Loading...
HomeMy WebLinkAboutBLD2006-00028 Geotechnical Report i - - Report Geotechnical Engineering Services' Subsurface Investigation Proposed Ludlow Cove Development Port Ludlow, Washington • March 22, 1995 MAP l.g,q5 :`ice For �. Pope Resources G e o E n g i n e e r s File No.2378-033-T03/032295 r T ®6a Geo kO Engineers March 22, 1995 Geotechnical, Geoenvironmental and • • Geologic Services r Pope Resources P.O. Box 1780 Poulsbo, Washington 98370 T Attention: Ms. Linda Mueller We are pleased to submit four copies of our "Report, Geotechnical Engineering Services, Subsurface Investigation, Proposed Ludlow Cove Development, Port Ludlow, Washington for Pope Resources." We appreciate the opportunity to be of service to Pope Resources. Please contact us if you have questions regarding this project or if we can provide additional services. Yours very truly, GeoEngineers, Inc. Gary W. Henderson Principal SLF:GWH:vc Document ID: 2378033R.R File No.2378-033-T03 cc: Pope Resources 781 Walker Way Port Ludlow, Washington 98365 Attn: Mr. Ray Welch GeoEngineers,Inc. 6240 Tacoma Mall Blvd,Suite 318 Tacoma,WA 98409 Telephone(206)471-0379 Fax(206)471-0521 s.v�.. • • T F CONTENTS • Page No. INTRODUCTION 2 SCOPE 2 3 " SITE DESCRIPTION 3 SURFACE CONDITIONS 3 General 3 Northern Portion 3 Log Yard Area 3 SUBSURFACE EXPLORATIONS 3 SUBSURFACE CONDITIONS 4 CONCLUSIONS AND RECOMMENDATION 5 LANDSLIDE HAZARD 5 SETBACKS 6 EROSION HAZARD 7 EROSION CONTROL 7 SEISMIC VULNERABILITY 8 EARTHWORK 8 General 8 Clearing and Site Preparation 8 Subgrade Preparation 9 Structural Fill 9 Suitability of On-Site Materials for Fill 10 Fill Placement on Slopes 10 Fill Slopes 10 Fill Drainage 10 Cut Slopes 11 Temporary Cut Slopes 11 Permanent Slopes 11 Utility Trenches 12 FOUNDATION SUPPORT 12 General 12 Foundation Design 12 Lateral Load Resistance 13 Foundation Settlement 13 FLOOR SLAB SUPPORT 14 RETAINING and SUBGRADE WALLS 14 Design Parameters 14 Backdrainage 15 Construction Considerations 15 Rockeries 15 DRAINAGE 16 PAVEMENT DESIGN AND SUBGRADE PREPARATION 16 G e o Engineers i File No.2378-033-T03/032295 r T • • CONTENTS (continued) LIMITATIONS 1 7 FIGURES Figure No. Vicinity Map/Site Plan 1 Foundation Detail 2 Soil Classification System 3 Test Pit Logs 4...6 4 ' APPENDICES Page No. Appendix A - Jefferson County Critical Areas Ordinance A-1 G e o E n g i n e e r s it File No.2378-033-T03/032295 • • t 1 REPORT GEOTECHNICAL ENGINEERING SERVICES SUBSURFACE INVESTIGATION PROPOSED LUDLOW COVE DEVELOPMENT PORT LUDLOW, WASHINGTON Y INTRODUCTION This report presents the results of our geotechnical engineering services for the Ludlow Cove residential development. The site is located in Port Ludlow, Washington as shown on the Vicinity map and Site Plan, Figure 1. Ludlow Cove is a proposed development located on the south side of Paradise Bay Road adjacent to Port Ludlow Bay. The 30 acre development will consist of 145 units in 34 buildings. Each building will have 4 or 5 units. The northern portion of the proposed development is currently undeveloped forested land with steep slope areas. The southwestern portion of the site has been used as a log yard for about 40 years. SCOPE The purpose of our services was to explore subsurface soil and ground water conditions at the site and provide geotechnical recommendations for the proposed development. Our specific scope of services for this project included the following: 1. Excavating a series of test pits at the site to explore subsurface soil and ground water conditions. 2. Determining the aerial extent and depth of wood waste/organic soils in the log yard area, as appropriate. 3. Obtaining samples from test pit excavations to evaluate physical and engineering properties of soils in the project area. 4. Evaluating the depth, extent and condition of fill placed in the log yard area, as appropriate. 5. Providing recommendations for site preparation and for earthwork including stripping requirements, hillside grading, evaluation of on-site soils for use as fill, and compaction criteria. 6. Providing recommendations for building setbacks in steep slope areas. 7. Providing recommendations for foundation and slab support of the proposed structures including allowable bearing values and estimates of settlement. 8. Providing recommendations for site drainage, as appropriate. 9. Providing recommendations for pavement design including subgrade preparation. 10. Preparing a report summarizing our findings together with our conclusions and recommendations. G e o E n g i n e e r s 2 File No.2378-033-T03/032295 • • t t SITE DESCRIPTION s SURFACE CONDITIONS General The site is located adjacent to the shoreline of Port Ludlow Bay, as shown on the Site Plan. The northern portion of the property consists of undeveloped forested land. The southwestern portion of the site is currently used as a log yard. Northern Portion The northern portion of the site has been previously logged. Vegetation over most of the area consists primarily of mature second growth cedar and Douglas fir trees with an understory of brush and ferns. Vegetation along the shoreline generally consists of alder and maple trees. Elevations range from sea level along the shoreline to about 80 feet MSL (mean sea level) in the northern part of the site. The site slopes to the south, with average slopes ranging from about 15 to 25 percent. A ravine bisects the eastern portion of the site. A creek flows southeast through the ravine. The slopes increase to about 40 percent along the shoreline on the eastern portion of the site. Minor wave undercutting was observed along portions of the shore line. We did not observe any evidence of instability or erosion on the site slopes. No ground water seepage or areas of hydrophilic vegetation were observed at the time of our site visit. Log Yard Area The southwestern portion of the site has been historically used as a log yard which is currently operated by Pope-Talbot. The log yard area is delineated on the Site Plan. Elevations in the log yard area range from sea level to about 50 MSL. The log yard area slopes down gently to the east. Slopes along the shoreline are typically inclined at 40 to 50 percent with a vertical relief ranging from about 10 to 20 feet. Minor wave undercutting was observed along portions of the shore line. The surface of the log yard is covered with wood debris typically on the order of 6 inches deep, overlying a surface of crushed basalt. We understand that wood debris has been removed from the log yard on at least two occasions in the past. SUBSURFACE EXPLORATIONS Subsurface soil and ground water conditions at the site were explored by excavating 10 test pits at the locations shown on the Site Plan. The test pits were excavated using a John Deere 310C rubber-tired backhoe on February 21, 1995. The excavations extended to depths ranging from 6 to 12 feet below the ground surface. The location of the test pits were determined