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HomeMy WebLinkAboutCOM2009-00011 GeoTech Report - COM Engineering / Geo-Tech Reports - 3/4/2009 GEOTECHNICAL TESTING LABORATORY HARMONY HILL 7362 EAST STATE ROUTE 106 UNION, WA 98592 RE: GEOTECHNICAL REPORT ADDENDUM PROJECT: HARMONY HILL GREENHOUSE 7362 EAST SR-106 UNION,WASHINGTON 98592 REPORT DATE: 3/4/2009 PARCEL: 322334400040 Gentlemen: As per your request,we have updated the original Geotechnical Report with this addendum and checklist for the project listed above. The original report, dated May 1, 2005, in conjunction with this updated addendum is expected to satisfy the most recent Development in the Landslide Hazard Areas requirements as set forth by Mason County. Attached with this addendum are the revised site plan and a cross section. Slope models have been updated to incorporate the new cross section and will be discussed later. We have provided three copies for your review and distribution. An appropriate site plan and cross-section is provided with this addendum. SITE CONDITIONS The site was visited by Curtis D Cushman and Vijay Chaudhary on March 4, 2009. The proposed greenhouse is located in an area of scattered residential and resort development in Union, Washington. The site elevation ranges from 40-feet to 240-feet. The building location has a moderate slope of approximately 13 percent. The onsite slope of the property ranges from 10 percent to 100 percent. The topography of the site indicates that the natural drainage flows towards the north of the proposed building. .l PROPOSED r oFc `M 10011 Blomberg Street SW,Olympia,WA 98512 1 Phone#(360)754-4612 Fax#(360)754-4848 GEOTECHNICAL TESTING LABORATORY No upland waterbodies and wetland were observed. No evidence of deep-seated of slope instability was observed on site. Trees near the building site were observed to be straight and vertical (as seen above). Research of available documents indicates that the area of interest does not have any mapped landslide features. GEOLOGIC SETTING The Geologic Map of Shelton Quadrangle(2003) by R Logan, has mapped the site geology as Alpine outwash (Qapo). The report reads: o Alpine outwash, pre—late Wisconsinan (Pleistocene)—Stratified sand, gravel, and cobbles; in the Quinault basin, clasts consist of sandstone and less-abundant basalt from the Olympic. Mountains core and peripheral rocks; in strcams draining the southern and southeast- cm Olympics, clasts consist primarily of Crescent Formation basalt with less-abundant Olympic-core sandstone; may include peat, silt, and clay, and may be capped by weathered loess; clasts are generally more rounded than those in till and lack facets and striations; poorly to moderately sorted; gray to subtle yellow with wispy orange weath- ering. This material is readily seen in the road � n.A cut of highway 106 and likely underlies the construction site. Vashon Till may overly the Qapo sediments further uphill �r to the south,but these are not important for the discussion in this report. Ile 7 ., This material is considered very good for construction. Soils are discussed in the original report. The proposed site for the = }, -+w,,, , ,;� `��:ate"` �e► ,` `- greenhouse is located in a currently outdoor garden having a very thick layer of gardening topsoil overlying native material or possibly some fill. All : �. organic soil must be removed and the underlying native/fill material must be * ''"`'� '•• ` compacted as per the original - recommendations. -- 10011 Blomberg Street SW,Olympia,WA 98512 2 Phone#(360)754-4612 Fax#(360)7544848 GEOTECHNICAL