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HomeMy WebLinkAboutRS_Geotechnical_Report_190916_v1O OTECH CONSULTANTS, INC. Rhodes Architecture and Light 4218 Southwest Alaska Street Seattle, Washington 98116 Attention: Tim Rhodes via email: tim@rhodesarchitecture.com Subject: Transmittal Letter — Geotechnical Engineering Study Proposed Building Addition Project 1300 Bronson Way North Renton, Washington Dear Mr. Rhodes 2401 10th Aire E Seattle, Washington 98102 (425) 747-5618 April 26, 2019 JN 19117 Attached to this transmittal letter is our geotechnical engineering report for the proposed building addition project in Renton, Washington. The scope of our services consisted of exploring site surface and subsurface conditions, and then developing this report to provide recommendations for general earthwork and design considerations for foundations. This work was authorized by your acceptance of our proposal, P-10323, dated March 13, 2019. The attached report contains a discussion of the study and our recommendations. Please contact us if there are any questions regarding this report, or for further assistance during the design and construction phases of this project. DRW:kg Respectfully submitted, GEOTECH CONSULTANTS, INC. D. Robert Ward, P.E. Principal GEOTECH CONSULTANTS, INC. GEOTECHNICAL ENGINEERING STUDY Proposed Building Addition Project 1300 Bronson Way North Renton, Washington This report presents the findings and recommendations of our geotechnical engineering study for the site of the proposed building addition project to be located Renton, Washington Based on information provide to us by Rhodes Architecture and Light, we understand that an upper level addition is proposed above the existing building. If the scope of the project changes from what we have described above, we should be provided with revised plans in order to determine if modifications to the recommendations and conclusions of this report are warranted. SITE CONDITIONS SURFACE The Vicinity Map, Plate 1, illustrates the general location of the site in Renton, located just northwest of Interstate 405 and just north of the Cedar River. In general, the site and nearby area is nearly flat. It is essentially developed with three different coverages: a building is located on approximately the western half, a grass area is located on the northeastern corner, and paved areas are located on the east -central and southeastern portions of the site; the paved area at the southeastern portion is up to a few feet higher than the remainder of the site. In addition to these coverages, a paved "alley" exists between the building and the other areas. The existing building was apparently built in sections in 1947, 1962, and 1967. It has a slab -on - grade similar to the surround flat grade. The one-story building generally has CMU walls underlain with concrete foundations. It is believed that conventional footings underlie the foundations at shallow depth; we probed the ground adjacent to the northern side of the building, and it appears that the top -of -footing exists at a depth of about 8 inches on that side. We observed the condition of the building from its exterior, and numerous vertical cracks are evident in the CMU walls and the concrete foundation. SUBSURFACE The subsurface conditions were explored by drilling two test borings at the approximate locations shown on the Site Exploration Plan, Plate 2. Our exploration program was based on the proposed construction, anticipated subsurface conditions and those encountered during exploration, and the scope of work outlined in our proposal. The test borings were drilled on April 11, 2019 using a trailer -mounted, hollow -stem auger drill. Samples were taken at approximate 2.5 to 5 -foot intervals with a standard penetration sampler. This split -spoon sampler, which has a 2 -inch outside diameter, is driven into the soil with a 140 - pound hammer falling 30 inches. The number of blows required to advance the sampler a given distance is an indication of the soil density or consistency. A geotechnical engineer from our staff GEOTECH CONSULTANTS, INC. Rhodes Architecture and Light JN 19117 April 26, 2019 Page 2 observed the drilling process, logged the test borings, and obtained representative samples of the soil encountered. The Test Boring Logs are attached as Plates 3 through 5. Soil Conditions The upper, approximate 8 to 10 feet of soil revealed in the test borings was in a loose to medium -dense (mostly loose) condition. The soil varied from unengineered fill to native sandy silt. Below these soils, native sand and gravel soils were encountered that had varied gravel contents and were revealed to the maximum explored depth of approximately 52 feet. The sand and gravel varied in denseness from medium -dense to very dense; some of the denseness may also have been slightly "skewed' due to gravel being directly encountered