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Report ( 61,tf 76'40 L O 550 PPk e S REDMOND & ASSOCIATES Geotechnical Investigation Proposed Pfaffel Street Cellular Tower Site SW Pfaffel Street and Hall Blvd ' r (Washington County), Oregon d (Wa gt ty), on g for AT & T Wireless Services 1 ' Project No. 110.072.G November 7, 1996 1 1 REDMOND & ASSOCIATES Project No. 110.072.G Page No. 1 ' November 7, 1996 ' Ms. Kathleen Creighton AT & T Wireless Services 1600 SW 4th Avenue Portland, Oregon 97201 Dear Ms. Creighton: Re: Geotechnical Investigation, Proposed Pfaffel Street Cellular Tower Site, SW Pfaffel Street & Hall Blvd Street, Tigard (Washington County), Oregon INTRODUCTION ' In accordance with the request of Ms. Kathleen Creighton of AT & T Wireless Services, we have completed our geotechnical investigation for the above subject cellular tower project. Our work ' was performed in general conformance with our verbal discussions with Ms. Creighton on October 22, 1996. Written authorization of our services was provided by Ms. Creighton on October 23, 1996. We understand that present plans are to remove an existing wooden mono -pole cellular tower and replace it with a new mono-pole cellular tower at the site. The tower reportedly will consist of an approximate 80 -feet tall self- support, steel mono-pole tower structure while the existing 12 by ' 28 feet in size equipment shelter reportedly will stay. The scope of work for this investigation included the drilling of one (1) exploratory test boring near the existing /proposed tower location on October 25, 1996 (see Site Vicinity Map, Figure No. ' 1). The test boring was drilled utilizing truck mounted, solid- flight, hollow -stem auger drilling equipment. The results of our investigation, including design and construction recommendations for the project, are summarized within this report. SITE CONDITIONS The subject tower site is located just south of SW Pfaffel Street and east of SW Hall Blvd and ' Hwy 217 at the existing Pfaffel Street cellular tower site in the city of Tigard (Washington County), Oregon (see Site Vicinity Map, Figure No. 1). The tower area is presently improved and consists of an approximate triangular shaped cell site. Topographically, the site is relatively flat -lying to gently sloping down to the west and is estimated at about Elevation 225 feet. Surface vegetation at the tower site generally consists of a few trees near the perimeter of the fenced cell site. 1 P.O. Box 301545 • Portland, OR 97294 • Phone: 252 -6882 • Fax: 252 -6414 I I Project No. 1 Page No. 2 I The subsurface soil conditions at the site consist of catastrophic flood silts and sands of Pleistocene age. Specifically, these subsurface materials were found to consist of an upper unit I of stiff to very stiff, sandy, clayey silt to a depth of about 22.0 feet beneath existing site grades. These clayey silt soils are best characterized by relatively low to moderate strength and compressibility. The clayey silt soils were intum underlain by medium dense, slightly clayey, silty fine sand to the maximum depth explored of about 30 feet beneath existing site grades. These I silty fine sand soil materials are best characterized by relatively moderate strength and low to moderate compressibility. Groundwater, in the form of seepage, was encountered within the exploratory boring at the time of drilling at a depth of about 13 feet. Topsoil materials were I . generally not encountered at the site due to the presence of about 12 inches of aggregate base rock. All soils were classified in accordance with the Unified Soil Classification System (USCS) which is outlined on Figure No. 3. I CONCLUSIONS AND RECOMMENDATIONS Based on the results