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HomeMy WebLinkAbout22-Geotech Report 03-07-2018associated earth sciences incorporated Associated Earth Sciences, Inc. 911 5th Avenue Kirkland, WA 98033 P (425) 827 7701 F (425) 827 5424 Subsurface Exploration, Geologic Hazard, and Geotechnical Engineering Report LIND AVENUE SW RESIDENCE Renton, Washington Prepared For: PLAN TO PERMIT, LLC Project No. 180037E001 March 7, 2018 ass0ciated earth sciences irrcrlil.rst'ated March 7,2Ot8 Project No. 180037E00L Plan to Permit, LLC 7233 Douglas Avenue SE Snoqualmie, WA 98065 Attention: Mr. George Steirer Subject:Subsurface Exploration, Geologic Hazard, and Geotechnical Engineering Report Lind Avenue SW Residence Parcel No. 184720-0005 Renton, Washington Dear Mr. Steirer: Associated Earth Sciences, lnc. (AESI) is pleased to present a copyof our referenced report. This report summarizes the results of our subsurface exploration, geologic hazard, and geotechnical engineering studies and offers geotechnical recommendations for the design and development of the proposed project. We have enjoyed working with you on this study and are confident that the recommendations presented in this report will aid in the successful completion of your project. lf you should have any questions, or if we can be of additional help to you, please do not hesitate to call. Sincerely, ASSOCIATED EARTH SC|ENCES, tNC. Kirkland, Washington Gary ozingo, 1.G.,G Engineeri GPM/ms - 180037E001-2 - Projects\20180034KE\WP Kirkland Office | 911 Fifth Avenue I Kirkland, WA 98033 P | 425.827.770IF| 425.827.5424 Everett Office | 29tt% Hewitt Avenue, Suite 2 | Everett, WA 98201 P | 425.259.0522F | 425.827.5424 Tacoma Office | 1552 Commerce Street, Suite 102 | Tacoma, WA 98402 P | 253.722.2992F | 253.722.2993 www.aesgeo.com SUBSURFACE EXPLORATION, GEOLOGIC HAZARD, AND GEOTECHNICAL ENGINEERING REPORT LIND AVENUE SW RESIDENCE Renton, Washington Prepared for: Plan to Permit, LLC 7233 Douglas Ave. SE Snoqualmie, Washington 98065 Prepared by: Associated Earth Sciences, Inc. 911 5th Avenue Kirkland, Washington 98033 425-827-7701 Fax: 425-827-5424 March 7, 2018 Project No. 180037E001 Subsurface Exploration, Geologic Hazard, and Lind Avenue SW Residence Geotechnical Engineering Report Renton, Washington Project and Site Conditions March 7, 2018 ASSOCIATED EARTH SCIENCES, INC. GPM/ms - 180037E001-2 - Projects\20180037\KE\WP Page 1 I. PROJECT AND SITE CONDITIONS 1.0 INTRODUCTION This report presents the results of our subsurface exploration, geologic hazard, and geotechnical engineering study for the proposed project. The location of the site is shown on the “Vicinity Map,” Figure 1, and the approximate locations of the explorations accomplished for this study are presented on the “Site and Exploration Plan,” Figure 2. Our recommendations are preliminary in that construction details have not been finalized at the time of this report. Once project plans become final, Associated Earth Sciences, Inc. (AESI) should review the plans to verify recommendations contained in our report are applicable for design and no modifications are needed. 1.1 Purpose and Scope The purpose of this study was to provide preliminary geotechnical recommendations to be used in the design and construction of the proposed project. Our study included a review of available geologic literature, completion of two exploration pits, and performance of geologic studies to assess the type, thickness, distribution, and physical properties of the subsurface materials and shallow groundwater conditions. Geotechnical engineering studies were also conducted to determine the type of suitable foundations, slab-on-grade support, and drainage considerations, and to provide recommendations for structural fill placement and compaction. This report summarizes our current fieldwork and offers development recommendations based on our present understanding of the project. 1.2 Authorization Written authorization to proceed with this study was provided by the client. Our work has been accomplished in general accordance with our proposal, dated January 25, 2018. This report has been prepared for the exclusive use of Plan to Permit, LLC, and their agents for specific application to this project. Within the limitations of scope, schedule, and budget, our services have been performed in accordance with generally accepted geotechnical engineering and engineering geology practices in effect in this area at the time our report was prepared. No other warranty, express or implied, is made. Subsurface Exploration, Geologic Hazard, and Lind Avenue SW Residence Geotechnical Engineering Report Renton, Washington Project and Site Conditions March 7, 2018 ASSOCIATED EARTH SCIENCES, INC. GPM/ms - 180037E001-2 - Projects\20180037\KE\WP Page 2 2.0 PROJECT AND SITE DESCRIPTION The subject site consists of a single-family residential parcel located on the east side of Lind Avenue SW, south of the intersection with South 134th Street in Renton, Washington. The property consists of a rectangular-shaped parcel (Parcel No. 184720-0005), is 0.1 acres in area, and is bounded by Lind Avenue SW to the west, a private access road to the south, a power transmission line easement to the east, and an easement for Seattle Public Utilities pipeline to the north. The property is a vacant lot vegetated with mature deciduous trees and shrubs. Overall relief across the sloping property is approximately 20 feet. Slope inclinations generally range from approximately 20 percent to 25 percent. A site-specific topographic survey provided by Plan to Permit, LLC, indicates that the steepest slope of 10 feet or higher has a gradient of less than 25 percent. Our understanding of the project is based on a conceptual site plan prepared by Plan to Permit, LLC, on January 10, 2018, which includes topographic survey data. We understand conceptual plans for development of the property include construction of a new 1- or 2-story single-family home with an attached garage and driveway. Other details regarding the design of the proposed new structure were not available at the time of preparation of this report. 3.0 SUBSURFACE EXPLORATION Our subsurface exploration program completed for this project consisted of advancing two exploration pits on February 22, 2018. The conclusions and recommendations presented in this report are based on the explorations completed for this study. Logs for the exploration pits are included in the Appendix. The locations and depths of the explorations were completed within site and budget constraints. 3.1 Exploration Pits The exploration pits were excavated with a track-mounted excavator that permitted direct, visual observation of the subsurface conditions. The exploration borings were continuously observed and logged by a geologist from our firm. All pits were backfilled immediately after examination and logging. Selected samples from the pits were transported to our laboratory for further visual classification and testing, as necessary. The exploration logs presented in the Appendix are based on the field logs, and review of the samples obtained. The approximate locations of the explorations are shown on the “Site and Exploration Plan,” Figure 2. Subsurface Exploration, Geologic Hazard, and Lind Avenue SW Residence Geotechnical Engineering Report Renton, Washington Project and Site Conditions March 7, 2018 ASSOCIATED EARTH SCIENCES, INC. GPM/ms - 180037E001-2 - Projects\20180037\KE\WP Page 3 4.0 SUBSURFACE CONDITIONS Subsurface conditions at the project site were inferred from the field explorations accomplished for this study, visual reconnaissance of the site, and review of applicable geologic literature. The following section presents more detailed subsurface information organized from the shallowest (youngest) to the deepest (oldest) sediment types. 4.1 Stratigraphy Duff/Topsoil A surficial layer of duff and organic topsoil was encountered at the location of each of the explorations to a depth of 8 to 10 inches. These materials are not considered suitable for structural support or for reuse in a structural fill. Fill Fill soils were not encountered at the exploration locations; however, they may be present in unexplored areas of the site, such as in existing utility trench areas or in previously graded areas. Due to their potentially variable condition, any existing fill soils are not suitable for foundation support. Tukwila Formation Underlying the duff/topsoil layer, sedimentary rock of the Tukwila Formation was encountered at shallow depths. Regionally, the Eocene-age Tukwila Formation consists predominantly of sandstone, conglomerate, siltstone, shale, and mudstone deposited across a broad volcanic upland. At this site, the Tukwila Formation consisted predominantly of moist, dense, oxidized brown, siltstone with lesser sandstone. The Tukwila Formation deposits extended to the bottom of the explorations, which were terminated at a depth of approximately 9 feet. The Tukwila Formation is considered suitable for support of structural loads when prepared as recommended in this report. Excavated Tukwila Formation deposits are suitable for reuse in structural fill applications if they are free of organics and other deleterious materials, and are within 1 to 2 percent of optimum moisture content for compaction purposes at the time of construction. Subsurface Exploration, Geologic Hazard, and Lind Avenue SW Residence Geotechnical Engineering Report Renton, Washington Project and Site Conditions March 7, 2018 ASSOCIATED EARTH SCIENCES, INC. GPM/ms - 180037E001-2 - Projects\20180037\KE\WP Page 4 4.2 Geologic Mapping Review of the regional geologic map titled The Geologic Map of the Renton Quadrangle, King County, Washington, 1965, (Booth, D.B., Waldron, H.H., U.S. Geological Survey, Scientific Investigations Map SIM-2855, scale 1:24,000) indicates that the area of the subject site is underlain by the upper member of the Tukwila Formation. Our interpretation of the materials encountered at the subject site is in general agreement with the regional geologic map. 4.3 Hydrology Groundwater was not encountered in our explorations, and the deposits encountered at the site typically allow for