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Report FOR OFFICE USE ONLY—SITE ADDRESS: This form is recognized by most building departments in the Tri-County area for transmitting information. Please complete this form when submitting information for plan review responses and revisions. This form and the information it provides helps the review process and response to your project. City of Tigard • COMMUNITY DEVELOPMENT DEPARTMENT III ■ Transmittal Letter i ;,\IZ r) 13125 SW Hall Blvd. • Tigard, Oregon 97223 • 503.718.2439 • www.tigard-or.gov TO: 4,--/ l wu DATE RE EIVFNEP DEPT: BUILDIN DIVISION,1 / FEB 12 2015 FROM: P a V - CITY OF f1(><ARD COMPANY: kip c- O J S fo M c A S f L 1- BUILDING DIVISION PHONE: e 60 S`Z ( ( ti y By: RE: /,j37 Si/. &4 i' J Tc -4 tJ% C�/ 17 —ooa l c (Site A dress) (Permit Num er) /t/e t/ CeA/12.l / J. (Project name or subdivision natfie and oft number ATTACHED ARE THE FOLLOWING ITEMS: Copies: I Description: Copies: Description: Additional set(s) of plans. Revisions: Cross section(s) and details. Wall bracing and/or lateral analysis. Floor/roof framing. Basement and retaining walls. Beam calculations. Engineer's calculations. Other(explain): fx °4- rF REMARKS: FOR OFFICE USE ONLY Routed to Permit Technician: Date: Initials: Fees Due: ❑ Yes ❑No Fee Description: Amount Due: $ $ $ $ Special Instructions: Reprint Permit(per PE): El Yes ❑ No ❑ Done Applicant Notified: Date: Initials: I:\Building\Fonns\TransmittalLetter-Revisions.doc 05/25/2012 RECEIVED FEB 12 2015 CITY OF TIGARD BUILDING DIVISION GEOTECHNICAL REPORT 13376 SW Benchview Terrace Tigard, Oregon For VP Custom Construction 12 February 2015 ,o.'=i1 Pp24.4, 12244 Q OREGON �1 HO- IE ,f Z,- wf� Rapid , SOIISOIWtIOflSLLC 3915 SW Plum Street Portland, OR 97219 503-285-1636 mia@rapidsoilsolutions.com Introduction Rapid Soil Solutions(RSS)has prepared this geotechnical report for the proposed new construction on the property located at the street address 13376 SW Benchview Terrace in Tigard, Oregon. The property site is located in the residential neighborhood of Bull Mountain within the city of Tigard and is zoned R-4.5, single family residential. The subject site is located on the south side of SW Benchview Terrace, approximately 0.05 miles east of its intersection with SW Benchview Place/SW Clearview Way and approximately 0.13 miles west of where SW Benchview Terrace terminates at SW Greenfield Drive. It is situated roughly a half mile south of SW Walnut Street and a half mile north of SW Bull Mountain Road. It is 0.93 miles west of SW 115th Ave and 1.4 miles west of SW Pacific Highway(99W). At the time of the writing of this report,the subject site consists of a single taxlot, situated in the southwest quarter of the southeast quarter of section 04,township 2S, range 1W, W.M. and is identified by Taxlot Identification Number 2S104DC00400 and R-number R2000323. The location of this 0.24 acre lot is indicated in Appendix A,Figure 1. SITE CONDITIONS Surface Conditions The subject site is located on a generally southeast facing slope in a residential neighborhood along the southern side of SW Benchview Terrace in Tigard, Oregon. It is situated on the side of a nearly NE-SW ridge along which SW Benchivew Terrace runs. The slope terminates approximately 240 feet to the southeast of the subject site,at a northeast flowing tributary to Summer Creek,which in turn is a tributary of Fanno Creek. Metromapl indicates that the elevation of the subject site starts at 482 feet in the westernmost boundary and goes down to 442 in the eastern corner. This abnormally shaped lot is nearly rectangular with the long axis oriented NNW-SSE with an elongated access extending towards SW Bench Terrace from the northwest corner of the subject site. The exact demotions are available in the Benchview Estates Plat map included in Appendix A,Figure 2. Prior to the new construction undertaken on the site in late 2014 and early 2015,the site was undeveloped and vacant, containing some forest and ground cover vegetation. Geology Current geologic literature2,3,4,5 classifies the slopes below the project site as part of the Columbia River Basalt group. This group is a thick accumulation of flood basalts was produced by dozens of fissure eruptions in eastern Oregon and Washington in the middle Miocene. These dark grey to black basalts can be divided into 8-10 distinct Columbia River Basalt flow types, comprised of as many as two dozen individual flows. They present in the region both as http://gis.oregonmetro.gov/metromap/ 2 Ma,L.,Madin,I.P.,Duplantis,S.,and Williams,K.J.,(2012),Lidar-based surficial geologic map and database of the greater Portland, Oregon, area, Clackamas, Columbia,Marion, Multnomah, Washington, and Yamhill Counties, Oregon, and Clark County, Washington:DOGAMI,Open-File Report 0-2012-02,scale 1:8,000. 