at the sample tube of the test boring No obstructions were revealed by our explorations. However, debris, buried utilities, and old foundation and slab elements are commonly encountered on sites that have had previous development. Groundwater Conditions Groundwater was revealed in the sand and gravel at the time of the drilling in the range of 17 feet. In addition, we installed a monitoring well in the northern test boring; we returned to the site a few weeks after the test boring were installed, and again the groundwater was revealed at a depth of 17 feet. In addition, we obtained the logs of other test boring done on the site in the past, and the groundwater was revealed at a very similar depth. Therefore, groundwater at 17 feet appears to be quite accurate, and thus groundwater will likely be at or very near this level throughout the year. The stratification lines on the logs represent the approximate boundaries between soil types at the exploration locations. The actual transition between soil types may be gradual, and subsurface conditions can vary between exploration locations. The logs provide specific subsurface information only at the locations tested. Where a transition in soil type occurred between samples in the borings, the depth of the transition was interpreted. The relative densities and moisture descriptions indicated on the test boring logs are interpretive descriptions based on the conditions observed during excavation drilling. SEISMIC CONSIDERATIONS In accordance with the International Building Code (IBC), the site class within 100 feet of the ground surface is best represented by Site Class Type D (Stiff Soil). As noted in the USGS website, the mapped spectral acceleration value for a 0.2 second (Ss) and 1.0 second period (S1) equals 1.43g and 0.54g, respectively. The IBC and ASCE 7 require that the potential for liquefaction (soil strength loss) during an earthquake be evaluated for the peak ground acceleration of the Maximum Considered Earthquake (MCE), which has a probability of occurring once in 2,475 years (2 percent probability of occurring in a 50 -year period). The MCE peak ground acceleration adjusted for site class effects (FPGA) equals 0.59g. Seismic liquefaction can potentially occur in saturated, sandy soil that are in a less than dense condition. The test borings indicate that the sandy soil below the groundwater table (which GEOTECH CONSULTANTS, INC. Rhodes Architecture and Light JN 19117 April 26, 2019 Page 3 therefore is saturated) very from medium -dense to very dense. Only the medium -dense layers have a potential to liquefy during and MCE, and thus there is only a relatively low potential of seismic liquefaction at the site. Based on analysis of the effects of the liquefaction potential at the site, we have calculated that there is a potential for approximately 1 to 2.5 inches of ground settlement during an MCE. We believe the potential for lateral spreading of the ground during seismic liquefaction is negligible. Sections 1803.5 of the IBC and 11.8 of ASCE 7 require that other seismic -related geotechnical design parameters (seismic surcharge for retaining wall design and slope stability) include the potential effects of .the Design Earthquake. The peak ground acceleration for the Design Earthquake is defined in Section 11.2 of ASCE 7 as two-thirds (2/3) of the MCE peak ground acceleration, or 0.39g. CONCLUSIONS AND RECOMMENDATIONS GENERAL THIS SECTION CONTAINS A SUMMARY OF OUR STUDY AND FINDINGS FOR THE PURPOSES OF A GENERAL OVERVIEW ONLY. MORE SPECIFIC RECOMMENDATIONS AND CONCLUSIONS ARE CONTAINED IN THE REMAINDER OF THIS REPORT. ANY PARTY RELYING ON THIS REPORT SHOULD READ THE ENTIRE DOCUMENT. The test borings conducted for this study encountered approximately 8 to 10 feet of loose fill and native soils overlying native sand soils that varied from a medium -dense to very dense condition. The groundwater table at the site was revealed at a depth of 17 feet. As noted earlier, there is a relatively low potential for seismic liquefaction of the saturated sand soil below the groundwater table, with ground settlements due to liquefaction calculated to be between approximately 1 to 2.5 inches. With the information we currently have regarding the site and building, it appears very likely that the building is founded on shallow footings. Because of the existence of loose, near -surface soils, as revealed in the test borings, it is very likely that the shallow footings bear on the loose soil. Unfortunately, this soil possesses only a low capacity for bearing building loads. The cracking walls of the building are likely a result of this low bearing capacity of the loose soil. Unless explorations are done next to some of the existing footings that indicate the footings are buried much deeper than is currently believed, a low bearing capacity of 1,000 psf should be assumed for the existing