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HomeMy WebLinkAboutSubsoils Report for Foundation DesignI (tA f,i'r*fi*:n#:;tifd-* An Employcc Owned Gompony 5020 County Road 154 Glenwood Springs, CO 81601 phone: (970)945-7988 fax: (970) 945-8454 email: kaglenwood@kurrarusa,com www.kumarusa.com OfIice Locations: Denver QIQ), Parker, Colorado Springs, Fort Collins, Glenwood Springs, and Summit County, Colorado November 18,2024 Peak 3 Sundance, LLC Attn: Bryant Ragan 310 Market Street Basalt, Colorado 81621 bryant@peak3aspen.com Project No.24-7-208.05 Subject: Subsoil Study for Foundation Design, Proposed Residence, Lot SD-5, Aspen Glen, Bald Eagle Wuy, Garfield County, Colorado Dear Bryant: As requested, Kumar & Associates, Inc. performed a subsoil study for design of foundations at the subject site. The study was conducted as supplemental to our agreement for geotechnical engineering services to Peak 3 Sundance LLC, dated March 13,2024. 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 be a two-story wood-frame structure with attached garage located on the site in the area of the pits shown on Figure 1 Ground floor wili be slab-on-grade for the garuge and structural over crawlspace for the living areas. Cut depths are expected to range between about 2 to 5 feet. Foundation loadings for this type of construction are assumed to be relatively light and typical of the proposed type of construction. If building 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: The subject site was vacant at the time of or field exploration. The ground surface was relatively flat and level. There was evidence of minor cut and fill overlot grading for subdivision development. Vegetation consists of grass. Subsurface Conditions: The subsurface conditions at the site were evaluated by excavating two exploratory pits at the approximate locations shown on Figure 1. The logs of the pits are presented on Figure 2. The subsoils encountered, below about I to lYz feet of topsoil, consist of sandy clay to between 4 and 4Yz feet deep where dense, silty gravel and cobbles was encountered to the maximum explored depth of 5 feet. Results of swell-consolidation testing performed on relatively undisturbed samples of sandy clay, presented on Figure 3, indicate moderate compressibility under existing low moisture conditions and light loading and a moderate to high collapse potential (settlement under constant load) when wetted. No free water was observed in the pits at the time of excavation and the soils were slightly moist. &atrel //b azt' $ Nrt s \s -2- d Foundation Recommcndations: 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 gravel soil, below the clay, designed for an allowable soil bearing pressure of 3,000 psf for support of the proposed residence. The gravel soils typically possess a low settlement potential and post-construction foundation settlement should be minor. Spead footings can be placed on the sandy clay soils with a risk of foundation settlement. Spread footings placed on the undisturbed natural sandy clay soil designed for an allowable soil bearing capacity of I ,000 psf for support of the proposed residence with a risk of settlement especially if the bearing soil become wet. Based on experience, we expect initial settlement of footings designed and constructed on sandy clay will be about %to I inch. Additional, post-construction, settlement could occur if the bearing soils become wet. The magnitude of additional settlement would depend on the depth and extent of wetting but could be on the order of % to one inch. The risk of additional settlement could be reduced by removing and replacing 3 feet of the onsite soils as compacted structural fill. Structural fill can consist of the onsite soil moisture conditioned to slightly above optimum moisture content and compacted to at least 98 percent of thc maximum standard Proctor density. Footings placed on granular soils should be a minimum width of 1 8 inches for continuous walls and 2 feet for columns. Continuous wall placed on the sandy clay or structural fill should be a minimum width of 24 inches. Loose disturbed soils and existing fill encountered at the foundation bearing level within the excavation should be removed and the footing bearing level extended down to the undisturbed natural soils. Exterior footings should be provided with adequate cover above their bearing elevations for frost protection. Placement of footings at least 36 inches belorv the exterior grade is typically used in this area. Continuous foundation walls 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 should be designed to resist a lateral earth pressure based on an equivalent fluid unit weight of at least 60 pcf for the on-site soil as backfill. 