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Geotech Report.pdfGE+OTECH CONSULTANTS, INC. Amit Sharma 1737A Northwest 60th Street Seattle, Washington 98107 via email. amit.sharma@docusign.com Subject: Geotechnical Engineering Study Proposed Single -Family Residence 15712 — 72nd Avenue West Edmonds, Washington 240 110th Ave E Seattle, Washington 98102 (425)747-5615 January 25, 2018 JN 18021 Our firm has prepared a geotechnical engineering study for the proposed Meadowview Estates short -plat project dated October 9, 2013. The proposed single-family residence that is under consideration in this report is on a lot located in the northeastern corner of the short -plat. This report relies on the information contained in the study for the short -plat property, and provides geotechnical engineering design parameters for the new residence proposed on the subject lot. We understand that a residence is proposed in the upper, eastern portion of the site, adjacent to the west side of 72nd Avenue West. The lot slopes gently to moderately down to the west from the street. It appears that the residence will have a main level near the street grade, and a basement level that daylights to the west. We understand that some retaining walls are proposed on the lot outside of the residence, likely on the more western, downslope portion. 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 the Meadowdale area of Edmonds. The subject lot is adjacent to the western, downslope edge of 72nd Avenue West. The site is mostly undeveloped, forested, and slopes gently to moderately downward to the west/southwest. However, an approximate 50 percent slope was graded on the western edge of the lot in the last few years in order to install a street within the Meadowdale Estates short -plat property; the paved street is now located at the base of this graded slope. This slope is covered with grass. We made a recent site visit, and we did not observe any indications of instability of the graded slope of natural slopes on the site. Per ECDC 23.80.020.A, based on soil conditions, any slope on the site that is greater than 15 percent is considered an Erosion Hazard Area. There are several areas that are steeper than 15 percent on the site. The only area on the site that is greater than 40 percent is on the western edge where the street excavation was made as noted above. However, per ECDC 23.80.020.13, these slope is considered to be a Landslide Hazard Area. GEOTECH CONSULTANTS, INC. Sharma January 25, 2018 JN 18021 Page 2 SUBSURFACE Several test pits and test borings were done on throughout the short -plat property in prior to our 2013 study. Two test pits were excavated on the subject lot, while a third test pit was just to the west. In addition, a test boring was just southwest of the lot. The approximate locations of these explorations, which were known as Test Pits 5, 6, and 7, and Test Boring 3, are shown on the Site Exploration Plan, Plate 1. The logs of these previous test pits and boring are attached to this report. The soil revealed in the upper portion of these explorations is native sand, with the first 2 to 3 feet being loose to medium -dense. Then the sand became dense — which was revealed to the bottom of the test pit of approximately 5 feet. In the nearby test boring, this dense sand was underlain at approximately 8 feet by medium -dense silty sand. At a depth of approximately 24 feet, again dense sand was revealed. The test boring was drilled to a maximum explored depth of approximately 26.5 feet. 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 If 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 pit and boring logs are interpretive descriptions based on the conditions observed during excavation and drilling. 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. Several test pits and borings were conducted on the short -plat property as noted in our 2013 study, with several on or near the subject lot. These explorations encountered dense sand soils at shallow depths. These soils are very competent for supporting building loads, and thus conventional footings that bear on this competent soil can be used as the foundation of the new residence. These soils also have high shear strength against slope instability. We understand that in addition to the residence, retaining walls are proposed on the site in order to provide some level areas on the site. The onsite sand soils are also very suitable to support the new retaining walls. Based on ECDC 23.80.070.A.2, "buffer requirements shall be ... consistent with recommendations provided in the geotechnical report to eliminate or minimize the risk of property damage, death, or injury resulting from landslides caused in whole or part by activities within the buffer area, based upon review of and concurrence with a critical areas report prepared by a qualified professional'. It is our professional opinion that no buffers are needed because: 1) most of the site slopes are less than 30 percent, the western slope that is about 50 percent was graded as part of the Meadowdale Estates development, and 3) the site soils are very competent at shallow depth. An "alteration" is needed per Edmonds Code for this project because of the lack of buffers (noted above) and because development is proposed on Erosion and Landslide Hazard Areas on the site. GEOTECH CONSULTANTS, INC. Sharma JN 18021 January 