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Home My WebLink AboutSubsoil Study for Foundation Design 03.08.17H-P~l<UMAR Geotechnical Engineering I Engineering Geology Materials Testing I Environmental 5020 County Road 154 Glenwood Springs, CO 81601 Phone: (970) 945-7988 Fax: (970) 945-8454 Email: hpkglenwood@kumarusa.com March 8, 2017 Office Locations: Parker, Glenwood Springs, and Summit County, Colorado Omar Delacruz 5387 County Road 154, #17 Glenwood Springs, Colorado 81601 (lacrossconcrete@outlook.com) Project No.17-7-194 Subject: Subsoil Study for Foundation Design, Proposed Residence, Lot E-9, Aspen Equestrian Estates, 42 Equestrian Way, Garfield County, Colorado Dear Mr. Delacruz: As requested, H-P/Kumar 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 February 22, 2017. The data obtained and our recommendations based on the proposed construction and subsurface conditions encountered are presented in this report. Hepworth-Pawlak Geotechnical, Inc. previously performed a preliminary geotechnical study for the subdivision development and reported their findings August 31, 1998, Job No. 198 501. Proposed Construction: The proposed residence will be two story wood frame construction with an attached garage. Ground floors will be slab-on-grade. Cut aepths are expecteCl to f ange between about 3 to 21-feet. Foundation loadings for this type of construction are assumed to he 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 property was vacant and free of snow at the time of our exploration. Vegetation consisted of grass and weeds. The ground surface was relatively flat with a slight slope down to the west. Subsidence Potential: Bedrock of the Pennsylvanian Age Eagle Valley Evaporite underlies the lower Roaring Fork Valley and the Aspen Equestrian Estates subdivision. These rocks are a - 2 - sequence of gypsiferious shale, fine-grained sandstone/siltstone and limestone with some massive beds of gypsum. There is a possibility that massive gypsum deposits associated with the Eagle Valley Evaporite underlie portions of the property. Dissolution of the gypsum under certain conditions can cause sinkholes to develop and can produce areas of localized subsidence. During previous work in the area, several broad subsidence areas and sinkholes have been observed. These sinkholes appear similar to others associated with the Eagle Valley Evaporite in areas of the Roaring Fork Valley. No evidence of subsidence or sinkholes were observed on the property or encountered in the subsurface materials, however, the exploratory pits were relatively shallow, for foundation design only. Based on our present knowledge of the subsurface conditions at the site, it can not be said for certain that sinkholes will not develop. The risk of future ground subsidence at the site throughout the service life of the structure, in our opinion is low, however the owner should be aware of the potential for sinkhole development. If further investigation of possible cavities in the bedrock below the site is desired, we should be contacted. 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 a few inches of topsoil, consist of silty sandy clay overlying silty sandy gravel with cobbles at a depth of about 5Y2 feet. Results of swell-consolidation testing performed on relatively undisturbed samples of the silty sandy clay, presented on Figure 3, indicate low to moderate compressibility under conditions of loading and wetting. 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, we recommend spreaa footings placed on the undisturbed natural soil designed fo,r an allowable soil bearing pressure of l,200 psf fQr support of the proposed residence. The sandy silty clay soils tend to compress when loaded and post construction settlements are expected to be on the order of 1 to 1 Yi inches. A low risk of settlement and building distress can be achieved by lowering the bearing level down to the sandy gravel and cobble soils and use of an allowable bearing pressure of 3,000 psf. Footings should be a minimum width of 18 inches for continuous walls and 2 feet for columns. H-P%!KUMAR Project No . 