in the field by taping or pacing from existing features, and should be considered approximate. A representative from our firm continuously monitored the excavations and kept a detailed log of the soil, rock and ground water conditions G e o E n g i n e e r s 3 File No.2378-033-T03/032295 • • encountered. Soils were classified visually in general accordance with ASTM D-2488-83, which s is described in Figure 3. The logs of our explorations are attached as Figures 4 through 7. The test pits were backfilled with the 'excavated soil. This soil was not compacted. If structures or pavement is to be located over these areas the backfill may need to be removed and compacted as structural fill. ' SUBSURFACE CONDITIONS Subsurface conditions at the site generally consist of recessional deposits of sand and gravel with varying amounts of silt. The recessional outwash deposit thins towards the north/northeast. Glacial till is exposed at the surface in the road cut along Oak Bay Road on the northeastern portion of the site and was encountered underlying the recessional deposits in that area. Recessional outwash was encountered in each of our excavations. Recessional outwash deposits are soils which were deposited by melt water stream in front of retreating glaciers. Outwash deposits at the site typically consist of yellowish brown to brown sand and gravel in a medium dense to dense condition. The amount of silt in the sand and gravel typically varies. Silt lenses also occur within the outwash in some areas. A layer of very stiff silt was encountered between 1.5 and 5.0 feet below the surface in test pit 4. Glacial till was encountered underlying the outwash in test pits 4, 9 and 10. Glacial till is soil which was deposited in front of advancing glaciers and subsequently overridden and consolidated by the advancing glacier. The till deposits at the site consist of gray silty sand and gravel with occasional cobbles in a very dense condition. Glacial till occurred at 9 feet below the surface in test pit 4, 3.5 feet below the ground surface in test pit 9, and at 8 feet below the surface in test pit 10. The till extended to the full depth explored (8 to 12 feet) in each of these explorations. We encountered 3 to 6 inches of forest duff on the ground surface at most of our test pit locations. The duff generally consists of organic material (leaves and plant debris) in various stages of decomposition. Duff was not encountered test pits 7 and 8, located in the log yard area. Approximately 2 feet of fill was observed on the surface in test pit 3. Test pits 7 and 8 were located in the southern portion of the log yard area. A layer of crushed basalt quarry spalls was encountered extending to a depths of about 1 to 3 feet. The layer of quarry spalls was about one foot thick in test pit 7, with rock sizes typically about 9 to 12 inches. The spall layer was about 3 feet thick in test pit 8, with rock sizes ranging from about 3 to 6 inches. We estimate that the quarry spall layers we observed contained less than 10 percent wood waste and organic material. Similar conditions were observed in a series of test pits excavated for archaeologic studies along the southern and eastern edges of the log yard between test pits 7 and 3. Our observations indicate that the quarry spall layer occurs over most of the log yard area. G e o Engineers 4 File No.2378-033-T03/032295 • Ground water seepage was encountered at about 8 feet below the surface in test pit 6, and F , at 5.5 and 6 feet below the surface in test pits 1 and 3. Ground water seepage was not observed in any of our other explorations. We expect that the ground water encountered in test pits 1 and 3 are influenced by tidal fluctuations and may vary. We also expect that seasonal perched ground water conditions may occur at the contact between the glacial till and more permeable overlying soils. CONCLUSIONS AND RECOMMENDATION We conclude that the site is suitable for the proposed development based on our observations of surface and subsurface conditions. We expect that some grading will be required to prepare building pads and construct roadways. General geotechnical considerations for site development addressed in this report include the following: • Structures may be founded on the medium dense to dense sand and gravel native soils at the site or on properly placed and compacted structural fill. • An average of about 6 inches of wood waste and organic material overlies the log yard area. This material should be removed from areas in which structures, roads, or parking areas are to be located. Structures may be founded on the quarry spalls or the underling native sand in the log yard area. • The on-site soils can be used as fill. It should be noted the on-site soils contain varying amounts of silt. The soils with over 10 percent silt will be moisture sensitive and will be difficult or impossible to compact when they contain excessive moisture. • Grading may include fills on slopes. All fill should be properly keyed into the slopes and drained, as appropriate. • Slopes at the site appear to be stable under existing conditions. Setback recommendations have been developed. • Ground water seepage is not expected to be a limiting factor to construction under current conditions. However, ground water may be seasonally perched in areas where the glacial till occurs at shallow depths, where less permeable layers of outwash occur, and near the shoreline in the vicinity of test pits 1 and 3. Site development should include drainage facilities as appropriate to intercept ground water seepage. LANDSLIDE HAZARD A copy of the Geologically Hazardous Areas Section of the Jefferson County Critical Areas Ordinance is attached as Appendix A. Jefferson County defines landslide hazard areas as: • Areas of historic failures, including areas of unstable slopes and old and recent landslides. • Areas potentially unstable as a result of rapid stream incision, stream bank erosion, or undercutting by wave action. G e o E n g i n e e r s 5 File No.2378-033-T03/032295 ! • • Areas described and mapped as having severe or very severe building limitations for dwellings without basements within the United States Department of Agriculture/Soil Conservation Service Soil Survey for Jefferson County. No evidence of landsliding or slope instability was observed on the site, except as noted below. However, we believe that surficial soils on the steeper slopes will be vulnerable to creep and/or sloughing if they are disturbed during construction, or if development increases or concentrates surface drainage or ground water seepage. Fills on or near slopes should be placed on properly proofrolled and compacted subgrade material, and should be keyed and drained as recommended below. Graded areas and fill slopes should be revegetated to reduce erosion potential. We recommend that a surface water drainage system be developed for the subdivision