, which will require minimal cut and up to 4 feet of fill relative to the existing site grades. Proposed site improvements are shown in Figure 2. Based on previous experience with similar structures, we expect that maximum interior column loads will be less than 125 kips and maximum continuous wall loads are estimated at less than 6 kips per lineal foot. The maximum floor slab loading will likely be less than 1 50 pounds per square foot (psf). ' 2.0 PURPOSE AND SCOPE The purpose of our geotechnical engineering evaluation was to explore the subsurface conditions at the site and provide geotechnical engineering recommendations for design and construction of the proposed addition and parking area. Our specific scope of work included: ' • Coordinate and manage the field investigation, including public utility locates, access preparation, and scheduling of subcontractors and GeoDesign field staff. ' • Complete the following explorations: • Complete one boring using mud -rotary drilling methods to a depth of 35.5 feet below ground surface (bgs) within the footprint of the proposed building expansion and one hand auger boring to a depth of 5.0 feet bgs in the area of the proposed parking lot expansion. • Evaluate liquefaction settlement using a cone penetrometer test (CPT) probe in the ' vicinity of Twality and Templeton schools. Complete two pore pressure dissipation measurements and shear wave velocity determinations at 1 -meter intervals at the CPT probe location. GEO DESIG N= 1 TigardTual -12- 01:091 703 Obtain soil samples for laboratory testing and maintain a log of encountered soil, rock, and • rY 9 9 groundwater conditions in each exploration. • Complete laboratory analyses on disturbed and undisturbed soil samples obtained from the explorations, as follows. ' • Complete moisture content and dry density tests on selected soil samples. • Complete particle grain -size analysis and percent fines determination on selected samples. ' • Provide recommendations for site preparation, grading and drainage, stripping depths, fill type for imported materials, compaction criteria, cut and fill slope criteria, procedures for use of on -site soils, and wet weather earthwork procedures. • Provide recommendations for design and construction of shallow spread foundations, including allowable design bearing pressure and minimum footing depth and width. • Provide recommendations for preparation of floor slab subgrade. ' • Recommend design criteria for retaining walls, including lateral earth pressures, backfill, compaction, and drainage, if necessary • Provide recommendations for construction of gravel surfaced or grass supporting open -block ' pavers for new emergency access roads. • Provide recommendations for the management of identified groundwater conditions that may affect the performance of structures or access drives. 1 • Prepare a site- specific seismic report in accordance with Uniform Building Code (UBC) requirements, including a discussion of seismic activity near the site. Provide recommendations for UBC seismic site coefficients and evaluate the risk of liquefaction. • Provide a report summarizing our explorations, laboratory testing, and recommendations. The seismic report will be included as an appendix to the geotechnical report. 3.0 SITE CONDITONS ' 3.1 SURFACE CONDITIONS The proposed building addition is located at the southwest corner of the existing building, west of the kitchen and south of the administration facilities. In addition, a new parking area, ' consisting of 16 new parking spaces, is to be located in a undeveloped area in the northwest corner of the lot. The footprints of the proposed building expansion and the additional parking are shown in Figure 2. The project site is generally flat dipping gently to the east. The site is primarily covered by buildings and associated parking areas, with landscaping or planter areas occupying ' undeveloped portions of the property. The portion of the site where the proposed building addition site is to be located currently consists of an asphalt paved parking lot. The area of the site in the location of the proposed parking area currently consists of landscaped grasses, trees, and shrubs. 3.2 SUBSURFACE CONDITIONS ' We explored subsurface conditions by completing one boring using a truck - mounted drill rig to a depth of 35.5 feet bgs (B -1), one boring using hand auger methods to a depth of 5.0 feet bgs (HA -1), and advancing one CPT probe (C -1) to a depth of 40.3 feet bgs. Boring B -1 is located in the footprint of proposed expansion, hand auger boring HA -1 is located in the proposed parking GEO DESI G N? 2 TigardTual -12- 01:091703 I lot area, and CPT probe C -1 is located approximately 250 feet to the southeast at the adjacent Templeton Elementary School. The approximate locations of the explorations are shown in Figure 2. The subsurface exploration and laboratory testing programs are described in Appendix A. Boring logs and laboratory test results are included in Appendix A. Results from the CPT exploration are included in Appendix B of this report. Subsurface conditions encountered in the explorations consisted of layered alluvial deposits consisting of medium stiff to stiff silt with varying amounts of fine sand and medium dense, fine sand with some silt. This material is underlain by soft decomposed bedrock at an approximate depth of 29.0 feet bgs. Based on field observations, an approximate 4- inch -thick root zone was present at the ground surface in the proposed parking improvement areas. Thicker root zones should be anticipated in the existing landscape areas. Approximately 3 inches of asphalt concrete (AC) underlain by 3 to 4 inches of base rock was present in the proposed building area. Select soil samples from the borings were tested to determine the natural moisture content and in place dry density. Laboratory testing of selected samples resulted in a moisture content varying between 15 and 46 percent and a dry density of approximately 89 pounds per cubic foot (pd). Groundwater was not observed in our borings. However, we estimate the groundwater elevation to be approximately 20 feet bgs based on pore water dissipation readings conducted in our CPT probe exploration C -1. 4.0 CONCLUSIONS AND RECOMMENDATIONS 4.1 GENERAL Based on the results of our subsurface explorations and analyses, it is our opinion that the proposed building and parking additions, with the anticipated foundation loads, can be supported on shallow foundations. Our foundation recommendations are provided in the "Shallow Foundations" section of this report. ' The native silt and silty sand can be sensitive to small changes in moisture content and difficult, if not impossible, to adequately compact during wet weather. If construction is planned for the ' wet season, the project budget should reflect the recommendations for wet weather contained in this report. A more detailed discussion is presented in the "Construction Considerations" and "Structural Fill" sections of this report. The results of our seismic hazard investigation indicate there is a low seismic hazard for landslides, fault rupture, tsunamis, and amplification at the site. Our site - specific seismic report is included in Appendix C. The following sections present specific geotechnical recommendations. ' 4.2 EROSION CONTROL The soil at this site is eroded easily by wind and water. Therefore, erosion control measures should be planned carefully and be in place before construction begins. Erosion control plans are ' required on construction projects located within Washington County and the City of Tigard. G Eb DESIGN? 