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HomeMy WebLinkAbout17545 GES Report - DME Construction.pdfCYEOTEC11 cONsui.Ta,rrTs, INC. DME Construction 410 Bellevue Way Southeast Suite 205 Bellevue, Washington 98004 Attention: Kathy Kilton via email: kathy@dmeconstruction.com Subject: Transmittal Letter — Geotechnical Engineering Study Proposed New Napoli Residence 3111 Mountain View Avenue North Renton, Washington Dear Ms. Kilton: 2401 10th Ave E Seattle, WashIhAton 98102 (425) 747-5618 November 15, 2017 JN 17545 We are pleased to present this geotechnical engineering report for the proposed new Napoli residence to be constructed 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, stormwater infiltration considerations, and design criteria for foundations and retaining walls. This work was authorized by your acceptance of our proposal, P-9859, dated August 7, 2017. 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. cc: Giovanni Napoli via email: gnapoli@kiddermathews.com ASM/MRM:mw Respectfully submitted, GEOTECH CONSULTANTS, INC. Adam S. Moyer Geotechnical Engineer GEOTECH CONSULTANTS, INC. GEOTECHNICAL ENGINEERING STUDY Proposed New Napoli Residence 3111 Mountain View Avenue North Renton, Washington This report presents the findings and recommendations of our geotechnical engineering study for the site of the proposed new Napoli residence to be located in Renton. Development of the property is in the planning stage, and detailed plans were not available at the time of this report. Based on conversations with DME Construction, we understand the existing residence will be demolished and a new two-story single-family residence will be constructed in its place, albeit with a footprint that extends farther west than the existing house. We anticipate that the new residence may include at least a partial daylight basement. 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 CONDI TIONS SURFACE The Vicinity Map, Plate 1, illustrates the general location of the site along the southeast edge of Lake Washington in Renton. The long, narrow, subject site is generally rectangular in shape with 65 feet of frontage along Mountain View Avenue North on its eastern side and a depth of 373 to 393 feet along its northern and southern property lines respectively. However, only the eastern 175 feet of the property is above the surface of Lake Washington; this eastern half of the property will subsequently be referred to as the subject site. A one-story single-family residence is located near the center of subject site overlying a full basement that daylights to the west. A carport extends off the east side of the residence. Most of the ground surface between the residence and Mountain View Avenue North to the east is covered by a large concrete driveway; the concrete driveway wraps around the southern end of the residence, becoming a boat access ramp along the length of the southern property line extending down to Lake Washington. The remainder of the property is covered with a grass lawn. The eastern half of the subject site is essentially flat, matching the elevation of the adjacent right- of-way to the east. The ground surface of the western half of the site slopes moderately downwards towards Lake Washington to the west at a relatively uniform inclination. Based on the contour lines on King County's online GIS mapping tool, the change in elevation across the western half of the site is approximately 15 feet at an inclination of 17 percent down to the concrete bulkhead. The topography of the subject site is consistent with the neighboring parcels to the north and south along Lake Washington. There are no steep slopes on, or near, the site. Two-story single-family residences are located on the adjacent properties to the north and south. The residence to the north is offset 11 feet from the subject site and overlies a full basement that daylights to the west; an attached three -car garage extends off the eastern end of the residence near the elevation of Mountain View Avenue North with a significant offset from the subject site. The western third of the neighboring residence to the south has a full daylight basement at an 11 - foot offset from the shared property line with the subject site. However, based on our site GEOTECH CONSULTANTS, INC. DME Construction (Napoli Residence) A 17545 November 15, 2017 Page 2 observations and information from King County Assessments Department, the eastern two thirds of the residence has a lowest finished floor near the upper eastern site grade, with an offset of 7 feet from the property line. 