of our field explorations, the tower site was found to be generally underlain I by catastrophic flood deposits of Pleistocene age. These subsurface materials were found to be stiff to very stiff, sandy, clayey silt soils within the upper 22.0 feet followed by medium dense, slightly clayey, silty fine sand to the maximum depth explored of 30 feet. As noted above, I groundwater, in the form of seepage, was encountered at the time of our field exploration work and is expected to be a factor during construction. In this regard, we are of the opinion that the site is suitable for the planned new self- support steel mono-pole tower structure provided that the following recommendations are incorporated into the design and construction of the project. I In general, we are of the opinion that excavations for the mono-pole tower structure will encounter only moderately hard drilling conditions within the stiff to very stiff and medium dense I clayey silt and silty fine sand soil deposits. Additionally, due to the cohesive nature of the subsurface soils at the site, we anticipate that an open drilled shaft excavation for the mono-pole tower structure will generally not encounter significant caving and /or sloughing conditions of the excavation under short-term conditions. However, due to the anticipation of some minor I groundwater seepage at the site, some minor caving and /or sloughing may occur. In this regard, we envision that the drilled shaft excavation will most likely not require the use of casing to maintain stability of the open excavation. The following soil strength parameters may be used for I foundation design purposes: Medium brown, sandy, clayey SILT (ML); I Allowable bearing pressure: 2,500 psf (above 2.0 feet) 3,500 psf (below 4.0 feet) Allowable lateral bearing pressure: 200 psf/ft I Soil unit weight (moist): 110 pcf Angle of internal friction (drained): 30 degrees Cohesion (undrained): 1,000 psf Coefficient of friction: 0.30 I . Passive earth pressure: 200 psf Adhesion of concrete to soil (ultimate): 750 psf I REDMOND & ASSOCIATES I • I Project No. 110.072.G Page No. 3 I . Olive -brown to orangish - b rown, slightly clayey, silty fine SAND (SM); I Allowable bearing pressure: 4,500 psf Allowable lateral bearing pressure: 300 psf/ft Soil unit weight (moist): 115 pcf I Angle of internal friction (drained): 34 degrees Cohesion (undrained): 200 psf Coefficient of friction: 0 Passive earth pressure: 300 psf I Adhesion of concrete to soil (ultimate): 1,000 psf Note: Allowable bearing pressures may be increased by one -third for short-term wind or seismic I loads. For conventional (lightly loaded) shallow foundations with at least 18 inches of embedment, such as those required for an equipment shelter, we recommend that an allowable contact bearing I pressure on the order of 2,500 psf be used for design where foundations are supported by the native, stiff clayey silt subgrade materials. A coefficient of friction between the clayey silt subgrade and footing elements of 0.30 is recommended. Settlements of foundations, for both the ' tower and any equipment shelter, designed and constructed in accordance with the above recommendations are expected to be less than 1/2 -inch. Site preparation is anticipated to consist generally of the excavation and drilling of a new mono- ' pole tower foundation shaft. Where structural fills are required, we recommend that structural fills be compacted to at least 92 percent of the ASTM D -1557 test procedures. Additionally, the on- site clayey silt subgrade materials are considered unsuitable for use /reuse as fill materials unless I they are free of rock fragments in excess of about 8 inches and near optimum moisture content at the