to collect drainage from impermeable surfaces and yard areas, and directed it away from slope areas. Recommendations for fill construction, drainage and erosion protection are presented in greater detail in following sections of this report. The stream which bisects the northeastern portion of the site does not appear to be undercutting site slopes under existing conditions. Minor wave undercutting was observed along the shoreline. The Coastal Zone Atlas of Washington published by the Department of Ecology describes the site slope stability as ranging from unstable to stable. A small area at the southwestern corner of the site is identified as unstable, as is the portion of the site east of the ravine which bisects the site. Portions of the shoreline of the log yard are identified as moderately stable. The balance of the site is described as stable. No landslide features are identified within the site. The site is located in an area mapped by the SCS (Soil Conservation Service) as having limitations to construction of dwellings without basements which range from moderate to severe depending on the soil type and slope. Site soils are included in the Alderwood and Everett series in the Soil Survey of Jefferson County. The soil survey describes the limitations to dwellings with basements of the Alderwood soils as moderate for slopes ranging from 0 to 15 percent and severe for slopes greater than 15 percent. The soil survey describes the limitations to dwellings with basements of the Everett soils as slight for slopes ranging from 0 to 8 percent, as moderate for slopes ranging from 8 to 15 percent, and as severe for slopes greater than 15 percent. Portions of the site meet the Jefferson County criteria for landslide hazard areas due to the SCS classification and the slope stability descriptions in the Coastal Zone Atlas. However, based on our site exploration and experience on similar sites it is our opinion that landslide hazards are not a limiting factor for this development provided the setbacks recommended below are maintained and our recommendations presented in other portions of this report are followed. SETBACKS In our opinion, a minimum horizontal setback of 15 feet should be maintained between foundations and the face of slopes steeper than 30 percent and greater than 10 feet in vertical height on this portion of the site, as illustrated in Figure 2. G e o E n g i n e e r s 6 File No.2378-033-T03/032295 • • EROSION HAZARD Jefferson County defines erosion hazard areas as those areas that are classified as having severe or very severe erosion potential by the SCS. The site is located in an area mapped by the SCS as having erosion hazards which range from slight to severe depending on slope. Site soils are included in the Alderwood and Everett series in the Soil Survey of Jefferson County. The soil survey describes the erosion hazard of the Alderwood soils as slight to moderate for slopes ranging from 0 to 15 percent, moderate to severe for slopes of 15 to 30 percent, and severe for . slopes of 30 to 50 percent. The soil survey describes the erosion hazard of the Everett soils as slight to moderate for slopes ranging from 0 to 30 percent and as moderate for slopes ranging from 30 to 50 percent. EROSION CONTROL It is our opinion that the potential erosion hazard of the site is not a limiting factor for the proposed development. The proposed development will be located primarily in the more gently sloping portions of the site. Temporary and permanent erosion control measures should be installed and maintained during construction or as soon as practical thereafter to limit the additional influx of water to exposed areas and protect potential receiving waters. Erosion control measures should include but not be limited to berms and swales with check dams to channel surface water runoff, ground cover/protection in exposed areas and silt fences. Removal of natural vegetation should be minimized and limited to the active construction areas, and reestablishment of vegetation should be undertaken as soon as possible. Graded areas should be shaped to avoid directing runoff onto cut or fill slopes, natural slopes or other erosion-sensitive areas. Temporary ground cover/protection such as jute matting, excelsior matting, wood chips or clear plastic sheeting should be used until permanent erosion protection is established. We recommend that graded or disturbed slopes be tracked in-place with the equipment running perpendicular to the slope contours so that the track grouser marks provide a texture to help resist erosion. Thereafter, all disturbed areas should be revegetated. We recommend that no loose fill be placed on the slopes and that no water be directed toward or discharged on the slope areas. Tightlines should be used to direct storm or other surface water across slope areas. Long term erosion control will require that the vegetative cover on the slopes be maintained. Any bare ground areas should be vegetated, as necessary. Erosion resistant plant species include: • Woody shrubs such as: oregon grape, service berry, and salal. • Grass mixtures including: rye, fescue, bent, and clover. • Other deep rooted site tolerant vegetation. G e o E n g i n e e r s File No.2375-033-'l'03/032295 • • T � SEISMIC VULNERABILITY R , In our opinion, the site does not contain seismic hazards areas as defined by Jefferson County criteria. The Puget Sound region is a seismically active area; all sites within this region can be expected to experience some damage in the event of a significant seismic event. Certain factors can result in increased probability or degree of damage at a particular site. We did not encounter conditions which in our opinion place this site at risk of unusual damage in the event z of a significant seismic event. Specifically, potentially liquefiable soils, loose sands and silty sands below the water table, were not encountered on the site. T ? EARTHWORK General We expect that the majority of the grading can be accomplished with conventional heavy earthmoving equipment. Surficial soils at the site generally contain high amounts of silt, and are therefore sensitive to disturbance when they become excessively wet. Operation of heavy equipment at the site under wet conditions can be expected to result in considerable disturbance to the exposed subgrade soils. During wet weather construction, it will probably be necessary to provide temporary haul roads consisting of quarry spalls, crushed rock or pit run sand and gravel. We _ recommend that earthwork be undertaken during periods of dry weather, if feasible, to minimize grading costs. Clearing and Site Preparation The work area should be cleared of all surface and subsurface debris including underbrush, tree stumps, roots and organic-laden soils. Portions of the project area has previously been cleared. Our observations indicate that the upper 1/2 to 1 foot of soil has been