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 borings were drilled on October 20, 2017 using a limited -access track -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 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 and 4. Soil Conditions Both borings conducted on the site encountered undisturbed dense silty sand with gravel at shallow depths below the existing ground surface. East of the existing residence, Boring 1 encountered the dense silty sand below a depth of 2.5 feet and dense sand below a depth of 8 feet. The underlying sand became very dense below 20 feet and extended to the maximum -explored depth of 26.5 feet. Boring 2, located west of the existing residence, encountered medium -dense, weathered, silty sand with gravel at 2.5 feet below a thin topsoil layer. The native silty sand became dense below 5 feet and very dense below a depth of 10 feet. The test boring was terminated in the very dense silty sand at a depth of 16.5 feet. 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 No groundwater seepage was observed in our explorations. The test borings were conducted following a dry summer, and left open for only a short time period. It should be noted that groundwater levels vary seasonally with rainfall and other factors. The soil became wet below a depth of approximately 20 feet in Boring 1. This is indicative of a seasonal water table. We anticipate that groundwater could be found in more permeable soil layers as well as perched above the dense silty sand. 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. 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 GEOTECH CONSULTANTS, INC. DME Construction (Napoli Residence) JN 17545 November 15, 2017 Page 3 on the test boring logs are interpretive descriptions based on the conditions observed during 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. The test borings conducted for this study encountered dense, undisturbed, silty sand at depths of 2.5 to 5 feet below the -existing ground surface on the eastern and western sides of the subject site respectively. Conventional shallow foundations bearing on these dense native soils are well-suited to support the proposed residence. Depending on the final design, some minor overexcavations may be necessary along the western end of the proposed residence to reach the competent underlying dense soils. The onsite silty sand soils are very moisture -sensitive and can easily become disturbed and softened from foot and equipment traffic when wet; we recommend footing subgrade soils be covered with several inches of clean crushed rock immediately after the excavation is completed to prevent the subgrade soils from becoming softened and to maintain the bearing capacity of the soils. The silty nature of the onsite soils also makes them very difficult to adequately compact if they are even 2 to 3 percent above their optimum moisture content. Therefore, we recommend any structural fill placed beneath foundations consist of large -aggregate, clean, crushed rock such as 2 - inch railroad ballast or 2- to 4 -inch quarry spalls. The onsite sand could be used for structural fill behind foundation walls, provided it can be placed at or near its optimum moisture content; this will likely not be feasible during the wetter winter months. It may be necessary to backfill portion of the existing basement to support new foundations. If so, it must first be verified that competent bearing soils have been reached. The placement and compaction of any structural fill beneath foundations should occur under the guidance of the project geotechnical engineer. The proposed residence is in the early development stages and no plans were provided to us; however, we anticipate the residence may overlie a daylight basement. The depth of a new basement floor and its offsets from the northern and southern property lines will be a large factor in the construction of the residence. We recommend temporary open cut slopes be inclined no steeper than a 1:1 (Horizontal:Vertical). If excavations cannot be maintained within the property lines, temporary excavation easements onto the neighboring properties will be required. If temporary easements cannot be obtained, temporary excavation shoring will be necessary. No un - shored excavations should extend below a 2:1 (H:V) line extended down from the base of the adjacent building footings. We can provide updated excavation and/or temporary excavation shoring recommendations once plans for the proposed residence have been developed. We anticipate that onsite infiltration of collected stormwater from impervious surfaces will be considered for the project. The silty sand revealed in our test borings has a very low permeability due to their high fines content and dense nature. As a result, there are no large or continuous pore spaces in the soil that can transmit water. This commonly results in groundwater becoming perched GEOTECH CONSULTANTS, INC. DME Construction (Napoli Residence) A 17545 November 15, 2017 Page 4 above the dense underlying silty sand in the Puget Sound Area. Considering this, it is our professional opinion that onsite infiltration of stormwater is not feasible for the subject site. The erosion control measures needed during the site development will depend heavily on the weather conditions that are encountered during the site work. The location of the site on the shore of Lake Washington will make proper erosion control implementation important to prevent adverse impacts to the lake. However, we have been associated with numerous waterfront projects that have avoided siltation of the lake and surrounding properties by exercising care and being pro- active with the maintenance and potential upgrading of the erosion control system through the entire construction process. One of the most important considerations, particularly during wet weather, is to immediately cover any bare soil to prevent accumulated water or runoff from the work area from becoming silty in the first place. Silty water cannot be discharged to the lake. A wire -backed silt fence bedded in compost, not native soil or sand, should be erected as close as possible to the planned work area, and the existing vegetation between the silt fence and the lake left in place. Rocked construction access and staging areas should be established wherever trucks will have to drive off of pavement, in order reduce the amount of soil or mud carried off the property by trucks and equipment. It will also be important to cap any existing drain lines found running toward the lake until excavation is completed. This includes old septic lines. This will reduce the potential for silty water finding an old pipe and flowing into the lake. Covering the base of the excavation with a layer of clean gravel or rock is also prudent to reduce the amount of mud and silty water generated. Utilities reaching between the house and the lake should not be installed during rainy weather, and any disturbed area caused by the utility installation should be minimized by using small equipment. Cut slopes and soil stockpiles should be covered with plastic during wet weather. Soil stockpiles should be minimized. Following rough grading, it may be necessary to mulch or hydroseed bare areas that will not be immediately covered with landscaping or an impervious surface. 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 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. As with any project that involves demolition of existing site buildings and/or extensive excavation and shoring, there is a potential risk of movement on surrounding properties. This can potentially translate into noticeable damage of surrounding on -grade elements, such as foundations and slabs. However, the demolition, shoring, and/or excavation work could just translate into perceived damage on adjacent properties. Unfortunately, it is becoming more and more common for adjacent property owners to make unsubstantiated damage claims on new projects that occur close to their GEOTECH CONSULTANTS, INC. DME Construction (Napoli Residence) A 17545 November 15, 2017 Page 5 developed lots. Therefore, we recommend making an extensive photographic and visual survey of the project vicinity, prior to demolition activities, installing shoring, and/or commencing with the excavation. This documents the condition of buildings, pavements, and utilities in the immediate vicinity of the site in order to avoid, and protect the owner from, unsubstantiated damage claims by surrounding property owners. Additionally, any adjacent structures should be monitored during construction to detect soil movements. To monitor their performance, we recommend establishing a series of survey reference points to measure any horizontal deflections of the shoring system. Control points should be established at a distance well away from the walls and slopes, and deflections from the reference points should be measured throughout construction by survey methods. 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 C (Very Dense Soil and Soft Rock). As noted in the USGS website, the mapped spectral acceleration value for a 0.2 second (SS) and 1.0 second period (Si) equals 1.45g and 0.55g, respectively. The IBC and ASCE 7 require that the potential for liquefaction (soil strength loss) 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 soils beneath the site are not susceptible to seismic liquefaction under the ground motions of the MCE because of their dense nature and the absence of near -surface groundwater. CONVENTIONAL FO UNDA TIONS The proposed structure can be supported on conventional continuous and spread footings bearing on undisturbed, dense, native soil. We recommend that continuous and individual spread footings have minimum widths of 12 and 16 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. Depending on the final site grades, overexcavation may be required below the footings to expose competent native soil. Unless lean concrete is used to fill an overexcavated hole, the overexcavation must be at least as wide at the bottom as the sum of the depth of the overexcavation and the footing width. For example, an overexcavation extending 2 feet below the bottom of a 2 -foot -wide footing must be at least 4 feet wide at the base of the excavation. If lean concrete is used, the overexcavation need only extend 6 inches beyond the edges of the footing. A typical detail for overexcavation beneath footings is attached as Plate 5. An allowable bearing pressure of 3,000 pounds per square foot (psf) is appropriate for footings supported on competent native soil. A one-third increase in this design bearing pressure may be GEOTECH CONSULTANTS, INC. DME Construction (Napoli Residence) JN 17545 November 15, 2017 Page 6 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 half-inch in a distance of 50 feet along a continuous footing with a uniform load. 