time of compaction. CLOSURE I The services p erformed by the geotechnical engineer for this project have been conducted with that level of care and skill ordinarily exercised by members of the profession currently practicing I in this area under similar budget and time restraints. No warranty, either expressed or implied, is made. We will be pleased to provide such additional assistance or information as you may require in I the balance of the design phase of this project and to aid in construction control or solution of unforeseen conditions which may arise during the construction period. I Sincerely, PROF F`r! y ` t � I e Q � Q tNFD LbNLA,4.,,,Q V �, 1 rg N s r Daniel M. Redmond, P.E. r� • . I President/Principal Engineer OREGON -VA ✓ <//y 15 192 O IS iFL M RED REDMOND & ASSOCIATES T. 1 I • • I ,� fi n: • - - .•) I ' 1 • `I; i/ /. /` l' per• 7�,. — ,,, y1� •.f- `I , 16 .1 \ :.y.. ce, --,:I�� •�IL_ Robins \ . ove. , a; � r , :�� • „ /., . / / ° ' -AR a �'' � �� f •, � . yfl� � 1 ♦ ��.ii � � ► riilFC�i�i/e J L =—� � � , ff ---.,-.-----,---- _ � —� .. .SIP' i . I I I I 27 I P0.4 T KO LQ' _ s - -; ... -• • . = . ,�'. SITE' .:,;,• " � �� i 4---... . • ! G;; A po . � �.aru �!:'• '' -�_. . ti 7•� • ' c Ara., • , ' " S �i O �� / • ■ I \ •�� ' ' F \ r _ Sch \ • • C c\ � ' . , ; */ ~ \ I \ 5 x'1 • • -� " � J . • • . Tiga 4, • /• \i:: , . E: ■ =' . 1� ° • • I . / /', 7 ., / , ,, w✓ 4, � �- • y � •� --� 1 \ iii / / r , ; i.� :'....;:z ./ . ...=: =•:-.7,f /1. . ; • • •"! '' • -- '',..' • -- .) ) c`i••• `.- s'.:\ ' s''' s \ ..-` : - " . 7-. - ' 1 BEAVERTON QUADRANGLE OREGON— WASHINGTON CO. I 7.5 MINUTE SERIES (TOPOGRAPHIC) NE.4 BEAVERTON 15' QUADRANGLE I 1 SCALE 1:24 000 0 1 MILE �-a —� 1000 0 1000 2000 3000 4000 5000 6000 7000 FEET H t--i t---I I I I I I I .5 0 I KILOMETER )---1 1—ti 1--I .--I t--+ CONTOUR INTERVAL 10 FEET NATIONAL GEODETIC VERTICAL DATUM OF 1929 I SITE VICINITY MAP I Project No. 110.072.G f PFAFFEL STREET CELL SITE I Figure No. 1 1 M Mil INNI IMIN Mil MIN I= MN NM IM Mil MN NIM MEN Mil NM MMO MN I= . • . NI • a . 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I Q Poorly graded gravels or gravel-sand mixtures, little or MORE THAN HALF (LESS THAN G p no fines. g g Q N OF COARSE 5 % FINES) to 2 O FRACTION IS GRAVEL GM Silty gravels, gravel- sand -silt mixtures, non - plastic fines. I 0 LL Z w LARGER THAN WITH Z Q ET) NO. 4 SIEVE FINES GC Clayey gravels. gravel- sand -clay mixtures. plastic fines. O u. C LEAN J = 2 o w SANDS SANDS SW Well graded sands, gravelly sands, little or no fines. I w Q ¢ N MORE THAN HALF cn OF COARSE C LESS THAN 5% FINES ) SP Poorly graded sands or gravelly sands, little or no fines. Q x J O w to FRACTION IS SANDS SM Silty sands, sand -silt mixtures, non - plastic fines. - O SMALLER THAN WITH I NO. 4 SIEVE FINES SC Clayey sands, sand -clay mixtures, plastic fines. w ML Inorganic silts and very fine sands, rock flour, silty, or co LL t t ►_+ SILTS AND CLAYS clayey fine sands or clayey. silts with slight plasticity. I U) O 6 Inorganic clays of low to medium plasticity, gravelly N LL Q w clays. sandy clays, silty clays, lean clays. 0 = tn N LESS THAN 50% LIQUID L IS C L OL Organic silts and organic silty clays of low plasticity. w I Z Z N Inorganic silts, micaceous or diatomaceous fine sandy or si Q N why soils, elastic silts. C7 Q W z 0 SILT A ND CLAYS MH LIQUID LIMIT IS CH Inorganic clays of high plasticity, fat clays. Z I f i- 'N AN AN 50% LL OH Organic clays of medium to high plasticity, organic silts. HIGHLY ORGANIC SOILS Pt Peat and other highly organic soils. DEFINITION OF TERMS U.S. STANDARD SERIES SIEVE CLEAR SQUARE SIEVE OPENINGS ' 200 40 10 4 3/4" 311 12" SAND GRAVEL SILTS AND CLAYS - COBBLES BOULDERS I FINE - MEDIUM COARSE