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geotech report.pdfP y- 4) �y; iw,d G Eu O TECH 13256 Northeast 20th Street. Suite 16 CONSULTANTS, INC. �� � 7 % Bellevue, 98005 (425)747-5618 FAX(425)747-8561 May 20, 2015 Classico Homes Inc. j'W JN 15193 PO Box 5012 j Lynnwood, Washington 98046 ilEW1OPMEal Attention: Joe Schmaus coiliv,43 via email. classicohomes@gmail.com Subject: Transmittal Letter — Geotechnical Engineering Study Proposed Two Single -Family Residences 532 — 71 Avenue South Edmonds, Washington Dear Mr. Schmaus: We are pleased to present this geotechnical engineering report for the two residences to be constructed in Edmonds, 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 criteria for foundations and retaining walls. This work was authorized by your acceptance of our proposal dated April 24, 2015. 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. Respectfully submitted, GEOTECH CONSULTANTS, INC. James H. Strange, P.E. Associate cc: Hagge Design /associates Inc. - Tom Hagge via email. hag et esign@msn, com TRC/JHS: at GEOTECH CONSULTANTS, INC. GEOTECHNICAL ENGINEERING STUDY Proposed Two Single -Family Residences 532 — 71 Avenue South Edmonds, Washington This report presents the findings and recommendations of our geotechnical engineering study for the site of the two proposed residences to be located in Edmonds. We were provided with a site plan, floor plans, and elevation views prepared by Hagge Design Associates Inc., dated April 29, 2015. Based on these plans, we understand that the development will consist of two single-family residences with two stories. The eastern residence Will have a partial basement that daylights toward the north. One residence will be located in the eastern portion of the site and another will be located in the southwestern portion. The north side of the residences will be close to the top of a steep, north -facing slope, and the west side of the southwest residence will be close to the top of a steep, west -facing slope. Both residences will have garages that will be accessed from a driveway along the south edge of the site, and the eastern residence will have an additional garage at its north end. The southwestern residence will have a deck north of the residence that will extend close to the steep northern slope. The southwest residence will be constructed close to the existing ground surface, as will the south half of the eastern residence. The garage and basement below the northern half of the east residence will have floor elevations 13 and 11 feet, respectively, below the floor of the main level. 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. SURFACE The Vicinity Map, Plate 1, illustrates the general location of the site in Edmonds. The site is bordered to the east by 711 Avenue South, and is otherwise surrounded with residences. We understand that a house formerly occupied the site but has been removed. The site appears to have been cleared, and is vegetated with sparse field grass. The ground surface in the southern half of the site has a high point near the center of the southern property line, and slopes gently down from the high point toward the west to east. Near the east edge of the site the slope steepens and declines to the adjacent roadway. A slope about 5 feet high near the southern property, line slopes steeply down from the neighboring property to the site. A concrete block wall faces about the west half of that steep slope, which was likely caused by an excavation to level the subject site. A short distance west of the southern half of the site the ground surface slopes down toward the west, at an inclination close to 2:1 (H:V). This slope has a height of about 15 to 20 feet. The ground surface in the northern half of the site slopes at an inclination of 1.51 (H:V) down toward the north. This slope is about 30 feet tall. A level pad on the east side of this slope is GEOTECH CONSULTANTS, INC. Classico Homes Inc. JN 15193 May 20, 2015 Page 2 accessible from the adjacent 71 Avenue South, and appears to have been graded by cutting into the slope and filling to the north. We did not observe `Indications of instability of the steep slopes within the site, and we unserstand that these slopes were granted a steep exemption based on previous study at the site (by others). SUBSURFACE The subsurface conditions were explored by excavating six test pits at the approximate locutions 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 pits were excavated on May 1, 2015 with a rubber -tracked excavator. A geotechnical engineer from our staff observed the excavation process, logged the test pits, and obtained representative