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HomeMy WebLinkAboutBLD2021-00319 - BLD Engineering / Geo-tech Reports - 3/31/2023 GEOTECHNICAL ENGINEERING STUDY For ASHLEY SOWLE RESIDENCE 201, WEST DOGGONE LANE MATLOCK, MASON COUNTY, WA 98560 Prepared For ASHLEY SOWLE 201, WEST DOGGONE LANE MATLOCK, MASON COUNTY, WA 98560 Prepared By PGEPacific Geo Engineering Geotechnical Engineering,Consulting A Inspection P.O. BOX 1419, ISSAQUAH, WASHINGTON 98027 PGE PROJECT NUMBER 23-649 March 31, 2023 PGEPacific Geo Engineering Geotechnical Engineering, Consulting & Inspection March 31,2023 Client: Ashley Sowle 201, W.Doggone Lane Matlock,WA 98560 Re: Proposed Single Family Residence Geotechnical Engineering Study 201,W. Doggone Lane Matlock,Mason County,WA 98560 PGE Project No.23-649 Dear Mr. Sowle: As per the request,Pacific Geo Engineering,LLC(PGE)has completed the geotechnical engineering study for the subject site in Matlock, Washington, which is shown in the Site & exploration Plan, Figure 1, prepared by Crater Land Use Consulting. This study includes soil investigation and the geotechnical engineering recommendations for the design and construction of the foundation for the proposed residence. This study is completed in accordance with the mutually agreed upon scope of services described in our proposal no. 23-03-711, dated March 8, 2023, which was authorized on March 10, 2023. The scope of services was developed based on the preliminary understanding of the proposed development obtained from the owner. 1.0 Proposed Development The general location of the site with the proposed single family residence is shown on the Site & Exploration Plan, Figure 1. The proposed development plan calls for building a 3-bedroom, single family residence of approximately 2,364 sq.ft footprint area in the subject site. Based on our experience with similar projects, we anticipate that wall loads will be in the range of 5 to 6 kips per lineal foot, isolated column loads in the range of 40 to 60 kips, and slab-on-grade floor loads of 150 pounds per square foot(psf). At the time of this study,the final building grades are not available to PGE;however,for the purpose of this study, we assume that only minor cut and fill depths will be required to achieve the final grades for the building foundations and the slab-on-grade concrete floor slab. The conclusions and recommendations contained in this report are based upon our current understanding of the proposed development. We recommend that PGE should be allowed to review the final PGEPec/tic Geo Engineering ieotWuuol E..p/neerny,c uvroiro rn.n.cebw Proposed Single Family Residence Geotechnical Engineering Study 201, West Doggone Ln Matlock,Matson County, WA 98560 PGE Project No.23-649 March 31,2023 Page 2 of 16 design grades and the actual features of the proposed development,and the final construction plan to verify that the geotechnical recommendations provided in this report are incorporated into the final construction documents.PGE's review of the final plan set would also allow PGE to re-evaluate their recommendations,and if necessary,to modify the recommendations before the construction begins. We believe this would be helpful for the project's speedy completion and success. 2.0 Scope of Services Based on the scope of this geotechnical study delineated in the contract agreement, the following items are accomplished - field exploration, geologic literature review, engineering evaluation of the field data, and geotechnical engineering recommendations for the design and construction of the foundation of the proposed residence. The scope of our work did not include any wetland study,or any environmental analysis or evaluation to find the presence of any hazardous or toxic materials in the soil, surface water, groundwater, or air in or around this site. Engineering Evaluation The results from the field investigation were evaluated and engineering analyses were performed to develop the design information and the geotechnical engineering recommendations for the following items of the proposed development: Soil&Groundwater Conditions • Descriptions of the subsurface conditions,including the soil and the groundwater conditions; • Soil Test Pit Logs; • Depth to water table and any sign of high water table,if encountered; • Native soil Classification as per USCS system; • Regional geologic unit as per USGS; Structure • Foundation type recommendation—conventional shallow spread and continuous footings • Allowable bearing capacity value for supporting the proposed footings and the residences; • Estimated total and differential settlements for the recommended bearing capacity value and observed soil conditions; • Frictional and passive values for the resistance of lateral forces; PGEPacIFc Geo Engineering 6eo(adinlol Enp//MN/ny Consu/tl/y.INppGbn Proposed Single Family Residence Geotechnical Engineering Study 201, West Doggone Ln Matlock Matson County, WA 98560 PGE Project No.23-649 March 31,2023 Page 3 of 16 • Subgrade preparation for footings and any other load-bearing structures such as pavement and sidewalk; • Slab-on-grade for the proposed building,and the subgrade preparation for slab-on-grade; • Seismic design recommendations,including the site co-efficient as per ASCE7-16 Standard& 2018 IBC; Geologic Hazard Mitigations • Geologic hazards evaluation: erosion,seismic, and landslide; • Erosion control measures; • Liquefaction potential evaluation of native soil; 3.0 Surface and Subsurface Features The proposed building site is located adjacent to an wetland area as shown in Figure 1. The building site has an access via a gravel driveway. The site is located within a region dominated by sparsely populated single family residences with farms. Currently, the proposed building site has been excavated to approximately one feet below the original adjacent grades. The current grades are consisted of soft, wet, brown silty deposit, covered with a thin layer of 5/8-inch crushed rocks recently been placed over the native soils. Building site is almost a level ground, with less than a few feet of elevation differential across the property. Surface water was observed at the building site at some localized areas at the time of our investigation. 