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Home My WebLink AboutSubsoil Study for Foundation Design 02.15.2022I (}rt ffç1fi'tr*fÉtrñ'"n3;, n " " An Employrc Owncd Compony 5020 County Road 154 Glenwood Springs, CO 81601 phone: (970)945-7988 fax: (970) 945-8454 email : kaglenwood@kumarusa.com wvvw. kttnrarttsa. colrl Office Locations: Denver (HQ), Parke¡ Colorado Springs, Fort Collins, Glenwood Springs, and Summit Count¡ Colorado SUBSOIL STUDY FOR FOUNDATION DESIGN T\ilO PROPOSED RESIDENCES LOT 3, RUIZ MINOR SUBDTVISION COUNTY ROAD 346, NEAR SILT GARFIELD COUNTY, COLORADO PROJECT NO. 21-7-855 FEBRUARY 15,2022 PREPARED FOR: JOSE GODINA P. O. BOX 41 BASALT, COLORADO 81621 vissionm.diana@gm ail.com TABLE OF CONTENTS PURPOSE AND SCOPE OF STUDY .... PROPOSED CONSTRUCTION ...... SITE CONDITIONS. FIELD EXPLORATION.. SUBSURFACE CONDITIONS FOUNDATION BEARING CONDITIONS ....... DESIGN RECOMMENDATIONS FOUNDATIONS FLOOR SLABS SURFACE DRAINAGE LIMITATIONS 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 1 1 1 1 -2- -J- a.-J .-J .-4 .-5 5 Kumar & Associates, lnc. @ Project No, 21-7-855 PURPOSE AND SCOPE OF STUDY This report presents the results of a subsoil study for two proposed residences to be located on Lot3, Ruiz Minor Subdivision, County Road 346, near Silt, Garfi County, Colorado. The project site is shown on Figure l 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 Jose Godina dated February 11,2022. 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 analyzedto 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. PROPOSAD CONSTRUCTION Development plans for the lot were conceptual at the time of our study. Two residences are proposed to be built on the lot. One residence is planned to be built generally near the Boring 1 location and the other near the Boring 3 location, see Figure 1. We understand the residences will probably be single-story wood frame structures with attached garages. Ground floors are likely to be structural over crawlspace in the living areas and slab-on-grade in the garages. Grading for the structures is expected to be relatively minor with cut depths between about 2 to 3 feet. We assume relatively light foundation loadings, typical of the proposed type of construction. When building locations, grading and loading information have been developed, we should be notified to re-evaluate the recommendations presented in this report. SITE CONDITIONS The lot was vacant and the ground surface appeared mostly natural at the time of our field exploration. The terrain is relatively flat and gently sloping down to the northwest. Elevation difference across the two building sites is estimated at about I to 10 feet, and about 2 to 3 feet Kumar & Associates, lnc. @ Project No. 21-7-855 a across the individual building sites. The Rising Sun inigation ditch is along the north border of the property and County Road 346 borders the south side of the lot as shown on Figure 1. Vegetation consists of grass and weeds. FIELD EXPLORATION The field exploration for the project was conducted on November 19,2021. Three exploratory borings were drilled at the locations shown on Figure 1 to evaluate the general subsurface conditions. The borings were field located by the client in the planned building areas. The borings were advanced with 4-inch diameter continuous flight auger powered by a truck- mounted CME-458 drill rig. The borings were logged by a representative of Kumar & Associates. Samples of the subsoils were taken with l%-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 encountered, below about I foot of topsoil, consisted of intermixed sand and silt that was typically clayey, loose to medium dense and stiff, and extended down to the depths drilled at Borings 1 and 3 of 21 feet. The sand and silt soils extended down to a depth of about 24Yz feet at Boring 2 where underlain by relatively dense, silty very sandy gravel and cobbles that extended down to the depth drilled of 26 feet. Laboratory testing performed on samples obtained from the borings included natural moisture content and density, and percent finer than sand grain size gradation analyses. Results of swell- consolidation testing performed on relatively undisturbed drive samples of the sand and silt soilsl, presented on Figures 4 and 5, indicate generally moderate compressibility under conditions of loading and wetting. One of the samples showed minor expansion potential when wetted under light loading which is probably an anomaly based on our experience in the area. The laboratory testing is summarizedin Table 