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Home My WebLink AboutSoils Report 07.16.1999G&ech July 16, 1999 Rando Construction Attn: Joe Rando P.O. Box 536 Silt, Colorado 81652 Hepworth-Pawlak Geotechnical, Inc. 5020 County Road 154 Glenwood Springs, Colorado 81601 Phone: 970.945.7988 Fax: 970.945.8454 hpgeo pgeotech.com Job No. 199 497 Subject: Subsoil Study for Foundation Design, Proposed Commercial Building, 252 County Road 167, Garfield County, Colorado Dear Mr. Rando: 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 you dated June 24, 1999. The data obtained and our recommendations based on the proposed construction and subsurface conditions encountered are presented in this report. Proposed Construction: The proposed building will be a large single story steel structure located on the site as shown on Fig. 1. The height of the building will be about 18 feet. Ground floor will be slab -on -grade. Cut depths are expected to range between about 2 to 4 feet. Foundation loadings for this type of construction are assumed to consist of relatively light wall loads and moderate column loads 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: A single story modular residence is located to the east of the proposed building. The ground surface slope is moderate down to the southwest with about 3 feet of elevation difference across the building site. There is a steep embankment down to Coryell Ridge Road. The embankment is partially comprised of man -placed fill. Vegetation consists of trees along the property lines and a landscaped lawn area. Subsidence Potential: This area of the Roaring Fork Valley is underlain by Pennsylvania age Eagle Valley Evaporite bedrock. The evaporite contain gypsum deposits. Dissolution of the gypsum under certain conditions can cause sinkholes to develop and can produce areas of localized subsidence. Sinkholes were not observed in the immediate area of the subject lot. 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 ground Rando Construction July 16, 1999 Page 2 subsidence on the property is low but the owner should—� be aware of the potential for - sinkhole potential. Subsurface Conditions: The subsurface conditions at the site were evaluated by excavating three exploratory pits at the approximate locations shown on Fig. 1. The Togs of the pits are presented on Fig. 2. The subsoils encountered generally consists of fill materials overlying relatively dense silty sandy gravel with cobbles and small boulders. Fill was exposed in Pit 2 to the depth of 4% feet. It appears the fill depth may exten [about 6 feet. One foot of topsoil and 2'/2 feet of silt sand overlies the gravels in Pit 1. Results of swell -consolidation testing performed on a relati,iely undisturbed sample of the silty sand soils, presented on Fig. 3, indicate low compressibility under existing low moisture conditions and light loading and a low collapse potential (settlement under constant load) when wetted. The sample showed moderate compressibility upon additional loading after wetting. Results of a gradation analysis performed on a sample of the underlying gravels (minus 5 inch fraction) obtained from the site are presented on Fig. 4. The laboratory testing is summarized on Table I. 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 gravel or compacted structural fill designed for an allowable soil bearing pressure of 2,500 psf for support of the proposed building. Footings should be a minimum width of 16 inches for continuous walls and 2 feet for columns. Existia fill and loose and 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 gravels. As an alternative design bearing level can be re-established with cpmpacted strjcturai fill. The structural fill should be granular material and compacted to 98% of maximum standard Proctor density. The fill should extend laterally out from footing edge at least the depth of fill beneath the footing. 