TESTING LABORATORY SLOPE STABILITY ANALYSIS In general, the undisturbed native materials of the site consist of a mixture of variable amounts of silt, sand and gravel. These soil materials are in a dense condition except where they have been disturbed by weathering activity. No evidence of significant recent erosion was observed onsite at the time of our investigation. However, weathering and associated surficial erosion is seen confined to the upper weathered or disturbed zone. Weathering, erosion, and the resultant surficial sloughing and landsliding are natural processes that affect slope areas. Significant weathering typically occurs in the upper 2 to 3 feet and is the result of oxidation, root penetration, wet/dry cycles and freeze/thaw cycles. These processes can be managed and the risk reduced through proper construction of the residence. Erosion control recommendations in the slope and buffer areas are provided in the`Building Setback"section in the original report and"Erosion Control"section of this report Our findings were compared with the slope. stability resources pertaining to the subject site These are as follows: 21 The Coastal Zone Atlas, Volume 9, Mason County(MA-8)maps the site as intermediate. 5 S s The Relative Slope Stability of the Southern J u Hood Canal Area, Washington by Smith & Carson (1977) has mapped the site as Class 2. -- The survey reads: • �'�` 24,000 �i • } 1•M If•D ia'e S Areas believed to be stable under normal conditions, but may become unstable if 0— Sister ` Pt - s disturbed by man's activities, if slope is oversteepened by erosion, or if subjected to strong seismic shaking. Slopes generally steeper L -N. ,. than 15 percent, but may be less in some areas of weak geologic materials. Includes areas underlain by: well-drained sand and gravel, mostly on valley sides that lack known slope failures; glacial till with steep slopes, and bedrock This section is included as an addendum to the previous report. Slope models have been updated to include the cross section profile as attached at the end of this letter. Soil parameters such as cohesion, shear, and unit weight used in the modeling have been used as in the previous report. 10011 Blomberg Street SW,Olympia,WA 98512 3 Phone#(360)754-4612 Fax#(360)754-4848 GEOTECHNICAL TESTING LABORATORY Slope stability was modeled using the GeoStudio 2004 program (version 6.20) in both static and dynamic conditions (ca = 0.15). "Static" condition refers to an "as is" state of a given slope. "Dynamic" puts seismic acceleration into the model for earthquake conditions. Factors of safety were determined using Bishop's, Janbu, and the Morgenstern-Price methods. The site was modeled monolithically based on the drill data from the original report. Under static conditions, the slope remained stable to deep-seated and shallow failure. See Figure 4 for the cross- sections. Under dynamic loading (Ca=0.15), the 3328 computations demonstrated that the slope is safe and not susceptible to a deep-seated movement. The following figure illustrates a moment F.S. for the cross-section. This solution is the lowest factor of safety generated b the model. The calculated Factors of Safe meet the requirements set forth b Mason County that g Y h' q Y tY is, 1.50 for static and 1.1 for dynamic loading scenarios. Based on our slope models representing critical slopes at the subject site, it is apparent that the building site is not susceptible to any deep-seated movements or instability. SLOPE MODEL SLOPE MODEL A STATIC FoS: 2.61 t 130 120 110 100 90 80 C °— 70 Description: GLACIAL TILL >> so Wt: 125 w 40 Cohesion: 200 30 Phi: 37 20 10 n_ ;0 100 150 200 2W 300 3W 400 4W Distance(ft) 10011 Blomberg Street SW,Olympia,WA 98512 4 Phone#(360)754-4612 Fax#(360)754-4848 GEOTECHNICAL TESTING LABORATORY SLOPE MODEL A ' DYNAMIC FoS: 1.47 130 ' 120 110 100 90 .. 