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(//://, IDES I GNz i September 13, 2016 Polygon Northwest Company 109 East 13th Street Vancouver, WA 98660 Attention: Mike Waddell Geotechnical Subgrade Observation Letter West River Terrace- Lots 55 through 59 and Lots 61 through 72 Tigard, Oregon GeoDesign Project: Polygon-123-03 This letter provides a summary of our foundation subgrade observations for the planned single- family homes located on Lots 55 through 59 and Lots 61 through 72 of the West River Terrace development. The street addresses and associated permit numbers of the lots are presented below. We prepared a geotechnical engineering report', dated December 5, 2014, providing geotechnical recommendations for the site. We also prepared aJuly 21, 2015, Lock+Load® retaining wall design memorandum2for the site. Mass grading plans indicate the lots required fills ranging between approximately 3.5 and 5.5 feet, with the exception of Lots 61 through 64, which required cuts. West River Terrace Lot Location Lot# Street Address Permit# 55 13727 SW 172^d Avenue MST2016-00168 56 13735 SW 172"d Avenue MST2016-00169 57 13741 SW 172nd Avenue MST2016-00170 58 13753 SW 172nd Avenue MST2016-00171 59 13765 SW 172nd Avenue MST2016-00172 61 17243 SW Jean Louise Road MST2016-00223 62 17255 SW Jean Louise Road MST2016-00224 63 17267 SW Jean Louise Road MST2016-00225 64 17289 SW Jean Louise Road MST2016-00226 'GeoDesign,Inc. Report of Geotechnical Engineering Services;West River Terrace;SW Roy Rogers Road;Tigard,Oregon, dated December 5, 2014. GeoDesign Project:Polygon-123-01 2GeoDesign, Inc. Memorandum, West River Terrace,Lock+Load®Retaining Wall Design,dated July 21, 2015. GeoDesign Project: Polygon-123-04 15575 SW Sequoia Pkwy,Suite 100 I Portland,OR 97224 1503.968.8787 www.geodesigninc.com d For foundations designed in accordance with the recommendations provided above, total post- construction settlement is expected to be less than 1 inch and differential settlement between adjacent foundation elements is expected to be less than% inch, given the anticipated building loads for wood-framed residences. In wet weather, we recommend placing a sufficient amount of crushed rock(typically 2 to 4 inches) to prevent disturbance to the foundation subgrades. The contractor is responsible for the construction sequencing and methodology for footing excavation and construction. Consequently, the actual amount of rock placed to protect foundation subgrades from disturbance in wet weather should be selected by the contractor. Rock used to protect the subgrades during wet weather should cover the foundation-bearing surfaces and be compacted until "well keyed." Any foundation subgrade soil that is disturbed should be removed prior to the placement of crushed rock and/or pouring of the foundations. Lateral loads on footings can be resisted by passive earth pressure on the sides of the structures and by friction on the base of the footings. Our analysis indicates that the available passive earth pressure for footings confined by structural fill, or footings constructed in direct contact with the undisturbed native soil or structural fill, is 350 pounds per cubic foot(pcf). Typically, the movement required to develop the available passive resistance may be relatively large; therefore, we recommend using a reduced passive pressure of 250 pcf. Adjacent floor slabs, pavements, 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. • • • G EODESIGN? 3 Polygon-123-03:091316 We appreciate the opportunity to work with you on this project. If you have questions concerning the information provided, please call. Sincerely, GeoDesign, Inc. *$$O PROP, 0 (<,�G1Nfi�`S�o 631)14P }}yE Reed S. Kistler, P.E. I O 'EGON, ! Staff Engineer r O tS',yq�N14 ; lG EXPIRES: /2131117 „ awn M. Dimke, P.E., G.E. Principal Engineer cc: Chris Walther, Polygon Homes (via email only) Mike White, City of Tigard (via email only) RSK:SMD:kt One copy submitted(via email only) Document ID:Polygon-123-03-091316-geol-lots_55_59-61_72-rev.docx ©2016 GeoDesign,Inc. All rights reserved. G EODES IGN= 4 Polygon-123-03:091316 Np L For foundations designed in accordance with the recommendations provided above, total post- construction settlement is expected to be less than 1 inch and differential settlement between adjacent foundation elements is expected to be less than% inch, given the anticipated building loads for wood-framed residences. In wet weather, we recommend placing a sufficient amount of crushed rock(typically 2 to 4 inches) to prevent disturbance to the foundation subgrades. The contractor is responsible for the construction sequencing and methodology for footing excavation and construction. Consequently, the actual amount of rock placed to protect foundation subgrades from disturbance in wet weather should be selected by the contractor. Rock used to protect the subgrades during wet weather should cover the foundation-bearing surfaces and be compacted until "well keyed." Any foundation subgrade soil that is disturbed should be removed prior to the placement of crushed rock and/or pouring of the foundations. Lateral loads on footings can be resisted by passive earth pressure on the sides of the structures and by friction on the base of the footings. Our analysis indicates that the available passive earth pressure for footings confined by structural fill, or footings constructed in direct contact with the undisturbed native soil or structural fill, is 350 pounds per cubic foot (pcf). Typically, the movement required to develop