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HomeMy WebLinkAbout02963 - Technical Information Report - Geotechnical t � : S'WP - 29(o3 • . . • GEOTF. `' • '13256 NE 20th Street,Suite 16 1,,., C H' .. • . P.O.Box 2054 • . CONSULTANTS, TNC. Bellevue,WA 98005 Tacoma,WA 98401 1 206-747-5618 FAX 747-8561 206-627-5990 FAX 627-2114 • April 8, 1997 JN 97100 SEB, Incorporated amD 4109 Bridgeport Way West, Suite CBAR - 4 1998 • Tacoma, Washington 98466 Attention: Steve Berg BUILDING DIVISION • Subject: Geotechnical Engineering Study Talbot Road Apartments j Talbc,t Road South at South 55th Street (South 192nd Street) RentdA, Washington Ii, Dear Mr. Berg: We are pleased to present this geotechnical engineering report for the Talbot Road Apartments to be constructed in Renton, Washington. The scope of our work consisted of exploring site surface and subsurface conditions, and then developing this report to provide recommendations for general earthwork and design criteria for foundations, retaining walls, and pavements. You j' authorized our work by accepting our proposal, P-4163, dated March 7, 1997. The subsurface conditions of the proposed building site were explored with twenty test pits that encountered 6 to 18 inches of topsoil, overlying native, weathered silty sands with varying amounts of gravel. The native sands typically became medium-dense at depths of 2-1/2 to 4-1/2 feet, and became dense to very dense between 4 and 8 feet. Slight to moderate groundwater was encountered perched above the medium dense soils in all of the test pits. The proposed buildings and bridges can be supported by conventional footings bearing on the medium-dense, native soils or on structural fill placed above these competent soils. The presence of groundwater and wet soils will make site earthwork difficult and more costly than on a "typical" site in the Puget Sound area. Subsurface drains will be necessary along the upslope side of the site prior to starting the earthwork process. Other subsurface drainage measures will likely be needed depending on the planned final grades and the conditions encountered during earthwork. Due to the high silt content of the native soils, they are moisture sensitive and will be very difficult • to grade. The high moisture content of the native, silty sands makes them useable as structural fill without substantial drying during hot, dry weather. This includes utility backfill. The native silt will not be useable as structural fill due to its low compacted strength. The costs associated with grading during wet weather will be substantially higher than those of grading operations t. undertaken in drier weather. Imported sandy fill will be required for structural pH if wet weather grading is attempted. ,, "N 29Co3 ii SEB, Incorporated JN 97100 April 8, 1997 Page 2 The attached report contains a discussion of the study and our recommendations. Please contact us, if there are any questions regarding this report orif we can be of further assistance during the design and construction phases of this project. I i' Respectfully submitted, GEOTECH CONSULTANTS, INC. Marc R. McGinnis, P.E. Associate I { jMRM:mmm •11.1 I `i. GEOTECII CONSULTANTS,INC. • • GEOTECHNICAL ENGINEERING STUDY Talbot Road Apartments Talbot Road South at South 55th Street (South 192nd Street) Renton, Washington This report presents the findings and recommendations of our geotechnical engineering study for I the site of the proposed apartment complex in Renton, Washington. The Vicinity Map; Plate 1, • illustrates the general location of the site. We were provided with a Concept Site Plan developed by Casey Group Architects and dated December 26, 1996. This plan showed a portion of the site boundaries, general topographic information, the approximate outline of the "wetlands", and the proposed building locations. No final grades were indicated on the provided plan. We anticipate that the development will consist of more than 35 two-story townhouse and apartment buildings, in addition to a recreation building with a swimming pool. Much of the area around the buildings will be paved for driveways and parking. According to the plan, the main roadway will enter the development at the north end, in line with South 61st Street. Bridges are proposed to cross the existing creeks t allow access to the southern portions of the site. j'. SITE CONDITIONS Surface The large, rectangular-shaped parcel covers an area of approximately 12 acres immediately northwest of the intersection of Talbot Road South and South 55th Street, which is also shown on some maps as South 192nd Street. The property was undeveloped at the time of our field work. The site is divided by a west-flowing stream into a large northern section and a smaller southern section. A drainage ditch flows westward from a culvert beneath Talbot Road South in the northern section of the property. Another culvert empties onto the site from beneath Talbot Road South on the south section. Along the eastern side of the property is a ditch that contained standing water at the time of our field work. The surface of Talbot Road South slopes toward this • ditch. A ditch •containing a substantial amount of running water was noted along the south boundary of the site. The heavily-vegetated site was covered primarily with blackberry vines and other