80 0 70 Description: GLACIAL TILL a so m Wt: 125 w 40 Cohesion: 200 30 Phi: 37 20 10 0 0 50 100 200 250 300 350 400 4W Distance(ft) Changes in the site plan have been made accordingly to incorporate the necessary landslide hazard area designation as well as a 50-foot vegetation buffer. Building setbacks from the active landslide hazard area are also included on the site plan. The total available setback for construction is marked on the site plan. Drainage recommendations, erosion control,vegetation management,potential septic, and other impacts will be discussed in the following sections. VEGETATIVE MANAGEMENT Some vegetation recommendations are located elsewhere in the report (such as "Erosion Control"). The following are general, and do not apply,the main part,to a garden application. Native species should be considered as the primary vegetation in areas away from lawn and ornamental plantings. Shallow rooted species, such as grass, should be planted closer than 10 feet from underground drainages, septic drainfields and their associated drains, etc. Densely rooted evergreen shrubs are preferable than tree species on slopes greater than 15% gradient. Tall trees may become unstable in wet soils under high wind conditions. Tall trees located on a steep slope may be taken out as long as the stumps remain in the ground. "No disturb" zones should be marked on final plans and flagged at the job-site. Exposed soils should be immediately revegetated with grass and local shrubs. The owner may remove trees within 15 feet of structures that require future access as well as those with damaged roots from the construction procedures. 10011 Blomberg Street SW,Olympia,WA 98512 5 Phone#(360)754-4612 Fax#(360)7544848 GEOTECHNICAL TESTING LABORATORY A Certified Arborist should perform view clearing, branch thinning, and maintenance. Conifers should not be topped. EROSION CONTROL Only minor surface erosion was observed on or surrounding the subject site. No ponding from rain run-off was observed onsite. It is our opinion that the potential erosion hazard of the site is not a limiting factor for the proposed development. Removal of natural vegetation should be minimized and limited to the active construction areas. Temporary and permanent erosion control measures should be implemented and maintained during construction and/or as soon as practical thereafter to limit the additional influx of water to exposed areas and protect potential receiving waters. Revegetation should occur immediately following construction. Erosion control measures should include, but not be limited to, silt fences, berms, and swales with ground cover/protection in exposed areas. Typical erosion control notes and a silt fence detail are included on Figure 2 Site Plan. Any re-contouring of the site will create a need for erosion control measures as recommended above. SEPTIC IMPACT No drainfield has been proposed. There are five existing septic drainfields located on the site Chapter 246- 272A-0210 of the Washington Administrative Code requires a minimal horizontal separation between septic drain fields and various facilities including footing drains. The proposed Greenhouse is well setback from all the existing drainfields, and poses no threat to these and vice-versa. In the present configuration we conclude