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HomeMy WebLinkAboutSubsoil StudyHEPWORTH - PAWL.AK GEOTECHNICAL I SUBSOIL STUDY FOR FOUNDATION DESIGN PROPOSED RESIDENCE LOT M38, ROARING FORK MESA ASPEN GLEN SUBDIVISION 11 CADDIS COURT GARFIELD COUNTY, COLORADO JOB NO. 113 111A MAY 9, 2013 PREPARED FOR: MAK KEELING c/o LAND + SHELTER ATTN: ANDI KORBER 215 N. 12TH STREET, UNIT C CARBONDALE, COLORADO 81623 andiMandandsheltcr.com Parlccr 303-841-71 19 0 Coltl(Jtlit 7l9-613-1)62 0 NlV-eythur w 970-40 It);qu TABLE OF CONTENTS PURPOSE AND SCOPE OF STUDY - I - PROPOSED CONSTRUCTION - 1 - SITE CONDITIONS - 2 - SUBSIDENCE POTENTIAL - 2 - FIELD EXPLORATION - 3 - SUBSURFACE CONDITIONS - 3 - FOUNDATION BEARING CONDITIONS - 4 - DESIGN RECOMMENDATIONS - 4 - FOUNDATIONS -4- FLOOR SLABS -5- UNDERDRAIN SYSTEM - 6 - SURFACE DRAINAGE - 7 - LIMITATIONS - 7 - REFERENCES -9- FIGURE 1 - LOCATIONS OF EXPLORATORY BORINGS FIGURE 2 - LOGS OF EXPLORATORY BORINGS FIGURE 3 - LEGEND AND NOTES FIGURE 4 - SWELL -CONSOLIDATION TEST RESULTS FIGURE 5 - GRADATION TEST RESULTS TABLE 1- SUMMARY OF LABORATORY TEST RESULTS PURPOSE AND SCOPE OF STUDY This report presents the results of a subsoil study for a proposed residence to be located at Lot M38, Roaring Fork Mesa, Aspen Glen Subdivision. 11 Caddis Court, Garfield County, Colorado. The project site is shown on Figure 1. The purpose of the study was to develop recommendations for the foundation design. The study was conducted in accordance with our proposal for geotechnical engineering services to Mac Keeling dated April 18, 2013. Chen -Northern, Inc. previously conducted a preliminary geotechnical engineering studies for the development and preliminary plat design (Chen -Northern, 1991 and 1993). A field exploration program consisting of exploratory borings was conducted to obtain information on the subsurface conditions. Samples of the subsoils obtained during the field exploration were tested in the laboratory to determine their classification, compressibility or swell and other engineering characteristics. The results of the field exploration and laboratory testing were analyzed to develop recommendations for foundation types, depths and allowable pressures for the proposed building foundation. This report summarizes the data obtained during this study and presents our conclusions, design recommendations and other geotechnical engineering considerations based on the proposed construction and the subsurface conditions encountered. PROPOSED CONSTRUCTION The proposed residence will be a two story structure over a crawlspace level. Ground floor will be structurally supported over crawlspace for the residence and slab -on -grade in the garage. Grading for the structure is assumed to be relatively minor with cut depths between about 3 to 5 feet. We assume relatively light foundation loadings, typical of the proposed type of construction. If building loadings, location or grading plans change significantly from those described above, we should be notified to re-evaluate the recommendations contained in this report. Job No. 113 111A G'igtechC -2 - SITE CONDITIONS The site was vacant at the time of our field exploration. The ground surface is relatively flat with a gentle slope down to the east. There could be some minor fill on the lot from overlot grading as part of the subdivision development. A pond is located along the east portion of the lot. An existing two story house is located to the south on Lot M39. Vegetation consists of grass and weeds. Scattered cobbles and small boulders were exposed at the ground surface across the lot. SUBSIDENCE POTENTIAL. Bedrock of the Pennsylvanian age Eagle Valley Evaporite underlies the Aspen Glen development. These rocks are a sequence of gypsiferous shale, fine-grained sandstone/siltstone and limestone with some massive beds of gypsum. There is a possibility that massive gypsum deposits associated with the Eagle Valley Evaporite underlie portions of the lot. Dissolution of the gypsum under certain conditions can cause sinkholes to develop and can produce areas of localized subsidence. During previous studies in the area, several broad subsidence areas and smaller size sinkhole areas were observed scattered throughout the Aspen Glen development, predominantly on the southeast side of the Roaring Fork River (Chen -Northern, Inc., 1993). These sinkholes appear similar to others associated with the Eagle Valley Evaporite in areas of the Roaring Fork Valley. Sinkholes were not observed in the immediate area of the subject lot, No evidence of cavities was encountered in the subsurface materials; however, the exploratory borings were relatively shallow, for foundation design only. Based on our present knowledge of the subsurface conditions