17-7-194 - 3 - Loose 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 soils. We should observe the completed foundation excavation for bearing conditions prior to concrete placement. 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 14 feet. Foundation walls acting as retaining structures (if any) 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. Floor Slabs: The natural on-site soils, exclusive of topsoil, are suitable to support lightly loaded slab-on-grade construction. The clay soils have variable settlement potential. 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 interior slabs 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 or imported granular soils devoid of vegetation, topsoil and rock larger than about 4 inches. Underdrain System: It is our l!mderstanding the finished :filoor elevation at the lowest level will be at or above the surrounding grade. Therefore, a foundation drain system is not required. 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, be protected from wetting and hydrostatic pressure buildup by an underdrain and wall drain system . H-P ~XUMAR Project No . 17-7-194 - 4 - If the finished floor devation of the proposed sttucture has a floor level below the surrol!lllding grade, we should be contacted to provide recommendations for an underdrain system. All earth retaining structures 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 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. 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 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 10 feet from the building. Consideration should be 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 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 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 H-P ~KUMAR Project No . 17-7-194 -5 - those descrihed 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, Reviewed by: ./ . 4¥ -'l ·:-,., ., ::i V' J. f .,., _. • _,, l .~ Steven L. Pawlak, P.E.t1 ·~~.:.. 3 l 0 /J1 :'/~· i ,13 ~ i.~, YO/) .c LEE/kac . ~ i.1,-;.;· ·~ ·'· .. • ... + .... , •I\ )-,,.. -• . 'K'/'··· . ,., .... ··~ 11"-l • t ~ Attachments Figure 1 -Lo'Ciition . --fExploratory Pits Figure 2 -Logs of.Exploratory Pits Figure 3 -Swell-Consolidation Test Results H-P""KUMAR Project No . 17-7-194 \ \ LOT E-8 "9-·--~; ,q 20 0 20 40 ~ ·, ,, APPROXIMATE SCALE-FEET BUILDING SETBACK LINE \ \ • PIT2 LOT E-9 PIT 1 • ----··-·----' . ..-.---··---- EQUESTRIAN WAY LOT E-10 i~ 17-7-194 H-P~KUMAR LOCATION OF EXPLORATORY PITS Fig. 1 1-w w u... I I I- Q_ w 0 PIT 1 0 5 WC=15.3 DD=108 PIT 2 WC=22.5 DD=98 0 5 10 10 LEGEND LJ CLAY (CL); SANDY, SILTY, MEDIUM STIFF TO VERY STIFF, MOIST, BROWN, LOCALLY BLOCKY. fZl GRAVEL (GP-GM); WITH COBBLES AND SMALL BOULDERS, SANDY, SILTY, DENSE, SLIGHTLY Ll MOIST TO MOIST, BROWN, ROUNDED ROCK. HAND DRIVEN LINER SAMPLE. DISTURBED BULK SAMPLE. NOTES 1. THE EXPLORATORY PITS WERE EXCAVATED WITH A BACKHOE ON FEBRUARY 27, 2017. 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 . f 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. ~ .!! ~ 7. LABORATORY TEST RESULTS: 1 WC = WATER CONTENT (%) (ASTM D 2216); j DD = DRY DENSITY (pcf) (ASTM D 221 6). 1 ! ~: !l ;( 1-w w u... I I I- Q_ w 0 ~;1--~~~~--.~~~~~~~~~~~~...-~~~~~~~~~~~~~~~~~~-.-~~~--1 H 11-1-194 ~~--~~~~--'~~~~~~~~~~~~---~~~~~~~~~~~~~~~~~~ ........ ~~~__, H-P~KUMAR LOGS OF EXPLORATORY PITS Fig. 2 f t i l f± ,....., ~ ......, _J _J LU 3: VJ z 0 i== <( 0 :J 0 VJ z 0 (..) ,....., ~ ......, _J _J LU 3: VJ z 0 i== <( 0 :J 0 VJ z 0 (..) 0 -1 -2 -3 -4 0 -1 -2 -3 -4 ~ :-..... r--..._ -..... '---,_ .I ---..._..._ ............. ....... ........ 'r--. .1 SAMPLE OF: Sandy Silty Clay FROM: Pit 1 @ 2' WC = 15.3 %, DD = 108 pcf --- NO MOVEMENT UPON WETTING '"H .. ~ ~ ""' ---- \ :\. _,_ -I->--\. ~ ~ _,_ \.0 APPLIED PRESSUR E -l<Sf 10 i__- ~<~ "" ""' )~ SAMPLE OF: Sandy Silty Clay FROM: Pit 2 @ 3' WC = 22.5 %, DD = 98 pcf L--..-'-'"" I-----ADDITIONAL COMPRESSION UNDER CONSTANT PRESSURE DUE TO WETTING -·--·l-i-1-+-I --I--- '\ \. 1.0 APPLI ED PRESS URE -Ksr 10 \00 100 ~€ it :=17=-=7=-=19=4==1 ==H==-=p=~==l(U==M==A==R====1 =_s-W=E=L=L-=C=O=N=S=O-L_l_D-A=T=IO=N=T=E=S--T--R=E_S-U=L=TS====F=ig=. =3=: