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Home My WebLink AboutSoils ReportHEPWORTH-PAWLAK GEOTECHNICAL ! le4nr ,rth-P;nt'Ink (kt1 echnica1, int. 5t)Z0 County !load 154 Glenwood Si+rinps, Colui,lcln 81601 Ph,,ne: 970-945-7988 Fat: 970-945-8454 t'lnai l: 111trCo3hpi;Cutcih.com SUBSOIL STUDY FOR FOUNDATION DESIGN PROPOSED RESIDENCE LOT 82, IRONBRIDGE PHASE 2, FILING 2, RIVER BANK LANE GARFIELD COUNTY, COLORADO JOB NO. 108 115A APRIL 14, 2008 PREPARED FOR: NORTHWAY CONSTRUCTION ATTN: RICK KOEHLER 981 COWEN DRIVE, UNIT D CARBONDALE, COLORADO 81623 Parker 303-S41-7119 0 Co!oral° Springs 719-633-5562 0 Silverr1iornc 970-468-1989 TABLE OF CONTENTS PURPOSE AND SCOPE OF STUDY - 1 - 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 - UNDERDRA.IN SYSTEM - 6 - SURFACE DRAINAGE - 6 - LIMITATIONS ._ - 7 - FIGURE 1 - LOCATION OF EXPLORATORY BORINGS FIGURE 2 - LOGS OF EXPLORATORY BORINGS FIGURE 3 - LEGEND AND NOTES FIGURES 4 AND 5- SWELL -CONSOLIDATION TEST RESULTS FIGURE 6 - GRADATION TEST RESULTS TABLE 1- SUMMARY OF LABORATORY TEST RESULTS PURPOSE AND SCOPE OF STUDY This report presents the results ofa subsoil study for a proposed residence to be Iocated at Lot 82, Ironbridge, Phase 2, Filing 2, River Bank Lane, Garfield County, Colorado. The project site is shown on Figure 1. The purpose ofthe study was to develop recommendations for the foundation design. The study was conducted in accordance with our agreement for geotechnical engineering services to Northway Construction dated March 24, 2008. Hepworth-Pawlak Geotechnical previously conducted geotechnical engineering studies for the subdivision development and presented their findings in reports dated October 29, 1997 and February 12, 1998, Job No. 197 327. 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 tall one story shed roof structure with an attached garage above a partial crawlspace and partial slab -on -grade floors. Grading for the structure is assumed to be relatively minor with cut depths between about 2 to 5 feet. We assume relatively light foundation loadings, typical ofthe 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. 108 115A G@~CPtech -2 - SITE CONDITIONS The site is located on the north end of River Bank Lane near the intersection of River Bend Way. The site was vacant of structures and clear of snow cover at the time of our exploration. Vegetation consists of grass and weeds with scattered brush. The ground surface slopes down to the east at a grade of about 4 to 5 percent in the building area. The Roaring Fork river borders the rear (east) side of the property. SUBSIDENCE POTENTIAL Bedrock of the Pennsylvanian age Eagle Valley Evaporite underlies the Ironbridge Development. These rocks are a sequence of gypsiferous shale, fine-grained sandstone and siltstone with some massive beds of gypsum and limestone. There is a possibility that massive gypsum deposits associated with the Eagle Valley Evaporite underlie portions ofthe lot. Dissolution ofthe gypsum under certain conditions can cause sinkholes to develop and can produce areas of localized subsidence. During previous studies for the subdivision development, several sinkholes were observed scattered throughout the Ironbridge Development. These sinkholes appear similar to others associated with the Eagle Valley Evaporite in areas of the Roaring Fork River valley. The closest mapped sinkhole is located roughly below the intersection of River Bank Lane and River Bend Way about 80 feet to the northwest. Another sinkhole is Iocated to the southwest in the 16th fairway. The subsidence evaluation for remediation of this sinkhole was presented in our report dated July 7, 2006, Job No. 105 115-4. Both of these sinkholes appear to be associated with the underlying bedrock condition. No evidence of cavities was encountered in the subsurface materials; however, the exploratory borings were relatively shallow, for Ibundation design only. Based on our present knowledge ofthe subsurface conditions at the site, it cannot be said for certain that sinkholes will not develop. The risk of future ground subsidence on Lot 82 throughout the service life of the proposed residence, in our opinion, is low and similar to other lots in the area; however, the owner should be made aware of the potential for Job No. 108 I C5A c ec t h -3 - sinkhole development. If further investigation of possible cavities in the bedrock below the site is desired, we should be contacted. FIELD EXPLORATION The field exploration for the project was conducted on April 2, 2008. Four 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% inch and 2 inch 1.0. 