at the site, it cannot be said for certain that sinkholes will not develop. The risk of fixture ground subsidence on Lot M38 throughout the service life of the proposed residence, in our opinion, is low; however, the owner should be made aware of the potential for sinkhole development. If further investigation of possible cavities in the bedrock below the site is desired, we should be contacted. Job No. 113 111A GecPtech -3 - FIELD EXPLORATION The field exploration for the project was conducted on April 29, 2013. Two exploratory borings were drilled at the locations shown on Figure 1 to evaluate the subsurface conditions. The borings were advanced with 4 inch diameter continuous flight augers powered by a truck -mounted CME -45B drill rig. The borings were logged by a representative of Hepworth-Pawlak Geotechnical, Inc. Samples of the subsoils were taken with 1'/8 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, Figure 2. The samples were returned to our laboratory for review by the project engineer and testing. SUBSURFACE CONDITIONS Graphic logs of the subsurface conditions encountered at the site are shown on Figure 2. The subsoils consist of about 6 inches of topsoil at Boring 1 and 1 foot of fill at Boring 2 overlying 81/2 to 12 feet of medium stiff to very stiff sandy silty clay. Medium dense to dense, slightly silty sandy gravel and cobbles with possible boulders was encountered below the clay at depths of 9 to 13 feet. The fill consisted of loose, silty sandy clay with gravels and cobbles with organics. Laboratory testing performed on samples obtained from the borings included natural moisture content and gradation analyses. Results of swell -consolidation testing performed on relatively undisturbed drive samples of the clay soils, presented on Figure 3, indicate low to moderate compressibility under conditions of loading and wetting and minor collapse potential when wetted under constant light surcharge loading. Results of Job No. 113 111A Ge Ptech -4 - gradation analyses performed on a small diameter drive sample (minus 11/2 inch fraction) of the natural granular subsoils are shown on Figure 4. The laboratory testing is summarized in Table 1. No free water was encountered in the borings at the time of drilling or when checked 4 days later and the subsoils were slightly moist to moist. FOUNDATION BEARING CONDITIONS The natural clay soils possess relatively low bearing capacity and moderate settlement potential when loaded and wetted. The underlying natural granular soils possess moderate bearing capacity with a low settlement potential. Lightly loaded spread footings can be used for support of the residence at the site provided the risk of settlement is acceptable to the owner if the soils were to become wetted. Extending the footings down to the natural granular soils would reduce the risk of settlement. Provided below are recommendations for spread footings bearing on the natural clay soils or bearing on the natural granular soils. DESIGN RECOMMENDATIONS FOUNDATIONS Considering the subsurface conditions encountered in the exploratory borings and the nature of the proposed construction, we recommend the building be founded with spread footings bearing on the natural fine grained soils. The design and construction criteria presented below should be observed for a spread footing foundation system. 1) Footings placed on the undisturbed natural clay soils should be designed for an allowable bearing pressure of 1,500 psf. Based on experience, we Job No. 113 111A Gegtech -5 - expect settlement of footings designed and constructed as discussed in this section will be about 1 inch or less. Additional settlement on the order of about 1 inch could occur if the bearing soils become wetted. Care should be taken to avoid wetting of the bearing soils by following the recommendations in the "Surface Drainage" section of this report. Footings placed on the underlying natural gravel soils could be designed for an allowable bearing pressure of 3,000 psf with a settlement potential of less than I inch. 2) The footings should have a minimum width of 18 inches for continuous walls and 2 feet for isolated pads. 3) Exterior footings and footings beneath unheated areas should be provided with adequate soil cover above their bearing elevation for frost protection. Placement of foundations at least 36 inches below exterior grade is typically used in this area. 4) Continuous foundation walls should be reinforced top and bottom to span local anomalies such as by assuming an unsupported length of at least 12 feet. Foundation walls acting as retaining structures should also be designed to resist a lateral earth pressure corresponding to an equivalent fluid unit weight of at least 50 pcf. 5) All existing fill, topsoil and any loose or disturbed soils should be removed and the footing bearing level extended down to the natural soils. The exposed soils in footing area should then be moistened and compacted. If water seepage is encountered, the footing areas should be dewatered before concrete placement. 