3 Gannett,M.W.,and Caldwell,R.R.,(1998).Geologic framework of the Willamette lowland aquifer system, Oregon and Washington: USGS,Professional Paper PP-1424-A,scale 1:250,000 °Schlicker,H.G.and Deacon,R.J.,(1967),Engineering geology of the Tualatin Valley region: DOGAMI,Bulletin 60,scale 1:48,000. 5 Bums, Scott,Growney,Larry,Brodersen,B.,Yeats,R.S.,and Popowski,T.A.,(1997),Map showing faults, bedrock geology, and sediment thickness of the western half of the Oregon City 1:100,000 quadrangle, Washington, Multnomah, and Marion Counties:DOGAMI,IMS-4,scale 1:100,000. weathered and unweatered flows and contain interflow zones of breccia, ash and baked soil. Unweathered materials are typically blue-black, dense and finely crystalline basalt with massive columnar to close cubic jointing. The weathered flows are reddish-brown to gray-brown, crumbly to medium dense basalt. The slopes below the subject site are further classified as Grande Ronde Basalts of the Columbia River Basalt Group. This unit is typically a light-to dark- grey color on fresh exposures,with flows typically displaying blocky t columnar jointing. The regional climate typically produces a thick layer of colluvium,composed of windblown silts (loess) and sand, clay and rock fragments produced from the breakdown of the bedrock units, that overlies the Columbia River Basalts. The slopes in the region are not mapped as including this surficial layer,but likely have at least a thin accumulation of loess and colluvium. In areas with steep slopes and thicker sediment accumulations,heavy rainfalls,small landslides and gravity can move these surficial materials downslope. 1. % At �_ t 1, 'Df l / Mff Elev. X 718 ft. Subject Site • B u /I M O U fl t o Br � Br .a 0 2,500 5,000 10,000 15,000 20,000 mom Feet Al Artificial Fill Ls ,Landslides(Df Debris Flow) Akk Creek Alluvium Mff Fine Grained Missoula Flood Sediments Br4 Bedrock(Columbia River Basalt Group)with a thick colluvium Br Bedrock(Columbia River Basalt Group) Soils observations Rapid Soil Solutions (RSS)was on site on and excavated two (2) test pits to determine the onsite soils. The soil was classified using the Unified Soil Classification and Visual Manual Procedure (ASTM-D 2488)and is classified as a silty CLAY. Excavations Excavations can be accomplished with conventional excavating equipment. All excavations for footings and subgrades in the fine-grained silt should be performed by an excavator or backhoe equipped with a smooth-faced bucket(no teeth). Because of safety considerations and the nature of temporary excavations, the Contractor should be made responsible for maintaining safe temporary cut slopes and supports for utility trenches, etc. We recommend that the Contractor incorporate all pertinent safety codes during construction, including the latest OSHA revised excavation requirements, and based on soil conditions and groundwater evidenced in cuts made during construction. Structural Fills Depending upon finished building pad elevations, structural fills may be required to raise the site grades. Additionally, fill may be required for the backfilling of the proposed new foundation walls. Native or imported material may be used for fill, provided the soil is free of organics, cobbles larger than 6 inches in maximum diameter, or other deleterious matter; is of low plasticity; and, is at the proper water content. Fills should be placed on level benches in thin lifts and compacted to a dry density of at least 92% of its Maximum Dry Density (MDD) as determined by the Modified Proctor Test (ASTM D-1557). For any over-excavation completed in the area of footings or slabs, the backfill material shall