underbrush. A large grassy area was noted bordering Talbot Road South toward the center of the site. Numerous small to medium-sized deciduous trees, and a few larger deciduous and evergreen trees, are scattered around the property. The ground surface generally slopes about 10 percent towards the west-southwest with a maximum slope of about 20 percent. There were no observed steep slopes in proximity to the proposed 5evelopment area. Most water from the upslope properties to the east flows to the site via the thr@e 18-inch culverts that cross under Talbot Road South. During the heavy rains that occurred while we conducted our explorations, these culverts carried heavy flows directly onto the site. The nprthwest portion of the site is relatively flat and low-lying, with standing water observed during our$xplorations. Development surrounding the site is varied. Across Talbot Road South and South 55th Street are numerous single-family residences. The Summit Park townhomes and condominiums are situated east of the! site at the 5100 block of Talbot Road South. The Talbot Park townhomes and CEOTECH CONSULTANTS,INC. • 'i' ' SEB, Incorporated JN 97100 1 . April 8, 1997 Page 2 condominiums were under construction to the northeast of the site at the 4700 block of Talbot Road South. The northern perimeter of the site abuts a single-family residence with several acres of pasture land. The western perimeter of the development area is defined entirely by a designated wetland. i . i ;' Subsurface The subsurface conditions were explored by excavating twenty test pits at the approximate locations shown on the Site Exploration Plan, Plate 2. The field exploration program was based upon the proposed construction and required design criteria, the site topography and access, the subsurface conditions revealed during excavation, the scope of work outlined in our proposal, and the time and budget constraints. The test pits were located by pacing from estimated property 1 corners. The test pits were excavated on March 18 and 19, 1997 with a large tracked excavator. A geotechnical engineer from our staff observed the excavation process, logged the test pits, and obtained represqytative samples of the soil encountered. "Grab" samples oflselpcted subsurface soil were collected from the backhoe bucket. The Test Pit Logs are attached to this report as Plates 3 through 12. The test pits generally encountered similar subsurface conditions in the areas that were explored. 6 to 18 inches of very moist, loose, silty sand topsoil were found beneath the surface vegetation, except in Test Pit 20, which exposed 2-1/2 feet of topsoil. Beneath the topsoil layer, the test pits all revealed very moist to wet, weathered, silty sands. The gravel content in these sands varied and the native soils typically became medium-dense below a depth of 2-1/2.to 4-1/2 feet. The medium-dense soils were not encountered until a depth of 6 feet in Test Pit 20. The native sands often became less silty below depths of 4 to 6 feet and below a depth of 4 to 8 feet, they became j dense. The final logs represent our interpretations of the field logs and laboratory tests. 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 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. • Groundwater Perched groundwater seepage and wet soils were observed in all tests pits, which were conducted • after several months of rainy weather. The seepage generally occurred at the interface between the loose and medium-dense,, native soils. Seepage was also observed in sandier zones within the medium-dense to dense soils. The test pits were left open for only a short time period. Therefore, the seepage levels on the logs represent the location of transient water seepage and may not indicate the static groundwater level. It should be noted that groundwater levels vary seasonally with rainfall and other factors. We anticipate that groundwater could be found most, or GEOTECH CONSULTANTS,INC. j :I SEB, Incorporated JN 97100 : • • April 8, 1997 Page 3 ll ��1`{ all, of the year in more permeable soil layers and between the near-surface, weathered soil and IH the underlying denser soil. I.; CONCLUSIONS AND RECOMMENDATIONS 1I General 11 . H Based on our test pit information, the construction of the proposed apartment buildings on the subject site appears feasible.from a geotechnical standpoint. The structures can be supported by conventional foundations bearing on the medium-dense to dense, weathered native soils. Depending on final grades, overexcavation may be required beneath the footings to expose ;1 competent, native soil. These overexcavations can be backfilled with structural fill or lean concrete. The main challenges during development of the site appear to be the substantial amount of subsurface water and the silty, moisture-sensitive nature of the native soils. The best way to I reduce the ihipiaict of both of these factors on the site development is to gbnduct earthwork operations in the drier summer months. If grading activities take place in dry weather, when drying I of the wetter soil by aeration is possible, the silty sands encountered in our test pits could be used { as structural fill. This process will be slow, as each loose lift of soil would need to dry for one or - more days before being compacted. Drying the excavated soils