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Home My WebLink AboutSubsoil Study for Foundation Design-\ . . ~tech HEPWORTH•PAWLAK GEOTECHNICAL SUBSOIL STUDY Hcpworlh-P1nvlak Gcolcchnic.ll, Inc. 5020 Cnunly Rn.,J 154 G\cnwt>Od Spring., Color..Jo 81601 Phunc: 970-945-7988 l?4X: 970-945-8454 13 miiil: hpgca(f!: hpgcolcch.com FOR FOUNDATION DESIGN PROPOSED RESIDENCE LOT C 4, ASPEN GLEN GARFIELD COUNTY, COLORADO JOB NO. 113 218A JULY 25, 2013 PREPARED FOR: GRUENEFELDT CONSTRUCTION ATTN: DAN GRUENEFELDT P.O. BOX 1910 BASALT, COLORADO 81621 dan<@gruenef eld t.com TABLE OF CONTENTS PURPOSE AND SCOPE OF STUDY ............................................................................ - 1 - PROPOSED CONSTRUCTION ..................................................................................... - 1 - SITE CONDITIONS ............................................................................................................. - 2 - SUBSIDENCE POTENTIAL ......................................................................................... - 2 - FIELD EXPLORATION ................................................................................................. -2 - SUBSURFACE CONDITIONS ...................................................................................... - 3 - FOUNDATION BEA RIN G CONDITIONS ................................................................... -3 - DESIGN RECOMMENDAT IONS ................................................................................. - 4 - FO UNDATIONS ......................................................................................................... - 4 - FLOOR SLABS .......................................................................................................... -5 - UNDE RD RAIN SYSTEM .......................................................................................... -6- SURF ACE DRAINAGE ............................................................................................. -6 - LIMITATIONS ........................................................................................ ,. . .,. ........................ -7 - REFERENCES ........................................................ ~······· .. ························· ............................. 8 .... FIG URE 1 -LOCATION OF EXP LORATORY BORINGS FIG URE 2 -LOGS OF EXPLORATORY BORINGS FIGURE 3 -LEGEND AND NOTES FIG URE S 4 AND 5 -SWELL-CONSOLIDATION TEST RES UL TS FIG URE 6 -GRADATION TEST RESULTS TABLE I-SUMMA RY OF LABORATORY TEST RESULTS Job No. 113 218A ' . PURPOSE AND SCOPE OF STUDY This report presents the results of a subsoil study for a proposed residence to be located at Lot C4, Aspen Glen, 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 agreement for geotechnical engineering services to Gruenefeldt Construction dated June 17, 2013. Chen-Northern, Inc. previously conducted geotechnical engineering studies for the Aspen Glen development and presented their findings in reports dated December 20, 1991 and May 28, 1993, Job No. 4 112 92. 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 one and two story wood frame construction with an attached garage. Ground floors will be slab-on-grade. Grading for the structure is assumed to be relatively minor with cut depths between about 2 to 4 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 218A -2- SITE CONDITIONS The property is vacant of structures and vegetated with grass and weeds. Overlot grading was perfonned during subdivision development with probable minor cutting in the area of the subject site. The ground surface is relatively flat with a slope of about 1 percent down to the northwest. An abandoned irrigation ditch crosses the rear part of the lot. SUBSIDENCE POTENTIAL Aspen Glen is underlain by Pennsylvania Age Eagle Valley Evaporite bedrock. The evaporite contains gypsum deposits. 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 sinkholes were observed scattered throughout the Aspen Glen development (Chen-Northern, Inc. 1991 and 1993). The building envelope is located about 775 feet east of a mapped broad subsidence area and 1,250 east of a mapped si nkh ole. Sinkholes were not observed in the immediate area of the subject lot. The exploratory borings were relatively shallow, for founda t ion design only. Based on our present knowledge of the site, it cannot be said fo r certain that sinkholes will not develop. In our opinion, the risk of ground subsidence at Lot C4 throughout the service li fe of the building is low and similar to other lots in the area but the owner should be aware of the potenti al for sinkhole development. FIELD EXPLORATION The fie ld exploration for the project was conducted on June 24, 20 13. Two exploratory borings were drill ed at the locations shown on Figure 1 to evaluate the subsurface conditions. The borings were advanced with 4 inch di ameter continuous flight augers powered by a truck-mounted CME-458 drill rig. The borings were logged by a representative of Hepworth-Pawlak Geotechnical, Inc. Job No. 113 218A -3- Samples of the subsoils were taken with lo/a inch and 2 inch l.