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Home My WebLink AboutSubsoils Report for Foundation DesignK+rf Hffififfi:ffinliivi** An Employcc Owncd ComPonY 5020 CountY Road I 54 Glenwood Springs, CO 81601 phone: (970) 945'1988 fax: (970) 945'8454 email: kaglenwood@kumarusa,com www.kumaEtsa.com Office Locafions: Dcnver (HQ), Parker, Colorado Springs, Fort Collins, Glenwood Springs, and Summit County'Colorado August 12,2024 Ed Baker P.O. Box 284 Parachute, Colorado 81635 bakeedburdicked@yahoo.com ProjectNo. 24-7424 Subject: Subsoil Study for Foundation Design, Proposed Residence, 7441 County Road 301, Garfield CountY, Colorado Ed: As requested, Kumar & Associates, Inc. perforrned a subsoil study for design of foundations at the subject site. The study was conducted in accordance with our agreement for geotechnical engineering services to you dated July 22,2024. 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 single-story modular structure above crawlspace and located generally as shown on Figure 1. Cut depths are expected to range between about 2 to 4 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 proposed residence site was vacant and vegetated with grass, weeds and sage brush. The ground surface has a strong slope down to the north with about 2 feet of elevation difference across the proposed building footprint. A pile of basalt boulders was observed to reportedly come from the excavation for existing bam. Subsurface Conditions: The subsurface conditions at the site were evaluated by excavating 2 exptoratory pits at the approximate locations shown on Figure 1. The logs of the pits are presented on Figure 2. The subsoils encountered, below abottt/'foot of topsoil, consist of about 2 to 3 feetof sandy silt and clay above calcareous sandy silt and gravel with basalt cobbles and boulders. Results of swell-consolidation tesfing performed on a relatively undisturbed sample of the upper silty sand, presented on Figure 4, indicate low compressibility under existing low moisfure cond-ition audigh1 loadrne aad a mqdqtale qqllapqe pole4lia! ( ettlgment un{er cgnstant load) when wetted. Results of a gradation analysis performed on a sample of silty sand and gravel (minus S-inch fraction) obtained from the site are presented on Figure 5. No free water was observed in the pits at the time of excavation and the soils were slightly moist. a Q S)\\ .\ ad a 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 calcareous silty sand and gravel soil designed for an allowable soil bearing pressure of psf for support of the proposed residence. The matrix soils tend to compress after wetting and there some foundation settlement. Footings should be a minfua116 width of 20 inches for continuous walls and2 feet for columns. The topsoil and loose disturbed soils within the foundation excavation should be removed down to the natural calcareous soils and the exposed soils moistened and compacted. We should observe the completed foundation excavation for bearing conditions. Exterior footings should be provided with adequate cover above their bearing elevations for frost protection. Placement of footings at leastJ6 iqches below the exterior grade is fypically 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 12 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 50 pcf for the on-site soil as backfill, excluding organics and rock larger than 6 inches. f,'Ioor Slabs: The onsite natural soils, exclusive of topsoil, are suitable to support lightly loaded slab-on-grade constnrcfion. 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 minimrtm 4-inch layer of relatively well graded sand and gravel (road base) should be placed beneath slabs for support. This material should consist of minus 2-rnch aggregate with less than 50% passing the No. 4 sieve and less thanI2%o passing the No. 200 sieve. Al1 fill materials for support of floor slabs should be compacted to at least95Yo of maximum standard Proctor density at a moisfure content near optimum. Required fill can consist of the onsite sandy soils devoid of vegetation, topsoil and oversized rock. Underdrain System: It is our understanding the proposed finished floor elevation at the lowest level is at or above the surrounding grade and the crawlspace is relatively shallow. 