previously disturbed. Stripping or recompaction of the soils to these depths may be required where previous site activities have softened surficial soils and/or mixed organic debris into the soil. If the clearing operations cause excessive disturbance, additional stripping depths may be necessary. Disturbance to a greater depth can also be expected if site preparation work is done during periods of wet weather. The organic laden strippings can be stockpiled and used later for landscaping purposes or be spread over disturbed areas following completion of grading. If spread out, the organic strippings should be in a layer less that 1 foot thick, and should not be placed on slopes. Materials which cannot be used for landscaping or protection of disturbed areas should be removed from the project site and wasted. In the log yard we recommend all wood debris be removed from areas in which structures, roads, or parking areas will be located. Although only a nominal thickness of wood debris was encountered in our explorations areas with thicker deposits of wood debris may occur in the log yard and a contingency should be included in the project budget for removal of this material. G e o E n g i n e e r s 8 File No.2378-033-T03/032295 T • • t Subgrade Preparation Following stripping, the exposed subgrade should be evaluated prior to placing structural fill, pavement materials or constructing foundations. During dry weather, subgrade evaluation should consist of proofrolling with heavy rubber-tired construction equipment. During wet weather, subgrade evaluation should be accomplished using hand probing. Any soft areas noted during proofrolling or probing should be overexcavated and replaced with structural fill as outlined below. We recommend that a GeoEngineers representative be present during proofrolling and/or probing to evaluate exposed subgrade soils. Prior to placement of structural fill, the exposed subgrade should be uniformly compacted to at least 90 percent of MDD (maximum dry density) determined in accordance with ASTM D-1557. Where foundations, slabs or pavement is to be founded directly on native material, we recommend that the subgrade soil be compacted to at least 95 percent of MDD. Surficial materials over portions of the site contain enough fines (material passing the No. 200 sieve) that compaction of subgrade will be difficult, if not impossible, to achieve during periods of wet weather. If grading takes place during the wet winter months, it may be necessary to overexcavate and replace native materials with compacted structural fill containing less than 5 percent fines beneath building and pavement areas. Where underlying subgrades are excessively wet, it may be necessary to stabilize the subgrade with a layer of quarry spalls, clean gravel, or by placing a layer of geotextile fabric (such as Mirafi 500x) between the subgrade and structural fill. Structural Fill All fill in embankments and beneath structures or pavements should be placed as structural fill. Structural fill material should be free of debris, organic contaminants and rock fragments larger than 6 inches. The workability of material for use as structural fill will depend on the gradation and moisture content of the soil. As the amount of fines (material passing the No. 200 sieve) increases, soil becomes increasingly more sensitive to small changes in moisture content and adequate compaction becomes more difficult or impossible to achieve. If fill material is imported to the site for wet weather construction, we recommend that it be a sand and gravel mixture, such as high quality pit run, with less than 5 percent fines. All structural fill should be compacted in horizontal lifts to at least 90 percent of the MDD per ASTM D-1557. The uppermost 24 inches of subgrade soils below structures, slabs-on-grade and pavements should be compacted to at least 95 percent of the MDD. We recommend that the fill prism supporting footings, defined by a plane extending down from the edges of the footing at 1 to 1 (horizontal to vertical) to native ground, be compacted to at least 95 percent of MDD. The lift size used during placement and compaction will depend on the moisture and gradation characteristics of the soil and the type of equipment being used. If necessary, the material should be moisture conditioned to near-optimum moisture content prior to compaction. During fill and backfill placement, sufficient testing of in-place density should be performed to verify that adequate compaction is being achieved. GeoEngineers 9 File No.2378-033-T03/032295 T T • • C t Suitability of On-Site Materials for Fill During dry weather construction, any nonorganic on-site soil and rock may be considered for use as structural fill provided it is at a suitable moisture content when placed and can be compacted as recommended. If the material is too wet when excavated, it will require aeration and drying prior to placement as structural fill. fi Fill Placement on Slopes All fill placed on slopes steeper than 5 to 1 (horizontal to vertical) should be benched into T r the slope face and include keyways and subdrains. Bench excavations should be level and extend into the slope face until a vertical step of about 3 feet is constructed. The excavated materials may be pushed out and compacted into the structural fill as it is brought up if adequate compaction can be achieved. Keyways should be located below fill embankment toe areas where new fills meet existing hillside slopes. Additional keyways may be necessary depending on the extent of the proposed fill and the quality of the soil underlying the embankment. Keyways should be embedded at least 2 feet into stable material in the toe area. The width of the keyway will depend on several factors, such as the vertical height of the fill above the keyway and the size of the equipment used to construct the keyway. In general, keyways should be at least 10 feet wide or about 11/ times the width of the equipment used for grading or compaction. Fill Slopes Permanent fill slopes should be constructed at inclinations of 2 to 1 (horizontal to vertical) or flatter, and should be blended into existing slopes with smooth transitions. To reduce postconstruction sloughing and ravelling, we recommend that fill slopes be overbuilt where possible and subsequently cut back to expose well compacted fill. Retaining structures should be used where cut and fill slopes 2 to 1 or flatter cannot be achieved. To minimize erosion, newly constructed slopes should be hydroseeded as soon as practical. Until the vegetation is established, some sloughing and ravelling of the slopes should be expected. Erosion control measures such as temporary covering with clear plastic sheeting, revegetation fabric or jute matting should be used to protect these slopes until vegetation is established. We also recommend that graded areas above slopes be shaped to direct surface water away