by aeration will be very difficult for utility trenches, which are usually excavated and backfilled relatively rapidly in short sections.. It is important to note that reuse of the native soils as structural fill will be impossible during wet weather. Even if earthwork is conducted in dry weather, it could be necessary to import clean Igravelly sands for structural fill and for the utility backfill in the areas of excessively wet soils. Wet soils could be dried chemically using kiln dust or cement during dry weather. This is also a slow ,; • process. Due to their low compacted strength, the native silts will not be useable as structural fill. We recommend installing subsurface interceptor, or "French", drains along the entire upslope edge of the proposed development area. These drains are intended to intercept subsurface water and should be installed early in the site clearing process. A typical detail for these drains is attached as Plate 15. Drains will also be needed where cuts of more than about 12 to 24 inches below the existing grade are planned for final grading. Additional subsurface drainage will be required where seepage is encountered in the development area. It is fairly common for some groundwater to bypass the upslope interceptor drain, requiring subsurface drains further downslope. Proper drainage behind all backfilled walls will be important, especially if they are adjacent to below-grade occupied spaces. Even if free-draining backfill is used behind the walls, it has been our experience that some seepage can be expected through the walls in the future if I real waterproofing, such as bentonite panels, is not used. Footing drains must be well- 3 constructed, and should be built using PVC pipe for best,long-term performance and easiest maintenance. Drainage along the edge of Talbot Road South appears fairly poor. The eastern ditch does not move water very well and should be sloped to drain better, then it should be lined or culverted, to minimize the amount of water that will percolate into the underlying soils. One existing culvert in • the central portion of the site is planned to be redirected so as not to discharge onto the proposed ?~ . building area. There is another culvert near the southeast corner of the site that is not shown on ' the provided plan that will need to be handled in a similar manner. GEOTECFI CONSULTANTS,INC. SEB, Incorporated April 8, 1997 JN 97100 Page 4 { • When wet, the silty native soils are subject to softening and disturbance by foot or equipment traffic. If the footings are constructed in wet weather, we recommend that all bearing surfaces be protected with a 2 to 4-inch layer of crushed rock, quarry spalls, or recycled concrete to prevent disturbance of the footing subgrades by workers during placement of forms and reinforcing steel. We anticipate that substantial amounts of this imported angular material will be needed for building pads and temporary site roads. 1 . Slabs and pavements that are placed over improperly-compacted fill soils will settle. Some • measures can be taken to reduce this, such as placing reinforcing steel in slabs, and constructing pavements over a thick layer of imported gravel base. However, the best way to prevent unacceptable post-construction settlement is to properly place and compact fill soils beneath all I on-grade elements. Substantial erosion control measures will be needed during this project. We anticipate that a silt fence Would need to be erected along the west side of the property, and along the sides of the streams that traverse the site. Additionally, shallow, rock-lined drainage swales and sedimentation ponds will probably be necessary. Cleared areas between the proposed buildings and the wetland bound1ies should be mulched with straw or a similar product duripg lkvet weather until permanent vegetation can be established. The' civil engineer should develop the temporary erosion control plan. Geotech Consultants, Inc. should be allowed to review the final development plans to verify that • the recommendations presented in this report are adequately addressed in the design. Such a plan review would be additional work beyond the current scope of work for this study, and it may include revisions to our recommendations to accommodate site, development, and geotechnical • constraints that become more evident during the review process. • Conventional Foundations • The proposed structures can be supported on conventional continuous and spread footings bearing on undisturbed, medium-dense, native, silty sands or on structural fill placed above these competent, native soils. See the later sub-section entitled General Earthwork and Structural Fill for recommendations regarding the placement and compaction of structural fill beneath structures. We recommend that continuous and individual spread footings have minimum widths of 12 and 16 inches, respectively. They should be bottomed at least 12 inches below the lowest adjacent finish ground surface for frost protection. 