3 TigardTual -1 2 -01 :091703 I Measures that can be employed to reduce erosion include the use of silt fences, hay bales, buffer zones of natural growth, sedimentation ponds, and granular haul roads. 4.3 SITE PREPARATION 4.3.1 General Trees from planters and undeveloped areas should be removed from all proposed building, pavement, and sidewalk areas. In addition, root balls should be grubbed out to the depth of the roots, which could exceed 3 feet bgs. Depending on the methods used to remove the root balls, considerable disturbance and loosening of the subgrade could occur during site grubbing. We recommend that soil disturbed during grubbing operations be removed to expose firm undisturbed subgrade. The resulting excavations should be backfilled with structural fill. The existing topsoil /root zone should be stripped and removed from existing landscape areas in 1 proposed building and new pavement areas and for a 5 -foot margin around such areas. Based on our observations during our explorations, the average depth of stripping will be approximately 2 to 3 inches, although greater stripping depths may be required to remove localized zones of loose or organic soil and should be expected in existing planter areas. The actual stripping depth should be based on field observations at the time of construction. Stripped material should be transported off site for disposal or used in landscaped areas. Existing structures, pavements, and utilities should be removed /relocated from all proposed building areas. Footings for the proposed structure should not be located over existing utilities. ,1 Depending on the methods used, considerable disturbance and loosening of the subgrade could occur during the removal of existing utilities. We recommend that any disturbed soil be removed to expose firm undisturbed subgrade. The resulting excavations should be backfilled with structural fill. Proofrolling should be conducted after site preparation activities have been completed and after mass grading. The subgrade should be proofrolled with a fully loaded dump truck or similar heavy rubber -tire construction equipment to identify soft, loose, or unsuitable areas. A member ' of our geotechnical staff should observe the proofroll to evaluate yielding of the ground surface. Soft or loose zones identified during proofrolling should be excavated and replaced with compacted structural fill. Areas that appear too wet or soft to support proofrolling equipment should be prepared in accordance with the following recommendations for wet weather construction. 4.4 CONSTRUCTION CONSIDERATIONS 4.4.1 General Trafficability of the silty (unpaved) areas of the sites may be difficult during or after extended wet periods or when the moisture content of the surface soil is more than a few percentage points above optimum moisture content. When wet, the silty surficial soils are easily disturbed and may provide inadequate support for construction equipment. Proofrolling of the subgrade should not be performed during wet weather or if wet ground conditions exist. Instead, the subgrade should be evaluated by probing. Soils that have been disturbed during site preparation activities, or soft or loose zones identified during probing, should be removed and replaced with ' compacted structural fill. G Eo DESIG Nz' 4 TigardTual -12 -01 :091703 I Granular haul roads and staging areas may be necessary for support of construction traffic in existing unimproved areas or in areas where the existing pavement has been removed. In addition, the existing pavement sections may be minimal and not capable of supporting repeated construction traffic. A 12 -inch thickness of imported granular material generally should be sufficient for light staging areas and the basic building pad, but is generally not expected to be adequate to support heavy equipment or truck traffic. Haul roads and areas with repeated heavy construction traffic should be constructed with a minimum thickness of 18 inches of imported granular material. The imported granular material should consist of crushed rock that has a maximum particle size of 4 inches, is well graded, and has less than 5 percent by weight passing the U.S. Standard No. 200 Sieve. We recommend that a geotextile be placed as a barrier between the subgrade and imported granular material in areas of repeated construction traffic. The geotextile should have a minimum Mullen burst strength of 250 pounds per square inch (psi) for puncture resistance and an apparent opening size (AOS) between an U.S. Standard No. 70 and No. 100 Sieve. ' We recommend that a minimum of 4 inches of imported granular material be placed at the base of footing excavations completed during wet weather conditions to reduce subgrade disturbance. 4.5 GROUNDWATER CONSIDERATIONS 4.5.1 General ' Based on pore water dissipation readings taken at the location of our CPT probe, we estimate the groundwater elevation at time of our explorations was approximately 20 feet bgs. Groundwater was not encountered in our boring or hand auger explorations. However, our field explorations were conducted after an extended period of dry weather. Accordingly, groundwater may be encountered at much shallower depths after extended periods of wet weather. 4.5.2 Site Drainage We recommend that all roof drains be connected to a tightline leading to storm drain facilities. ' Pavement surfaces and open space areas should be sloped such that surface water runoff is collected and routed to suitable discharge points. We also recommend that ground surfaces adjacent to buildings be sloped away from the buildings to facilitate drainage away from the buildings. 4.6 STRUCTURAL FILL 4.6.1 General All material used as structural fill should be free of organic material or other unsuitable materials and particles larger than 4 inches in diameter. 4.6.2 On -site Material Within the upper approximately 10 feet, the on -site materials consist primarily of silt. Silty soils are generally sensitive to small changes in moisture content and are difficult, if not impossible, to compact adequately during wet weather or when their moisture content is more than a few percentage points above the optimum moisture content. Laboratory testing indicates that the moisture content of the on -site materials is considerably greater than the optimum moisture GEODESIGNz' 5 TigardTual -12 -01 :091 703 I content of 15 ercent required for satisfactory compaction. Therefore, moisture conditioning will p q rY p 9 be required to achieve adequate compaction. We recommend using imported granular material for structural fill if the on -site material cannot be properly moisture conditioned. When used as structural fill, the on -site material should be placed in lifts with a maximum uncompacted thickness of 6 to 8 inches and compacted to not less than 92 percent of the maximum dry density, as determined by American Society for Testing and Materials ' (ASTM) D 1557. 