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 below about I foot of topsoil consist of 7 to 10 feet of very silty sandy clay overlying silty sandy gravel with cobbles . Drilling in the dense granular soils with auger equipment was difficult due to the cobbles and boulders and drilling refusal was encountered in the deposit at Boring 2. Laboratory testing perfonned 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, presented on Figures 4 and 5, indicate low compressibility under light loading and a moderate collapse potential (settlement under constant load) when wetted. The samples showed high compressibility under increased loading after wetting. Results of gradation analyses perfonned on a small diameter drive sample (minus I Yi inch fraction) of the coarse granular subsoils are shown on Figure 6. The laboratory testing is summarized in Table I. No free water was encountered in the borings at the time of drilling and the subsoils were slightly moist to moist. FOUNDATION BEARING CONDITIONS The upper clay soils have low bearing capacity with variable settlement potential. These soils are typically known to be compressible under loading when wetted. The Job No. 113 218A -4- groundwater level in the area is relatively deep but possible sources of wetting include utility line leaks, drainage and lawn irrigation. Keeping the bearing soils from getti ng wet will be critical to the long term perforrnance of the structure. The owner should be made aware of the risk. The underlying gravel soils have moderate bearing capacity and minor settlement potential. A basement level beari ng on the underlying gravel should be considered. DESIGN RECOMMENDATIONS FOUNDATIONS Considering the subsurface conditions encountered in the exploratory borings and th e nature of the proposed construction, we recommend the bui lding be founded with spread footings bearing on the natural soils. The design and construction criteria presented below should be observed for a spread footing foundation system. I) Footings placed on the undisturbed natural c lay soils should be designed for an allowable bearing pressure of 1,000 psf. Based on experience, we expect initial settlement of footings designed and constructed as discussed in this section will be about I inch or less. Additional settlement on the order of2 to 3 inches is possible if the bearing soils become wet. If the risk of this amount of settlement is not tolerable, the footings should be placed on the underlying dense gravel. 2) The footings should have a minimum width of20 inches for continuous walls and 30 inches 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 3 6 inches below exterior grade is typically used in this area. Job No. tl3 218A -5- 4) Continuous foundation walls should be reinforced top and bottom to span local anomalies such as by assuming an unsupported length of at least 14 feet. Foundation walls acting as retaining structures (if any) 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 relatively undisturbed 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 topsoil, are suitable to support lightly loaded slab- on-grade construction with variable settlement potential if the subsoils become wet. To reduce the effects of some differential movement, 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 the on-site granular soils devoid of vegetation, topsoil and oversized rock. Job No. 113 218A UNDERDRAIN SYSTEM Although free water was not encountered during our exploration, it has been our experience in the area that local perched groundwater can develop during times of heavy precipitation or seasonal runoff. Frozen ground during spring runoff can create a perched condition. We recommend below-grade construction , such as a basement level, be protected from wetting and hydrostatic pressure buildup by an underdrain system. The proposed slab-on-grade construction should not requ ire an underdrain system. The drains (if placed) should consist of drainpipe placed in the bottom of the wall backfil l surrounded above the invert level with free-dra ining granular material. The drain should be placed at each level of excavation and at least I foot below lowest adjacent fin ish grade and sloped at a minimum 1 % to a suitable outlet such as a dryweU 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 of2 inches. The drain gravel backfi ll should be at least l Vi feet deep . SURF ACE 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 fi rst 10 feet in paved areas. Job No. 113 218A -7- Free-draining wall backtiJI 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 l 0 feet from foundation walls. Consideration should be given to use ofxeriscape 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 based upon the data obtained from the exploratory borings drilled at the locations indicated on Figure 1, 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 Job No. 113 218A -8- 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. Louis E. Eller Reviewed by: Daniel E. Hardin, P .E. LEE/ksw REFE RE NCES 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 218A APPROXIMATE SCALE 1" =30' LOTC5 113 218A I I THUNDERSTORM --~ --' r------ 1 '\ I • \ I BORING2 \ I \ I \ LOTC3 I \ I \ I \ I \ / LOT C4 \ I \ I \ I \ I \ I \ I \ / BORING 1 \ L__ • /) ~~-~--/ --------0'/ \ \ BENCH MARK: GROUND AT BUILDING ENVELOPE CORNER; ELEV. • 100.0', ASSUMED . --_____ ..,,, GOLF COURSE LOCATION OF EXPLORATORY BORINGS Figure 1 100 95 .... Cl.> Cl.> u. 90 I c: 0 ~ ~ w 85 BO 113 218A BORING 1 ELEV.= 98.4 1 19/12 WC =7.1 00 ~92 -200 =79 5/12 34/12 BORING2 ELEV.= 97.51 10/12 WC =6.7 DD =89 34/12 WC=t .6 +4 =41 -200=17 Note: Explanation of symbols Is shown on Figure 3. LOGS OF EXPLORATORY BORINGS 100 95 ~ 90 • c: 0 l jjj 85 80 Figure 2 LEGEND: ~ TOPSOIL; organic silt and clay, firm . slightly moist, dark reddish brown. D CLAY (CL): very silty, sandy, medium stiff to stiff, slightly moist, reddish brown. ~ GRAVEL (GM); with cobbles and scattered boulders, sandy, silty, dense, slightly moist, reddish brown. p Relatively undisturbed drive sample: 2-inch 1.0. California liner sample. -Drive sample; standard penetration test (SPT), 1 3/8inch1.0. split spoon sample, ASTM 0-1586 . 19112 Drive sample blow count; indicates that 19 blows of 140 pound hammer falling 30 inches were required to drive the California or SPT sampler 12 inches. T Practical drilling refusal. NOTES: 1. Exploratory borings were drilled on June 24 , 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 measured by instrument level and refer to the Bench Mark shown on Figure 1. 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 lime of drilling . 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 218A LEGEND AND NOTES Figure 3 '#. z 0 en en w a: a.. :? 0 0 0 ~ 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 0.1 113 218A I I I I Moisture Content = 7.1 percent ' I Dry Density = 92 pct ' ! I Sample of: Very Silty Sandy Clay I I From: Boring 1 at 4 Feet ~I I I "1~ I Compression I ' I ~ ,,,,. upon wetting I / (/ I ' I I I I ' ! I ~ \ ' \ I I I . I \ \ I \ I \ I \ ' .., 1.0 10 100 APPLIED PRESSURE ( ksf) SWELL-CONSOLIDATION TEST RESULTS Figure 4 1 113218A Moisture Content = 6. 7 Dry Density = 89 Sample of: Very Silty Sandy Clay From : Boring 2 at 5 Feet 1.0 10 APPLIED PRESSURE ( ksf) percent pct ' I I 100 SWELL-CONSOLIDATION TEST RESULTS Figure 5 I DfAtB I RYl56~ ANALYii!I I TIME READINGS U.S. STN«)AN) SERIES CLEAR SQUARE Ol'ENIHGS :.HJI. 7HFI -t5MR 15Mlt. _, __ 0.llN. 11o11H. l:IOO 1100 •SO -... " /14 :...-314' 11/Z' "J" 5' II' r 0 I 100 ---::. --I :/ ----------I - ---. 90 10 / __ --I - -------------I --- ---- I ' BO 20 f --. - 30 --70 -l . -1 I --. --- ----------·· ------I -. 0 .co 60 Cl w ~v I z z -li5 ~ ... ---. ----------------= -1_-___ -· --~ ----a: 50 'I 50 !z v 1 --!z I -· w / -w ----0 (,) I -a: ----a: w -----w Cl.. 60 I -"" Cl.. ,V ---. ----I --- ----,_ -------------I --- 70 ---------30 v; -· -. = ----------I -----· ---. -· ---I -/ - BO I -20 I/ I I -------· ·-----.. -· ·-I ------90 10 -· I --------------------1 -~ --· --------------- ---I 100 0 J)01 J)(l2 .om .DOii .DI~ .1137 m• .150 .300 .IOO 1.11 2.311 4.75 u 12.5 111.(1 ~., 70..Z 171152 203 DIAMETER OF PARTICLES IN MIWMETERS I 1:+ 1~E ORA~ I CUIYTO SA..T I C08Bl.U FWE FINE COARSE Gravel 4 1 % Sand 42 % Silt and Clay 17 % Liquid Limit % Plasticity Index % Sample of ~ Silty Sand and Gravel From: Boring 2 at 10 Feet 11 3 218A ~ HEPWOR'TM-PAWLAK GEOT1tCHNIC::AL GRADATION TEST RESULTS Figure 6 HEPWORTH-PAWLAK GEOTECHNICAL, INC. TABLE 1 Job No. 113 218A SUMMARY OF LABORATORY TEST RESULTS SAMPLl LOCATION NATURAL NATURAL GRADATION PERCENT ATTERIERG UMITS UNCONFINED MOISTURE DRY GRAVEL ~D PASSING LIQUID PWTIC COMPRESSIVE sotLOR BORING DEPTH CONTENT DENSITY "'' '"' N0.200 UMIT INDEX STRENGTH BEDROCK lYP! SIM lffl OC.I lpcf) "'' OC.I IPSFJ I 4 7. l 92 79 Very Silty Sandy Clay 2 5 6 .7 89 Very Silty Sandy Clay 10 1.6 41 42 17 Silty Sand and Gravel