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: PARAMETERI ULTIMATE VALUE 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: PARAMETER Active Earth Pressure * 35 pcf Passive Earth Pressure 300 pcf 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 GEOTECH CONSULTANTS, INC. DME Construction (Napoli Residence) A 17545 November 15, 2017 Page 7 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 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. Retaininq Wall Backfill and Waterproofin_g 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. Free -draining backfill or gravel should be used for the entire width of the backfill where seepage is encountered. For increased protection, drainage composites should be placed along cut slope faces, and the walls should be backfilled entirely with free -draining soil. 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. GEOTECH CONSULTANTS, INC. DME Construction (Napoli Residence) November 15, 2017 JN 17545 Page S 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. 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 non-organic native soil, 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. GEOTECH CONSULTANTS, INC. DME Construction (Napoli Residence) A 17545 November 15, 2017 Page 9 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 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 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 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. All permanent cuts into native soil should be inclined no steeper than 2:1 (H:V). Fill slopes should not be constructed with an inclination greater than 2.5:1 (H:V). To reduce the potential for shallow sloughing, fill must be compacted to the face of these slopes. This can be accomplished by GEOTECH CONSULTANTS, INC. DME Construction (Napoli Residence) JN 17545 November 15, 2017 Page 10 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. A typical footing drain detail is attached to this report as Plate 6. For the best long-term performance, perforated PVC pipe is recommended for all 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. No groundwater was observed during our field work. If seepage is encountered in an excavation, it should be drained from the site by directing it through drainage ditches, perforated pipe, or French drains, or by pumping it from sumps interconnected by shallow connector trenches at the bottom of the excavation. 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 a building 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. 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. GEOTECH CONSULTANTS, INC. DME Construction (Napoli Residence) JN 17545 November 15, 2017 Page 11 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. Fills placed on sloping ground should be keyed into the dense native soils. This is typically accomplished by placing and compacting the structural fill on level benches that are cut into the competent soils. 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. The following table presents recommended relative compactions for structural fill: LOCATION s i PLACEMENT COMPACTION Beneath slabs or 95% 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). Use of On -Site Soil If grading activities take place during wet weather, or when the silty, on-site soil is wet, site preparation costs may be higher because of delays due to rain and the potential need to import granular fill. The on-site soil is generally silty and therefore moisture sensitive. Grading operations will be difficult during wet weather, or when the moisture content of this soil exceeds the optimum moisture content. The moisture content of the silty, on-site soil must be at, or near, the optimum moisture content, as the soil cannot be consistently compacted to the required density when the moisture content is significantly greater than optimum. The moisture content of the on-site soil was generally above the estimated optimum moisture content at the time of our explorations. The on-site sand and silty sand underlying the topsoil could be used as structural fill, if grading operations are conducted during hot, dry weather, when drying the wetter soil by aeration is possible. During excessively dry weather, however, it may be necessary to add water to achieve the optimum moisture content. Moisture -sensitive soil may also be susceptible to excessive softening and "pumping" from construction equipment, or even foot traffic, when the moisture content is greater than the GEOTECH CONSULTANTS, INC. DME Construction (Napoli Residence) November 15, 2017 JN 17545 Page 12 optimum moisture content. It may be beneficial to protect subgrades with a layer of imported sand or crushed rock to limit disturbance from traffic. The General section should be reviewed for considerations related to the reuse of on-site soils. 