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Home My WebLink AboutGeologic Site Assessmentr~ i ,_ [ [ [ [ [ [ [ [ [ [ [ [ L [ E [ HEPWORTH-PAWLAK GEOTECHNICAL, INC. 5020 Road 154 GlenwDod Springs, C0~1601. Fax 970 945-8454 Phone 970 945-7988 GEOLOGIC SITE ASSESSlYIENT AND PRELIMINARY GEOTECHNICAL STUDY PROPOSED RESIDENTIAL DEVELOPMENT FILING 4, OAK MEADOWS SUBDIVISION GARFIBLDCOUNTY,COLORADO JOB NO. 196 420 APRIL 15, 1998 PREPARED FOR: OAK MEADOWS DEVELOPMENT CORPORATION ATTN: RALPH DELANEY P.O. BOX 1298 GLENWOODSPRINGS,COLORADO [ [ [ [ [ [ [ [ [ r L c c E [ c c [ E [ HEPWORTH~ PAWLAK GEOTECHNICAL, INC. April 15, 1998 Oak Meadows Development Corporation Attn: "Ralph Delaney. P.O. Box 1298 Glenwood Springs, Colorado 81602 Job No. 196 420 Subject: Report Transmittal, Preliminary Geotechnical Study, Proposed Residential Development, Filing 4, Oak Meadows Subdivision, Garfield County, Colorado Dear Mr. Delaney: As requested, we have conducted a geologic site assessment and preliminary geotecbnical engineering study for the proposed residential development at the subject site. The purpose of the study was to review the geologic and subsurface conditions in the area for if potentially hazardous conditions or conditions that could have a significant impact on the proposed development. Development of the filing as planned should not encounter severe geologic constraints or potential hazards. Geologic conditions that should be couSidered in project planning include landslide stability, construction induced slope instability, flooding, expansive soils and earthquakes. It should be feasible to use spread footings placed on the natural subsoils at most building sites. An allowable soil bearing pressure between 1,500 psfto 3,000 psf appears suitable for building support. Due to the expansive potential of the clays the footings may also need to be designed for minimum dead load. The geotechnical conditions should be evaluated on a site specific basis. The report which follows describes our investigation, summarizes our findings, and presents our recommendations suitable for planning and preliminary design. It is important that we provide consultation during design, and field services during construction to review and monitor the implementation of the geotechnical recommendations. If you have any questions regarding this report, please contact us. Sincerely, JIE~1QRTH -PAWLAK GEOTECHNICAL, INC. -I E ~ L [ L [ I [_ [ [ [ [ [ TABLE OF CONTENTS PURPOSE AND SCOPE OF STUDY . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 PROPOSED DEVELOPMENT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 SITE CONDITIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2. GEOLOGIC SETTING . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 PROJECT SITE GEOLOGY ..................................... 3 •.. FIELD EXPLORATION ................................ : . . . . . . 5 SUBSURFACE CONDITIONS ................................... 5 GEOLOGIC ASSESSMENT ................................ , : .. ;.c6 · PRELIMINARY GEOTECHNICAL ENGINEERING EVALUATION ......... 8 FOUNDATION BEARING CONDITIONS . . . . . . . . . . . . . . . . . . . . . . 8 FLOOR SLABS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 UNDERDRAIN SYSTEM . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 SITE GRADING . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 SURFACE DRAINAGE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . IO PAVEMENT SUBGRADE ................................ 10 LIMITATIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 REFERENCES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 FIGURE 1 -GEOLOGY MAP AND BORING LOCATIONS FIGURES 2 & 3 -LOGS OF EXPLORATORY BORINGS FIGURE 4 -LEGEND AND NOTES FIGURES 5 -8 -SWELL-CONSOLIDATION TEST RESULTS FIGURE 9 -GRADATION TEST RESULTS TABLE I-SUMMARY OF LABORATORY TEST RESULTS L ·-I L.:.: [ [ [ [ [ [ [ [ L F L c [ [ PURPOSE AND SCOPE OF STUDY This report presents the results of a geologic site assessment and pre1!1ffinarY geotechnical study for the proposed residential development of Oak Meadows, Filing 4, Garfield County, Colorado. The project area is shown on Fig. 1. The purpose of the study was to access the geologic and subsurface conditions for potentially hazardous conditions or conditions that could have a significant impact on the proposed development. Geologic conditions in the project area were observed during a field reconnaissance on March 27, 1998. In addition, we have looked at aerial photographs of the area and have reviewed geologic literature. The study was conducted in accordance with our agreement for professional engineering services to Oak Meadows Development Corporation, dated March 16, 1998. Hepworth -Pawlak Geotechnical, Inc. previously conducted a subsoil study for a proposed settling pond and 11 lots in the northern part of Filing 4 and presented our findings in reports dated October 9 and 15, Job No. 196 420. Eleven exploratory borings were drilled to evaluate the ·general subsurface conditions. Samples of the subsoils obtained dudng the field exploration were tested in the laboratory to determine their classification, compressibility or swell and other engineering characteristics. A project area geologic map has been completed based on our field observations, aerial photograph interpretations and published regional geologic maps. The results of the field exploration and laboratory testing were analyzed to develop recommendations for project planning and preliminary design. This report summarizes the data obtained during this study and presents our conclusions and recommendations based on the proposed development and subsurface conditions encountered. H-P GEOTECH .