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, some overexcavation will likely 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 3-foot-wide footing must be at least 5 feet wide at the base of the gxcavation. If lean concrete is used, the overexcavation need only extend 6 inches beyond the edges of the footing. GEOTECFI CONSULTANTS,INC. I i . SEB, Incorporated JN 97100 1 April 8, 1997 Page 5 1 2 The following allowable bearing pressures are appropriate for footings constructed according to the above recommendations: i • Allowable Bearing Condition Bearing Pressure '! Placed directly on competent, 3,000 psf • ` • native soil i Supported on structural fill placed 2,000 psf. above competent, native soil I 1 H Where: I i psf is pounds per square foot. A one-third increase in the above design bearing pressures may be used when considering short- ; term wind or'seJ.mic loads. For the above design criteria, it is anticipates' thtt the total post- I construction settlement of footings founded on competent, native soil, or on structural fill up to 5 feet in thickness, will be about three-quarters of an inch, with differential settlements on the order ! of one-half inch in a distance of 50 feet along a continuous footing. 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 surrounded.by level, structural•fill. We recommend using the i • following design values for the foundation's resistance to lateral loading: jj Parameter Design Value I • Coefficient of Friction 0.40 • I Passive Earth Pressure 300 pcf i Where: ' 1. pcf is pounds per cubic foot. 2: 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 I 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 design values. s J { t Seismic Considerations The site is located within Seismic Zone 3, as illustrated on Figure No. 16-2 oflthe 1994 Uniform Building Code (UBC). In accordance with Table 16-J of;the 1994 UBC, the site soil profile is best represented by Profile Type.52. The medium-dense td dense soils that underlie the site:are not susceptible to seismic liquefaction. ,1 OEOTECII CONSULTANTS,INC. SEB, Incorporated April 8, 1997 JN 97100 Page 6 Slabs-on-Grade The building floors may be constructed as slabs-on-grade atop undisturbed, native soils that underlie the topsoil. 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 structural fill. All slabs-on-grade should be underlain by a capillary break or drainage layer consisting of a minimum 4-inch thickness of coarse, free-draining, structural fill with a gradation similar to that discussed later in Permanent Foundation and Retaining Walls. In areas where the passage of moisture through the slab is undesirable, a vapor barrier, such as a 6-mil plastic membrane, should be placed beneath the slab. Additionally, sand should be used in the fine-grading process to reduce damage to the vapor barrier, to provide uniform support under the slab, and to reduce • shrinkage cracking by improving the concrete curing process. I I ,�.• Permanent 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 design parameters are for walls that restrain level backfill: Parameter Design Value Active Earth Pressure* 40 pcf Passive Earth Pressure 300 pcf Coefficient of Friction 0.40 • Soil Unit Weight 130 pcf Where: 1. pcf is pounds per cubic foot. 2. Active and passive earth pressures are computed usingthe equivalent fluid • densities. • * 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 values given above are to be used to design permanent foundation and rdtaining walls only. • The passive pressure given is appropriate for the depth of level, structural fill placed in front of a retaining or foundation wall only. We recommend a safety factor of at least 1.5 for overturning and sliding, when using the above values to design, the walls. GEOTECEI CONSULTANTS,INC. SEB, Incorporated April 8, 1997 JN 97100 7 Page 7 • • The design values given above do not include the effects of any hydrostatic pressures behind the • walls and assume that no surcharge slopes or loads, such as vehicles, will be placed behind the walls. If these conditions exist, those pressures should be added to the above lateral soil pressures. Also, if 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 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. Retaining Wall Backfill Backfill placed behind retaining or foundation walls should be coarse„free-draining, structural fill containingno 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, at least 12 inches of free-draining gravel should be placed against the walls. Inareas of active seepage, retaining wall backfill must consist of free-draining gravel. I 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. The to 12 to 18 inchesof 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. The sub-section entitled General Earthwork and Structural Fill contains recommendations regarding the placement and compaction of structural fill behind retaining and foundation walls. The above' recommendations are not intended to waterproof the below-grade walls. If some seepage through the walls or moist conditions are not acceptable, damp-proofing or waterproofing should be provided. This could include limiting cold-joints and wall penetrations, and possibly using bentonite panels or membranes on the outside of the walls. Applying a thin coat of asphalt emulsion is not considered waterproofing, but it will help to prevent moisture, generated from water vapor or capillary action, from seeping through the concrete. Rockeries - We anticipate that rockeries may be used in the site development. A rockery is not intended to function as an engineered structure to resist lateral