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 DME Construction and its 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. DME Construction (Napoli Residence) November 15, 2017 The following plates are attached to complete this report: Plate 1 Vicinity Map Plate 2 Site Exploration Plan Plates 3 - 4 Test Boring Logs Plate 5 Typical Footing Overexcavation Plate 6 Typical Footing Drain Detail JN 17545 Page 13 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. ASM/MRM:mw Respectfully submitted, GEOTECH CONSULTANTS, INC. Ala m S. Moyer Geotechnical Engineer R. Ale S�pF WASJ�la, '�cP vISTF, SsjONAL V, //S 17 Marc R. McGinnis, P.E. Principal GEOTECH CONSULTANTS, INC. 1% (Source: Microsoft MapPoint, 2013) VICINITY MAP 3111 Mountain View Avenue North Renton, Washington Job No: Date: Plate: 17545 Nov. 2017 1 ifaWr i £ ...E € 4 j} I Lh L 5 '- Vi£ lk F € { € (Source: Microsoft MapPoint, 2013) VICINITY MAP 3111 Mountain View Avenue North Renton, Washington Job No: Date: Plate: 17545 Nov. 2017 1 i r 2 € { € t S' f � y 4 r g (Source: Microsoft MapPoint, 2013) VICINITY MAP 3111 Mountain View Avenue North Renton, Washington Job No: Date: Plate: 17545 Nov. 2017 1 Legend: Test Boring Location GEOTECH CONSULTANTS, INC. SITE EXPLORATION PLAN 3111 Mountain View Avenue North Renton, Washington Job No: Date: I Plate: 17545 Nov. 2017 No Scale 2 5 10 15 20 25 Kill C-1 � 00 CO 44 47 1 33 "I 53 65 BORING 1 Description Gray -brown silty SAND with gravel, fine-grained, moist, dense 4 Fs -ml: 2 • Test boring was terminated at 26.5 feet on October 20, 2017. • No groundwater was encountered during drilling. GEOTECH CONSULTANTS,, INC. TEST BORING LOG 3111 Mountain View Avenue North Renton, Washington Job Date: Logged by: I Plate: j 17545 Nov. 2017 ASM 3 10 15 20 25 K%] BORING 2 Description GEOTECH CONSULTANTS, INC. TEST BORING LOG 3111 Mountain View Avenue North Renton, Washington Job Date:Logged by: Plate: 17545 Nov. 2017 ASM 4 ad, Brown silty SAND with gravel and occasional roots, fine to medium -grain t moist to dry, medium -dense *7/4" 1 € € € € € *stopped driving sampler due to obstruction 41 2 k€€ -becomes gray -brown, fine-grained, dense sM1': 3 64 3 -becomes very dense 71 4 �: EEE E iE€E E * Test boring was terminated at 16.5 feet on October 20, 2017. * No groundwater was encountered during drilling. GEOTECH CONSULTANTS, INC. TEST BORING LOG 3111 Mountain View Avenue North Renton, Washington Job Date:Logged by: Plate: 17545 Nov. 2017 ASM 4 ad, Unsuitable Soils �0.o.C''a°° O C°, :O°°°0oD0.0°'CO°0c�0,°ao,'O° O'0 °o d00o oo�oD?'C6% oaoo0c C 0 > o, .0� o, .D61 o .0. o 0 D °° D° o D ° a..+_ x.0�°��.Q, °00 op°•0p� op°•o�� 00' ciD°•o"O o0°'0 o0D°•o ° oD o oa C'o 0 oQ 0'0 oQ 0'co0'0 0 oa D'o o -o�J D'c °o'° q o°°a'° q o°°o'° o °o'^ q o°°a°a ^ q o .00 . o> •�r7 . o. 'c'O . o, ° . > o• ° .DO •`�O ° o, ° .o a°0 .o � CI'0� ooo°Width of 'overexcavation00 'O,,°,:O� D O° n a v n° v O o.nv 0'0 ° D Structural Fill (refer to report for gradation and compaction requirements). See Note 2 for condition where lean concrete is used to backfill the overexcavation. Suitable Bearing Soil (Refer to report for description) verify by Geotechnical Engineer prior to placing Structural Fill. �pIIFF�- Width of Overexcavation = Footing Width (FW) + Depth of Overexcavation NOTES: 1. Refer to report text for additional overexcavation, foundation, and structural fill considerations. 2. Where lean concrete (minimum 1-1/2 sacks of cement per cubic yard) is used to backfill the overexcavation, the overexcavation must extend only 6 inches beyond the edges of the footing. GEOTECH CONSULTANTS, INC. TYPICAL FOOTING OVEREXCAVATION 3111 Mountain View Avenue North Renton, Washington Job No: Date: Plate: 17545 Nov. 2017 1 1 5 Slope backfill away from foundation. Provide surface drains where necessary. Backfill (See text for requirements) Washed Rock (7/8" min. size) 4" min. Nonwoven Geotextile Filter Fabric �0 0 0 0 0 T00O""oOo 0 0 0 0 O 0 0 0 0 oOoOo Oo0o 0 ' O — o_a Tightline Roof Drain (Do not connect to footing drain) Possible Slab _ aQ.�" p •�, p •Q a "° p .� ° "° p ,Q o p .a a p ,Q ° "° p ,Q o,°°' o p o.° ° o �odo0'o oppoQ 0'0 0 Qom 0'0 0 �o/J 0'0 o pp0Q 0a 0'0 0 �0 °�'° 0 + O o a 0 o O p O o o O.O. .0 J .0 0 0 0 0 0 O O O O O p .D .o .p •o °o .o • n D n •n• n ' � III �Illldllll 4" Perforated Hard PVC Pipe (Invert at least 6 inches below slab or crawl space. Slope to drain to appropriate outfall. Place holes downward.) 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 CONSULTAN'T'S, INC. FOOTING DRAIN DETAIL 3111 Mountain View Avenue North Renton, Washington Job No: Date: Plate: 17545 Nov. 2017 1 1 6