6) A representative of the geotechnical engineer should observe all footing excavations prior to concrete placement to evaluate bearing conditions. FLOOR SLABS The natural on-site soils, exclusive of fill and topsoil, are suitable to support lightly loaded slab -on -grade construction. To reduce the effects of some differential movement, Job No. 113 IIIA GecPteat -6 - floor slabs should be separated from all bearing walls and columns with expansion joints which allow unrestrained vertical movement. Floor slab control joints should be used to reduce damage due to shrinkage cracking. The requirements for joint spacing and slab reinforcement should be established by the designer based on experience and the intended slab use. A minimum 4 inch layer of free -draining gravel should be placed beneath basement level slabs to facilitate drainage. This material should consist of minus 2 inch aggregate with at least 50% retained on the No. 4 sieve and less than 2% passing the No. 200 sieve. All fill materials for support of floor slabs should be compacted to at least 95% of maximum standard Proctor density at a moisture content near optimum. Required fill can consist of suitable imported granular soils devoid of vegetation, topsoil and oversized rock. UNDERDRAIN SYSTEM Although free water was not encountered during our exploration, it has been our experience in mountainous areas that local perched groundwater can develop during times of heavy precipitation or seasonal runoff. Frozen ground during spring runoff can also create a perched condition. We recommend below -grade construction, such as retaining walls, crawlspace and basement areas, be protected from wetting and hydrostatic pressure buildup by an underdrain system. The drains should consist of drainpipe placed in the bottom of the wall backfill 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 1% to a suitable gravity outlet, drywell or sump and pump. Free -draining granular material used in the underdrain 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 backfill should be at least 1'/ feet deep. An impervious membrane such as 20 mil PVC should be placed beneath the drain gravel in a Job No. 113 111A Ge Ptech -7 - trough shape and attached to the foundation wall with mastic to prevent wetting of the bearing soils. SURFACE DRAINAGE The following drainage precautions should be observed during construction and maintained at all times after the residence has been completed: 1) Inundation of the foundation excavations and underslab areas should be avoided during construction. 2) Exterior backfill should be adjusted to near optimum moisture and compacted to at least 95% of the maximum standard Proctor density in pavement and slab areas and to at least 90% of the maximum standard Proctor density in landscape areas. 3) The ground surface surrounding the exterior of the building should be sloped to drain away from the foundation in all directions. We recommend a minimum slope of 6 inches in the first 10 feet in unpaved areas and a minimum slope of 3 inches in the first 10 feet in paved areas. Free -draining wall backfill should be capped with about 2 feet of the on- site soils to reduce surface water infiltration. 4) Roof downspouts and drains should discharge well beyond the limits of all backfill. 5) Landscaping which requires regular heavy irrigation should be located at least 5 feet from foundation walls. Consideration should be given to use of xeriscape to reduce the potential for wetting of soils below the building caused by irrigation. LIMITATIONS This study has been conducted in accordance with generally accepted geotechnical engineering principles and practices in this area at this time. We make no warranty either express or implied. The conclusions and recommendations submitted in this report are Job No. 113 111A GC-'rtech -8 - based upon the data obtained from the exploratory borings drilled at the locations indicated on Figure I, the proposed type of construction and our experience in the area. . Our services do not include determining the presence, prevention or possibility of mold or other biological contaminants (MOBC) developing in the future. If the client is concerned about MOBC, then a professional in this special field of practice should be consulted. 