earth pressures, as a retaining wall would do. The primary function of a rockery is to cover the exposed, excavated surface and thereby retard the erosion process. Due to the loose condition of the near-surface soils, we recommend limiting rockeries in cut or fill areas to a height of 5 fe t. Proper drainage must be.provided behind all rockeries, including at least a 12-inch width of qu rry spalls behind the rocks. GEOTECEI CON ULTANTS,INC. ii • SEB, Incorporated April 8, 1997 JN 97100 Page 8 The construction of rockeries is to a large extent an art not entirely controllable by engineering methods and standards. It is imperative that rockeries, if used, are constructed with care and in a proper manner by an experienced contractor with proven ability in rockery construction. The rockeries should be constructed with hard, sound, durable rock in accordance with accepted local practice and City of Renton standards. Soft rock, or rock with a significant number of fractures or inclusions, should not be used, in order to limit the amount of maintenance and repair needed over time. Provisions for maintenance, such as access to the rockery, should be considered in the design. In general, we recommend that rockeries have a minimum dimension of one-third the height of the rockery. 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. Based upon Washington Administrative Code (WAC) 296, Part N, the soil type at the subject site would generally be classified as Type B. Therefore, temporary cut slopes greater than 4 feet in height cannot be excavated at an inclination steeper than 1.5:1 (Horizontal:Vertical), extending continuously between the top and the bottom of a cut. The above-recommended temporary slope inclination is based on what has been successful at other sites with similar soil conditions. 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. The cut slopes should also be backfilled or retained as soon as possible to reduce the potential for instability. Please note that loose soil can cave suddenly and without warning. Utility contractors should be made especially aware of this potential danger. All permanent cuts into native soil where groundwater seepage is not occurring should be inclined no steeper than 2.5:1 (H:V). Fill slopes comprised of compacted on-site, or similar silty, soils 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 could be accomplished by overbuilding the compacted fill and then trimming it back to its final inclination. Water should not be allowed to flow uncontrolled over. the top of any temporary or permanent slope. Also, 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 We recommend the use of footing drains at the base of footings, 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 backfilled, earth-retaining walls. These drains should be surrounded by at least 6 'nches of 1-inch- minus, washed rock and then wrapped in non-woven, geotextile filter fabric (Mir�fi 140N, Supac 4NP, or similar material). At its highest point, a perforated pipe invert should be at least as low as. the bottom of the footing, and it should be sloped for drainage. Drainage should also be provided inside the footprint of a structure, where (1) a crawl 'space will slope or be lower than the surrounding ground surface, (2) an excavation 'encounters significant seepage, or (3) an GEOTECH CONSULTANTS,INC. Ij SEB, Incorporated I April 8, 1997 JN 97100 Page 9 excavation for a building will be close to the expected high groundwater elevations. We can provide recommendations for interior drains, should they become necessary, during excavation and foundation construction. All roof and surface water drains must be kept separate from the foundation drain system. A typical drain detail is attached to this report as Plate 16. For the best long-term performance, perforated PVC pipe is recommended for all subsurface drains. Clean-outs should be provided for all subsurface and footing drains. Groundwater was observed during our field work. Seepage will likely be encountered in at least some of the excavations. This water 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 buildings should j1t slope away at !past 2 percent, except where the area is paved. I N 1 N1 Pavement Areas • All pavement sections may be supported on competent, native soil or structural fill, provided these soils can be compacted to a 95 percent density and are in a stable, non-yielding condition at the time of paving. Structural fill or fabric may be needed to stabilize soft, wet, or unstable areas. We recommend using Supac 5NP, manufactured by Phillips Petroleum Company, or a non-woven fabric with equivalent.strength and permeability characteristics. In most instances where unstable subgrade conditions are encountered, 12 inches of granular, structural fill will stabilize the subgrade, except for very soft areas where additional fill could be required. The subgrade should be evaluated by Geotech Consultants, Inc., after the site is stripped and cut to grade. Recommendations for the compaction of structural fill beneath pavements are given in a later sub- section entitled General Earthwork and Structural Fill. The performance of site pavements is directly related to the strength and stability of the underlying subgrade. Based on the silty, moisture-sensitive condition of the on-site