4.0 Field Investigation Our field exploration was performed on March 24, 2023. Two (2) test pits were excavated outside the building site at its two corners to determine the soil and groundwater conditions of the site. The test pit locations are shown on the Site Plan,Figure 1,attached with this report. Test pits were excavated to depths of approximately 6 to 8 feet below the existing grades as shown in the soil test pit log(Appendix A). The test pits were backfilled with loosely compacted excavated soils. The location of the test pits in Figure 3 should be considered accurate only to the degree implied by the measuring methods.The test pits were completed using a backhoe provided by PGE. A geotechnical engineer from PGE observed the field explorations including the test pit excavations, soil sampling, continuously logging the subsurface conditions in the test pits, collecting representative bulk samples from different soil layers at different depths of the test pits, and visually-manually classifying the soil samples in the field as per the methods described in the ASTM D-2488-93 (based on soil samples' density/consistency, moisture condition, grain size, and plasticity estimations). The engineer also observed PGEPacitic Goo Engineering ,�,E....,..�� .. Proposed Single Family Residence Geotechnical Engineering Study 201, West Doggone Ln Matlock Matson County, WA 98560 PGE Project No.23-649 March 31,2023 Page 4 of 16 the pertinent site features and took notes. The soil samples were designated according to the test pit number and sampling depth, stored in watertight plastic containers, and later on transported to our laboratory for further visual examination and testing. Results of the field investigation are presented in the soil test pit logs (Appendix A). The final exploration logs were prepared with our observation and interpretation of the test pit excavations, and visual examination of the samples in the field and later on in the laboratory. The soils were classified according to the methods presented in figure'Key to Exploration Logs' in Appendix A. This figure also provides a legend explaining the symbols and abbreviations used in the soil exploration logs. The soil logs indicate the depth where the soils change. It should be noted that the indicated stratification lines on the logs represent the approximate boundaries between soil types. The actual transitions of varying soil strata may be more gradual in the field. 5.0 Site Geology—Geological Unit Geologic information for the project site was obtained from the interactive Geologic Map of Washington State, published by the Washington State Department of Natural Resources (DNR). According to the referenced maps, subsurface soils mapped near the project are consists of Glacial Outwash(Qa)at the project site. Glacial Outwash is generally defined as irregularly layered sands and gravels deposited in river and stream channels, with silts, clays, and peats deposited in the surrounding floodplain. In general, our explorations in the test pits encountered alluvium in the form of predominantly silt (USCS classification: ML)extending up to approximately 3 feet below the grades, and glacial outwash i.e., very gravely sand with cobbles and boulders below it. 6.0 Site Soil and Groundwater Conditions A topsoil layer of approximately 12 inches thickness consisted of black, silt with roots and organics (USCS classification: OL) is encountered at the test pit locations. The topsoil is almost in wet condition and in soft state. The topsoil is underlain by alluvium deposit consisted of brown, soft, silt (USCS soil classification: ML) up to approximately 3 feet depth below the grades, which is then underlain by olive brown, medium dense, glacial outwash consisted of very gravelly sand with cobbles and boulders (USCS soil classification: GW).The outwash presents up to the bottom of the test pits. The digging through the alluvium was easy whereas it was difficult through the sand with gravel deposit because of the severe cave-in of the glacial outwash. PGEPaciFc Geo Engineering 6ao[hMWEnofn �a c MW& Man Proposed Single Family Residence Geotechnical Engineering Study 201, West Doggone Ln Matlock Matson County, WA 98560 PGE Project No.23-649 March 31,2023 Page 5 of 16 Hydrogeologic Condition Groundwater water was encountered in the test pits at approximately same depth glacial outwash was encountered, i.e., at 3 feet below the grades. Also, some signs of mottling were noticed in the upper alluvium deposit and in the glacial outwash deposit at the contact point with the alluvium. Mottling signs are typically evidence of seasonal groundwater fluctuations, typical in Puget Sound area. Typically the fluctuations depend on the amount and level of groundwater rise due to the seasonal variations in the amount of rainfall, surface runoff, and other factors not apparent at the time of our explorations. Typically, the groundwater level rises higher and the flow rate increases during the wet winter months. The possibility of the fluctuations and the presence of groundwater at the current grades should be considered when the footings will be built in this site. Considering this scenario, PGE has provided recommendations for the design and construction of the footings for the proposed residence later on in Section of this report. The preceding discussion on the subsurface conditions of the site is intended as a general review to highlight the major subsurface stratification features and material characteristics. For more complete and specific information at individual test pit location, please review the Soil Test Pit Log (Figure A-1) in Appendix A. The logs include soil descriptions,stratification,and location of the samples,and the laboratory test results. It should be noted that the stratification lines shown on the logs represent the approximate boundaries between various soil strata; actual transitions may be more gradual or more severe. The subsurface conditions depicted in the soil logs are for the test pit locations indicated only, and it should not necessarily be expected that these conditions are representative at other locations of the site. 7.0 Conclusions and Recommendations 7.1 Fill Placement and Compaction Requirements Generally, quarry spalls, controlled density fills (CDF), lean mix concrete (LMC) do not require special placement and compaction procedures. In contrast, clean sand, crushed rock, soil mixtures and recycled concrete should be placed under special placement and compaction procedures and specifications described here. The structural fills under structural elements should be placed in uniform loose lifts not exceeding 12 inches in thickness if the compaction is to be done with a big, heavy, vibratory roller, or a walk-behind heavy-duty vibratory