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 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. The shallow crawlspace should not need to be protected with an underdrain with proper foundation wall backfill and surface grading. Kumar & Associates, lnc. o Proiect No. 24.7424 -3 - If the finished floor elevation of the proposed structure 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 struchrres should be properly drained. Surface Drainage: The following drainage precautions should be observed during construction and maintained at all times after the residence has been completed: 1) Inundation ofthe foundation excavations andunderslab areas shouldbe avoided during constmction. 2) Exterior backfill should be adjusted to near optimum moisture and compacted to at least 95%o of themaximum 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 12 inches in the fust 10 feet in unpaved areas and 4 minimum slope of 3 inches in the fnst 10 feet in pavement and walkway areas' 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 l0 feet from the building. Consideration shouldbe given to the use of xeriscape to limit potential wetting of soils below the foundation 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 warranfy 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 1 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 fmdings 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 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 interpretations by others of our information. As the project evolves, we shoul&provide oontinued eonsultation and f,eld services during-construet-io! to revlalc md monitor the implementation of our recommendations, and to veriff that the recommendations have been appropriately interpreted. Significant design changes may require additional analysis Kumar & Associates, lnc' o ProjectNo. 2&7424 -4- 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. Respectfu lly Submitted, Kumar & Associates, Steven L. Pawlak, P Reviewedby: Daniel E. Hardin, P.E. SLP/kac Attachments: Figure I * Location of Exploratory Pits Figure 2 -Logs of Exploratory Pits Figure 3 - Legend and Notes Figure 4 - Swell-Consolidation Test Results Figure 5 - Gradation Test Results Table 1 - Summary of Laboratory Test Results a 1na2 Kumar & Associates, lnc. @ Profect No. 24-7-424 PP-2 o z. =ocl LI(LoJln PP.1r I I I 60' 40 l_ Plr I J 5 30 PIT 2 _t @ POWERI 5 -=-] 50'70 10' BARN PROPOSED RESIDENCE NOT TO SCALE Fig. 1LOCATION OF EXPLORATORY PITSKumar & Associates24-7-424 LEGEND N TOPSOIL ORGANIC SANDY SILT AND CLAY' DRY, BROWN. CLAY (CL); SILTY, SANDY, VERY STIFF, SLIGHTLY MOIST, BRoWN' RooT HoLES' SAND AND SIL CALCAREOUS, T (SM-ML); SLIGHTLY CLAYEY, STIFF, SLIGHTLY MOIST' LIGHT BROWN' SLIGHTLY ORGANIC. GRAVEL AND SILT (CU-V[-); SANDY, BASALT COBBLES & BOULDERS, DENSE' SLIGHTLY MOIST, WHITE AND GRAY, CALCAREOUS. HAND DRIVEN 2-INCH DIAMETER LINER SAMPLE. DISTURBED BULK SAMPLE. PRACTICAL REFUSAL TO THE EXCAVATION NOTES 1. THE EXPLORATORY PITS WERE EXCAVATED WITH A BACKHOE ON AUGUST 1, 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 IMPLIED 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 (%) (ASTM D 2216); DD = DRY DENSITY (pcf) (ASTM D 2216); +4 = PERCENTAGE RETAiNED ON NO. 4 SIEVE (ASTM D A22): -2oo= PERCENTAGE PASSING NO. 2OO SIEVE (ASTM D 1140)' F Ii t Fig. 3LEGEND AND NOTESKumar & Associates24-7-424 I 2 td 90 ao 70 60 50 4 m 20 to o o lo 20 s 4 s s 70 & 90 t@ .@ OF CLAY TO SILT COBBLES GRAVEL 35 X UQUID LIMIT SAND 11 % PLASTICITY INDEX SILT AND CLAY 21 % SAMPLE OF: Cclcoreous Silty Sond ond Grqvel FROM:Pll1O5'-6' HYDROUETER ANALYSIS IYE 7H6 SIEVE ANALYSIS OPENNOSu.5. / / I I I I I I j I I I I I I I I I GRAVELSAND FINE COARSEMEOTUM lCOrnseFINE Fig. 5GRADATION TEST RESULTSKumar & Associates24-7-424 l(+Amfimm*liil-"' -= TABLE 1 SUMMARY OF LABORATORY TEST RESULTS Project No, 24-7-424 1 SAMPLE LOCATION NATURAL MOISTURE CONTENT NATUR.AL DRY DENSITY GRADATION ATTERBERG PIT DEPTH GRAVEL %t SAND (/"1 PERCENT PASSING NO, 200 slEvE LIQUID LIMIT PLASTIC INDEX 5-6 J 1% 10.3 8.2 64 84 35 4 I .A 34 UNCONFINED COMPRESSIVE STRENGTH lnsf) Calcareous Silty Sand and Gravel Calcareous Silty Sand Calcareous Silty Clayey Sand SOIL TYPE SAMPLE OF: Colcoreous Silty Sond FROM:Pit1O3' WC = 10.3 %, DD = 64 pcf ffi ADDITIONAL COMPRESSION UNDER CONSTANT PRESSURE DUE TO WETTING 2 0 2 -4 6 _B -10 -12 JJld =tn I z.o F (f, fo UIz.oo - KSF t0t.0 Fig. 4Kumar & Associates SWELL-CONSOLIDATION TEST RESULTS24-7-424 PIT 1 PIT 2 0 0 WC=8.2 DD=84 -2AO=34 F TJ LrJ L II F L trlo WC=10.3 DD=64 FLJ trJtL I-F(L lrlo 5 I ++=ss - -2OO=24 5 10 10 2;:7../: Fi1. 2LOGS OF EXPLORATORY PITSKumar & Associates24-7-424