FINE COARSE GRAIN SIZES I SANDS,GRAVELS AND CLAYS AND STRENGTH BLOWS /FOOT NON PLASTIC SILTS PLASTIC SILTS I VERY LOOSE 0 - 4 VERY SOFT 0 - 1/4 0 - 2 SOFT 1 1/4 - 1/2 2 - 4 LOOSE 4 - 10 FIRM 1/2 - 1 4 - 8 • MEDIUM DENSE 10 - 30 STIFF 1 - 2 8 - 16 I DENSE 30 - 50 VERY STIFF 2 - 4 16 - 32 VERY DENSE OVER 50 HARD OVER 4 OVER 32 ' RELATIVE DENSITY CONSISTENCY ( Number of blows of 140 pound hammer falling 30 inches to drive a 2 inch O.D. C1 -3/8 inch I.D.) split spoon CASTM D- 1586). I 4Unconfined compressive strength in tons /sq. ft. as determined by laboratory testing or approximated by the standard penetration test CASTM D- 1586), pocket penetrometer, torvane, or visual observation. I KEY TO EXPLORATORY BORING LOGS Unified Soil Classification System CASTM D -2487) I REDMOND & ASSOCIATES PFAFFLE STREET CELL SITE • P.O. Box 301545 • Portland, OR 97230 Tigard, Oregon PROJECT NO. DATE I Figure 3 110.072.G Nov. 7, 1996 • 1 DRILLING COMPANY: CriSman Drilling RIG: CM 55 DATE: 10/25/96 I BORING DIAMETER: 6.0" DRIVE WEIGHT: 140# DROP: 30" ELEVATION: F- W a I- > W7 y ^ - w a 2 o y j i- < y SOIL DESCRIPTION = y W 3 Q. p w BORING NO. 1 a a > OO > g 0, H 2 0 m 0 CO 0 U II o GM FILL: Gray, damp, moderately compacted, silty, sandy GRAVEL (Aggregate base rock) I - ML NATIVE GROUND: Medium brown, very moist, stiff to very stiff, sandy, clayey SILT x t19 26.4 5 _ I - _ , Becomes very moist-to wet x {13 33.8 0 10— L • I - - • Encontered groundwater seepage at 13 feet x + 18 . 27.1 , 15 - - II Becomes light olive -brown x j 12 23.7 20 --1 - I - SM Olive- brown, - moist to very moist, medium dense, silty, fine SAND x 112 19.8 I 25 — Becomes orange to reddish -brown II _ / Total Depth = 30.0 feet . x 17 18.9 Groundwater seepage encountered at 13 feet 30 BORING LOG . I PROJECT NO I PFAFFLE 110 STREET CELL SITE (FIGURE NO. 4 I REDMOND & ASSOCIATES I UNIFIED SOIL CLASSIFICATION SYSTEM (ASTM D 422.72) I U. 5. STANDARD SIEVE SIZES 7 6 3 2 1 3 1/2 1/4 4 e 10 16 20 30 • • 50 60 SO 100 200 325 100 0 ■ ��MB��Ul�� ■ � 0. _ —.- �__ ∎• ��_ Na �� I iM• aa1= i�� MI= =I MOM MNOM= aiIN i■1=1• =\Wt410,11=1 IMMIMI 61•1•■•MEMO II■IMIi 10 ■mu∎I IIMa■aaNIff∎ ate ∎tea 1∎1.1 0 •1111•1=1wsII■IIM aMMIN u=n••=w■ ■ate INaa■I.la■0 ■E�� 1∎1 1 so 01111111■1=1M■t=MMISIM14■01M■INIMMIMINOMMUMEIMONINIBMIMMIMIIMILsVAlinis■IsMwm1S■ 20 ■ aaaa��a�� aa��i� � ��aWa� .��.� to I ■ ��w�� s• �_� —IMO _ 7 0 �� a � �.i��E��a � :1 60 • 611==■011111•1■AMII■IMMINIMIMMIMMIINIMBNIIMOB=SIMMIII■11.=.1==.11•1011MIBI1017111•=MIMIMIMMMOMMIMI=MINIMrl■ 40 111 r. ese!ININIIIIMINIMINIIIIIIIIIMM11■111 NIMINIMMINIMIMMIll■INIMMIXIMIIII■r•IMEIMBINSIMMIIMMII■ sl■IS■3•1= 'MEMOIR MEMO= sr•riIIMM II�li•��s so _ aw∎�� ■ �� U so ■ 'ERA —_� �� a�i��NM Win• �M.�a��MIM_s■ • 4iM�gM IA'aa. alaata∎ 60 _ i 40 ■aa■l�il��mia�i��miai I&w.■ ■mlls ■a aa��awa .waa�aaa��4w��IN�1•aaw� 1asa� ∎� 70 30 It=■■•=113MBINMESMEN ■ a1■IMIaa .a■•10l ∎.aaaIM■.aa.a.a.a.a ■im•Mm ∎a∎d•=1 _"==leMMIeM=1.1 I 20 sw4■44mman■limonmommmammosis■ww■mu■Bimmt•mm■immuscW.,4win■alo7■=u1=1■11■ so ■WIOMIMO NIMIII aaMI NMI MIfaMIIM ■ s• a•1•M IMaalIM�IMla��laaallaiaIMiMM�mes1� >•��GO�� ■��— �1�� -� .001 0 ua��un• lo■ uM�lMnpn�nMa, �n■ aul�usM■ uMmulO�MaEul�M■�■,�auosMu�ao�M�� s•�a�.� 100 I 100 50 10.0 5.0 1.0 0.5 0.1 .05 .01 PARTICLE SIZE IN MILLIMETERS I GRAVEL SAND SILT AND CLAY COBBLES COARSE I FINE COARSE I MEDIUM FINE I I UNIFIED KEY BORING SAMPLE ELEV. SOIL SAMPLE DESCRIPTION DEPTH (feet) CLASSIFICATION SYMBOL N0. (feet) SYMBOL ' —e— B -1 9.5 ML Medium brown, sandy, clayey SILT I B - 24.5 SM Orangish- brown, silty, fine SAND I I GRADATION TEST DATA • REDMOND & ASSOCIATES PFAFFEL STREET CELL SITE t P.O. Boa 301545 • Portland, OR 97230 Tigard, Oregon PROJECT NO. • DATE 5 110.072.G Nov. 7, 1996 FIGURE