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Home My WebLink AboutSubsoil Study for Foundation Design 07.27.2023I( A Kumar & Associates1 Inc. s + Geotechnical and Materials Engineers and Env iron men1a l Sci entists An Employee Owned Company 5020 County Road 154 Glenwood Springs, CO 81601 phone: (970) 945-7988 fax: (970) 945-8454 email: kaglenwood@kumarusa.com www.kumarusa .com Office Locations: Denver (HQ), Paiker, Colorado Springs, Fort Collins, Glenwood Springs, and Summit Cmmty, Cdl~ o • f July 27, 2023 Watali.e Lgpe~ A~Cot.t-tl/"1.. .? ;-J . ¼ P.O. Qg:x: 946Ar G/Of? /Sv,'IJl/4-h/ C-/Mlt:; L,PLt.,E)I 11'/«-G;, Aspen, Colorado 8161::l natal iefeinberglopez@gmail .com Subject: Dear Natalie: Project No. 23-7-298 Subsoil Study for Foundation Design, Proposed Residence, Lot 67, Filing 9, Los Amigos Ranch, 3426 Elk Springs Drive, Garfield County, Colorado As requested, Kumar & Associates, Inc. performed 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 May 19, 2023. The data obtained and our recommendations based on the proposed construction and subsurface conditions encountered are presented in this report. Proposed Construction: Development plans for the lot were not available at the time of our study. The proposed residence will be located in the general area of the exploratory pits shown on Figure 1. Ground floor could be structural over crawlspace or slab-on-grade in living areas and slab-on-grade in the garage. Cut depths are expected to range between about 3 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 lot was vacant and undeveloped at the time of our field exploration. The ground surface slope was relatively uniform at about 5% down to the south with about 2 to 3 feet of elevation difference across the general building area. Vegetation consists of grasses, sage brush and juniper trees. 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 ½ foot of topsoil, consist of approximately 1 ½ feet of stiff, silty, sandy clay overlying dense basalt gravel, cobbles, and boulders in a sandy silt matrix. Results of swell-consolidation testing performed on a relatively undisturbed sample of silty, sandy clay, presented on Figure 3, indicate low compressibility under existing moisture conditions and light loading and moderate compressibility when wetted. ,· -2- Results of a gradation analysis performed on a sample of the silty, sandy gravel (minus 3-inch fraction) obtained from the site are presented on Figure 4. The laboratory test results are summarized in Table 1. Digging in the basalt cobbles and boulders was difficult and practical digging refusal was encountered at a depth of 4 feet in both exploratory pits. No free water was observed in the pits at the time of excavation and the soils were slightly moist. Foundation Recommendations: Considering the subsoil conditions encountered in the exploratory pits and the nature of the proposed construction, the upper clay soils should be removed and spread footings placed entirely on the undisturbed ncmmtl g1anular soil designed for an allowable soil bearing pressure of2,000 psf. The matrix soils tend to compress after wetting and there could be some post-construction foundation settlement. Footings should be a minimum width of 16 inches for continuous walls and 2 feet for columns. Loose and disturbed soils encountered at the foundation bearing level within the excavation should be removed and the footing bearing level extended down to the undisturbed natural granular soils. Exterior footings should be provided with adequate cover above their bearing elevations for frost protection. Placement of footings at least 36 inches below the exterior grade is typically used in this area. Continuous foundation walls should be 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 55 pcf for the on-site soil as backfill. Structural fill placed for foundation support should consist of relatively well graded granular material such as road base compacted to at least 98% of standard Proctor density at a near-optimum moisture content. Floor Slabs: The natural on-site soils, exclusive of topsoil, are suitable to support lightly loaded slab-on-grade construction with a risk of movement due to the upper clay soils. 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 should be placed beneath slabs on grade for support. This material should consist of minus 2-inch aggregate with less than 50% passing 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 95% 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; or imported granular material such as road base. Kumar & Associates, Inc. e Project No. 23-7-298 -3 - Underdrain System: Although free water was not encountered during our exploration, it has been our experience in the area 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, crawlspace and basement areas (if any), be protected from wetting and hydrostatic pressure buildup by an underdrain system. The drains should consist of 4-inch diameter rigid 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 1 foot below lowest adjacent finish grade and sloped at a minimum 1 % to a suitable gravity outlet. Free-draining granular material used in the underdrain system should contain less than 2% passing the No. 200 sieve, less than 50% passing the No. 4 sieve and have a maximum size of 2 inches. The drain gravel backfill should be at least 1 ½ feet deep and be covered by a filter fabric such as Mirafi 140N or 160N. Surface Drainage: 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 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 6 inches in the first 10 feet in unpaved areas and a minimum slope of 3 inches in the first 1 O 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 10 feet from the building. 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 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 Kumar & Associates, Inc. 41 Project No. 23-7-298 -4- 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 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 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. If you have any questions or if we may be of further assistance, please let us know. Respectfully Submitted, Kumar & Associates , Inc. ~I /\. v<,~ ~ 0 ~ Paul J. Graf, Staff Engineer ~~~ Reviewed by: Robert L. Duran, P .E RLD/kac Attachments Figure I ploratory Pits Figure 2 -Logs of Exploratory Pits Figure 3 -Swell-Consolidation Test Results Figure 4 -Gradation Test Results Table I -Summary of Laboratory Test Results Kumar & Associates, Inc. ® Project No. 23-7-298 ! I I £2 n~ --- ELK SPRINGS, FILING 9 LOS AMIGOS RANCH P. U. .0. LOT 59 LOT 68 -----50 0 50 100 APPROXIMATE SCALE-FEET ~!1 ne 23-7-298 Kumar & Associates LOCATION OF EXPLORATORY PITS Fig. 1 t~.__ _____________ ___._ ______________ ...._ __ __. f }.. i ~ ~ 1 f 1. !i ti~ I!! 0 I-w w i... I :I: I-c.. w C 5 PIT 1 PIT 2 EL. 100' EL. 98' WC=11.4 DD=98 J WC=7.9 +4=43 -200=17 LEGEND ~ TOPSOIL; SILT ANO CLAY, SLIGHTLY SANDY, FIRM, SLIGHTLY MOIST, DARK BROWN . n CLAY (CL); SILTY, SLIGHTLY SANDY, SLIGHTLY GRAVELLY, MEDIUM STIFF, SLIGHTLY MOIST, u DARK BROWN. ~ GRAVEL AND COBBLES (GM); VERY SANDY, SLIGHTLY SILTY, DENSE, SLIGHTLY MOIST, TAN . ~ BASALT FRAGMENTS. p HAND DRIVE SAMPLE. ~] DISTURBED BULK SAMPLE. f PRACTICAL DIGGING REFUSAL. NOTES 1. THE EXPLORATORY PITS WERE EXCAVATED WITH A BACKHOE ON JULY 19, 2023. 0 5 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 MEASURED BY HAND LEVEL AND REFER TO PIT 1 AS AN ASSUMED ELEVATION OF 100'. 4. THE EXPLORATORY PIT 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 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 422); -200= PERCENTAGE PASSING NO. 200 SIEVE (ASTM D 1140). I-w w i... I :I: I-c.. w C sJ t-------------------..-------------------...-----1 "..-iii 23-7-298 i"~ ,u _____ _._ ___________ .._ _________________ _._ ___ _. Kumar & Associates LOGS OF EXPLORATORY PITS Fig. 2 -0 ~ ...., ..J -1 ..J L,J 31:; 1/1 -2 z 0 ~ -3 :::::J 0 11'1 z 0 u -4 l ... i' fl~ .I 1.0 SAMPLE OF: SIity Sandy Clay FROM: Boring 2 0 1.5' WC = 1 1.4 %, DD = 98 pcf NO APPLIED PRESSURE -KSF MOVEMENT UPON WETTING 100 ~l---------------------------------1 if t1 23-7-298 Kumar & Associates SWELL-CONSOLIDATION TEST RESULTS Fig. 3 f~-------------------...... ------------------------- f ' I l i!! ~ ~ I ll HYDROMETER ANALYSIS SIEVE ANALYSIS TIME READINGS U.S. STAHOAIID !Eltlts Cl.EAR SOU.VU: OPSNINGS 80 IIO 2' HRS 7 HRS ··-··-.. u. ~ .. ,,. . . ;s r7•• I I ✓:___ . a••· J • ........ f~ MIM -MW ••~IM -N 11 N •• •10 .. • i I .. I -I 1 l -I -l I _/ --I -,-I I I ---I I -i ---! 1-L ' ---_r 1--· ··---------· --·-- 0 10 10 70 •i-I-I . ,-~- ----------,----l ----r 7 = ----,---1:: -----· ------r ---,-!----' .!O -------· ----------, -,--,, ---r - I f / -l ., I ~"' -I -l I -- 30 20 10 ---. --i/ ~-I .L, -I ---.r ! -- -/ i I -I . I -I ---~ -I .f----------I -,,. '---'--'---l--,___ I -==t: -,----.----I • i.:: -·; --1 I I - 70 IO tO -I I I I I I I I 11 .-I I I I 1 1 1 -I I I I 1111 r I I II I 11 t ll I I I I 11 II I I I ,_ 0 .00 1 .om .005 .OOI .01• .017 .0711 .150 .300 I ,IOO 1.11 1 2-R 4.75 .. , 11 311.1 76.2 10G 200 1U 127 ..us ~o OIAMETER OF' PARTICLES IN MILLIMETERS CLAY TO SILT SAND GRAVEL ---,-,N-E-----.---M-E_D_IU-M----,--jc_o_A_R_S_E--F'-IN_E_--.-_C_O_A_R_S_E--t COBBLES GRAVEL -43 " SAND 40 X SILT AND CLAY 17 " LIQUID LIMIT PLASTICITY INDEX SAMPLE OF: Slightly SIity Very Sandy Gravels FROM: Pit 1 0 4' 11 Thea• te.t ,-ulte apply only to the l sampla wh!Gh were ~ Th • £ t.t1119 report •hall not be reproduced, '!! -pt In ful ~ wllbout the wrltt.n !;, ';I apptoYGI af Kumar a Aaocfola, Inc. ij ~ SI..,. onalyel• -ng 11 performed In II~ acoorclan.,. with ASTM 099 fl, ASTW D782.8, 6' ASTM C136 and/or ASTW D11-4(). i~i-----~-------------------------4 !if 23-7-298 Kumar & Associates GRADATION TEST RESULTS Fig. 4 f~._ _______ ._ ________________ ... _______________________________ _ I( A Kumar & Associates, Inc.~ + Geotechnical and Materia ls Engineers and Environmental Scienti sts ~ -::: ~ SAMPLE LOCATION PIT DEPlli lftl 1 4 2 1½ NATURAL NATURAL MOISTURE DRY CONTENT DENSITY 1%1 (ocfl 7.9 11.4 98 TABLE 1 SUMMARY OF LABORATORY TEST RESULTS Project No. 23-7-298 GRADATION ATTERBERG LIMITS UNCONFINED GRAVEL SAND PERCENT PLASTIC COMPRESSIVE PASSING NO. LIQUID LIMIT INDEX STRENGTH SOIL TYPE (%) (%) 200SIEVE (%\ 1%1 (psft 43 40 17 Slightly Silty Very Sandy Gravels Silty Sandy Clay