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HomeMy WebLinkAboutSoils Report 10.22.2007rttrz4b13454 H EPWORTH - PAWLAK GEOTECHNICAL October 22, 2007 Oary Krill P.O. Box 143 Woody Creek, Colorado 81656 To:197892 3a39 P. 2/8 lttl•,i.xilh tonl,rliiuruhint d, In. 50:11 t v.rntr; tt.u.t i '4 Cilriia.%ti.l Si„ingi, t'.4(NJllt. Nlhl11 Phi 9]a194S 7SIh1 En Q70.'i4+ N4i4 molt (I ahitget Ii i,uu Job No.107 0775 Subject: Subsoil Study for Foundation Design, Proposed Residence, Lot 94, Filing 7, Elk Springs Subdivision, Elk Springs Drive, Garfield County, Colorado Dear Mr. Krill: As requested, Hepworth-Pawtak Geotechnical, 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 September 25, 2007. 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 perfiormed a preliminary geotechnical study for Filings 6 through 9 ofthe Elk Springs subdivision (formerly Los Amigos Ranch PUD) and presented our fundings in a report dated February 14, 1997, Job No. 196 617. Proposed Construction: The proposed residence will consist of a single story wood frame structure ever a partial basement and partial crawlspacc. The attached garage and basement floors will be slab -on -grade. Cut depths are assumed to range between about 3 to 8 feet. Foundation Loadings for this type of construction are relatively light and typical of the proposed type of construction. If building conditions or foundation loadings are significantly different Gam those described above, we should be notified to re-evaluate the recommendations presented in this report. Site Conditions: Lot 94 is located on the uphill, northwest side of Elk Springs Drive and was vacant at the time ()four field exploration. There is an existing dry drainage in the northern portion ofthe lot. The ground surface in the building envelope is relatively flat with a strong slope down; to the east at a grade up to about 12%. There is about G to 8 feet of elevation difference across the building area. Vegetation consists of sagebrush, grass and weeds. Cedar trees are located in the existing drainage. Subsurface Conditions; The subsurface conditions at the site were evaluated by excavating three 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 1 foot of topsoil, consist of 3 to 6% feet of medium stiff to stiff, sandy silty clay. Relatively dense, basalt gravel, cobbles and boulders in a sandy silt matrix were encountered beneath the clay soils at depths between 4 and 7% feet. Results of swell -consolidation testing performed on relatively undisturbed samples ofthe clay soils, presented on Figure Parker 103.841-7119 • Colorado Spnngs 719-633-5562 • Silveri -home 970.468- f 9N9 OCT -29-2007 15:45 Fr om: HP-LIECt i CH 9709458454 -2- To:19709 8 P.3'8 3, indicate low compreeehility fonder existing moisture conditions and light loading and a low collapse potential (settlement under constant load) when wetted. The samples showed high compressibility upon increased loading after westing. No free water was observed in the pits at the time of excavation 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 spread footings placed on the undisturbed natural soil designed for as allowable soil bearing pressure of 1,500 psf for support of the proposal residence. The upper -finer grained soils and matrix soils are compressible after wetting and there could be some post -construction foundation settlement ifthe bearing soil become wet. Care shoukd be taken to prevent wetting of the bearing sots as described later in this report. The settlement could be differential between footings bearing on the upper fines graded soils and footings bearing on the basalt TO ck soils. 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 finning bearing level extended down to the undisturbed natural soils. Excavations into the basalt rode snits may require rock excavating techniques such as blasting and chipping. Voids created from boulder removal at footing grade should be backfilled with compacted sand and gravel, such as road base, or with concrete. Exterior footing should be provided with adequate cover above their bearing elevations for f% potation. Placement of footings at least 36 inches below the exterior grade is typically used in this area. Continuous foundation wails should be reinforced top and bottom to span focal anomalies snub as by assuming an unsupported length of at least 12 fleet. 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, excluding vegetation, topsoil or oversized rock, as backfill. Floor Slabs: The natural on-site soils, exclusive of topsoil, are suitable to support lightly loaded slab -on -grade construction. The clay and basalt matrix soils are compressible when wetted and there could be some slab settlement and distress if the bearing soils become wet. To reduce the effects of some dill movement. floor slabs should be separated from all bearing walls and columns with expansion joints which albw unrestrained vertical movement. Floor slab control joints should be used to reduce damage due to stainkago cracking. The requirements fbr 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 free -draining gravel should be placed beneath basement level slabs to facilitate drainage This material should consist ofminua 2 inch aggregate with leas than 50% passing the No. 4 sieve and less than 2% 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 a suitable imported material such as road base devoid of vegetation, topsoil and oversized rock. TJnderdraln 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 Job No.107 0775 OCT -29-2007 15:45 From:HP-620TECH 9709458454 - 3 - To:19709203036 P.4/8 times of heavy precipitation or seasonal runoff FrOzeat ground during spring runoffcan create a perched condition. We recommend below -grade construction, such as retaining wails, crawispace and basement areas, be protected from wetting and hydrostatic pressure buildup by an underdrain system. The drains should consist of drainpipe placed in the bottom ofthe wall backfill stmmunded above the invert level with free -draining granular material. The drain should be placed at each level of excavation and at least 1 frot below lowest adjacent finish grade and sloped at a minimum 1% to a suitable gravity outlet. Frey -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 inch. 