infiltration of surface waters. Due to the variable silt content, localized perched groundwater may be encountered. Groundwater conditions should be expected to vary in response to changes in season, weather, on- and off-site land use, and other factors. Subsurface Exploration, Geologic Hazard, and Lind Avenue SW Residence Geotechnical Engineering Report Renton, Washington Geologic Hazards and Mitigations March 7, 2018 ASSOCIATED EARTH SCIENCES, INC. GPM/ms - 180037E001-2 - Projects\20180037\KE\WP Page 5 II. GEOLOGIC HAZARDS AND MITIGATIONS The following discussion of potential geologic hazards is based on the geologic, slope, and ground and surface water conditions, as observed and discussed herein. The discussion will be limited to slope stability, seismic, and erosion issues. 5.0 LANDSLIDE HAZARDS AND MITIGATIONS It is our opinion that the risk of damage to the structure by landsliding is low due to gentle slope inclinations and the presence of medium dense to dense soils observed at relatively shallow depths beneath the surface of the site. No detailed slope stability analyses were completed as part of this study, and none are warranted, in our opinion. Based on our review of the City of Renton Critical Areas Regulations, and based on the soil types, and maximum slope gradient of less than 25 percent, it does not appear that the site contains areas that are considered to be governed by regulations associated with steep slopes, erosion hazards, and landslide hazards. 6.0 SEISMIC HAZARDS AND MITIGATION Earthquakes occur in the Puget Lowland with great regularity. The vast majority of these events are small and are usually not felt. However, large earthquakes do occur, as evidenced by the 1949, 7.2-magnitude event; the 1965, 6.5-magnitude event; and the 2001, 6.8-magnitude event. The 1949 earthquake appears to have been the largest in this area during recorded history. Evaluation of return rates indicates that an earthquake of the magnitude between 6.0 and 7.0 is likely within an approximate 25- to 40-year time interval in the Puget Sound area. Generally, there are four types of potential geologic hazards associated with large seismic events: 1) surficial ground rupture, 2) seismically induced landslides, 3) liquefaction, and 4) ground motion. The potential for each of these hazards to adversely impact the proposed project is discussed below. Subsurface Exploration, Geologic Hazard, and Lind Avenue SW Residence Geotechnical Engineering Report Renton, Washington Geologic Hazards and Mitigations March 7, 2018 ASSOCIATED EARTH SCIENCES, INC. GPM/ms - 180037E001-2 - Projects\20180037\KE\WP Page 6 6.1 Surficial Ground Rupture The project site is situated approximately 3.4 miles south of the Seattle Fault Zone. Recent studies by the U.S. Geological Survey (USGS) (e.g., Johnson et al., 1994, Origin and Evolution of the Seattle Fault and Seattle Basin, Washington, Geology, v. 22, p.71-74, and Johnson et al., 1999, Active Tectonics of the Seattle Fault and Central Puget Sound Washington - Implications for Earthquake Hazards, Geological Society of America Bulletin, July 1999, v. 111, n. 7, p. 1042-1053) have provided evidence of surficial ground rupture along a northern splay of the Seattle Fault. The recognition of this fault is relatively new and data pertaining to it are limited with the studies still ongoing. According to the USGS studies, the latest movement of this fault was about 1,100 years ago when about 20 feet of surficial displacement took place. This displacement can presently be seen in the form of raised, wave-cut beach terraces along Alki Point in West Seattle and Restoration Point at the south end of Bainbridge Island. The recurrence interval of movement along this fault system is still unknown, although it is hypothesized to be in excess of several thousand years. Due to the suspected long recurrence interval and the distance of the site from the Seattle Fault, the potential for surficial ground rupture is considered to be low during the expected life of the new additions, and no mitigation efforts beyond complying with the current (2015) International Building Code (IBC) are recommended. 6.2 Seismically Induced Landslides Given the observed subsurface conditions described in Section 4.0 and as discussed in Section 5.0, “Landslide Hazards and Mitigations,” it is our opinion that the risk of seismically induced landslides to the proposed structure is low. No quantitative slope stability analysis was completed as part of this study, and none is warranted, in our opinion. 