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 12 feet. Floor Slabs: The natural sand and gravel soils below the topsoil and existing fill are suitable to support lightly to moderately 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 H -P GEOTECH Rando Construction July 16, 1999 Page 3 4 inch layer of sand and gravel should be placed beneath the slabs for subgrade 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 granular soils or imported granular fill devoid of vegetation, topsoil and oversized rock. The existing fill should be completely removed before placing the under slab fill. Surface Drainage: The following drainage precautions should be observed during construction and maintained at all times after the building 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 6 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. 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 expressed 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 Fig. 1 and to the depths shown on Fig. 2, the proposed type of construction, and our experience in the area. 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 H -P GEOTECH Rando Construction July 16, 1999 Page 4 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. Sincerely, HEPWORTH - PAWLAK GEOTECHNICAL, INC. spa REG/6, Z••NAD•f••,rte ''111""1,'; Jordy Z. Adamson, Jr. P. 297 i J Reviewed By: ��., ffI rthr Steven L. Pawlak, P.E. _ � JZA/ksm attachments cc: Schmueser Gordon Meyer - Attn: Jeff Simonson H -P GEOTECH PROPERTY LINES 1 r '1 EXISTING RESIDENCE .1 OZ L ` r r O 199 497 -.C1"1 00 r fi 0 HEPWORTH - PAWLAK GEOTECHNICAL, INC. APPROXIMATE SCALE 1"-60' LOCATION OF EXPLORATORY PITS Fig. 1 e 0 ...,.... 5 - 10 LEGEND: 4 rte/ NOTES: PIT 1 WC= 6.5 DD=101 j ▪ +4=62 ▪ —200=14 PIT 2 PIT 3 0 5 10 FILL; silty sand and gravel with cobbles and small boulders, some trash, loose to medium dense. moist, red, angular rocks. TOPSOIL; sandy silt, organic, medium stiff, moist, dark brown. SAND (SM); silty, loose, moist, brown_ GRAVEL, COBBLES AND BOULDERS (GP—GM); slightly silty, sandy, dense, moist, light brown, subrounded rocks. 2" Diameter hand driven liner sample. Disturbed bulk sample. 1. Exploratory pits were excavated on June 25 and 28, 1999 with o backhoe. 2. Locations of exploratory pits were measured approximately by pacing from features on the site plan provided. 3. Elevations of exploratory pits were not measured and logs of exploratory pits are drawn to depth. 4. The exploratory pit locations should be considered occurate only to the degree implied by the method used. 5. The lines between materials shown on the exploratory pit Togs represent the approximate boundaries between material types and transitions may be grodual. 6. No free water was encountered in the pits at the time of excavating. Fluctuations in water level may occur with time. 7. Laboratory Testing Results: WC = Water Content ( % ) DD = Dry Density ( pcf ) +4 = Percent retained on No. 4 sieve —200 = Percent passing No. 200 sieve Depth — Feet 199 497 HEPWORTH - PAWLAK GEOTECHNICAL, INC. LOGS OF EXPLORATORY PITS Fig. 2 0 1 2 N E0. 3 0 U 4 5 0.1 199 497 1.0 10 APPLIED PRESSURE — ksf HEPWORTH -- PAWLAK GEOTECHNICAL, INC. SWELL—CONSOLIDATION TEST RESULTS 100 Fig. 3 Moisture Content = 6.5 percent Dry Density Weight = 101 pcf Sample of: Silty Sand From: Pit 1 at 2.5 Feet Compression upon awm ittNi wetting \ - - .y 0.1 199 497 1.0 10 APPLIED PRESSURE — ksf HEPWORTH -- PAWLAK GEOTECHNICAL, INC. SWELL—CONSOLIDATION TEST RESULTS 100 Fig. 3 •i . S_ NeI VOV8 WoncirrAM = ILEMEMEIMNIALMEZIMEgfi NNEWIDIORDIM D z N OV r- r- -1 m 70 V) S 8 O 0' 8 O PERCENT PASSING 0 0 0 1111111111111111111101111111 mmommoutimmommi 11E1 11111111111MMIN 111•111111 Imuall111111111 11111 111111•111111111111 111111111 11111 11111 1111= IIII 1111111 1E111 I,. 111111:111 - main milimumm 0 O PERCENT RETAINED O O b O • a HEPWORTH-PAWLAK GEOTECHNICAL, INC. TABLE 1 SUMMARY OF LABORATORY TEST RESULTS i JOB NO. 199 497 SAMPLE LOCATION NATURAL MOISTURE CONTENT 1%1 NATURAL GRADATION PERCENT ATTERBERG LIMITS UNCONFINED COMPRESSIVE STRENGTH IPSFI SOIL OR BEDROCK TYPE PIT DEPTH Hoed DRY DENSITY Ipc11 GRAVEL 1%1 SAND 1%I PASSING NO. 200 SIEVE LIOUID LIMIT 1%1 PLASTIC INDEX 1%1 1 2 Y2 6.5 101 Silty Sand l 31/2 to 4 Y2 62 24 14 Silty Sandy Gravel with Cobbles i r 4 �y