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Report • �,► West River Terrace Lot Location (continued) Lot# Street Address Permit# 65 13778 SW Sabrina Avenue MST2016-00239 66 13762 SW Sabrina Avenue MST2016-00240 67 13746 SW Sabrina Avenue MST2016-00241 68 13730 SW Sabrina Avenue MST2016-00101 69 13718 SW Sabrina Avenue Not available 70 13702 SW Sabrina Avenue Not available 71 13690 SW Sabrina Avenue MST2016-00242 72 13678 SW Sabrina Avenue Not available Construction for the West River Terrace residential development began in September 2015 and is ongoing. We observed stripping of Lots 55 through 59 and Lots 61 through 72 on October 1, 2015. We observed prepared lot fill from October 21, 2015 through October 23, 2016 and then from June 23, 2016 through July 6, 2016. We used a Troxler 3430 nuclear density gauge to test compaction of the fill. We observed the prepared lot subgrades on September 8, 2016. Some soft or loose areas were identified on September 8, 2016; however, they were outside the planned foundation subgrade areas. Members of our geotechnical staff observed geotechnical-related tasks identified above on an intermittent and on-call basis. The results of our site visits were summarized in daily field reports, copies of which have been provided to Polygon Northwest, Pacific Community Design, and members of the design and construction team. To the extent observed, the construction outlined above for subgrade preparation of Lots 55 through 59 and Lots 61 through 72 at the West River Terrace residential development have been completed in general conformance with the intent of the project plans, specifications, and our geotechnical recommendations. Footings for the residences on all the lots at the site can be designed and constructed in accordance with the following recommendations from our December 5, 2014 geotechnical report. Footings can be proportioned for an allowable soil bearing pressure of 2,000 pounds per square foot. A higher value may be possible, depending on the grading plan. The allowable bearing pressure is a net bearing pressure; the weight of the footing and overlying backfill can be ignored in calculating footing size. The allowable bearing pressure applies to the total of dead plus long-term live loads and may be doubled for short-term loads, such as those resulting from wind or seismic forces. Continuous wall and spread footings should be at least 15 and 24 inches wide, respectively. The bottom of exterior footings should be at least 18 inches below the lowest adjacent final grade. The bottom of interior footings should be placed at least 12 inches below the base of the floor slab. G EODESIGNg 2 Polygon-123-03:091316 i' 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%z 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 L . `i We appreciate the opportunity to work with you on this project. If you have questions concerning the information provided, please call. Sincerely, GeoDesign, Inc. t�t.so PROFFS' �\c,4.�G 1 �d'i0 63114PE Reed S. Kistler, P.E. OREGON Staff Engineer ch 14 r 2°` kq 14'N D O- /?' . EXPIRES: 12/31/17 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. [DESIGN? 4 Polygon-123-03:091316