~ ! ! . L [ [ E [ - 2 - PROPOSED DEVELOPMENT The proposed residential development will consist of 67 single family and }8 duplex lots as shown on Fig. 1. We assume the residences will be typical of the area and be two to three stories with a partial or full basement. The development will include the construction of a water storage tank and a waste water treatment plant. Several roads will be constructed to provide access to the lots. If development plans change significantly from those described, we should be notified to re-evaluate the recommendations presented in this report. SITE CONDITIONS Oak Meadows Filing 4 is in the Oak Meadows subdivision on Four Mile Creek about seven miles south of Glenwood Springs. The filing lies to the west of the creek in the western part of Section 15, T. 7 S., R. 89 W. The general topography in the area is shown on Fig. 1. The eastern part of the filing is on moderately sloping alluvial fans that slope down to the northeast at about 10%. The moderately sloping fans transition abruptly to steeply sloping hillsides in the western part of the filing. Slope of the hillsides is typically about 30% to 40%. In places, the steep hillsides are broken by benches that slope at about 15% to 25%. Drainages with perennial streams are not present in the filing. Four Mile Creek borders the east side of the development and is about 60 feet lower in elevation. In the past, most of the alluvial fans in the filing were irrigated pasture and hay fields. Oak and other brush is present on the valley side in the.western part of the filing. Developed parts of Oak Meadows border Filing 4 on the east and south. Undeveloped land is present to the north and west. The existing water storage reservoir in the southwestern part of the filing near Boring 7 will be upgraded. At the time of our field review overflow from the storage tanks was discharging directly onto the steep hillside to the east of the tanks. There are numerous basalt boulders scattered throughout the project area. H-P GEOTECH i . L E [ - 3 - GEOLOGIC SETTING The project site is located on the Grand Hogback monocline. The Grand Hogback forms _the western limb of the White River uplift. Both are first order geologic structures that resulted from compressional stresses during the Laramide Orogeny about 40 to 70 million years ago. Four Mile Creek in the project area is in a strike valley underlain by the Mancos Shale to the west of the second-order Dakota Sandstone hogback. Bedding in these Cretaceous-age sedimentary rock formations strikes about N 25 ° W with dips between 50° and 60° to the west. Surficial soil deposits in the area consist of high-level basaltic gravels, alluvial fans, landslide deposits, and stream valley alluvium. A series of northwest trending bedding plane faults are present in the upper part of the Mancos Shale and lower part of the Mesaverde Group in this part of the Grand Hogback monocline (Kirkham and Others, 1996). The mapped faults lie to the west of the project area and are believed to be associated with crustal strains associated with solution and flowage in the Eagle Valley Evaporite in the Roaring Fork valley to the east (Kirkham and Widmann, 1997). PROJECT SITE GEOLOGY The main geologic features in the project area are shown on Fig. 1 and described in the following sections. MAN-PLACED FILL AND DISTURBED GROUND There is a small area of man-placed fill and ground disturbed by grading (af) in the northern part of the filing. The area is about V. acre and lies within part of a proposed lot. The excavation in this area is partly backfilled with large basalt boulders. The fill and disturbed ground should be evaluated for foundation support by a site specific investigation, if a building is planned in the area H-P GeOTECH r l [ [ [ [ [ c [ E [ -4- POORLY DRAINED GROUND A moderate size spring and poorly drained ground (Qpdg) is located in the northern part of the filing. The slope to the southwest of the spring could have relatively shallow ground water. The preliminary development plan indicates that construction is not proposed in the poorly drained area. A street and one lot are planned to the southwest of the spring. In this area, the street will be in a fill section with a maximum depth of about 8 feet at centerline. A subdrain will probably be needed below the street fill to prevent water level buildup from the spring. This area should be evaluated at the time of construction to determine street subdrain requirements. LANDSLIDE DEPOSIT . The western part of the subdivision is on the toe of an old landslide (Qls) deposit (Kirkham and Others, 1996). The landslide is a large complex that extends about 7,500 feet upslope to the west. The complex covers more than one square mile and has an average surface slope of about 23%. Slopes within the complex vary from 20% to 50%. Judging from the size of the complex, the depth to the basal shear surface is probably greater than 100 feet. The landslide has displaced the high-level basaltic gravels and may extend into the upper parts of the Mancos Shale and Mesaverde Group. The high-level basaltic gravels consist of sub-angular to rounded, predominantly basalt gravel, cobbles and boulders in a sandy clay matrix. Topography consisting of an irregular slope profile is indicative of past landslide movements. The landslide topography is not sharply defined, it has been modified considerably by erosion and deposition particularly in the toe area. This indicates that the landslide complex has been dormant with respect to large scale movements in the toe area for a long time, probably longer than 5,000 years. There are some indications on aerial photographs of possible small, local landslide reactivations upslope of the filing. Because of snow cover the upper part of the landslide complex could not be reviewed in the field at the time of this study. H-P GEOTECH r- 1 L- r- L r ! !_ [ [ L r [ [ [ r [ -s - ALLUVIAL FANS Coalesc~g alluvial fans fonn a nearly continuous apron of alluvium on moderately sloping ground along the toe of the landslide complex in the eastern part of the filing. Large scale landslide movements do not appear to have occurred at the toe of the landslide complex since the fans developed. The fans probably developed during the late Pleistocene and early Holocene, over 5,000 years ago, as a result of flash flood and debris flow deposition. The fan deposits consist of sandy clay with varying amounts of rock. The rock is predominantly sub-angular to rounded, basalt and sandstone gravel, cobbles and boulders. FIELD EXPLORATION The field exploration for the project was conducted on March 17 and 18, 1998. Eleven exploratory borings were drilled at the locations shown on Fig. 1 to evaluate the subsurface conditions. The borings were advanced with 4 inch diameter continuous flight auger powered by a track-mounted CME-45 drill rig. The borings were logged by .a representative of Hepworth-Pawlak Geotechnical, Inc. Samples of the subsoils were taken with 13/s inch and 2 inch I.D. spoon samplers. The samplers were driven into the subsoils at various depths with blows from a 140 pound hammer falling 30 inches. This test is similar to the standard penetration test described by ASTM Method D-1586. The penetration resistance values are an indication of the relative density or consistency of the subsoils. Depths at which the samples were taken and the penetration resistance values are shown on the Logs of Exploratory Borings, Figs. 2 and 3. The samples were returned to our laboratory for review by the project engineer and testing. SUJ!SURFACE CONDITIONS Graphic logs of the subsurface conditions encountered at the site are shown on Figs. 2 and 3. The subsoils consist of about 1h to 31h feet of topsoil overlying nil to 23 H-P GEOTECH L. ,- L r [ [ r~ L [ [ c [ E [ - 6 - feet of stiff silty sandy clay. Relatively dense silty to clayey sand and gravel with basalt and sandstone 'fragments to boulder size wa:s encountered beneath the clay at depths between 1 and 20 feet. Laboratory testing performed on samples obtained from the borings included natural moisture content and density, Atterberg limits, unconfined compressive \ strength, gradation an;l.lyses and Hveem stabilometer 'R' value. Results of swell-. consolidation testing performed on relatively undisturbed drive samples, presented on \ Figs. 5 through 8, generally indicate low to moderate compressibility un~er conditions{ .. of loading and wetting. A minor to low expansion potential was g~nerally indicated ) when the samples were wetted at a light confining pressure. The sample from Boring f v at 4 feet depth showed a high expansion potential after it~-5). Results of gradation analyses performed on small·diameter drive samples (minus l 1h inch fraction) of the coarser subsoils are shown on Fig. 9. The laboratory testing is surnniarized in Table I. No free water was encountered in the borings at the time of drilling or when checked 1 to 2 days later. The subsoils were slightly moist to moist. GEOLOGIC ASSESSMENT r Development of the filing as planned should not encounter severe geologic l constraints or potential hazards. There are several conditions of a geologic nature that l l should be considered in development planning for Filing 4. These conditions are described in this section along with potential risks and possible mitig~tion options. LANDSIDE DEPOSIT The toe of the landslide. complex in the project area appears to have been dormant with respect to large scale movements for several thousands of years or longer. Based on this, is seems unlikely that a large scale reactivation of the landslide could occur during the service life of the development. There could be some potential for local slope instability from grading and surface drainage modifications associated with development. H·P GEOTECH [ [ [ [ [ [ [ ,. L [ [ [ -7- The impacts and risks of this condition can be reduced by limiting development on the landslide deposit. Additional subsurface exploration, ground water and slope movement monitoring could be performed to evaluate the stability condition of the landslide complex. The monitoring would continue for at least one snowpack melt season. The developer and individual lot owners should be aware of the landslide condition and that building on landslides is not totally risk free, even if they have been dormant for a long time. The water tank over flow is on the steep slope above planned residential lots and should be improved as a confined channel. FLOODING · The potential for flash flooding should be included in the storm water management plan for the filing. A hydrologist should evaluate the flood potential for the drainage basins above the alluvial fans and the capacity of the natural fan channels. Flooding on the large fan in the southern part of the filing could include hyperconcentrated debris flood and debris flows. Mitigation, if needed, could include channel improvements, deflection structures or flood proofing and direct building protection. EARTHQUAKE CONSIDERATIONS The project area could experience moderately strong earthquake related ground shaking. Modified Mercal!i Intensity VI ground shaking should be expected during a reasonable service life for the development, but the probability for stronger ground shaking is low. Intensity VI ground shaking is felt by most people and causes general alarm; but results in negligible damage to structures of good design and construction. The faults in the region, in our opinion, do not increase the seismic potential of the site. All occupied structures should be designed to withstand moderately strong ground shaking with little or no damage and not to collapse under stronger ground shaki.ng. The region is in the Uniform Building Code, Seismic Risk Zone 1. Based on our current wtderstanding of the earthquake hazard in this part of Colorado, we see no reason to increase the commonly accepted seismic risk zone for the area. H-P GEOTECH [ [ [ [ [ [ [ [ [ F L [ E [ - 8 - PRELIMINARY GEOTECHNICAL ENGINEERING EVALUATION The geotechnical evaluations and recommendations presented below are based on our current understanding of the proposed devdopment, ,o;ubsurface conditions encountered in the exploratory borings, the laboratory testing and our experience in the area. The recommendations are suitable for planning and preliminary design but site specific studies should. be conducted for individual lot development. FOUNDATION BEARING CONDITIONS Bearing conditions will vary depending on the specific location of the building on the property. In most areas sandy clay and clayey sand and gravel will be encountered at typical foundation bearing depths for buildings with and without basements. Based on the nature of the proposed construction spread footings bearing on the natural subsoils should be suitable for building support with some risk of movement if the bearing soils become wetted. We expect the footings can be sized for an allowable bearing pressure in the range of 1,500 psf to 3,000 psf. The footings may need to be designed to impose a minimum dead load pressure to limit potential heave of expansive clays. A drilled pier foundation system may be an option in moderate to high expansive areas. The expansion potential should be evaluated on a site specific basis. Foundation walls should be heavily reinforced to span local anomalies, better withstand the effects of differential movements and to resist lateral earth loadings when acting as retaining structures. Below grade areas and retaining walls should be protected from wetting and hydrostatic loading by use of an underdrain system. The footings should have a minimum depth of 36 inches for frost protection. Large boulders and difficult excavation conditions could be encountered. FLOOR SLABS It should be feasible to use slab-on-grade construction at most building sites. There could be some post construction slab movement at sites with expansive clays. H-P GEOTECH I r L - 9 - Structural floors above crawlspace may be advisable if highly expansive conditions are encountered at the building site. To reduce the adverse effects of differential slab movement, floor slabs should be separated from all bearing walls and columns with expansion joints. Floor slab control joints should be used to reduce damage due to shrinkage cracking. UNDERDRAINSYSTEM Because of the potential for temporary perched groundwater following periods of heavy precipitation or seasonal snow melt, it is recommended that below grade construction be protected by an underdrain system. The drains should consist of drainpipe surrounded above the invert level with free-draining granular material. The drain should be placed at each level of excavation and at least 1 foot below