The URL can be used to link to this page

Home My WebLink AboutSubsoil StudyI(+rtimffi:ifmifú*" Ân Emptoycc Owrud Conrpony 5020 County Road 154 Glenq,ood Springs, CO 81601 phone: (970) 945-7988 fax (97û) 945-8454 email ka glenrvood@kurnanmacom wwwkumarusa.com Office l-ocalions: IDanner (HQ), Padrer, Colorado Springg Fo¡t Ct¡lins, Glenrvood Springs, âtrd Sl¡Irm*t Cot¡ttty, Cnlmado April29,2021 Alius Design Group Attn: Michael Edinger 108 Diamond A Ranch Road Carbondale, Colorado 87 623 michaelØaliusdc.com Project No.2l-7-267 Subject: Subsoil Study for Foundation Design, Proposed Residence, Lot H6, The Homestead, Aspen Glen Subdivision, 17 Spire Ridge, Garfield County, Colorado Dear Michael: 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 Alius Design Group dated March 15,2A21. The data obtained and our recommendations based on the proposed construction and subsurface conditions encountered are presented in this report. Proposed Construction: Plans for the proposed construction were not available at the time of our study. The proposed residence is assumed to be a one- or two-story wood-frame structure over crawlspace or basement with attached garage located on the site in the area of the pits shown on Figure 1. Ground floors will likely be slab-on-grade or structural over crawlspace. Cut depths are expected to range between about 2 to 8 feet. Foundation loadings 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 our field exploration. The ground surface was relatively flat with scattered cobbles and small boulders exposed at the surface. Vegetation consists of grass and weeds. Subsidence Potential: Bcdrock of the Pennqylvanian age Fagle Valley Evaporite underlies the Aspen Glen Subdivision. These rocks are a sequence of gypsiferous shale, fine-grained sandstone and siltstone with some massive beds of gypsum and limestone. There is a possibility ., that rnassive gypsmil deposits associatetl wth the Eagle Valley Evaporite untlerlie purtions of the lot. Dissolution of the rypsum under certain conditions can cause sinkholes to develop arìd can produce areas of localized subsidence. During previous work in the area, several sinkholes were observed scattered throughout the Aspen Glen Subdivision. These sinkholes appear similar to others associated with the Eagle Valley Evaporite in areas of the lower Roaring Fork River Valley The nearest mapped sinkhole is 900 feet to the southeast of this lot. Sinkholes were not observed in the immediate area of the subject lot. No evidence of cavities was encountered in the subsurface materials; however, the exploratory pits were relatively shallow, for foundation design only. Based on our present knowledge of the site, it cannot be said for certain that sinkholes will not develop. In our opinion, the risk of grourd subsidence at Lot H6 is low and similar to other lots in the area but the owner should be aware of the potential for sinkhole development. Subsudace Conditions: The subsurface conditions at the site were evaluated by excavating two exploratory pits at the approximate locations shovvn on Figure L The logs of the pits are presented on Figure 2. The subsoils encountered, below about Yz to 1. foot of topsoil, consist of stiff, sandy clay soils with gravel layers tlowrr to 3YzL<:4 feet deep where clettse, silty sandy gravel with cobbles w¿Ìs encountered dor¡'n to the maximum explored depth of 6Yz feet. Results of a gradation analysis performed on a sample of clayey gravel (minus 3-inch fraction) obtained from the site are presented on Figure 3. No free water was observed in the pits at the time of excavation and the soils were slightly moist. tr'oundation Recommendations: Considering the subsoil conditions encountered in the exploratory pits and the nature of the oroposed construction, we recommend removing the clav soils and placing spread footings on the undisturbednatural granular soil for support ofthe proposed residence. Spread footings placed on the undisturbed natural granular soils can be designed for an allowable soil bearing pressure of 2,500 psf. The soils tend to compress after wetting and there could be some post-construction foundation settlement. Footings should be a minimum width of 16 inohes for continuous walls and 2 feet for oolumns. The clay soils, any loose disturbed soils and existing fill encountered at the foundation bearing level within the excavation should be removed and the f'ooting bearing level extended dor¡vn to the relatively dense natural granular soils. Exterior footings should be provided with adequate cover above Kumr & Associafes, Inc. e Project No. 21-7-26f -3 - 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 l0 feet. Foundation walls acting as retaining structures should be designed to resist alateral earth pressure based on an equivalent fluid unit weight of at least 50 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 -inch layer of free-draining gravel should be placed beneath basement level slabs to facilitate drainage. This material should consist of minus Z-inch aggregate with less than 50o/o passing the No. 4 sieve and less than 2Yopassingthe No. 200 sieve. All fill materials for support of floor slabs should be compacted to at least 95Yo 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 areathat local perched groundwater can develop during times of heary precipitation or seasonal runoff. Frozen ground during spring runoffcan create aperched condition. We recommend below-grade construction, such as retaining walls and crawlspace areas, be protected from wetting and hydrostatic pressure buildup by an underdrain system. The drains should consist of 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 andat least I footbelowlowest adjacent finish grade and sloped at aminimumlYoto a suitable gravity outlet or drywell or sump and pump. Free-draining granular material used in the underdrain system should contain less than 2Yopassingthe No. 200 sieve,less than 50% passing the No. 4 sieve and have a maximum size of 2 inches. The drain gravel backfrll should be at least IYzfeet deep. Kumar &Asssciates, lnc. 3 Pnoiect No. 21-7-267 -4- Surface Drainage: The following clrainage precantions shor¡lcl be observed drtring 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 optimun 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 are¿N. Free-draining wall backfill should be covered with filter fabric and capped with about2 feet of the on-site, finer gaded 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 l0 feet in pavement and walkway areas. 4) Roof downspouts and drains should discharge well beyond the limits of all backfill Limitations: This shrcly has heen conclucted in accordance with generally accepted geotechnical engineering principles and practices in this arca 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 arid to the depths shown on Figure 2, thc proposcd typc of construction, end 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 concemed about MOBC then a nrofessional in this snecial field- of nractiee shoulcl be eonsulted. Our-r--'--_ - r-----__ findings include interpolation and exhapolation 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 appeil 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 exclusivc 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 Kumar & Associ¿les, l¡¡c. 3 Project No. 2'l-7-267 -5- monitor the implementation of our recommendations, and to verify that the recommendations have been appropriately interpreted. Signifrcant 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 & Åssociates. James H. Parsons, P Reviewed by: Daniel E. Hardin, P.E. JHP/kac attachments Figure 1 - Location of Exploratory Pits Figure 2 * Logs of Exploratory Pits Figure 3 - Gradation Test Results Kumar & Associates, lnc.'1r Project No, 21-l-267 a Å*r F. e,oÉ \lN'{f Jk 'çr*É ti'. lFr úluó 0ts '+ j- 1 o Ptl 2 z 7ê LOT H-6 .¡a- ¡f.;tt -' I a PIT I .{f t iê '-'*'.4, "t' ¿F #"a f fffe- *-t l.* ¡Ê t! 0 APPROXIMAI E SCALE-I'EET Fig. 121 -7 -267 Kumar & Associates LOCATION OF EXPLORATORY PITS : I PIT 1 PIT 2 0 0 Fl¡ll¡lt! IIFo- UJo 5 5 F t¡J L¡Jt! IIF-o- LJôl+4=63 200=6 10 10 LEGEND TOPSOIL; cLAY, SANDY, RooTS AND ORGANICS, SCATTERED C0BBLES, MEDIUM DENSE, SLIGHTLY MOIST, BROWN. CLAY (CL); SANDY TO VERY SANDY, STIFF, SLIGHTLY MolST, BROWN cRAVEL (GC); SANDY, CLAYEY, COBBLES, DENSE, SLIGHTLY MOIST, BROWN GRAVEL (GM); SANDY, SILTY, COBBLES, SMALL BOULDERS, DENSE, SLIGHTLY MO|ST, BROWN ÀND GRÄY. li DISTURBED BULK SAMPLE NOTES 1, THE EXPLORATORY PITS WERE EXCAVATED WITH A BACKHOE ON MARCH 29,2021. 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 EXPLORÄTORY 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 BACKFILLED SUBSEQUENT TO SAMPLING. 7, LABORATORY TEST RESULTS: +4 = PERCENTAGE RETAINED 0N N0. 4 SIEVE (ASTM D a22); -2OO= PERCENTAGE PASSING NO, 2OO SIEVE (ASTM D 1 1 4O). PITS WERE 21 -7-267 Kumar & Associates LOGS OF EXPLORATORY PITS Fî9. 2 û too gô ao 70 €o 50 € 30 20 to o 0 to 20 JO 10 50 80 70 ao 90 to0 ¿ Ë H .ool .005 .009 .o19 .o37 .o75 .150 .500 I .600 -425 t.t a Ì 2.ı6 2.O OF SINM METERS CLAY TO SILT COBBLES GRAVEL 63 % SAND 31 LIQUID LIMIT SAMPLE 0F: Slightly Silly Sondy Grovel %SILT AND CLAY 6 % PLASTICITY INDEX FROM:Boringlg6'-6.5' Ihos6 losl r.sull3 opply only lo lhc sompl.s which waÞ l.st.d, lh. loollig roporl aholl nol b. r.produo.d, oxc€pt ln full, vllhoul lh6 wrltloñ oppaovol of Kumdr & Asaoc¡olôs, lnc. Slcvc qnqly3¡! lo'l¡ng is pcrlorm€d inqccordqnc! wilh ASTM 06913, ASTM 07928, ASIM clJti ond/or ASIM Ult40. HYDROMETER ANALYSIS SIEVE ANALYSIS ÏHE RruINGS ?{ HFS 7 HRS U.S. STANDARO SERIÉ CEÆ SATIARE OPENING I /I ¡ I / i / 1 I I I I I t t .l 'i I SAND GRAVEL FINE MEDIUM COARSE FINE COARSE 21 -7 -267 Kumar & Associates GRADATION TEST RTSULTS Fig. 3