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HomeMy WebLinkAboutSoils Report 05.31.2016Gech HEPWORTH-PAWLAK GEOTECHNICAL May 31, 2016 Garvik Construction Attn: Quinn Garvik P.O. Box 2257 Basalt, Colorado 81621 (ci rrarvik @gniail.com) 1-Ik1snxth-13,v,v1 G_otechnica1, Int 5020 County Road 154 Glcn ru,KJ Strings, Colorado 81601 Phone: 970.945.7988 F,,t• 970-945-8454 em;111: hrpcL@11pf„'et cclLcoln Job No.116 200A Subject: Subsoil Study for Foundation Design, Proposed Residence, Lot 1, Callicotte Ranch, Pinyon Woods Lane, Garfield County, Colorado Dear Mr. Garvik: As requested, Hepworth-Pawlak 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 Garvik Construction dated May 20, 2016. The data obtained and our recommendations based on the proposed construction and subsurface conditions encountered are presented in this report. We previously performed a preliminary subsoil study and geologic hazards evaluation for the Callicotte Ranch Subdivision in 2001, reported under our Job No. 101 821. Proposed Construction: The proposed residence will be one and two story wood frame construction with an attached garage. The structure will be above a crawlspace or possible basement. Basement and garage floors will be slab -on -grade. Cut depths are expected to range between about 3 to 9 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 lot is vacant and vegetated with grass and weeds in the building area. The ground surface slopes gently down to the west at a grade of about 10 percent, Minor surface disturbance from subdivision development was observed. A pond is located below the building area to the southwest. 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 6 inches of topsoil, consist of sandy silty clay down to the bottom of the pits at 7 feet deep. Results of swell -consolidation testing performed on relatively undisturbed samples of the sandy silty clay, presented on Figures 3 and 4, indicate low compressibility under existing Parker 303-841-7119 • Colorado Strings 719-633-5562 • Silvers horse 970-468-1989 -2 - moisture conditions and light loading and a minor collapse potential (settlement under constant load) when wetted. The clay samples were moderately to highly compressible under increased loading after wetting. No free water was observed in the pits at the time of excavation and the soils were slightly moist. Foundation Bearing Conditions: Spread footings bearing on the natural soils should be feasible for foundation support of the building with some risk of settlement. The risk of settlement is primarily if the bearing soils become wetted and precautions should be taken to prevent wetting. Settlements up to 1 inch are possible depending on the depth and extent of the wetting. 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 an allowable soil bearing pressure of 1,200 psf for support of the proposed residence. The soils tend to compress after wetting and there could be some post -construction foundation settlement. Footings should be a minimum width of 18 inches for continuous walls and 2 feet for columns. Loose and disturbed soils and existing fill encountered at the foundation bearing level within the excavation should be removed and the footing bearing level extended down to the undisturbed natural 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 14 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. A representative of the geotechnical engineer should observe all footing excavations prior to concrete placement to evaluate bearing conditions. Floor Slabs: The natural on-site soils, exclusive of topsoil, are suitable to support Iightly to moderately loaded slab -on -grade construction. There is a risk of slab settlement if the subgrade becomes wetted as discussed above. 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 free -draining gravel should be placed beneath basement level slabs to facilitate drainage. This material should consist of minus 2 inch aggregate with less 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 devoid of vegetation and topsoil. Underdrain System: Although groundwater was not encountered during our exploration, it has been our experience in the area and where clayey soils are present, that Job No. 1 16 200A Ggistech -3 - local perched groundwater can develop during times of heavy precipitation or seasonal runoff. Frozen ground during spring runoff can also create a perched condition. Therefore, we recommend below -grade construction, such as crawlspace and basement areas, be protected from wetting by an underdrain system. The drain should also act to prevent buildup of hydrostatic pressures behind foundation walls. A drain around shallow crawlspace areas (less than 4 feet deep) may not be needed with adequate compaction of foundation backfill and positive surface drainage away from foundation walls. The underdrain system should consist of a drainpipe surrounded by free -draining granular material placed at the bottom of the wall backfill. The drain lines should be placed at each level of excavation and at least 1 foot below lowest adjacent finish grade, and sloped at a minimum 1% grade to a suitable gravity outlet. Free -draining granular material used in the drain system should consist of minus 2 inch aggregate with less than 50% passing the No. 4 sieve and less than 2% passing the No. 200 sieve. The drain gravel should be at least 11/2 feet deep. An impervious liner such as 20 to 30 mil PVC should be placed below the drain gravel in a trough shape and attached to the foundation wall to prevent wetting of the bearing soils. 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 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. A swale may be needed uphill to direct surface runoff around the residence. 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 Joh No. 116 200A G Beech -4 - 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 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, HEPWORTH - PAWLAK GEOTECHNICAL, INC. L Reviewed by: • Daniel E. Hardie CI 2 4 443 • LEE/ksw1;*---A- attachments Figure 1 — Location of Exploratory Pits Figure 2 — Logs of Exploratory Pits Figures 3 and 4 — Swell -Consolidation Test Results Table 1 -- Summary of Laboratory Testing Job No. t 1 b 200A —TTl V/ 0 Slid AHOIVHO1dX3 d0 NOIlVOOI n / / �� \ /3 0-01`N� \ \ .. 13 1ti \ f 1 _' \• + -1 0 (-) 0 im ocn -C) r m 4m• emb PINYON WOODS LANE LI- CZ 0 5 PIT 1 PIT 2 WC -198 DD -83 WC=16 7 DD- 87 WC -17,2 OD -101 0 5 10 10 LEGEND: TOPSOIL; organic sandy silt and clay, firm, moist, dark brown. ./ CLAY (CL); sandy, silty, scattered cobbles, some gravelly sand layers, stiff, moist light brown, calcareous. Ig 2" Diameter hand driven liner sample. NOTES: 1. Exploratory pits were excavated on May 20, 2016 with a Bobcat mini -excavator. 2. Locations of exploratory pits were measured approximately by pacing from features shown on the site plan provided. 3. Elevations of exploratory pits were not measured and the togs of exploratory pits are drawn to depth. 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 transitions may be gradual. 6. No free water was encountered in the pits at the time of excavating. Fluctuation in water level may occur with time. 7. Laboratory Testing Results: WC = Water Content (%) OD = Dry Density (pcf) LL 0. 0 Compression % Compression % 0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 C`� Maisture Content 19.8 percent Dry Density 83 pcf Sample of: Sandy Silty Clay From: Pit 1 al 3 Feet N\ Compression upon wetting 0.1 1.0 10 APPLIED PRESSURE - ksf 100 Moisture Content = 16.7 Dry Density = 87 Sample of: Sandy Silty Clay From: Pit 1 at 6 Feet Compression upon wetting percent poi 0.1 1.0 10 APPLIED PRESSURE - ksf 100 Compression % 0 1 2 3 Moisture Content 17.2 percent Dry Density = 101 pcf Sample of: Sandy Silty Clay From: Pit 2 at 2 Y Feet No movement upon wetting 4.1.1011 01 1.0 APPLIED PRESSURE - ksf 10 100 HEPWORTH-PAWLAK GEOTECHNICAL, INC. TABLE 1 SUMMARY OF LABORATORY TEST RESULTS Job No. 116 200A SAMPLE LOCATION NATURAL MOISTURE CONTENT (%) NATURAL DRY DENSITY (pcf) GRADATION PERCENT PASSING NO. 200 SIEVE ATTER BERG LIMITS UNCONFINED COMPRESSIVE STRENGTH (PSF) SOIL TYPE PIT DEPTH (ft) GRAVEL I%) SAND {%O LIQUID LIMIT (%) PLASTIC INDEX (%) 1 3 19.8 83 [ Sandy Silty Clay 6 16.7 87 I Sandy Silty Clay 2 21 17.2 101 Sandy Silty Clay t r i