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HomeMy WebLinkAboutSoils Report 08.28.2019Kumar & Associates, Inc.® Geotechnical and Materials Engineers and Environmental Scientists 5020 County Road 154 Glenwood Springs, CO 81601 phone: (970) 945-7988 fax: (970) 945-8454 email: kaglenwood@kumarusa.com An Employee Owned Company www.kumarusa.com Office Locations: Denver (HQ), Parker, Colorado Springs, Fort Collins, Glenwood Springs, and Summit County, Colorado SUBSOIL STUDY FOR FOUNDATION DESIGN PROPOSED RESIDENCE LOT 70, FILING 2, PINYON MESA PINYON MESA DRIVE GARFIELD COUNTY, COLORADO PROJECT NO. 19-7-221.01 AUGUST 28, 2019 PREPARED FOR: PMGC2, LLC ATTN: RON NORMAN 6300 RIGLEA PLACE, SUITE 900 FORT WORTH, TEXAS 76116 (urn oi-man(iusbcgtobal.net) TABLE OF CONTENTS PURPOSE AND SCOPE OF STUDY - 1 - PROPOSED CONSTRUCTION - 1 - SITE CONDITIONS - 1 - SUBSIDENCE POTENTIAL - 2 - FIELD EXPLORATION - 2 - SUBSURFACE CONDITIONS 3 - FOUNDATION BEARING CONDITIONS - 3 - DESIGN RECOMMENDATIONS - 4 - FOUNDATIONS - 4 - FLOOR SLABS - 5 - UNDERDRAIN SYSTEM - 5 - SURFACE DRAINAGE - 6 - LIMITATIONS - 7 - FIGURE 1 - LOCATION OF EXPLORATORY BORING FIGURE 2 - LOG OF EXPLORATORY BORING FIGURES 3 and 4 - SWELL -CONSOLIDATION TEST RESULTS TABLE 1- SUMMARY OF LABORATORY TEST RESULTS Kumar & Associates, Inc. ® Project No. 19-7-221.01 4 PURPOSE AND SCOPE OF STUDY This report presents the results of a subsoil study for a proposed residence to be located on Lot 70, Filing 2, Pinyon Mesa, Pinyon Mesa Drive, Garfield County, Colorado. The project site is shown on Figure 1. The purpose of the study was to develop recommendations for foundation design. The study was conducted as supplemental services to and in accordance with our agreement for geotechnical engineering services to PMGC2, LLC, dated April 8, 2019. A field exploration program consisting of an exploratory boring was conducted to obtain information on subsurface conditions. Samples of the subsoils obtained during the field exploration were tested in the laboratory to determine their classification, compressibility or swell and other engineering characteristics. The results of the field exploration and laboratory testing were analyzed to develop recommendations for foundation types, depths and allowable pressures for the proposed building foundation. This report summarizes the data obtained during this study and presents our conclusions, design recommendations and other geotechnical engineering considerations based on the proposed construction and the subsoil conditions encountered. PROPOSED CONSTRUCTION At the time of our study, design plans for the residence had not been developed. The building is proposed in the area of the exploratory boring location shown on Figure 1. For the purpose of our study, we assume below grade levels will not be constructed but there could be a walkout lower level. Grading for the structure is assumed to be relatively minor with cut depths between 2 and 8 feet. For the purpose of our analysis, foundation loadings for the structure were assumed to be relatively light and typical of the proposed type of construction. When building loadings, location and grading plans are available we should be notified to re- evaluate the recommendations contained in this report. SITE CONDITIONS The property was vacant at the time of our exploration. The boring was drilled within the building area. The site is vegetated with grass, weeds and sagebrush. The ground surface is Kumar & Associates, lnc.® Project No. 19.7-221.01 2 relatively flat and slopes moderately down to the north with about 6 feet of elevation differenqe across the building area. SUBSIDENCE POTENTIAL Bedrock of the Pennsylvanian age Eagle Valley Evaporite underlies the subject site. These rocks are a sequence of gypsiferous shale, fine-grained sandstone and siltstone with some massive beds of gypsum and limestone. There is a possibility that massive gypsum deposits associated with the Eagle Valley Evaporite underlie portions of the lot. Dissolution of the gypsum under certain conditions can cause sinkholes to develop and can produce areas of localized subsidence. During previous work in the area, sinkholes have been observed scattered throughout the lower Roaring Fork Valley. These sinkholes appear similar to others associated with the Eagle Valley Evaporite in this area. Sinkholes were not observed in the immediate area of the subject lot. No evidence of cavities was encountered in the subsurface materials; however, the exploratory boring was relatively shallow, for foundation design only. Based on our present knowledge of the subsurface conditions at the site, it cannot be said for certain that sinkholes will not develop. The risk of future ground subsidence on Lot 70 throughout the service life of the proposed residence, in our opinion, is low; however, the owner should be made aware of the potential for sinkhole development. If further investigation of possible cavities in the bedrock below the site is desired, we should be contacted. FIELD EXPLORATION The field exploration for the project was conducted on August 5, 2019. One exploratory boring was drilled at the location shown on Figure 1 to evaluate the subsurface conditions. The boring was advanced with a 4 -inch diameter continuous flight auger powered by a truck -mounted CME - 45B drill rig. The boring was logged by a representative of Kumar & Associates. Samples of the subsoils were taken with a 2 -inch I.D. spoon sampler. The sampler was driven into the subsoils at various depths with blows from a 140 -pound hammer falling 30 inches. This test is similar to the standard penetration test described by ASTM Method D-1586. The penetration resistance values are an indication of the relative density or consistency of the Kumar & Associates, Inc. ® Project No. 19-7-221.01 3 subsoils and hardness of the bedrock. Depths at which the samples were taken, and the penetration resistance values are shown on the Log of Exploratory Boring, Figure 2. The samples were returned to our laboratory for review by the project engineer and testing. SUBSURFACE CONDITIONS A graphic log of the subsurface conditions encountered at the site is shown on Figure 2. Below the minor root zone, the subsoils consist stiff to very stiff, sandy silt and clay down to about 36 where dense, silty sand and gravel was encountered. Below a depth of about 10 feet, the soils were moderately calcareous and contained gypsum and rock fragments. The soils encountered in the boring are variable and generally similar to the soils encountered at other nearby lots. Laboratory testing performed on samples obtained during the field exploration included natural moisture content and density, and percent fines (percent passing the No. 200 sieve). Swell - consolidation testing was performed on relatively undisturbed drive samples of the silt and clay subsoils. The swell -consolidation test results, presented on Figures 3 and 4, indicate low compressibility under relatively light surcharge loading and generally a low collapse potential when wetted under constant pressure. The upper silt and clay soils can be highly compressible under additional loading after wetting. The laboratory testing is summarized in Table 1. No free water was encountered in the boring at the time of drilling and the subsoils were slightly moist. FOUNDATION BEARING CONDITIONS The upper sandy silt and clay soils encountered at expected shallow cut depth typically tend to settle when they become wetted. The expansion potential measured on the sample from 10 feet appears to be an anomaly and can be neglected in the foundation design. A shallow foundation placed on the sandy silt and clay soils will have a high risk of movement if the subsoils become wetted. It will be critical to the long-term performance of the structure that the recommendations for surface grading and drainage contained in this report be followed to limit potential wetting of the bearing soils. The amount of movement, if the bearing soils become wet, will mainly be related to the depth and extent of subsurface wetting. Movement in the event of subsurface wetting could be 1 to 2 inches and likely cause building distress. Mitigation methods such as deep compaction, a deep foundation (such as piles or piers extending down around 30 feet below Kumar & Associates, Inc.° Project No. 19-7-221.01 -4 existing ground surface) pr a heavily reinforced mat foundation designed by the structural engineer can be used to support the proposed house with a lower risk of movement. Presented below are recommendations for shallow spread footings and slab -on -grade floor bearing on compacted structural fill. If a deep foundation or mat foundation is desired, we should be contacted to provide further design recommendations. DESIGN RECOMMENDATIONS FOUNDATIONS Considering the subsurface conditions encountered in the exploratory boring and the nature of the proposed construction, the building can be founded with spread footings bearing on compacted structural fill with a risk of movement and possible building distress. The design and construction criteria presented below should be observed for a spread footing foundation system. 