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HomeMy WebLinkAboutSoils Report 11.29.2018H-P:KU MAR Geotechnical Engineering I Engineering Geology Materials 'Testing I Fnv+irorenental 5020 County Road 154 Glenwood Springs, CO 81601 Phone: (970) 945-7988 Fax: (970) 945-8454 Email: hpkglenwood©kumarusa.com Office Locations: Denver (HQ), Parker, Colorado Springs, Fort Collins, Glenwood Springs, Summit County, Colorado November 29, 2018 Daniel & Donna Miller c/o Dan Gruenefeldt P. O. Box 1910 Basalt, Colorado 81621 ucnefe]dt.cotxt Project No.18-7-630 Subject: Subsoil Study for Foundation Design, Proposed Residence(s), Lots 41 and 42, Roaring Fork Mesa, Aspen Glen Subdivision, 21 Tellico Court and 79 Golden Stone Drive, Garfield County, Colorado Dear Dan: As requested, H-P/Kumar performed a subsoil study for design of foundations at the subject sites. The study was conducted in accordance with our agreement for geotechnical engineering services to Daniel and Donna Miller dated October 10, 2018. The data obtained and our recommendations based on the proposed construction and subsurface conditions encountered are presented in this report. Proposed Construction: We understand that the properties may be developed with a single family residence on each lot or the lots may be combined with one residence on the combined lots. We assume the proposed residence(s) will be one to two story, wood frame structures over full basement or crawlspace with attached garage. Basement and garage floors will be slab -on - grade. Cut depths are expected to range between about 3 to 10 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 lots were vacant at the time of our site visit. The lots are relatively flat and slope gently down to the south-southeast. There is a shallow pond located on the north side of both lots. Vegetation consists of grass and weeds. There has likely been overlot grading and -2 - site disturbance during subdivision development particularly around the parts of the lots adjacent to the pond and roadways. Subsidence Potential: Aspen Glen is underlain by Pennsylvania Age Eagle Valley Evaporite bedrock. The evaporite contains gypsum deposits. 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 were observed in Aspen Glen, mainly on the east side of the Roaring Fork River. The closest mapped sinkhole on the west side of the river is about 3,000 feet northwest of Lots 41 and 42. The nearest mapped sinkhole on the east side of the river is about 2,000 feet to the east. Sinkholes were not observed in the immediate area of the subject lot. 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 subsidence at Lots 41 and 42 is low and similar to other lots in the area but the owner should be aware of the potential for sinkhole development. Subsurface Conditions: The subsurface conditions at the site were evaluated by excavating 7 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 1 to 4% feet of stiff, sandy silty clay overlying relatively dense silty sandy gravel with cobbles and small boulders. The dense gravel was encountered at depths of 2 to 51/2 feet and extended down to the maximum depth explored of 6 feet. In general, the greater depths to gravels were encountered in the higher elevation pits on the north side of the lots (Pits 3, 4 and 6). Refusal to backhoe digging was encountered at the bottom of all seven pits at depths of 21/2 to 6 feet. Results of swell -consolidation testing performed on relatively undisturbed samples of the shallow clay soils, presented on Figures 4 and 5, indicate low compressibility under existing low moisture condition and light loading and a low 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 to moist. Foundation Recommendations: Considering the subsoil conditions encountered in the exploratory pits and the nature of the proposed construction, we recommend spread footings -P40,1 MAR -3 - placed on the undisturbed natural gravel soil (below all clay soils) designed for an allowable soil bearing pressure of 3,000 psf for support of the proposed residence(s). Footings should be a minimum width of 16 inches for continuous walls and 2 feet for columns. Loose and disturbed soils and existing fill and clay soils encountered at the foundation bearing level within the excavation should be removed and the footing bearing level extended down to the undisturbed natural gravel 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 10 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 50 pcf for the on-site soil as backfill. Floor Slabs: The natural on-site soils, exclusive of topsoil, are suitable to support lightly loaded slab -on -grade construction. The upper clay soils have a potential to settle when wetted similar to that described 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 gravel soils or imported road base gravel devoid of vegetation, topsoil and oversized rock. Underdrain System: Although free water was not encountered during our exploration, it has been our experience in this 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 retaining walls, crawlspace and f'roj( No. I t3-7-aao 4 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, drywell or sump and pump. 