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 residence has been completed: 1) Inundation ofthe foinedation 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% 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 &.et ofthe onsite, finer graded soils to reduce suriircee water infiltration. 3) The ground surface surrounding the exterior ofthe 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 area and a minimum slope of 3 inches in the first 10 fret in pavement and walkway areas. 4} Roof downspouts and drains mould discharge well beyond the limits of all backfill. 5) Irrigation sp rinlclrr heads and landscaping which requires regular heavy irrigation, such as sod, should be located at least 5 feet from foundation walls. 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 inure. 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 Job No.107 0775 OCT -29-8007 15:46 From:HP-COIECH 3709458454 To:19709203038 -4- report, we should be notified at once so re-evaluation ofthe recommendations may be made. P.5r8 This report has been prepared 1r the eacluaive use by our client for design purposes. We aro not responsible for technical interpretations by others of our information. As the project evolves, we should provide continued consultation and field =vices during construction to review and monitor the implementation of our recommendations, and to verify that the recommendations have been appropriately interpreted. Significant design ogee may require additional analysis or modifications to the recommendation presented herein. We recommend on-site observation of excavations and Sawtdation 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, IHEPWDRTH - PAWLAIC GEOTECHNICAL, INC. JonIy Z. Adamson, Jr., P.E. Reviewed by: Daniel E. Hardin, P.B. JZAilcsw attachments Figure 1 —Location ofExploratory Pits Figure 2 — Logs ofExploratory Pits Figuro 3 — Swell -Consolidation Test Results OCT -29-2007 15:96 From:HP-GEOTECH 979943E1454 To:19709203038 P.6'8 t APPROXIMATE SCALE 1"=BO' 107 0775 I LOT 93 1000 7'w / ... OW4t4t � -PIT 91 PIT1 PIT3 ■ 990 PROPOSED RESIDENCE 1 1 1 1 1 1 t t LOT 94 1 1 FILING 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 HICAIKOMWOIEIVICILL 1000 1 900 LOCATION OF EXPLORATORY PITS IFigure 1 IOCT -29-2007 15:46 From:HP-GEOTECH 9709458454 Ta:197092038 P.7/8 - 0 • - 5 i__... 10 LEGEND: "77•70 PIT 1 ELEV.- 989' WC- 11.1 00 ••73 PIT 2 ELEV.za 992 —7 v✓ WC•41.6 DDT PIT 3 ELEV.s 998' 0 5 • 10-- -. TOPSOL: sandy silty day, organics, roots, flrrn, slightly moist, dark brown. CLAY (CO: siftY, sandy, medium el lff to stiff, slightly moist to moist, brown to reddish brown, calcareous. BASALT {RAVEL AND COBBLES (GM); in a sandy silt mabrbc, with boulders, deme, silghdy moist, light brown to white, caicareoue. is) 2' Diameter hand driven line' sempts. NOTES: 1. Exploratory pits were excavated an October 10, 2007 with a mini -excavator. 2. Locations of satploratory pits were measured approxlrnateiy by paaing from features shown on the aifa dart provided. 3. Elevations of eocpioi atory pits were gained by interpolation between contotae shown on the site pian provided. Logs are drawn to depth. 4. The exploratory pit locations and elevations should be consldemd accurate only to the degree implied by the method used. 5. The lines between materlaia shown on the exp*uratory pit lows represent the approximate bourldasies between material types and transitions may be gradual. 8. No free water was encountered In the pits at the time of excavating. Ructuetlon in water level may occur with time. 7. Laboratory Testing Results: WC Water Content (%) DD Dry Density (pct) 107 0775agilegli LOGS OF EXPLORATORY PITS Figure 2 OCT -29-2007 15:46 Fr om: HP-COTECH 97994454 To:19709203038 P.8'$ 0 1 2 4 5 7 Moisture Content - 11.1 percent Dry Density = 73 pd Sample o1: Sandy Silty Clay From: Pit 1 of 4 Feet Compression upon welting 8 0. 0 1 2 5 6 7 a .0 10 100 APPUED PRESSURE - knr Moisture Content as 8.5 patent Dry Density mg 83 Peg Sample 01: Sandy Silty Clay r From: Pit 2 at 4 Feet Compression weltfng 0.1 107 0775 c SWELL -CONSOLIDATION TEST RESULTS Figure 3 1.0 10 APPLIED PRESSURE - kSf 100 -29-2007 15:45 From:HP-CEOTECH 9709458454 G&tech FAX TRANSMITTAL FORM DATE: 16,- 2.1 -b7 TO: (itri.) 4i 1 FROM: eit+KI le/nt.e)(- Number of Pages: MESSAGE: lincludfri�this page) To:19709203058 P.1/8 HEPWORTH - PAWLAK GEOTECHNICAL, INC. 5020 County Road 154 Glenwood Springs. Colorado 81801 Phone: 970-945-7988 Fax: 870-945.9454 e-md: hpgeo@hpgeoteeh-cam PROJECT NO.: FAX NO: 92079/16./-618 The original of this transmittal will be sent by: Ordinary Mall is• Fax Only 1i Overnight Other Si The information contained in this facsimile message is confidential and intended for the sole use of the individual named above. If you are not the intended recipient, received this communication in error, or if problems occur with transmission, please notify us at 970-945-7988. • Sent By: