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Home My WebLink About932200216 Geotech AssessmentCobalt Geosciences, LLC P.O. Box 82243 Kenmore, Washington 98028 www.cobaltgeo.com (206) 331-1097 July 30, 2022 RR Foundation Specialist Attn: Alesha Stickles alesha@rrspecialist.net RE: Limited Geotechnical Evaluation Foundation Mitigation 642 Beckett Point Road Port Townsend, Washington In accordance with your authorization, Cobalt Geosciences, LLC has prepared this letter to discuss the results of our limited geotechnical evaluation at the above-referenced location. Site and Project Description The site is located at 642 Beckett Point Road in Port Townsend, Washington. The site consists of one irregularly shaped parcel (No. 932200216) with a total area of about 0.06 acres. The central portion of the site is developed with a residence and driveway. The remainder of the property is vegetated with grasses, shrubs, bushes, understory and variable diameter trees. The site is nearly level to slightly sloping downward to the northwest. There are local modular block walls within the property, mostly near property lines. There is a steep slope northwest of the residence, extending downward to the northwest. The slope has relief of about 50 feet and magnitudes of 40 to 90 percent (approximately). The slope is heavily vegetated. The site is bordered to the northeast, northwest, and southwest by residences, and to the southeast by Beckett Point Road. We understand that the residence has settled up to 3 inches over time, likely beginning after construction and potentially continuing today. The settlement is widespread. The project includes installation of at least 19 helical anchors extending to refusal below affected foundation elements. Anchors will be attached with steel brackets and angle iron if necessary. Lifting will be performed as feasible. Area Geology The site lies within the Puget Lowland. The lowland is part of a regional north-south trending trough that extends from southwestern British Columbia to near Eugene, Oregon. North of Olympia, Washington, this lowland is glacially carved, with a depositional and erosional history including at least four separate glacial advances/retreats. The Puget Lowland is bounded to the west by the Olympic Mountains and to the east by the Cascade Range. The lowland is filled with glacial and non-glacial sediments consisting of interbedded gravel, sand, silt, till, and peat lenses. The Geologic Map of the Gardiner Quadrangle, indicates that the site is underlain by Vashon Advance Outwash. The outwash deposits include poorly graded sand with lesser gravels and silt/clay interbeds. These deposits are typically medium dense to very dense below a weathered zone. RECEIVED BY DCD 8/9/2022 July 30, 2022 Page 2 of 4 Limited Geotechnical Evaluation www.cobaltgeo.com (206) 331-1097 Soil & Groundwater Conditions As part of our evaluation, we excavated one hand boring to 5 feet below grade. The hand boring encountered about 6 inches of topsoil and vegetation underlain by loose to medium dense, silty- fine to medium grained sand with gravel (Weathered Advance Outwash) which extended to the termination depth of the hand boring. We reviewed a boring log from a nearby site. The boring encountered relatively dense outwash at shallow depths. The boring was drilled by Myers Biodynamics in 2005. Conclusions and Recommendation Based on our observations, it appears likely that the settlement is likely the result of consolidation of areas of loose weathered soils that overlie denser native soils at relatively shallow depths. Contributing factors could be downspout leakage into the near surface soils, age of the foundation, and possibly insufficient design controls of the existing foundation system. The proposed mitigation utilizing helical piers with steel connections appears suitable to reduce settlement and support the affected portions of the residence. Based on our observations, we anticipate that piers may extend 7 to 15 feet (or more) below grade. Helical Piers® Helical Piers® may be used to support the foundation systems of the residence. The Helical Piers® could be installed using portable rotary tools, truck mounted rotary tools, backhoe mounted rotary tools, caisson drills, or skid-steer loaders. It is important that the torque output, rotational speed, down pressure capability, and angle control of the installation equipment is compatible with the required foundation system. The pile installation