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 design purposes. We are not responsible for technical interpretations by others of our information. As the project evolves, we should provide continued consultation and field services during construction to review and monitor the implementation of our recommendations, and to verify that the recommendations have been appropriately interpreted. Significant design changes may require additional analysis or 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, HEPWORTH - PAWLAK GEOTECHNICAL, INC. Robert E. Stempihar Reviewed by: too uRuCys/' 1�rct . Daniel E. Hardin, P. i 2� RES/ksw 3 q AA, 5 ���3 1 p 11 � ALN *p Job No. 113 111A Gegtech -9 - REFERENCES Chen -Northern, Inc., 1991, Preliminary Geotechnical Engineering Study, Proposed Aspen Glen Development, Garfield County, Colorado, prepared for Aspen Glen Company, dated December 20, 1991, Job No. 4 112 92. Chen -Northern, Inc., 1993, Geotechnical Engineering Study for Preliminary Plat Design, Aspen Glen Development, Garfield County, Colorado, prepared for Aspen Glen Company, dated May 28, 1993, Job No. 4 112 92. Job No. 113 111A Gec`i.Pitech 99 96 97 APPROXIMATE SCALE: 1"=30' LOT M38 ROARING FORK MES • AT ASPEN GLEN / CADDIS COURT 113 111A LOT M39 HP JOB NO. 105 234 Gerech H EPWORT tGEOTECIiNICAL LOCATIONS OF EXPLORATORY BORINGS FIGURE 1 Elevation - Feet 100 95 90 85 80 BORING 1 ELEV.=96' 10/12 7/12 WC=16.7 DD=96 99/12 88/12 BORING 2 ELEV.=98' 27/12 11/12 WC=7.4 DD=98 -200=77 7/12 WC=14.6 DD=105 40/12 WC=2.0 +4=59 -200=8 Note: Explanation of symbols is shown on Figure 3. 100 95 90 85 80 Elevation - Feet 113 111A Gtech HEP W ORTH-PAW LAK GEOTECHNICAL LOGS OF EXPLORATORY BORINGS FIGURE 2 LEGEND: x x N FILL; silty sandy clay with gravel and cobbles, organics, loose, slightly moist, dark brown to brown. TOPSOIL; organic sandy silty clay, roots, slightly moist, dark brown. CLAY (CL); sandy, silty, medium stiff to very stiff, slightly moist to moist, brown, low to medium plastic, trace calcareous, slightly porous. GRAVEL AND COBBLES (GM -GP); slightly silty, sandy, boulders possible, medium dense to dense, slightly moist, brown. Relatively undisturbed drive sample; 2 -inch I.D. California liner sample. Drive sample; standard penetration test (SPT), 1 3/8 inch I.D. split spoon sample, ASTM D-1586. Drive sample blow count; indicates that 10 blows of a 140 pound hammer falling 30 inches were required to drive the California or SPT sampler 12 inches. NOTES: 1. Exploratory borings were drilled on April 29, 2013 with 4 -inch diameter continuous flight power auger. 2. Locations of exploratory borings were measured approximately by pacing from features shown on the site plan provided. 3. Elevations of exploratory borings were obtained by interpolation between contours shown on the site plan provided. 4. The exploratory boring locations and 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 types and transitions may be gradual. 6. No free water was encountered in the borings at the time of drilling or when checked 4 days later. Fluctuation in water level may occur with time, 7. Laboratory Testing Results: WC = Water Content (%) DD = Dry Density (pcf) +4 = Percent retained on the No. 4 sieve -200 = Percent passing No. 200 sieve 113 111A Ge Lech HEPWORTH-PAWLAK GEOTECHNICAL LEGEND AND NOTES FIGURE 3 Compression Compression % 0 1 2 3 4 0 1 2 3 4 Moisture Content = 16.7 percent Dry Density = 96 pcf Sample of: Sandy Silty Clay From: Boring 1 at 5 Feet Compression upon wetting 0.1 1.0 10 APPLIED PRESSURE - ksf 100 Moisture Content = 14.6 percent Dry Density = 105 pcf Sample of: Sandy Silty Clay From: Boring 2 at 10 Feet Compression upon wetting 0.1 1.0 10 APPLIED PRESSURE - ksf 100 113 111A Ge Piech HEPWGRTHPAWLAK GEOTECHNICAL SWELL -CONSOLIDATION TEST RESULTS FIGURE 4 • ' ETAI '[moi` HYDROMETER ANALYSIS I SIEVE ANALYSIS 2 {{p TIME READINGS U.S. STANDARD SERIES 1 CLEAR SQUARE OPENINGS 0 45 MIN. 15 MIN. 60MIN19MIN.4 MIN. 1 MIN. #200 #100 #50 #30 #16 #8 #4 3/8" 3/4" 1 1/2" 3' 5"6" 8" 100 10 20 30 40 50 60 70 80 90 100 .001 002 .005 .009 .019 CLAY TO SILT .037 .074 .150 .300 .600 1.18 2.36 DIAMETER OF PARTICLES IN MILLIMETERS SAND 4.75 FINE 1 MEDIUM ICOARSE 9.5 19.0 12.5 GRAVEL 37.5 NNE 1 COARSE 76.2 152 127 COBBLES 90 80 70 60 50 40 30 20 10 0 203 GRAVEL 59 SAMPLE OF: Slightly Silty Sandy Gravel 113 111A Ge Ptech HEPWORTH-PAWLAK GEOTECHNICAL SAND 33 % SILT AND CLAY 8 % FROM: Boring 2 at 15 Feet GRADATION TEST RESULTS T PASSI e, FIGURE 5 Job No. 113 111A co Z J J (n < • cc Z co = w U F W >, o x w O0 g ra YWre -J O m m < 1- n. u. = O } O a 2 a 2 w 2 m SOIL TYPE Sandy Silty Clay Sandy Silty Clay A cd U t. C4 b CC bT 0 ' c4 C7) ATTERBERG LIMITS LIQUID PLASTIC LIMIT INDEX (%) (%) PERCENT PASSING NO. 200 SIEVE 77 8 P O a 0 Z :,3: W CO O GRAVEL (%) 59 NATURAL DRY DENSITY (pcf) vp � co 0 onN NATURAL MOISTURE CONTENT (°%) vS r ti N LOCATION DEPTH (ft) 5 5 10 to N SAMPLE BORING