6.3 Liquefaction Liquefaction is a process through which unconsolidated soil loses strength as a result of vibratory shaking, such as that which occurs during a seismic event. During normal conditions, the weight of the soil is supported by both grain-to-grain contacts and by the pressure within the pore spaces of the soil below the water table. Extreme vibratory shaking can disrupt the grain-to-grain contact, increase the pore pressure, and result in a decrease in soil shear strength. The soil is said to be liquefied when nearly all of the weight of the soil is supported by pore pressure alone. Liquefaction can result in deformation of the sediment and settlement of overlying structures. Areas most susceptible to liquefaction include those areas underlain by clean sand or silt with low relative densities accompanied by a shallow water table. Subsurface Exploration, Geologic Hazard, and Lind Avenue SW Residence Geotechnical Engineering Report Renton, Washington Geologic Hazards and Mitigations March 7, 2018 ASSOCIATED EARTH SCIENCES, INC. GPM/ms - 180037E001-2 - Projects\20180037\KE\WP Page 7 Based on subsurface conditions observed in our exploration borings site soils pose a very low risk of liquefaction-induced settlements due to the absence of groundwater, and relative high density of the Tukwila Formation bedrock. No quantitative liquefaction analysis was completed as part of this study, and none is warranted, in our opinion. 6.4 Ground Motion Structural design of the improvements should follow 2015 IBC standards using Site Class “D” as defined in Table 20.3-1 of American Society of Civil Engineers (ASCE) 7 - Minimum Design Loads for Buildings and Other Structures. 7.0 EROSION HAZARDS AND MITIGATION The following discussion addresses Washington State Department of Ecology (Ecology) erosion control regulations that will be applicable to the project. We anticipate that if the project complies with Washington State requirements, the development project will comply with the City and will not increase the risk of erosion or landslide to the site slopes or walls. A properly developed, constructed, and maintained erosion control plan consistent with the City’s standards and best management erosion control practices may be required for this project. It will be necessary to make adjustments and provide additional measures to the Temporary Erosion and Sedimentation Control (TESC) plan in order to improve its effectiveness. Ultimately, the success of the TESC plan depends on a proactive approach to project planning and contractor implementation and maintenance. The erosion potential of the site soils is moderate. Maintaining cover measures atop disturbed ground typically provides the greatest reduction to the potential generation of turbid runoff and sediment transport. During the local wet season (October 1st through March 31st), exposed soil should not remain uncovered for more than 2 days unless it is actively being worked. Ground-cover measures can include erosion control matting, plastic sheeting, straw mulch, crushed rock or recycled concrete, or mature hydroseed. Subsurface Exploration, Geologic Hazard, and Lind Avenue SW Residence Geotechnical Engineering Report Renton, Washington Geologic Hazards and Mitigations March 7, 2018 ASSOCIATED EARTH SCIENCES, INC. GPM/ms - 180037E001-2 - Projects\20180037\KE\WP Page 8 7.1 Erosion Hazard Mitigation Project planning and construction should follow local standards of practice with respect to TESC. Best management practices (BMPs) should include, but not be limited to: • Provide storm drain inlet protection; • Provide silt fencing along the perimeter of the disturbed areas; • Route surface water away from work areas; • Route surface water away from the moderate to steep-sloped areas and walls; • Avoid clearing vegetation on any site slopes where possible; • Stripped areas not actively being worked on should have cover measures; • All surface water conveyance should have check dams and be “armored” with crushed rock or other ground-cover product; • Keep staging areas and travel areas clean and free of track-out; • Provide rocked construction or paved construction entrance; • Cover work areas and stockpiled soils when not in use; • Complete earthwork during dry weather and site conditions, if possible; and • No stormwater shall be allowed to discharge on or near the slope. Subsurface Exploration, Geologic Hazard, and Lind Avenue SW Residence Geotechnical Engineering Report Renton, Washington Design Recommendations March 7, 2018 ASSOCIATED EARTH SCIENCES, INC. GPM/ms - 180037E001-2 - Projects\20180037\KE\WP Page 9 III. DESIGN RECOMMENDATIONS 8.0 INTRODUCTION Our exploration indicates that, from a geotechnical standpoint, the parcel is suitable for construction of the proposed building provided the recommendations contained herein are properly followed. The foundation-bearing stratum is relatively shallow, and conventional spread footing foundations may be utilized. 9.0 SITE PREPARATION 9.1 Clearing and Stripping Following demolition of any existing structures, all topsoil, vegetation, and any other deleterious materials should be stripped from the proposed building and pavement areas. Areas where loose surficial soils exist due to grubbing and demolition operations should be considered as fill to the depth of disturbance and treated as subsequently recommended for structural fill placement. Any existing fill soils located below the building area should be stripped down to the underlying, medium dense to dense, natural bedrock deposits. 