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REVIEWED BLD BLD2022-0015+GEO REVIEW+1.6.2022_8.30.05_AM+2605995NELSON GEOTECHNICAL ASSOCIATES. INC. January 5, 2022 Mike and Sabina Norton VIA Email: sabinanorton@vahoo.com Geotechnical Plan Review Norton Garage Review 812 Cary Road Edmonds, Washington NGA File No. 104351321 17311-1351h Ave. N.E. Suite A-500 Woodinville, WA 98072 (425) 486-1669 www.nelsongeotech.com Dear Mike and Sabina: This letter documents our geotechnical plan review and response to comments regarding the planned garage addition project located at 812 Cary Road in Edmonds, Washington, as shown on the Vicinity Map in Figure 1. INTRODUCTION We understand a previous geotechnical report regarding the development of a single-family residence structure within the site titled "Geotechnical Engineering Investigation Proposed Single Family Residence 812 Cary Road Edmonds, Washington" and dated July 14, 2006 was Prepared by Krazan & Associates, Inc., who was the geotechnical engineer of record at the time. We were retained in 2018 as the new geotechnical engineer and have since prepared a Stormwater Infiltration Letter for this site titled "Stormwater infiltration Letter — Norton Residence Infiltration — 806 Cary Road — Edmonds, Washington", dated June 19, 2018. We have recently been retained to provide plan review and construction monitoring services as needed, as detailed in the services agreement that was signed by you on December 17, 2021. For use in preparing this letter we were also provide with architectural plans titled "Permit Set - Norton Residence, 812 Cary Road, Edmonds, WA 98020" dated November 19, 2021, and prepared by H2D Architecture + Design. As part of our previous work, we visited the site to explore surface and subsurface conditions on May 30, 2018. The subject property consists of a roughly rectangular parcel covering approximately 2.24 acres. The site is currently occupied by an existing residence structure. The property is bordered by Cary Road to the west and by residential properties to all other sides. Geotechnical Plan Review NGA File No. 104351321 Norton Garage Review January 5, 2022 Edmonds, Washington Page 2 Topographically, the site slopes gently to the east with a moderate east -facing slope below the residence structure supported by an existing rockery in the central portion of the site. Vegetation across the site consisted of grass yard area bordered by young to mature trees and landscaping plants. Attached to this letter are our previous exploration locations and logs in Figures 2 through 4, as well as data from the original Krazan report in Appendix A. We present a summary of the interpreted subsurface conditions in the following paragraph. For a detailed description of the subsurface conditions, exploration logs in Figure 4 and in Appendix A should be reviewed. Explorations were generally consistent across the site. Typical stratigraphy across the site consisted of a surficial layer of dark brown to brown fill about 2.7 to 3.0-feet-thick, underlain by gray, silty, fine to medium sand with gravel and iron oxidation in an increasingly dense condition, which we interpreted as native glacial till soils. At depth in all test pits, gray, well -cemented, silty fine to medium sand with gravel in a dense to very dense condition was encountered, which we interpret as native, bearing, glacial till soils. We understand the City of Edmonds is requesting the geotechnical review of plans for the proposed garage addition to ensure they align with geotechnical recommendations. In