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Report (39) 0 E Ir c (,o /i GROC zi 0 R filv.vort.Itt .Akt, ocytEct1cAt.'cowpyo.rrs vock4pr.4.70 16190 s'w I13 Avenue SUBJECT: : WOODSPIRTNOAPARIVENTS,;:BUILBINO:3 11(00i,:0rOW: Per hc 074.01MINIPALEPOis.MILIAPQN:::: ieq nest of Mr Chns Rar�eld .....,:. o bserve the :: 00040104 t 01# )/00441404#4 0#014#04***4404.10,0070sliti.;:44.ppp404*-4*. .:..... :14i,mm4:#4,4*.cf4000/ ntyoftheatIopdwthp : .`JlosibioOniiii4Ifitilbogi:Tho:elititopotimeteriorthe , Weit:'creek.-iliipo:ittici:iiterceri . itisuifioo:ywate from flowing wer *be slope 1ce An apoxntate 2400t high retith1iig wall and pit tW:1*Itfititi14 aecordaxtee with the :litf6iiiiNtb*404A0filt 203 and with subscp*ntpnijcet That - 001.4 ,b4:0Wlitar146,1 . :Afk:40.:1**:**:00.400 4414 '41 :„. . NitOV.*:tE. Wa'sky:$ „- PiOjeO(EOgio* l '•:. - - - ". • • IWO : ] !41 4 4 , 00 . 01« :..P 9N I 4pho 00 tr2s416-4- WOODSPRING 5036244952 11/18/05 0S:14pm P. 002 U GEOCON NORTHWEST,INC. GEOTECHNICAL CONSULTANTS ;F Project P1324 -05 -02 November 15, 2005 U Ms. Susan Rothe Woodspring Apartments 16100 SW 113 Avenue Tigard, Oregon 97224 SUBJECT: WOODSPRING APARTMENTS, BUILDING 3 TIGARD, OREGON GEOTECHNICAL CONSULTATION Dear Ms. Rothe: Geocon Northwest is leased to provide p ovlde the following geotechnical consultation regarding slope I movement that has occurred on the east side of the Woodspring Apartments property (see Figure 1, Site Vicinity Map). The area of consultation consists of an east - facing slope that grades down from Building 3 to a drainage creek. Geocon Northwest provided recommendations for the repair of a N shallow slope failure that occurred at the site in April 2005. This area of slope failure was repaired in September 2005. An additional shallow slope failure has recently occurred to the south of the April 11/ slope movement. Additional erosion at the base of the slope is also visible immediately north of the April repair. The slope has been saturated during recent rain events due to leaking gutters and poor routing of surface runoff water. A copy of the architectural plans for the original construction of the apartment complex was P reviewed, Based on the topography map illustrating the existing conditions prior to construction and the grading plans showing proposed finished floor elevations, it appears the east edge of Building 3 may be bearing on 1 to 2 feet of fill soil. The topographic survey of the existing conditions prior to construction indicate an approximate slope inclination ranging from 4H:1 V to 6H:1 V. Measurements made at the site using a tape and leveling scope indicate that the slope is now at an inclination p slightly less than 2H:1V. Stream erosion at the base of the slope has left portions standing vertical at a maximum height of 6 feet. Minor erosion and undercutting of the east creek bank was also observed in several locations. SUBSURFACE CONDITIONS The subsurface conditions at the site were evaluated through the e completion of three hand auger borings. The borings extended to depths ranging from 6 to 12 feet below the existing ground surface and were completed in the approximately locations as shown in Figure 2, Site Plan, at the end of this letter. The subsurface conditions generally consisted of approximately 3 feet of soft, wet 1 8283 SW Cirrus Drive P Beaverton, Oregon 97008 • Telephone (503) 626 -9889 R Fax (503) 626 -8611 WOODSPRING 5038244952 11/18/05 05:14pm P. 003 ! Woodspring Apartments, Building 3 Project P1324 -05 -02 Tigard, Oregon November 15, 2005 Geotechnical Consultation Page 2 ' brown /gray clayey silt which is likely fill from past grading operations. It does not appearthat this material was compacted as structural fill within the slope area. Beneath the fill, a native deposit of medium stiff to stiff, moist, brown fine- grained sandy silt was observed to the terminal depths in all 1 borings. The soil became wet to saturated at a depth of 12 feet. Boring logs documenting the subsurface conditions may be found at the end of this letter. CONCLUSIONS AND RECOMMENDATIONS Slope stability analyses were completed using the measured slope geometry as described previously with