samples of the soil encountered. "Grab" samples of selected subsurface soil were collected from the excavator bucket. The Test Pit Logs are attached to this report as Plates 3 through 5. Soil Conditions Test Pits 1, 4, 5, and 6 were located on or close to the steep northern slope. These exploration encountered similar conditions that consisted of sand with gravel that was loose or loose to medium -dense to depths of at least 6 feet. In Test Pits 1 and 5 the sand with gravel was medium -dense below 6 and 7.5 feet, respectively. The loose to medium -dense soil extended to the base of Test Pits 4 and 6 at depths of 6 and 6.5 feet. Test Pits 2 and 3 were located in the western portion of the site, more than 15 feet from the tops of steep slopes. These explorations revealed loose to medium -dense sand with gravel that became medium -dense 2.5 feet below the ground surface, and continued to the maximum explored depths of 4.5 and 6 feet. Groundwater Conditions No groundwater seepage was observed in the test pits. It should be noted that groundwater levels vary seasonally with rainfall and other factors, 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. The relative densities and moisture descriptions indicated on the test pit logs are interpretive descriptions based on the conditions observed, during excavation. The compaction of test pit backfill was not in the scope of our services. Loose soil will therefore be found in the area of the test pits. If this presents a problem, the backfill will need to be removed and replaced with structural fill during construction. GEOTECH CONSULTANTS, INC. Classico Homes Inc. May 20, 2015 at 41 M No !M11101k, GENERAL JN 15193 Page 3 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 pits conducted for this study encountered sand with gravel that was loose or loose to medium -dense on or close to steep slopes„ and was medium -dense at shallow depths in our explorations that were more than 15 feet from the slopes. We recommend that the northern sides of the residences and the west side of the southwest residence be supported by pipe piles driven to refusal. Decks that extend from the residences toward the adjacent steep slopes should also be supported with pipe piles and be tied back to the main foundations with continuous footings. This foundation system will provide vertical support of the structures by transferring vertical loads past the near -surface loose soil and into the underlying medium -dense soil, It will also avoid placing any loads from the foundations onto the slope. The remainder of the residence structural loads can be supported with conventional footing foundations, provided they bear on native, medium -dense native soil. Based on the soils revealed at the site, the soils at the core of the steep slopes are granular and medium -dense. Therefore, it is our opinion the site slopes are stable with respect to deep-seated slope failures. However, as with any steep slope in the Puget Bound area, the site slopes do have a potential for shallow slope failures. We expect that any failures would be shallow skin slides up to a few feet in depth. Such shallow soil movement will not impact the residences provided pipe piles are used to support the portions of the residences close to the steep slopes, as recommended above. To lower the potential for shallow soil movement, no fill soils should be placed between the proposed residences and the steep slopes, and stormwater runoff should not be directed onto steep slopes. Although the sandy soils that underlie the site have a fairly high permeability, in our opinion stormwater infiltration is not feasible for the project due to the steep slopes close to the proposed development. The erosion control measures needed during the site development will depend heavily on the weather conditions that are encountered. We anticipate that a silt fence will be needed around the downslope sides of any cleared areas. Existing pavements, ground cover, and landscaping should be left in place wherever possible to minimize the amount of exposed soil. locked 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. Out 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 GEOTECH CONSULTANTS, INC. Classico Homes Inc. JN 15193 May 20, 2015 Page 4 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. 