the following section, we summarize the results of our geotechnical plan review. PLAN REVIEW We have reviewed the geotechnical aspects of the provided plans and found the plans to be in general compliance with the drainage recommendation provide by Nelson Geotechnical as well as the geotechnical recommendations regarding foundation support supplied in the geotechnical report prepared by Krazan & Associates Inc. Project plans indicate that the building foundations will be supported on conventional foundations founded on competent native soils. The soil bearing value used in the foundation designs was 2000 psf for the detached garage structure, which is consistent with the recommendations provided in the report, that states that the design for onsite native soils are not to exceed 2000 psf. Additionally, a 300 pcf passive resistance and coefficient of friction of 0.35 were used in designing the foundation elements, which should be sufficient to support planned loads. Cuts and fills overall will remain minimal, with excavations for the footings extending approximately 3-feet to ensure all foundations for the planned garage are supported on competent bearing soils. We should be on site during foundation subgrade preparation to approve exposed surfaces prior to pouring concrete. NELSON GEOTECHNICAL ASSOCIATES, INC. Geotechnical Plan Review Norton Garage Review Edmonds, Washington NGA File No. 104351321 January 5, 2022 Page 3 Reviewing the permit sets for the garage, Best Management Practices (BMPs) that will be used include filter silt fences bordering the areas to be stripped to prevent soil from leaving the site and tree protection fencing to maintain existing vegetation during construction. We understand that the western side of the existing driveway will be used as a construction entrance and eastern portion will be used as a stockpile location of excavation spoils. We understand the drainage plan for the proposed garage includes the use of a splashblocks on the northwest and southwest corners of the structure with 25-foot and 37-foot vegetated flow paths, respectively. This is in accordance with our previous recommendation to utilize low impact infiltration within the site. All other recommendations provided in the previous geotechnical report prepared by Krazan & Associates, Inc. and the stormwater infiltration letter prepared by NGA should be strictly followed. CLOSURE We strongly recommend that NGA, as the new geotechnical engineer of record, be retained to provide monitoring and consultation services during construction to confirm that the conditions encountered are consistent with those indicated by the explorations, to provide recommendations for design changes should the conditions revealed during the work differ from those anticipated, and to evaluate whether or not earthwork activities comply with contract plans and specifications. DIM*,, NELSON GEOTECHNICAL ASSOCIATES, INC. Geotechnical Plan Review Norton Garage Review Edmonds, Washington NGA File No. 104351321 January 5, 2022 Page 4 We appreciate the opportunity to provide service to you on this project. If you have any questions or require further information, please call. Sincerely, NELSON GEOTECHNICAL ASSOCIATES, INC. Sarah L. Dunn Staff Geologist I 1.05.2022 Khaled M. Shawish, PE Principal SLD:KMS:dy Attachments: Four Figures Appendix A— Krazan Logs NELSON GEOTECHNICAL ASSOCIATES, INC. VICINITY MAP Not to Scale v17 ,r Cherry st 3 lqo '• `0 a 0 A1 0 �r Wr f N t O w j� D o Q � Project = °'�c = Maplewood Rock Q Site Pugety% & Gem Club z Edmonds s < Maplewood Elementary Q School Z Park nmc. r; Ln T D -c m z Caspers St © Edmonds United ht S'!! _ Methodist Church Vista PI THE BOWL Brackett's Landing OF EDMONDS Shoreline ca+onvay � .tl.,.: ;: Sanctuary.., Glen clan 4< s Brackett's r: , , : Daley St Landing North Civic Center Sprague Si Brackett's Playfield Landing South y e`ys, o t' an S r � 3 � h7$ Bell S' eeeh < BoII V mdsQ z � ,s z Edmoncis ponds Kingston Ferry Toll Booth Dayton St cl Main S: s cs m Maple Way > Maple St n > n Maple St N N v. Vl Alder St t Alder St n A4ter s1 Deck L. Bak L H Yost P�'.rk Wwnut Sl Walnut St Edmonds, WA M:Ln St I m Project Number II son GEOTECHnICAL No. Date Revision By cK o 104351321 Norton Garage Development , ASSOCIATES, inc 1 6/10/18 Original DPN ABR VicinityMa ,-�. •/ Woodinville Office Wenatchee Office 2 1/4/22 Revision DPN E' SLD Ea Figure 1 11311-135th Ave. NE, A-500 105 Palouse St. Woodinville, WA 98072 Wenatchee, WA 98801 OV ww.nelsongeotech.con (425) 486-1669 / Fax 481-2510 (509) 665-7696 / Fax: 665-7692 L -0 C) (1) Site Plan .4, 0, (n Z L Cr 49ZI9' (ROS-r)(C) — — — — — — — 474.51: '751 -g` .8 i-C3 VAUL. 448.30 z fows) 0 W (11 174 M.) 0 clZ Ratu, -W. EDGE WEILAND C/) (D I F-1 LAWN • A- T 0 Jk ... .. . IA (D SCAM 0 "3900 FORESTED tA-4 L Z -0 TRUST SW3 W •T41d9S F. 3 PP N Y/ •IAW I ........... ... HOUSE BUFFER WEnAHO- TP-3 GUEST ............... A-J ...... HOUSE P■ - 0 ZOO, F. M O. LAWN A-2 1511 G MIS CD Lat to, Si CA r SS Al M wow FENCE AA-1 CD "00 Existing Guest House Existing House Hip C-D $1RI :0 r- LEGEND z 91— Property line 23 INF-1 ;13 0 -0— Number and approximate location 0 60 120 of infiltration test pit (NGA, 2018) 1 0 O Number and approximate location Scale: 1 inch = 60 feet Iof test pit (Krazan, 2006) 0 Reference: Site Ign based on a Mn dated February 1. 2018 titled "Preliminary Short Plat for Mike & Sabina Norton," Prenared by West Alliance. 4 5,3 Norton Ga rage ffilftcornpanyX20211 NGA Project Folders% W Review EdMonds\DraftinqkSP.dw_q UNIFIED SOIL CLASSIFICATION SYSTEM GROUP MAJOR DIVISIONS GROUP NAME SYMBOL CLEAN GW WELL -GRADED, FINE TO COARSE GRAVEL COARSE- GRAVEL GRAVEL GP POORLY -GRADED GRAVEL GRAINED MORE THAN 50 GM OF COARSE FRACTION OF SILTY GRAVEL RETAINED ON SOILS NO.4 SIEVE WITH FINES GC CLAYEY GRAVEL SAND CLEAN SW WELL -GRADED SAND, FINE TO COARSE SAND SAND SP POORLY GRADED SAND MORE THAN 50 % RETAINED ON MORE THAN 50 % NO. 200 SIEVE OF COARSE FRACTION SAND SM SILTY SAND PASSES NO. 4 SIEVE WITH FINES SC CLAYEY SAND FINE - SILT AND CLAY ML SILT INORGANIC GRAINED LIQUID LIMIT CL CLAY LESS THAN 50 % SOILS ORGANIC OL ORGANIC SILT, ORGANIC CLAY SILT AND CLAY MH SILT OF HIGH PLASTICITY, ELASTIC SILT INORGANIC MORE THAN 50 % PASSES LIQUID LIMIT CH CLAY OF HIGH PLASTICITY, FAT CLAY NO. 200 SIEVE 50 % OR MORE ORGANIC CH ORGANIC CLAY, ORGANIC SILT HIGHLY ORGANIC SOILS PT PEAT NOTES: 1) Field classification is based on visual SOIL MOISTURE MODIFIERS: examination of soil in general accordance with ASTM D 2488-93. Dry - Absence of moisture, dusty, dry to the touch 2) Soil classification using laboratory tests is based on ASTM D 2488-93. Moist - Damp, but no visible water. 