the approximate 6 -foot vertical surface at the toe. The results of the analysis indicate that the surface of the slope is marginally stable with a factor of safety near 1. This result is consistent with the observed sloughing of the upper 3 to 4 feet of material that has occurred during the past 6 months. The sloughed soil appears to consist of the uncompacted fill material that was likely placed during original grading operations for the apartment complex. The failures were initiated by saturation of the slope surface by stormwater runoff and erosion at the base of the slope from the creek. Deep- seated failures occurring within the medium stiff to stiff native soil are not expected and have a factor of safety of approximately 1.5. ' The results of the geotechnical field investigation and slope stability analyses have confirmed our original conclusion that the slope is globally stable and potential impact on the existing structures is minor. However, given the lack of proper surface drainage near the slope top and erosion at the base of the slope by the stream, it is likely that surficial sloughing may continue. t The following paragraphs provide two options for slope repair. The first recommendation is provided as an option if the owner will accept that further shallow sloughing may occur, but will not impact the structures. It provides repair recommendations for existing failures, as well as a bank protection scheme to prevent further erosion. The second recommendation outlines a complete rehabilitation of the entire slope which will essentially remove the potential for shallow slope failure. A French drain should be installed in either case to prevent saturation of the slope face due to stormwater runoff. FRENCH DRAIN Installation of a French drain at the crest of the slope along buildings 3 and 7 is recommended to intercept surface runoff from saturating the slope face. The French drain should be 2 to 3 feet deep, 6 to 12 inches wide, and contain a perforated pipe at the bottom. Backfill of the trench should consist of free - draining pea gravel and the surface should not be covered with topsoil. Maintenance of the French drain will be required to ensure that the surface does not become impermeable with topsoil. The drain pipe should be routed to a suitable catch basin or to a solid I WOODSPRING S0962449S2 11/18/05 0S:14pm P. 004 I Woodspring Apartments, Building 3 Project P1324 -05 -02 Tigard, Oregon November 15, 2005 Geotechnical Consultation Page 3 pipe that extends completely down the slope to the stream. The pipe should not exit within the slope face. Figure 3 illustrates the French drain recommendations. OPTION 1 The locations of the slope that have been eroded by the stream forming a vertical face should be backfilled with 4 to 6 -inch diameter pit run rock such as was used in the repair of the slope in September (see Figure 3). A geotextile filter fabric should be placed between the rock and soil. The rock should also be placed at the base of the slope along the stream length bordered by Buildings 3 and 7. The rock backfill will prevent further erosion at the toe and will form a buttress to reduce additional sloughing of the upper slope. This option will not entirely remove the potential for sloughing in other locations along the slope. OPTION 2 The owner may choose, in lieu of the previous recommendation, to repair the entire slope to a condition that will provide negligible potential for additional sloughing. This option would include excavating the slope face down to firm native soil which is expected at a depth of approximately 3 feet. The excavation should be backfilled with four to six -inch open - graded pit run or similar product placed over a geotextile filter fabric. A buttress made of a cast -in -place concrete wal, gabion baskets, or concrete blocks, should be installed at the base of the slope similar to the previous slope repair (see Figure 3). Minor erosion and undercutting of the east creek bank was observed in several locations. The east bank has a relatively flat slope and is not considered to be susceptible to significant slope movements. No requirements for protection of the east