footings. The 1000 psf bearing capacity should also be used for any future shallow footings. This bearing capacity should be used in the structural analysis of the existing building. The only way to increase this bearing capacity if to uncover some existing footings in the building to determine if the footings are buried much deeper than we currently believe (which is about 18 inches deep and founded on the loose soil). The structural analysis should also include a potential for up to approximately 1.5 inches of differential settlement between building columns to account for liquefaction settlement that could occur during an MCE event. If this low bearing capacity is not suitable for the foundation of the updated building, then using driven pipe piles to support building loads is the next alternative. We recommend that the building be founded on only one foundation type, be that footings or driven pipe piles. The two foundation types should not be intermixed for this building because of the potential of differential settlement and reactions to long-term settlement and a potential MCE event. GEOTECH CONSULTANTS, INC. Rhodes Architecture and Light JN 19117 April 26, 2019 Page 4 The drainage and/or waterproofing recommendations presented in this report are intended only to prevent active seepage from flowing through concrete walls or slabs. Even in the absence of active seepage into and beneath structures, water vapor can migrate through walls, slabs, and floors from the surrounding soil, and can even be transmitted from slabs and foundation walls due to the concrete curing process. Water vapor also results from occupant uses, such as cooking, cleaning, and bathing. Excessive water vapor trapped within structures can result in a variety of undesirable conditions, including, but not limited to, moisture problems with flooring systems, excessively moist air within occupied areas, and the growth of molds, fungi, and other biological organisms that may be harmful to the health of the occupants. The designer or architect must consider the potential vapor sources and likely occupant uses, and provide sufficient ventilation, either passive or mechanical, to prevent a build up of excessive water vapor within the planned structure. Geotech Consultants, Inc. should be allowed to review the final development plans to verify that the recommendations presented in this report are adequately addressed in the design. Such a plan review would be additional work beyond the current scope of work for this study, and it may include revisions to our recommendations to accommodate site, development, and geotechnical constraints that become more evident during the review process. CONVENTIONAL FOUNDATIONS As noted earlier, loose soil was revealed in the test borings to depths of approximately 8 to 10 feet. Because it appears that the existing footings are shallow, unless can be proved otherwise, a low bearing capacity of 1,000 psf should assumed for the existing footings. This bearing capacity should be assumed for any new footings used for the building. However, if any loose soil is revealed at the proposed subgrade We recommend that any new, continuous and individual spread footings have minimum widths of 16 and 24 inches, respectively. Exterior footings should also be bottomed at least 18 inches below the lowest adjacent finish ground surface for protection against frost and erosion. The local building codes should be reviewed to determine if different footing widths or embedment depths are required. Footing subgrades must be cleaned of loose or disturbed soil prior to pouring concrete. Depending upon site and equipment constraints, this may require removing the disturbed soil by hand. A one-third increase in 1000 psf design bearing capacity may be used when considering short-term wind or seismic loads. For the above design criteria, it is anticipated that the total post -construction settlement of footings founded on competent native soil, will be about one inch, with differential settlements on the order of one inch in a distance of 50 feet along a continuous footing with a uniform load. The General section of this report should also be reviewed for information on differential settlements that could occur between building columns during and MCE event. Lateral loads due to wind or seismic forces may be resisted by friction between the foundation and the bearing soil, or by passive earth pressure acting on the vertical, embedded portions of the foundation. For the latter condition, the foundation must be either poured directly against relatively level, undisturbed soil or be surrounded by level, well -compacted fill. GEOTECH CONSULTANTS, INC. Rhodes Architecture and Light JN 19117 April 26, 2019 Page 5 We recommend using the following ultimate values for the foundation's resistance to lateral loading: ULTIMATE PARAMETER VALUE Coefficient of Friction 0.40 Passive Earth Pressure 300 pcf Where: pcf is Pounds per Cubic Foot, and Passive Earth Pressure is computed using the Equivalent Fluid Density. If the ground in front of a foundation is loose or sloping, the passive earth pressure given above will not be appropriate. The above ultimate values for passive earth pressure and coefficient of friction do not include a safety factor. FOUNDATION AND RETAINING WALLS Retaining walls backfilled on only one side should be designed to resist the lateral earth pressures imposed by the soil they retain. The following recommended parameters are for walls that restrain level backfill: PARAMETER Active Earth Pressure * VALUE 35 pcf. Passive Earth Pressure 300 pcf Coefficient of Friction 0.40 Soil Unit Weight 120 pcf Where: pcf is Pounds per Cubic Foot, and Active and Passive Earth Pressures are computed using the Equivalent Fluid Pressures. * For a restrained wall that cannot deflect at least 0.002 times its height, a uniform lateral pressure equal to 10 psf times the height of the wall should be added to the above active equivalent fluid pressure. This applies only to walls with level backfill. The design values given above do not include the effects of any hydrostatic pressures behind the walls and assume that no surcharges, such as those caused by slopes, vehicles, or adjacent foundations will be exerted on the walls. If these conditions exist, those pressures should be added to the above lateral soil pressures. Where sloping backfill is desired behind the walls, we will need to be given the wall dimensions and the slope of the backfill in order to provide the appropriate design earth pressures. The surcharge due to traffic loads behind a wall can typically be accounted for by adding a uniform pressure equal to 2 feet multiplied by the above active fluid density. Heavy construction equipment should not be operated behind retaining and foundation walls within a distance equal to the height of a wall, unless the walls are designed for the additional lateral pressures resulting from the equipment. The values given above are to be used to design only permanent foundation and retaining walls that are to be backfilled, such as conventional walls constructed of reinforced concrete or masonry. It is not appropriate to use the above earth pressures and soil unit weight to back -calculate soil GEOTECH CONSULTANTS, INC. Rhodes Architecture and Light April 26, 2019 JN 19117 Page 6 strength parameters for design of other types of retaining walls, such as soldier pile, reinforced earth, modular or soil nail walls. We can assist with design of these types of walls, if desired. The passive pressure given is appropriate only for a shear key poured directly against undisturbed native soil, or for the depth of level, well -compacted fill placed in front of a retaining or foundation wall. The values for friction and passive resistance are ultimate values and do not include a safety factor. Restrained wall soil parameters should be utilized the wall and reinforcing design for a distance of 1.5 times the wall height from corners or bends in the walls, or from other points of restraint. This is intended to reduce the amount of cracking that can occur where a wall is restrained by a corner. Wall Pressures Due to Seismic Forces The surcharge wall loads that could be imposed by the design earthquake can be modeled by adding a uniform lateral pressure to the above -recommended active pressure. The recommended surcharge pressure is 7H pounds per square foot (psf), where H is the design retention height of the wall. Using this increased pressure, the safety factor against sliding and overturning can be reduced to 1.2 for the seismic analysis. Retaining Wall Backfill and Waterproofing Backfill placed behind retaining or foundation walls should be coarse, free -draining structural fill containing no organics. This backfill should contain no more than 5 percent silt or clay particles and have no gravel greater than 4 inches in diameter. The percentage of particles passing the No. 4 sieve should be between 25 and 70 percent. The purpose of these backfill requirements is to ensure that the design criteria for a retaining wall are not exceeded because of a build-up of hydrostatic pressure behind the wall. Also, subsurface drainage systems are not intended to handle large volumes of water from surface runoff. The top 12 to 18 inches of the backfill should consist of a compacted, relatively impermeable soil or topsoil, or the surface should be paved. The ground surface must also slope away from backfilled walls at one to 2 percent to reduce the potential for surface water to percolate into the backfill. Water percolating through pervious surfaces (pavers, gravel, permeable pavement, etc.) must also be prevented from flowing toward walls or into the backfill zone. Foundation drainage and waterproofing systems are not intended to