equipment should have adequate torque capacity to prevent refusal conditions at relatively shallower depths that are well above recommended bearing depths or layers. A Helical Pier® consists of an anchor (lead section) with 1, 2, 3 or more helical flights on a shaft. The number and diameter of the helices on the anchor are dependent on the soil characteristics of the site and the design loads to be applied to the pier. Based on these parameters the anchor helix configuration is chosen to best fit the site conditions. As the anchor is advanced into the soil extension sections (shaft) are placed on the lead section. The shaft configuration is based on the design loads and anticipated installation torque. The static compression load capacity of a Helical Pier® is the sum of all individual helix capacities below liquefiable soils and in bearing layer. Individual helix static compression capacity is the result of the projected area of the helix, and its bearing pressure. It is recommended that the piers penetrate into relatively dense native soils a minimum of 5 feet, or until refusal whichever is shallower. The bearing layer will be at variable depths below the existing ground surface due to previously natural slope conditions (anticipated to be 7 to 15 feet). Increased capacity can be obtained with increased penetration, and additional helical flights on the lead section. RECEIVED BY DCD 8/9/2022 July 30, 2022 Page 3 of 4 Limited Geotechnical Evaluation www.cobaltgeo.com (206) 331-1097 Helical Pier® installation should be monitored to verify installation torque, and proper embedment into the presumed bearing layer. The Helical Pier® lengths may need to be modified during construction if it is determined that the depth to the bearing layer varies. Helical Pier® anchors are well suited to field adjustments as length can be varied by merely adding or deleting extension sections (shafts) during installation. Monitoring installation torque in the field is used to estimate the anchor compression capacity, and also as a quality control during anchor installation, provided that the anchor is bearing in dense or hard soils. Dependent on the pile size and the equipment used to install the anchors, an empirical factor is multiplied by the average torque over the final 3 feet of installation to estimate ultimate capacity. Allowable Helical Pier Compression Capacity Pa may be estimated from the following equation provided that the pier is in the recommended bearing soils: Pa = Kt x T/FoS, Where T is the applied torque, Kt is the empirical ratio factor. The following industry standards apply to shafts with blades spaced along the shaft at 2.5 to 3.5 times the average blade diameter on-center and meeting the manufacturer’s specifications. 1.5" and 1.75" Square Shafts - Kt = 9 ft-1 2.875" O.D. Round Shafts - Kt = 9 ft-1 3.0" O.D. Round Shafts - Kt = 8 ft-1 3.5" O.D. Round Shafts - Kt = 7 ft-1 Proof testing of at least twenty percent of the helical piers in eight equal increments up to 200 percent of the design load, if required by the permitting authority. Each load increment up to the 200 percent of design load should be held for five (5) minutes and the vertical strain monitored. If the total strain between 1 and 5 minutes is less than 0.04 inches, the helical pier may be considered acceptable. If the recorded strain exceeds 0.04 inches, the helical pier should either be deepened and retested or abandoned and a new helical pier shall be installed and tested. Closure The information presented herein is based upon professional interpretation utilizing standard practices and a degree of conservatism deemed proper for this project. We emphasize that this report is valid for this project as outlined above and for the current site conditions and should not be used for any other site. Our work did not include borings or slope stability analyses. RECEIVED BY DCD 8/9/2022 July 30, 2022 Page 4 of 4 Limited Geotechnical Evaluation www.cobaltgeo.com (206) 331-1097 Sincerely, Cobalt Geosciences, LLC 7/30/2022 Phil Haberman, PE, LG, LEG Principal Figure 1; Site Plan Figure 2; Repair Plan Figure 3; Hand Boring Log RECEIVED BY DCD 8/9/2022 N Cobalt Geosciences, LLC P.O. Box 82243 Kenmore, WA 98028 206) 331-1097 www.cobaltgeo.com cobaltgeo@gmail.com SITE MAP FIGURE 1 Subject Property HB-1 Foundation Mitigation 642 Beckett Point Road Port Townsend, Washington RECEIVED BY DCD 8/9/2022 REPAIR PLAN FIGURE 2 Cobalt Geosciences, LLC P.O. Box 82243 Kenmore, WA 98028 206) 331-1097 www.cobaltgeo.com cobaltgeo@gmail.com Foundation Mitigation 642 Beckett Point Road Port Townsend, Washington RECEIVED BY DCD 8/9/2022 PT Well-graded gravels, gravels, gravel-sand mixtures, little or no fines Poorly graded gravels, gravel-sand mixtures, little or no fines Silty gravels, gravel-sand-silt mixtures Clayey gravels, gravel-sand-clay mixtures Well-graded sands, gravelly sands, little or no fines COARSE GRAINED SOILS more than 50% retained on No. 200 sieve) Primarily organic matter, dark in color, and organic odor Peat, humus, swamp soils with high organic content (ASTM D4427)HIGHLY ORGANIC SOILS FINE GRAINED SOILS 50% or more passes the No. 200 sieve) MAJOR DIVISIONS SYMBOL TYPICAL DESCRIPTION Gravels more than 50% of coarse fraction retained on No. 4 sieve) Sands 50% or more of coarse fraction passes the No. 4 sieve) Silts and Clays liquid limit less than 50) Silts and Clays liquid limit 50 or more) Organic Inorganic Organic Inorganic Sands with Fines more than 12% fines) Clean Sands less than 5% fines) Gravels with Fines more than 12% fines) Clean Gravels less than 5% fines) Unified Soil Classification System (USCS) Poorly graded sand, gravelly sands, little or no fines Silty sands, sand-silt mixtures Clayey sands, sand-clay mixtures Inorganic silts of low to medium plasticity, sandy silts, gravelly silts, or clayey silts with slight plasticity Inorganic clays of low to medium plasticity, gravelly clays, sandy clays, silty clays, lean clays Organic silts and organic silty clays of low plasticity Inorganic silts, micaceous or diatomaceous fine sands or silty soils, elastic silt Inorganic clays of medium to high plasticity, sandy fat clay, or gravelly fat clay Organic clays of medium to high plasticity, organic silts Moisture Content Definitions Grain Size Definitions Dry Absence of moisture, dusty, dry to the touch Moist Damp but no visible water Wet Visible free water, from below water table Grain Size Definitions Description Sieve Number and/or Size Fines <#200 (0.08 mm) Sand Fine Medium Coarse Gravel Fine Coarse Cobbles Boulders 200 to #40 (0.08 to 0.4 mm) 40 to #10 (0.4 to 2 mm) 10 to #4 (2 to 5 mm) 4 to 3/4 inch (5 to 19 mm) 3/4 to 3 inches (19 to 76 mm) 3 to 12 inches (75 to 305 mm) 12 inches (305 mm) Classification of Soil Constituents MAJOR constituents compose more than 50 percent, by weight, of the soil. Major constituents are capitalized i.e., SAND). Minor constituents compose 12 to 50 percent of the soil and precede the major constituents (i.e., silty SAND). Minor constituents preceded by “slightly” compose 5 to 12 percent of the soil (i.e., slightly silty SAND). Trace constituents compose 0 to 5 percent of the soil i.e., slightly silty SAND, trace gravel). Relative Density Consistency Coarse Grained Soils) (Fine Grained Soils) N, SPT, Relative Blows/FT Density 0 - 4 Very loose 4 - 10 Loose 10 - 30 Medium dense 30 - 50 Dense Over 50 Very dense N, SPT, Relative Blows/FT Consistency Under 2 Very soft 2 - 4 Soft 4 - 8 Medium stiff 8 - 15 Stiff 15 - 30 Very stiff Over 30 Hard Cobalt Geosciences, LLC P.O. Box 82243 Kenmore, WA 98028 206) 331-1097 www.cobaltgeo.com cobaltgeo@gmail.com Soil Classification Chart Figure C1 RECEIVED BY DCD 8/9/2022 Log of Hand Boring HB-1 Date: June 2022 Contractor: Method: Hand Auger Depth: ’ 5 Elevation: N/A Logged By: PH Checked By: SC Initial Groundwater: None Sample Type: Grab Final Groundwater: N/A Material Description SPT N-Value Moisture Content (%) Plastic Limit Liquid Limit 10 20 30400 50 1 2 3 4 5 6 7 8 9 10 End of Hand Boring 5 Vegetation/Topsoil Loose, fine to medium grained sand dark yellowish brown to yellowish brown,trace gravel Weathered Outwash)moist SP Medium dense, fine to medium grained sand gravel,with yellowish brown to grayish brown, moist. ()AdvanceOutwashSP Cobalt Geosciences, LLC P.O. Box 82243 Kenmore, WA 98028 206) 331-1097 www.cobaltgeo.com cobaltgeo@gmail.com Foundation Mitigation 642 Beckett Point Road Port Townsend, Washington Hand Boring Log RECEIVED BY DCD 8/9/2022 Discovery Bay t ',,.,.:, VICINITY MAP 2/:3f~ Approximate Scale: 1 inch = 250 feet 0 125 250 GEOLOGICALLY HAZARDOUS AREAS ASSESSMENT Beckett Point Wastewater Treatment System Jefferson County, Washington LEGEND: 8-1 Approx. Boring Location (this report) Approx.· Test Pit Location (May 2005 report) 0 AfW.1 Existing Monitoring Well Location (by others) At t' Generalized Subsurface Cross-Section A -A' Proposed Pump Station Locations Approximate Sewerage System Alignment Area of hydrophytic vegetation and "Spring House". NOTES: 1. Plan based on "Beckett Point Site Map" provided by Parametrix, dated 03/01/05. 2. Boring locations are approximate. 3. Monitoring Well locations (installed by others) are approximate and based on current field observations. Other monitoring wells reportedly located on the site were not found . FIGURE NO. PFIOJECT NO. 2 SITE AND EXPLORATION PLAN 041136A-5 June2005 RECEIVED BY DCD 8/9/2022 ORING LOG B-2 This log applies only to boring location at the time of drilling. Subsurface conditions may differ at other locations and may also change over time. This log Is a simpHfied interpretation of the actual cond#ions. Ii: J: Ii: w Q 5 10 15 20 h~ - z Cl) Beckett Point 0 :..I! lnzijUJ0 0 Cl) = a:1-w ij w ; Jefferson County, Washington > :::,Z I-.. J a: 1-W a: > a. == W..J Cl) I-ww :ii: 0 Cl) ..J -z :c ..J ~ ..J DESCRIPTION mw oo I-w Cl) m o:= :i!:O 0 Grasses I trace Topsoil over 6 S-1 7 Slighf'l, Gravelt Fine to Medium SAND; medium dense, yellow brown to red brown, 69 8 slighty moist, race coarse sand, trace organics (1/4-mch root) Slightly Gravelly Fine to Medium SAND; dense, gray brown, slightly moist, trace10 S-2 17 coarse sand · 64 20 17 Slightly Gravelly Fine to Coarse SAND; ve,y dense, gray brown, slightly moistS-3 40 59 33 rough drilling, increased gravel content U !015" S-4 Slightly Gravelly Silty to Ve,y Silty SAND to Sandy SILT, ve,y dense*, gray brown, moist 54 Sampler bouncing on pravel /' ;;i - rougn drilling at 2 foo -depth i. _. v -,· ':. 33· a:· .. 3f· ' ,,,. .. .. - n17 Ve,y Fine SAND to SILT; ve,y dense, gray brown, slightly moist, faint partings, -S-5 Oh 29 granular non-olastic - DATE DRILLED Myers Blodynamlcs Inc. Rolling Bay Mercantile Bldg. 11254 Sunrise Drive ELEVATION IFT) 74 _+ PROJECT Ni41136A-5 Bainbridge Island, WA 98110 i....---------' 7 RECEIVED BY DCD 8/9/2022 eaoRING LOG 8-2 cont. This log applles only lo boring location at the time of drilling. Subsurface conditions may differ at othar locations and may also change over lime. This log is a simplified Interpretation of the actual conditions. t: I- D. UJ C z = 0 en iaijUJ J D. 3: ~ 0 J <( ..J UJ en m .. ,, s-sJ 49 z Beckett Point 0 ij Jefferson County, Washington ~ 1-------,---,---,-~---,---,----,_----,----,---,---,---,---,---,---,---,---,-,----,---iUJ..JU,..J DESCruPTION ~; Very Fine SAND tq SILT; very dense, gray brown, slightly moist, faint partings, granular non-plastic Very Fine S~ND to Siltv Fine SAND; very dense, light gray to gray brown, slightly moist to moist grades (o Fine Sandy SILT to SILT; hard, gray brown, moist, one sand parting with iron staining grades to Fine sand at bottom of sampler 2 inches SILT to Silty Fine SAND at top of sampler, faint partings Fine SAND; very dense, gray brown to light gray, slightly moist, trace medium to coarse sand Very Fine SAND to SILT; hard, gray brown, slightly moist, granular non-plastic, fine sand partings, trace iron staining in sand parting SILT; hard, gray brown, slightly moist, massive Fine SAND; very dense, fight gray, slightly moist l l Fine SAND; very dense, light gray to gray brown, slightly moist grades to .silt in a 2-inch zone at 50 foot depth DATE DRILLED Rolling Bay Mercantile Bldg. ti UJO UJ a:1-I-::, ffi a: ........ w Y.?z :c oo 01-~o Myers Biodynamics inc. 11254 Sunrise Drive ELEVATION tfl) Bainbridge Island, WA 98110 _______ 7_4_±_. L.------....1 RECEIVED BY DCD 8/9/2022 tt30RING LOG B-2 cont. This log applies only to boring location at the time of drilling. Subsurface conditions may differ at other locations and may also change over time. This log is a simplified interpretation of the actual conditions. ti: i I- 0. w C vv 55 60 65 70 Beckett Point z (/) 0 ~ ~ z ij WO 0 (/) ~ . Jefferson County, Washington a:1-w ij w us > :::,Z I- J a: 1-W a: > 0. 3: W..J (/) I-w w :a 0 (/) ..J -z :c .. J <( ..J DESCRIPTION [ QW oo I-w (/) IXI 03: :ao 0 T bu50 Slightly Grave!JY Fine SAND; very dense, light gray, slightly moist, trace medium s-10 to coarse san - 21 s-11 33 Fine SAND; very dense, liff!!t gray to gr1{ brown, sightly moist 19 1-inch Silty Fine SAND to ine Sandy S T moist zone at approximately 40 50-foot depth 21 IS-12 40 Fine SAND; very dense, light gray, slightly moist 14 50 Bottom of boring at 60.5 foot depth 9 4 q I - J~3r -•.; DATE DRILLED Rolling Bay Mercantile Bldg. Myer& Blodynamlc& inc. 11254 Sunrise Drive ELEVATION tFT) Bainbridge Island, WA 98110 ..._ _____ 7_4 __ _,+ '---------' RECEIVED BY DCD 8/9/2022