consist of free-draining, well-graded, crushed aggregate base with a maximum particle size of 3/4 inch. The rock shall not contain more than 5% fines (material passing the No. 200 sieve,as tested by ASTM D-1140). The rock shall be compacted to a dry density of at least 92%of its MDD. Foundation Design Based on the field exploration and our experience with this soil formation it is our opinion that the foundation should consist of conventional spread footings. RSS found no stability issues with the site. Footing excavations should be evaluated by the Engineer to confirm suitable bearing conditions. Observations should also confirm that all loose or soft material, organics, unsuitable fill, prior topsoil zones, and softened subgrades, if present, have been removed. Localized deepening of footing excavations may be required to penetrate through the upper, softer site soils. In order to reduce disturbance to the silty soil found at the site, we recommend all excavations for footings be accomplished with an excavator or backhoe equipped with a smooth-faced bucket (e.g., no teeth). If the bases of the footing excavations are disturbed by man or equipment, the bases should be compacted to a smooth,unyielding surface with a plate compactor. All concrete footings should be founded at least 2.0 feet below the lowest exterior grade, and 16 inches below the finished floor elevation, whichever is deeper. Interior footings may also be founded at a depth of 16 inches below the finished floor elevation. The new footings should be designed for a maximum allowable bearing pressure of 1,500 pounds per square foot (psf) as per scribed in 2009 IBC code book under section 1804.2 Table 2 Allowable Foundation and Lateral Pressures. When sizing footings for seismic considerations, the allowable bearing pressure may be increased by 1/3 to 2,000 psf. Lateral pressures may be resisted by friction between the bases of the footings and the underlying ground surface. Settlement Based on our knowledge of the project scope, and for footings designed as described in the preceding paragraphs, maximum settlement should not exceed 1 inch. Differential settlement should be on the order of 50 to 75% of the maximum settlement over 50 feet. Our settlement estimate assumes that no disturbance to the foundation soils would be permitted during excavation and construction, and that footings are prepared as described in the preceding paragraphs. Retaining walls and embedded basement walls Default lateral soil load for the design of basement and retaining walls supporting level backfill shall be 35 psf/ft for laterally unrestrained retaining walls and 60 psf/ft for laterally restrained retaining walls. For embedded building walls, a superimposed seismic lateral force should be calculated based on a dynamic force of 5H2 pounds per lineal foot of wall, where H is the height of the wall in feet, and applied at 0.6H from the base of the wall. The coefficient of friction for allowable lateral sliding can be taken as 0.25. The wall footings should be designed in accordance with the guidelines provided in the"Foundation Design"section of this report. These design parameters have been provided assuming that back-of-wall drains will be installed to prevent buildup of hydrostatic pressures behind all walls. The backfill material placed behind the walls and extending a horizontal distance equal to at least half of the height of the retaining wall should consist of granular retaining wall backfill as specified in the "Structural Fill" section of this report. The wall backfill should be compacted to a minimum of 95 percent of the maximum dry density, as determined by ASTM D698. However, backfill located within a horizontal distance of 3 feet from the retaining walls should only be compacted to approximately 92 percent of the maximum dry density, as determined by ASTM D698. Backfill placed within 3 feet of the wall should be compacted in lifts less than 6 inches thick using hand-operated tamping equipment(e.g.,jumping jack or vibratory plate compactors). If flat work (e.g., sidewalks or pavements) will be placed atop the wall backfill, we recommend that the upper 2 feet of material be compacted to 95 percent of the maximum dry density, as determined