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Home My WebLink AboutB12-0318 / B12-0319 OPEN HOLE REPORT039` u Hepworth - Pawlak Geotechnical, Inc. 1—1 fn 5020 County Road 154 G4!��h 0tech Glenwood Springs, Colorado 81601 Phone: 970- 945 -7988 HEPWORTH - PAWLAK GEOTECHNICAL Fax: 970. 945 -8454 email: hpgeo@hpgeotech.com September 27, 2012 Sunder, Inc. Attn: John Sunderland P. O. Box 1393 Edwards, Colorado 81632 jpsunderga vail.net OCT 0 4 2012 1.yoP.M. V TOWN OF VAIL Job No. 112 252A Subject: Subsoil Study for Foundation Design, Proposed Zuckerman Duplex, Lot 3, Bighorn Subdivision Second Addition, 3807 Lupine Drive, Vail, Colorado Dear J P: As requested, Hepworth - Pawlak Geotechnical, Inc. performed a subsoil study for design of foundations at the subject site. The study was conducted in general accordance with our agreement for geotechnical engineering services to Sunder, Inc. dated July 24, 2012. The data obtained and our recommendations based on the proposed construction and subsurface conditions encountered are presented in this report. We recently observed the foundation excavation for a portion of the residence and submitted our findings, as well as interim findings of our subsoil study, in a report dated September 17, 2012 under the above job number. The rockfall assessment for the lot was presented in our report dated May 30, 2012, Job No 112 134A. Proposed Construction: The duplex will be a two story structure over a walkout basement level with attached garages on the south side at the main level. Ground floors will be slab -on- grade. Cut depths are expected to range between about 4 to 8 feet. Foundation loadings for this type of construction are assumed to be relatively light and typical of the proposed type of construction. Spread footings have been assumed for foundation support of the building using an allowable soil bearing pressure of 2,000 psf. 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 was occupied by an existing older residence that was to be removed for the new construction. The terrain is strongly sloping down to the north towards Gore Creek which borders the north side of the lot. Vegetation consists of landscape grasses and bushes with mature spruce trees. Subsurface Conditions: The subsurface conditions at the site were evaluated by excavating two exploratory pits at the locations shown on Figure 1. The logs of the pits Parker 303 - 841 -7119 • Colorado Springs 719 - 633 -5562 • Silverthorne 970- 468 -1989 Sunder, Inc. September 27, 2012 Page 2 are presented on Figure 2. The subsoils encountered in Pit 1, below about 4 feet of fill, consisted of about 1 %2 feet of stiff, very sandy silty clay underlain by relatively dense, slightly silty sandy gravel and cobbles with probable boulders. The subsoils encountered in Pit 2, below about 1 foot of organic topsoil, consisted of about 5'/2 feet of medium dense, clayey silty sand underlain by relatively dense, slightly silty sandy gravel and cobbles with probable boulders. Results of swell - consolidation testing performed on relatively undisturbed samples of the clay and sand soils, presented on Figure 3, indicate moderate compressibility. Results of a gradation analysis performed on a sample of the natural coarse granular soils (minus 3 inch fraction) obtained from Pit 1 are presented on Figure 3. The laboratory testing is summarized in Table 1. Free water was encountered n Pit 1 at a depth of about 7 feet and no free water was encountered in Pit 2 at the time of excavation. The soils were moist to very moist becoming wet with depth in Pit 1. Foundation Recommendations: Considering the subsoil conditions encountered in the exploratory pits and the nature of the proposed construction, we recommend spread footings placed entirely on the undisturbed natural coarse granular soils designed for an allowable bearing pressure of 2,000 psf for support of the proposed duplex. This may require subexcavation of unsuitable soils down to below design bearing elevation. Footings should be a minimum width of 16 inches for continuous walls and 2 feet for columns. The existing fill, topsoil, fine grained clay and sand soils, and any loose disturbed materials encountered at the foundation bearing level within the excavation should be removed and the footing bearing level extended down to the undisturbed natural coarse granular soils. Exterior footings should be provided