that the proposed construction will cause no on-site or off-site impacts. LIMITATIONS We have prepared this addendum, which along with the original Geotechnical report dated May 1, 2005, is for the exclusive use of Harmony Hill team and their authorized agents for the proposed building construction in Mason County, Washington. This addendum, along with the original report, is intended to meet the requirements of the Mason County Critical Areas Ordinance. This addendum does not specify setbacks for: line-of-sight setbacks, FWHCA setbacks, eagle tree setbacks, wetland setbacks, or property line setbacks. Within the limitations of scope, schedule and budget, our services have been executed in accordance with generally accepted practices in the field of geotechnical engineering in this area at the time this report was prepared. No warranty or other conditions, expressed or implied, should be understood. 10011 Blomberg Street SW,Olympia,WA 98512 6 Phone#(360)754-4612 Fax#(360)754-4848 GEOTECHNICAL TESTING LABORATORY CONTRACTORS ARE RESPONSIBLE FOR SITE SAFETY ON THEIR OWN CONSTRUCTION PROJECTS Our geotechnical recommendations are not intended to direct the contractor's procedures, methods, schedule or management of the work site. The contractor is solely responsible for job site safety and for managing construction operations to minimize risks to onsite personnel and to adjacent properties. READ THESE PROVISIONS CLOSELY Some clients, design professionals, and contractors may not recognize that the geoscience practices (geotechnical engineering or geology) are far less exact than other engineering and natural science disciplines. This lack of understanding can create unrealistic expectations that could lead to disappointments, claims and disputes. Geotechnical Testing Laboratory includes these explanatory "limitations" provisions in our reports to help reduce such risks. Please confer with Geotechnical Testing Laboratory if you are unclear how these "Limitations"apply to your project or site. The equipment, techniques and personnel used to perform an environmental study differ significantly from those used to perform a geotechnical or geologic study and vice versa. For that reason, geotechnical engineering or geologic reporting does not usually relate any environmental findings, conclusions or recommendations; e.g., about the likelihood of encountering underground storage tanks or regulated contaminants. Similarly, environmental reports are not used to address geotechnical or geologic concerns regarding a specific project. Often, because of design and construction details that occur on a project, questions arise concerning soil conditions. We would be pleased to continue our role as geotechnical consultants during the project implementation. We appreciate this opportunity to be of service to you and we look forward to working with you in the future. If you have any questions concerning the above items,the procedures used, or if we can be of any further assistance please call us at the phone number listed below. Respectfully Submitted, o{ Wash; GEOTECHNICAL TESTING LABORATORY e �07 co nglne ring Geologist .