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HomeMy WebLinkAboutSoils Report 07.24.2015July 24, 2015 3C Construction Corporation Attn: Steve Lcc 700 Latigo loop Carbondale, Colorado 8162.1 ) Joh No 115 315A Subject: Subsoil Study for Foundation Design and Percolation Test, Proposed Residence, Lot 16, Stirling Ranch, Pinnacle Court, Garfield County. Colorado Dear Mr. Lee: As requested. Hepworth-Pawlalc Geotechnical, Inc. performed a subsoil study and percolation test for foundation and septic disposal designs at the subject site. The study was conducted in accordance with our agreement for geotechnical engineering services to 3C Construction Corporation dated July 8. 2015. The data obtained and our recommendations based on the proposed construction and subsurface conditions encountered are presented in this report. Proposed Construction: The proposed residence will he one and two story wood frame construction above a crawlspace and with an attached gage. The residence will be located on the site as shown on Figure I. Garage floor is proposed to be slab -on -grade. Cut depths are expected to range between about 3 to 5 feet. Foundation loadings for this type of construction are assumed to be relatively Tight and typical of the proposed type of construction. The septic disposal system is proposed to be located downhill and southwest of the Lesidence. lfbuilding conditions or foundation loadings are significantly different from those described above, we should be notified to re-evaluate the recommendations presented in this report. Site Conditions: '1'Iie vacant lot is vegetated with scattered juniper trees, sage brush, grass and weeds. The ground surface is relatively flat and slopes down to the southeast at a grade of about 6 percent. Basalt cobbles and boulders are scattered on the round surface. 2 Subsurface Conditions: The subsurface conditions at the site were evaluated by excavating two exploratory pits in the building area and one profile pit in the septic disposal area at the approximate locations shown on Figure 1. The logs of the pits are presented on Figure 2. The subsoils encountered, below about one foot of topsoil, consist of sandy silty clay. A gravel and clay layer was encountered in the Profile Pit from I %x to 4 feet. Results of swell -consolidation testing performed on relatively undisturbed samples of the sandy silty clay, presented on Figure 3, indicate Low compressibility under existing low moisture condition and light loading and a low collapse potential (settlement under constant load) or low expansion potential when wetted. Results of an USDA soil texture gradation analysis performed on a sample of gravelly cobbly loam (minus 6 inch fraction) obtained from the Profile Pit are presented on Figure 4. The laboratory test results arc summarized in Table 1. No free water was observed in the pits at the time of excavation and the soils were slightly moist to moist. Foundation Recommendations: Considering the subsoil conditions encountered in the exploratory pits and the nature of the proposed construction, we recommend spread footings placed on the undisturbed natural soil designed for an allowable soil bearing pressure of 1,500 psf for support of the proposed residence. The soils tend to compress or expand after wetting and there could be post -construction foundation movement on the order of 1 to I IA inches for a limited wetted depth of 5 to 10 feet or less. Footings should be a minimum width of 18 inches for continuous walls and 2 feet for columns. The topsoil and loose disturbed soils encountered at the foundation bearing level within the excavation should be removed. The soils exposed in footing areas should then be compacted. Exterior footings should be provided with adequate cover above their hearing elevations for frost protection. Placement of footings at least 36 inches below the exterior grade is typically used in this area. Continuous foundation walls should be reinforced top and bottom to span local anomalies such as by assuming an unsupported length of at Least 12 feel. Foundation walls acting as retaining structures should be designed to resist a lateral earth pressure based on an equivalent fluid unit weight of at least 55 pcf for the on- site soil as backfill. A representative of the geotechnical engineer should observe all footing excavations prior to concrete placement to evacuate bearing conditions. Floor Slabs: The natural on- site soils, exclusive of topsoil, are suitable to support lightly loaded slab -on -grade construction with a risk of movement similar to that described above. 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.115 315A GecRech -3 - reinforcement should be established by the designer based on experience and the intended slab use. A minimum 4 inch layer of relatively well graded sand and gravel such as road base should be placed beneath interior slabs for support. This material should consist of minus 2 inch aggregate with less than 50% passing the No. 4 sieve and less than 12% passing the No. 200 sieve. All till 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 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 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 retaining walls and crawlspacc 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 aminimum 1% 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 1 h feet deep. An impervious liner such as 20 mil PVC membrane should be placed below the drain gravel in a trough shape and attached to the foundation wall with mastic to prevent wetting of the bearing soils. Surface Drainage: Proper grading and drainage will be critical to keeping the bearing soils dry and limiting potential movement. The following drainage precautions should be observed during construction and maintained at all tinges 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. Free -draining wall backfill should be capped with about 2 feet of the on-site, finer graded soils to reduce surface water infiltration. Job No.1 15 315A —tech -4- 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 pavement and walkway arcas. A swale may be needed uphill to direct surface runoff around the residence. 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 10 feet from the building. Consideration should be given to the use of xeriscape to limit potential wetting of soils below the building caused by irrigation. Percolation Testing: Percolation tests were conducted on July 15, 2015 to evaluate the feasibility of an infiltration septic disposal system at the site. One profile pit and three percolation holes were dug at the locations shown on Figure 1. The test holes (nominal 12 inch diameter by 12 inch deep) were hand dug at the bottom of shallow hackhoe pits and soaked with water one day prior to testing. The soils exposed in the percolation holes are similar to those exposed in the Profile Pit shown on Figure 2 and consist of about 1% feet of topsoil overlying gravel and clay to 4 feet and sandy silty clay to the bottom pit depth of 8% feet. A USDA soil texture gradation was performed on a sample from the Profile Pit and the test results are shown on Figure 4. The percolation test results are presented in Table 2. Based on the subsurface conditions encountered and the percolation test results, the tested area should be suitable for a conventional infiltration septic disposal system. A civil engineer should design the infiltration septic disposal system. 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 arc based upon the data obtained from the exploratory pits excavated at the locations indicated on Figure 1, the proposed type of construction and our experience in the area. Our services do not include determining he presence, prevention or possibility of mold or other biological contaminants (MOBC) developing in the future. Tithe 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 pits and variations in the subsurface conditions may not become evident until excavation is performed. If conditions encountered during Job N0.115 315A - S - construction appear different from those described in this report, we should be notified at once so re-evaluation of the recommendations may he 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 verity 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 hearing strata and testing of structural fill by a representative of the geotechnical engineer. If you have any questions or if we may be of further assistance, please let us know. Respecttully Submitted, IIPPWORI'H - PAWLAK CiEOTFCHNICAT,, INC. Louis E. Eller Reviewed by: Steven L. Pawiak, P.E. e -X 4' ?5222 o 9q 7/, vp-,1,1 I.EErksw •'• j•• c��• ,rl •.wont attachments Figure 1 Lox `'` b > arA� � a�--�. ator4 Pits and Percolation Test Holes Figure 2 — Logs o exp oratory Pin Figure 3 - Swell -Consolidation Test Results Figure 4 — USDA Gradation Test Results Table 1 Summary of Laboratory Ter Results Table 2 — Percolation Test Results Job \o 1 315A tech APPROXIMATE SCALE 1"=6D' LOT 17 r f PIT ■ / r LOT 16 1 / / / / A P 1 cpi PROFILE PIT P2 OPEN SPACE 115 315A P3A I-1 PROPOSED RESIDENCE ■ PIT 2 LOT 15 Hepworth—PaWck Geatechnkoal LOCATION OF EXPLORATORY PITS AND PERCOLATION TEST HOLES Figure 1 0 U 5 10 LEGEND: PIT 1 ELEV.= 7087' WC= -10.6 DD=B9 -200=85 PIT 2 ELEV. 7093 WC=18.4 00=84 pTOPSOIL; organic sandy stt and clay, firm moist, dark brown. r 51%1 NOTES: PROFILE PIT ELEV.= 7092' GRAVEL = 33 - SAND=16 j SiL.T=37 CLAY=14 WC=1 2 8 CLAY (CL); sandy. si ty, gravelly with depth, medium stiff to stiff, moist, light brown, calcareous. 0 GRAVEL AND CLAY (GC -CL); sandy, silly, medium stiff/medium dense, moist, light blown, calcareous, basalt rock. 2' Diameter hand driven finer sample. Disturbed bulk sample 1. Exploratory pits were excavated on Ju y 14, 2015 with a treckhoe. 2. Locations of exploratory pits were measured approximately by pacing from features shown on the site plan provided. 3. Elevations of exploratory pits were obtained by interpolation between contours shown on the site plan provided. el. The exploratory pit locations and elevations should be considered accurate only to the degree implied by the method used. 5. The Tines between materials shown on the exploratory pit logs represent the approximate boundaries between material types and transitions may be gradual. 6. No free water was encountered in the pits at the time of excavating. Fluctuation in water levet may occur with time. 7. Laboratory Testing Results WC _ Water Content (%) DD = Dry Dens ty (pcl) -200 = Percent pass ng No. 200 sieve 115315A HEP'WOATH•PAW[_A!C G EertCCH W CAL Gravel = Percent retained on No. 10 Sieve Send = Percent passing No. 10 sieve and retained on No. 325 sieve Silt = Percent passing No. 325 sieve to panicle size 002mm Clay = Percent smaller than particle size .002rnm LOGS OF EXPLORATORY PETS Figure Compression % Compression - Expansion % 0 1 2 3 4 2 1 0 1 2 0.1 Moisture Content = 10.6 percent Dry Density = 89 pcf Sample of: Sandy Silty Clay From: Pit 1 at 2 Feet Compression upon wetting i 1.0 10 APPJED PRESSURE - kst 100 1.0 10 APPLIED PRESSURE - kst 115 315A H Hep+varth-Pawlak GeotecliNml 100 SWELL -CONSOLIDATION TEST RESULTS Figure Moisture Cul 'lent = 18.4 percent Dry Density = 84 pcf Sample of: Sandy Silty Clay From: Plt 2 at 6 Feel I Expansion upon wetting - `" " i _ 1 - 1.0 10 APPLIED PRESSURE - kst 115 315A H Hep+varth-Pawlak GeotecliNml 100 SWELL -CONSOLIDATION TEST RESULTS Figure HYDROMETER ANALYSIS HHFR--� TIME READINGS 0 ^sdq M!N 16MIN. 6OMIN1WIN. 4 MIN, M #325 10 20 30 SIEVE ANALYS 5 U.S. STANDARD SERIES #143 #60 #35 #10 i11I0 1/4 CLEAR SCUARE OPENINGS 3/8" 314" 1 1t2' s^ 5' 6' a 1 CO r 9+0 — 70 60 .mommiimomrwlw-- 50 MINIM= IN 70 60 90 100 MEN -rrrr1mNIINI■r.i.I .001 .0O2 .005 .000 .010 .045 .106 .025 .500 1.00 2.00 DIAh1=7CA CF PARTICLES IN NJLLIME'TE1 S Wm' E T L.75 Y.5 19.0 37.5 76.2 152 203 tlNis t Fen 1 1•EOIIN !Calk. (.: CCW -V11 GRAVEL 33 % SAND i "n % t.'ni.FL Etur 1 Mrtllt'M 1 LlHCF COM F,S SILT 37 % CLAY 14 % USDA SOIL TYPE Gravelly Cobbly Loam FROM: Profile Pit at 3 to 4 Feat 115 315A H 50 20 10 0 - - 1 `AS INS HEPWDATFiPA WLAK G EOTCcHHIGH. USDA GRADATION TEST RESULTS Figure 2 z a w v D w U w >- o LLI UJQ m� 5 H m LL 0 cd 0) HEPWORTH-PA Job No.115 315A Sandy Silty Clay Gravelly Cohbly Loam Gravelly Cobb!), Loam USDA SOIL TEXTURE a J w 0 GRADATION 0 Z aP- m SAMPLE LOCATION 00 HOLE NO. HEPWORTH-PAWLAK GEOTECHNICAL, INC. TABLE 2 PERCOLATION TEST RESULTS HOLE DEPTH (INCHES) LENGTH OF INTERVAL (MIN) WATER DEPTH AT START OF INTERVAL (INCHES) WATER DROP IN DEPTH AT WATER END OF LEVEL INTERVAL (INCHES) (INCHES) P1 46 10 8 71/4 JOB NO. 115 315A 71/4 7 1.4 7 6% 1/2 61/2 53/4 7A 5% 514 1.4 5/ 43/4 1� 43/4 41/4 41/4 3% 3'/4 P2 40 10 8'/a 734 1/ 1/2 1/4 7'/ 7/ 1/4 7Y2 7 1r 7 1/4 6% 61/2 14 61/4 �4 614 6 1/4 6 5% 10 8'/2 8 1/4 AVERAGE PERCOLATION RATE (MINJINCH) 20 40 1% 714 *la 7% 61/2 2/4 61/2 6 y2 6 51/4 /4 51/4 4/4 41/2 3/4 41/2 4 14 4 31/4 3/4 31/4 2% 21/2 L 1% a/4 13 Note: Percolation test holes were hand dug in the bottom of backhoe pits and soaked on July 14, 2015. Percolation tests were conducted on July 15, 2015. The average percolation rates were based on the last three readings of each test.