plate compactor (Bomag, Multiquip #MVH128GH). If the fills are to be placed in 4 inches thickness then the compaction is to be done with a hand held smaller and lighter compaction equipment such as a vibratory plate compactor. Each lift should be compacted to a minimum of 95 percent of PGEPach7c Engineering Proposed Single Family Residence Geotechnical Engineering Study 201, West Doggone Ln Matlock Matson County, WA 98560 PGE Project No.23-649 March 31,2023 Page 6 of 16 the fill's maximum dry density as to be determined in the laboratory by ASTM Test Designation D-1557 (Modified Proctor) method, or to the applicable minimum City or County standard, whichever is the more conservative. The fill should be moisture conditioned such that its final moisture content at the time of compaction should be at or near (typically within about 2 percent) of its optimum moisture content, as determined by the ASTM method. If the fill materials are on the wet side of optimum, they can be dried by periodic windrowing and aeration or by intermixing lime or cement powder to absorb excess moisture. The compacted structural fill pad should extend outside all foundations and other load bearing structures elements such as the pavement and sidewalk a minimum distance equal to the thickness of the fill pad. We recommend that compaction of the fills be tested periodically throughout the fill placement. A field compaction testing program should be prepared by the contractor with the assistance from the project geotechnical engineer. If field density tests indicate that the last lift of compacted fills has not been achieved the required percent of compaction or the surface is pumping and weaving under loading,then the fill should be scarified, moisture-conditioned to near optimum moisture content, re-compacted, and re-tested prior to placing additional lifts. No heavy compaction equipment such as hoe pack or big vibratory roller or walk-behind heavy-duty vibratory plate compactor should be used to compact the backfills to be placed behind the footing stem walls and the retaining walls, within the horizontal distance equal to the heights of the walls. Use of the heavy compaction equipment will impose excess surcharge load on the walls, which may cause permanent lateral instability to the walls. 7.2 Site Drainage Surface Drainage The final site grades of the finished development must be such that surface runoff will flow by gravity away from the building and other structure, such as the pavement and sidewalks, using sloped and drainage gradients towards the local stormwater collection system. We recommend providing a minimum drainage gradient of about 2%for a minimum distance of about 10 feet from the building perimeter. Surface water should not be allowed to pond and soak into the ground surface near buildings or paved areas during or after constructions. A combination of using controlled surface drainage and capping of the building surroundings by concrete, asphalt, or low permeability silty soils will help minimize or preclude surface water infiltration around the perimeter of the building and beneath the garage basement floor slab. Paved areas should be graded to direct runoff to catch basins and or other collection facilities. Collected water should be directed to the on-site drainage facilities by means of properly sized smooth walled PVC pipe. Interceptor ditches or trenches or low earthen berms should be installed along the upgrade perimeters of the PG=Pacific Geo Engineering 6eotor nfol ff p�n y Cb IdM•Inyectbn Proposed Single Family Residence Geotechnical Engineering Study 201, West Doggone Ln Matlock Matson County, WA 98560 PGE Project No.23-649 March 31,2023 Page 7 of 16 site to prevent surface water runoff from precipitation or other sources entering in to the lower area of the lot. It should be noted that surface water runoff from precipitation flows as a sheet flow over slope is considered to be the primary cause of surficial sloughing and triggering slope failure. Therefore, the surface drainage system should be designed in such a way that stormwater runoff over the finished lot must not create any sheet flow over the sloped areas of the site,instead,the stormwater runoff must be collected in drain pipes to discharge in approved discharge points at the toe of the slope. Surface drainage system and the water collection facilities should be designed by a professional civil engineer. Footing Drai Footing drains should be used where(1)crawl spaces or basements will be below a structure,(2)a slab below the outside grade, and (3) the outside grade does not slope downward from a building. To reduce the potential for groundwater and surface water to seep into the interior spaces of the building we recommend that an exterior footing drain system be constructed around the perimeter of the building foundations as shown in the typical Footing Drain, Figure 2. The drains must be laid with a gradient sufficient to promote positive flow by gravity to a controlled point of approved discharge. The foundation drains should be tightlined separately from the roof drains to this discharge point.Footing drains should consist of at least 6-inch diameter, heavy-walled, perforated PVC pipe or equivalent. The pipe should be surrounded by at least 6 inches of free-draining gravel over the pipe and 3 inches of free-draining gravel below the pipe. The free-draining material may consist of open-graded drain rocks consisted of 3/a" minus washed gravels should be wrapped up by a non-woven geotextile filter fabric (Mirafi 140N)to limit the ingress of fines into the gravel and the pipe. The free-draining material should contain less than 2 percent by weight passing the U.S. Standard No. 200 sieve (based on a wet sieve analysis of that portion passing the U.S. Standard No. 4 sieve). The drains should be located along the outside perimeter of the spread footings or the footing stem walls. Also,the invert of the footing pipe should be placed at approximately the same elevation as the bottom of the footing or 12 inches below the adjacent floor slab grade, whichever is deeper, so that water will not seep through walls or floor slabs. The footing drains should discharge to an approved drain system and include cleanouts to allow periodic maintenance and inspection. Downspout or Roof Drain These should be installed once the building roof in place.They should discharge directly in tightlines to a positive, permanent stormwater collection system. Under no circumstances connect these tightlines to the perimeter footing drains. Pacific Geo Engineering P Pacific Proposed Single Family Residence Geotechnical Engineering Study 201, West Doggone Ln Matlock Matson County, WA 98560 PGE Project No.23-649 March 31,2023 Page 8 of 16 7.3 Building Foundation Recommendations Foundation support for the proposed residence may be consisted of shallow conventional continuous strip footings and/or isolated speared footings. The following recommendations should be adopted to build the final footing subgrades. The upper alluvium soils consisted of brown,soft,wet,silty soils must be completely removed up to the top of the glacial outwash,consisted of very gravelly sand with cobbles and boulders. The void areas should be filled up with 2 to 4-inch size quarry spalls up to the seasonal highest flood level. As per our conversation with the owner's representative on-site,the seasonal highest flood level rise almost upto the current grades, i.e., upto the crushed rock layer recently placed in the building site. We recommend that the seasonal highest flood level will be determined by the owner of the project based on their past experiences in the property and in its adjacent properties. The quarry spalls must be placed in one foot, individually compacted lifts. The quarry spalls should be compacted with a big, heavy, vibratory roller to rearrange the quarry spalls. The actual thickness of the quarry spalls should be placed up to the highest seasonal flood level to be determined by the owner. Following the completion of the quarry spall layer placement, 5/8- inch crushed rocks should be placed over the quarry spalls for at least upto 2 feet above the seasonal highest flood water level to maintain a minimum 2 feet of vertical separation between the highest flood level and the seasonal highest flood level. The 5/8-inch crushed rocks must be placed in individually compacted one foot lifts.The compaction should be done to at least 95%or more of the fill's Modified Proctor dry density value to be determined from the ASTM 1557 laboratory test method as recommended earlier in Section 7.1, 'Fill Placement and Compaction Requirements' of this report. Alternatively,the adequate compaction can be accepted and approved by a geotechnical engineer by observing the compaction of each layer compacted to firm and unyielding conditions. A T-probe should be used to determine the denseness of the fill pad. Another criterion to meet the footing depth requirement is to set the footings at least 18 inches below the final building pad grade to achieve the frost protection depth. The buried portion of the footing in the fill pad would also help the footing to achieve the required lateral resistance against the sliding of the footing. The fill pad preparation needs overexcavation beyond the edges of the building footprint area, which should extend laterally beyond the edge of the each side of the footing for a horizontal distance equal to the thickness of the fill pad above the quarry spalls. This will prevent the exerting of the loading from the footing within the pad thickness,which otherwise,would burst the fill pad edges. PGEPacific Geo Engineering .,4, ��. Proposed Single Family Residence Geotechnical Engineering Study 201, West Doggone Ln Matlock,Matson County, WA 98560 PGE Project No.23-649 March 31,2023 Page 9 of 16 Allowable Bearing Capacity We recommend that a maximum net allowable bearing capacity of 2,000 pounds per square foot (psf) can be used for the design of the footings to be placed above the adequately compacted fill pad as described above. The"net allowable bearing pressure"refers to the pressure that can be imposed on the final fill subgrade at foundation level resulting from the total of all dead loads plus the live loads, exclusive of the weight of the footing or any backfill placed above the footing. For short-term loads, such as wind and seismic, a 1/3 increase in the above net allowable capacity can be used. We recommend that continuous footings have a minimum width of 18 inches and individual column footings a minimum width of 24 inches. All exterior footings should bear at least 18 inches below the final adjacent finish grade to provide adequate confinement of the bearing materials and frost protection. Settlement Based on our settlement potential evaluation of the above shallow foundation options,we anticipate that properly designed and constructed foundations supported on the recommended materials should experience total settlement of less than 1 inch and differential settlement between two adjacent load-bearing components supported on competent soil should be less that about one half of the total settlement. This estimation was done without the aid of any laboratory consolidation test data,but on the basis of our experience with similar types of structures and subsoil conditions. The soil response to applied stresses caused by building and other loads is expected to be predominantly elastic in nature with most of the settlements occurring during construction as loads are applied. Lateral Load Resistance Lateral foundation loads can be resisted by friction between the foundation base and the underlying supporting fill pad, and by passive earth pressure acting on the face of the embedded portion of the foundation below the final grades. For frictional resistance, a coefficient of 0.35 can be used. For passive earth pressure,the available resistance can be computed using an equivalent fluid pressure of 300 pcf, which includes a factor of safety of 1.5. This value assumes the foundation must be poured "neat" against the structural fill placed and compacted as described earlier in Section 7.1, 'Fill Placement and Compaction Requirements'of this report. Footing Subgrade Inspection We recommend that PGE representative examine the bearing materials prior to placing forms or rebar. PGEPacif'.c Geo Engineering _- -- GeOteUnbl Enplrod/np,Cduv/tlnp a➢Ypctbn Proposed Single Family Residence Geotechnical Engineering Study 201, West Doggone Ln Matlock Matson County, WA 98560 PGE Project No.23-649 March 31,2023 Page 10 of 16 7.4 Slab-on-grade Floor In our opinion, the slab-on-grade floor may be supported over the adequately compacted 5/8-inch crushed rock fill pad. Slab-on-grade floors should not be placed on topsoils, upper soft and unyielding, wet native soils.The fill pad must be compacted adequately to firm and unyielding, and stable condition, following the procedures described above for the footings and recommended earlier in