3) Descriptions of soil density or Wet - Visible free water or saturated, consistency are based on usually soil is obtained from interpretation of blowcount data, below water table visual appearance of soils, and/or test data. Project Number IIELSOn GEOTECHnICAL No. Date Revision By cK 104351321 Norton Garage Development Soil Classification Chart ASSOCIATES, inc 1 1/4/22 Original DPN SLID Figure 3 Woodinville Office Wenatchee Office 11311-135th Ave. NE, A-500 105 Palouse St. Woodinville, WA 98072 Wenatchee, WA 98801 ww.nelsongeotech.com (425) 486-1669 / Fax: 481-2510 (509) 665-7696 / Fax: 665-7692 LOG OF EXPLORATION DEPTH (FEET) USC INFILTRATION PIT ONE 0.0 - 2.7 2.7 - 6.0 SM INFILTRATION PIT TWO 0.0 - 2.3 2.3 - 3.0 3.0 - 6.0 SM ABR:KMS SOIL DESCRIPTION GRASS UNDERLAIN BY DARK BROWN TO ORANGE -BROWN, SILTY FINE TO MEDIUM SAND WITH ROOTS, ORGANICS, GRAVEL, AND IRON -OXIDE STAINING (LOOSE TO MEDIUM DENSE, MOIST) (TOPSOIL) GRAY, WELL -CEMENTED SILTY FINE TO MEDIUM SAND WITH GRAVEL, IRON -OXIDE STAINING, AND TRACE COBBLES (MEDIUM DENSE TO VERY DENSE, MOIST) SAMPLE WAS COLLECTED AT 4.5 FEET GROUNDWATER SEEPAGE WAS NOT ENCOUNTERED TEST PIT CAVING WAS NOT ENCOUNTERED TEST PIT WAS COMPLETED AT 6.0 FEET ON 5/30/2018 GRASS UNDERLAIN BY DARK BROWN, SILTY FINE TO MEDIUM SAND WITH GRAVEL, ROOTS, ORGANICS, AND TRACE PLASTIC (LOOSE TO MEDIUM DENSE, MOIST) (FILL) ORANGE TO REDDISH BROWN, SILTY FINE TO MEDIUM SAND WITH SCATTERED ROOTS, GRAVEL, AND TRACE ORGANICS (MEDIUM DENSE TO DENSE, MOIST) (FILL) GRAY -BROWN TO GRAY, SILTY FINE TO MEDIUM SAND WITH GRAVEL AND IRON -OXIDE STAINING (MEDIUM DENSE TO DENSE, MOIST) SAMPLE WAS COLLECTED AT 6.0 FEET GROUNDWATER SEEPAGE WAS NOT ENCOUNTERED TEST PIT CAVING WAS NOT ENCOUNTERED TEST PIT WAS COMPLETED AT 6.0 FEET ON 5/30/2018 NELSON GEOTECHNICAL ASSOCIATES, INC. FILE NO 104351321 FIGURE 4 APPENDIX A Project: Norton Single Family Residence Log of Test Pat TP-1 Project No: 092-06119 Client: Sabina Norton Surface Elevation: Figure No: A-1 Location: Edmonds, Washington Datum: Logged By: CM Depth to Water Initial: Not Encountered At Completion: SUBSURFACE PROFILE SAMPLE Dynamic Cone y Water Content rn E � Penetration (ado) Description a o Test (Blows/1-3/4 in) L m uJ d Y a) o 40 (D T aa) ai 20 40 60 80 20 60I 01 0_ Ground Surface SILTY SAND (SM) ' Loose, fine to medium grained sand, dark brown, moist. Roots and other organic material. -Grab ---------STapsoilfj,------------------ SILTY SAND WITH GRAVEL (SM) Loose, fine to coarse grained sand, reddish brown, moist. Rootlets, occasional organic material, and trasJSome- 5_::' ' iron oxide staining - Decrease in silt content beginning at 3 feet. _____ (Weathered Whidbey FormationZ__ POORLY GRADED SAND WITH GRAVEL (S Dense to very dense, very fine to fine grained s trace silt, grayish brown, moist. - Test pit terminated at 5.5 feet due to refusal. (Whidbey Form ion 10—• End of Test Pit 15— 20 Excavation Method: Bobcat 435ZHS Trackhoe Krazan and Associates Test Pit Date: 26 June 06 1 501 144th Ave. NE #F-300 Contractor: Client Provided Woodinville, WA 98072 Sample Method: Grab Sheet: 1 of 1 Project: Norton Single Family Residence Log of Test Pit TP-2 Project No: 092-06119 Client: Sabina Norton Surface Elevation: Figure No: A-2 Location: Edmonds, Washington Datum: Logged By: CM Depth to Water Initial: Not Encountered At Completion: SUBSURFACE PROFILE SAMPLE Dynamic Cone Water Content m rn Penetration (%) Description o Test (Blows/1-3/4 in) L E a E n f/1 Q Y a)a C� Wp �- 0 -� WI am > o cn U) T a) o o a) co a a 20 40 60 80 20 40 60 80 0_ Ground Surface SILTY SAND (SM) - Loose, fine to medium grained sand with occasional gravel, dark brown, moist. Rootlets _ --------LToQsailY------------------- • - t'r " SILTY SAND (SM) Loose, fine to medium grained sand with occasional small gravel, yellowish brown, moist. Rootlets Iron oxideGrab 5_ staining beginning at 21 inches ------ jWeathered Whidbey Formationi------- POORLY GRADED SAND WITH GRAVEL (SP) Dense to very dense, very fine to fine grained sand with trace silt, olive brown to grayish brown, moist Some iron oxide staining. - Fine grained (SW) interbedded sand layer between 28 and 36 inches. 10— (WhibeX Formation End of Test Pit 15- 20- 25— Excavation Method: Bobcat 435ZHS Trackhoe Krazan and Associates Test Pit Date: 26 June 06 19501 144th Ave, NE #F-3 0 Contractor: Client Provided Woodinville, Wry 98072 Sample Method: Grab Sheet: 1 of 1 Project: Norton Single Family Residence Log of Test Pit TP-3 Project NO: 092-06119 Client: Sabina Norton Surface Elevation: Figure No: A-3 Location: Edmonds, Washington Datum: Logged By: CM Depth to Water Initial: Not Encountered At Completion: SUBSURFACE PROFILE SAMPLE Dynamic Cone Water Content i aD rn m Penetration (%) Description � o Test (Blows11-314 in) CL CL m v o a) W 0--- W I I80 W o >, rn rn >1 (D F- o n 0- 20 40 60 80 20 40 60 _. 0_ Ground Surface SILTY SAND (SM) Loose, fine to medium grained sand, dark brown, moist. Roots. • _ ---------tTopsoilL------------------ - SILLY SAND WITH GRAVEL (SM) _ Loose, fine to medium grained sand, dark yellowish brown to olive brown, moist. Iron oxide staining begins at 2.5 - ra 5 feet. - -----SWeathered Whidbey Formationl-------- POORLY GRADED SAND WITH GRAVEL (SP) Dense to very dense, very fine to fine grained sand. olive brown to grayish brown, moist. Some iron oxide staining. - Fine grained, laminated sand lense from 4 to 4.5 feet. (Whidbey Formation) 10— End of Test Pit 15- 20- 25— Excavation Method: Bobcat 435ZHS Trackhoe rasa and Associates Test Pit Date: 26 June 06 19501 144th Ave. NE #F-300 Contractor: Client Provided Woodinville, WA 98072 Sample Method: Grab Sheet: 1 of 1 Particle Size Distribution Report 100 90 80 70 0= W 60 Z_ Ll Z 50 LU U Ir W 40 30 20 10 0 I I I 1 1 1 1 1 I 1 1 I I I I I 1 1 k,1 I 1 i I I I 1 V I I r I 1 t 1 I , I I I I I 1 I 1 I 1 + 1. .L� , L'.- 1 I r 1 1 I I 1 1 1 1 I I 1 + i ..i- fi f 1 r 1 1 I 1 i•-- I I i 1 1 1 I I I I I I 1 I I 1 I 1 { I 1 r I 1 - - -- - I i T I 1I 1 1 1 I l 1 I 1 � 1 I 1 I 1 f 1k 1 1 cnn 1 CIA 1 n 1 0.1 0.01 0.001 (RAIN S17E - mm %COBBLES % GRAVEL % SAND CRS, MEDIUM FINE % FINES CRS. FINE SILT CLAY 0.0 19.0 11.8 3.8 11.3 38.2 15.9 SIEVE SIZE PERCENT FINER SPEC." PERCENT PASS? (X=NO) 1.5 in. 100.0 1 in. 85.5 .5 in. 78.0 .375 in. 74.2 #4 69.2 #10 65.4 #20 62.2 #40 54.1 #60 36.4 #100 24.6 #200 15.9 Material Description Yellowish -brown silty SAND with gravel. Atterbero Limits PL= LL= P1= Coefficients D85= 24.9 D60= 0.598 D50= 0.370 D30= 0.198 D15= D10= Cu= Cc= Classification USCS= SM AASHTO= A-2-4(0) Remarks Sample ID: 23199-13. TP-3/S-2 @ 1.83' (no specification provided) Sample No.: 23199-B Source of Sample: Test Pit Samples Location: Test Pit 3, Sample No. 2 Date: 7-3-06 Elev./Depth : 1.83' 100 90 8C 7C Cr W 6C Z U_ Z 5C W C) Ir LU 4C d 3C 2( 1( 0 500 Particle Size Distribution Report C 2 N W � N 2 4 8 $ � N 1 Y717 I V _- GRAIN GRAIN SIZE - mm GRAVEL % SAND % FINES %COBBLES CRS. FINE CRS. I MEDIUM FINE SILT I CLAY 0.0 7.3 9.9 1 3.8 1 8.2 30.2 40.6 SIEVE SIZE PERCENT FINER SPEC! PERCENT PASS? (X=NO) 1.25 in. 100.0 1 in. 95.8 .5 in. 89.7 .375 in. 86.5 #4 82.8 #10 79.0 #20 75.5 #40 70.8 #60 65.0 #100 56.6 #200 40.6 Material Description Yellowish -brown silty SAND with gravel. Atterbera Limits PL= LL= PI Coefficients D85= 7.95 Dgp= 0-180 D50= 0.111 D30= 1315= D10= Cu= Cc= Classification USCS= SM AASHTO= A-4(0) Remarks Sample ID: 23199-A TP-2/S-5 @ 4' - (no specification provided) Sample No.: 23199-A Source of Sample: Test Pit Samples Location: Test Pit 2, Sample No. 5 KRAZAN & ASSOCIATES, INC. Date: 7-3-06 Elev./Depth: 4'