the available passive resistance may be relatively large; therefore, we recommend using a reduced passive pressure of 250 pcf. Adjacent floor slabs, pavements, 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. • • • G EODESIGN= 3 Polygon-123-03:091316 GEODESIGNY FIELD REPORT Page 1 of 1 GDI Project: Polygon-123-03 Prepared By: Daniel Stai Project Name: /1 West River Terrace Date: 9/8/16 Location: Roy Rogers and SWJean Louise Rd Report#: 116 Arrival: 1400 Departure: 1530 .: _ Weather: Sunny, 70's Permit#: TBA Site Visit Requested By: Mike (Polygon) Met With (on site): Mike via Phone, Strauss Reps Purpose:p Evaluate Subgrade for Lots 53-72 Outstanding Issues: i' FR 16& 17(1 0/21 & 1 0/22)Areas of fill with low density and high moisture contents in lots 1-9 Lots 53-72 Upon arrival, I observed foundation crews installing concrete forms for lots 56-59 and 61-64. Lots 53, 54, 60, and 65:72, had not yet been excavated to finish subgrade elevation yet. Subgrade soils generally consisted of brown silt; with to minor gravel. I used a%2 inch diameter steel "T" probe to evaluate subgrade relative consistency for lots 53- 72. Lots 53, 54, and 60 had soil stockpiled over the majority of the lot area. I probed around the edges of the stockpiles. Lot subgrades were generally observed to be very stiff to hard. Lots 65-72 had 6 to 12 inches of loose soil on west side of lot(see attached site plan). I also observed loose utility trench backfill in some of the lots under proposed garage footings. The probe penetrated between 12 to 36 inches into the loose backfill. Strauss representative also informed me that they had over excavated up to 12 inches of loose fill in lots 55-59. Concrete forms will be extended down to account for over excavation. Based on observations, the subgrades for lots 53-72 evaluated today (excluding loose utility trenches) have been prepared in general accordance with our geotechnical recommendations. Distribution: Attachments: Site Plan (1) Reviewed by: SMD This report presents opinions formed as a result of our observation of activities relating to geotechnical engineering or environmental services Wyrely on t ontra o�ply with the plan{and specifications throughout the duration of the project irrespective of the presence of our representative Our work does not include supervision dr dire of the co cto,.,the contr_4ctorS employees or agents Our firm is not responsible for site safety This field report is a DRAFT representation of our field observations,testing,a prerimu,a orn r,dat The repoonl be considered final upon review of the GeoDesign project manager,as indicated by initials in the'Reviewed By'section Y Signature:/ .,,� �_..- • 15575 SW Sequoia Parkway,Suite 100 I Portland,OR 97224 I Off 503.968.8787 I Fax 503.968.3068 GEODESIGNY FIELD REPORT Page 1 of 1 . GDI Project: Polygon-123-03 Prepared By: Daniel Stai Project Name: i West River Terrace Date: 9/8/16 Location: I Roy Rogers and SW Jean Louise Rd Report#: 116 Arrival: 1400 Departure: 1530 . Weather: .. . Sunny, 70's Permit#: , TBA Site Visit Requested By: Mike (Polygon)Y9 ) Met With (on site): Mike via Phone, Strauss Reps Purpose:P Evaluate Subgrade for Lots 53-72 Outstanding Issues: FR 16& 17(10/21 & 10/22)Areas of fill with low density and high moisture contents in lots 1-9 Lots 53-72 V— Upon arrival, I observed foundation crews installing concrete forms for lots 56-59 and 61-64. Lots 53, 54, 60, and 65=72, had not yet been excavated to finish subgrade elevation yet. Subgrade soils generally consisted of brown silt; with to minor gravel. I used a%2 inch diameter steel "T" probe to evaluate subgrade relative consistency for lots 53- 72. Lots 53, 54, and 60 had soil stockpiled over the majority of the lot area. I probed around the edges of the stockpiles. Lot subgrades were generally observed to be very stiff to hard. Lots 65-72 had 6 to 12 inches of loose soil on west side of lot(see attached site plan). I also observed loose utility trench backfill in some of the lots under proposed garage footings. The probe penetrated between 12 to 36 inches into the loose backfill. Strauss representative also informed me that they had over excavated up to 12 inches of loose fill in lots 55-59. Concrete forms will be extended down to account for over excavation. Based on observations, the subgrades for lots 53-72 evaluated today(excluding loose utility trenches) have been prepared in general accordance with our geotechnical recommendations. Distribution: Attachments: Site Plan (1) Reviewed by: SMD This report presents opinions formed as a result of our observation of activities relating to geotechnical engineering or environmental services W Wetly on t yr/ omply with the plansand specifications throughout the duration of the project Irrespective of the presence of our representative Our work does not include supervision iii drrec of he contr 1's employees or agents Our firm is not responsible for site safety This field report is a DRAFT representation of our field observations,testing.a elimuu orn erconsidered final upon review of the GeoDesign project manager,as indicated by initials in the`Reviewed By"sectionpo r only be — Signature: 15575 SW Sequoia Parkway,Suite 100 I Portland,OR 97224 I Off 503.968.8787 I Fax 503.968.3068 L • / • , ..... ri uriE raga LINE TABLE -I ---- -CUR-4 TABU 1 ,-1.e.,..l_f_I 7.:.0„5_2,:1_.7--.e.,...-.i.._.77,,,,0.3_7.7_ _1.1.....7.1,.176, St A.e .• 4 , -•177105.:,7aieRC.,..7.:7 76.77•7•, 1. :Me ben Pr NI t :• eye e•1 ee,.ry,,4 y ! 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