handle large volumes of infiltrated water. The compacted subgrade below pervious surfaces and any associated drainage layer should therefore be sloped away. Alternatively, a membrane and subsurface collection system could be provided below a pervious surface. It is critical that the wall backfill be placed in lifts and be properly compacted, in order for the above -recommended design earth pressures to be appropriate. The recommended wall design criteria assume that the backfill will be well -compacted in lifts no thicker than 12 inches. The compaction of backfill near the walls should be accomplished with hand - operated equipment to prevent the walls from being overloaded by the higher soil forces that occur during compaction. The section entitled General Earthwork and Structural Fill contains additional recommendations regarding the placement and compaction of structural fill behind retaining and foundation walls. GEOTECH CONSULTANTS, INC. Rhodes Architecture and Light April 26, 2019 JN 19117 Page 7 The above recommendations are not intended to waterproof below -grade walls, or to prevent the formation of mold, mildew or fungi in interior spaces. Over time, the performance of subsurface drainage systems can degrade, subsurface groundwater flow patterns can change, and utilities can break or develop leaks. Therefore, waterproofing should be provided where future seepage through the walls is not acceptable. This typically includes limiting cold -joints and wall penetrations, and using bentonite panels or membranes on the outside of the walls. There are a variety of different waterproofing materials and systems, which should be installed by an experienced contractor familiar with the anticipated construction and subsurface conditions. Applying a thin coat of asphalt emulsion to the outside face of a wall is not considered waterproofing, and will only help to reduce moisture generated from water vapor or capillary action from seeping through the concrete. As with any project, adequate ventilation of basement and crawl space areas is important to prevent a buildup of water vapor that is commonly transmitted through concrete walls from the surrounding soil, even when seepage is not present. This is appropriate even when waterproofing is applied to the outside of foundation and retaining walls. We recommend that you contact an experienced envelope consultant if detailed recommendations or specifications related to waterproofing design, or minimizing the potential for infestations of mold and mildew are desired. The General, Slabs -On -Grade, and Drainage Considerations sections should be reviewed for additional recommendations related to the control of groundwater and excess water vapor for the anticipated construction. SLABS -ON -GRADE The building floors can be constructed as slabs -on -grade atop or on structural fill. The subgrade soil must be in a firm, non -yielding condition at the time of slab construction or underslab fill placement. Any soft areas encountered should be excavated and replaced with select, imported structural fill. Even where the exposed soils appear dry, water vapor will tend to naturally migrate upward through the soil to the new constructed space above it. This can affect moisture -sensitive flooring, cause imperfections or damage to the slab, or simply allow excessive water vapor into the space above the slab. All interior slabs -on -grade should be underlain by a capillary break drainage layer consisting of a minimum 4 -inch thickness of clean gravel or crushed rock that has a fines content (percent passing the No. 200 sieve) of less than 3 percent and a sand content (percent passing the No. 4 sieve) of no more than 10 percent. Pea gravel or crushed rock are typically used for this layer. As noted by the American Concrete Institute (ACI) in the Guides for Concrete Floor and Slab Structures, proper moisture protection is desirable immediately below any on -grade slab that will be covered by tile, wood, carpet, impermeable floor coverings, or any moisture -sensitive equipment or products. ACI recommends a minimum 10 -mil thickness vapor retarder for better durability and long term performance than is provided by 6 -mil plastic sheeting that has historically been used. A vapor retarder is defined as a material with a permeance of less than 0.3 perms, as determined by ASTM E 96. It is possible that concrete admixtures may meet this specification, although the manufacturers of the admixtures should be consulted. Where vapor retarders are used under slabs, their edges should overlap by at least 6 inches and be sealed with adhesive tape. The sheeting should extend to the foundation walls for maximum vapor protection. GEOTECH CONSULTANTS, INC. Rhodes Architecture and Light JN 19117 April 26, 2019 Page 8 If no potential for vapor passage through the slab is desired, a vapor barrier should be used. A vapor barrier, as