by ASTM D698. A minimum 12-inch-wide zone of drain rock, extending from the base of the wall to within 6 inches of finished grade, should be placed against the back of all retaining walls. Perforated collector pipes should be embedded at the base of the drain rock. The drain rock should meet the requirements provided in the "Structural Fill" section of this report. The perforated collector pipes should discharge at an appropriate location away from the base of the wall. The discharge pipe(s) should not be tied directly into storm water drain systems, unless measures are taken to prevent backflow into the wall's drainage system. 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. Engineering values summary C,(3"0 j ) Bearing capacity 00psf 2-11915 Coefficient of friction 0.35 Active pressure 35pcf Passive pressure 350pcf Drainage The Contractor should be made responsible for temporary drainage of surface water and groundwater as necessary to prevent standing water and/or erosion at the working surface. Water should not be allowed to "pond" or collect anywhere on the site. The ground surface around the structure should be sloped to create a minimum gradient of 2% away from the building foundations for a distance of at least 5 feet. Surface water should be directed away from all buildings into drainage swales or into a storm drainage system. "Trapped" planting areas should not be created next to any buildings without providing means for drainage. The roof downspouts shall discharge out to pipes that are connect to curb cut outs .Footing drains should be installed around the building perimeter to help intercept any water migrating towards the building subgrade. The footing drain and any slab drains shall remain independent of surface water drain systems(e.g. downspouts, etc.)and pumped up to street. We recommend that typical footing drains be placed on the exterior of the foundations to intercept any water "chasing" the utility lines, or that an impermeable trench plug (e.g. concrete, etc.)be installed to stop water before it reaches the building envelope. Geohazard review RSS site reconnaissance on 29 January 2015 did not find any seeps, cracks, hummocks or any signs of slope instability. The Oregon HazVu: Statewide Geohazard Viewer6 was reviewed on February 9th, 2015 to investigated mapped geological hazards see figure 3. This review indicates that the project site is situated outside the 100-year floodplain. The expected earthquake-shaking hazard is classified as `very strong' with a no classified earthquake liquefaction hazard. The nearest mapped active fault is a NW-SE oriented fault situated over 1.5 miles to the east of the subject site. IMS-157 rates the site vicinity as having a peak horizontal acceleration of 0.4 to 0.5 g for a magnitude 6.8 Portland Hills Fault earthquake. This movement class is described by the Modified Mercalli Intensity as `severe shaking', capable of producing slight damage in specially designed structures,considerable damage in ordinary substantial buildings with partial collapse,and can 6 http://www.oregongeology.org/hazvu/ Wong,I.,Silva,W.,Bott,J.,Wright,D.,Thomas,P.,Gregor,N.,Li,S.,Mabey,M., Sojouner,A.,and Wang,Y., (2000),Earthquake scenario ground shaking map for the Portland, Oregon, metropolitan area:Portland Hills Fault M 6.8 earthquake, Peak horizontal acceleration(g)at the ground surface:DOGAMI,IMS-15.Scale 1:62,500 result in great damage in poorly built structures. Slopes in this drainage and adjacent drainages contain small earth flows,but none of these are located on or directly adjacent to the subject site. Limitations This report has been prepared for the exclusive use of the addressee, and their architects and engineers for aiding in the design and construction of the proposed development. It is the addressee's responsibility to provide this report to the appropriate design professionals,building officials and contractors to ensure correct implementation of the recommendations. The opinions, comments and conclusions presented in this report were based upon information derived from our literature review, field investigation and laboratory testing. Conditions between, or beyond,my exploratory test pits may vary from those encountered. Unanticipated soil conditions and seasonal soil moisture variations are commonly encountered and cannot be fully determined by merely taking soil samples. Such variations may result in changes to our recommendations and may require that additional expenditures be made to attain a properly constructed project. Therefore, some contingency fund is recommended to accommodate such potential extra costs. UNITED STATES t 1lrl'y for BEAVERTON QUADRANGLE DEPARTMENT OF THE INTERIOR ' t4 '.