1. Kumar & Associates, lnc. @ Project No. 21-7-855 -3- No groundwater was encountered in the borings at the time of drilling and the subsoils were slightly moist to occasionally moist. FOUNDATION BEARING CONDITIONS The upper fine-grained sand and silt soils possess a low bearing capacity and, in general, a moderate settlement potential, especially when wetted. Lightly loaded spread footings bearing on the natural soils can be used for foundation support with some risk of settlement, primarily if the bearing soils were to become wetted, and precautions should be taken to prevent wetting of the bearing soils. Some of the soils may exhibit a minor expansion potential when wetted and the subgrade soils should be fuither evaluated at the time of excavation for possible removal. A lower risk foundation system would be piles or piers bearing in the relatively incompressible coarse granular soils encountered below about 24%feet depth at the site. Provided below are recommendations for spread footings bearing on the natural soils. If recommendations for piles or piers are desired, we should be contacted. DESIGN RECOMMENDATIONS FOUNDATIONS Considering the subsurface conditions encountered in the exploratory borings and the nature of the proposed construction, we believe the buildings can be founded with spread footings bearing on the natural soils with some risk of settlement and building distress. 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 allowable Based on experience, we expect settlement of footings designed and constructed as discussed in this section will be about 1 inch or less. There could be some additional settlement if the bearing soils were to become wetted. The magnitude of the additional settlement would depend on the depth and extent of the wetting but may be on the order of I to l% inches. 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. of 1,500 Kumar & Associates, lnc. @ Project No. 2l-7-855 -4- s) Continuous foundation walls should be heavily reinforced top and bottom to span local anomalies and better withstand the effects of some differential settlement 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 55 pcf. All topsoil and any loose 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. 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 slab settlement if the subgrade were to 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 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'/o-inchbase course should be placed immediately beneath floor "slabs at grade" for support. This material should consist of minus 2-inch aggregate with at least 50%o retained on the No. 4 sieve and less than l2Yo passing the No. 200 sieve. All fill materials for support of floor slabs should be compacted to at least 95o/o of maximum standard Proctor density at a moisture content near optimum. Required frll can consist of the on- site soils devoid of vegetation, topsoil and oversized rocks. LTNDERDRAIN SYSTEM It is our understanding the proposed finished floor elevation at the lowest levels of the residences will be at or above the surrounding grade. Therefore, a foundation drain system is not required. It has been our experience in the areathat local perched groundwater can develop during times of heavy precipitation or seasonal runoff. Frozen ground during spring runoffcan also create a perched condition. We recommend below-grade construction, such as retaining walls and basement areas, be protected from wetting and hydrostatic pressure buildup by an underdrain and wall drain system. A areas (less than 4) 6) Kumar & Associates, lnc. @ founda Project No, 21-7-855 5 4 feet deep) should not be needed with adequate compaction of foundation backfill andpsitive surface drainage away from foundation walls. If the finished floor elevation of the proposed structures is revised to have a floor level below the surrounding grade, we should be contacted to provide recommendations for an underdrain system. All earth retaining structures should be properly drained. SURFACE DRAINAGE tive surface is an important aspect of the project to prevent wetting of the bearing soils. The following drainage precautions should be observed during construction and maintained at all times after the residences have 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 95o/o of the maximum standard Proctor density in pavement and slab areas and to at least 90%o of the maximum standard Proctor density in landscape areas. 3) The ground surface sunounding 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. 4) Roof downspouts and drains should discharge well beyond the limits of all backfill. 5) Landscaping which requires regular heavy irrigation, such as sod, and lawn sprinkler heads should be located at least 5 feet from foundation walls. LIMITATIONS This study has been conducted in accordance with generally accepted geotechnical engineering principles and practices in this area at this time. V/e 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 Kumar & Associates, lnc. o Project No.21,7-855 -6- 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. Vy'e 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 verifu that the recommendations have been appropriately interpreted. Significant design changes may require additional analysis or modifications to the rçcommendations 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 & Associates, lnc" VrûrtA"T. Pq+c+t2.- James H. Parsons, P.E Reviewed by: David A. Young, JHP/kac Kumar & Associates, lnc. !'Project No" 21"7-855 t_llJ-3tv3s llvnlxouddv o0z 00 r I Låffi-¡tç i9 h' ), tttL'tp1¡*rq¡nJ tn!¡,@rt¡{r ¡}4? I *¡arô *Å; #*t¡rç ry, 6 .F!*i d, ¿,1 F4{9tî ovou ^INnocÉr--rr¡nf --r L2 t fl,lã.E I a Fr¡úl .lü 8Íw lü ¿tt {'t'î g wl vrqt.d l9$1il d,r/ u&v$*{'/ _¿ l¡ 1¡z Lo1 .4't Y lat lft¡ ei¡ 1* ÊatÈ{r¡H¡xrqryrf¿.{,\ "/./ HCIlQ Nos '¡¿fftt u{ F.'{1 ""'rdl ! t4Í}{r!'ts¿Éf 0tü I tot 4 rû lüf¡tnf tEl iùll t{}n lstËt5¡Ësf !{ \F¡óof .it.et I CNtUOg o z cNtuog o r cNtuos o r úff,¡'tÄ tS &¡¡.H/, û,qt @rtn, úy t{ ç98- L- tZsolercossv 8 JeunyscNruo8 ^uolvuotdxl r0 N0t1v30rL '6r¡ I l I BORING EL. I 00 1 BORING 2 EL. 97.5' BORING 3 EL. 93' 0 0 16/12 13/ 12 WC=3.4 DD=94 -2OO=62 e/12 5 11/12 WC=3.5 DD= 1 00 -200=55 q e/12 WC=5.4 DD=96 11 /12 10 10s/ 12 WC= 1 3.1 DD=99 -200=8 1 12/ 12 WC=3.1 DD=99 11 /12 F- L¡J t¡J LL I-f-(L t¡Jo 15 15 F L¡J LJ I'L I-t-(L t¡Jô 7 /12 14/12 11/12 WC=3.4 DD=101 20 20s/12 1o/ 12 WC=4.9 DD= 1 01 -200=38 21/12 25 25 28/ 12 30 50 21 -7 -855 Kumar & Associates LOGS OF TXPLORATORY BORINGS Fig. 2 ¡ F ð I È F lJ I Þ I LEGEND TOPSOIL: SAND AND SILT, CLAYEY, ORGANICS, SOFT TO FIRM, MOIST, BROWN SAND AND SILT (SM-ML): INTERLAYERED SAND AND SILT, SLIGHTLY CLAYEY TO CLAYEY, LOOSE TO MEDIUM DENSE, STIFF TO VERY STIFF, SLIGHTLY MOIST, TAN. GRAVEL DENSE, (cu): SLIGH SANDY TO VERY SANDY, SLIGHTLY SILTY TO SILTY, MEDIUM TLY MOIST, TAN. ! i DRIVE SAMPLE, 2-INCH I.D. CALIFORNIA LINER SAMPLE DRrVE SAMPLE, 1 5/8-rNCH l.D. SPLIT SPOON STANDARD PENETRATTON TEST ic /1. DRIVE SAMPLE BLOW COUNT. INDICATES THAT 16 BLOWS OF A 140-POUND HAMMERt e/ t 1 FALLINc so tNcHES wERE REeUIRED To DRtvE THE SAMpLER 12 tNcHES. NOTES 1. THE EXPLORATORY BORINGS WERE DRILLED ON NOVEMBER 19,2021 WITH A 4_INCH-DIAMETER CONTINUOUS-FLIGHT POWER AUGER. 2. THE EXPLORATORY BORINGS WERE LOCATED BY THE CLIENT 3. THE ELEVATIONS OF THE EXPLORATORY BORINGS WERE MEASURED BY HAND LEVEL AND REFER TO BORING 1 AS A lOO' ASSUMED BENCHMARK _. 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 WAS NOT ENCOUNTERED IN THE BORINGS AT THE TIME OF DRILLING 7. LABORATORY TEST RESULTS: WC = WATER CONTENT (%) (ASTM D2216); DD = DRY DENSITY (PCT) (ASTV D2216); -2aO= PERCENTAGE PASSING NO. 200 SIEVE (ASTM D1 140) 21 -7 -855 Kumar & Associates LEGTND AND NOTES Fig. 3 ! s ¡ I ç n I .: SAMPLE 0F: Sond ond Silt FROM:Boringl@5' WC = 5.4 %, DD = 96 pcf ADDITIONAL COMPRESSION UNDER CONSTANT PRESSURE DUE TO WETTING 0 ñ -JJ l¡J =U) I zotr ô =oØzo() -1 -2 -3 -4 -5 -6 -7 1 't.0 APPLIED PRESSURE - KSF 10 100 21 -7 -855 Kumar & Associates SWELL-CONSOLIDATION TEST RTSULT Fig. 4 ç SAMPLE OF: Sond ond Silt FROM: Boring 2 @ 10' WC = 3.1 %, DD = 99 pcf EXPANSION UNDER CONSTANT PRESSURE UPON WETTING JJ UJ =tJ', I z.o F ô Jolnzo(J 1 0 -1 2 -3 I 1.0 APPLIED PRESSURE - KSF 10 100 1 JJ L!, =U) I zotr o =o U1z.oo 0 -1 2 3 -4 -5 1.0 APPLIED PRESSURE - KSF t0 100 SAMPLE OF: Sond ond Silt FROM: Boring 3 @ 15' WC = 3.4 %, DD = 101 pcf ond A$ociotæ, lnc. Sw.ll not b. r€produced, êxc€pt in without th. writt.n opprovol of NO MOVEMENT UPON WETTING 21 -7 -855 Kumar & Associates SWELL-CONSOLIDATION TTSÏ RTSULTS Fig. 5 l(t iiçiffii'ffffii*rÏiå*"' TABLE 1 SUMMARY OF LABORATORY TEST RESULTS No.2l-7-855 Sandy Clayey Silt Sandy Silt SOIL TYPE Very Silty Clayey Sand Very Sandy Clayey Silt Sandy Clayey Silt Sandy Silt Very Sandy Silt (ps0 UNCONFINED COMPRESSIVE STRENGIH ("/"1 PLASTIC INDEX AÏTERBERG LIMITS ("/"1 LIQUID LIMIT 1I 62 38 55 PERCENT PASSING NO 200 stEvE(/") SAND %t GRAVEL GRADATIOI.¡SAMPLE LOCATION DEPTHBORING NATURAL DRY DENSITY NATURAL MOISTURE CONTENT 96 99 94 99 I01 100 I01 5.4 1J1 3.4 1J 4.9 3.5 3.4 5 10 I-l 0I 20 5 51 2 J I