9.2 Temporary and Permanent Cut Slopes In our opinion, stable construction slopes should be the responsibility of the contractor and should be determined during construction based on the local conditions encountered at that time. For planning purposes, we anticipate that temporary, unsupported cut slopes within fill deposits or highly weathered bedrock can be made at a maximum slope of 1.5H:1V (Horizontal:Vertical), and 1H:1V within dense, hard, less weathered bedrock deposits. Flatter inclinations may be recommended in areas of seepage. As is typical with earthwork operations, some sloughing and raveling may occur, and cut slopes may have to be adjusted in the field. In addition, WISHA/OSHA regulations should be followed at all times. Permanent cut slopes should not exceed an inclination of 2H:1V. 9.3 Site Disturbance The surficial sediments and highly weathered bedrock underlying the site contain a high percentage of fine-grained material. When disturbed, these materials can be highly Subsurface Exploration, Geologic Hazard, and Lind Avenue SW Residence Geotechnical Engineering Report Renton, Washington Design Recommendations March 7, 2018 ASSOCIATED EARTH SCIENCES, INC. GPM/ms - 180037E001-2 - Projects\20180037\KE\WP Page 10 moisture-sensitive and subject to disturbance when wet. The contractor must use care during site preparation and excavation operations so that the underlying soils are not softened. If disturbance occurs, the softened soils should be removed and the area brought to grade with structural fill. Consideration should be given to protecting access and staging areas with an appropriate section of crushed rock or asphalt treated base (ATB). If crushed rock is considered for the access and staging areas, it should be underlain by engineering stabilization fabric (such as TenCate Mirafi 500X or approved equivalent) to reduce the potential of fine-grained materials pumping up through the rock during wet weather and turning the area to mud. The fabric will also aid in supporting construction equipment, thus reducing the amount of crushed rock required. We recommend that at least 10 inches of rock be placed over the fabric. Crushed rock used for access and staging areas should be of at least 2-inch size. 10.0 STRUCTURAL FILL Placement of structural fill may be necessary to establish desired grades in some areas or to backfill utility trenches or around foundations. All references to structural fill in this report refer to subgrade preparation, fill type, and placement and compaction of materials as discussed in this section. If a percentage of compaction is specified under another section of this report, the value given in that section should be used. 10.1 Subgrade Compaction After overexcavation/stripping has been performed to the satisfaction of the geotechnical engineer/engineering geologist, the upper 12 inches of exposed ground should be recompacted to a firm and unyielding condition. If the subgrade contains too much moisture, suitable recompaction may be difficult or impossible to attain and should probably not be attempted. In lieu of recompaction, the area to receive fill should be blanketed with washed rock or quarry spalls to act as a capillary break between the new fill and the wet subgrade. Where the exposed ground remains soft and further overexcavation is impractical, placement of an engineering stabilization fabric may be necessary to prevent contamination of the free-draining layer by silt migration from below. After recompaction of the exposed ground is tested and approved, or a free-draining rock course is laid, structural fill may be placed to attain desired grades. Subsurface Exploration, Geologic Hazard, and Lind Avenue SW Residence Geotechnical Engineering Report Renton, Washington Design Recommendations March 7, 2018 ASSOCIATED EARTH SCIENCES, INC. GPM/ms - 180037E001-2 - Projects\20180037\KE\WP Page 11 10.2 Structural Fill Compaction Structural fill is defined as non-organic soil, acceptable to the geotechnical engineer, placed in maximum 8-inch loose lifts, with each lift being compacted to at least 95 percent of the modified Proctor maximum dry density using American Society for Testing and Materials (ASTM) D-1557 as the standard. Utility trench backfill should be placed and compacted in accordance with applicable municipal codes and standards. The top of the compacted fill should extend horizontally a minimum distance of 3 feet beyond footings or pavement edges before sloping down at an angle no steeper than 2H:1V. Fill slopes should either be overbuilt and trimmed back to final grade or surface-compacted to the specified density. 10.3 Moisture-Sensitive Fill Soils in which the amount of fine-grained material (smaller than No. 200 sieve) is greater than approximately 5 percent (measured on the minus No. 4 sieve size) should be considered moisture-sensitive. Use of moisture-sensitive soil in structural fills should be limited to favorable dry weather conditions. The on-site bedrock deposits are suitable for use as structural fill provided they are free of roots or other deleterious materials and have a moisture content suitable for achieving the specified compaction. These materials contain a high percentage of fine-grained material and can be highly moisture-sensitive. If the moisture content of the on-site soils are outside of optimum at the time of construction, they should be moisture-conditioned prior to their use as structural fill. For soils that are too dry, this would involve adding water to the soil. For soils that are too wet, such moisture-conditioning could consist of spreading out and aerating the soil during periods of warm, dry weather. Construction equipment traversing the site when the silty soils are very moist or wet can cause considerable disturbance. If fill is placed during wet weather, or if proper compaction cannot be attained, a select import material consisting of a clean, free-draining gravel and/or sand should be used. Free-draining fill consists of non-organic soil with the amount of fine-grained material limited to 5 percent by weight when measured on the minus No. 4 sieve fraction. 10.4 Structural Fill Testing The contractor should note that any proposed fill soils must be evaluated by AESI prior to their use in fills. This would require that we have a sample of the material at least 3 business days in advance to perform a Proctor test and determine its field compaction standard. Subsurface Exploration, Geologic Hazard, and Lind Avenue SW Residence Geotechnical Engineering Report Renton, Washington Design Recommendations March 7, 2018 ASSOCIATED EARTH SCIENCES, INC. GPM/ms - 180037E001-2 - Projects\20180037\KE\WP Page 12 A representative from our firm should inspect the stripped subgrade and be present during placement of structural fill to observe the work and perform a representative number of in-place density tests. In this way, the adequacy of the earthwork may be evaluated as filling progresses and any problem areas may be corrected at that time. It is important to understand that taking random compaction tests on a part-time basis will not assure uniformity or acceptable performance of a fill. As such, we are available to aid the owner in developing a suitable monitoring and testing frequency. 11.0 FOUNDATIONS 11.1 Allowable Soil Bearing Pressure Spread footings may be used for building support when founded either directly on the medium dense to dense bedrock strata, or on structural fill placed over these materials. We recommend that an allowable foundation soil bearing pressure of 2,500 pounds per square foot (psf) be used for design purposes, including both dead and live loads. An increase in the allowable bearing pressure of one-third may be used for short-term wind or seismic loading. If structural fill is placed below footing areas, the structural fill should extend horizontally beyond the footing edges a distance equal to or greater than the thickness of the fill. 11.2 Footing Depths Perimeter footings for the proposed buildings should be buried a minimum of 18 inches into the surrounding soil for frost protection. No minimum burial depth is required for interior footings; however, all footings must penetrate to the prescribed stratum, and no footings should be founded in or above loose, organic, or existing fill soils. 11.3 Footings Adjacent to Cuts The area bounded by lines extending downward at 1H:1V from any footing must not intersect another footing or intersect a filled area that has not been compacted to at least 95 percent of ASTM D-1557. In addition, a 1.5H:1V line extending down from any footing must not daylight because sloughing or raveling may eventually undermine the footing. Thus, footings should not be placed near the edges of steps or cuts in the bearing soils. Subsurface Exploration, Geologic Hazard, and Lind Avenue SW Residence Geotechnical Engineering Report Renton, Washington Design Recommendations March 7, 2018 ASSOCIATED EARTH SCIENCES, INC. GPM/ms - 180037E001-2 - Projects\20180037\KE\WP Page 13 11.4 Footing Settlement Anticipated settlement of footings founded as described above should be on the order of 1 inch or less. However, disturbed soil not removed from footing excavations prior to footing placement could result in increased settlements. 11.5 Footing Subgrade Bearing Verification All footing areas should be observed by AESI prior to placing concrete to verify that the exposed soils can support the design foundation bearing pressure and that construction conforms with the recommendations in this report. Foundation bearing verification may also be required by the City of Renton. 11.6 Foundation Drainage Perimeter footing drains should be provided as discussed under the “Drainage Considerations” section of this report. 12.0 LATERAL WALL PRESSURES All backfill behind walls or around foundations should be placed following our recommendations for structural fill and as described in this section of the report. Horizontally backfilled walls that are free to yield laterally at least 0.1 percent of their height may be designed using an equivalent fluid equal to 35 pounds per cubic foot (pcf). Fully restrained, horizontally backfilled, rigid walls that cannot yield should be designed for an equivalent fluid of 55 pcf. Walls that retain sloping backfill at a maximum angle of 50 percent should be designed for 45 pcf for yielding conditions and 65 pcf for restrained conditions. If parking areas or driveways are adjacent to walls, a surcharge equivalent to 2 feet of retained soil should be added to the wall height in determining lateral design forces. 12.1 Wall Backfill The lateral pressures presented above are based on the conditions of a uniform backfill consisting of imported sand and gravel compacted to 90 to 95 percent of ASTM D-1557. A higher degree of compaction is not recommended, as this will increase the pressure acting on the walls. A lower compaction may result in unacceptable settlement behind the walls. Thus, the compaction level is critical and must be tested by our firm during placement. Subsurface Exploration, Geologic Hazard, and Lind Avenue SW Residence Geotechnical Engineering Report Renton, Washington Design Recommendations March 7, 2018 ASSOCIATED EARTH SCIENCES, INC. GPM/ms - 180037E001-2 - Projects\20180037\KE\WP Page 14 12.2 Wall Drainage It is imperative that proper drainage be provided so that hydrostatic pressures do not develop against the walls. This would involve installation of a minimum 1-foot-wide blanket drain for the full wall height using imported, washed gravel against the walls. 12.3 Passive Resistance and Friction Factor Lateral loads can be resisted by friction between the foundation and the supporting natural deposits or structural fill soils, or by passive earth pressure acting on the buried portions of the foundations. The foundations must be backfilled with compacted structural fill to achieve the passive resistance provided below. We recommend the following design parameters: • Passive equivalent fluid = 300 pcf • Coefficient of friction = 0.35 The above values are allowable. 12.4 Seismic Surcharge As required by the 2015 IBC, retaining wall design should include a seismic surcharge pressure in addition to the equivalent fluid pressures presented above. We recommend a seismic surcharge pressure of 8H and 10H psf where H is the wall height in feet for the active and at-rest loading conditions, respectively. The seismic surcharge should be modeled as a rectangular distribution with the resultant applied at the midpoint of the wall. 13.0 FLOOR SUPPORT Slab-on-grade floors may be constructed either directly on the medium dense to dense bedrock deposits, or on structural fill placed over these materials. Areas of the slab subgrade that are disturbed (loosened) during construction should be recompacted to an unyielding condition prior to placing the pea gravel, as described below. If moisture intrusion through slab-on-grade floors is to be limited, the floors should be constructed atop a capillary break consisting of a minimum thickness of 4 inches of washed pea gravel or washed crushed rock. The washed gravel should be overlain by a 10-mil (minimum thickness) plastic vapor retarder. Subsurface Exploration, Geologic Hazard, and Lind Avenue SW Residence Geotechnical Engineering Report Renton, Washington Design Recommendations March 7, 2018 ASSOCIATED EARTH SCIENCES, INC. GPM/ms - 180037E001-2 - Projects\20180037\KE\WP Page 15 14.0 DRAINAGE CONSIDERATIONS Surficial sediment and highly weathered bedrock contain a high percentage of silt and are considered to be highly moisture-sensitive. Traffic from vehicles and construction equipment across these deposits when they are very moist or wet will result in disturbance of the otherwise firm stratum. Therefore, prior to site work and construction, the contractor should be prepared to provide drainage and subgrade protection, as necessary. 14.1 Wall/Foundation Drains All retaining and perimeter footing walls should be provided with a drain at the footing elevation. The drains should consist of rigid, perforated, polyvinyl chloride (PVC) pipe surrounded by washed gravel. The level of the perforations in the pipe should be set approximately 2 inches below the bottom of the footing, and the drains should be constructed with sufficient gradient to allow gravity discharge away from the buildings. All retaining walls should be lined with a minimum, 12-inch-thick, washed gravel blanket provided to within 1 foot of finish grade, and which ties into the footing drain. Roof and surface runoff should not discharge into the footing drain system, but should be handled by a separate, rigid, tightline drain. Exterior grades adjacent to walls should be sloped downward away from the structure to achieve surface drainage. Final exterior grades should promote free and positive drainage away from the buildings at all times. Water must not be allowed to pond or to collect adjacent to the foundation or within the immediate building area. It is recommended that a gradient of at least 3 percent for a minimum distance of 10 feet from the building perimeter be provided, except in paved locations. In paved locations, a minimum gradient of 1 percent should be provided unless provisions are included for collection and disposal of surface water adjacent to the structure. Additionally, pavement subgrades should be crowned to provide drainage toward catch basins and pavement edges. 15.0 STORMWATER INFILTRATION The bedrock deposits encountered are not likely a suitable infiltration receptor due to the high silt content and high density. Based on this, an evaluation of on-site infiltration was not performed. Lind Avenue SW Residence Renton, Washinqton Subsurface Exploration, Geologic Hazord, ond G eotech nica I Eng i nee ri ng Re po rt Desiq n Reco m me ndatio ns 16.0 PROJECT DESIGN AND CONSTRUCTION MONITORING We are available to provide additional geotechnical consultation as the project design develops and possibly changes from that upon which this report is based. lf significant changes in grading are made, we recommend that AESI perform a geotechnical review of the plans prior to final design completion. ln this way, our earthwork and foundation recommendations may be properly interpreted and implemented in the design. We are also available to provide geotechnical engineering and monitoring services during construction. The integrity of the foundations depends on proper site preparation and construction procedures. ln addition, engineering decisions may have to be made in the field in the event that variations in subsurface conditions become apparent. Construction monitoring services are not part of this current scope of work. lf these services are desired, please let us know, and we will prepare a proposal. We have enjoyed working with you on this study and are confident these recommendations will aid in the successful completion of your project. lf you should have any questions or require further assistance, please do not hesitate to call. Sincerely, ASSOCIATED EARTH SCIENCES, INC. Kirkland, Washington Ga . Mozingo,., L.E.G.Kurt D. Merriman, P.E. Senior Principal Engineerate Engin ring Geologist Attachments: Figure L: Figure 2: Appendix: Vicinity Map Site and Exploration Plan Exploration Logs 2358 ST Morch 7, 2078 G PM/ns - 780037E007-2 - Projects\20780037\KE\WP ASSOCIATED EARTH SCIENCES, INC, Page L6 KING COUNTY BlackRiverForest FortDentPark Cedar RiverNatural Zone Copyright:© 2013 National Geographic Society, i-cubed 0 20001000 FEET ± NOTE: BLACK AND WHITEREPRODUCTION OF THIS COLORORIGINAL MAY REDUCE ITSEFFECTIVENESS AND LEAD TOINCORRECT INTERPRETATION VICINITY MAP PROJ NO. DATE: FIGURE:180037E001 3/18 1Document Path: G:\GIS_Projects\aaY2018\VM\180037E001 F1 VM_Lind.mxdDATA SOURCES / REFERENCES:USGS: 7.5' SERIES TOPOGRAPHIC MAPS, ESRI/I-CUBED/NGS 2013KING CO: STREETS, PARCELS, CITY LIMITS 1/18 LOCATIONS AND DISTANCES SHOWN ARE APPROXIMATE KitsapCounty Snohomish County Pierce County King County Lind Ave SWS 134th St SW Lan g s t o n R dStevensAveSW !( ¬«167 SITE ¥405 LIND AVE SW RESIDENCE RENTON, WASHINGTON LIND AVENUE SW RESIDENCE RENTON, WASHINGTON 180037 Lind Ave Residence \ 180037E001 F2 S-E Plan.cdrBASE MAP REFERENCE: PLAN TO PERMIT, LLC; LIND AVENUE VARIANCE; SHEET P1.0; DATED 1/10/18 SITE AND EXPLORATION PLAN PROJ NO.DATE:FIGURE: 180037E001 3/18 2 NOTE: BLACK AND WHITE REPRODUCTION OF THIS COLOR ORIGINAL MAY REDUCE ITS EFFECTIVENESS AND LEAD TO INCORRECT INTERPRETATION. a s s o c i a t e d e a r t h s c i e n c e s i n c o r p o r a t e d FEET 10 200 N NOTE: LOCATION AND DISTANCES SHOWN ARE APPROXIMATE. LEGEND: EXPLORATION PIT SITE BOUNDARY EPEP CONTOUR INTERVAL = 2’ EP-1 EP-2 APPENDIX Elev: 156 ft Forest Duff - 10 inches Tukwila Formation Soft, moist, oxidized brown, SILTSTONE; highly weathered. Becomes hard, moderately weathered. Moderately hard, moist, oxidized brown, SILTSTONE/SANDSTONE; highly weathered. Bottom of exploration pit at depth 9 feetNo seepage. No caving. DESCRIPTION Renton, WA Lind Avenue SW Residence 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 This log is part of the report prepared by Associated Earth Sciences, Inc. (AESI) for the named project and should be readtogether with that report for complete interpretation. This summary applies only to the location of this trench at the time ofexcavation. Subsurface conditions may change at this location with the passage of time. The data presented are a simplficationof actual conditions encountered. Logged by: DV Approved by: CJK 2/22/18 Project No. 180037E001 LOG OF EXPLORATION PIT NO. EP-1 Depth (ft)KCTP3 180037.GPJ March 5, 2018 Elev: 150 ft Forest Duff - 8 inches Tukwila Formation Soft, moist, oxidized brown, SILTSTONE; highly weathered. Becomes hard, moderately weathered. Bottom of exploration pit at depth 8 feetNo seepage. No caving. DESCRIPTION Renton, WA Lind Avenue SW Residence 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 This log is part of the report prepared by Associated Earth Sciences, Inc. (AESI) for the named project and should be readtogether with that report for complete interpretation. This summary applies only to the location of this trench at the time ofexcavation. Subsurface conditions may change at this location with the passage of time. The data presented are a simplficationof actual conditions encountered. Logged by: DV Approved by: CJK 2/22/18 Project No. 180037E001 LOG OF EXPLORATION PIT NO. EP-2 Depth (ft)KCTP3 180037.GPJ March 5, 2018