--.� »'!' OREGON-WASHINGTON CO. GEOLOGICAL SURVEY tF F.ati�..-,>ti or 4, : a 1•� 7.5 MINUTE SERIES TOPOGRAPHIC) • 1.. {` t _�- �� . .�:J r� _ �� it �n..••F _,5 1 ��_y.4.;14 _ .-aj X� -•- � •1 Trr'+�L 66�__f g 7:•-��^ ' T R1 - 7 te.�"'^• />� ,-�:__ a e, _ ` Aso t�tr�..- 1, f trot.• r b: - ", a f Q c1 > '.'s'' .: I•r$, 1$410 ._ - V' � !!° i _ _ .`er;••••-iiilit {�, • �o el"'• a - AMR' tic,— ��' a' 'Eer ..0 --1 1 1 i - 35.. 1 ' . . �� .:I I ...N.,.,,::... n _f. .. ... . -- - ' \ tUi �8�= az K .,.....cii—mi.abi.ir,,:,10.„.i..-. _.: _Le,..... . ..„ : ' t _ I 4 air : >� `�.`all, , !�, ' c`• - - - ' "I'Y,---.' ,,,- -.•,' 1 / •' ..,/-• '-a. 4\,(, ,'it...' . ::. ..41:40e;* Ni.L.,\,:!..:-:i■-.T:::::47- 1/2. ...- .GAtt L l Subject.Site ' r. * - , - :. ''''''.."..■''2' ..''::''.. ....--.'.7::.;=••••• 1.4.t.=:.41,I''-`.......' fry , F^. �r r} .� �.. s � 1� 1M r �;.;y h * • H Uf - ' / .7..,t-t.,.. r- `'^— ?•- i...:' r ( ,` to a '` •7 •4, . ( , A( 1 r « 'r* p /•• t ..,... 100.•3?''."- 4 w \ n• y �� . _ . ^,J'- J S ,cam_ S ,.. • I S. " _ 1111 •t• S. La.--- - ...441.-1..`.� _" � _ - 44 .rte. 4 j` V' 1 - . _ , ( l o lwo woo mm .000 wm moo m_oo FEET .l.,;i• BEAVERTON. DREG. E ra.",RION.5 NNAOR w;NE OREGON ' •-Tw-ln-t—_!:—. 0 —..... 1 FiLow ER , 4517207 TF-024 + a e CONTOUR INTERVAL 10 FEET 1961 PMOTOREVISEO 1984 ,_ OwGwIGEE,LE'.InCN - NATIONAL GEODETIC VERTICAL DATUM OF 1929 - Ri n,1 i ! DMA >♦'v M! SERIES V., Figure 1: Site Location - 7, .65---- ..... • 4.,-. ______---------•— ,---" • . r3 NI G° •C : ,, S.W. ort1/4CI /e ....------:7--'•\-- N`l. . -4, ITa#5.00•teaot ,c, i .• . / .• • / . $•,••'' ' 43 * ,t• ,...i., 4). • • P. ! a 7 4) .• . . ". • • •' 'V 4,,.•_• .,' sa vc • _ __ ....., t cl .-- ,,,, 5 72•3112 ... ,L.... .."......• .-r• 1 -- It r C7 8 . I i ' 1 I LA, ta.tv o cror ‘t c-4 re. , . .... .. ‘--: -lc II .: % ,e.,:c • • ,3 • • -.. .4 • ,,- ut 1., III : . .\ ,,oi .,,. • rn''''.` \-- • . IS' "7,1 e..cr. 7, 1,." u!' SIGNED ON: a - •.i..*0 TP#1 --''' az cr.- C REGISTERED , - -z • 39 s. f .....•,), • -,' r • 1. PROFESSIONAL - e:. .,...:. ,....1-. .....- . y ta ' t•• CC ..e. . as 1 •,/-7. ,,, G.■ •-• ,..., LAND SURVEYOR ilt i Q., ,,. T..) "V 'I- ....,--'. 1 \ ...,,f,' 7 950 .,...._._........ .... .... ..........,,..............,—..."„........;.....>— . _. .gi. V' .17i n 64'1 JAMES BURTON BROWN EA Stu ",' Y 14 60379 3E.I.Eg F - VAUD THROUGH DECEMBER 31, 2015 Figure 2-Site plan with testing locations ... Fe ;,..3 al, " tliPZ t MS I low Pe 1 ' 5 cie St VI Go° .. . 04t,.. U ra o O. co arde SI 2 . 1.. oletrace SW Greenfithl Cy (11 CO N I"— U 3 M.' 1(11110,11Uaftie p 1°1r1117:4‘111-144‘)CIA44st''4'll :::k$14' CI C 2 m 22 D t10 4 .4.' 6 3 4is • TP#1 Surface Elevation:476 A �,� 0� � � oJ� ��Q �a��e Boring Date: 1129/15 Qr mat tiy�/Oe o,�C' �Q� � Boring Location:Portland,OR �e moo act 00 ya/�a Drilling Method: Excavator h' 0 – Top Soil a- is 0 ML-CL Damp,medium brown,very stiff,fine grained silty CLAY $- 0 g-1 0 s ' 1 _ F2 ' z - z L- ;', 3 cr — - _ s-4 i I - o� j5 ca — � 1 is y —6 End test pit L.7 LOG OF BORING 13376 SW Benchview Terrace Rapid Soil Solutions Plate 1 VP Custom Construction I TP#21 Surface Elevation:468 �y `0`\1 c'.' 6> c�cP \e�3° Boring Date: 1/29/15 Qti'c �� .�c,'�� < ..O ? ,`5, Boring Location: Portland,OR O° �A �° O� 4„,o. q,,- ..tv , Drilling Method: Excavator < Top Soil a i i<>:', >a<a m ML-CL • Damp, blueish gray stiff,fine grained silty CLAY Q. I s —t I a ti- 3 t U G 3 cn - c ` -2 I ■ t _ sf I a i h 0 F c I 3 3 l I z I Y gl 1 i ! I 1 r-L I ! 1 __I �4 i/ ML-Cl Damp,medium brown,stiff fine grained silty CLAY ii ii I a { , U /( 1 u I�/- 3- I A" 1� h 6 i I 11 Test pit completed at depth of 6 a to_ 1 —7 --_._._. .. -___. —i__. I LOG OF BORING 13376 SW Benchview Terrace Rapid Soil Solutions VP Custom Construction Plate .1