defined by ACI, is a product with a water transmission rate of 0.01 perms when tested in accordance with ASTM E 96. Reinforced membranes having sealed overlaps can meet this requirement. We recommend that the contractor, the project materials engineer, and the owner discuss these issues and review recent ACI literature and ASTM E-1643 for installation guidelines and guidance on the use of the protection/blotter material. The General, Permanent Foundation and Retaining Walls, and Drainage Considerations sections should be reviewed for additional recommendations related to the control of groundwater and excess water vapor for the anticipated construction. EXCAVATIONS AND SLOPES No excavated slopes are anticipated other than for utility trenches. Temporary excavation slopes should not exceed the limits specified in local, state, and national government safety regulations. Also, temporary cuts should be planned to provide a minimum 2 to 3 feet of space for construction of foundations, walls, and drainage. Temporary cuts to a maximum overall depth of about 4 feet may be attempted vertically in unsaturated soil, if there are no indications of slope instability. However, vertical cuts should not be made near property boundaries, or existing utilities and structures. Based upon Washington Administrative Code (WAC) 296, Part N, the soil at the subject site would generally be classified as Type B. Therefore, temporary cut slopes greater than 4 feet in height should not be excavated at an inclination steeper than 1:1 (Horizontal:Vertical), extending continuously between the top and the bottom of a cut. The above -recommended temporary slope inclination is based on. the conditions exposed in our explorations, and on what has been successful at other sites with similar soil conditions. It is possible that variations in soil and groundwater conditions will require modifications to the inclination at which temporary slopes can stand. Temporary cuts are those that will remain unsupported for a relatively short duration to allow for the construction of foundations, retaining walls, or utilities. Temporary cut slopes should be protected with plastic sheeting during wet weather. It is also important that surface runoff be directed away from the top of temporary slope cuts. Cut slopes should also be backfilled or retained as soon as possible to reduce the potential for instability. Please note that sand or loose soil can cave suddenly and without warning. Excavation, foundation, and utility contractors should be made especially aware of this potential danger. These recommendations may need to be modified if the area near the potential cuts has been disturbed in the past by utility installation, or if settlement -sensitive utilities are located nearby. DRAINAGE CONSIDERATIONS Footing drains are only needed for projects where: (1)' crawl spaces or basements will be below a structure; (2) a slab is below the outside grade; or, (3) the outside grade does not slope downward from a building. Drains should also be placed at the base of all earth -retaining walls. These drains should be surrounded by at least 6 inches of 1 -inch -minus, washed rock that is encircled with non- woven, geotextile filter fabric (Mirafi 140N, Supac 4NP, or similar material). At its highest point, a perforated pipe invert should be at least 6 inches below the bottom of a slab floor or the level of a crawl space. The discharge pipe for subsurface drains should be sloped for flow to the outlet point. Roof and surface water drains must not discharge into the foundation drain system. GEOTECH CONSULTANTS, INC. Rhodes Architecture and Light JN 19117 April 26, 2019 Page 9 If the structure includes an elevator, it may be necessary to provide special drainage or waterproofing measures for the elevator pit. If no seepage into the elevator pit is acceptable, it will be necessary to provide a footing drain and free -draining wall backfill, and the walls should be waterproofed. If the footing drain will be too low to connect to the storm drainage system, then it will likely be necessary to install a pumped sump to discharge the collected water. Alternatively, the elevator pit could be designed to be entirely waterproof; this would include designing the pit structure to resist hydrostatic uplift pressures. As a minimum, a vapor retarder, as defined in the Slabs -On -Grade section, should be provided in any crawl space area to limit the transmission of water vapor from the underlying soils. Crawl space grades are sometimes left near the elevation of the bottom of the footings. As a result, an outlet drain is recommended for all crawl spaces to prevent an accumulation of any water that may bypass the footing drains. Providing a few inches of free draining gravel underneath the vapor retarder is also prudent to limit the potential for seepage to build up on top of the vapor retarder. GENERAL EARTHWORK AND STRUCTURAL FILL All building and pavement areas should be stripped of surface vegetation, topsoil, organic soil, and other deleterious material. It is important that existing foundations be removed before site development. The stripped or removed materials should not be mixed with any materials to be used as structural fill, but they could be used in non-structural areas, such as landscape beds. Structural fill is defined as any fill, including utility backfill, placed under, or close to, a building, or in other areas where the underlying soil needs to support loads. All structural fill should be placed in horizontal lifts with a moisture content at, or near, the optimum moisture content. The optimum moisture content is that moisture content that results in the greatest compacted dry density. The moisture content of fill is very important and must be closely controlled during the filling and compaction process. The allowable thickness of the fill lift will depend on the material type selected, the compaction equipment used, and the number of passes made to compact the lift. The loose lift thickness should not exceed 12 inches, but should be thinner if small, hand -operated compactors are used. We recommend testing structural fill as it is placed. If the fill is not sufficiently compacted, it should be recompacted before another lift is placed. This eliminates the need to remove the fill to achieve the required compaction. The following table presents recommended levels of relative compaction for compacted fill: LOCATION PLACEMENT COMPACTION Beneath footings, slabs 95% or walkways Filled slopes and behind 90% retaining walls 95% for upper 12 inches of Beneath pavements subgrade; 90% below that level Where: Minimum Relative Compaction is the ratio, expressed in percentages, of the compacted dry density to the maximum dry density, as determined in accordance with ASTM Test Designation D 1557-91 (Modified Proctor). GEOTECH CONSULTANTS, INC. Rhodes Architecture and Light JN 19117 April 26, 2019 Page 10 Structural fill that will be placed in wet weather should consist of a coarse, granular soil with a silt or clay content of no more than 5 percent. The percentage of particles passing the No. 200 sieve should be measured from that portion of soil passing the three -quarter -inch sieve. LIMITATIONS The conclusions and recommendations contained in this report are based on site conditions as they existed at the time of our exploration and assume that the soil and groundwater conditions encountered. in the test borings are representative of subsurface conditions on the site. If the subsurface conditions encountered during construction are significantly different from those observed in our explorations, we should be advised at once so that we can review these conditions and reconsider our recommendations where necessary. Unanticipated conditions are commonly encountered on construction sites and cannot be fully anticipated by merely taking samples in test borings. Subsurface conditions can also vary between exploration locations. Such unexpected conditions frequently require making additional expenditures to attain a properly constructed project. It is recommended that the owner consider providing a contingency fund to accommodate such potential extra costs and risks. This is a standard recommendation for all projects. This report has been prepared for the exclusive use of Rhodes Architecture and Light, the property owners, and their representatives, for specific application to this project and site. Our conclusions and recommendations are professional opinions derived in accordance with our understanding of current local standards of, practice, and within the scope of our services. No warranty is expressed or implied. The scope of our services does not include services related to construction safety precautions, and our recommendations are not intended to direct the contractor's methods, techniques, sequences, or procedures, except as specifically described in our report for consideration in design. Our services also do not include. assessing or minimizing the potential for biological hazards, such as mold, bacteria, mildew and fungi in either the existing or proposed site development. ADDITIONAL SERVICES In addition to reviewing the final plans, Geotech Consultants, Inc. should be retained to provide geotechnical consultation, testing, and observation services during construction. This is to confirm that subsurface conditions are consistent with those indicated by our exploration, to evaluate whether earthwork and foundation construction activities comply with the general intent of the recommendations presented in this report, and to provide suggestions for design changes in the event subsurface conditions differ from those anticipated prior to the start of construction. However, our work would not include the supervision or direction of the actual work of the contractor and its employees or agents. Also, job and site safety, and dimensional measurements, will be the responsibility of the contractor. During the construction phase, we will provide geotechnical observation and testing services when requested by you or your representatives. Please be aware that we can only document site work we actually observe. It is still the responsibility of your contractor or on-site construction team to verify that our recommendations are being followed, whether we are present at the site or not. GEOTECH CONSULTANTS, INC. Rhodes Architecture and Light JN 19117 April 26, 2019 Page 11 The following plates are attached to complete this report: Plate 1 Vicinity Map Plate 2 Site Exploration Plan Plates 3 - 5 Test Pit Boring Logs We appreciate the opportunity to be of service on this project. Please contact us if you have any questions, or if we can be of further assistance. Respectfully subMitted, GEOTECH C QjN�ULTANTS, INC. 04/26/19 D. Robert Ward, P.E. Principal GEOTECH CONSULTANTS, INC. GEOTECH CONSULTANTS, INC. (Source: Microsoft MapPoint, 2013) VICINITY MAP 1300 Bronson Way North Renton, Washington Job No: Date: 1 Plate: 19117 Apr. 2019 1 1 1 .. 'AMR, North 2nd Street --- .._ ................ Legend: (;� Test Boring Location SITE EXPLORATION PLAN GEOTECH 1300 Bronson Way North CONSULTANTS. INC. Renton, Washington Job No: Date: Plate: 19117 1 Apr. 2019 No Scale 1 2 5 10 15 20 25 30 e��r�` 0�5y�a�°��°°�5°��°°V 0 \` '0 6 � J5 4 13 32** 32** T 41 55 48 Description GEOTECH CONSULTANTS, INC. TEST BORING LOG 1300 Bronson Way North Renton, Washington Job Date: Logged by. Plate: 19117 1 Apr. 2019 1 ASM 1 3 Brown, sandy SILT with occasional sand seams, non -plastic, fine-grained, moist, loose ML 1 2M Brown, silty SAND, very fine-grained, moist, loose to medium -dense 3 SM - becomes gray -brown with rust mottling Rust SAND fine to -brown with occasional gravel, medium -grained, moist, medium -dense 4 SP - becomes gray -brown, gravelly, fine to coarse-grained - becomes dense 5 - becomes wet YloiYl•. ' �• �r Gray -brown, sandy, GRAVEL with trace silt and occasional sand seams, fine 6 �eI to coarse-grained, very moist to wet, medium -dense to dense MGW with 8" sand layer, fine to medium -grained, (hydrocarbon odor) 7•� 1�s• e s e n e • '� "►SIM -, � - i Y - ® - - - Imo. - Y i s - - - i - - s i - - e Y * Test Boring 1 is continued on Plate 4 GEOTECH CONSULTANTS, INC. TEST BORING LOG 1300 Bronson Way North Renton, Washington Job Date: Logged by. Plate: 19117 1 Apr. 2019 1 ASM 1 3 1 � 04 e�o����e 301 1 1Y, 40 R 50 61.1 60 BORING 1 (Continued) J5G Description 27 8 °is;ii stYr®IY 23 9 74 21 25 Gray -brown, sandy, GRAVEL with trace silt and occasional sand seams, fine to coarse-grained, very moist to wet, medium -dense to dense Rust -brown GRAVEL with sand, fine to coarse-grained, wet, medium -dense, 12 GP (no odor) * Test boring was terminated at 51.5 feet on April 11, 2019. * Groundwater was encountered below 18.8 feet during drilling. ** Blows may be overstated due to driving on cobbles. GE®TECH CONSULTANTS, INC. TEST BORING LOG 1300 Bronson Way North Renton, Washington Job Date: Logged by: Plate: 19117 Apr. 2019 1 ASM 4 Description nark -brown, silty SAND with gravel and organics, fine to medium -grained, moist, FILL loose (FILL) 30 55** um -grained, Rust -brown, sandy SILT, non -plastic, fine-grained, moist, loose Gray -brown, sandy GRAVEL with trace silt, fine to coarse-grained, moist, ,: ° ::` • medium -dense to dense -becomes rust -brown, slightly increased silt content 4 P°a•♦ i 5 *� :.OP - becomes gray -brown G;,! - becomes wet g ° - with occasional sand seams, medium -grained 7 9`°•° I4 IP • •il � a ♦P 8 becomes rust -brown 9 ;::;'z - becomes dark -rust -brown, grades to gravelly sand * Test boring was terminated at 31.5 feet on April 11, 2019. * Groundwater was encountered below 17.5 feet during drilling. ** Blows may be overstated due to driving on cobbles. GE®TECH CONSULTANTS, INC. TEST BORING LOG 1300 Bronson Way North Renton, Washington Job Date: Logged by: Plate: 19117 Apr. 2019 1 ASM 1 5 38 a 30 55** um -grained, Rust -brown, sandy SILT, non -plastic, fine-grained, moist, loose Gray -brown, sandy GRAVEL with trace silt, fine to coarse-grained, moist, ,: ° ::` • medium -dense to dense -becomes rust -brown, slightly increased silt content 4 P°a•♦ i 5 *� :.OP - becomes gray -brown G;,! - becomes wet g ° - with occasional sand seams, medium -grained 7 9`°•° I4 IP • •il � a ♦P 8 becomes rust -brown 9 ;::;'z - becomes dark -rust -brown, grades to gravelly sand * Test boring was terminated at 31.5 feet on April 11, 2019. * Groundwater was encountered below 17.5 feet during drilling. ** Blows may be overstated due to driving on cobbles. GE®TECH CONSULTANTS, INC. TEST BORING LOG 1300 Bronson Way North Renton, Washington Job Date: Logged by: Plate: 19117 Apr. 2019 1 ASM 1 5