The URL can be used to link to this page

Home My WebLink AboutSubsoil Study for Foundation Design 11.30.2007HEPWORTH - PAWLAK G EOTECHNICAL Hcpu'orth"Pawlnk Gcotcclrlical, Inc. 5020 CoLurty Road 154 (ìlenrçctxl S¡rings, (-'olorarkr B I 60 I Irhone: 970-945-7988 Fax: 970"945'8454 erùiril: lìpger)@hpgeÒtech.coln November 30,2007 Michael Maxson 165 Cresent Lane Glenwood Springs, Colorado 81601 Job No.107 0823 Subsoil Study for Foundation Design, Proposed Residence, Lot27, Filing 6, Elk Springs, Garfreld County, Colorado Dear Mr. Maxon: As requested, Hepworth-Pawlak Geotechnical, Inc. performed a subsoil study for design of foundations at the subject site. The study was conducted in accordancÊ ïr/ith our agreement for geotechnical engineering services to Michael Maxson dated October 29, 2007, The data obtained and our recommendations based on the proposed construction ancl subsurface conditions encountered are presented in this report. Hepworth-Pawlak Geotechnical, fnc., previously peîformed a preliminary geotechnical study for filings 6 through 9, Elk Springs (fotmuly Los Amigos Ranch PUD) and reported our findings on February 74, 1997, Job No, 197 617. Proposed Construction: The proposed residence witl be one storywood with a two story garage and will be strawbale construction. The residence will be located on the site as shown on Figure 1. Ground floors will be slab-on-grade. Cut depths are expected to range between about 2 to 6 feet. Foundation loadings for this type of constmction arq 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 site is located on the southem edge of a rolling upland mesa. Vegetation consists of a pinion and juniper forest with a ground cover of grass, weecls and cactus. The ground surface slopes down to the south at a gracle of 16 percent in the upper H Subject Parker 303.8+1"7119 o Cololaclo Springs '119-633-5567 o Silvcrth<irnc 970-468.1989 portion of the building area to 20 percent in the lower part. Numerous basalt cobbles and boulders are visible on the ground surface. 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 encorurtered, below about one foot of topsoil, consist of basalt cobbles and boulders in a sand and silt matrix. Possible sheet flows of basalt rock may be encountered. Results of a gradation analysis performed on a sample of sandy gravel (minus 5 inch fraction) obtained from the site are presented on Figure 3. No free water was obseived in the pits at the time of exoavation and the soils were slightly moist to moist. Foundation Recommendations: Considering the subsoil conditions encountered in the exploratory pits and the nature of the proposed construction, we recommend the strawbale foundation be plaoed on the undisturbed natural grarìular soil designed for an allowable soilbearingpressureof2,000psfforsupportoftheproposedresidence. Concrete footings should be a minimurn width of 16 inches for continuous walls and 2 feet for columns. Utility trenches and deep cut areas below about 3 feet may require rock excavating techniques such as chipping or blasting. Our experience in the area is that a large trackhoe can typically excavate 2 to 3 feet deeper than the bottom of our pits in the rnain house excavation. Loose and disturbed soils encountered at the forlrdation bearing level within the excavation should be removed and the footing bearing level extended down to the undisturbed natural soils. Voids created from boulder removal at footing grade should be filled with a structural rnaterial such as road base cornpacted to 98 percent standard Proctor density at a moisture content near optimum or cnncrete. Exterior footings should be provided with adequate cover above their bearing elevations for fi'ost protection. Placement of footings at least 3ó inches below the exterior grade is typically used in this area. Continuous foundation walls shoulcl be reinforced top and bottom to span local anornalies such as by assuming an unsupported length of at least 12 feet. Foundation walls acting as retaining structures (if any) should be designed to resist a Job No. 107 0823 cåEtectr -3- Iateral 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, exolusive oftopsoil, 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 shririkage cracking. The requirements for joint spacing and slab reinforcernent should be established by the designer based on experience and the intended slab use. A minimum 4 inch layer of free-draining gravel should be placed beneath basement level slabs to facilitate drainage. This material should consist of minus 2 jnch aggregate with less than 50% passing the No, 4 sieve and less thanZVo passing the No. 200 sieve, UnderdraÍn System: Although free water ïvas 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. lVe recommend below-grade construction, such as retaining walls, be protected from wetting and hydrostatic pressure