Section 7.1, 'Fill Placement and Compaction Requirements'of this report. Based on the fill pad preparation as described above, a modulus of subgrade reaction value of about 100 pounds per cubic inch (pci) may be used to estimate slab deflections, which could arise due to elastic compression of the subgrades. After subgrade preparation is completed,the slab should be provided with a`capillary break layer' to retard the upward wicking of ground moisture beneath the floor slab. The `capillary break layer' would consist of a minimum of 6-inch thick compacted, clean, free-draining gravel with less than 2 percent of fines passing the U.S. Standard Sieve No.200 sieve. Alternatively, `Gravel Backfill for Drains' per 2014 WSDOT Standard Specifications 9-03.12(4)can be used as capillary break materials, with the added requirement that the material consist of a crushed, angular aggregate material be used as capillary break material. The purpose of this layer is to provide a uniform support for the slab,provide a capillary break layer,and act as a drainage layer. Where moisture by vapor transmission is undesirable, we recommend the use of a `vapor barrier' such as a 10- to 15-mil thick durable polyethylene sheeting (such as Crossstuff, Moistop, or Visqueen) between the capillary break layer and the floor slab (i.e., right below the slab) to prevent the upward migration of ground moisture vapors through the slab. The sheeting should be installed and sealed in accordance with the manufacturer's instructions. If moisture control within the building is critical, we recommend an inspection of the `vapor barrier' membrane to verify that all openings have been properly sealed. During the casting of the slab, care should be taken to avoid puncturing the `vapor barrier'. The American Concrete Institute (ACI) guidelines suggest that the slab may either be poured directly on the `vapor barrier' membrane or on a granular curing layer placed over the `vapor barrier' membrane depending on the conditions anticipated during construction. We recommend that the architect or structural engineer specify if a curing layer should be used.Use of a curing layer is generally recommended during drier months of the year and and/or when limited rain is expected during the slab-on-grade construction process.If the slab will be constructed during the wet season, exposed to rain after construction, or the site may be potentially wet,we do not recommend that the use of curing layer as excessive moisture emissions through the slab may occur.At owner's or architecture's discretion,the `vapor barrier' membrane may be covered with 2 inches of PGEPaciflc Geo Engineering ,o.... . Proposed Single Family Residence Geotechnical Engineering Study 201, West Doggone Ln Matlock;Matson County, WA 98560 PGE Project No.23-649 March 31,2023 Page I of 16 clean, moist sand as a `curing course' to guard against damage during construction and to facilitate uniform curing of the overlying concrete slab. The addition of 2 inches of sand over the `vapor barrier' is a non- structural recommendation. Styrofoam, as an additional layer can be placed between the concrete floor slab and the `capillary break layer' where heated area for provision of better insulation is to be required.A typical slab-on-grade section with the above features is provided in Figure 2 of this report. 8.0 Geologic Hazards The site is level ground so landslide hazard potential in this site nil hence no specific mitigations for this hazard is not required for this project. Site development is anticipated to include a Washington State Department of Ecology Construction Storm Water General Permit to mitigate the erosion potential of soils exposed during construction or site grading activities. In order to meet the criteria established by the Department of Ecology, an erosion control plan consistent with the local governing municipal standards and best management practices will be required for this project.The contractor will be responsible for implementing the erosion control plan as established in the plans and specifications approved by the governing municipality for the project. PGE has provided the following recommendations for the erosion control measurements. 8.1 Erosion Control Measurements The erosion hazard can be mitigated if the following measurements are implemented. Miti atg ions All erosion sediment control measures must conform to the Thurston County requirements. As a minimum, we recommend implementing the following erosion and sediment control Department of Ecology (DOE) best Management Practices (BMPs) prior to, during, and immediately after clearing and grading activities at the site. • Mass grading activities and the earthwork should be completed within the dry summer period since the site soils consist of fine grained soils (silt with sand, alluvium deposit), containing high percentage of fines of approximately 80 percent. • Limit disturbance to areas where construction is imminent. If possible, site clearing and grading should be performed in stages, with successive stages not being cleared until erosion control measures for the previous stages are in place. • Determine staging areas for temporary stockpiles of excavated soils as part of the excavation planning. PGEPacific Geo Engineering - --- - - caw.v'.bi Ev�..e«fo,coavrom�+.y«uon Proposed Single Family Residence Geotechnical Engineering Study 201, West Doggone Ln Matlock,Matson County, WA 98560 PGE Project No.23-649 March 31,2023 Page 12 of 16 • Provide temporary cover for denuded areas including cut slopes and soil stockpiles during periods of inactivity. From October 1 to April 30, no soil shall remain un-stabilized for more than 48 hours. From May 1 to September 13, no soil shall remain un-stabilized for more than seven days. Temporary cover may consist of straw mulch or plastic sheeting that is securely anchored to the ground surface. Plastic covering should be placed and anchored,as specified in BMP C 123 provided in Chapter 4.1 of the Stormwater Management Manual for Western Washington.Mulching should be conform to the guide lines outlined in the BMP C 121 provided in Chapter 4.1 of the Stormwater Management Manual for Western Washington • Establish permanent covers for exposed areas that will not be worked for period of 30 days or more by seeding in conjunction with a mulch cover or appropriate hydroseeding. Seeding should conform to the specifications outlined in BMP C 120 provided in Chapter 4.1 of the Stormwater Management Manual for Western