from the slope face. Fill Drainage Subdrains should be installed at the rear of each keyway and at other locations beneath fill embankments where ground water seepage is encountered during grading. The subdrains can be installed concurrently with fill placement, or in trenches excavated after filling, where the trench depth would not exceed about 4 feet. G e o E n g i n e e r s 10 File No.2378-033-T03/032295 • M � The drains should consist of a free-draining sand and gravel drainage material, placed in T s a trench about 2 feet wide, fully encapsulated within a suitable nonwoven, geotextile filter fabric, such as Mirafi 140N (or similar material). The drainage material should extend the full height of the rear keyway wall. Where subdrains are used to intercept ground water seepage at locations other than at keyways, the drainage material should be at least 3 feet high. A heavy-wall (SDR-35 or heavier) perforated pipe should be installed near the bottom of - each subdrain and bedded in drainage material. Pipes should have minimum slopes of 1 percent and should drain to suitable collector and discharge points. All subdrain lines should include cleanout risers. We recommend that the cleanout risers be covered with tamper-proof locking caps. Discharge pipes should be covered with heavy galvanized wire mesh to prevent rodent access. Cut Slopes Permanent cut slopes in soils should be inclined at 2 to 1 (horizontal to vertical) or flatter, or should be retained with a properly designed retaining structure. Cut slopes should be hydroseeded shortly after completion of grading to prevent erosion. Temporary erosion protection may be necessary as discussed above for newly constructed fill slopes. Temporary Cut Slopes Temporary cut slopes are anticipated for construction of underground utilities. All temporary cut slopes and shoring must comply with the provisions of Title 296 WAC, Part N, "Excavation, Trenching and Shoring." The contractor performing the work must have the primary responsibility for protection of workmen and adjacent improvements, deciding whether or not to use shoring, and for establishing the safe inclination for open-cut slopes. Temporary unsupported cut slopes more than 4 feet high may be inclined at 1H:1V (horizontal to vertical) maximum steepness within native till or structural fill. Flatter slopes may be necessary if seepage is present on the cut face. Some sloughing and ravelling of the cut slopes should be expected. Temporary covering with heavy plastic sheeting should be used to protect these slopes during periods of wet weather. Permanent Slopes We recommend that any permanent fill slopes be constructed no steeper than 2H:1V. To achieve uniform compaction, we recommend that fill slopes be overbuilt slightly and subsequently cut back to expose well compacted fill. To minimize erosion, newly constructed slopes should be planted or hydroseeded shortly after completion of grading. Until the vegetation is established, some sloughing and ravelling of the slopes should be expected. These may require localized repairs and reseeded. Temporary covering, such as clear heavy plastic sheeting,jute fabric, loose straw or excelsior matting could be used to protect the slopes during periods of rainfall. G e o E n g i n e e r s 11 File No.2378-033-T03/032295 T • • T Utility Trenches ▪ T Trench excavation, pipe bedding, and trench backfilling should be completed using the general procedures described in WSDOT Standard Specifications, Section 7-17, or other suitable procedures specified by the project civil engineer. Utility pipes should be bedded in sand and smooth rounded gravel, such as specified in WSDOT Standard Specifications, Section 9-03.15. Additionally, we recommend that the pipe be covered with bedding material to at least one foot above the pipe. This bedding material should be lightly tamped into place. Backfill placed above the bedding material shall consist of structural fill quality material as discussed above. Utility trench backfill can be placed in lifts of 12 inches or less (loose thickness) below a depth of 5 feet from finish grade. Within 5 feet of finish grade, backfill should be placed in lifts of 8 inches or less (loose thickness) such that adequate compaction can be achieved throughout the lift. Each lift must be compacted prior to placing the subsequent lift. Prior to compaction, the backfill should be moisture conditioned to near optimum moisture content, if necessary. The backfill should be compacted in accordance with the criteria discussed above. FOUNDATION SUPPORT General We recommend that residential structures be supported on conventional spread footings founded on medium dense to dense native soil, or structural fill, prepared as recommended in the "Earthwork" section of this report. Shallow spread footings designed and constructed as described below may be used where minimum setback distances can be achieved on moderate slopes. Foundation Design We recommend that all footing elements be embedded a minimum of 18 inches below lowest adjacent finished grade. Where footings are placed on sloping ground, the horizontal distance from the bottom of the footing to the ground surface should not be less than 8 feet. We recommend a minimum width of 2 feet for isolated footings and at least 16 inches for continuous wall footings. Deeper footing embedment may be required where minimum building setbacks cannot be achieved, and we recommend that design criteria for footings located on or near slopes be evaluated by a representative from our firm on a site-specific basis. Footings founded as described above can be designed using an allowable soil bearing pressure of 2,500 psf (pounds per square foot) for combined dead and long-term live loads, exclusive of the weight of the footing and any overlying backfill. This value may be increased by one-third for transient loads such as those induced by seismic events or wind loadings. Where a crawlspace is used, footing pads for floor support may be cast on the ground, providing that the ground is firm and level. These pads should be designed using an allowable bearing of 1,000 psf applied to dead and live loads. G e o E n g i n e e r s 12 File No.2378-033-T03/032295 w • - z Structures constructed across mixed subgrade conditions could experience distress because - of differential performance of the subgrade materials. This is a concern at the contact between cuts and fills and at contacts between dissimilar materials within cuts. Where contacts between dissimilar materials are exposed at pad or footing grade, we recommend that the subgrade beneath the structure be overexcavated at least 1 foot below design grade, and the overexcavation backfilled with structural fill compacted to at least 95 percent of the MDD. The limits of the overexcavation and structural fill placement should extend at least 1 foot outside of the building footprint or footing area. Loose or