� << 2439 �� Curtis D Cushman ceased GeOX0 Senior Engineering Geologist ^''13 DEVo l CUSHMAN 10011 Blomberg Street SW,Olympia,WA 98512 7 Phone#(360)754-4612 Fax#(360)754-4848 SITE PLAN PROVIDED BY THE CLIENT. FILTER FABRIC MATERIAL 60'NADE ROLLS USE STAPLES OR WIRE RING TO ATTACH Geotechnical FABRIC TO WIRE FABRIC GAUGE WIRE FABRIC R EQUIVALENT r Testing s� FACE ,�, Laboratory 2 6 MAX 2 R4'WOOD POSTS,STANDARD OR BURY BOTTOM OF FILTER BETTER OR EQUAL ALTERNATE: MATERIAL IN M12'TRENCH STEEL FENCE POSTS "Ell I FILTER FABRIC C 2-A2'X14 GAUGE WIRE FABRIC R EQUIVALENT T GROUND SURFACE 9J7 PROVIDE 3/4'-1 1P7 WASHED GRAVEL BACKFILL IN TRENCH 17 AND ON BOTH SIDES OF FILTER FENCE FABRIC ONTHE SURFACE 6r MIN \ I I I I 27(f'WOOD POSTS ALT.STEEL FENCE POSTS Geotechnical Services _--) I FILTER FABRIC FENCE NOTES: \ I I _-_J I.FILTER FABRIC SHALL BE PURCHASED INA CONTINUOUS ROLL CUT To QA/QC Services THE LENGTH OF THE BARRIER TO AVOID USE OF MINTS.AMEN MINf3 Testing Services ARE NECESSARY,FILTER CLOTH SHALL BE SPLICED TOGETHER ONLY AT-- _/ _ \ FASTENED ATUPPORT S BOTH THENDS MOTHE POST. UMS-INCH OVERLAP AND SECURELY F ( 2.POSTS SHALL BE SPACED A MAXIMUM OF 6 FEET APART AND DRIVEN FOOTPATH �\ Q8p0 \\ \ ISECURELY INTO THE ROUND(MINIMUM OF 30 INCHES)///' ;/ /////' \`\\ \\ AIM j `\ \.• f 1\\ 3,A TRENCH SHALL BEEXCAVATED APPROXIMATELY 6 INCHES WDE AND 12 10011 Blomberg St.SW INCHES DEEP ALONG THE LINE OF POSTS AND UPSLRE FROM THE BARRIER Olympia,WA 98512 1 O 1 1 4.WHEN STANDARD STRENGTH FILTER FABRIC IS USED,A HARE MESH I I SUPPORT FENCE SHALL BE FASTENED SECURELY TO THE UPSLOPESIDE Phone:(360)754-4612 OF THE POSTS USING HEAVY-DUTY HARE STAPLES AT LEAST 1 INCH I Fax:(360)754-4848 1 1 LONG. WIRES MINIMUM HOGRINDS,THE SHALL HALLEXTENDIRO THE 1 1 INCHESTRENC ABOVEH OF 4INAL GROUND SURF NOT EXTEND MORE THAN 36 1 INCHES ABOVE THE ORIGINAL ROUND SURFACE. ,1 5.THE STANDARD STRENGTH FILTER FABRIC SHALL BE STAPLED R WIRED Date: 03/2/2009 1 TO THE FENCE AND 20 INCHES OF FABRIC SHALL BE EXTENDED INTO THE TRENCH.THE FABRIC SHALL NOT EXTEND MORE THAN 36 Designed by:MICHAEL WHALE INCHES ABOVE THE ORIGINAL ROUND SURFACE.FILTER FABRIC SHALL Drawn by: VC I NOT BE STAPLED TO THE EXISTING TREES. 11 '1 ' 6.WHENEXTRASTRENGTH FILTER FABRIC AND CLOSER POST SPA CINGIS Checked b CDC USED,THE MARE MESH SUPPORT FENCE MAP BE ELIMINATED,IN SUCH y 1 201 01 A GSE,THE FILTER FABRIC IS STAPLED R"RED DIRECTLY TO THE Dwg#:03-03-09-003 I POSTS WITH ALL OTHER PROVISIONS OR ABOVE NOTES APPLYING. QepO � 1 p GUE 4 � \ 1 HOOD CANAL 801 COTT OE I, III 1 7.FILTER FABRIC FENCES SHALL NOT BE REMOVED BEFORE THE UPSLRE AREA HAS BEEN PERMANENTLY STABILIZED. 6.FILTER FABRIC FENCES SWILL BE INSPECTED IMMEDIATELY AFTER EACH , RANFALL AND AT LEAST DAILY DURING PROLONGED RAINFALL.ANY \ 1 \ REQUIRED REPAIRS SHALL BE MADE IMMEDIATELY. 100, \ ENTRYDRN AY 120' --�1 \ \1 1 GENERAL EROSION CONTROL NOTES: / I 1 II ,p Fs 1 1 1 I 1. EROSION CONTROL MEASURES SHALL BE IN PUCE PRIOR TO THE I 1 BE GINNING OF CONSTRUCTION.THE PROJECT ENGINEER AND THE COUNTY SHALL INSPECT AND APPROVE THE INSTALLATION OF 140' ; Qapo 1 EROSION CONTROL MEASURES PRIOR TO BEGINNING CONSTRUCTOR 160,\ j ,1 11 \ � J I It \ 2.EROSION CONTROL MEASURES ARE NOT UNITED TO THE ITEMS �/� \ R THIS PLAN.THE CONTRACTOR IS RESPONSIBLE FOR THE 180,V' j II \\ \\ GARDEN ti \\ \ A INSTALLATION AND MAINTAINANCE OF ALL EROSION CONTROL MEASURES. MULTI I P'1p'Y' \ NO SILTATION R EXISTING OR PROPOSED DRAINAGE FACILITIES \\ 1 I 1 1 PURPOSE I \ 1 I SHALL BE ALLOWED.CARE SHALL BE TAKEN TO PREVENT MIGRATION \ 20O' ; II BUILDING I , , I Of SILTS TO OFF SITE PROPERTIES. PROJECT NAME: 220' ,`\ \\\ '\ DRAIN FIELD ; 1 } '\ ` I I 3.THE CONTRACTOR SHALL MAKE DAILY SURVEILLANCE OF ALL EROSION HARMONY HILL GREENHOUSE / 240' `\ \\ \ \\ I I , MAIN �I I 1 I CONTROL MEASURES AND MAKE AM NECESSARY REPAIRS OR ADDITIONS / L 1 \\ \\ \\ \ \ 1 11 1{ / / II 1 TO THE EROSION CONTROL MEASURES.THE CONTRACTOR SHALL PROVIDE 7362 EAST SR-106 ADDITIONAL EROSION CONTROL MEASURES AS DETERMINED NECESSARY -1 1 \ \\ \ \\\ 