soils, more crushed rock than usual should be provided beneath the asphalt to reduce the potential for softening of the underlying soils. The pavement for lightly loaded traffic and parking areas should consist of 2 inches of asphalt concrete (AC) over 6 inches of crushed rock base (CRB) or 4 inches of asphalt-treated base (ATB). We recommend providing heavily loaded areas with 3 inches of AC over 8 inches of CRB or 6 inches of ATB. Heavily loaded areas are typically main driveways, dumpster sites, or areas with truck traffic. • The pavement section recommendations and guidelines presented in this report are based on our experience in the area and on what has been successful in similar situations. Some maintenance and repair of limited areas can be expected: To provide for a design without the need for any repair would be uneconomical. • GEOTECH CONSULTANTS,INC. i '•• SEB, Incorporated , 1 • April 8, 1997 JN 97100 ;.I Page 10 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 11 materials to be used as structural fill, but they could be used in non-structural areas, such as i landscape beds. Structural fill is defined as any fill placed under 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 i i content. The optimum moisture content is that moisture content that results in the greatest Iil I compacted dry density. The moisture content of fill is very important and must be closely controlled during the filling and compaction process. • The allowable thickness of the fill lift will depend on the material type selected, the compaction I 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 I, compacted to specifications, it can be recompacted before another lift is placed. i This eliminates jthe need to remove the fill to achieve the required compaction. The following table presents recommended relative compactions for structural fill: I i Minimum Location of Fill Placement Relative Compaction I '• Beneath footings, slabs, 95% {i or walkways Behind retaining walls 90% I Beneath pavements 95% for upper 12 I inches of subgrade, I 90% below that level i , 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 1557-78 (Modified Proctor). Ideally, 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. 7: i , -I GEOTECH CONSULTANTS,INC. i {•. SEB, Incorporated - April 8, 1997 JN 97100 Page 11 LIMITATIONS ' The analyses, 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 encountered in the test pits is 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 soil conditions are commonly encountered on construction sites and cannot be fully anticipated by merely taking soil 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. This report has been prepared for the exclusive use of SEB Incorporated and its representatives for specific application to this project and site. Our recommendations and conclusions are based on observed sitg materials, and selective laboratory testing and engineering {analyses. Our conclusions and 'recommendations are professional opinions derived in accordance with current standards of practice within the scope of our services and within budget and time constraints. 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. We recommend including this report, in its entirety, in the project contract documents so the contractor may be aware of our findings. 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. • The scope of our work did not include an environmental assessment, but we can provide this service, if requested. • GEOTECH CONSULTANTS,INC. �' SEB, Incorporated • iI April 8, 1997 JN 97100 I Page 12 ; The following plates are attached to completethis report: Plate 1 Vicinity Map Plate 2 Site Exploration Plan Plates 3 - 12 Test Pit Logs • Plate 1.3 - 14 Grain Size Analysis • • Plate 15 Footing Drain Detail Plate 16 • Subsurface Drain Detail We appreciate the opportunity to be of service on this project. If you have any questions, or if We may be of further service, please do not hesitate to contact us. II ' . Respectfully submitted, GEOTECH CONSULTANTS, INC. • q a„14,,, ttp. " ? .5 278'S 9 `.. I�ar1 " .STE?•1) tie- w i :$,,,`95jONAL EN°: ^11/8/97 ifli ES 10i 5X97 1 Marc R. McGinnis, P.E. 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SrL 'r,,t . ...... 1 VICINITY MAP - - =— GEOTECH. TALBOT ROAD S AT S 55th STREET CONSULTANTS :: ' •. Looped By: Platt:7 1 • ; • i i 44 0 0 0 Uo �tS ++0 ,5t 11° 'j 1 11 1 -. / / I 1. 1 s'), / 1 • 1 ' / f- 1 ` I I + 1 -I_ / .I 1 %\\\ I I \ 1 .1 I TP-13.6 ® i i I 1 t \ \ \ ''-'1 \\ \ I 1 i , i TP-�\5 \ \ \\ .1 III 1 �1 \ \A \\ & 1111:":1 4. N \° ' i 1 1 ` \TP-16 \ \ t . i I \ 1 \ \ \ ` - �. -112 \ \ \ \ \ -�.. 12 \ \ \ 0 ,�; 2 ( \ \--` �` I .Tt-\8I 1 \ o• . \ \ , ) ., . I) • 1 ) \ Tc-11 A / : / f� ) \ � \ \ \ I / 1I ) 2 1 \ \ -1 I I I / / / TP-)10 \. °< .> \\ \\Tb-8• )0 ,ia% (i Q� W . o �\\ j TP-9 #i + -201 : i\ \\ \ \Ta-7 V. \ \ \ ( 33 \ 0 WETLAND .BOUNDARY `1 \ 1\ •\ 0 \\ \\ ®�•P\51 a I \\ `\\\ \ \� .TPt6 \� \\ • H\P;71 1 (I \\ ®lTP14 % \ • I \ \ 0.< �\ 1 \\ \\ \\ \ 11 \ \ \ \\ \ \ \ I \1 \ \\\\\ \\ t TP\9� \ h, 1 . TP-3 WETLAND , \\ \ \0 \1 \\ \ • BOUNDARY ` ((/ \ \\ I \\ 1 l P-� \ \\ \ .°to Y�-- - \ `\ LEGEND: 1 S 55th STREET 47.< °t . ®.. EXISTING CULVERTS 0 APPROXIMATE TEST PIT LOCATIONS SITE EXPLORATION PLAN GEOT ENH CH TALBOT ROADS AT SI I55th STREET CONSULRENTON, WA • l t„—, y____ot.