tuildup by an underdrain system. The drains should consist of drainpìpe placed in the bottom of the wall backfill surrounded above the invert level with free-draining granulal 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 lYo to a suitable gravity outlet. Free-dr¿ining granular rnaterial used in the undcrclrain 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% feet deep. Surface Drainage: The following drainage precautions should be observed during construction and maintained at all times after the resitlence has been cornpleted: l) Inundation ofthe foundation excavations and underslab areas should be avo ided during construotion, Job No. l 07 0823 cäBtecrr 4 3) Exterior backfill should he adjusted to near optimum moisture and compacted to at least 95% ofthe 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-sitq finer graded soils to reduce zurface water infiltration. 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 füst 10 feet in pavement and walkway areas. A swale may be needed uphill to direct surface runoff around the residence. Roof downspouts and drains should discharge well beyond the limits of all backfill. 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 inigation. s) 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 wmranty either express or implied. The conclusions and recommendations submitted in thi.s repoú are based upon the data obtained fromthe exploratory pits excavated at the locations indicated on Figure 1 and to the depths shown on Figrue 2, the proposed type of construction, ând our experience in the area. Our services do not include determining the presencq prevention or possibility of mold or other biological contaminants (MOBC) developing in the firture. Ifthe 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 conditious encountered during construction appear different from those described ín this 2) 4) Job No.107 0823 GåFtectr -5- tepoft, we should be notified at once so re-evaluation ofthe recornmendations may be made. This report has been prepared for the exclusive use by oul client for design purposes. V/e are not resporuible for technical interpreiations by others of our information. As the project wolves, we should provide continued consultation and field services during construction to review and rnonitor the implementation ofour recommendations, and to verify that the recommendations have been appropriately interpreted. Significant design changes may requite 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 ofthe geotechnical engineer. If you have any questions or ifwe may be of further assistance, please let us know. Respectfully Submitted, HEPWORTH . PAWLAK GEOTECHNICAL, INC. Loiri-s p-Eller Reviewed by: Daniel E. Hardin, P,E. LEE/vad attachments Figure l -Lo cation Pits Figure 2 - Logs of Exploratory Pits Figure 3 - Gradation Test Results cc: Ron Robertson Árchitects, Attnl Matthew Tracy Job No. 1 07 0823 cåFtecrr LOT 5/, APPROXIMATE SCALE 1":40' .c't 27 (1.99s Ac) ii _or ?6 r .,. j. -, i-v ;l 'Prr 2 l.-l.\. i 'ì.,'.),')i :i ::.i';i, l l"ì; r,'ì Ii,líj LOS AM1GOS DRIVT 107 0823 LOCATION OF EXPLORATORY PITS Figure 1 PIT 1 ELËV.: 1029' P¡T 2 ELEV.: 1022' 0 LEGEND: d ry ooLL ¡ ! o_ (¡)Õ 5 d) o) LL -c o_ o)o t: r+4:65 - J -2oo=15 TOPSOIL; organic sandy silt and clay, firm, slightly moist to moist, dark brown. 10 5 10 BASALT COBBLES AND BOULDERS (GM); in a sand and silt matrix, dense, slighlly moist, light brown, calcareous. Disturbed bulk sample Practical digging refusal in basalt boulders. NOTES: 1. Exploratory pits were excavated on November 14,2007 with a Cat 403C trackhoe. 2, Locations of exploratory pits were measured approximately by pacing from fealures shown on the sito plân provided. 3. Elevations of exploratory pits were obtained by interpolation between contours shown on the site plan provided. 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 materialVpes and transitions may be gradual. 6. No free water was encountered in the pits at the time of excavating. Fluctuaiion in water level may occur with time. 7. Laboratory Testing Results: +4 : Percent retained on the No. 4 sieve -200 : Percent passing No. 200 sieve ffi 107 0823 LOGS OF EXPLORATOFY PITS Figure 2 ==- ------+-----_f -{-+- -l.+ts +1- -{+ -.¡-l- TIME READINGS U,S. STANDARD SERIES #s0 #30 #16 #8 CLEAR SOUAHË OPËNINGS o î8 fiffi. råflfur.60û,/lNl9MlN.4MlN. 1 MlN. #200 #4 3/8" 3/4', 1 112" 3" 5',6- 8',100 s0 80 7A 10 20 o LJz a.F l¡J E, t-z.ul C) rEtdfL 30 40 50 60 50 40 (9-ø UI (L l-2 IJ() fr(L 60 70 30 BO 20 90 10 100 .001 .002 .0oS ,009 .01s .O3T .A74 .1b0 .000 .600 1.18 2.36 4.75 9.5 12.5 DIAMETER OF PARTICLES IN MILLIMETERS 19.0 37.5 16,2 152 203 127 CLÄYTO SILT COSBLES GRAVEL 65 %SAND 20 %S¡LTAND CLAY 15 % LIQUID LIMIT %PLASTICITY INDEX O/O FROM:Pitl atSto4FeetSAMPLE OF: Silty Sandy Gravel with Cobbles 107 0823 GRADATION TEST HESULTS Figure 3