4.6.3 Imported Granular Material Imported granular material for structural fill should be pit or quarry-run rock, crushed rock, or crushed gravel and sand. It should be fairly well graded between coarse and fine material and have less than 5 percent by weight passing the U.S. Standard No. 200 Sieve. The material should be placed in lifts with a maximum uncompacted thickness of 12 inches and compacted to not 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 should be approximately 18 inches in uncompacted thickness and should be compacted by rolling with a smooth drum roller without use of a drum vibrator. 1 4.6.4 Trench Backfill Trench backfill for the utility pipe base and pipe zone should consist of well - graded granular material with a maximum particle size of 3 / inch and less than 8 percent by weight passing the U.S. Standard No. 200 Sieve. The material should be free of roots, organic matter, and other unsuitable materials. Backfill for the pipe base and pipe zone should be compacted to at least 90 percent of the maximum dry density, as determined by ASTM D 1557, or as recommended by the pipe manufacturer. Within building and pavement areas, trench backfill placed above the pipe zone should be compacted to at least 92 percent of ASTM D 1 557 at depths greater than 2 feet below the finished subgrade and as recommended for structural fill within 2 feet of finished subgrade. In all other areas, trench backfill above the pipe zone should be compacted to at least 90 percent of the maximum dry density, as determined by ASTM D 1 557. 1 4.7 SHALLOW FOUNDATIONS 4.7.1 Allowable Bearing Pressure 1 Based on the results of our subsurface explorations and analyses, it is our opinion that the proposed structure, with the anticipated design foundation loads as previously described, can be supported on shallow foundations. Footings should be founded on undisturbed medium stiff native silt, medium dense silty sand, or structural fill placed on this material. We recommend an allowable bearing pressure of 2,500 psf. This is a net bearing pressure; the weight of the footing and overlying backfill can be ignored in calculating footing sizes. The recommended allowable bearing pressure may be increased by up to one -third for short -term loads such as those resulting from wind or seismic forces. Spread footings should be at least 24 inches wide founded at least 18 inches below the lowest adjacent final grade. , 1 GEODESIGNz 6 TigardTual -12 -01 :091703 Foundations should not be supported on soft soils. If soft soil or fill material is encountered at the base of footing excavations, it will be necessary to overexcavate to firm native soil and support the footings on structural fill. We recommend that a member of our geotechnical staff observe the prepared footing subgrades. 4.7.2 Resistance to Sliding Lateral loads on footings can be resisted by passive earth pressure on the sides of the footing and by friction at the base of the footing. Our analysis indicates that the available passive earth pressure for footings confined by structural fill or for footings constructed in direct contact with the undisturbed native silt soil is 350 pcf. Typically, the movement required to develop the 1 available passive resistance may be relatively large. Therefore, we recommend using a reduced passive pressure of 250 pcf. Adjacent pavements, sidewalks, or the upper 12 -inch depth of adjacent unpaved areas should not be considered when calculating passive resistance. A coefficient of friction equal to 0.35 may be used when calculating resistance to sliding. ' 4.7.3 Settlement Total settlement of footings founded as recommended is anticipated to be less than 1 inch. Differential settlements should not exceed %2 inch. 4.8 FLOOR SLABS Satisfactory subgrade support for building floor slabs supporting up to 150 -psf area loading can ' be obtained on the existing undisturbed native medium stiff to stiff silts or on structural fill. A minimum 6- inch -thick layer of base rock (imported granular material) should be placed and compacted over the prepared subgrade to assist as a capillary break. The base rock should be crushed rock or crushed gravel and sand that is fairly well - graded 1 between coarse and fine, contain no deleterious materials, have a maximum particle size of 1Y2 inches, and have less than 5 percent by weight passing the U.S. Standard No. 200 Sieve. The imported granular material should be placed in one lift and compacted to not less than 95 percent of the maximum dry density as determined by ASTM D 1557. Settlement of floor slabs supporting the anticipated design loads and constructed as recommended is not expected to exceed about %2 inch. Flooring manufacturers often require vapor barriers to protect flooring and flooring adhesives. Many flooring manufacturers will warrant their product only if a vapor barrier is installed according to their recommendations. Selection and design of an appropriate vapor barrier, if needed, should be based on discussions among members of the design team. We can provide additional information to assist you with your decision. 4.9 RETAINING STRUCTURES ' Our retaining wall design recommendations are based on the following assumptions: (1) the walls consist of conventional, cantilevered retaining walls or embedded building walls; (2) the walls are less than 10 feet in height; and (3) the backfill is level, drained, and consists of 1 CEO DESI G N? 7 TigardTual -12 -01 :091703 I imported granular materials. Reevaluation of our recommendations will be required if the retaining wall design criteria for the project vary from these assumptions. For walls not restrained from rotation, an equivalent fluid pressure of 38 pcf should be used for design. An equivalent fluid pressure of 55 pcf should be used for design of walls restrained from rotation. Footings for the retaining walls should be designed as recommended for shallow foundations. When computing resistance to lateral loads, a base friction coefficient of 0.35 can ' be used. As stated above, our recommendations are based on the assumption of drained conditions. ' Drains that consist of a 4- to 6- inch - diameter, perforated drainpipe wrapped in a geotextile filter should be installed behind all retaining structures. The pipe should be embedded in a minimum 2- foot -wide zone of drain rock and sloped to drain (minimum slope of 0.5 percent) toward a suitable discharge. The geotextile should have an AOS between the U.S. Standard No. 70 and No. 100 Sieve and a water permittivity greater than 1.5 sec'. The drain rock should be uniformly graded, have a maximum particle size of 3 inches, and have less than 2 percent passing the U.S. ' Standard No. 200 Sieve (washed analysis). Backfill material placed behind the wall and extending a horizontal distance of %ZH, where H is the ' height of the retaining wall, should consist of the well - graded sand or gravel, with not more than 5 percent by weight passing the U.S. Standard No. 200 Sieve. Alternatively, the on -site soils can be used as backfill material provided a minimum 2- foot -wide column of drain rock wrapped in a geotextile is placed against the wall. The rock column should extend from the perforated drainpipe or foundation drains to within approximately 1 foot of the ground surface. The drain rock should consist of well - graded gravel, with not more than 2 percent by weight passing the U.S. Standard No. 200 Sieve. Backfill should be placed and compacted as recommended for structural fill, with the exception of backfill placed immediately adjacent to walls. Backfill adjacent to walls should be compacted to a lesser standard to reduce the potential for generation of excessive pressure on the walls. Backfill located within a horizontal distance of 3 feet from the retaining walls should be compacted to approximately 90 percent of the maximum dry density, as determined by ASTM D 1557. Backfill placed within 3 feet of the wall should be compacted in lifts less than 6 inches thick using hand - 1 operated tamping equipment (such as jumping jack or vibratory plate compactors). If flat work (slabs, sidewalk, or pavement) will be placed adjacent to the wall, we recommend that the upper 2 feet of fill be compacted to 95 percent of the maximum dry density, as determined by ASTM D 1 557. Settlements of up to 1 percent of the wall height commonly occur immediately adjacent to the wall as the wall rotates and develops active lateral earth pressures. Consequently, we recommend that construction of flat work adjacent to retaining walls be postponed at least four weeks after construction, unless survey data indicates that settlement is complete prior to that time. 4.10 TRENCH EXCAVATION 4.10.1 Trench Cuts and Shoring Trench cuts should stand vertical to a depth of approximately 4 feet, provided no groundwater seepage is observed in the trench walls. Open excavation techniques may be used to excavate G EO DESI G N? 8 TigardTual -12 -01 :091703 ,' 111 trenches with p depths between 4.0 and 10.0 feet, provided the walls of the excavation are cut at a p I slope of 1.5 horizontal to 1 vertical and groundwater seepage is not present. Sloughing and caving may occur if the excavation extends below the groundwater table. The walls of the trench should be flattened or braced for stability and the area dewatered if seepage is encountered. Use of a trench box or other approved temporary shoring is recommended for cuts below the water table. If shoring is used, we recommend that the type and design of the shoring system be the responsibility of the contractor, who is in the best position to choose a system that fits the overall I plan of operation. 4.10.2 Dewatering A sump located within the trench excavation likely will be sufficient to remove the accumulated water, depending on the amount and persistence of water seepage and the length of time the trench is left open. Flow rates for dewatering are likely to vary depending on location, soil type, I and the season during which the excavation occurs. The dewatering systems should be capable of adapting to variable flows. I If groundwater is present in the base of the utility trench excavation, we recommend overexcavating the trench by 12 to 18 inches and placing trench stabilization material in the base. Trench stabilization material should consist of well - graded, crushed rock, or crushed gravel '1 with a maximum particle size of 4 inches and free of deleterious materials. The percent passing the U.S. Standard No. 200 Sieve shall be less than 5 percent by weight when tested in accordance with ASTM C 1 17. 1� 4.10.3 Safety All excavations should be made in accordance with applicable Occupational Safety and Health 1 Administration and state regulations. While we have described certain approaches to utility trench excavations in the foregoing discussion, the contractor should be responsible for selecting the excavation and dewatering methods, monitoring the trench excavations for safety, and I providing shoring as required to protect personnel and adjacent areas. 4.11 PAVEMENTS I 4.11.1 General The pavement subgrade should be prepared in accordance with the previously described site I preparation, wet weather construction, and structural fill recommendations. Our pavement recommendations are based on an assumed soil resilient modulus value of 6,000 psi and a design life of 20 years. 4.11.2 Asphalt Pavements We do not have specific information on the type and frequency of the vehicles that will use the I area. Our pavement recommendations assume that traffic in parking areas will consist primarily of passenger cars and small trucks. We assumed traffic in driveway and other heavy traffic area will consist primarily of two- and three -axle buses and trucks. For analysis purposes, we have I assumed three bus and truck traffic levels consisting of 10, 20, and 50 two- to four -axle buses or trucks per day. We conducted our analyses using American Association of State Highway and Transportation Officials (AASHTO) design methods. I I G EO DESIG N= 9 TigardTual -12- 01:091703 Our avement design sections are presented in the following table. p g p g ' Base Rock Pavement Area Number of AC Thickness Thickness Trucks /Day (inches) (inches) CRB' Passenger Cars Only -- 2.5 8.0 ' Driveways /Heavy 10 3.0 10.0 20 3.5 12.0 Traffic Areas 50 4.0 14.0 1 1. CRB: crushed rock base We recommend that a geotextile separation layer be placed on the undisturbed subgrade and under the CRB in driveways and other heavy pavement areas to prevent migration of the silt up ' into the base course. The geotextile should meet the requirements previously presented in the "Construction Considerations" section of this report. Geotextile is not necessary where subgrades are amended. 11 All thicknesses are intended to be the minimum acceptable. The design of the recommended pavement section is based on the assumption that construction will be completed during an extended period of dry weather. This design base rock thickness will not support construction traffic or pavement construction when the subgrade soils are wet. Accordingly, if construction is planned for periods when the subgrade soils are not dry and firm, the subgrade should be prepared as recommended in the "Construction Considerations" section of this report. The AC pavement should conform to Section 00745 for standard- and heavy -duty AC, and the ' portland cement concrete should conform to Section 00755 for standard and heavy -duty pavements of the Standard Specifications for Highway Construction, Oregon State Highway Division, 1996 Edition. The CRB should conform to Section 02630 of these specifications and have less than 5 percent passing the U.S. Standard No. 200 Sieve. CRB should be placed in one lift and compacted to not less than 95 percent of the maximum dry density, as determined by ASTM D 1557. ' 4.1 1.3 Masonry Pavers We understand that emergency access lanes and driveways may be paved using pre -cast masonry pavers. We do not have specific information on the traffic levels for these access lanes. However, for design purposes, we have assumed that traffic levels will be less than 30,000 equivalent single -axle loads for the life of the pavement. Our analysis is based on a resilient modulus of 6,000 psi and was made using the paver design software "LockPave" using the 1993 AASHTO design methods. Our pavement design section is presented in the following table. GEODESIGN? 10 TigardTual -12 -01 :091 703 I I I Pavement Area Paver Bedding /CRB 1 Emergency Access Lanes 3-1/8-inch concrete -inch bedding sand 6 inches CRB 4.12 SEISMIC CONSIDERATIONS 4.12.1 Background I The State of Oregon Structural Specialty Code (SOSSC) currently requires a seismic hazard investigation for "special occupancy structures." Special occupancy structures include "buildings for every public, private or parochial school through secondary level or day care centers with a I capacity greater than 250 individuals." Our scope included a seismic hazard study for the site. The results of our evaluation are presented in Appendix C. 1 4.12.2 UBC Design Criteria We recommend that the building be designed using the applicable provisions of the SOSSC for Zone 3. Based on the results of our analysis, we recommend a seismic coefficient of C = 0.36 I and C = 0.54, for site conditions corresponding to the amplification of a S soil profile. 4.12.3 Liquefaction and Lateral Spreading i l We completed analyses for liquefaction based on site explorations and using CPT- (Olsen, Robertson) based analyses methods. Based on our analysis, discrete layers of loose sand, silty I sand, and soft sandy silt at depths between approximately 20 and 30 feet bgs may be susceptible to liquefaction. Based on this analysis of field and laboratory data, in our opinion, liquefaction settlement and lateral spreading at this site are not excessive and do not pose a I significant safety hazard. 5.0 OBSERVATION OF CONSTRUCTION I Satisfactory foundation and earthwork performance depends to a large degree on quality of construction. Sufficient monitoring of the contractor's activities is a key part of determining that I the work is completed in accordance with the construction drawings and specifications. Subsurface conditions observed during construction should be compared with those encountered during the subsurface exploration. Recognition of changed conditions often requires experience; I therefore, qualified personnel should visit the site with sufficient frequency to detect if subsurface conditions change significantly from those anticipated. I We recommend that GeoDesign be retained to observe earthwork activities, including stripping, proofrolling of the subgrade and repair of soft areas, footing subgrade preparation, performing laboratory compaction and field moisture - density tests, observing final proofrolling of the I pavement subgrade and base rock, and asphalt placement and compaction. 6.0 LIMITATIONS I We have prepared this report for use by Tigard-Tualatin School District 23j and its design and Y 9 9 construction team for the proposed project. The data and report can be used for bidding or I GEODESIGN? 11 TigardTual -1 2 -01 :091703 I estimating purposes, but our report, conclusions and interpretations should not be construed as warranty of the subsurface conditions and are not applicable to other sites. Exploration observations indicate soil conditions only at specific locations and only to the depths penetrated. They do not necessarily reflect soil strata or water level variations that may exist between exploration locations. If subsurface conditions differing from those described are noted during the course of excavation and construction, reevaluation will be necessary. ' The site development plans and design details were preliminary at the time this report was prepared. When the design has been finalized and if there are changes in the site grades or location, configuration, design loads, or type of construction for the buildings, the conclusions and recommendations presented may not be applicable. If design changes are made, we request that we be retained to review our conclusions and recommendations and to provide a written modification or verification. The scope of our services does not include services related to construction safety precautions, and our recommendations are not intended to direct the contractor's methods, techniques, sequences, or procedures, except as specifically described in our report for consideration in design. Within the limitations of scope, schedule, and budget, our services have been executed in accordance with generally accepted practices in this area at the time the report was prepared. No I warranty, express or implied, should be understood. We appreciate the opportunity to be of continued service to you. Please call if you have questions concerning this report or if we can provide additional services. Sincerely, sign, Inc. ' Paul D. Richards, E.I.T. W , � f cc 7325 Geotechnical Engineering Staff 4 (Y. 4/OREGON >` ° 13,2 Q` Tacia C. Miller, P.E. Geotechn I Project Engineer [(FIRES: 12/31/200H Ge r e nders, P.E. 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M.7,!;',:7; A. ,, ,, .., ,l _ . ..,.„. , ,, , m4eki, 7.v.ogno B QUADRANGLE MAP z - ... . , 1961 L '' ,7 ,,. ''') ':, ; ':; . . P H OTO R EV I S E D 1984 ,:41-1411 „Iti?'!--;::, ,, I co 0 VICINITY MAP •• i 1U • GE0D EsIGINz I _ TIGARDTUAL-12 0 1 ac SEPTEMBER 2003 FIGURE] ' '� I 5w 3N ZGf - , \ , N ce \ 4 I ,; I I '7. \ \ ‘‘ HA-1 ir I I OS IN M ENTS _._..__._. . • rn o PROP ED'PARK G IMPgOV, : � � .r\ � � I • j+` _ - m ce a. 1 , ,f. i � f` I ' H i f - `' ../ t er ms '� \ '�. i s f r I H F F ; i /;,,I l J.., �Y CD • f f i` . ' ' ; 1 , . . :: ' „ / / a ,A �. Vi "r ` f fi � p j • ce ,i' FY PRpPO BUILDI i :" • F. /11 .,,,,r I I `° 1 ., ` • , _ ,{;y . -. _ _; IIII J, y I ' f � N, _ '.:y { Y `r i. ;� f ;_ '' ''',..,4 I r - : p v ! �" " �l '� < s ,.. T .'`'a .� r • i ° i ' .1 s � Z �... _ s w 7 EXPLANATION: XPLANATI N' W o " ''''''''-"\'\k' B-1 BORING " , - <' ' k\\\\\\\\\\\'‘'., HA 1 HAND AUGER 0 ,. -.. / `' ,: ''E C -1 A CONE PENETROMETER 0 p N z f' 0 t l uT_ s 3 I 200 L„ ' i , , s ''/� ?� ; �.; , ? (IN FEET) C� 1,2:___;•;/ . :x. 1 ,„. ....4. I / Q SITE PLAN BASED ON DRAWING o ; PROVIDED BY DULL OLSON i `/ �< WEEKES ARCHITECTS, P.C. ' APPENDIX A FIELD EXPLORATIONS ' GENERAL Subsurface conditions at the site were explored by advancing a boring (B -1) to a depth of 35.5 feet bgs using mud -rotary drilling methods and one CPT probe to refusal at a depth of 40.3 feet bgs. Boring B -1 and CPT probe C -1 were completed by Geo -Tech Explorations of Tualatin, Oregon, on July 24, 2003, and were observed by a member of our geotechnical staff. A hand auger boring (HA -1) was completed to a depth of 5.0 feet bgs on September 9, 2003 by a ' member of our geotechnical staff. The borings was located in the proposed footprint of the building and parking lot expansions. Boring logs are included in this appendix and CPT data are included in Appendix B. The approximate locations of the explorations are shown in Figure 2. Exploration locations were chosen based on a site plan provided by Dull Olson Weekes Architects, P.C. The locations of the explorations were determined in the field by pacing from site features. This information should be considered accurate to the degree implied by the methods used. SOIL SAMPLING ' We obtained disturbed and undisturbed samples of the various soils encountered in the explorations for geotechnical laboratory testing. Classifications and sampling intervals are shown in the boring logs included in this appendix. ' Samples were obtained from the borings using a 1.5- inch - inside diameter, split -spoon sampler in general accordance with guidelines presented in ASTM D 1586. The split -spoon samplers were ' driven into the soil a total of 18 inches with a 140 -pound hammer free - falling 30 inches. The number of blows required to drive the sampler the final 12 inches is recorded in the boring logs, unless otherwise noted. Relatively undisturbed samples were obtained using a standard Shelby tube in general accordance with ASTM D 1587, the Standard Practice for Thin - walled Tube Sampling of Soils. ' SOIL CLASSIFICATION The soil samples were classified in accordance with the "Key to Test Pit and Boring Logs Symbols" and "Soil Classification System and Guidelines," copies of which are included in this appendix. The boring logs indicate the depths at which the soils or their characteristics change, although the change actually could be gradual. If the change occurred between sample locations, the depth was interpreted. Classifications and sampling intervals are shown in the boring logs included in this appendix. LABORATORY TESTING ' The soil samples were classified in the laboratory to confirm field classifications. The laboratory classifications are included in the boring logs if those classifications differed from the field classifications. 1 GEODESIGN= A -1 TigardTual -12- 01:091703 MOISTURE CONTENT ' We tested the natural moisture content of selected soil samples in general accordance with ASTM D 2216. The natural moisture content is a ratio of the weight of the water to soil in a test sample and is expressed as a percentage. The moisture contents are included in the boring logs ' presented in this appendix. DRY DENSITY ' We tested selected soil samples to determine the in -situ dry density. The tests were performed in general accordance with ASTM D 2937. The dry density is defined as the ratio of the dry weight of the soil sample to the volume. of that sample. The dry density typically is expressed in pounds per cubic foot. The dry densities are included in the boring logs presented in this appendix. I, GEODESICN? A -2 TigardTual -12- 01:091703 KEY TO TEST PIT AND BORING LOG SYMBOLS I SYMBOL SOIL DESCRIPTION I 11 Location of sample obtained in general accordance with ASTM D 1 586 Standard Penetration Test with recovery Ii Location of sample obtained using thin wall, shelby tube, or Geoprobe® sampler in general accordance with ASTM D 1 587 with recovery I I Location of sample obtained using Dames & Moore sampler and 300 -pound hammer or pushed with recovery I N Location of grab sample Rock coring interval I Water level during drilling I 1 Water level taken on date shown GEOTECHNICAL TESTING EXPLANATIONS I PP Pocket Penetrometer SIEV Sieve Gradation I TOR Torvane DD Dry Density CON Consolidation ATT Atterberg Limits I DS Direct Shear CBR California Bearing Ratio P200 Percent Passing U.S. Standard No. 200 OC Organic Content Sieve I HYD Hydrometer Gradation P Pushed Sample ENVIRONMENTAL TESTING EXPLANATIONS CA Sample Submitted for Chemical Analysis ND Not Detected I PID Photoionization Detector Headspace Analysis NS No Visible Sheen SS Slight Sheen ppm Parts Per Million I P Pushed Sample MS Moderate Sheen HS Heavy Sheen I I KEY TO TEST PIT AND G EODESIGN � BORING LOG SYMBOLS I TABLE A -1 SOIL CLASSIFICATION SYSTEM I CONSISTANCY - COARSE - GRAINED SOILS CONSISTANCY - FINE - GRAINED SOILS Standard Standard Unconfined I Relative Density Penetration Consistency Penetration Resistance Compressive Resistance Strength (tsf) Very Loose 0 - 4 Very Soft Less than 2 Less than 0.25 Loose 4 - 10 Soft 2 - 4 0.25 - 0.50 I Medium Dense 10 - 30 Medium Stiff 4 - 8 0.50 - 1.0 Dense 30 - 50 Stiff 8 - 15 1.0 - 2.0 Very Dense More than 50 Very Stiff 1 5 - 30 2.0 - 4.0 I Hard More than 30 More than 4.0 SOIL CLASSIFICATION NAME I Name and Modifier Terms GRAVEL, SAND Constituent Percentage >50% sandy, gravelly 30 - 50% I silty, clayey 15 - 50% Coarse grained some (gravel, sand) 1 5 - 30% some (silt, clay) 5 - 1 5% I trace (gravel, sand) trace (silt, clay) <5% CLAY, SILT >50% silty, clayey 30 - 50% sandy, gravelly Fine - grained some (sand, gravel) 15 - 30% 1 some trace ( (siltsan d , clay) , gravel) 5 - 1 5% trace (silt, clay) PEAT 50 - 100% I Organic organic (soil name) 15 - 50% (soil name) with some organics 5 - 1 5% MOISTURE CLASSIFICATION I Term Field Test dry very low moisture, dry to touch I moist wet damp, without visible moisture visible free water, usually saturated • GRAIN SIZE CLASSIFICATION 1 Description Sieve* Observed Size boulders >1 2" cobbles - 3"-12" I gravel coarse 0.75 " -3" 0.75 " -3" fine #4 0.75" 0.1 9" - 0.75" coarse #10 - #4 0.079" - 0.19" sand medium #40 #10 0.017" 0.079" fine #200 #40 00029" - 0.01 7" fines < #200 <0.0029" I * Use of #200 field sieve encouraged GEODESIGN SOIL CL ASSIFICATION SYSTEM z AND GUIDELINES TABLE A -2 I ROCK CLASSIFICATION GUIDELINES I HARDNESS DESCRIPTION Extremely Soft (RO) Indented by thumbnail I Very Soft (R1) Can be peeled by pocket knife or scratched with finger nail Soft (R2) Can be peeled by a pocket knife with difficulty I Medium Hard (R3) Can be scratched by knife or pick Hard (R4) Can be scratched with knife or pick only with difficulty Very Hard (R5) Can't be scratched with knife or sharp pick I WEATHERING DESCRIPTION I Decomposed Rock mass is completely decomposed Predominantly Decomposed Rock mass is more than 50% decomposed I Moderately Weathered Rock mass is decomposed locally Slightly Weathered Rock mass is generally fresh Fresh No discoloration in rock fabric 1 JOINT SPACING DESCRIPTION I Very Close Less than 2 inches Close 2 inches to 1 foot Moderate Close 1 foot to 3 feet III Wide 3 feet to 10 feet Very Wide Greater than 10 feet I FRACTURING FRACTURE SPACING Very Intensely Fractured Chips and fragments with a few scattered short core lengths I Intensely Fractured 0.1 foot to 0.3 foot with scattered fragments intervals Moderately Fractured 0.3 foot to 1 foot with most lengths 0.6 foot Slightly Fractured 1 foot to 3 feet I Very Slightly Fractured Greater than 3 feet Unfractured No fractures I HEALING DESCRIPTION Not Healed Discontinuity surface, fractured zone, sheared material or filling not I recemented Partly Healed Less than 50% of fractured or sheared material I Moderately Healed Greater than 50% of fractured or sheared material Totally Healed All fragments bonded I ROCK CLASSIFICATION GUIDELINES G EODESIGN z ' TABLE A -3 I v 9 DEPTH � I Z w • N -VALUE INSTALLATION AND I FEET MATERIAL DESCRIPTION w I- g • MOISTURE CONTENT % COMMENTS W'0 W 1171 RQD% V/.1 CORE REC% o I - 0 50 100 —°—.1.1 . 1- 1.,0,6— h ASPHALT CONCRETE (3 inches thick). _j 0 3 I _ ` BASE ROCK (3 to 4 inches thick). j Very stiff, brown SILT with trace to some 06 fine sand; dry, nonplastic (Alluvium). . . 23 • 5— ` 21 . . DD ! - i ; • DD = 89 pa P • 1 10— lj I Medium dense, brown, silty, fine SAND; 14.0 1 15 —;,1:; dry. --..:.2.-:-. !] . ` • I I 20— becomes loose with some silt; moist to �9 wet at 20.0 feet • Stiff, brown SILT; moist, nonplastic. 22.0 hrs I 25 — P • — • • I I I I Extremely soft (RO), rust and dark brown 29.0 • 30 — 1 11 1 BASALT; dry, decomposed. I • 14 -20 -50/3' I 0 1 1� I 1111 CD 1 1 1 1 • 0 1111 111 w 35 I � becomes very soft (Rl) at 35.0 feet 35.5 F . • 5°/6� $ Borin completed at 35.5 feet. . W • a c. Q • m I 0 40 0 50 t00 PROJECT NAME. Twality Middle School LOGGED BY. BBP DRILLED BY: Geo -Tech Explorations, Inc COMPLETED' 7/24/03 N BORING METHOD, mud rotary (see report text) BORING DIAMETER. 4 718 inch LOCATION: 14650 SW 97th 0 cc I BORING B -1 GEODESIGN_ I co Portland, OR TIGARDTUAL -1 2 -01 JULY 2003 FIGURE A -1 0 m I u ° I u • N -VALUE INSTALLATION AND z I D FEET a MATERIAL DESCRIPTION Jo_ H • g • MOISTURE CONTENT % COMMENTS w 0 UT T1 RQD% I/ /I CORE REC% 0 u 0 50 100 — Stiff to very stiff, brown SILT; dry (4 -inch- I = thick root zone). Medium dense, red - brown, silty SAND; s.s ' moist. 5 Boring completed at 5.0 feet. 5.0 I I 10 — • I • I • 15 _ • ' ' . • 20 • I _ • 25 I 30 0 o • 0 111 z 0 35 w 0 w o a • x m 0 ' 40 - 0 50 100 PROJECT NAME: TwaI,ty Middle School LOGGED BY BCF DRILLED BY: GeoDesign, Inc staff COM PLETED 9/09/03 J Q t— BORING METHOD hand auger (see report text) BORING DIAMETER: LOCATION. 14650 SW 97th 0 a a ' BORING HA -1 G EO D ESIGN z Portla nd, OR TIGARDTUAL -12 -01 JULY 2003 FIGURE A - o to APPENDIX B CONE PENETROMETER RESULTS ' Geo -Tech Explorations of Tualatin, Oregon, advanced one CPT probe (C -1) on July 24, 2003. The CPT probe was completed using a seismic electronic CPT manufactured by Hogentogler & Company, Inc. The probe was advanced to refusal at a depth of 40.3 feet bgs. Shear wave ' velocity tests were completed at 1 -meter intervals, and pore water dissipation readings were conducted at 27.7 and 30.5 feet bgs. The approximate location of the probe is shown on Figure 2. ;1 1 I I G Eta DESIG Nz B -1 TigardTual -12- 01:091703 I I NORMALIZED Qc (kg /cm2) 0 20 40 60 80 100 1 20 140 1 60 180 200 - - _-'-- - ' --=-- -_._ ---1�� I , 10 I 20 - f r - L - p I- 1 d -} Q �r 30 40 — s+ m m u 1 ! 0 To I H I m 50 i ! 0.0 1.0 2.0 3.0 4.0 5.0 6.0 7.0 8.0 9.0 10.0 ro I z NORMALIZED FRICTION RATIO ( %) 0 N V I c6 O G EODESIGNz CONE PENETROMETER (C -1) I ti TIGARDTUAL -12 -01 SEPTEMBER 2003 FIGURE B - 1 APPENDIX C ' SITE- SPECIFIC SEISMIC HAZARD REPORT INTRODUCTION This appendix presents the results of GeoDesign's site - specific seismic hazard analysis for the ' building addition to the Twality Middle School. The school is located at 14650 SW 97th Avenue in Tigard, Oregon. Additionally, this report is also applicable to the Templeton Elementary School, located adjacent and directly southeast of the Twality site. The site location relative to surrounding physical features is shown in Figure 1. This report is prepared to meet the requirements of SOSSC Section 1804 as the structure is classified as a "Special Occupancy Structure." GEOLOGIC SETTING The project site is located in the southeast portion of the Tualatin Basin physiographic province. The Coast Range and Chehalem Mountains bound the basin to the west and the Tualatin Mountains and Portland Hills bound the basin to the east. The geologic profile in the vicinity of the site consists of over 30 to 40 feet of catastrophic flood deposits underlain by basaltic lava of the Columbia River Basalt. The Columbia River Basalt is considered as the basement material at ' this site and is present below depths of 30 to 40 feet (Burns, et al., 1997; Madin, 1 990; Schlicker and Deacon, 1967). The near surface geologic unit is mapped as Pleistocene Age (15,500 to 13,000 years before present) catastrophic flood deposits (Off), specifically the fine - grained deposits. The unit consists of poorly consolidated, fine- to coarse - grained sand, silt, and clay. The catastrophic flood ' deposits originated from multiple outburst floods from glacial Lake Missoula during the last episode of glaciations (Orr, et al, 1992). The thickness of this unit is in excess of 50 feet in the site vicinity based on our boring logs and a review of water well logs in the site vicinity. ' The Pleistocene to Miocene Age (5.3 to 1.6 million years before present) fluvial and lacustrine deposits (Tfs) underlies the catastrophic flood deposits and extends to a depth of approximately 300 feet in the site vicinity (Burns, et al., 1997; Schlicker and Deacon, 1967). The unit consists of moderately to poorly cemented micaceous siltstone, claystone, and fine sandstone. The unit is considered to be equivalent to the Sandy River Mudstone. The middle Miocene Age (16 to ' 6 million years before present) Columbia River Basalt Group (Tcr) underlies the fluvial and lacustrine deposits and forms the basement material at this site. ' The geologic profile and the range of shear wave velocity for each geologic unit are shown in Table 1 below (Mabey et al., 1993; Mabey and Madin, 1995; Wong, 2000; Pratt et al., 2001). GEODESIGN? C -1 TigardTual -12 -01 :091 703 I . Table 1 - Geologic Profile Summary Profile Depth Shear Wave Velocity (feet) Geologic Unit (meters /s) 0 to 40 Catastrophic flood deposits (Off) 200 to 300 40 + Columbia River Basalt Group (Tcr) 770 to 1,300 SUBSURFACE CONDITIONS The details of our field exploration program, subsurface conditions, and measured groundwater levels are provided in the main text of the report. A site plan showing our field exploration locations is provided as Figure 2. GROUNDWATER Groundwater was not observed in our explorations. However, based on a review of the soil conditions encountered in our borings, CPT data, and a review of water well logs on file with Oregon Water Resources Department, we estimate the depth to regional groundwater to be approximately 15 to 20 feet bgs. DESIGN EARTHQUAKES SEISMICITY Recorded seismicity in the site vicinity is relatively limited, with only a few recorded earthquakes exceeding magnitude M =5 in the Tualatin Basin. The historical seismicity in relation to the project site is shown on Figure C -1, accompanied with a table listing earthquakes with a magnitude M,>5.0 located within a 50 -mile radius of the site. Studies (Yelin & Patton) of small earthquakes in the basin indicate that most crustal earthquake activity is occurring at depths of 10 to 20 kilometers (km). EARTHQUAKE SOURCES We have evaluated three potential earthquake sources which could impact building design at the site. These include Cascadia Subduction Zone (CSZ) interface earthquakes, CSZ intraplate earthquakes (also referred to as Benioff Zone or intraslab), and local crustal earthquakes. Geologic evidence indicates that CSZ interface earthquakes occur approximately every 100 to 1,000 years with average recurrence intervals of approximately 400 years. Based on postulated rupture lengths, widths, and displacements as well as historical Pacific tsunamis, coastal I subsidence, and liquefaction evidence, magnitudes for such earthquakes are estimated to range from approximately M = 7.0 to 9.0. The building code recommends use of M =8.5, which likely w w corresponds to a 10 percent chance of being exceeded in 50 years. A magnitude M =9.0 event likely corresponds to approximately a 2 percent chance of being exceeded in 50 years. These earthquakes are postulated to have epicenters approximately 100 to 130 km from the site and q p p pp Y depths of 20 to 40 km. We have used an epicentral distance of 120 km and a depth of 30 km for I our analyses. This corresponds to peak base rock accelerations of approximately 0.11 g and 0.15g (using Young's attenuations procedures) for a 10 percent and 2 percent chance of being 1 ,1 exceeded, respectively. I GEODESIGN? C -2 TigardTual -12 -01 :091703 Table 3 - Input Earthquake Parameters ' PHGA PHGA at Site Using Measured Attenuation Relationships PHGA Used (g's) (g's) (g's) Crustal Earthquake Models El Centro 0.32 0.22 0.22 ' Taft 0.1 8 0.2 2 0.2 2 Topanga /Northridge 0.33 0.22 0.22 CSZ Interface Models t Michoacan 0.16 0.11 0.11 Petrolia /Cape Mendocino 0.42 0.11 0.11 ' SEISMIC HAZARDS Based on our subsurface exploration, literature review, and experience, a summary of the seismic ' hazards at the site are as follows: • Earthquake induced landslides - The site vicinity currently has slight to moderate slopes, but will be graded to have relatively flat slopes during development. Site soils are not susceptible to earthquake slope instability at these inclinations. Based on relative earthquake hazard mapping completed in the site vicinity (Mabey et al., 1995), the site has a low hazard for earthquake induced landslides over a majority of the site. • Liquefaction /Settlement- Liquefaction analysis was conducted using procedures suggested in ' 1998 NCEER. The CPT sounding data (C -1) and standard penetration blow counts from the borings was used to evaluate liquefaction potential at the site. Liquefaction analysis was conducted for a design earthquake of magnitude 6.5 with a PHGA of 0.3 g. Liquefaction analysis indicates that several layers of loose to medium dense sands between the depths of 15 to 25 feet may liquefy during the design seismic event. However, the post - liquefaction settlement was calculated to be less than 2.5 inches, which is not considered to be ' detrimental to the life- safety performance of the building. Additionally, liquefaction induced settlements of this magnitude will not manifest itself on the ground surface due to the presence of a 15 feet non - liquefiable layer of soil. • Fault surface rupture - The closest mapped fault to the site possibly capable of surface rupture is the Sherwood Fault with its inferred extension approximately 3 km north of the site (Burns, et al., 1997). Other local crustal faults are listed in the preceding text. No faults are mapped as crossing the site, and the potential for site fault surface rupture is therefore low. • Tsunami inundation /seiche /subsidence - The site is inland and elevated away from tsunami ' inundation and subsidence zones and away from large bodies of water that may develop seiches. 1 GEODESIGN? C -4 TigardTual -1 2 -Ol :091703 • Amplification - Analyses of average site response spectra with PROSHAKE with 5 percent ' damping and multiple crustal and CSZ interface models for the profile discussed earlier indicates that the site specific spectra is generally bounded by the UBC Spectra for Zone 3, Soil profile S (Figures C -2 and C -3). We thus recommend that the UBC spectra for Zone 3 ' with a soil profile type S be used for the seismic design of the building. This is especially true for buildings with low fundamental period of vibration which is where most of the one to two story buildings lies. ' RECOMMENDED SEISMIC DESIGN CRITERIA Based on our analysis, we recommend that the building be designed using the applicable provisions of the SOSSC for Zone 3. Site conditions correspond to a soil profile type S and seismic coefficients, C = 0.36 and C = 0.54. w REFERENCES Bott, D.J. and Wong I.G., "Historical Earthquakes in and Around Portland, Oregon," Oregon Geology, Volume 55, Number 5, September 1993. ' Burns, Scott, Growney, Lawrence, Brodersen, Brett, Yeats, Robert S., Popowski, Thomas A., 1997, Map showing faults, bedrock geology, and sediment thickness of the western half of the Oregon City 1:100,000 quadrangle, Washington, Multnomah, Cackamas, and Marion Counties, Oregon, Oregon Department of Geology and Mineral Industries, IMS -75, scale 1:100,000. ' Geomatrix, 1995, "Seismic Design Mapping, State of Oregon," prepared for Oregon Department of Transportation. Johnson, A.J., Scofield, D.H., and Madin, I.P., 1994, Earthquake Database for Oregon, 1833 - October 25, 1993, Oregon Department of Geology and Mineral Industries, Open -File Report 0 -94- 04. ' Mabey, Matthew A., Madin, Ian P., 1995, Downhole and Seismic Cone Penetrometer Shear -Wave Velocity Measurements for the Portland Metropolitan Area, 1993 and 1994, Oregon Department of Geology and Mineral Industries, Open -File Report 0 -95 -7. Mabey, Matthew A., Black, Gerald L., Madin, Ian P., Meier, Dan B., Youd, Leslie T., Jones, Celinda F., and Rice, Benjamin J., 1997, Relative Earthquake Hazard Map of the Portland Metro Region, Clackamas, Multnomah and Washington Counties, Oregon, Oregon Department of Geology and Mineral Industries, IMS -1 , scale 1:62,500. Madin, Ian P., 1990, Earthquake Hazard Geology Maps of the Portland Metropolitan Area, Oregon: Test and Map Explanation, DOGAMI Open File Report 0 -90 -2. Orr, Elizabeth L., Orr, William N., and Baldwin, Ewart M., 1992, Geology of Oregon, Kendall /Hunt Publishing Company, Dubuque, Iowa, 254p. GEODESIGN= C -5 TigardTual -1 2 -01 :091703 Pratt, T.L., Odum J., Stephenson, W. Williams, R. Dadisman, S. Holmes, M. and Haug, B. 2001, Late Pleistocene and Holocene Tectonics of the Portland Basin, Oregon and Washington, from High - Resolution Seismic Profiling, Bulletin of the Seismological Society of America, 91, pp. 637- 650. Seed, H.B. and I.M. Idriss, 1969, "Rock Motion Accelerograms for High Magnitude Earthquakes," EERC, University of California, Berkeley. Schlicker, Herbert G., and Deacon, Robert)., 1967, Engineering Geology of the Tualatin Valley Region, Oregon: Oregon Department of Geology and Mineral Industries Bulletin 60, 103 p. Schlicker, Herbert G. and Finlayson, Christopher T., 1979, Geology and Geologic Hazards of Northwestern Clackamas County, Oregon, Oregon Department of Geology and Mineral Industries ' Bulletin 99, 79p. United States Department of Interior, Bureau of Reclamation, "Seismictectonic Evaluation Scoggins ' Dam Tualatin Project Final Report," April 1994. Wilson, Doyle C., 1998, Post - middle Miocene Geologic Evolution of the Tualatin Basin, Oregon, ' Oregon Geology, vol. 60, no. 5., p. 99 -1 16. Wong, Silva I., et al., 2000, Earthquake Scenario and Probabilistic Ground Shaking Maps for the Portland, Oregon, Metropolitan Area, Portland Hills Fault M 6.8 Earthquake, Peak Horizontal Acceleration (g) at the Ground Surface, Department of Geology and Mineral Industries, IMS -1 5, Scale 1:62,500. Wong, Silva I., et al., 2000, Earthquake Scenario and Probabilistic Ground Shaking Maps for the ' Portland, Oregon, Metropolitan Area, Department of Geology and Mineral Industries, IMS -16, Scale 1:62,500. 1 I I GEODESIGN= C -6 TigardTual -12- 01:091 703 I lw ` � • • : , w • cowL�IrT ' • • • • l « ?. -� * • • , CLATSOP • • • • CO LUMBIA • • • SKAI ANIA •� • * • • • ' • ' � ' tep • • • CILARK • • • • • • • ' •• ( re `' • 1 • __ W, • • Y, '4. , I .,, MUL►.TNOMAH HOOD RIVER 41' .. ,� • • • • • TILLAMOOK • ;.. • • • S ITE 31 • • • ; I • YAMHILL • • 0 • • « CLACKAMAS ' ' • • • . •' I • • • • • • • • MARION © POL • • • • I • • 50 -mile radius '• I Map provided by Mapinfo I Earthquakes by Magnitude I DATE MAGNITUDE DISTANCE •7 1 + N (intensity) (miles) 1 1962 5.3 20 5.1 to 7 2 1993 5.6 27 I •3.1 to 5 • 0 to 3 I Historical earthquake information provided by Johnson and Schofield, 1994. G EODESIGN HISTORICAL SEISMICITY 1 TIGARDTUAL -12 -01 SEPTEMBER 2003 FIGURE C - r r r r r r r r ■■■ — r r r r— MN it - r 1 6000 UBC- Zone 3, Soil Sd - El Centro 1.4000 Taft - Topanga Ave rg ae 1.2000 1( p 1.0000 it cu L v u 0.8000 - - Q 1 L u 0- 0.6000 ; 0.4000 0.2000 - - 0.0000 0 1 2 3 4 5 6 Period (second) SITE - SPECIFIC SPECTRA - G EO CRUSTAL EARTHQUAKE TIGARDTUAL -12 -01 SEPTEMBER 2003 FIGURE C -2 - - - - - - - - - - - - - - - - - - - 1.4000 - UBC- Zone 3, Soil Sd - Petrolia 1.2000 Michoacan — Avergae 1.0000 L. I 0.8000 a, v Q " 0.6000 v a a 0.4000 0.2000 0.0000 0 1 2 3 4 5 6 Period (second) SITE - SPECIFIC SPECTRA - G EODESIGN z SUBDUCTION EARTHQUAKE TIGARDTUAL -12 -01 SEPTEMBER 2003 FIGURE C -3 •