The URL can be used to link to this page

Home My WebLink AboutSubsoil Studyrc ii,çifi'ffnfüfnnÍå*'" An Employcc Owncd Compony 5020 County Road 154 Glenwood Springs, CO 81601 phone: (970)945-7988 fax: (970) 945-8454 email: kaglenwood@kumarusa.com wwwkumarusa.com Ofüce Locations: Denver (HQ), Parker, Colorado Springs, Fort Collins, Glenwood Springs, and Summit County, Colorado SUBSOIL STUDY FOR FOUNDATION DESIGN PROPOSED RESIDENCE LOT 266,IRONBRTDGE RIVER VISTA GARFTELD COUNTY, COLORADO PROJECT NO. 20-7-789 JANUARY 29,2021 PREPARED FOR: scrB, LLc ATTN: LUKE GOSDA 0115 BOOMERANG ROAD, SUITE 52018 ASPEN, COLORADO 81611 TABLE OF CONTENTS PURPOSE AND SCOPE OF STUDY .... BACKGROUND INFORMATION ....... LIMITATIONS FIGURE 1 - LOCATION OF EXPLORATORY BORING FIGURE 2 - LOG OF EXPLORATORY BORING FIGURE 3 - SÏI/ELL-CONSOLIDATION TEST RESULTS FIGURE 4 _ GRADATION TEST RESULTS TABLE 1- SUMMARY OF LABORATORY TEST RESULTS -1 1- PROPOSED CONSTRUCTION ......- 1 - SUBSURFACE CONDITIONS .......- 3 - SITE CONDITIONS 1 SUBSIDENCE POTENTIAL a FIELD EXPLORATION 'l FOUNDATION BEARING CONDITIONS ..-J- DESIGN RECOMMENDATIONS .....- 4 - FOUNDATIONS FOUNDATION AND RETAINING WALLS NONSTRUCTURAL FLOOR SLAB S UNDERDRAIN SYSTEM ............. SITE GRADING.......... SURFACE DRAINAGE............... 4- 5- 6- 7- 7- 8- -8- Kumar & Associates, lnc. o Project No.20.7.789 PURPOSE AND SCOPE OF STUDY This report presents the results ofa subsoil study for a proposed residence to be located on Lot266,Ironbridge, River Vista, Garfield County, Colorado. The project site is shown on Figure 1. The pu{pose 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 SCIB, LLC dated December 3I,2020. An exploratory boring was drilled 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. BACKGROUND INFORMATION The proposed residence is located in the existing Ironbridge development. Hepworth-Pawlak Geotechnical, Inc. (now Kumar & Associates) previously conducted subsurface exploration and geotechnical evaluation for the development of Villas North and Villas South parcels, Job No. 105 115-6, report dated September 14,2005, and performed observation and testing services during the infrastructure construction, Job No. 106 0367, between April 2006 and April 2007 . The information provided in these previous reports has been considered in the current study of Lot266. PROPOSED CONSTRUCTION At the time of our study, design plans for the residence had not been developed. The residence will likely be a ONE OR two-story, wood-frame structure with structural slab foundation and no basement or crawlspace. Grading for the structure is assumed to be relatively minor with cut depths between about I to 3 feet. We assume relatively light foundation loadings, typical of the proposed type of construction. Kumar & Associates, lnc, o Project No.20-7-789 n 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 subject site was vacant at the time of our field exploration. The lot is located in the Villas South Parcel. The natural terrain prior to development in 2006 sloped down to the east at about 5o/o grade. The subdivision area was elevated by filling on the order of 6 feet above the original ground surface to create a relatively flat building site off River Vista. Vegetation consists of grass and weeds with scattered sage brush. A relatively tall,2-tiered modular block wall is located immediately west of the lot. We understand that recurring seepage from the bottom of the wall flows east into adjacent Lot267 then onto Lot266. SUBSIDE,NCD POTDNTIAL Eagle Valley Evaporite underlies the project area which is known to be associated with sinkholes andlocalized ground subsidence in the Roaring Fork Valley. A sinkhole opened in the cart storage parking lot located east of the Pro Shop and north of the Villas South parcel in January 2005. Irregular surface features were not observed in the Villas South parcel that could indicate an unusual risk of future ground subsidence andlocalized variable depths of the debris fan soils were generally not encountered by the previous September 14,2005 geotechnical study. The current subsurface exploration performed in the area of the proposed residence on Lot 266 did not encounter voids. In our opinion, the risk of future ground subsidence on Lot 266 throughout the service life of the proposed resiúence is low and similar [u ul.her areas of the Roaring Fork Valley where there have not been indications of ground subsidence. FIELD EXPLORATION The field exploration for the project was conducted on January 11,2021. One exploratory boring was drilled at the location shown on Figure 1 to evaluate the subsurface corrditions. The boring was advanced with 4 inch diameter continuous flight augers powered by a truck-mounted CME-458 drill rig. The boring was logged by a representative of Kumar & Associates, Inc. Samples of the subsoils were taken with ITs 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 Kumar & Associates, Inc. o Project No.20-7-789 -J- 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 Log of Exploratory Boring, Figure 2. The samples were returned to our laboratory for review by the project engineer and testing. SUBSURFACE CONDITIONS A graphic log of the subsurface conditions encountered at the site is shown on Figure 2. The subsoils consist of about 1 foot of topsoil overlying compacted fill soils to 6 feet deep overlying medium dense/stiff, sand and silt soils (alluvial fan deposits) underlain by dense, sandy gravel with cobbles (river gravel alluvium) at a depth of about 26 feet to the maximum drilled depth of 31 feet. The fill materials were mainly placed in 2006 and consist of medium dense, mixed silt, sand and gravel. Laboratory testing performed on samples obtained from the boring included natural moisture content and density and gradation analyses. Results of swell-consolidation testing performed on relatively undisturbed drive samples of the sand and silt soils, presented on Figure 3, indicate low to moderate compressibility under conditions of loading and wetting. Results of a gradation analysis performed on small diameter drive samples (minus llz-inch fraction) of the coarse granular subsoils are shown on Figure 4. The laboratory testing is summarizedin Table 1. No free water was encountered in the boring at the time of drilling and the subsoils were slightly moist to moist. FOUNDATION BEARING CONDITIONS The upper 6 feet of soils encountered in the boring consist of fill placed mainly in 2006 as part of the subdivision development. This depth of fill is shallower than other nearby lots. A shallower depth of fill may result in an increased risk of foundation settlement due to the increased potential for the underlying soils to become wetted. The field penetration tests and laboratory tests performed for the study, and review of the field density tests performed during the fill construction indicate the structural fill was placed and compacted to the project specified minimum 95o/o of sfandard Proctor density. Alluvial fan soils which tend to collapse (settle Kumar & Associates, lnc. @ Project No,20-7-789 -4- under constant load) when wetted were encountered below the hll. The amount of settlement will depend on the thickness of the compressible soils due to potential collapse when wetted, and the future compression of the wetted soils following construction. Relatively deep structural fill also has some potential for long-term settlement but should be significantly less than the alluvial fan deposits. Proper grading, drainage and compaction as presented in the Surfoce Drainage section will help to keep the subsoils dry and reduce the settlement risks. A heavily reinforced structural slab or post-tensioned slab foundation designed for significant differential settlements is recommended for the building support. As an alternative, a deep foundation that extends down into the underlying dense, river gravel alluvium could be used to reduce the building settlement risk. Regardless of the selected foundation, the recurring water seepage from the base of the modular block retaining wall must be intercepted at the wall base and routed around Lot 266 in a solid pipe to suitable gravity outlet. A civil engineer should design the piping system detailed on Lot 266 drawings for future reference and maintenance if needed. DESIGN RECOMMENDATIONS FOUNDATIONS Considering the subsurface conditions encountered in the exploratory boring and the nature of the proposed construction, we recommend the building be founded with a heavily reinforced structural slab or post-tensioned slab foundation bearing on at least 6 feet of the existing compacted structural f,rll. If a deep foundation system is considered for building support, we should be contacted for additional recommendations. The design and construction criteria presented below should be observed for a heavily reinforced structural slab or post-tensioned slab foundation system. 1) A heavily reinforced structural slab or post-tensioned slab placed on compacted structural fill should be designed for an allowable bearing pressrrre of 1,500 psf. The post-tensioned slab placed on structural fill should be designed for a wcttcd distance of 10 feet or at least half of the slab width, whichever is greater. Settlement of the foundation is estimated to be about 1 inch based on the long- term compressibility of the fill. Adclitional differential settlement of about l%to 2Yz inches is estimatecl clepencling on the clepth ancl wefting of the unclerlying debris fan soils. Kumar & Associates, lnc. @ ProJect No.20.7.789 -5- 2)The thickened sections of the slab for support of concentrated loads should have a minimum width of 20 inches. The perimeter turn-down section of the slab 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. If a frost- protected foundation is used, the perimeter turn-down section should have at least 18 inches of soil cover. The foundation should be constructed in a "box-like" configuration rather than with irregular extensions which can settle differentially to the main building area. The foundation walls, where provided, should be heavily 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 lateral earth pressures as discussed in the "Foundation and Retaining'Walls" section of this report. The root zone and any loose or disturbed soils should be removed. Additional structural fill placed below the slab should be compacted to at least 98Yo of the maximum standard Proctor density within 2percentage points of the optimum moisture content. A representative of the geotechnical engineer should evaluate the compaction of the filI materials and observe all footing excavations prior to concrete placement to evaluate bearing conditions. 3) 4) FOUNDATION AND RETAINING WALLS Foundation walls and retaining structures (if any) which are laterally supported and can be expected to undergo only a slight amount of deflection should be designed for a lateral earth pressure computed on the basis of an equivalent fluid unit weight of at least 50 pcf for backfill consisting of the on-site soils. Cantilevered retaining structures which are separate from the residence and can be expected to deflect sufficiently to mobilize the full active earth pressure condition should be designed for a lateral earth pressure computed on the basis of an equivalent fluid unit weight of at least 40 pcf for backfill consisting of the on-site soils. 5) 6) Kumar & Associates, lnc. o Project No.20-7-789 -6- All foundation and rctaining structures should be designed fbr appropriate hydrostatic and surcharge pressures such as adjacent footings, traffic, construction materials and equipment. The pressures recommended above assume drained conditions behind the walls and a horizontal backfill surface. The buildup of water behind a wall or an upward sloping backfill surface will increase the lateral pressure imposed on a foundation wall or retaining structure. An underdrain should be providecl to prevent hyclrostatic pressure buildup behind walls. Backfill should be placed in uniform lifts and compacted to at least 90% of the maximum standard Proctor density at a moisture content near optimum. Backfill placed in pavement and walkway areas should be compacted to at least 95o/o of the maximum standard Proctor density. Care should be taken not to overcompact the backfill or use large equipment near the wall, since this could cause excessive lateral pressure on the wall. Some settlement of deep foundation wall backfill should be expected, even if the material is placed correctly, and could result in distress to facilities constnrcted on the backfill. The lateral resistance of foundation or retaining wall footings will be a combination of the sliding resistance of the footing on the foundation materials and passive earth pressure against the side of the footing. Resistance to sliding at the bottoms of the footings can be calculated based on a coeff,tcient of friction of 0.35. Passive pressure of compacted backfill against the sides of the footings can be calculated using an equivalent fluid unit weight of 325 pcf. The coefficient of friction and passive pressure values recommended above assume ultimate soil strength. Suitable factors of safety should be included in the design to limit the strain which will occur at the ultimate streugth, particulady in the case of passive resistanue. Fill plauuú against the sides of the footings to resist lateral loads should be compacted to at least 95o/o of the maximum standard Proctor density at a moisture content near optimum. NONSTRUCTURAL FLOOR SLAB S Compacted structural fìll can be used to support lightly loaded slab-on-grade construction separate from the building foundation. The frll soils and underlying natural soils can be courpressible when wetted attd can resulf. in some post-conslruction settlement. To reduce the effects of some differential movement, nonstructural floor slabs should be separated from buildings to allow unrestrained vertical movement. Floor slab control joints should be used to Kumar & Associates, lnc. @ Project No.20-7-789 -7 - 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 road base, should be placed beneath slabs as subgrade support. This material should consist of minus 2-inch aggregate with at least 50Yo retained on the No. 4 sieve and less than 12% 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 fill can consist of the on- site mainly granular soils devoid of vegetation, topsoil and oversized rock. UNDERDRAIN SYSTEM It is our understanding the finished floor elevation at the lowest level is at or above the surrounding grade. Therefore, a foundation drain system is not required. It has been our experience in the arcathat local perched groundwater can develop during times of healy precipitation or seasonal runoff. Frozen ground during spring runoff can create a perched condition. 'We recommend below-grade construction, such as retaining walls, be protected from wetting and hydrostatic pressure buildup by an underdrain and wall drain system. If the finished floor elevation of the proposed structure has 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. SITE GRADING Extensive grading was performed as part of the existing Villas South development. Additional placement and compaction of the debris fan soils could be needed to elevate the site to design grades and reduce the risk of excessive differential settlements and building distress. In addition, the water and sewer pipe joints should be mechanically restrained to reduce the risk ofjoint separation in the event of excessive differential settlement. Additional structural fill placed below foundation bearing level should be compacted to at least 98Yo of the maximum standard Proctor density within 2o/o of optimum moisture content. Prior to fill placement, the subgrade should be carefully prepared by removing any vegetation and organic soils and compacting to at Kumar & Associates, lnc. @ Project No, 20-7-789 -8- least 95% of the maximum standard Proctor density at near optimum moisture content. The fill should be benched into slopes that exceed 20o/o grade. Permanent unretained cut and fill slopes should be graded at?horizontal to I vertical or flatter and protected against erosion by revegetation or other means. This office should review site grading plans for the project prior to construction. SURFACE DRAINAGE Precautions to prevent wetting of the bearing soils, such as proper backfill construction, positive backhll slopes, restricting landscape irrigation and use of roof gutters, need to be taken to help limit settlement and building distress. The following drainage precautions should be observed during construction and maintained at all times after the residence has been completed: 1) Inundation of the building structural slab foundation excavations 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 nonstructural slab areas and to at least 90o/o 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 5 feet in unpaved areas and a minimum slope of 3 inches in the first 10 feet in paved areas. Graded swales should have a minimum slope of 3%. 4) Roof downspouts and drains should discharge at least 5 feet beyond the foundation and preferably into a subsurface solid drainpipe. 5) Landscaping which requires regular heavy inigation should be located at least 10 feet from foundation walls. Consideration should be given to use of xeriscape to recluce the potential for wetting of soils below the building causecl by irrigation. LIMITATIONS This study has been conducted in accorclance with generally acceptecl geotechnical engineering principles and practices in this area af this time. We make no warranty either express or implied. Kumar & Associates, lnc. o Project No.20-7-789 -9- The conclusions and recoÍlmendations submitted in this report are based upon the data obtained from the exploratory boring drilled at the location 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 friture. 