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 soil profile within 100 feet of the ground surface is best represented by Site Class Type C (Stiff Site Class). As noted in the BSGS website, the mapped spectral acceleration value for a 0.2 second (Ss) and 1.0 second period (Si) equals 1.27g and 0.50g, respectively. The IBC states that a site-specific seismic study need not be performed provided that the peak ground acceleration be equal to SDS/2.5, where SDs is determined in ASCD 7. It is noted that SDS is equal to 2/3Sms. SMs equals Fe times Ss, where Fa is determined in Table 11.4-1. For our site, F. 1.0. The calculated peak ground acceleration that we utilized' for the seismic -related parameters (earth pressures and seismic surcharges) of this report equals 0.348. The site soils are not susceptible to seismic liquefaction because of their medium -dense nature and the absence of near -surface groundwater. CONVENTIONAL FOUNDATIONS The proposed structure can be supported on conventional continuous and - on undisturbed, medium -dense, native soil. We recommend that continuous and individual y •••- minimum widthsof _ • 16 inches, respectively. •••tings ••• 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 subg!rade!s must be cleaned of loose or Asturbed soil prior to pouring concrete. Depending upon site and equipment constraints, this may require removing the disturbed soil by hiand. An allowable bearing pressure of 2,000 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. Classico Homes Inc. JN 15193 May 20, 2015 Page 5 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 30 feet along a continuous footing with a uniform load. Lateral loads due to wired 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: Coefficient of Friction 0.45 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. PIPE PILES Three- or 4 -inch -diameter pipe piles driven with a 650- or 800- or 1,100 -pound hydraulic jackhammer to the following final penetration rates may be assigned the following compressive capacities, 3 inches 12 sec/inch 10 sec/inch6 sec/inch 6 tons 4 inches 20 sec/inch 15 sec/inch±7��10 sec/inch 10 tons Note: The refusal criteria indicated in the above table ,are valid only for pipe piles that are installed using a hydraulic impact hammer carried on leads that allow the hammer to sit on the top of the pile during driving. If the piles are installed by alternative methods, such as a vibratory hammer or a hammer that is hard -mounted to the installation machine, numerous load tests to 200 percent of the design capacity would be necessary to substantiate the allowable pile load, The appropriate number of load tests would need to be determined at the time the contractor and installiation method are chosen, As a minimum, Schedule 40 pipe should be used. The site soils should not be highly corrosive. Considering this, it is our opinion that standard "black" pipe can be used, and corrosion protection, such as galvanizing, is not necessary for the pipe piles. Smaller, 2 -inch -diameter pipe piles with less capacity can be used to support unroofed decks close to steep slopes, A 2-inch-diamieter pipe pile driven with a minimum 90 -pound jackhammer or a 140-piound Rhino hammer to a final penetration rate of 1 -inch or less for one minute of continuous GEOTECH CONSULTANTS, INC. Classico Homes Inc. JN 15193 May 20, 2015 Page 6 driving may be assigned an allowable compressive load of 2 tons. Extra -strong steel pipe should be used for these 2 -inch piles. We recommend a minimum pile length of 15 feet to achieve embedment into medium -dense, native soils. This is simply a minimum length needed to develop sufficient capacity. Our experience with installation of small -diameter pipe piles indicates that it is likely that they will be longer than this minimum length to reach refusal. Pile caps and grade beams should be used to transmit loads to the piles. Isolated pile caps should include a minimum of two piles to reduce the potential for eccentric loads being applied to the piles and any outboard deck supports on the slope side of the residences should be attached to the main foundation with nominally reinforced footings to restrain the pile tops laterally. Subsequent sections of pipe can be connected with slip or threaded couplers, or they can be welded together. If slip couplers are used, they should fit snugly into the pipe sections. This may require that shims be used or that beads of welding flux be applied to the outside of the coupler. Lateral loads due to wind or seismic forces may be resisted by passive earth pressure acting on the vertical, embedded portions of the foundation. For this condition, the foundation must be either poured directly against relatively level, undisturbed soil or be surrounded by level compacted fill. We recommend using a passive earth pressure of 250 pounds per cubic foot (pcf) for this resistance. If the ground in front of a foundation is loose or sloping (on the downslope side of the houses/decks), the passive earth pressure given above will not be appropriate. We recommend a safety factor of at least 1.5 for the foundation's resistance to lateral loading, when using the above ultimate passive value. Due to their small diameter, the lateral capacity of vertical pipe piles is relatively small. However, if lateral resistance in addition to passive soil resistance is required, we recommend driving battered piles in the same direction as the applied lateral load. The lateral capacity of a battered pile is equal to one-half of the lateral component of the allowable compressive load, with a maximum allowable lateral capacity of 1,000 pounds. The allowable vertical capacity of battered piles does not need to be reduced if the piles are battered steeper than 1:5 (Horizontal:Vertical). 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: 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 waif afwauld be added to the above active equivalent fluid pressure. GEOTECH CONSULTANTS, INC. Classico Homes Inc. JN 15193 May 20, 2015 Page 7 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 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, 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. Retajg6ga Wall Back frltl and IJLiate roo&xr 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 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 preventedfrom flowing toward walls or into the backfill zone. The compacted subgrade below pervious surfaces and any associated GEOTECH CONSULTANTS, INC. Classico Homes Inc. May 20, 2015 JN 15193 Page 6 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. 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 build up 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 competent 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. Classico Homes Inc. JN 15193 May 20, 2015 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. In the recent past, ACI (Section 4.1,6) recommended that a minimum of 4 inches of well -graded compactible 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-1643-96 "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), extend'ing continuously between the top and the bottom of GEOTECH CONSULTANTS, INC. Classico Homes Inc. JN 15193 May 20, 2015 Page 10 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). 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, Topsoil is often placed on regraded slopes to promote growth of vegetation. Proper preparation of the regraded surface, and use of appropriate topsoil is necessary to prevent the topsoil from sliding off the slope. This is most likely to occur following extended wet weather if a silty topsoil is used. On steeper slopes, it may be necessary to "track walk" the slope or cut small grooves across the slope prior to placing the topsoil. 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, () 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 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 -Om -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 GEOTECH CONSULTANTS, INC. Classico Homes Inc. JN 15193 May 20, 2015 Page 11 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 buildings 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 tightlined 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. 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 competent 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: 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. Classico Homes Inc. JN 15193 May 20, 2015 Page 12 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 pits 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 pits. 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. The recommendations presented in this report are directed toward the protection of only the proposed structures from damage due to slope movement. Predicting the future behavior of steep slopes and the potential effects of development on their stability is an inexact and imperfect science that is currently based mostly on the past behavior of slopes with similar characteristics. Landslides and soil movement can occur on steep slopes before, during, or after the development of property. At additional cost, we can provide recommendations for reducing the risk of future movement on the steep slopes, which could involve regrading the slopes or installing subsurface drains or costly retaining structures, The owner of any property containing, or located close to steep slopes must ultimately accept the possibility that some slope movement could occur, resulting in possible loss of ground or damage to the facilities around the proposed building residences. This report has been prepared for the exclusive use of Classico Homes Inc. 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 Oeotech 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 GEOTECH CONSULTANTS, INC. Classico Homes Inc. May 20, 2015 JN 15193 Page 13 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. The following plates are attached to complete this report: Plate 1 Vicinity Map Plate 2 Site Exploration Plan Plates 3 - 5 Test Pit Logs Plate 6 Typical Footing Drain Detail 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. TRC/JHS:at Respectfully submitted, GEOTECH CONSULTANTS, INC. James H. Strange, Jr., RE, Associate GEOTECH CONSULTANTS, INC. GEOT'ECH. CONSULTANTS, MC. (Source: M Owft Mapft64 2013) VICINITY MAP 532 - 7th Avenue South Edmonds, Washington Job No: Date: Plate: 15193 1 May 2015 TP -4 Nem 2 S TOR Y Rew NOE w T TP -3 CNIST&Y CAR AT FIR5T FLCCR AT 4d -PIM 4AAAM dw /-2—To T TP ILI— A,201-0- MOE ACCEM AND I UTUTY EABEPINT logo Lsg"n : (j Test Pit Location GEOTECH CONSULTANTS, INC. DWYeWAY tl AT LCUOR GARAGE r a 0 U) 67ACKEP IBLQ= RVANNO 10A. 1, rrp. 'hl SITE EXPLORMION PLAN 532 - 7th Avenue South Edmonds, Washington Job No: Vale: to: 15193 L May 2015 L No Scale 21 a MUNI E LOT 2 LOT TP -4 Nem 2 S TOR Y Rew NOE w T TP -3 CNIST&Y CAR AT FIR5T FLCCR AT 4d -PIM 4AAAM dw /-2—To T TP ILI— A,201-0- MOE ACCEM AND I UTUTY EABEPINT logo Lsg"n : (j Test Pit Location GEOTECH CONSULTANTS, INC. DWYeWAY tl AT LCUOR GARAGE r a 0 U) 67ACKEP IBLQ= RVANNO 10A. 1, rrp. 'hl SITE EXPLORMION PLAN 532 - 7th Avenue South Edmonds, Washington Job No: Vale: to: 15193 L May 2015 L No Scale 21 5 10 15 5 10 15 o 'ep TEST PIT 1 Description l opsoil over; FILL Gray"brown SAND with gravel, fine to coarse-grained, moist, loose (FILL) SW [.1 uray-brown SAND with gravel, fine to coarse-grained, moist, medium -dense * Test Pit terminated at 11 feet on May 1, 2015. * No groundwater observed during excavation. * Caving observed below 0 feet during excavation. 50 0 10- 0J s TEST PIT 2 Description i opsin over; Cray -brown SAND with gravel, fine to coarse-grained, moist, loose to medium -dense -becomes medium -dense * Test Pit terminated at 6 feet on May 1, 2015. * No groundwater observed during excavation. * No caving observed during excavation. GEOTLCH CONSULTANTS, INC. TEST PIT LOG 532 - 7th Avenue South Edmonds, Washington Job Date: Logged by: Plate: 15193 May 2015 1 TRC 3 5 10 15 M 10 15 oe ' Oxo S TEST PIT 3 Description opsoi over; Brown SAND with gravel, fine to coarse-grained, moist, loose to medium -dense -becomes medium -dense and gray -brown * Test Pit terminated at 4.5 feet on May 1, 2015. * No groundwater observed during excavation. * No caving observed during excavation. TEST PIT 4 Description 04",1 opsoi over; S, Brown SAND with gravel, fine to coarse-grained, moist, loose (Fill) -becomes loose to medium -dense and gray -brown (Possible Fill) r« * Test Pit terminated at 6 feet on May 1, 2015. * No groundwater observed during excavation. * Caving observed below 0 feet during excavation. GEOTECH CONSULTANT'S, INC. TEST PIT LOG 532 - 7th Avenue South Edmonds, Washington Job Date: Logged by: P/ete: 15193 May 2015 TRC ,4 5 10 15 b1 10 i6" TEST PIT 5 Description ............................... Topsoil over; Brown SAND with gravel, fine to coarse-grained, moist, loose to medium -dense (FI rown SAND with gravel, fine to coarse-grained, moist, loose to medium -dense * Test Pit terminated at 8 feet on May 1, 2015. * No groundwater observed during excavation. * No caving observed during excavation. �911-111 �. TEST PIT 6 Description Topsoil over; Brown SAND with gravel, fine to coarse-grained, moist, loose to medium -dense * Test Pit terminated at 6.5 feet on May 1, 2015. * No groundwater observed during excavation. * No caving observed during excavation. G EOT CH CONSULTANTS, INC. TEST PIT LOG 532 - 7th Avenue South Edmonds, Washington Job Date: Logged bY: Plate: 15193 May 2015 TRC 5 Slope backfill away from foundation. Provide surface drains where necessary. Backfill (See text for requirements) Nonwoven Geotextile Washed Rock Filter Fabric (7/8" min. size) Tightline Roof Drain (Do not connect to footing drain) Possible Slab O,� .�%��,¢id�cr Bop t? o a p w o 'w"?, o « C.Y rr ro � e��. *�, w� ��C? 6 a 4" min. 'o o"1 Vapor Retarder/Barrier and Capillary Break/Drainage Layer (Refer to Report text) 4" Perforated Hard PVC Pipe (Invert at least 6 inches below slab or crawl space. Slope to drain to appropriate outfall. Place holes downward.) 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. G OTECH CONSULTANTS, INC. FOOTING DRAIN DETAIL 532 - 7th Avenue South Edmonds, Washington Job Nd I Dale: Plate: 15193 Mav 2015 L 1 6