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 6 inches to 18 inches o f topsoil consist of 3'/ to 6!rz feet of silt and sand overlying relatively dense slightly silty sandy gravel and cobbles with boulders. About 2'2 feet of sandy silty clay was encountered over the silt and sand in Boring 4. 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. Laboratory testing performed on samples obtained from the borings included natural moisture content and gradation analyses. Results of swell -consolidation testing Job Na. 108 115A —.... GetPtech -4 - performed on relatively undisturbed drive samples ofthe silt and sand, presented on Figures 4 and 5, indicate low compressibility under existing moisture conditions and light loading with a high compression potential after wetting and under additional loading. Results of gradation analyses performed on a small diameter drive sample (minus 1!/2 inch fraction) ofthe coarse granular subsoils are shown on Figure 6. The Iaboratory testing is summarized in Table I. Free water was encountered in Boring 1 at a depth of 8 feet at time of drilling and 7 !:& feet the following day. No free water was encountered in Borings 2, 3 and 4 at the time of drilling or when checked 1 day later and the subsoils were slightly moist to moist. FOUNDATION BEARING CONDITIONS The soils expected at the relatively shallow cut depths proposed consist mainly of loose silt and sand suitable for support of shallow spread footings with a moderate settlement potential. The silt and sand soils encountered above the natural granular soils are compressible after wetting and under loading and there will be a risk of settlement. Extending the bearing level down to the dense gravel (about 3 to 4 feet below the assumed footing grade) would reduce the settlement potential and risk of building distress. An alternative with a low risk of settlement would be to excavate down to the sandy gravel soils and re-establish design bearing level with compacted structural till. 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 granular soils. The design and construction criteria presented below should be observed for a spread footing foundation system. I) Footings placed on the undisturbed natural granular soils or compacted structural fill should be designed for an allowable bearing pressure of Job No. 108 115A Gtech -5- 3,000 psf. Based on experience, we expect settlement of footings designed and constructed as discussed in this section will be about 1 inch or less. 2) The footings should have a minimum width of 16 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 Iength of at least 10 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 pc£ 5) Any existing fill, topsoil, silt and sand soils and loose or disturbed soils should be removed and the footing bearing level extended down to the natural granular soils. The exposed soils in footing areas should be moisture adjusted to near optimum and compacted prior to constructing footings or placing fill. Structural fill used to re-establish design bearing level should consist of a granular soil similar to the on-site gravel soils and be compacted to at least 100° o of standard Proctor density at near optimum moisture content. 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. There is some risk of differential settlement if the underslab soils become wetted. 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 Job No. 108 115A Gagtech -6 - 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. UNDERDRAIN SYSTEM Although free water was encountered below expected excavation depths during our exploration, it has been our experience in the area that the ground water can rise during spring runoff and local perched groundwater can develop during times of heavy precipitation or season& runoff Frozen ground during spring runoff can create a perched condition. We recommend below -grade construction, such as retaining walls and crawlspace 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 I% to a suitable gravity outlet. 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 11.: feet deep. SURFACE DRAINAGE The following drainage precautions should be observed during construction and maintained at all times after the residence ]ias been completed: Job No. 103 115A Gtech -7- 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% ofthe 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 12 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 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 ofthe subsurface conditions identified at the exploratory borings and variations in the subsurface Jab No. 108 115Av� GgEtech -8 - 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. Louis E. Eller Reviewed by: Daniel E. Hardin, P.E. LE E;'vad Job No. 108 t 15A GgEth APPROXIMATE SCALE 1'=30' LOT 83 1 • RNER BANK 1-P,NE 5950 5945 i 5935 - - - 108 115A H Hepworth--Pawlak Geatechnlcal 5930 ROAR/NGFORK R/!ER LOCATION OF EXPLORATORY BORINGS II 1 LOT 81 Figure 1 Elevation - Feet 5940 5935 5930 5925 5920 BORING 1 ELEV. =5936' BORING 2 ELEV.= 5937' FINISH FLOOR = 5938' 7/12 WC -3 8 DD=91 9/12 3716,5019 T r.. 9112 WC -5.2 UD -76 200 59 ;; ;i --I 10/12 . YaPR BORING 3 ELEV. - 5938' 14/12 7/12 WC=4.3 DD -79 -200-63 40/6 BORING 4 ELEV. =5929' Note: Explanation of symbols is shown on Figure 3. 13/12 6/12 WC 6.3 DD=84 50/12 WC -2.7 -4=44 -200=11 5940 5935 5930 5925 5920 Elevation - Feet 108 115A H Hepworth—Powlak GeotechnIca! LOGS OF EXPLORATORY BORINGS Figure 2 LEGEND: ® TOPSOIL; organic sandy silt and clay, moist, dark brown. CLAY (CL); silty, sandy, stiff, moist, brown. SILT AND SAND (ML -SM); stratified, loose, slightly moist, light brown. GRAVEL (GM -GP); with cobbles and boulders, sandy, slightly silty, dense, moist to wet with depth, light brown, rounded rock. 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. -7 111 7/12 0,1 T Drive sample blow count; indicates that 7 blows of a 140 pound hammer falling 30 inches were required to drive the California or SPT sampler 12 inches. Free water level in boring and number of days after drilling measurement was made. Depth at which boring caved. Practical drilling refusal. Where shown above bottom of log, indicates that multiple attempts were made to to advance the boring. NOTES: 1. Exploratory borings were drilled on April 2, 2008 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. Water level readings shown on the logs were made at the time and under the conditions indicated. Fluctuations 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 108 115A Hepworth—Pawlak CsotachnIcal LEGEND AND NOTES Figure 3 Compression % 0 1 2 3 4 5 6 7 8 9 10 11 12 Moisture Content = 3.8 percent Dry Density = 91 pcf Sample of: Silt and Sand From: Boring 1 at 2 Feet Compression upon wetting 0.1 1.0 APPLIED PRESSURE - ksf 10 100 108 115A Hapworth—Pawlak Geotechnical SWELL -CONSOLIDATION TEST RESULTS Figure 4 Compression % 0 2 4 6 8 10 12 14 16 18 0.1 108 115A Moisture Content = 6.3 percent Dry Density = 84 pct Sample o6: Silt and Sand From: Boring 4 at 4 Feet I-1 1.0 Hepworth—Pawlok Geotechnical APPLIED PRESSURE - ksf Compression upon wetting 10 SWELL -CONSOLIDATION TEST RESULTS 100 Figure 5 1.121a0.igi*EIPIX. HYDROMETER ANALYSIS I 5 EVE ANALYSIS I }}��qq� TME READINGS I.I S STANDARD SERIES 1 CLEAR SQUARE OPEN;NGS l 0 24 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' tpp 10 20 30 40 50 60 70 80 90 100 001 Sas' - MESIM -air - - SIS — Sal ■Sat - NISI !ate -a --as arai SlMI la --1- MI SI al --- —a— la �raa--a- !IS!----- rare--r— a--- !Man S as aa•M_-SWISS ■.moi_-- aA ar I Mai-- a- Sal SS Mea - SSI Mar — wales — r—r — Sal lana. - — Sala SI - - aa1---a- �_a---a— -r ---r- aM MMM - SIRS. e- SS i --1S —,----1- raa---1- ■al_--Sa- -a- --a �M_---a -1aM S-aaaarSIMS __a_-_-_--aS a aaa— arms Harm Sal Sal Mala r- --as----w— rear---a- -a— aaa - --rrra.ar--a— ilast SI S ---Sa- a -i as -i --a- q_ rear---a— MM---Sa- -ANiiaa----15 �- -al- SEM a -away--- ISM -1- - aaa rr- aaaasaSEM - Sal! SI waw---a s'A -w- SS - - --- a- -- - !wear --a- WS -a- - - MI MMa---a- -a- a -a— -1SEEMS SIS iw--i-a- -ai--- waaal SE, i -a- -- -1- -as-i-- MMaw---al- araa-iii-----al- -.— 1S SIM rS-- waw- ---a- r�----waw ii— al- -T- w aw-a--1- rli---1- ----aa•- ----- w -i --l- --- -a a, s -a - a- wawa ---a -fes waw -A- -a- --- --rarrr aaaaaa--- SO! Mar r SI S. A w MMM --S a - -a r -a mar � s— a—ars a -a aaaaa�- arr a aw---1 w MMM--- IN -a- Mali--Sa- arStSol --a- -a- -a- nn aa\ 1•1 002 005 009 .019 037 074 150 .300 600 1 18 2 36 4 75 9 512 519 0 37.5 DIAMETER OF PARTICLES IN M WMETERS 76 2 152 203 127 CLAY TO SLT IFI I � I CC ARSE GRAVEL EINE 1 COARSE ICOBBLES GRAVEL 44 % LIQUID LIMIT % SAND 45 % SILT AND CLAY 11 % PLASTICITY INDEX % FROM: Boring 4 at 9 Feet SAMPLE OF: Slightly Silty Sand and Gravel 108115A H Hepworth--Pawlck Geotechnical GRADATION TEST RESULTS 90 80 70 60 50 40 30 20 10 0 `aottei isgwii►It Figure 6 Job No. 108 115A IT z J 4-4 J' QW V De = LL! U LU O 5LUO QCCI J am CL • L_ ' O 0 a X LLJ _ (J SOIL OR BEDROCK TYPE 10 q c� ea 4- Silt and Sand 11 Silt and Sand 11 Silt and Sand 11 Slightly Silty Sand and Gravel UNCONFINED COMPRESSIVE STRENGTH (PSF) ATTERBERG LIMITS LIQUID PLASTIC LIMIT INDEX (%) (%) PERCENT PASSING NO. 200 SIEVE inell i-4 o P 0 g La 0 in GRAVEL (%) 4 NATURAL DRY p DENSITY () — a 76 ON t-- 84 NATURAL MOISTURE CONTENT (%) 00 00 [*1 N U'1 M 4 M ,,0 [..- N g 50 9 J z t e N N ..4-G1 z 1 E *-+ N M NI- 1