creek bank are recommended at this time. LIMITATIONS Unanticipated soil conditions are commonly encountered during construction and cannot always be determined by a normally acceptable subsurface exploration program. The recommendations of this report pertain only to the site investigated and are based upon the assumption that the soil conditions do not deviate from those disclosed in the investigation. If variations or undesirable w conditions are encountered during construction, or if the proposed construction will differ from that anticipated herein, Geocon Northwest, Inc. should be notified so that supplemental recommendations can be given. The findings of this report are valid as of the present date. However, changes in the conditions of a property can occur with the passage of time, whether they are due to natural processes or the works of man on this or adjacent properties. In addition, changes in applicable or appropriate standards a • WOODSPRING 5096244952 11/19/05 0S:14pm P. 00S • I Woodspring Apartments, Building 3 Project P1324 -05 -02 Tigard, Oregon November 15, 2005 Geotechnical Consultation Page 4 may occur, whether they result from legislation or the broadening of knowledge. Accordingly, the findings of this report may be invalidated wholly or partially by changes outside our control. Therefore, the conclusions and recommendations provided in this letter are subject to review should such changes occur. If you have any questions regarding the information herewith, or if you desire further information, i please contact the undersigned at (503) 626 -9889. Sincerely, Geocon Northwest, Inc. Q*4 //1 41/1---- (/ Bryan Wavra, P.E. Wesley Spang, P.E., h.D. Geotechnical Engineer Principal Engineer \ < ?.D P ROF F9 GINe / k. 18281 9 J ✓y y 16 9 , 6 of. sP EXPIRATION DATE: 613006 I I t I I 1 WOODSPRING APARTMENTS ( ------ F - RENCI - T --- NETAIL DRAIN DETAIL SLOPE STABILIZATION OPTION #1 TIGARD, OREGON .f _ , _P EA . » . . EAST WALL d . ..;G RAVEL A PPROX. X8 1 BLDG.3 co � . y¢ I Z PER RATED '1 N NTS DRAIN PIPE °' o . i ' .:..................7)1 SLOPE 15 APPROXIMATELY 1.5H:1V -2H: �, �� FRENCH DRAIN F — - iz (SEE DETAIL) i 4- a 4" - 5" DIAMETER w PIT RUN �Vj j W STREAM OPTION #2 EAST WALL APPROX. 18' BLDG.3 0 0 - VDY� N. SLOPE IS APPROXIMATELY o ° e . ' o : N 1.5H:1V -2H:1V ° ° o ° 0) r N. ° APPROX. 0 o � � • FRENCH DRAIN o . °0 3' (B (SEE DETAIL) p r • ►� �:�T�T - ° • ' 0 ° ° ' FIRM, NATIVE SOIL � . m. tO �_ GABIAN BASKET '� �• o GEOCON I OR i � �. 0 1s,!., CAST-IN-PLACE -yam NORTHWEST, INC. v �Y GEOTKHNKAI CONSJITAlYiS OR ► ^� ' O ' S' 82835WCIRRUSDRIV E •B'cAVEATON,ORE�ON97W B•bdd9 0 CONCRETE BLOCK �.�w 5 WALL °1%' PHONE 503 626 -9689 •FAX SA 3626Ab11 .: PROJECT NO. P1324 -05 -02 co % SCALE 1" = 5' FIGURE 3 �_� $ �� DATE 111151200 STREAM .ISIL -05-C1JW-¢W NU. WOODSPRING S0362449E2 11/18/05 OS:14pm P. 007 • II • • • . . , . ii • • 1111 . -.....,,. c„, . .. „. ....... • .. r - • ..:•-• ; .:. 4..1.: . • 1 ..,...,,,, ..;: '. •.:. *.,....?I. ft , .5, i r • 1,.... • a,•.,; y• .a:'} • . r.• v , L: ' " • � iY �' ': - t 4 p ' l ' ' • r lr' w• ; " A T . �J • • .i ^ .. S itt:...'• ~�7 ''+,. : ' ; e:Y sr .'.. ,1 ^ .•.!N ^ /r�, .. ■Ott � � ��� • t � *. y � + +�T� f-�.X. ' * ' l "• ,• 5. T .. 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LEGEND II _ APPROXIMATE LOCATION OF BORINGS N 1"---.40' piqcpi SITE PLAN H W E S T WOODSPRING APARTMENTS GEOTECHNICAL CONSULTANTS 8380 SW NIMBUS AVENUE- BEAVERTON, OREGON 97008 TIGARD, OREGON rn PHONE 503 626 -9889 - FAX 603 626 -8611 8JW / RSS 1 I ISK/ X0000 11/15 /2005 P1324 -05 -02 FIG 2 S • City of Tigard 13125 SW Hall Blvd. � Tigard, OR 97223 S 503- 639 -4171 T I GARD FAX TRANSMITTAL Date Wednesday, March 29, 2006 Number of pages including this cover sheet 1 To: Andrew Spear From: Albert Shields Co: Arbor Mortgage Co: City of Tigard Fax: 972 - 788 -1002 Fax: 503 - 624 -3681 Phone: 503 - 718 -2426 SUBJECT: Woodspring Apts., 16100 SW 113th Ave, Tigard, OR MESSAGE: Re your inquiry, at this time we have no record of any outstanding building code violations at the above property. Albert Shields, Building Codes Enforcement 0i ficer * ** PLEASE DELIVER IMMEDIATELY TO ADDRESSEE * **