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 relatively well graded sand and gravel such as road base should be placed beneath slabs- on-grade to facilitate drainage. This material should consist of minus 2-inch aggregate with less than 50Yo passing the No. 4 sieve and less than l2o/o 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 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 and where clay soils are present that local perched groundwater Kumar & Associates, lnc. @ Project No. 24-7-208.05 -3- 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 deeper than about 4 feet, be protected from wetting and hydrostatic pressure buildup by an underdrain system. Crawlspace areas less that 4 feet deep and slab-on-grade foundation areas should not need an underdrain system. The drains should consist of rigid perforated PVC 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 I foot below lowest adjacent finish grade and sloped at a minimum/zYo to a suitable gravity outlet or sump and pump. Free-draining granular material used in the underdrain system should contain less than 2% passing the No. 200 sieve, less than 507o passing the No. 4 sieve and have a maximum size of 2 inches. The drain gravel backfill should be at least l% feet deep and covered with filter fabric such as Mirafi 140N or 160N. 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: Providing and maintaining proper surface drainage will be critical to the long-term, satisfactory perforrnance of the proposed residence. The following drainage precautions should be observed during construction and maintained at all times 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 covered with filter fabric and capped with about 2 feet of the on-site, finer graded soils to reduce surface water infiltration. 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 l0 feet in pavement and walkway areas. 4) Roof downspouts and drains should discharge well beyond the limits of all backfill. 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 pits excavated at the locations indicated on Figure I and to the depths shown on Figure 2,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 Kumar & Associates, lnc. @ Project No. 24-7-208.05 4 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 perfunned. If conditions encountered during construction appear different from those described in this report, we should be notified at once so 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 interprotations 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 ourrecommendations, and to verifu 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 shata 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. Respectfully Submitted, Kllmar & Assoeintes, I James H. Parsons, P Reviewed by: h Daniel E. Hardin, P.E. JHP/kac aitacirments Figure i - Location of Expioratory Pits Figure 2 - Logs of Exploratory Pits Figures 3 and 4 - Swell-Consolidation Test Results Table I - Summary of Laboratory Test Results ILh u 58069 t /ztt z Kumar & &sscciales, !ne. o Frniect Nn ?ll-?"9tl$ flli ct / {i" .sta .g @ & a.r.' P-1 e+'! \f LOT SD6 P-2 o !LOT SD4 sD3LOT fc # *** '.? =' 2502550 APPROXIN4ATI SCAt-E_ FI[T 24*7 *248.05 Kumar & Associates LOCATION OF IXPLORATORY PITS [ig. 1 I e PIT 1 PIT 2 0 0 FLilLI L'- I-F n.. Lrlo WC=9.0 DD=9 1 FLILI [L IIFo- trJo WC=6.5 DD=98 -200=9 1 WC=6.8 DD=93 5 5 LEGEND TOPSOIL, ORGANIC SANDY SILTY CLAY, SOFT, MOIST, DARK BROWN CLAY (CL); SANDY, SLIGHTLY CALCAREOUS, VERY STIFF, SLIGHTLY MOIST, RED BROWN. GRAVEL AND COBBLES (CU); SANDY, SILTY, CLAYEY, MEDIUM DENSE TO DENSE, SLIGHTLY MOIST, BROWN. F HAND DRIVEN LINER SAMPLE NOTES 1. THE EXPLORATORY PITS WERE EXCAVATED WITH A BACKHOE ON NOVEMBER 8, 2024. 2. THE LOCATIONS OF THE EXPLORATORY PITS WERE MEASURED APPROXIMATELY BY PACING FROM FEATURES SHOWN ON THE SITE PLAN PROVIDED. 3. THE ELEVATIONS OF THE EXPLORATORY PITS WERE NOT MEASURED AND THE LOGS OF THE EXPLORATORY PITS ARE PLOTTED TO DEPTH. 4. THE EXPLORATORY PIT LOCATIONS SHOULD BE CONSIDERED ACCURATE ONLY TO THE DEGREE IMPI-IED BY THE METHOD USED- 5. THE LINES BETWEEN MATERIALS SHOWN ON THE EXPLORATORY PIT LOGS REPRESENT THE APPROXIMATE BOUNDARIES BETWEEN MATERIAL TYPES AND THE TRANSITIONS MAY BE GRADUAL. 6. GROUNDWATER WAS NOT ENCOUNTERED IN THE PITS AT THE TIME OF EXCAVATION. PITS WERE BACKFILLED SUBSEQUENT TO SAMPLING. 7, LABORATORY TEST RESULTS: WC = WATER CONTENT ('6) (AsTM D ?,216); DD = DRY DENSITY (PCt) (ASTU D 2216); _2OO= PERCENTAGE PASSING NO. 2OO SIEVE (ASTM D 1140), 24-7 -208.5 Kumar & Associates LOGS OF EXPLORATORY PITS Fig. 2 E s* I SAMPLE OF: Slightly Sondy Cloy FROM: Pit 1 @ 1.5' WC = 9.0 %, DD = 91 pcf r.produdd,th. atu fr. ln oppFwl SKll lnrga. :i ii ADDITIONAL COMPRESSION UNDER CONSTANT PRESSURE DUE TO WETTING ' ''i '-' i _ ..1_ '__' I :::i t:i - : .-.i... --'--.-.-:.:] 2 d:q JJlrl =a I z.9F o Jo UIz.o() 0 2. -4 -6 -8 -10 -12 -14 1.0 100 24-7-208.05 Kumar & Associates SWELL-CONSOLIDATION TEST RESULTS Fig. 3 SAMPLE 0F: Slightly Sondy Cloy FROM:Pil 2@5.5' WC = 6.8 %, DD = 93 pcf of In not b elthout th bstd- tu ADDITIONAL COMPRESS1ON UNDER CONSTANT PRESSURE DUE TO WETTING ",' ': i! ii I ! '-'l J illr I I I ii i!l 10APPUED PRESSURE - 2 0 2 4 -6 -6 -10 -12 -14 N JJl*l =an I zotr o JoazoO 24-7-208.05 Kumar & Associates SWELL-CONSOLIDATION TEST RESULTS Fig. 4 l(t t*ffififfiffig'Y:d** TABLE 1 SUMMARY OF LABORATORYTEST RESULTS Project No. 24-7-208.05 z 1 PIT 3v, zvz 1% DEPTH {ft} 6.8 6.5 9.0 NATURAL MOISTURE CONTENT Iolol 93 98 9 I NATURAL DRY DENSIW {pcf) ATTERBERG LIMITS UNCONFINED COMPRESSIVE STRENGTH GRAVEL SAND PERCENT PASSING NO, 200 srEvE PLASTIC INDEXLIQUID LIMIT SOIL TYPE$t (%') Slightly Sandy Clay 9l Slightly Sandy Clay Slightly Sandy Clay