lowest adjacent finish grade and sloped at a minimum l % to a suitable gravity outlet. Free- draining granular material used in the underdraiII system should contain less than 2 % passing the No. 200 sieve, less than 50% passing the No. 4 sieve and have a maximum size of 2 inches. The drain gravel should be at least l'h feet deep. SITE GRADING The risk of construction-induced slope instability at the site appears low provided the buildings are located in the less steep lower part of the property as generally planned and cut and fill depths are limited. Cut and fill depths for the buildings, driveways and subdivision roads should not exceed about 10 to 12 feet. Deeper cuts and fills may be feasible and should be studied on an individual basis. Structural embankment fills should be compacted to at least 95 3 of the maximum standard Proctor density near optimum moisture content. Prior to fill placement, the subgrade should be carefully prepared by removing all vegetation and topsoil. The fill should be benched into the portions of the hillside exceeding 203 grade. The on-site soils excluding oversized rock and topsoil should be suitable for use in embankment fills. H-P GEOTECH [ [ r L r L f ~ L. [ [ [ [ c I~ L r [ [ -10 - Permanent unretained cut and fill slopes should be graded at 2 horizontal to 1 vertical or flatter and protected against erosion by revegetation, rock riprap or other means. Oversized rock from embankment fill construction will tend to collect on the outer face. Care should be taken to prevent rockfall into developed areas downslope of the embankment toe. This ·Office should review site grading plans for the project prior to construction. SURFACE DRAINAGE The grading plan for the subdivision should consider runoff from steep uphill slopes through the project and at individual sites. Water should not be allowed to pond which could impact slope stability and foundations. To limit infiltratfon into the bearing soils next to buildings, exterior backfill should be well compacted and have a positive slope away from the building for a distance of at least 10 feet. Roof downspouts and drains should discharge well beyond the limits of all backfill and landscape irrigation should be restricted. PAVEMENTSUBGRADE A pavement section is a layered system designed to distribute concentrated traffic loads to the subgrade. Performance of the pavement structure is directly related to the ,Physical properties of the sub grade soils and traffic loadings. Soils are represented for pavement design purposes by means of a soil support value for flexible pavements and a modulus of subgrade reaction for rigid pavements. Both values are empirically related to strength. The subgrade soils will likely vary throughout the development. In general, it appears that medium plastic clays will be encountered at shallow depth. An Hveem 'R' value of 5 was determined for a sample of the plasticity clays. When the streets are near finished grade, it is recommended that specific sampling and testing be performed to determine appropriated subgrade 'R' values for the actual subgrade conditions. We expect the clays will have a typical 'R' value of 10 and the gravelly soils will have typical 'R' value of 20 to 30. Structural fill placed for H·P GEOTECH [ [ [ [ [ [ E [ [ C [ t [ -11 - road subgrade should be compacted to at least 95 % of standard Proctor density at a moisture content near optimum. The on-site soils, exclusive of topsoil and oversized rock, are suitable for road fill. Soft subgrade may be encountered in areas of shallow or perched groundwater and could require improvement. In soft areas, improvements may require partial stripping and placement with a geotextile and reinforcement mat (such as Tensar SS-1 geogrid) and additional subbase aggregate. The geotextile and reinforcement mat should be installed according to manufacturer's sp~cifications. The road subgrade should be proof rolled with a heavily loaded rubber-tired vehicle and soft deflecting areas stabilized prior to placement of the pavement section. We can assist with the pavement design when the subgrade conditions and traffic loading are better known. LIMITATIONS This study has been conducted according to generally accepted geotechnical engineering principles and practices in this area at this time. We make no warranty either expressed or implied. The conclusions and recommendations submitted in this report are based upon the data obtained from the field reconnaissance, review of published geologic reports, the exploratory borings located as shown on Fig. 1, the proposed type of construction and our experience in the area. Our findings include interpolation and extrapolation of the subsurface conditions identified at the exploratory borings and variations in the subsurface conditions may not become evident until excavation is performed. If conditions encountered during construction appear different from those described in this report, we should be notifted so that re-evaluation of the recommendations may be made. This report has been prepared for the exclusive use by our client for planning and preliminary design purposes. We are not responsible for technical interpretations by others of our information. As the project evolves, we should provide continued consuitation, conduct additional evaluations and review and monitor tb.e implementation of our recommendations. Significant design changes may require additional analysis or H-P GEOTECH -12 - modifications to the recommendations presented herein. We recommend on-site observation of excavations and foundation bearing strata and testing of structural fill by a representative of the geotechnical engineer. Respectfully Submitted, ~X-~~ Steven L. Pawlak P.E. JZNksm cc: Jerome Gamba & Associates, Inc. -Attn: Robert Pennington Western Slope Consulting -Attn: Davis Farrar REFERENCES Kirkham, R.M. and Others, 1996, Geology Map a/the Cattle Creek Quadrangle, Garfield County, Colorado: Colorado Geological Survey Open File Report 96-1. Kirkham, R.M. and Widmann, 1997, Geology Map of the Carbondale Quadrangle, Garfield County, Colorado: Colorado Geological Survey Open File Report 97-3. H-P GEOTECH I . .J i :J J ., J l cJ J r . I d ~ : l 1 __, 1 ._J J J J J J . 10. Permanent unretained cut and fill slopes should be graded at 2 horizontal to 1 vertical or flatter· and protected ·against erosion by revegetation, rock riprap or other means. Oversized rock from embankment fill construction will tend to collect on the outer face. Care should be taken to prevent rockfall into developed areas downslope of the embankment toe. This .office should review site grading plans for the project prior to construction. · SURFACE DRAINAGE The grading plan for the subdivision should consider runoff from steep uphill slopes through the project and at individual sites. Water should not be allowed to pond which could impact slope stability and foundations. To limit infiltration into the bearing soils next to buildings, exterior backfill should be well compacted and have a positive slope away from the building for a distance of at least 10 feet. Roof downspouts and drains s.hould discharge well beyond the limits of all backfill and landscape irrigation should be restricted. PAVEMENTSUBGRADE A pavement section is a layered system designed to distribute concentrated traffic loads to the subgrade. Performance of the pavement structure is directly related to the.physical properties of the subgrade soils and traffic loadings. Soils are represented for pavement design purposes by means of a soil support value for flexible pavements and a modulus of subgrade reaction for rigid pavements. Both values are empirically related to strength. The subgrade soils will likely vary throughout the development. In general, it appears that medium plastic clays will be encountered at shallow depth. An Hveem 'R' value of 5 was determined for a sample of the plasticity clays. When the streets are near finished grade, it is recommended that specific sampling and testing be performed to determine appropriated subgrade 'R' values for the actual subgrade conditions. We expect the clays will have a typical 'R' value of 10 and the gravelly soils will have typical 'R' value of 20 to 30. Structural fill placed for · H-P GEOTECH J 'l J ~. J ;i j J J ' J J . , I d 'l l J 1 _J J J J ] j J -11 - road sub grade should be compacted to at least 95 % of standard Proctor density at a moisture content near optimum. The on-site soils, exclusive of topsoil and oversized rock, are suitable for road fill. Soft subgrade may be encountered in areas of shallow or perched groundwater and could require improvement. In soft areas, improvements may require partial stripping and placement with a geotextile and reinforcement mat (such as Tensar SS-1 geogrid) and additional subbase aggregate. The geotextile and reinforcement mat should be installed according to manufacturer's s~cifications. The road subgrade should be proof rolled with a heavily loaded rubber-tired vehicle and soft deflecting areas stabilized prior to placement of the pavement section. We can assist with the pavement design when the subgrade conditions and traffic loading are better known . LIMITATIONS This study has been conducted according to general! y accepted geotechnical engineering principles and practices in this area at this time. We make no warranty either expressed or implied. The conclusions and recommendations submitted in this report are based upon the data obtained from the field reconnaissance, review of published geologic reports, the exploratory borings located as shown on_ Fig. l, the proposed type of construction and our experience in the area. Our findings include interpolation and extrapolation of the subsurface conditions identified at the exploratory borings and variations in the subsurface conditions may not become evident until excavation is performed. If conditions encountered during construction appear different from those described in this report, we should be notified so that re-evaluation of the recommendations may be made. This report has been prepared for the exclusive use by our client for planning and preliminary design purposes. We are not responsible for technical interpretations by others of our information. As the project evolves, we should provide continued consultation, conduct additional evaluations and review and monitor the implementation of our recommendations. Significant design changes may require additional analysis or H-P GEOTECH L r L [ [ [ [ [ [ [ [ E L [ -12 - modifications to the recommendations presented herein. We recommend on-site observation of excavations and fowidation bearing strata and testing of structural fill by a representative of the geotechnical engineer. Respectfully Submitted, o9Jr. P.E. ~X-~~ StevenL. Pawlak P.E. JZA/ksm cc: Jerome Gamba & Associates, Inc. -Attn: Robert Pennington Western Slope Consulting -Attn: Davis Farrar REFERENCES Kirkham, R.M. and Others, 1996, Geology Map of the Cattle Creek Quadrangle, Garfield County, Colorado: Colorado Geological Survey Open File Report 96-1. Kirkham, R.M. and Widmann, 1997, Geology Map of the Carbondale Quadrangle, Garfield County, Colorado: Colorado Geological Survey Open File Report 97-3. H-P GEOTECH ' I , • _4, "0 ~~:{: : ""·'"/- I ~-~i" ' ._ ··. . . -. _· . ,_ . ·~·~,. ......_, ---~ - .'!:( ·. -~. '"" J!;: ~ UWn" , -- \ ' ~,ie'i~AiiA1\'1Y;, & .~"- '· 4-::.ri:,,-..;v/g l"~/ ~ J • i i i I I 1 I ! --JI I i I ' .. \ ·-' ' LJ r ' i-~ • l ,--...,i -u1 I I I ( . ~ ) I. ~i· r--. \-r\7 /--.. ;.,, .. . \ I I i ~·· .. . ~ \ ""'" .. "'\. . ~ (') F::::2!I \"\ /~ ·-HEPWORTH·PAWLAK 196 420 I GEOTECHNICAL, Inc. 1" EXPLANATION of Mon-Placed Fill a \ Qpdg Poorly Drain~ ~r1 ' \ Oaf Alluvial Fan \ Qls Landslide Deposit \ • Exploratory Borins 0 Pit Excavated for \ 1996, Job No .. 19· OAK MEADOWS FILING • ·Disturbed Ground nd !rilled for this Study tudy Dated October 9, 420 0. SlJ)J ~ .· "::::J > '•:::. . •. ;!Ii ~ 0 I ZS · 2.:10 SOO APPROXIMATE SCAL~ IN FE€T . . . . 'CONTOUR INTERVAL = 20 FEET GEOLOGY MAP AND BORING LOCA nONS flt. 1 l .. _j •. , J l J 1. J . -1 r -1 l .- ~1 BORING 1 BORING 2 BORING 3 BORING 4 BORING 5 ELEV. = 6936' ELEV. = 69B1' ELEV. = 691 o' ELEV. = 7013' ELEV. = 5982' .j>. "' 0 Q-;t .........-o r=-> =-> =-> ,..,,_.., ~ 0 fTJ !Tl 0 '1l --_18/12 ril 2§ I o;o 14/12 30/12 I +4-2 I:t I -200-11 12/6,20/4 WC=21.1 '7/12 I l.L=J8 z 5 00=102 I Pl-23 Ci I l'i0o11.0 WC-12.J -' 5 )> '1l 00-112 00=116 J7/12 +4=2.4 .:> -200•42 -:::;: zr 22/12 ~11P ~f 48/12 ...... o> 0 .1o_j 0 . " .. 1J/12 WC=20.3 :~ 26/12 "' " ~ 10 00-108 -0 =s-WC=I0.8 -;:: ~ -200-58 =s- I ,, i~/o Gl 50/12 j ..,, r .. ~ " 0 ~~"' " G"> ~ (/) 20/6,10/0 0 15 . p;:<;(J 15 ,, !Tl x -0 r 0 E-20 ' rr 20/12 ;;o -> : WCo::16.4 ~a ll0/12 d .~ 00=11J 20 :::0 - . -200=49 -< ~1 J= I f:'tl.h 50/10 z ~I l-25 25 " if)' "' Note: Explanation of symbols Is shown on Fig. 4_ r1 r--:: r::-:1 r:::iJ i."! r-1 lO Ol .j>. "' 0 G) I fTl fT1 0 ""[] rl ~ o::o I ;t z (ii )> -0 r )> -=E ~zs;: o .. ~ ::.- 5 G) (/) 0 ..., fT1 x ""[] r- 0 ;o )> d ;;o -< CJ 0 ;;2 z fh "T] .a· (,I ;,:i m ~ 0 5 10 15 . 20 25 BORING 6 E.LEV. -7093' 13/12 WC=2.'.5,J 00~102 UC=-4000 41/12 WC=IB.2 00-110 -2.0()t:.;64 20/5.20/D 11/a.:io/o 30/6,40/2 r-1 l:") t--:1 11] 1--:l [ --1 BORING 7 ELEV. = 7154' 00/7 50/J BORING 8 ELEV. = 7018' 9/12 -' ' ' I ' ... 9/12 BORING 9 BORING 10 BORING 11 ELEV. = 6871' ELEV. = 6679' ELEV. = 6831' 8/12 -200-87 LL-46 Pl•.'.51 R•5 ... wc~1s.J 00-101 24/12 19/12 WC=1B.5 00:..109 LL=42 p1 .. 30 20/12 WC=16.1 00-113 UC=10,000 15/12 WC=20.4 00-105 19/12 16/12 JB/12 37/12 21/12 00/J 34/12 Ba/11 Note: Explanation of symbols ls shown on Fig. 4. 0 5 10 15 20 25 I. 0 m .,, ~ ::.- ..., " " ~ - ~ ~ [ [ [ [ [ LEGEND: ~ TOPSOIL: ·sandy silty cloy, organic, medium stiff, moist, block to dork brown. D CLAY (CL): silty, slightly sandy to sandy, scattered grovel, cobbles and possible boulders, stiff to very stiff/hard, moist to very moist, yellowish brown to brown, siltstone/sandstone and basalt fragments, medium to high plasticity. SAND AND GRAVEL {SC-GC): clayey, silty, with silty send (SM) pockets, scattered cobbles ~ and boulders, dense to very dense, sllghtly moist to moist, brown to yeliowlsh brown, subangular to rounded basalt and sandstone fragments, calcareous zones. p Relatively undisturbed drive sample; 2-inch l.D. California liner sample. ~ Drive sample; standord penetration test ( SPT ), 1 3/8-inch l.D. split spoon sample, ASThl D -1586. 41/12 Drive 'sample blow count; indicates that 41 blows of a 140-pound hammer foiling JO inches were required to drive the California or SPT sampler 12 inches. T Practical rig refusal. , __ J Disturbed bulk sample. NOTES: 1. Exploratory borings were drilled on March 17 and 18, 1998 with o 4-inch diameter continuous flight power auger. 2. Locations of exploratory borings were measured appro><imotely by pacing from features shown an the site plan provided. 3. Elevations of exploratory borings were obtained by interpolation between contours on the site plan provided. Logs are drawn to depth. 4. The exploratory boring locations end elevations should be considered accurate only to the degree Implied by the method used. 5. The lines between materials shown on the exploratory boring logs represent the approximate boundaries between material t~es and transitions may be gradual. 6. No free water was encountered in the borings ot the time of drilling or when checked 1 to 2 days later. Fluctuation In water level may occur with time. 7. Laboratory Testing Results: WC = Weter Con tent ( % ) DD = Dry Density ( pcf ) +4 = Percent retained on No. 4 sieve. -200 = Percent passing No. 200 sieve. UC = Unconfined Compressive Strength ( psf ) LL = Liquid Limit ( % ) Pl = Plasticity Index ( % ) R = Hveem Stabilometer "R" Value 196 420 HEPWORTH -PAWLAK GEOTECHNICAL, INC. LEGEND AND NOTES Fig. 4 [ r L. [ [ [ 4 3 2 ~ c 0 'iii 1 c D 0. " w I 0 c 0 'ii "' " 1 ~ a. E <> ll 2 0.1 Q ~ 1 c 0 r;; "' " 2 ~ 0. E 0 ll 3 4 0.1 196 420 .. Moisture Content = 11.0 percent Dry Density = 112 pcf Sample of: Sandy Silty Clay lo~ From: Boring 1 ot 4 Feet "I "\ ' Note: Sample was cir dried \ overnight before wetting. Expansion I\ upon wetting '\ \ r-..... - ' \~ 1.0 10 100 APPLIED PRESSURE -ksf Moisture Content = 21.1 percent Dry Density = 102 pcf Semple of: Silty Clay From: Boring 2 at 3 Feet -r--r-... ...... ,......._...._ ... No movemen upon ' wetting ""' ' 1.0 10 100 APPLIED PRESSURE -ksf HEPWORTH -PAWLAK SWELL-CONSOLIDATION TEST RESULTS Fig. 5 GEOTECHNICAL, INC. I L [ [ [ [ [ [ E '"" [ [ "' c 0 a ';; c " 0.. x w 1 I c: ,Q I/) 2 I/) " ... Q. E 0 0 3 0.1 "' c .Q " 0 c: " 0. x w I 1 c: ,Q "' " 2 " .... 0. E 0 0 3 0.1 196 420 Moisture Content = 20.3 percent Dry Density = 108 pcf Sample of: Silty Cloy From: Soring 2 at 8 Feet -'""" r.... .... ,.., ~ "--- " '\ p Expansion I upon wetting 1.0 10 100 APPLIED PRESSURE -ksf Moisture Content = 18.2 percent Dry Density = 110 pcf Sample of: Sandy Cloy From: Boring 6 at 9 Feet ;-... r.:... - ~ .......__., " \ " ) Expansion upon wetting 1.0 10 100 APPLIED PRESSURE -ksf HEPWORTH -PAWLAK SWELL-CONSOLIDATION TEST RESULTS Fig. 6 GEOTECHNICAL, INC. Moioture Content = 15.3 percent Dry Density = 101 pcf Sample of: Sandy Silty Clay "' From: Boring 9 at 4 Feet c: .Q 0 en c: 0 a. --i-... ~ )( U,J 1 ---I \ ..., " c: ·a 2 "' UI " Exponsion ~ a. E upon 8 wetting 0.1 1.0 10 100 APPLIED PRESSURE -ksf Moisture Content = 1B.5 percent Dry Density = 109 pcf Sample of: Sandy Silty Cloy From: Boring 9 at 14 Feet "' 0 'LI-. c: ._i'-N ~ ........... 0 'iii 1 UI \ ......._ "' ~ I'. ) Cl. E 0 2 I u Expansion upon wetting "" i . L 0.1 1.0 10 100 APPLIED PRESSURE -ksf 196 420 HEPWORTH -PAWLAK SWELL-CONSOLI DA TlON TEST RESULTS Fig. 7 GEOTECHNICAL, INC. '[ [ [ [ [ [ [ [ [ F L c c ,- '' L [ [ L [ 0 1 ~ " 2 0 ·;;; "' " ~ "-3 E 8 4 0.1 196 420 Moisture Content -20.4 percent Ory Density Weight = 106 pcf Sample of: Silty Cloy From: Boring 10 ct 9 Feat r-r-.. ..... ,...~ -........._ r-No movement ~ upon wetting '\ ' ' b I 1.0 10 100 APPLIED PRESSURE -ksf HEPWORTH -PAWLAK SWELL-CONSOLI QA TION TEST RESULTS Fig. 8 GEOTECHNICAL, INC. L r L. ! I Lo [ [ r L [ c c [ [ [ E [ L [ I tm!f!;ONmJ .UW.'YS!S I SEVE ANAl.X§!S Tl« ~ING:!! U,!. STo\NOAAD !Eftl[;! I a.!AR SQUAR! CIPOllNGS 24 HR. 7 llR 45 ~-15 lllN. ID 1.11(.111 UlfL 4 wt. 1 Mil. -DO .. .. • • .. )lf/'1/~314'" 11 fl'" , . . .... 100 •• "' "' "' z iii 80 UJ <( a. .. .... z ~ "' 5 JO a. 20 10 • ,001 ..., .005 .009 ,GISI ,D.37 .07.+ ·''° .JOO ·"" 1.1B ~" .. 75 0,5!2.S 19.Q 37.S 7U , .. DIAMETER OF PARTICLES IN MILLIMETERS 127 Cl..AY TO :!LT I ""' I ~ I """"" I ONE "'1"'1. @RSE I COIBLS GRAVEL 24 % SANO 34 % SILT ANO CJJ. Y 42 % LIQUID LIMIT % PLASTICITY INDEX % SAMPLE OF: Clayey Sand with Gravel FROM: Boring 3 at 4 Feet I H'!llROIE1ER ...... ,,.. I SI~ AHN.,''1'5S --U.:i. STANDARD :5EH!ES I a.tAfl SQUARE OP!lllffGS 24 HR. 7 HR ~ rr-1fi.•314• 11 f2.. 45 MIN. 15 WIN. eo \ilN.19 JllN.. 4 MIN, 1 MIN. ,. OD .. • '" • • ~ ,. .... 100 "" 80 "' 70 z iii .. UJ <( 0.. .., .... z w .. () "' w JO a. 20 10 0 ,001 -,005 .ocs .018 ,D.37 .07'i-.... .JOO .800 1.18 ""' .. ,. ~.512.5 111.0 31.S ,, .. ,,. DIAMETER OF PARTICLES IN MILLIMETERS 127 Ct.A.YTD 51..t I FINE I ~. !@MSE I BNE: me COARSf I COO!l.Eli GRAVEL 2 % SAND 27 % SILT AND CLAY 71 7. LIQUID LIMIT 38 3 PLASTICITY INDEX 23 % SAMPLE OF: Sandy Silty Clay FROM: Boring 5 at 2 tnru 5 Feet 196 420 HEPWORTH -PAWLAK GRADATION TEST RESULTS GEOTECHNICAL. INC. I ~ 0 ,. "' "° Gl "' ~ "' 00 "' .... z IO "' u "' JC LU Cl. "' ao 100 203 I ,. 0 10 20 JO Cl w z "' :;;: .... w so "' .... z 80 w u "' 70 w a. BO "" '"" '°' Fig. 9 r-. r: ~. rlTI r---i :-i r-J r-i . ") I HEPWORTH-PAWLAK GEOTECHNICAL, INC. TABLE I JOB NO. 196 420 SUMMARY OF LABORATORY TEST RESULTS SAMPLE LOCATION NATURAL NATURAL GRADA.TION PU\CENT A TIERBEBG LIMJTS UNCONFINED HVEEM .•. BORING D.EPTH MOl&YuRe DRY GMIJEL SAND I" ASSING LIQUID PLASTIC COMPRESSIV! SOR.OR VALUE lkdl CONTENT DENSITY 1%1 1%1 NO. 200 i.JMIT INDEX STRENGTH BEDROCK TYPE "'" lpctl SIEVe "" "" CPSFI 1 4 11.0 112 Sandy Silty Clay 9 10.8 58 Sandy Silt with Gravel 2 3 21.1 102 Silty Clay 8 20.3 108 Silty Clay 18 16.4 113 49 Sand and Clay 3 4 12.3 116 24 34 42 Clayey Sand with Gravel ' 5 2 to 5 2 27 71 38 23 Sandy Silty Clay 6 4 23.3 102 4000 Sandy Clay 9 18.2 110 84 Sandy Clay 9 2 to 5 87 46 31 5 Sandy Clay 4 15.3 101 Sandy Silty Clay 14 18.5 109 42 30 Sandy Silty Clay 10 4 16.1 113 10,000 Sandy Clay 9 20.4 106 Silty Clay