„ Jab No.: Doter Rale: 97100 MAR 1897 2 ll • I' TEST PIT 1 4- 443. 4' 0° USCS Description I 0 _ Dark brown, silty SAND with roots, fine-grained, very moist, loose — (Topsoil) . 1. .. "' -- "r-- Orangish/brown,-slightly gravelly;-silty'SAND, fine-grained,-'--•- _ very moist to wet, loose 5 — -becomes mottled and medium-dense, very moist . j — : SM I - - ..._._... !11 - . . -becomes less mottled and very dense • '.I 10 _ • _ Test pit terminated at 11 feet below grade on 3-18-97. ' 15_ Slight groundwater seepage encountered at 3 feet during excavation. . Slight caving above 4 feet. . .... . ..._ .. _- . .. .. ........:_..__ . 4, ' I TEST PIT 2 q5. o%c 0 4G° USCS Description - . Dark brown, silty SAND with organics, fine-grained, moist,loose (Topsoil) _ Orangish brown, mottled with gray,-slightly gravelly, silty SAND, fine-- _ . :I]?�i grained, very moist to wet,loose • �sM -becomes medium-dense 5 — _ . I Light gray, silty SAND with occasional gravel, fine-grained, very moist _ sM to wet, dense -becomes very dense 10 _ •::III • - Test pit terminated at 9.5 feet below grade on 3-18-97. . 15 _ . Slight groundwater seepage encountered at 3 feet during excavation. Moderate groundwater seepage encountered at 6.5 feet during excavation. ' • Slight caving below 4 feet. - • TEST PIT 4OGS ,11 GEOTECIE[ TALBOT ROAD S AT 8 55th STREET CONSULTANTS, INC. RENTON, WA ‘ , Job No: Date: Logged by: Plate: 97100 MAR 1997 JMJ -. 3 I; , TEST PIT 3. . - ._.. .. -- _.. O c: USCS Description • H. Topsoil Orange/brown, mottled with gray, fine-grained, very moist, loose I -becomes medium-dense, wet 5 — 19.6% M:: -becomes less mottled _ -becomes dense 10 — — Test pit terminated at 9 feet below grade on 3-18-97. Slight groundwater seepage encountered at 4 feet during excavation. — Slight caving above 4 feet. I 15_• _ • TEST.PIT 4 q9. 0`$ O4 's.C? USCS Description ' _-___., Topsoil • — Orangish brown, silty SAND, fine-grained, very moist to wet, loose — . -becomes medium-dense Mr -becomes dense • 10 _ Test pit terminated at 7.5 feet below grade on 3-18-97. Slight groundwater seepage encountered at 2 feet during excavation. — Slight caving below 2.5 feet. 15_ • TEST PIT !LOGS._. . .-. "._� GEOTECH TALBOT ROAD S Alf S 55th STREET CONSULTANTS, INC. RENTON, WA Job No: Date: Logged by: Plate: 97100 MAR 1997 JMJ 4 • T TEST PIT 7 a 045) G? USCS � Description _ Topsoil _ M Orange/brown, silty SAND with organics, fine-grained, very moist to wet, . 18.2%x % loose Orange/brown, mottled with gray, silty SAND with some gravel, 5 _ fine-grained, very moist to wet, medium-dense SM — -becomes dense • • 10 _ _ • Test pit terminated at 7.5 feet below grade on 3-18-97. _ Slight to moderate groundwater seepage encountered at 2.5 feet during excavation. Slight caving below 4 feet. 15 • TEST PIT 8 r 5�, , tc, . 0 4 G° USCS Description t f ,,,,•, . Topsoil • sM : Reddish brown,mottled with gray, silty SAND with some gravel, — \ fine-grained, very moist to wet,loose Orange/brown, mottled with gray, silty SAND with some gravel, —5 .— Ism -becomes very moist to wet, loose' becomes medium-dense . — -becomes dense • 10 _ • . • — Test pit terminated at 7.5-feet below grade on 3-18-97. • = Slight to moderate groundwater seepage encountered at 2 feetduring excavation. _ _ Moderate caving below 4 feet. 15_ • • • TEST PIT LOGS <.lAi. GEOTECH TALBOT ROADS AT SS 55th STREET CONSULTANTS, )NC. RENTON, WA �: Job No: Date: Logged by: Plate: 97100 MAR 1997 JMJ • 6 • I . TEST PIT 9 G USCS Description 0 • , . '1'o soil — :ism.] Light brown, silty SAND with organics, fine-grained, very moist to wet,loose I _ Orange/brown, mottled gray, silty SAND with gravel and some silty 5 — •. sM seams, fine-grained, very moist to wet, loose — ••- r -becomes medium-dense. — becomes dense , . 10 _ • Test pit terminated at 7 feet below grade on 3-18-97. — Slight groundwater seepage encountered at 2 feet during excavation. Slight caving below2 feet. • 15 Ii ' I • • ' TEST PIT 10 , ��, •6� , •4 0�c r 0 SCF USCS Description _ Topsoil _ 8 • sM Orange/brown, silty SAND with organics, fine-grained,very moist to • _ wet, loose • _ Orange/brown, mottled with gray, silty SAND with some gravel, fine- 5 — :Ism grained, very moist to wet,loose _ -becomes medium-dense — becomes dense 10 _ Test pit terminated at 7 feet below grade on 3-18-97. Slight groundwater seepage encountered at 2 feet during excavation. • No caving. — • 15 TEST PIT DOGS rAGEOTECH TALBOT ROAD S ATS 55th STREET CONSULTANTS, INC. RENTON, WA i.�s ----e— „__, JJobNo: 1 Date: 1997 jLoggedby: (Plate:7 I • TEST PIT 11. c. • ? qqa _o g CP USCS 0 Description _ Topsoil Orange/brown, silty SAND, mottled with gray, some gravel, - 17 2% fine-grained,very moist to wet, loose • — ::slut I: -becomes medium-dense 5 - - -becomes more sandy, less mottled, dense - • 10 — Test pit terminated at 6.5 feet below grade on 3-19-97. Slight groundwater seepage encountered at 1 foot during excavation. No caving. • 15 TEST PIT 12 ,, •4- C.- 0 C) USCS Description _ Y Topsoil. -- _Orange/brown, silty SAND with.some-gravel,fine-grained,very.moist__.... Tv •. to wet, loose _ -becomes dense . 5 -becomes very dense — Test pit terminated at 5.5 feet below grade on 3-19-97. Slight groundwater seepage encountered at 1 foot during excavation. 10 — No caving. 15_ TEST PIT IhOGS „al GEOTECH[ TALBOT ROAD S AT'S 55th STREET CONSULTANTS, INC. RENTON, WA 1 ��-.�� 1JobNo: 1Date: 1997 1Log.gedby: JP/a(e: 8 1 . • • TEST PIT 13 sc.SS ` , 61. os�e qF , . e • 0 'G? USCS Description _ 77,..r-.., Topsoil rr .. sM " Light brown, silty SAND with organics, fine-grained, very moist _ �•I•I•I•I••5\ to wet, loose - ........_: sM i• Orange/brown, siltySAND fine- rained withm soe ravel li ht _-. — oxidation,wet to vry moist, loose 5 —. -becomes medium-dense -becomes hard • — 10 _• Test pit terminated at 5.5 feet below grade on 3-19-97. Moderate groundwater seepage encountered at'15 feet during excavation. — Slight caving below 3 feet. 15 _ • • TEST PIT 14c. i - a r., ... . 0 • us. Description ••• - Topsoil 2 Pii: Reddish/brown, silty SAND with organics, fine-grained,very moist • _ \ to wet, loose Orange/brown, slightly mottled with gray, silty SAND with some gravel, • 5 _ sM fine-grained, very moist to wet, loose -becomes medium-dense becomes dense 10 _ Test pit terminated at 7 feet below grade on 3-19-97. L. — Slight groundwater seepage encountered at 2 feet during excavation. .. Slight caving at 2 feet. .. . . . -- -• .- • - - • • . 15—.. . ..._.. __ . . .... ._... . .. . ... . .... ... . . • V _ TEST PITILOGS • `:._ C-EOTECH . TALBOT ROAD S AT S 55th STREET CONSULTANTS, INC. • RENTON, WA • Job No: Date: Logged by: Plate: 97100 MAR 1997 JMJ 9 • • • • TEST PIT 15 ,•s• q , . .... Go .. -USCS .. . .. _.. ......_.. . .. Description 0 _ Topsoil r sM Brown, silty SAND with organics, fine-grained, very moist to wet, loose . 21.2 Orange/brown, mottled with gray, siltly SAND with gravel, fine-grained, very moist to wet, loose 5 — -becomes medium-dense • — SM -becomes dense 10 _ • Test pit terminated at 9.5 feet below grade on 3-19-97. Moderate to heavy groundwater seepage encountered at 2 feet during excavati. , Slight caving below 2 feet. Moderate caving below 4 feet 15_ . • • • • TEST PIT 16 1 O uscs Description Topsoil Orange-brown mottled with gray silty sand with some gravel, fine-grained, very moist, loose : SM :: 5 — -becomes medium-dense -becomes dense • _ Test pit terminated at 7 feet below grade on 3-19-97. 10 _ - Heavy groundwater seepage encountered at 1.5 feet during excavation. Moderate caving between 1.5 and 4 feet. • 15_ TEST PIT IJ.OGS • C-EOTECH TALBOT ROADS ATS 55th STREET CONSULTANTS, INC: RENTON, WA Job No: Date: Logged by.: Plate: 97100 MAR 1997 JMJ 10 • .• .1 , LSIEVE ANALYSIS HYDROMETER ANALYSIS SIZE OF.OPENING IN INCHES I NUMBER OF MESH PER INCH US STD GRAIN SIZE IN MILLIMETERS • - N. 8 \ W O m N W N 0 m 0 O O O O O O_ O O O 0 OIOUN 01 A W NNS 'SCSI A a 0 O O O 00 O O 001 A W N W 01 A W N 0 ,j3L- . 90 � IO A- -....,....1\44 til I f P1 DO -.......*.`,..%.. , 20 2 ni ( m l� 33 CO m TO ) \® 30 Z } �� • 7 Zn ZGD .. - 40 00 D �x I. CO Z 30 30 m m •. 3 :\\ S ,. co f. - _ m • k \ a 2 30- r0 _1 � .x > J 0 0 - o W 2060 O 9 10 90 n O 33 m 0 I I L I I I I I I ' TILE 1 11 1 1 1 I 1 1 1 1 �n 00o0 CD Z v O O 0 0 0 0 0 O 0 m a W N - ro 01 A W N m 01 A W N 0 0 0 0 0 O 0 O CO p A ti N V /n Fl O. > P1 GRAIN SIZE IN MILLIMETERS Z "'I COBBLES COARSE I FINE COARSE . I MEDIUM I FINE FINES m GRAVEL SAND > 01 > BORING/ rt r . itTEST PIT DEPTH SAMPLE MOISTURE KEY SYMBOL SOIL CLASSIFICATION 7 2.5.' I 18•z'i S M Slcry 5AN0 -+ �' 11 31 1 17.2% arTh9 S M SILTY Mag . a m 13 '1, 2. 13.7° e--- e Sri 5I L'ry SA.M Q C., --I. . • • .a a . - SIEVE ANALYSIS HYDROMETER ANALYSIS 1 _ SIZE OF OPENING IN INCHES 1 NUMBER OF MESH PER INCH US STD GRAIN SIZE IN MILLIMETERS W \ W \ O O N W y W 0 0 0 0 0 O O O O 0 0 0 0 0 8 . N 0 d W N \ N d a 0 O O O 0 0 O p O o• d W N — O O O O O 0 cod W Al 100 La.man 0 fbL--' 0133- .t �%.fl ~ LJn i i� 90 'n SO El — i, O M 80 —':- 20 m `1 z �=�� 30 73 �yO 13 mTo _ 11 PfF•"i —1 •�.rri M .� I r. Z60 int_I/ CO z(l ., g Ct Z 2 en Z so m x L= 73 X40 `v som 3 CI To x Zs. -1 30, CD 0 —S 00 r 2080 0 0 • 90 o X 10 73 m Z O I 1111 I I I I 1 1 1 1 1 I I I III I Jill -100 m Z • '0 0) 00 00 0 O O O O O O 0 0 a W N — 0• 0• d W N _ Om A a W N O 00 0 A W0 0 N o l y' -4 z D m GRAIN SIZE IN MILLIMETERS COARSE I FINE COARSE j MEDIUM I FINE COBBLES FINES ``.2 'C N D GRAVEL SAND • > w > cri rTEST PIT DEPTH SAMPLE MOISTURE KEY SYMBOL SOIL CLASSIFICATION Ca I5 5' 2. 21.z% ®e SM spry 5AINA 13 CD "' 20 `i� I 20.7.. al-----€1S M slcy SAWV a 9. m m A.n •--i . 1 e 0 • • • • • • • Slope backfill away from foundation. TIGHTLIN£ ROOF DRAIN ® Do no/ connect to fooling drain. 1. 1 I I i BACKFILL See text for VAPOR BARRIER requirements. WASHED ROCK • 11 " • 6 min /1•e� FREE-DR.A/N/NG NONWOVEN GEOTEXTILE SAND/GRAVEL FILTER FABRIC • 4"PERFORATED HARD PVC P/PE Inver/ at leas/ as /ow as footing and/or crawl space. Slope to drain. Place weepholes downward. • • • 4 FOOTING DRAINDETAIL GEOTECH CONSULTANTS TALBOT ROAD S ATS 55th STREET 7 RENTON, WA ^"1 •� ✓o0 No.: Dore: Stole:t+ar Plate: 97100 MAR 1997 N.T.S. 15 { Yt • I ' % i it I _ 1 4 .. MINIMUM 18' ! 12' of SILTY, I I ' RELATIVELY / IMPERMEABLE r SOIL OR PAVING ! 0 o 0 O 0 8i o 0 0 0 0 0 I l t co 0 'i i w O 0 O r.1n j 00 0 0 00 ii _ 0 0 0 0 O O .O 0 �' O 0 I 6' PERFORATED I •PVC PIPE O 0 0 0 0 0 O 0 O O O. 0 I, 0 !! 4 _o— . 0 12' MINIMUM EMBEDMENT 't O O . 0 O p INTO DENSE SOIL , APPROXIMATELY 6' , o 0 Q .. 0 / ,,i \'ff \" O O 1 i t ! . i •. I 1 '., SUBSURFACE DRAIN � GEOTECH TALBOT ROAD S AT IS 55th STREET CONSULTANTS J RENTON, WA 2.: " .fob No.: Vole: Hole: - 97100 MAR 1997 16 1 i ! J