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. Surface Drainage: The following drainage precautions should be observed during construction and maintained at all times after the residence(s) has/have been completed: 1) 2) 3) 4) Inundation of the foundation excavations and underslab areas should be avoided during construction. 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. 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. 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 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 f "•_'Z TKLIMA1_= -5— 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, H -Pt KUMAR Daniel E. Hardin, P Reviewed by: k 0MRAl 6. N. 24443 z; �f rr13e cik NAL Steven L. Pawlak, P.E. DEH/kac attachments Figure 1 — Location of Exploratory Pits Figure 2 — Logs of Exploratory Pits Figure 3 — Legend and Notes Figures 4 and 5 — Swell -Consolidation Test Results Table 1 — Summary of Laboratory Test Results HvP' KUMAfa CONSOLIDATION - SWELL 2 —2 —4 —6 —8 —10 —12 —14 FM.. 1.11 lte opp nary to N. .e'..0s. lolled- lh. 1HIIr, lyeei .0,,J nas e. •ar+edtten ...npi In reit, .;tho.1 the written npprenel Cemex end s..ncwl.., rne. seen cen.o9d.Uen Inlla ITen. irr cccerda.ce .00 u1..�"na-nsia- 18-7-630 SAMPLE OF: Sandy Silty Clay FROM: Pit 1 0 1.5' WC = 7.6 %, DD = 89 pcf 10 APPLIED PRESSURE — KSF H-PAIKUMAR ADDITIONAL COMPRESSION UNDER CONSTANT PRESSURE DUE TO WETTING 10 100 SWELL -CONSOLIDATION TEST RESULTS Fig. 4 LEGEND I/// TOPSOIL, ORGANIC SANDY, SILTY CLAY, FIRM, MOIST, DARK BROWN. CLAY (CL): SILTY SANDY, STIFF, SLIGHTLY MOIST, BROWN. GRAVEL AND SILT (CL—ML): SANDY, STIFF, SLIGHTLY MOIST, REDDISH BROWN. GRAVEL (GM) SANDY, SILTY WITH COBBLES AND SMALL BOULDERS, DENSE, SLIGHTLY MOIST, LIGHT BROWN TO REDDISH BROWN. Is HAND DRIVEN 2—INCH DIAMETER LINER SAMPLE. t PRACTICAL DIGGING REFUSAL. NOTES 1. THE EXPLORATORY PITS WERE EXCAVATED WITH A BACKHOE ON NOVEMBER 14, 2018. 2. THE LOCATIONS OF THE EXPLORATORY PITS WERE MEASURED APPROXIMATELY BY PACING FROM FEATURES SHOWN ON THE SITE PLAN PROVIDED. 3. THE ELEVATIONS OF THE EXPLORATORY PITS WERE OBTAINED BY INTERPOLATION BETWEEN CONTOURS ON THE SITE PLAN PROVIDED. 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 THE TRANSITIONS MAY BE GRADUAL. 6. GROUNDWATER WAS NOT ENCOUNTERED IN THE PITS AT THE TIME OF DIGGING. PITS WERE BACKFILLED SUBSEQUENT TO SAMPLING. 7. LABORATORY TEST RESULTS: WC = WATER CONTENT (%) (ASTM D 2216); DD = DRY DENSITY (pcf) (ASTM D 2216). ,a m'e If 18-7-630 z0 H-PKUMAR LEGEND AND NOTES Fig. 3 f - W W W H a W 0 F- W W a W 0 PIT 1 EL. 6064' f�.-E r — 5 — 10 0 5 WC=7.6 DD=89 PIT 5 EL. 6065' PIT 2 EL. 6063.5' PIT 3 EL 6065' PIT 6 EL. 6066' PIT 4 EL. 6066' PIT 7 EL. 6064.5' WC=7.7 DD=85 0 5- 10 — 10 0 5— L 10 10 18-7-630 H -P- KUMAR LOGS OF EXPLORATORY PITS F- W F a W 0 Fig. 2 x a 1 a '� Pond i /f '1.S%. ..� / N. mya� / s, 40 "\ / N.,/ 701 Utfin Drainage • N ' aS. C44444,41.4 N / Pond , 7 .0o, / 1 1 !/ a .1 ,�r/ / -'`'s f , rte4-\ ,, F11 /la LPf \\r-� // \ .\ / o 10.0 / 1\ 14 � — ' PIT 1 Lot 42 17 653 Sq Ft 0.41 M. (Y.o.nf) PR 6 ■ — Lot 41 \\ 13,571 0e. Sq Ft \ 0.31 z/_ hmlemma 11lM1a RNaw 10.0' B I g 5.lbaah 4. 1/ 15 0 34 APPROXIMATE SCALE—FEET 18-7-630 41 uti 9)0 5q 1 5 / \ i �1 1 III Ili ..i .// \�\ I\ / /I /,—' PIT 2 PIT 1 ��rEneWa M1■ I / / I `i 1i/ / x0 11 1$--- -- ------ f•ur 04640 oilogirlo \.-----'i 1W�PI rOmM01 Lot 40 / 1 IBM ,j `" Elev.= • .� H-P--~KUMAR LOCATION OF EXPLORATORY PITS Fig. 1 2 .. 0 —2 — 4 — 6 —8 —10 CONSOLIDATION - SWELL SAMPLE OF: Sandy Silty Clay FROM: Boring 7 0 2' WC = 7.7 %, DD = 85 pcf 11 • tot MYNA appb apy to th. ▪ p4a !Mood- by gllno wad wad • not bo ,.prod**. *moot lo 1d1, Nheul pr xr1tt.n avowal of IiuTW pod Mwclat.l. Mo s. o .c4:2Mlon Goll rtomrd In ADDITIONAL COMPRESSION UNDER CONSTANT PRESSURE DUE TO WETTING 18-7-630 1.0 APPLIED PRESSURE — KSF 10 100 H -P-- KUMAR SWELL—CONSOLIDATION TEST RESULTS Fig. 5 H-PdKUMA� TABLE 1 SUMMARY OF LABORATORY TEST RESULTS Project No. 18-7-630 SAMPLE LOCATION NATURAL MOISTURE CONTENT (%) NATURAL DRY DENSITY(%) (pct) GRADATION PERCENT PASSING NO. 200 SIEVE ATTERBERG LIMITS UNCONFINED COMPRESSIVE STRENGTH (psfl SOIL TYPE PIT _ DEPTH (ft) GRAVEL I SAND (%) LIQUID PLASTIC LIMIT INDEX (%) (%) 1 1'h 7.6 89 Sandy Silty Clay 7 2 7.7 85 Sandy Silty Clay