25, 2018 Page 3 Based on ECDC•23.80.060A, an alteration to a Landslide Hazard Area and associated buffer may occur for activities that: 1. Will not increase the threat of the geologic hazard to adjacent properties beyond predevelopment conditions; 2. Will not adversely affect other critical areas; 3. Are designed so that the hazard to the project is eliminated or mitigated to a level equal to or less that predevelopment conditions; and 4. Are certified as safe as designed and under anticipated conditions by a qualified engineer licensed in the State of Washington. In addition, ECDC 23.80.070.A.3 indicates that alterations of a Landslide Hazard Area and buffer may occur for activities for which a hazards analysis is submitted and certifies that: 1. The development will not increase surface water discharge or sedimentation to adjacent properties beyond predevelopment conditions; 2. The development will not decrease slope stability on adjacent properties; and 3. Such alterations will not adversely impact other critical areas. It is our professional opinion the alteration is appropriate because all of these criterial is met, provided the recommendations in this report are followed and the stormwater from the site is connected to the stormwater system of Meadowdale Estates (as is planned). We strongly believe that this development can be done safe and development will be as stable as the current conditions. It will not affect adjacent properties from a geotechnical engineering standpoint. As noted earlier, the area on the site are considered Erosion Hazard Areas per the ECDC. However, we point out that potential erosion hazards on sites such as this only occur only during construction when the existing vegetation is removed and prior to placing buildings, and hardscaping and landscaping features. Thus, during construction, erosion control measures are needed to mitigate the potential for erosion. For this project, we recommend that a silt fence will be needed around the downslope sides of any cleared areas. Existing ground cover should be left in place wherever possible to minimize the amount of exposed soil. Rocked staging areas and construction access roads should be provided to reduce the amount of soil or mud carried off the property by trucks and equipment. Wherever possible, the access roads should follow the alignment of planned pavements. Trucks should not be allowed to drive off of the rock -covered areas. Cut slopes and soil stockpiles should be covered with plastic during wet weather. Following clearing or rough grading, it may be necessary to mulch or hydroseed bare areas that will not be immediately covered with landscaping or an impervious surface. On most construction projects, it is necessary to periodically maintain or modify temporary erosion control measures to address specific site and weather conditions. 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 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 GEOTECH CONSULTANTS, INC. Sharma JN 18021 January 25, 2018 Page 4 mechanical, to prevent a buildup 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. We recommend including this report, in its entirety, in the project contract documents. This report should also be provided to any future property owners so they will be aware of our findings and recommendations. 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. We recommend including this report, in its entirety, in the project contract documents. This report should also be provided to any future property owners so they will be aware of our findings and recommendations. 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 Class). As noted in the USGS website, the mapped spectral acceleration value for a 0.2 second (S5) and 1.0 second period (S1) equals 1.33g and 0.52g, respectively. The site soils are not susceptible to seismic liquefaction during a large earthquake because of their dense nature and/or the absence of near -surface groundwater. CONVENTIONAL FOUNDATIONS The proposed residence and the retaining walls can be supported on conventional continuous and spread footings bearing on undisturbed, dense, native sand soil or medium -dense silty sand revealed below the dense sand. We recommend that 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. An allowable bearing pressure of 3,000 pounds per square foot (psf) is appropriate for footings supported on the competent native sand soils. A one-third increase in this design bearing pressure 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-half inch, with differential settlements on the order of one-half inch in a distance of 50 feet along a continuous footing with a uniform load. GEOTECH CONSULTANTS, INC. Sharma JN 18021 January 25, 2018 Page 5 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. We recommend using the following ultimate values for the foundation's resistance to lateral loading: ULTMATE VALUIE Coefficient of Friction 0.50 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. We recommend maintaining a safety factor of at least 1.5 for the foundation's resistance to lateral loading, when using the above ultimate values. 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: Active Earth Pressure * F357cf Passive Earth Pressure 300 Coefficient of Friction 0.50 Soil Unit Weight 130 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. 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 GEOTECH CONSULTANTS, INC. Sharma January 25, 2018 JN 18021 Page 6 constructed of reinforced concrete or masonry. It is not appropriate to use the above earth pressures and soil unit weight to back -calculate soil 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 for a distance of 1.5 times the wall height from corners or bends in the walls. 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 8H 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. If the native sand is used as backfill, a drainage composite similar to Miradrain 6000 should be placed against the backfilled retaining walls. The drainage composites should be hydraulically connected to the foundation drain system. The later section entitled Drainage Considerations should also be reviewed for recommendations related to subsurface drainage behind foundation and retaining walls. 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 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. 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 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. Sharma January 25, 2018 JN 18021 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 firm, native, non -organic sand 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 also notes that vapor retarders such as 6-mil plastic sheeting have been used in the past but are now recommending a minimum 10-mil thickness for better durability and long term performance. 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. 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 GEOTECH CONSULTANTS, INC. Sharma JN 18021 January 25, 2018 Page 8 accordance with ASTM E 96. Reinforced membranes having sealed overlaps can meet this requirement. In the recent past, ACI (Section 4.1.5) recommended that a minimum of 4 inches of well -graded compactable granular material, such as a 5/8-inch-minus crushed rock pavement base, be placed over the vapor retarder or barrier for their protection, and as a "blotter" to aid in the curing of the concrete slab. Sand was not recommended by ACI for this purpose. However, the use of material over the vapor retarder is controversial as noted in current ACI literature because of the potential that the protection/blotter material can become wet between the time of its placement and the installation of the slab. If the material is wet prior to slab placement, which is always possible in the Puget Sound area, it could cause vapor transmission to occur up through the slab in the future, essentially destroying the purpose of the vapor barrier retarder. Therefore, if there is a potential that the protection/blotter- material will become wet before the slab is installed, ACI now recommends that no protection/blotter material be used. However, ACI then recommends that, because there is a potential for slab curl due to the loss of the blotter material, joint spacing in the slab be reduced, a low shrinkage concrete mixture be used, and 'other measures" (steel reinforcing, etc.) be used. ASTM E-1643-98 "Standard Practice for Installation of Water Vapor Retarders Used in Contact with Earth or Granular Fill Under Concrete Slabs" generally agrees with the recent ACI literature. 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 Excavation slopes should not exceed the limits specified in local, state, and national government safety regulations. Temporary cuts to a 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 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. GEOTECH CONSULTANTS, INC. Sharma JN 18021 January 25, 2018 Page 9 All permanent cuts into native soil should be inclined no steeper than 2:1 (H:V). Compacted fill slopes should also not be constructed with an inclination greater than 2:1 (H:V). To reduce the potential for shallow sloughing, fill must be compacted to the face of these slopes. This can be accomplished by overbuilding the compacted fill and then trimming it back to its final inclination. Adequate compaction of the slope face is important for long-term stability and is necessary to prevent excessive settlement of patios, slabs, foundations, or other improvements that may be placed near the edge of the slope. Water should not be allowed to flow uncontrolled over the top of any temporary or permanent slope. All permanently exposed slopes should be seeded with an appropriate species of vegetation to reduce erosion and improve the stability of the surficial layer of soil. DRAINAGE CONSIDERATIONS Footing drains should be used 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. See Plate 2 for other recommendations regarding subsurface drains. 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 even a few inches of free draining gravel underneath the vapor retarder limits the potential for seepage to build up on top of the vapor retarder. The excavation and site should be graded so that surface water is directed off the site and away from the tops of slopes. Water should not be allowed to stand in any area where foundations, slabs, or pavements are to be constructed. Final site grading in areas adjacent to the residence should slope away at least 2 percent, except where the area is paved. Surface drains should be provided where necessary to prevent ponding of water behind foundation or retaining walls. A discussion of grading and drainage related to pervious surfaces near walls and structures is contained in the Foundation and Retaining Walls section. Water from roof, storm water, and foundation drains should not be discharged onto slopes; it should be tight lined to a suitable outfall located away from any slopes. GENERAL EARTHWORK AND STRUCTURAL FILL All building and pavement areas should be stripped of surface vegetation, topsoil, organic soil, and other deleterious material. 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. The onsite sand soils can be used as structural fill provided they do contain organics and are in a moist condition. GEOTECH CONSULTANTS, INC. Sharma JN 18021 January 25, 2018 Page 10 Structural fill is defined as any fill, including utility backfill, placed under, or close to, a building, behind permanent retaining or foundation walls, 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. We recommend testing the fill as it is placed. If the fill is not sufficiently compacted, it can be recompacted before another lift is placed. This eliminates the need to remove the fill to achieve the required compaction. Fills placed on sloping ground should be keyed into the competent soils. This is typically accomplished by placing and compacting the structural fill on level benches that are cut into the competent soils. The following table presents recommended relative compactions for structural fill: Beneath footings, slabs 95% or walkways Filled slopes and behind 90% retaininq 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). LIMITATIONS The conclusions and recommendations contained in this report are based on site conditions as they existed at the time of our explorations and assume that the soil and groundwater conditions encountered in earlier explorations on and near the subject site 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 explorations. 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 Amit Sharma and his 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 GEOTECH CONSULTANTS, INC. Sharma JN 18021 January 25, 2018 Page 11 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. We trust that this letter meets your immediate needs for the proposed development. Please contact us if we can be of further service. Respectfully submitted, GEOTECH CONSULTANTS, INC. 01/25/18 D. Robert Ward, P.E. Principal Attachments: Site Exploration — Plate 1 Footing Drain Detail — Plate 2 2013 Test Pits and Boring Logs DRW:kg GEOTECH CONSULTANTS, INC. ::.�!�','".ro"°�aaa' . "£':•'�'::'^,�+ .:., ° � ,may 8 .-s ;.'�. �•.e, �� '�� _ . . . . . ,^ . -. ,wamrm9%�aHawiyxi�a •� .1d a a � � �� rcf .� SM.o,nrwR S n r _ 0 a La p� r . ���� R��` „ 1, • ,'•,,. k, S2 0: - J n^\ >W h+� > 0�\ VJ cj 0-�11 Q c� r O W = -0 w r— W �I Un ro U U) O z co F) N Slope backfill away from foundation. Provide surface drains where necessary. Washed Roc (7/8" min. size) 4" min. Backfill (See text for requirements) Nonwoven Geotextile Filter Fabric v v v v v o O 0 0 0 �0'0' �0 c0 0 o Qo e o 0o Q 0 O O O o� off' 0 oL/� Tightline Roof Drain (Do not connect to footing drain) 11 Possible Slab 4" Perforated Hard PVC Pipe (Invert at least 6 inches below slab or crawl space. Slope to drain to appropriate outfall. Place holes downward.) �o0. 0C)JDapO�JO o �:.o_]JO PCQ;,2 n Vapor Retarder/Barrier and Capillary Break/Drainage Layer (Refer to Report text) NOTES: (1) In crawl spaces, provide an outlet drain to prevent buildup of water that bypasses the perimeter footing drains. (2) Refer to report text for additional drainage, waterproofing, and slab considerations. GEOTECH CONSULTANT'S, INC. FOOTING DRAIN DETAIL 15712 - 72nd Avenue West Edmonds, Washington Job No: Date: Plate: 18021 1 January 2018 1 :2] 5 10 y 10 TEST PIT 5 Topsoil over; Description Brown, slightly silty, gravelly SAND, few organics, loose to moist -becomes mostly gray, no organics, moist, dense * Test Pit terminated at 4.0 feet on July 3, 2013. * No groundwater seepage was observed during excavation. * No caving observed during excavation. JS0 0 TEST PIT 6 Description Gray, very gravelly SAND, coarse grained, medium dense -becomes dense * Test Pit terminated at 3.0 feet on July 3, 2013. * No groundwater seepage was observed during excavation. * No caving observed during excavation. GEOTECH CONSULTANTS, INC. TEST PIT LOG 15620 72nd Avenue West Edmonds, Washington Job Date: Logged by: Plate: 13245 1 July 2013 DRW 5 1i 10 TEST PIT 7 Topsoil over; Description Brown, slightly silty, gravelly SAND with organics, loose to medium dense -becomes dense, more gray, no organics * Test Pit terminated at 4.0 feet on July 3, 2013. * No groundwater seepage was observed during excavation. No caving observed during excavation. GEOTECH CONSULTANTS, INC. TEST PIT LOG 15620 72nd Avenue West Edmonds, Washington Job Date: 1 Logged by. P/ate: 13245 July 2013 DRW :J6 5 1 5014 2 24 15 [7 1 3 1 25 2017 1 - 4 1 - 20 - I BORING 3' Brown/mottled, silty SAND 'with-,,grav6l-veiy,.-wet,, loose -:---'---.'.-- -lens of silt Brown, gravelly SAND, some silt, coarse -grained; wet, dense' Gray, silty SAND, very fine-grained, wet, medium -dense -becomes less silty, moist -becomes wet -lens of silt . . . . . . . . . . 95 ray SAND, medium- rained, moist, dense 5 53 30 Test boring was terminated at 26.5 feet below grade on 1- 18-97, Groundwater seepage was encountered at 3' during drilling. 35 40 GEOTECH CONSULTANTS, INC. TEST BORING LOG 15620 - 76TH AVENUE WEST - - EDMONDS, WA Job NO: Date.' 1409g;94by; 177 13245 JAN 1997 W