1) Footings placed on at least 3 feet of compacted structural fill should be designed for an allowable bearing pressure of 1,500 psf. Based on experience, we expect initial settlement of footings designed and constructed as discussed in this section will be about 1 inch or less. Additional movement on the order of 1 to 2 inches or more could occur if deep wetting of the subsoils were to occur. 2) The footings should have a minimum width of 20 inches for continuous walls and 2 feet for isolated pads. 3) Exterior footings and footings beneath unheated areas should be provided with adequate soil cover above their bearing elevation for frost protection. Placement of foundations at least 36 inches below exterior grade is typically used in this area. 4) Continuous foundation walls should be heavily 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 also be designed to resist a lateral earth pressure corresponding to an equivalent fluid unit weight of at least 55 pcf for the onsite soils as backfill. 5) The topsoil and any loose or disturbed soils should be removed in the building area. The natural silt and clay soils or silty sand soils in footing areas should be sub -excavated to at least 3 feet below design bearing level and to at least 1Y2 feet Kumar & Associates, Inc.1, Project No. 19-7-221.01 5 beyond footing edges, The exposed soils in footing area should then be , moistened and compacted. Structural fill can consist of the onsite silt and clay soils compacted to at least 98% of standard Proctor density at near optimum moisture content. 6) A representative of the geotechnical engineer should conduct compaction testing during structural fill placement and observe all footing excavations prior to concrete placement to evaluate bearing conditions. FLOOR SLABS The natural on-site soils, exclusive of topsoil, can be used to support lightly loaded slab -on -grade construction with a risk of settlement similar to that for spread footings. The subgrade should be evaluated for expansion potential and the need for sub -excavation and compaction. 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 relatively well graded sand and gravel such as road base should be placed beneath interior slabs for support. This material should consist of minus 2 -inch aggregate with at least 50% retained on 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 silty soils or a suitable imported granular soil devoid of vegetation, topsoil and oversized rock. UNDERDRAIN 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 times of heavy precipitation or seasonal runoff. Frozen ground during spring runoff can create a perched condition. We recommend below -grade construction such as basement areas be protected from wetting and hydrostatic pressure buildup by an underdrain system. Slab -on -grade areas and crawlspaces less than 4 feet deep should not be provided with an underdrain. Kumar & Associates, Inc. Project No. 19-7-221.01 6 Where needed, the drains should consist of drainpipe placed in the bQttom 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 1'/2 feet deep. An impervious membrane such as 20 mil PVC should be placed beneath the drain gravel in a trough shape and attached to the foundation wall with mastic to prevent wetting of the bearing soils. SURFACE DRAINAGE Providing proper surface grading and drainage will be critical to keeping the bearing soils dry and limiting potential for building settlement and distress. 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. 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 paved areas. Free -draining wall backfill (if any) should be covered with filter fabric and capped with about 2 feet of the on-site soils to reduce surface water infiltration. 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 foundation walls. Consideration should be given to use of xeriscape to reduce the potential for wetting of soils below the building caused by irrigation. Kumar & Associates, Inc. Project No. 19-7-221.01 7 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 boring drilled at the location indicated on Figure 1, 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 boring and variations in the subsurface conditions may not become evident until excavation is performed. If conditions encountered during construction appear to be 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 of 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. Sincerely, Kumar & Associates, Inc. Shane J. Robat, P.E. Reviewed by: Steven L. Pawia SJR/kac cc: Integrated — t td i I lardrealtor(awnu ail .corn) Kumar & Associates, Inc. Project No. 19.7.221.01 I / 1.-----'..."., 2\ + �, / \ I f !1 + 1 I I / \\ I / � � 1 1 \ r , ' J LOT 72 ,' //\ \ , \ J � l r / , .. Ja.._] / ,\ , LOT 71 .,N(//1//‹./1 \ \ ' / '' /- / ' , \\-s \ BORING 1/70 /, 1 \ 1 ! LOT 70 f rr .r , • I , , r . / Ir r „V I r IM 20 0 70 APPROXIMATE SCALE -FEET % 1 ) ✓ , / r , ^ rr • r r/ ,/r/ / r/ LOT 66 r / r J r / rr LOT 69 .\\N/FrV‹ 19-7-221.1 j Kumar & Associates LOCATION OF EXPLORATORY BORING Fig. 1 BORING 1/70 LEGEND TOPSOIL; SANDY SILT AND CLAY, FIRM, SLIGHTLY MOIST, 0 DARK BROWN. — r 11/12 SILT AND CLAY (ML -CL); SLIGHTLY SANDY TO SANDY, STIFF / /WC -9.0 / f TO VERY STIFF, SLIGHTLY MOIST, LIGHT BROWN, SLIGHTLY _ >� DD=104 POROUS, MODERATELY CALCAREOUS WITH ROCK FRAGMENTS BELOW ABOUT 10 FEET. /H 20/12 SAND AND GRAVEL (SM -GM); SILTY, DENSE, SLIGHTLY 5 / /- WC=6.2 ''"� MOIST, BROWN. DD=101 — / -200=88 DRIVE SAMPLE, 2 -INCH I.D. CALIFORNIA LINER SAMPLE. — 2 — , 37/12 5/12 DRIOF 0 APOUND HAMMER FALLINGE AMPLE BLOW COUNT. INDICATES 30 INCHES WERETHAT 5LR REQUIRED 10 — ,1 //-1 WC=9.4 TO DRIVE THE SAMPLER 12 INCHES. — / DD=115 — / / NOTES 1 5 //1 53/12 1. THE EXPLORATORY BORING WAS DRILLED ON AUGUST 5, 2019 `.1 ~_ V WITH A 4 -INCH DIAMETER CONTINUOUS FLIGHT POWER AUGER. z ~.. o LA o _ — / / / 2. THE LOCATION OF THE EXPLORATORY BORING WAS MEASURED APPROXIMATELY BY PACING FROM FEATURES SHOWN ON THE SITE PLAN PROVIDED. 207 / 1 25/12 3. THE ELEVATION OF THE EXPLORATORY BORING WAS NOT — r- WC=6.8 MEASURED AND THE LOG OF THE EXPLORATORY BORING IS / -200=84 PLOTTED TO DEPTH. / 4. THE EXPLORATORY BORING LOCATION SHOULD BE CONSIDERED / ACCURATE ONLY TO THE DEGREE IMPLIED BY THE METHOD USED. --- 25 / 2912 5. / THE LINES BETWEEN MATERIALS SHOWN ON THE EXPLORATORY BORING LOG REPRESENT THE APPROXIMATE BOUNDARIES BETWEEN / T WC=5.5 MATERIAL TYPES AND THE TRANSITIONS MAY BE GRADUAL. // DD=102 / f 6. GROUNDWATER WAS NOT ENCOUNTERED IN THE BORING AT THE TIME OF DRILLING. — // 7. LABORATORY TEST RESULTS: 3 0 / ] 39/12 WC = WATER CONTENT (%) (ASTM D 2216); / DD = DRY DENSITY (pcf) (ASTM D 2216); .— / -200 = PERCENTAGE PASSING NO. 200 SIEVE (ASTM D 1140). // / / 35 — — 40 41/6, 52/6 19-7-221.01 Kumar & Associates LOG OF EXPLORATORY BORING Fig. 2 F CONSOLIDATION - SWELL CONSOLIDATION - SWELL 1 —2 2 1 0 —2 SAMPLE OF: Sandy Clay and Silt FROM: Boring 1/70 ® 2.5' WC = 9.0 %, DD = 104 pcf NO MOVEMENT UPON WETTING 1.0 APPLIED PRESSURE - KSF 10 100 SAMPLE OF: Calcareous Sandy Clay and Silt FROM: Boring 1/70 ® 10' WC = 9.4 %, DD = 115 pcf Then lent requite apply only to the eonlplee Iorled. The testing report ehp11 not be reproduced, ekcepl In lull, +ilhoul the written approval of Rumor and Aeeoclelee, Inc. Swell Ccnaceidellon leetInp performed in occordnnce .al, AMU. ❑-6516 EXPANSION UNDER CONSTANT PRESSURE UPON WETTING 1.0 APPUEU PRESSURE - KSF 10 100 19-7-221.1 Kumar & Associates SWELL—CONSOLIDATION TEST RESULTS Fig. 3 CONSOLIDATION - SWELL SAMPLE OF: Calcareous Sandy Clay and Silt FROM: Boring 1/70 © 25' WC = 5.5 %, DD = 102 pcf 'Thome last Paiute opply Poly to the .amp o@ touted. The uetinp mood *WO not be reproduced. pcept Vn lull. without the written approval of Humor and Associates. Inc. Swell Cpneapdatlort SHltnp performed�� In af aaodenee with AMU ADDITIONAL COMPRESSION - UNDER CONSTANT PRESSURE DUE TO WETTING 1.0 APPLIED PRESSURE - KSF 10 140 19-7-221.1 Kumar & Associates SWELL—CONSOLIDATION TEST RESULTS Fig. 4 K+A Kumar & Associates, Inc. ® Geotechnical and Materials Engineers and Environmental Scientists TABLE 1 SUMMARY OF LABORATORY TEST RESULTS Project No. 19-7-221.01 Lot 70 SAMPLE LOCATION 1 NATURAL MOISTURE CONTENT (%) NATURAL DRY DENSITY (pcf) GRADATION PERCENT PASSING sIEVE . 200(ft) 1 ATTERBERG LIMITS UNCONFINED COMPRESSNE STRENGTH SOIL TYPE (Psf) BORING DEPTH GRAVEL SAND c%) (%) LIQUID LIMIT (%) PLASTIC INDEX (%) 1/70 2',4 9.0 104 Sandy Clay and Silt 5 6.2 101 88 Slightly Sandy Clay and Silt 10 9.4 115 Calcareous Sandy Clay and Silt 20 6.8 84 Sandy Clay and Silt 25 5.5 102 Calcareous Sandy Clay and Silt