1 � rtt rBcf I / / I I 1 BY THE COUNTY INSPECTOR ANDIOR THEPROJECT ENGINEER.FAILURE UNION,WASHINGTON \\ \\ `\ \\ 1 I 11 j TO COMPLY MATH ALL LOCAL AND STATE EROSION CONTROL MAY RESULT IN CIVIL PENA AIL 10O N �S _ _ 1 II II I AGAISTITTHE CONTRACTOR ANWORPROJECTEOWNE'R. LEVIED PARCEL 322334400040 \\ / M�\\ Q8 `\ \ \ I I , / I 1 4.DURING THE NET SEASON(NOVEMBER TO MARCH)ALL DISTURBED SLLS \ \ 1�^� \ \\ OFF I i SHALL BE STABILIZED WITHIN 46 HOURS AFTER STOP R MRK EROSION e,/I I/�L1(. CONTROL MEASURES SHALL INCLUDE,BUT NOT BE LIMITED TO, RewSlons. \ \ \ \ I I COVERING THE EFFECTED AREA INCLUDING SPOIL PI MATH /% PLASTIC SHEETING,STRAW MATTING.JUTE MATTING,STRAW MULCH, \\ \\ \\ `I I 4E0. II I/ I I OR WOOD CHIPS.SEEDING OF THE DISTURBED AREAS SHALL TAKE PLACE AS WEATHER PERMITS. 5.ALL SEEDED OR SODDED AREAS SHALL BE CHECKED REGULARLY TOMAKE SURE VEGETATIVE COVERAGE IS COMLETE.AREAS SHALL BE REPAIRED,RESEEDED,AND FERTILIZED AS REQUIREDuFFM . �. I I 6,TRA KING OF IS TRACKED ONTO AL OCOUNTY STREEFFSME WILL T,R SHALLT BEL BE RE D.IF BY(THE END OF THAT WORKING DAY.AM FURTHER TRACKINGOFM TEEN /,__ 1 I BE MA PREVENTED BY SWEEPING OR WASHING OF THE VEHICLES WILL TIRES Op og \ I I 1 {�J '"� /.V I I BEFORE DRIVING R A COUNTY STREET. / S".- 7.NO MORE SI NL 500 LF OF TRENCH ONA DOWNSLOPE OF MORE THAN 5 �F�v�( PERCENT SMALL BE OPENED AT ONE TIME, B.EXCAVATED MATERIAL SHALL BE PLACED ON THE UPHILL SIDE OF TRENCHES. 9,TRENCH DEVATERING DEVICES SHALL BE DISCHARGED IN MANNER THAT WILL NOT ADVERSELY AFFECT FLO✓NNG STREAMS.DRAINAGE SYSTEMS OR OFFSITE PROPERTIES. 10,ALL STORM SEWER INLETS RECEIVING RUNOFF FROM THE PROJECT DURING SCALE:1 inch=125 feet CONSTRUCTION SHALL BE PROTECTED SO THAT SEDIMENT-LADEN WATER SCALE: 1 = 125 FEET WILL BE FILTERED BEFORE ENTERINGTHE CONVEYANCE SYSTEM. It ALL OFFSITE CATCH BASINS IMMEDIATELY ADJACENT TO THE SITE SHALL BE PROTECTED FROM SILTATION. O 50 100 200 12 ALL DISTURBED AREAS SHALL BE SEEDED OR SODDED UPON COMPLETION R WORK THE CONTRACTOR SHALL BE RESPONSIBLE TO ENSURE THAT COMPLETE COVERAGE OF THE DISTURBED AREAS IS PROVIDED 6 THAT FIGURE 2 GROWTH R THE VEGETATION IS ESTABLISHED. 19.GTC BASINS SMALL TRAP SEDIMENT OR FILTER FABRIC MUST BE SITE P LA N PLACED A D UNDER GTE AP VEGETATION IS ESTABLISHED. CROSS-SECTION A (SOUTH-NORTH) 1PROPOSel) GREENHOUSE 110 100 . . .. . . . .... . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . 90 . . . . . . . . . . . . .... .. .. .. .. .. .. . . .. .... ...... .. ... . .. . . . . . . . . . . . LL 80 Q LL apo. . . . . . . . . . . . . . . . . . ..-D . . . . . . .. . . . . . . . . . . . . . . . . . . . .. .. .... .... .... ..... .. .. .. .. .. .. . + , '' * . . . . . . . . . . 70 . . . . . . . . . . . . .. . . .. . .. . . . .. .. .. 60 .... . ... . . .. . . .... .. . . . . . . . . Lu . . . . . . . . . . _j 50 .. . . ... . . ... . . . . . . . .. . . . . . . . . . ... . . . . . . . . . . . . . .. . Ao( u_ 40 .. . . . . . . . . . .. w SR . . . . . . . . . . . . . ....... .. . . . . . 0. . . . . . . . . . . . . . . . . . . . . . . . . . ... . . . . . . . . I . . . . . .. . . . . . . . . . . . . . > 30 . . . . . . . . . . . . . . . . .L . . . . . . . . .. .. . . . . . . . . . . . 20 . . . . . .. . . . . LL Qapo . . . . . . . ... . . . . . . . . . . . . . . . . . . . . . . . . ... . .. . . .... . . . .. . . . . . . . . . . . 10 . . . .. . . . . . . . . 0 0 150 1100 1150 1200 1250 300 1350 400 450 Geotechnical Testing Laboratory Geotechnical Services 10011 Blomberg St.SW FIGURE 4 QA/QC services Oty�p.0,WA 98512 SCALE ry Phon":(360)754-012 50' CROSS-SECTIONS Testing Services 1..(360)754-4848