with adequate soil cover above their bearing elevations for frost protection. Placement of footings at least 48 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 10 feet. Foundation walls acting as retaining structures should also be designed to resist a lateral earth pressure based on an equivalent fluid unit weight of at least 50 pcf for the on -site soils as backfill. The backfill should not contain vegetation, topsoil or oversized rocks. Floor Slabs: The natural on -site soils, exclusive of topsoil, are suitable to support lightly loaded slab -on -grade construction. There could be some settlement of slabs underlain by the fine grained soils. The fine grained soils could be removed and replaced with compacted structural fill to reduce the settlement risk. 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 Job No. 112 252A G95t~ ech Sunder, Inc. September 27, 2012 Page 3 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 granular soils devoid of topsoil and oversized rocks. Underdrain System: Free water was encountered in one of our exploratory pits and it has been our experience in that the area that groundwater level can rise seasonally or local perched groundwater can develop during times of heavy precipitation or seasonal runoff. Frozen ground during spring runoff can also 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 system. The drains should consist of drainpipe placed in the bottom of the wall backfill surrounded above the invert level with free - draining granular 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 1 % to a suitable gravity outlet. Free - 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 inches. The drain gravel backfill should be at least 11/2 feet deep and extend to above any seepage level in the excavation cut level. The drain gravel should be separated from the on -site soils with filter fabric such as Mirafi 140N. Surface Drainage: The following drainage precautions should be observed during construction and maintained at all times after the duplex 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 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. Excavation Observations: On September 14, we observed the foundation excavation for the northwestern portion of the proposed building to evaluate the exposed soil bearing Job No. 112 252A G9&eCh Sunder, Inc. September 27, 2012 Page 4 conditions. As discussed in our September 17, 2012 letter, free water was encountered in the excavation and dewatering and subexcavation and replacement of the coarse granular soils with imported crushed rock was needed to achieve adequate bearing conditions. We subsequently observed the remainder of the foundation excavation on September 17, 19 and 24, 2012. On September 17, we observed the northeast and eastern portion of the excavation and found from about 1' /2 to 3 feet in depth of unsuitable soils below design bearing elevation that were recommended to be removed to achieve adequate bearing. On September 19, we observed the southeastern and southern portion of the excavation with natural coarse granular soils encountered generally at design bearing elevation. At the time of our September 24b site visit, the foundation excavation was essentially complete and had been cut in multiple levels from about 3 to 8 feet below the adjacent ground surface. The soils exposed in the bottom of the excavation consisted of relatively dense, slightly silty sandy gravel and cobbles. No free water was encountered in these portions of the excavation and the soils were moist to very moist. The coarse granular soil conditions exposed in the excavation are consistent with those previously encountered on the site and suitable for support of spread footings designed for the recommended allowable bearing pressure of 2,000 psf. Loose and disturbed soils should be removed in the footing areas to expose the undisturbed natural coarse granular soils. The water seepage into the excavation should continue to be collected and diverted away from the footing areas and any softened soils and mud removed before concrete placement. Other recommendations presented in the preceding reports which are applicable should also be observed. 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 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 Job No. 112 252A G99tL-Ch Sunder, Inc. September 27, 2012 Page 5 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 6�' ICAL, INC. itl IFjj/ f A. • • David A. Young, P. IS .� �i 32216 Reviewed by: �ir,S. •.....•••• �``e� Steven L. Pawlak, P.E. DAY/ksw attachments Figure 1, Locations of Exploratory Pits Figure 2, Logs of Exploratory Pits Figure 3, Swell- Consolidation Test Results Figure 4, Gradation Test Results Table 1, Summary of Laboratory Test Results Job No. 112 252A Gg to \ \ PIT 1 \\ LOT 4 � � \ • \ LOWE LEVEL % -'r x f f ' - .,. PIT 2 ,APPROXIMATE SCALE: 30 J LOT 2 T, 112 252A I teCrn I LOCATIONS OF EXPLORATORY PITS I FIGURE 1 HEPWORTH- PAWLAK GEOTECHNICAL 10 10 LEGEND: ®FILL; about 1 foot of organic sandy silty clay over sandy silty clay, medium stiff, moist, brown to dark brown. CLAY (CL); silty, very sandy, stiff, very moist, brown, low to medium plasticity. 0§0 GRAVEL and COBBLES (GM -GP); probale boulders, sandy, slightly silty, dense, moist to wet with depth in Pit 1, brown. TOPSOIL; organic sandy silty clay, moist, dark brown. SAND (SC); clayey, silty, medium dense, moist to very moist, brown, slightly porous, low to medium plasticity. 2" Diameter hand driven liner sample. Disturbed bulk sample. _ J Free water depth measured in the pit at the time of excavation. NOTES: 1. Exploratory pits were excavated on July 27, 2012 with a John Deere 35D 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 obtained by interpolation between contours shown on the site plan provided. The logs 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. Water level readings shown on the logs were made at the time and under the conditions indicated. No free water wsa encountered in Pit 2. Fluctuations in water level may occur with time. 7. Laboratory Testing Results: WC = Water Content ( %) DD = Dry Density (pcf) +4 = Percent retained on the No. 4 sieve -200 = Percent passing No. 200 sieve 112 252A t i E P W O RTH -PA W LAK G EOTEC H N ICAL H w w U_ 2 F- a u1 0 LOGS OF EXPLORATORY PITS I FIGURE 2 PIT 1 PIT 2 ELEV. =8660' ELEV. = 8365' 0 0 WC =12.9 W DD =104 LL WC =28.9 - 200 =29 5 DD-96 5 2 a oo.; WC =23.6 W ::: ': DD =94 - 200 =10 ,o. J 10 10 LEGEND: ®FILL; about 1 foot of organic sandy silty clay over sandy silty clay, medium stiff, moist, brown to dark brown. CLAY (CL); silty, very sandy, stiff, very moist, brown, low to medium plasticity. 0§0 GRAVEL and COBBLES (GM -GP); probale boulders, sandy, slightly silty, dense, moist to wet with depth in Pit 1, brown. TOPSOIL; organic sandy silty clay, moist, dark brown. SAND (SC); clayey, silty, medium dense, moist to very moist, brown, slightly porous, low to medium plasticity. 2" Diameter hand driven liner sample. Disturbed bulk sample. _ J Free water depth measured in the pit at the time of excavation. NOTES: 1. Exploratory pits were excavated on July 27, 2012 with a John Deere 35D 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 obtained by interpolation between contours shown on the site plan provided. The logs 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. Water level readings shown on the logs were made at the time and under the conditions indicated. No free water wsa encountered in Pit 2. Fluctuations in water level may occur with time. 7. Laboratory Testing Results: WC = Water Content ( %) DD = Dry Density (pcf) +4 = Percent retained on the No. 4 sieve -200 = Percent passing No. 200 sieve 112 252A t i E P W O RTH -PA W LAK G EOTEC H N ICAL H w w U_ 2 F- a u1 0 LOGS OF EXPLORATORY PITS I FIGURE 2 0 .o OR 0 1 c cC{ Q X w 2 c 0 U) 3 0 Q E 0 U 5 0 1 2 3 C_ 0 Q) a 4 E 0 U 6 Moisture Content = 28.9 Dry Density = 96 Sample of: Very Sandy Silty Clay From: Pit 1 at 4 Feet Expansion upon wetting percent pcf 0.1 1.0 10 100 APPLIED PRESSURE - ksf 7 L- 0.1 Moisture Content = 23.6 Dry Density = 94 Sample of: Clayey Silty Sand From: Pit 2 at 6 Feet Compression upon wetting percent pcf 1.0 10 100 APPLIED PRESSURE - ksf 112 252A C -< ,"cecn SWELL- CONSOLIDATION TEST RESULTS FIGURE 3 HEPWORTH- PAWLAK GEOTECHNICAL HEPWORTH - PAWLAK GEOTECHNICAL, INC. TABLE 1 SUMMARY OF LABORATORY TEST RESULTS Job No. 112 252A SAMPLE LOCATION NATURAL MOISTURE CONTENT (%1 NATURAL DRY DENSITY (pd) GRADATION PERCENT PASSING NO. 200 SIEVE ATTERBERG LIMITS AASHTO CLASSIFICATION SOIL OR BEDROCK TYPE PIT DEPTH (ft) GRAVEL M SAND (%) LIQUID LIMIT 1 %1 PLASTIC INDEX l %1 1 4 28.9 96 Very Sandy Silty Clay 7-71/2 49 41 10 Slightly Silty Sandy Gravel 2 2'/2 12.9 104 29 Clayey Silty Sand 6 23.6 94 Clayey Silty Sand