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 boring 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 veri$r 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 frll by a representative of the geotechnical engineer. Respectfully Submitted, Kumar & Associates, Inc. J E.I. Reviewed by: Steven L. Pawlak, JHPlkac Kumar & Associates, lnc. @ Project No. 20'7-789 I 5970 W ttiO i¡Þ LlNE LO't 267 EX MODULAR SITE WALL 1 LAA 266 (to{(¡ $r* BORING Ia APPROXIMATE SCALE_FEET 20-7 -789 Kumar & Associates LOCATION OF EXPLORATORY BORING Fig. 1 Ê BORING 1 EL. 5972' L TJ TOPSO|L: SILTY CLAYEY SAND, GRAVELLY, R00TS AND ORGANICS, FIRM, MOIST, BROWN. 53/ 12 WC=6.4 DD=115 -200=65 1s/12 WC=3.3 DD=122 -200=37 FILL: MIXED GRAVEL, SAND AND SILT, CLAYEY, MEDIUM DENSE, SLIGHTLY MOIST, MIXED BROWN. 5 SAND AND SILT MOIST, BROWN, (SV-VT); MEDIUM DENSE/STIFF, SLIGHTLY SLIGHTLY CALCAREOUS. GRAVEL (GM-GP); SANDY T0 VERY SANDY, SILTY, COBBLES, VERY DENSE, SLIGHTLY MOIST, MIXED BROWN. ROUNDED ROCK. 10 11 /12 WC=1 1.0 DD= 1 03 ! i DRIVE SAMPLE, 2-INCH I,D. CALIFORNIA LINER SAMPLE. DRTVE SAMPLE, 1 3/8-|NCH t.D. SPLTT SPOoN STANDARD PENETRATION TEST. 15 11 /12 .'r." DRIVE SAMPLE BLOW COUNT. INDICATES THAT 53 BLOWS 0Frrl tL ^ 14o-pouNo HAMMER FALLTNG J0 TNcHES wERE REQUTRED TO DRIVE THE SAMPLER 12 INCHES.F t¡.I t¡J t! I-FfL L¡Jo NOTES 20 s/12 WC= 10.7 DD= 1 03 -200=75 1 THE EXPLORATORY BORING WAS DRILLED ON JANUARY 11, 2021 WITH A 4-INCH DIAMETER CONTINUOUS FLIGHT POWIR AUGER. 2. THE LOCATION OF THE EXPLORATORY BORING WAS MEASURED APPROXIMATELY BY PACING FROM FEATURTS SHOWN ON THE SITE PLAN PROVIDED. 25 14/12 3. THE ELEVATION OF THE EXPLORATORY BORING WAS OBTAINED BY INTERPOLATION BETWEEN CONTOURS ON THE SITE PLAN PROVIDED. 4, THE EXPLORATORY BORING LOCATION AND ELEVATION SHOULD BE CONSIDERID ACCURATE ONLY TO THE DEGREE IMPLIED BY THE METHOD USED. 30 58/ 12 WC='1 .9 +4=38 -200= 1 I 5. THE LINES BETWEEN MATTRIALS SHOWN ON THE EXPLORATORY BORING LOG REPRESENT THE APPROXIMATE BOUNDARIES BETWEEN MATERIAL TYPES AND THE TRANSITIONS MAY BE GRADUAL. 6 GROUNDWATER WAS NOT ENCOUNTERED IN THE BORING AT THE TIME OF DRILLING. 35 7. LABORATORY TEST RESULTS: WC = WATER C0NTENT (%) (ASTM D 2216); DD = DRY DENSTTY (pcf) (rSrU O ZZ1O); +4 = PERCENTAGE RETAINED ON NO.4 SIEVE (ISTU O OSI¡); -200 = PERCENTAGE PASSING N0. 200 SIEVE (ASTM D 1140); 20-7 -789 Kumar & Associates LOG OF EXPLORATORY BORING Fig. 2 I È 3 f SAMPLE 0F¡ Sond ond Sill FROM; Boring 1 @10' WC = 1 l.O %, DD = 103 pcf ii l I I i ADDIÏIONAL COMPRESSION UNDER CONSTANT PRESSURE DUE TO WETTING JJ UJ =a.t1 I zo l- ô =o anz.oo \oo\ J l¡¡ =tt1 I zo F. ôfo tt1z.o() 1 0 -1 -2 -3 -4 1 0 -1 -2 -5 t0 100 SAMPLE OF: Sondy Silt FROM:Boringl@20' WC = 1O.7 %, DD = 103 pcf -ZQO = 75 % I I I f, l l lr- I l l l l I : ,.!- I I l I I I I l l i i i l l I l I i ADDITIONAL COMPRESSION UNDER ÇONSTANT PRESSURE DUE TO WETTING 20-7 -789 Kumar & Associates SWELL-CONSOLIDATION TEST RESULTS Fig. 3 E 2 ø E roo 90 ao 70 ôo 50 40 30 20 lo o HYDROMETER ANALYSIS SIEVE ANALYSIS ÎI}¡E READINGS ¿¿a HRS 7 HRS ivtN It CLEAR SQUARE OPENINCS 1 o lo 20 50 ¿0 50 60 70 a0 90 100 ¡ þ, Ê E ,125 2.O 152 DIAMETER CLAY TO SILT COBBLES GRAVEL 38 % SAND LIQUID LIMIÏ SAMPLE OF: Sllty Sond ond Grovel 44% PLASTICITY INDEX SILT AND CLAY 18 % FROM:BorlnglO30' Thas! bsl rrsulls qpply only lo lh€ sqmplos whlch were lssled. The hsllng rcporl sholl nol b. rcproduced, €xc€pl ln full, wllhoul lho wrlll€nqpprqvql of Kumqr & Assoclqlos, lnc. Slcv! onqlysls l.sllng ls pcrformad ln oocordonco wlth ASTM 06913, ASTM D7928, ASTM C156 qnd,/or ASTM Dl1,10. SAND GRAVEL FINE MEDIUM COARSE FINE COARSE 20-7 -789 Kumar & Associates GRADATION TEST RESULTS Fig. 4 I(+'Tl(u¡mr & Associates, Inc. oGeotechnical and Materials Engineenand Environmental ScientistsTABLE 1SUMMARY OF LABORATORY TEST RESULTSNo.20-7-789I,IATURALMOISTURECON'ÍENTNATURALDRYDENSITYGRADATIONATTERBERG LIMITSUNCONFINEDCOMPRESSIVESTRENGTHBORINGDEPTHGRAVEL(%)SANDl"/"1PERCENTPASSING NO.200 slEvELIQUID LIMITPLASTICINDEXSOIL TYPE12,%6.411s65Sandy Gravelly Silt (Fill)J.J122a-JISiþ Cþey Sand andGravel1011.0103Sand and Silt20t0.710375Sandy Silt30r.9384418Silty Sand and Gravel