disturbed subgrade soils in footing excavations may result in increased settlement. The native soils are susceptible to disturbance if allowed to become wet. If footings are constructed during wet weather, concrete should be placed as soon as possible after the footings are excavated. It also may be appropriate to place a lean concrete "mud mat" or a layer of crushed rock in footing excavation bottoms to protect the subgrades from disturbance. We recommend that all completed footing excavations be observed by a representative of our firm prior to reinforcing steel and structural concrete placement. Our representative will confirm that the bearing surface has been prepared in a manner consistent with our recommendations and that the subsurface conditions are as expected. Lateral Load Resistance Lateral loads can be resisted by a combination of friction between the footing and the supporting soil, and by the passive lateral resistance of the soil surrounding the embedded portions of the footings. A coefficient of friction between concrete and soil of 0.35 and a passive lateral resistance corresponding to an equivalent fluid density of 300 pcf(pounds per cubic foot) may be used for design. The friction coefficient and passive lateral resistance are allowable values, and incorporate factors of safety of approximately 1.5. If soils adjacent to footings are disturbed during construction, the disturbed soils must be recompacted, otherwise the lateral passive resistance value must be reduced. Foundation Settlement We estimate that the postconstruction settlement of shallow footings supported on native till or on structural fill may range from about '/a to '/z inch. Maximum differential settlement should be less than '/a inch, measured along 25 feet of continuous wall footing. We expect that settlements for these conditions will tend to occur rapidly after the loads are applied. Immediately prior to placing concrete, all debris and soil slough that accumulated in the footings during forming and steel placement must be removed. Debris or loose soils not removed from the footing excavations will result in increased settlement. G e o Engineers 13 File No.2378-033-T03/032295 • 1110 FLOOR SLAB SUPPORT Floor slabs may be supported on-grade provided that the subgrade soils are prepared as previously recommended. Any areas disturbed by construction activities should be recompacted before proceeding with slab construction. We recommend that slabs-on-grade be constructed on a gravel layer to provide uniform support and to act as a capillary break. The gravel layer should consist of at least 4 inches of clean fine gravel or crushed rock, with negligible sand or silt. A vapor barrier should be placed over the gravel layer. We recommend that the vapor barrier be covered with 2 inches of sand to protect it during construction and to aid in curing of the slab concrete. This sand should not be allowed to become wet prior to casting the slab concrete, otherwise curing of the concrete may be adversely affected. In areas where ground water is near the surface, we recommend that underdrainage be provided to collect and discharge ground water from below the slabs. This can be accomplished by thickening the gravel layer below the slabs to 6 inches, and installing a 4-inch-diameter perforated collector pipe in a shallow trench placed below the gravel layer. The collector pipe should be oriented along the center, long axis of the structure. The trench should measure about 1 foot wide by 1 foot deep and should be backfilled with clean gravel. The collector pipe should be sloped to drain and discharge into the storm water collection system to convey the water off site. This pipe should also incorporate a cleanout. RETAINING and SUBGRADE WALLS Design Parameters We recommend that retaining and subgrade walls be designed using an active lateral earth pressure corresponding to an equivalent fluid density of 35 pcf. This lateral earth pressure is for a wall with level backfill. For walls with backfill sloping up at 2H:1 V, the design lateral earth pressure should be increased to 55 pcf. If vehicles can approach the wall to within '/ the height of the wall, a traffic surcharge should be added to the wall pressure. For car parking areas, the traffic surcharge can be approximated by the equivalent weight of an additional 1 foot of soil backfill behind the wall. For delivery truck parking areas and access driveway areas, the traffic surcharge can be approximated by the equivalent weight of an additional 2 feet of soil backfill behind the wall. These recommendations are based on the assumption that any retaining walls at this project will be provided with backdrainage and will be unrestrained against slight top rotation. If the walls will be restrained, higher pressures will be appropriate. Walls are assumed to be restrained if top movement during backfilling is less than H/1000, where H is the wall height. The values for soil bearing, frictional resistance and passive resistance presented above for foundation design are applicable to retaining wall design. G e o E n g i n e e r s 14 File No.2378-033-T03/032295 • i Backdrainage The retaining walls could be exposed to water from ground or surface water sources, or from landscape watering. As the proposed structure will utilize the retaining wall as a basement wall, we recommend that the buried portions of the wall be waterproofed. To reduce the potential for hydrostatic water pressure buildup behind the retaining walls, we recommend that the walls be provided with backdrainage. Backdrainage can be achieved by using free draining material or prefabricated drainage panel products,with perforated pipes to discharge the collected water. Free draining material should consist of sand and gravel containing less than 3 percent fines. The draining material should be 2 feet wide and should extend from the base of the wall to within 1 foot of the ground surface. The free draining material should be covered with 1 foot of less permeable material, such as the on-site silty sand. Prefabricated drainage panel products,such as Mirafi Miradrain 6000(or similar material), consist of a geotextile filter fabric bonded to a molded plastic drainage element. The drainage panel is placed directly behind the wall, and should extend from the base of the wall to about 1 foot from finished grade. The panel should be covered with 1 foot of less permeable material, such as the on-site silty sand. Wall backdrains should include a perforated pipe with a minimum diameter of 6-inches. We recommend using either heavy-wall solid pipe or rigid corrugated polyethylene pipe. We recommend against using flexible tubing for wall backdrain pipe. The pipe should be installed with about 3 inches of drainage material below the pipe, or the drainage panel geotextile filter fabric should extend from the panel to wrap around the pipe. The pipes should be laid with minimum slopes of one percent and discharge to appropriate disposal points to convey the water away from the retaining walls. The pipe installations should include cleanout risers located at the upper end of each pipe run. We recommend that the cleanouts be provided with tamper-proof locking caps, completed within flush mounted utility boxes. We recommend that roof downspouts not discharge into the perforated pipes providing wall backdrainage. Construction Considerations Care should be taken by the contractor during backfilling to avoid overstressing the retaining walls. Backfill placed within about 5 feet of the walls should be compacted with hand- operated or small self-propelled equipment. Heavy compactors or other heavy construction equipment should not be used within about 5 feet of the walls. Rockeries Rockeries may be planned in areas with grade transitions. Rockeries essentially serve as protection against erosion and minor sloughing along existing stable slopes and provide little "retaining" support. Rockeries are best suited for use along stable slopes cut in competent soils. When a rockery is constructed along the face of a fill embankment, adequate compaction of the G e o E n g i n e e r s 15 File No.2378-033-T03/032295 • i fill behind the rockery is critical for long-term stability; the fill should be compacted to at least 95 percent of the MDD, and the fill height should be limited to about 4 feet. Any surcharge conditions above a rockery or seepage conditions within the fill embankment behind a rockery can lead to distress or failure of a rockery-faced slope. The potential need for maintenance of rockeries should be recognized. We recommend that rockeries be constructed in accordance with the most current edition of "The Association of Rockery Contractors Standard Rockery Construction Guidelines." For planning purposes, we recommend that all rockeries be limited to a maximum height of 8 feet. DRAINAGE All ground surfaces, pavements and sidewalks should slope away from structures. Surface water runoff should be controlled by a system of curbs, berms, drainage swales, and/or catch basins, and conveyed off-site through a storm water collection system. Surface water should not be discharged over slopes or into subdrains. Roof drains should be tightlined to discharge into the storm water collection system or to an appropriate outlet structure. Roof drain water should not be discharged to footing drains. Footing, wall and underslab drainage systems may be needed depending on final design grades and localized ground water conditions. Footing drains with an invert elevation at the base of the footing are generally effective to limit water seepage into crawlspaces. The crawlspace should not be excavated deeper than the invert of the footing drains, or additional areal drains will need to be provided. Permanent drainage systems should be installed at the top and/or bottom of cut and fill slopes to intercept surface runoff and to prevent it from flowing in an uncontrolled manner across the slopes. PAVEMENT DESIGN AND SUBGRADE PREPARATION Parking area and access drive pavement subgrades should be prepared as described previously in the EARTHWORK section of this report. We recommend the pavement in areas to be used exclusively by automobiles consist of 2 inches of Class B asphalt concrete over 4 inches of crushed surfacing base course. For pavement in access roads and truck parking areas, we recommend providing 3 inches of asphalt concrete over 6 inches of crushed surfacing base course. The base course should be compacted to at least 95 percent of the maximum dry density (ASTM D1557). The crushed base course should comply with Washington Department of Transportation Standard Specifications for Road, Bridge and Municipal Construction, 1988, Section 9-03.9(3) "Base Course." The asphalt concrete materials and procedures should comply with specifications in that document for Class B Asphalt Concrete Pavement. G e o E n g i n e e r s 16 File No. 2378-033-T03/032295 * LIMITATIONS We have prepared this report for use by Pope Resources and members of the project team involved in the Ludlow Cove residential development. The data and report should be provided to prospective contractors for bidding or estimating purposes; but our report, conclusions and interpretations should not be construed as a warranty of the subsurface conditions. Our scope 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. The project was in the design development stage at the time this report was prepared. We expect that further consultation regarding specific design elements will be necessary. If there are any changes in the grades, location, configuration or type of construction planned, the conclusions and recommendations presented in this report might not be fully applicable. If such changes are made, we should be given the opportunity to review our conclusions and recommendations and to provide written modification or verification, as appropriate. When the design is finalized, we recommend that we be given the opportunity to review those portions of the specifications and drawings that relate to geotechnical considerations to see that our recommendations have been interpreted and implemented as intended. There are possible variations in subsurface conditions between the locations of the explorations and also with time. Some contingency for unanticipated conditions should be included in the project budget and schedule. We recommend that sufficient monitoring, testing and consultation be provided by our firm during construction to confirm that the conditions encountered are consistent with those indicated by the explorations; to provide recommendations for design changes should the conditions revealed during the work differ from those anticipated; and to evaluate whether or not earthwork and foundation installation activities comply with the contract plans and specifications. Within the limitations of scope, schedule and budget, our services have been executed in accordance with generally accepted practices in this area at the time the report was prepared. No other conditions, express or implied, should be understood. O ► G e o E n g i n e e r s 17 File No.2378-033-T03/032295 • • We appreciate the opportunity of working with you on this project. If you have any questions or need further assistance, please call. Yours very truly, oo �'�' �. GeoEngineers, Inc. • .' 515 ///7--------j7 � �Ort�, 31000 ,�' ' Thomas V. May - - �'S'�4'G1 R�Cs Geotechnical Engineer SIGNAL E EXPIRES:6/14/ C4 4) Gary W. Henderson Principal TVM:GWH:cdl:vc Document ID:2378033R.R Attachments Four copies submitted cc: Pope Resources 781 Walker Way Port Ludlow, Washington 98365 Attn: Mr. Ray Welch GeoEngineers 18 File No.2378-033-T03/032295 SLF:SPS 2378033.DWG 2378033T03:030995 \ 93 o 1 VIilim . N ' o A N n p o O CD ... \ -S , . it 4 ( _ _ co .„.„ Z latitt,44016....". \ SO 1 'lllll5. � f • cn ------Alli, r1: 1 o Hf \-........,..........„, a 11444.„8-_„dtok 4 , 4i*J .,‘ 1 cn 121) 4741kikSIIWO \1040k. O. ' AAA 4 ,di . e 0 < .117/ No, N. c"Mil ),\4:A,P `\904pi 4/' 1\t i ( ;0 m I /\ : 'fr+7V±: - • / ;--, § \ _.< T. 'k' £*M*Ek \W1 ,„fMU \\,,, r „ ,;., 9, VIS''' *1/4 :‘t' '4"11, ' ' \\\ n r:';',; = —I x - %,,:,„ 844 . ., ic. * AlliN lit , _ , ,,,,, .,,,,s; ,„„);,,,, ,,,,, , „ . . rri _ _, , ( i ti..,:14*(41,4, '4VAt'' r.6'.7, 1' -'57 \ 7 4l4%i i- 7‘ ' oNo a O m *4 +III%. N‘\..\• , ►4,NL 0, 1 1 .,5 I 1=1 Akk_NOV4441*ft,'-V\‘ --, ‘" ' '' \r''P A \ 0 g NI (in 6 2 6 -.3 ( klt._\_, :akt• ii. - ‘b.. ‘‘, - . 1 411‘, 4,- ,,, 0 , *ireivo.,_;,t,..x \ , 0 _< Nk*:141417NtsX 4 i li 1A,' It \ It\ 1w. 1,r1. ,`,,\, '\ i&..-s g ill .! in, '. , tfta4A. . 1110.*. ,,��- 11\r w I l, ' )iN\ ..„. N 1 11 In ' g c. \ \*Ol':"*Virli ' li 1 cn 0 litIWS11•14\ Lk 1, ..., , f ' At' li --11 *4''*-'(. --`4A.4 r- -. 4, > (. ikbli1/4A ';''; '\ la op—co- rn o °" _„r_z_y_.__ 0 ( limvoi.vp_1 ,, .. \\ • :, . \ " - VO b \ I . r- lHlam, , .., , ,liiil!IV ri rii o ‘61- 1 / titilii \`.44;) -. .. ' d Z 1. / 11,7 t . \\, ..- „ ,,l'it ! / ") a) o •_., ( I \\woo Ai M. � ,,, _ -p' rill rfAt +.13 \ d` tit • � 4 • ��. (_,4 m . , i_\_., v. '\:_ ,,,wi, N 4„,p, ,,,,„,,,,,,,, a) ...---- / Nt, ' N.7:4,k.,isN. e mA i „... gu m . A 4' 'i . \ \ \ *% Z\, \ N CO O rirIN ,---4,,, ,\ , . < _a, 0 co 7-1 o z � O � � m � � N 0 CFE- �Om Tlm O N @ i' c m sc�1a � " I 0 cl. l • IOW xi 0bH I• VI 5 ; Y � � �_� w N QOON < z yS{71 m• y ego fin* Ai ?li>JJJJ N2)(II cn 1�)> � 0 -0 n 0 • • Foundation a' e a . . %�!4. i�i�i�i�i�i "''� • • °. • G�-##��!��!i. _E •• N4:�. 15' Minimum Dense Native Soil or M Properly Compacted Structural Fill 0 O O 0 In O M NOT TO SCALE 0 z 0 U- g° FOUNDATION DETAIL Geo Engineers � FIGURE 2 • • • • tr SOIL CLASSIFICATION SYSTEM GROUP MAJOR DIVISIONS SYMBOL GROUP NAME GRAVEL CLEAN GW WELL-GRADED GRAVEL,FINE TO COARSE GRAVEL COARSE GRAVEL = GRAINED GP POORLY-GRADED GRAVEL SOILS More Than 50% of Coarse Fraction GRAVEL GM SILTY GRAVEL Retained WITH FINES on No. 4 Sieve GC CLAYEY GRAVEL More Than 50% Retained on SAND CLEAN SAND SW WELL-GRADED SAND, FINE TO COARSE SAND No. 200 Sieve SP POORLY-GRADED SAND More Than 50% of Coarse Fraction SAND SM SILTY SAND Passes WITH FINES No. 4 Sieve SC CLAYEY SAND FINE SILT AND CLAY ML SILT GRAINED INORGANIC SOILS CL CLAY Liquid Limit Less Than 50 ORGANIC OL ORGANIC SILT, ORGANIC CLAY More Than 50% SILT AND CLAY MH SILT OF HIGH PLASTICITY, ELASTIC SILT Passes INORGANIC CH CLAY OF HIGH PLASTICITY, FAT CLAY No. 200 Sieve Liquid Limit 50 or More ORGANIC OH ORGANIC CLAY, ORGANIC SILT HIGHLY ORGANIC SOILS PT PEAT NOTES: SOIL MOISTURE MODIFIERS: 1. Field classification is based on visual examination of soil Dry- Absence of moisture, dusty, dry to the touch in general accordance with ASTM D2488-90. Moist- Damp, but no visible water 2. Soil classification using laboratory tests is based on ASTM D2487-90. Wet- Visible free water or saturated, usually soil is obtained from below water table 3. Descriptions of soil density or consistency are based on interpretation of blow count data, visual appearance of soils, and/or test data. SOIL CLASSIFICATION SYSTEM Geo O Engineers FIGURE 3 tr • • LOG OF TEST PIT DEPTH BELOW SOIL GROUP GROUND SURFACE CLASSIFICATION (FEET) SYMBOL DESCRIPTION TEST PIT 1 0.0-0.3 3" sod 0.3-2.0 SP Sand with gravel(medium dense,moist) 2.0-2.5 ML Tan to gray silt and very fine sand(medium dense to stiff, moist) 2.5-7.0 SP Sand with gravel(medium dense to dense,moist) Test pit completed at 7.0 feet due to refusal on 02/21/95 Rapid ground water seepage at 5.5 feet Caving observed at 2.5 to 7.0 feet TEST PIT 2 0.0-0.4 4"duff 0.4-6.0 SP Gray sand with gravel(dense,moist) Test pit completed at a depth of 6.0 feet on 02/21/95 No ground water seepage observed No caving observed TEST PIT 3 0.0-0.3 3"duff 0.3-2.0 SM Reddish brown silty sand with gravel(medium dense,moist)(fill) 2.0-2.3 OL Organic material layer-original ground surface 2.3-6.0 SP Orange fine to medium sand with gravel and a trace of silt(medium dense,moist) 6.0-9.0 SM Tan silty fine sand 9.0-12.0 SP Gray fine to medium sand with a trace of silt(medium dense to dense,moist) Test pit completed at a depth of 12.0 feet on 02/21/95 Slight ground water seepage observed at a depth of 6.0 feet,rapid seepage at 9.0 feet Caving observed at a depth of 9.0 to 12.0 feet THE DEPTHS ON THE TEST PIT LOGS,ALTHOUGH SHOWN TO 0.1 FOOT,ARE BASED ON AN AVERAGE OF MEASUREMENTS ACROSS THE TEST PIT AND SHOULD BE CONSIDERED ACCURATE TO 0.5 FOOT. tat; LOG OF TEST PIT GeoEngineers FIGURE 4 . ,. • • LOG OF TEST PIT DEPTH BELOW SOIL GROUP GROUND SURFACE CLASSIFICATION F (FEET) SYMBOL DESCRIPTION TEST PIT 4 0.0-0.4 4"duff 0.4- 1.5 SM Reddish brown silty sand with gravel(medium dense,moist) 1.5-5.0 ML Tan silt with fme sand(very stiff, moist) 5.0-9.0 SP Gray sand with gravel(dense,moist) 9.0- 10.0 GP Gray silty gravel with sand(very dense,moist)(glacial till) Test pit completed at a depth of 10.0 feet on 02/21/95 No ground water seepage observed No caving observed TEST PIT 5 0.0-0.5 4"-6"duff 0.5-2.0 SM Reddish orange silty sand with gravel(dense,moist) 2.0- 11.0 GP Grayish sandy gravel(dense,moist) Test pit completed at a depth of 11.0 feet on 02/21/95 No ground water seepage observed No caving observed TEST PIT 6 0.0-0.6 6"duff 0.6-8.0 SM/SP Reddish brown silty sand(medium dense,moist) Grades to brown fine to medium sand with a trace of silt(dense,moist) 8.0- 11.0 GP Sandy gravel(very dense,wet) Test pit completed at a depth of 11.0 feet on 02/21/95 Slight ground water seepage observed at a depth of 5.5 feet, rapid seepage at 8.0 to 10.0 feet Minor caving observed at 8.0 to 11.0 feet THE DEPTHS ON THE TEST PIT LOGS,ALTHOUGH SHOWN TO 0.1 FOOT,ARE BASED ON AN AVERAGE OF MEASUREMENTS ACROSS THE TEST PIT AND SHOULD BE CONSIDERED ACCURATE TO 0.5 FOOT. LOG OF TEST PIT Geo., ---,Engineers FIGURE 5 • • LOG OF TEST PIT DEPTH BELOW SOIL GROUP GROUND SURFACE CLASSIFICATION (FEET) SYMBOL DESCRIPTION TEST PIT 7 0.0- 1.0 GM Quarry spalls 9-24" sized with less than 10 percent organic material (very dense) (fill) 1.0-3.0 SP Yellowish medium sand with gravel(dense,moist)(weakly cemented) 3.0- 12.0 SP Fine to medium sand with silt(dense,moist) Grades to gray fine to medium sand(dense,moist) Test pit completed at a depth of 12.0 feet on 02/21/95 No ground water seepage observed No caving observed TEST PIT 8 0.0-3.0 GM Quarry spalls (3" to 6") with less than 10 percent organic material (very dense, moist)(fill) 3.0- 11.0 SP Yellow fine to medium sand with occasional gravel(medium dense to dense,moist) Test pit completed at a depth of 11.0 feet on 02/21/95 No ground water seepage observed No caving observed THE DEPTHS ON THE TEST PIT LOGS,ALTHOUGH SHOWN TO 0.1 FOOT,ARE BASED ON AN AVERAGE OF MEASUREMENTS ACROSS THE TEST PIT AND SHOULD BE CONSIDERED ACCURATE TO 0.5 FOOT. ØEngineers LOG OF TEST PIT Geo\ FIGURE 6