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HomeMy WebLinkAboutSoils Report 07.29.2016H-PiKUMAR Geotechnical Engineering 1 Engineering Geology Materials Testing 1 Environmental 5020 County Road 154 Glenwood Springs, CO 81601 Phone: (970) 945-7988 Fax: (970) 945-8454 Email: hpkglenwood@kumarusa.com Office Locations: Parker, Glenwood Springs, and Silverthorne, Colorado SUBSOIL STUDY FOR FOUNDATION DESIGN PROPOSED RESIDENCE AND SHOP BUILDING LOT 7, SUN MEADOW ESTATES NORTH MEADOW DRIVE GARFIELD COUNTY, COLORAO JOB NO. 16-7-222 JULY 29, 2016 PREPARED FOR: LUCAS BETHELL 143 SOUTH BILL CREEK ROAD CARBONDALE, COLORADO 81623 (73hotrod @gmail.com) TABLE OF CONTENTS PURPOSE AND SCOPE OF STUDY - 1 - PROPOSED CONSTRUCTION - 1 - SITE CONDITIONS - 2 - FIELD EXPLORATION - 2 - SUBSURFACE CONDITIONS - 2 - DESIGN RECOMMENDATIONS - 3 - FOUNDATIONS - 3 - FLOOR SLABS - 4 - UNDERDRAIN SYSTEM - 5 - SURFACE DRAINAGE - 5 - LIMITATIONS - 6 - 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 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 and shop building to be located at Lot 7, Sun Meadow Estates, North Meadow Drive, 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 you dated July 15, 2016. We previously performed a preliminary geotechnical study for the Sun Meadow Estates Subdivision (Mamm's View) and reported our findings March 28, 2000, .lob No. 100 169. 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 story wood frame construction above a crawlspace. The shop building will be a tall one story structure with slab -on -grade floor. Grading for the structures is assumed to be relatively minor with cut depths between about 3 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. SITE CONDITIONS The vacant lot is vegetated with grass and weeds. The ground surface is relatively flat with a slight slope down to the southwest. FIELD EXPLORATION The field exploration for the project was conducted on July 18, 20I6. 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 -45 drill rig. The borings were logged by a representative of Hepworth-Pawlak Geotechnical, Inc. Samples of the subsoils were taken with a 2 inch I.D. spoon sampler. The sampler was 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 I' feet of topsoil overlying 111/2 to 221 feet of very stiff sandy silt and clay. Medium dense silty to clayey sand was encountered below 13 to 24 feet down to the maximum depth drilled, 60 feet. Laboratory testing performed on samples obtained from the borings included natural moisture content, density and percent finer then sand size gradation analyses. Results of -3 - swell -consolidation testing performed on relatively undisturbed drive samples, presented on Figures 4 and 5, indicate a low to minor expansion potential under conditions of loading and wetting. The laboratory testing is summarized in Table 1. No free water was encountered in the borings at the time of drilling and the subsoils were slightly moist to moist. Free water was measured at 521 feet in Boring 2 ten days following drilling. Free water was measured at 521/ feet in Boring 2, ten days following drilling. DESIGN RECOMMENDATIONS FOUNDATIONS Considering the subsurface conditions encountered in the exploratory borings and the nature of the proposed construction, we recommend the residence and shop building be founded with spread footings bearing on the natural soils below topsoil, provided some settlement is tolerable and precautions are taken to prevent wetting of the bearing soils. The design and construction criteria presented below should be observed for a spread footing foundation system. 1) Footings placed on the undisturbed natural soils should be designed for an 2) allowable bearing pressure of 1,500 psf. Based on experience, we expect settlement of footings designed and constructed as discussed in this section will be about I inch. Additional settlement could occur if the bearing soils become wet. The amount of settlement would be related to the depth and extent of wetting but could be 2 to 3 inches for wetting down to 20 feet. This risk of settlement could be mitigated by installing a deep foundation such as micropiles at depths greater than 50 feet. The footings should have a minimum width of 18 inches for continuous walls and 2 feet for isolated pads. * ice Add.c144u.+44 l,tffti! {rows Hp 400-449_ a/15/1r0 H -P `. KUMAR -4- 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 14 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 topsoil and any loose or disturbed soils should be removed and the footing bearing level extended down to the relatively firm natural soils. The exposed soils in footing area should then be moistened and compacted. 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. 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 slabs to act as a break for capillary moisture rise. 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 (3/4 inch screened rock). H -P _: KUMAR -5 - 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 and topsoil. 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 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 An underdrain should not be needed where slab -on -grade floors are at or above the exterior grade. 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 sump and pump. Free -draining granular material used in the underdrain system should contain less than 27e: passing the No. 200 sieve, less than 50% passing the No. 4 sieve and have a maximum size of 2 inches (3/4 inch screened rock). The drain gravel backfill should be at least 1!.'i feet deep. An impervious membrane such as 20 mil PVC should be placed beneath the drain gravel in a 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 and shop have been completed: 1) Inundation of the foundation excavations and underslab areas should be avoided during construction. -6- 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 10 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 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 -7_ 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, KUMAR 1;/ Louis Eller Reviewed by: Daniel E. Hardin, P.E. LEE/ksw _ •\\4L Fi IIM En LOT 6 30 0 30 60 APPROXIMATE SCALE—FEET 16-7-222 KUMAR BORING 2 (HOUSE) • •BORING 1 (SHOP) LOT 7 LOT 8 1 LOCATION OF EXPLORATORY BORINGS 3AIdO MOOV3 M H1 ON Fig. 1 • 100 - 90 - 80 - 70 - 50 - 40 BORING 1 BORING 2 EL. 100' EL 98.5' SHOP HOUSE 21/12 WC=5.4 DD=105 21/12 WC=5.1 DD=118 17/12 21/12 19/12 19/12 17/12 WC=7.8 DD=97 -200=88 / /J 22/12 / /\ 16/12 / WC=5.6 // DD=101 / 20/12 / WC=5.5 DD=106 -200=79 31/12 WC=5.7 D0 DD=12121 -200=37 /0 19/12 19/12 24/12 WC=4.8 DD=114 100 - 90 - 80 70 60 50 40 30 30 NOTE: EXPLANATION OF SYMBOLS PRESENTED ON FIGURE 3. - 20 20 ELEVATION--FEET 16-7-222 H -P- KUMAR LOGS OF EXPLORATORY BORINGS Fig. 2 LEGEND —7 // TOPSOIL; ORGANIC SANDY SILT CLAY, FIRM, SLIGHTLY MOIST, DARK BROWN. SILT AND CLAY (CL); SANDY TO VERY SANDY, VERY STIFF, SLIGHTLY MOIST, LIGHT REDDISH BROWN TO BROWN, OCCASIONAL SANDY CLAYEY SILT LAYERS. SAND (SM—SC); SILTY TO CLAYEY, MEDIUM DENSE, SLIGHTLY MOIST TO MOIST, GRAY BROWN TO BROWN. RELATIVELY UNDISTURBED DRIVE SAMPLE; 2—INCH I.D. CALIFORNIA LINER SAMPLE. 21/12 DRIVE SAMPLE BLOW COUNT. INDICATES THAT 21 BLOWS OF A 140—POUND HAMMER FALLING 30 INCHES WERE REQUIRED TO DRIVE THE CALIFORNIA SAMPLER 12 INCHES. 11_ TO WATER LEVEL AND NUMBER OF DAYS AFTER DRILLING MEASUREMENT WAS MADE. —► DEPTH AT WHICH BORING CAVED. NOTES 1. THE EXPLORATORY BORINGS WERE DRILLED ON JULY 18, 2016 WITH A 4—INCH DIAMETER CONTINUOUS FLIGHT POWER AUGER. 2. THE LOCATIONS OF THE EXPLORATORY BORINGS WERE MEASURED APPROXIMATELY BY PACING FROM FEATURES SHOWN ON THE SITE PLAN PROVIDED. 3. THE ELEVATIONS OF THE EXPLORATORY BORINGS WERE MEASURED BY HAND LEVEL AND REFER TO BORING 1 AS ELEVATION = 100'. 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 THE TRANSITIONS MAY BE GRADUAL. 6. GROUNDWATER LEVELS SHOWN ON THE LOGS WERE MEASURED AT THE TIME AND UNDER CONDITIONS INDICATED. FLUCTUATIONS IN THE WATER LEVEL MAY OCCUR WITH TIME. 7. LABORATORY TEST RESULTS: WC = WATER CONTENT (x) (ASTM D 2216); DD = DRY DENSITY (pcf) (ASTM D 2216); —200= PERCENTAGE PASSING NO. 200 SIEVE (ASTM 0 1140). 16-7-222 H - P 4 KU MAR LEGEND AND NOTES Fig. 3 CONSOLIDATION - SWELL CONSOLIDATION - SWELL 2 0 —1 —2 SAMPLE OF: Silty Cloy FROM: Boring 1 0 2.5' WC = 5.4 %, 0D = 105 pcf NO MOVEMENT UPON WETTING 1.0 APPLIED PRESSURE — KSF 10 I00 SAMPLE OF: Sandy Sflty Clay FROM: Boring 1 Q 10' WC = 5.1 %, DD = 118 pcf non. tis nowt. copy .rdr to n+. concis. UMW. 7n. t.tINQ typal .nal not a '.produced, s.cept b k .without Oho tonne, .pprowl of korner end A.nmlatp. Me. S..d Comopdellan conal N xmrdonc..M a 9-..7a1. EXPANSION UNDER CONSTANT PRESSURE UPON WETTING 1.0 APPLIED PRESSURE — KSF 10 100 16-7-222 KUMAR SWELL -CONSOLIDATION TEST RESULTS Fig. 4 CONSOLIDATION CONSOLIDATION - SWELL 1 0 — 1 — 2 — 3 SAMPLE OF: Sandy Clayey Silt FROM: Boring 2 0 5' WC = 5.6 %, DD = 101 pcf EXPANSION UNDER CONSTANT PRESSURE UPON WETTING 1.0 APPLIED PRESSURE - KSF 10 100 SAMPLE OF: Sandy Clayey Silt FROM: Boring 2 0 15' WC = 4.8 %.DD=114 pcf three bit melba eepb ebb Is the .poet.. t..ted. Sb. betel nowt Met net be l.peseee.e. beept .s fA, .tesp,t leo bitten eppwst d Kerner eM bQJstw. k. Sane CeeM/Wetpe t..Vep pwfpmW etesreblee .nu 4SIM G-4 1I. EXPANSION UNDER CONSTANT PRESSURE UPON WETTING 1.0 APPLIED PRESSURE - KSF 10 100 16-7-222 H -P= KUMAR SWELL—CONSOLIDATION TEST RESULTS Fig. 5 Job No. 16-7-222 SOIL OR BEDROCK TYPE Sandy Clayey Silt Slightly Sandy Silty Clay Sandy Silty Clay Sandy Clayey Silt Sandy Clayey Silt Sandy Clayey Silt Silty Sand UNCONFINED COMPRESSIVE STRENGTH (PSF) RG LIMITS PLASTIC INDEX (%) ATTERBEI o1_ J PASSING NO. 200 SIEVE 88 0, 37 GRADATION 0 Q co GRAVEL (%) NATURAL DRY DENSITY (Pcf? O .-r n oo - Q ,-r 0 ,--� 114 N .-. NATURAL MOISTURE CONTENT (%) d 00 .-- ,D V'1 00 N LOCATION 1 DEPTH (ft) 10 20 SAMPLE BORING .-r N H-P�KUMAR Geotechnical Engineering 1 Engineering Geology Materials Testing 1 Environmental 5020 County Road 154 Glenwood Springs, CO 81601 Phone: (970) 945-7988 Fax: (970) 945-8454 Email: hpkglenwood@kumarusa.com September 15, 2016 Lucas Bethell 143 South Bill Creek Road Carbondale, Colorado 81623 73hotrod@gmail.com Office Locations: Parker, Glenwood Springs, and Silverthome, Colorado Job No. 16-7-222 Subject: Addendum to Previous Subsoil Study, Lot 7 Sun Meadow Estates, North Meadow Drive, Garfield County, Colorado Dear Mr. Bethell: As requested, H -P Kumar is providing this addendum to our previous report and the recommendations for the foundation design contained in this letter should be considered as part of our previous report. We previously conducted a subsoil study for design of foundations at the site and presented our findings in a report dated July 29, 2016, Job No. 16-7-222. The second half of the fourth sentence in subsection 1 of the Foundations portion of the Design Recommendations section of our previous report, "but could be 2 to 3 inches for wetting down to 20 feet" should be removed and replaced with the following so that the rest of the paragraph reads: "The amount of settlement would be related to the depth and extent of wetting. Care should be taken to avoid subsurface wetting by following the recommendations contained in the Surface Drainage section of this report. In the event of subsurface wetting, some settlement should be expected. This settlement could be partly mitigated to on the order of 1 inch of additional settlement by removing 3 feet of the existing soil below footing grade and extending out at least 2 feet beyond the footing edges. Design footing grade should then be re-established with structural fill consisting of the excavated material moistened and compacted to at least 98% of the standard Proctor density at a moisture content near optimum. The risk of settlement due to subsurface wetting could also be lowered by installing a deep foundation such as micropiles to depths greater than 50 feet." If you have any questions or need further assistance, please call our office. Sincerely, H -P= KU MAR Daniel E. Hardin, P.E.'' . 24443 z; 4 Rev. by: SLP '; • 4 /G ``r` : {SiONAL EN �=r DEH/ksw {'-.: -- cc: Westar. Inc. — Stephen Kesler westar@rof.net Jeff Johnson (jjarch@rof.net)