Washington. • Measurements such as the control of surface water must be maintained during construction. • Vegetation clearing must be kept very limited in this site to reduce the exposed surface areas. It is recommended that following the clearing of the vegetations, grading the open exposed areas should be covered with mulch or hydroseed. • No disturbance or removal of the existing vegetations, tress, and undergrowths should be made beyond the proposed construction area. • Temporary erosion and sedimentary control (TESC) plan, as a part of the Best Management Practices(BMP)must be developed and implemented as well.The TESC plan should include the use of geotextile barriers(silt fences)along any down-slope, straw bales to de-energize downward flow, controlled surface grading, limited work areas, equipment washing, storm drain inlet protection, and sediment traps. The TESC plan may need to be reviewed and modified periodically to address the changing site conditions during ongoing progress of the construction and the weather. • A permanent erosion control plan is to be implemented following the completion of the construction. Permanent erosion control measurements such as establishment of landscaping, replantation of trees and groundcover vegetations as soon as feasible in areas that are necessarily disturbed by earthwork activities,control of downspouts and surface drains, control of sheet flow over the excavation slope, prevention of discharging water over the excavation slope and at the toe of the slope are to be implemented following the completion of the construction. • Install temporary or permanent tightline pipes, where necessary and practical, to convey stormwater from above slope to appropriate downslope facilities on flatter terrain. • Install permanent stormwater runoff diversion systems, such as swales, curbs, berms, or pipes, to prevent flow directly over any final slope grades. • We recommend that completed graded-areas be restricted from traffic or protected prior to wet weather conditions. The graded areas may be protected by paving, placing asphalt-treated base, a layer of free-graining material such as pit run sand and gravel or clean crushed rock material containing less than 5 percent fines,or some combination of the above. PGEPacltic Geo EnV=r n9 Gaotrinb/Erq/Mriny OonsuM�q!InWlebn Proposed Single Family Residence Geotechnical Engineering Study 201, West Doggone Ln Matlock,Matson County, WA 98560 PGE Project No.23-649 March 31,2023 Page 13 of 16 Containment • Install a silt fence along the downhill side of the construction area that will be disturbed. The silt fence should be placed before cleaning and grading is initiated and should conform to the specifications outlined in BMP C233 provided in Chapter 4.2 of the Stormwater Management Manual for Western Washington. • Construct interceptor dikes and shallow drainage swales to intercept surface water flow and route the flow away from the construction tare to be stabilized and approved point of controlled discharge. Some small detention ponds with pipe slope drains may be incorporated with the swales in order to collect and transport the runoff to the discharge point. • Provide on-site sediment retention for collected runoff.Runoff should not flow freely over the top of the slope or off the site. • The on-site contractor should perform daily review and maintenance of all erosion and sedimentation control measures at the site to ensure their proper working order. Provided the recommended erosion and sedimentation control BMP's are properly implemented and maintained, it is our opinion that the planned development will not increase the potential for erosion at the site or on adjacent properties. 8.2 Seismically Induced Geotechnical Hazard-Liquefaction As part of the seismic evaluation of the site,the liquefaction potential of the site was also evaluated. Liquefaction is a phenomenon,which takes place due to the reduction or complete loss of soil strength due to increased pore water pressure during a major earthquake event. Liquefaction primarily affects geologically recent deposits of fine-grained sands that are below the groundwater table. Our on-site explorations encountered medium dense glacial outwash consisted of very gravelly sand with cobbles and boulders at approximately 3 feet below the grades. The above soils are considered as non-liquefiable soils, therefore, potential for widespread liquefaction and its associated hazards over the site during a seismic event is none. The above condition does not warrant additional mitigation techniques relating to liquefaction hazards. 8.2.1 Seismic Design Parameters Seismic Site Class Based on the NEHRP Site Class Map,the subject property is mapped as a seismic Site Class`D'. This matches with our observation of the very dense nature of the native soils in the test pits. PGEPacific Geo Engineering eaoexn,.bi ena�mm+�a,taw.smdro a nq,scNon Proposed Single Family Residence Geotechnical Engineering Study 201, West Doggone Ln Matlock Matson County, WA 98560 PGE Project No.23-649 March 31,2023 Page 14 of 16 Seismic Design Parameters According to the 2016 ASCE 7-16 code standards, Table 20.3-1, the seismic site classifies as Site Class `D',for determining the seismic design parameters for the structural design of the building. Seismic Design Parameters Spectral Response Acceleration(SRA)and Site Coefficients I Short Period(0.2 sec) Maximum Considered Earthquake(MCE) SS=1.574g Site Response Coefficient(Site Class D) Fa= 1.2 Adjusted Spectral Response Acceleration(SRA)of MCE Sms=S,x Fa= 1.889g Design SRA SDs=2/3 x SMs= 1.259g Spectral Response Acceleration(SRA)and Site Coefficients One Second Period(1 sec) Maximum Considered Earthquake(MCE) S1=0.64g Site Response Coefficient(Site Class D) F,= 1.4 Adjusted Spectral Response Acceleration(SRA)of MCE SM1=S, x Fv=0.0.896g Design SRA SDI =2/3 x Sys =0.598g Peak Ground Acceleration The MCEG mapped peak ground acceleration(PGA) for this site is 0.702g. To account for site class, the PGA is multiplied by a site amplification factor (FPG,) of 1.2. The resulting site modified peak ground acceleration(PGAM)is 0.842g. 9.0 Construction-time Testing and Inspection As the geotechnical engineer of record for the proposed development, at owner's option, PGE can provide geotechnical consultation, material testing, and construction monitoring services during the construction of the project. These services are important and necessary for the project to confirm that the earthwork and the general site development are in compliance with the general intent of design concepts, specifications, and the geotechnical recommendations presented in this report. Also, participation of PGE during the construction will help PGE engineers to make on-site engineering decisions in the event that any variations in subsurface conditions are encountered or any revisions in design and plan are made. PGE can assist the owner before construction begins to develop an appropriate monitoring and testing plan to aid in accomplishing a fast and cost-effective construction process. PGEpac/Fc Geo Engineering Proposed Single Family Residence Geotechnical Engineering Study 201, West Doggone Ln Matlock,Matson County, WA 98560 PGE Project No.23-649 March 31,2023 Page 15 of 16 10.0 Report Limitations The conclusions and recommendations presented in this report are based on our soil investigation, geological literature review, and our engineering evaluation. The study was performed using a mutually agreed-upon scope of work between PGE and the client. It should be noted that PGE cannot take the responsibility regarding the accuracy of the information provided by the client and project plan prepared by other consultants. If any of the information considered during this study is not correct or if there are any revisions to the plans for this project, PGE should be notified immediately of such information and the revisions so that necessary amendment of our geotechnical recommendations can be made. If such information and revisions are not notified to PGE, no responsibility should be implied on PGE for the impact of such information and the revisions on the project. Variations in subsurface(soil and groundwater)conditions may reveal during the construction of the proposed below grade infiltration system. The nature and the extent of the subsurface variations may not be evident until construction occurs. If any subsurface conditions are encountered at the site that are different from those described in this report, we should be notified immediately to review the applicability of our recommendations if there are any changes in the project scope. This report may be used only by the client and for the purposes stated,within a reasonable time from its issuance. Land use, site conditions (both off and on-site), or others factors including advances in our understanding of applied science,may change over time and could materially affect our findings. Therefore, this report should not be relied upon after 24 months from its issuance. PGE should be notified if the project is delayed by more than 24 months from the date of this report so that we may review to determine that the conclusions and recommendations of this report remain applicable to the changed conditions. The scope of our work does not include services related to construction safety precautions. Our recommendations are not intended to direct the contractors' method, techniques, sequences or procedures, except as specifically described in our report for consideration in design.Additionally,the scope of our work specifically excludes the assessment of environmental characteristics, particularly those involving hazardous substances. This report including its evaluation, conclusions, specifications, recommendations, or professional advice has been prepared for planning and design purposes for specific application to the proposed project in accordance with the generally accepted standards of local practice at the time this report was written. No warranty,express or implied,is made. PG =Pacific Geo Engineering Ge.ted nb/EIp/ms/ny C-ftft.•Pup.ctbn Proposed Single Family Residence Geotechnical Engineering Study 201, West Doggone Ln Matlock,Matson County, WA 98560 PGE Project No.23-649 March 31,2023 Page 16 of 16 This report is the property of our client Ashley Sowle,and has been prepared for the exclusive use of our client and its authorized representatives for the specific application to the proposed development at the subject site in Matlock, Washington. It is the client's responsibility to see that all parties to this project, including the civil engineer, designer,contractor, subcontractor,future homeowner, etc., are made aware of this report in its entirety. The use of information contained in this report for bidding purposes should be done at the contractor's option and risk. Any party other than the client who wishes to use this report shall notify PGE of such intended use and for permission to copy this report. Based on the intended use of the report, PGE may require that additional work be performed and that and updated report be reissued. Noncompliance with any of these requirements will release PGE from any liability resulting from the use this report. 11.0 Closure We trust the information presented in this report is sufficient for your current needs. We appreciate the opportunity to provide the geotechnical services at this phase of the project and look forward to continued participation during the design and construction phase of this project. Should you have any questions or concerns,which have not been addressed, or if we may be of additional assistance, please do not hesitate to call us at 425-218-9316 or 425-643-2616. Respectfully submitted, U Santanu Mowar,P.E. ,�� h�q a Pacific Goo Engineering PGE - 3T�3 D:\Geotechnical\2023-proj\23-649 S I TIE,��vp� slONAL Attachments: EXPIRES o l-01-2 0 24 Figure 1 Site& Exploration Plan Appendix A Soil Test Pit Log PROPOSE PROJECT fw(j2)BLACK COTTONWOOD 35 WESTERN HAWTHORN — CONCEPTUAL PLANT LAYOUT #PLANTSOVER-- . 12 CASCARA 36 SALMONBERRY ENTIRE PROJECT 12 WILLOW 36 BLACK TWINBERRY 35 CRABAPPLE 36 DOUGLAS SPIREA 35 VINE MAPLE , 35 MARSHMARIGOLD 30'x 30' -40- / I TP-1 / - - -- -- -- - ..- - - - - - -- - 3 BORW12 BATH SFR FOOTPRINT 2,364 SO.FT. / 140' (INCLUDING:GARAGE, / PATIOS.HEAT PUMP) 7 MAX.ROOF OVERHANG 'SEE STRUCI"URE BLUEPRINTS / FOR FURTHER DETAIL TP-2cv ■ S / 40'x 50' SEPTIO'TANKS / SEPTIC DRAINFIELD B RESERVE 'SEE SEPTIC DESIGN FOR / FURTHER DETAIL v Al , 5, � r m -- MDT AStRE:VLocan �ONSMeASUrmMENTSAREAt�O)OAAE. �----- WETLAND I_ _! 150'TYPE F STREAM BUFFER BUILDING FOOTPRINT DRIVEWAY 800 SF e 15'WETLAND SETBACK Q RESTORATION AREA 12,400 SF : 2'ROOF OVERHANG SEPTIC TYPE F STREAM Im DEVELOPMENT ENVELOPE 12,400 SF CONCRETE PAD 100'WELL BUFFER(NEIGHBOR) DATE- 10 SEPTEMBER 2022 v CLIENT- SOWLE CRATER LAND USE CONSULTING PROJECT- HOME CONSTRUCTION 0 10 20 40 Feet e 477 PARPALA ROAD, NASELLE,WA 98638 COUNTY- MASON ( ( 1 I I I I I I 509-942-9309 RYAN@CRATERLUC.COM PARCEL- 620177500023 SITUS- 201 W DOGGONE LN Figure 1 - Site & Exploration Plan NOTES:- FOOTING DRAIN Schematic Only Op Backfills in the void areas between the (Not a construction drawing) excavation face&the footing must be placed and compacted to 95%of fills'Mod.Proc. Max,d ry density value as per ASTM D 1557. Fills must contain no organic&other deleterious materials.Fills must be placed in 6 inch or 12 inch thk individually compacted lifts.For a 6 inch thk lift a walk-behind Floor Level regular plate compactor can be used.For a 12 inch thk lift a walk-behind big vibratory Concrete slab-on-grade Slope backfill w/minor slope plate compactor must be used.No hoe-pack should be used because of the proximity of A the footing wall Compacted Backfills B Stormwater roof drain,must be tightlined B Roof Drain and must not be connected to footing drain. Styrofoam L Pipe should be sloped towards approved Vapor Barrier K C Excavation Slope discharge point so that no backflow should Footing Wa11--) occur into the pipe. 6"min.gravel on top Excavation face slope to be determined based Capillary Break J CO A D Mirafi 140N on actual soil and groundwater conditions to Final Slab Subgrade I be revealed during the construction E Drain Pipe Non-woven Geotextile Filter Fabric-Mira fi Fill oad—5/8"minus crushed F Drain Rocks O 140 N must wrap around the drain rocks rocks must be compacted to firm 3"min.gravel at bottom 6"dia.rigid PVC nine w/ erforations 1/4" &unyielding conditions as inOp O S P ( max.dia.)to be in the lower half of pipe,& Gravel Base H G Final Footing Subgrade lower quadrant segment un-perforated to facilitate flow of water.The pipe must be placed as low as possible(at least 6 inches below slab or crawl space.Pipe should be OFinal footine suberade must be adequately proofrolled to firm&unyielding conditions;the allowable bearing sloped towards approved discharge point so capacity of 2500 psf to be verified on-site by geotechnical engineer prior to the placing of rebars and forms that no backflow should occur into the pipe. OH Gravel Base of min.6"thk.,compacted to 95%or more,must be extended 6"beyond both sides of the footing OF The pipe must be enveloped by drain rocks consisted of/."minus washed gravel(free OFinal slab suberade must be adequately proofrolled to firm&unyielding conditions to be verified on-site by draining) geotechnical engineer OCapillary Break laver—min.6"thk,of free-draining 5/8-inch crushed rocks containing no more than 2%fines.Slab- Figure 2 Not to Scale on-grade floor should be placed directly on a capillary break layer in unheated areas eg.,garage,storage rooms Project—Ashley Sowle Residence O201,West Doggone Lane,Matlock,WA Vapor Barrier—a durable 10 to 15-mil.plastic membrane be placed over capillary break layer as a vapor retarder Project No.—23-649 O Styrofoam,as an additional layer can be placed between the slab and the capillary break layer where heated Pradft 00 ftklooft areas for provision of better insulation ✓�rrrrrwrrrr.�sraar.r Appendix A Soil Test Pit Lot TEST PIT-1 &2 Date of Excavation 03/04/2023 Surface Elev.Ft. Sod Soil Layer Descriptions USCS Sample Sample Laboratory Test Results Test Pit Width Test Pit 1ay1r Sod Nos. Depth Moist. -4200Sieve Depth Depth Class 2 ft Content 2 It Oft 0 ft 0-I ft Ol Top Soil- Blk.Silt w/roots& OL S-1 @ 0.5 it 42.5% (il organics,Wet,Soft - ---- 1 It 1 ft-3 ft Reddish Bra.,Silt(Alluvium) NIL S-2 (a 1.5 It 46 0/ ----& 2 It Wet,Soft Moderate signs of mottling Easy digging ' 3 ft ------- - 3 ft-8 ft O3 Olive Brn.,Very Gravelly Sand with GW S-3 'd,5 ft F -----------------------j ----------i 4 ft Cobbles&Boulders(Glacial Outwash) Wet,Med.Dense t--------- -----<------------- ----------- 5 ft Difficult digging because of severe cave-in Moderate signs of mottling noticed ' near the contact with alluvial deposit i -` 8 ft Visual-Manual Soil Identification by ASTM D2488-17 Field Logging by ASTM D5437121 Soil Sampling by ASTM D-75-19 Figure A-1 Not to Scale Notes- Project-Ashley Sowle Residence Test Pit Location See site plan Mottling Depth Moderate mottling signs in upper alluvium 201,West Doggone Lane,Matlock,WA Ground Cover Grass Water/Seepage Depth Groundwater at approximately 3 feet below grade Project No.-23-649 Test Pit Depth 8 g Cave in Depth Severe cave-in in glacial outwash ME=��►� � arrsrtw�rr.occur s rrrr Permeability PGEL82'!,',c—.-Q/neerinQ,ConsYltlnQ•Inspect>tOn KEY TO EXPLORATION LOG Sample Descriptions: Classification of soils in this report is based on visual field and laboratory observations, which include density/consistency, moisture condition,grain size,and plasticity estimates, and should not be construed to imply field or laboratory testing unless presented herein. Visual-manual classification methods in accordance with ASTM D-2488-17 were used as an identification guide. Where laboratory data available, soil classifications are in general accordance with ASTM D2487-17. Soil density/consistency in borings is related primarily to the Standard Penetration Resistance values.Soil density/consistency in test pits is estimated based on visual observations of excavations.Undrained shear strength='h unconfined compression strength. RELATIVE DENSITY OR CONSITENCY VS. SPT N-VALUE COARSE GRAINED SOILS:SAND OR GRAVEL FINE GRAINED SOILS:SILT OR CLAY Density N Approx.Relative Density Consistency N(Blows/ft.) Approx.Undrained Blows/ft. % Shear Strength s Very Loose 0-4 0- 15 Very Soft 0-2 <250 Loose 4-10 15—35 Soft 2-4 250—500 Medium Dense 10—30 35—65 Medium Stiff 4-8 500—1000 Dense 30—50 65—85 Stiff 8—15 1000—2000 Very Dense >50 85—100 Very Stiff 15—30 2000—4000 Hard >50 >4000 MOISTURE CONTENT DEFINITIONS Dry Absence of moisture,dusty,dry to the touch Moist Damp but no visible water Wet Visible free water,from below water table DESCRIPTIONS FOR SOIL STRATA AND STRUCTURE General Thickness or Spacing Structure General Attitude Parting <1/16 in Pocket Erratic,discontinuous deposit of limited extent Near Horizontal 0-10 deg Seam 1/16-1/2 in Lens Lenticular deposit Low Angle 10-45 deg Layer 'h-12 in Varved Alternating seams of silt and clay High Angle 45-80 deg Stratum >12 in Laminated Alternating seams Near Vertical 80-90 deg Scattered <1 per ft Interbedded Alternating Layers Numerous >1 per ft Fractured Breaks easily along definite fractured planes Slickensided Polished,glossy,fractured planes Blocky,Diced Breaks easily into small angular lumps Sheared Disturbed texture,mix of strengths Homogeneous Same color and appearance throughout