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HomeMy WebLinkAboutSoils Report 02.05.2018H-PKUMAR Geotechnical Engineering J Engineering Geology Materials Testing 1 Environmental 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 SUBSOIL STUDY FOR FOUNDATION DESIGN PROPOSED RESIDENCE LOT 15, SPRING RIDGE RESERVE SPRING VIEW DRIVE GARFIELD COUNTY, COLORADO PROJECT NO. 17-7-896 FEBRUARY 5, 2018 PREPARED FOR: DESIGN SOURCE BUILD, LLC ATTN: SLAWEK WOJCIUCH P.O. BOX D ASPEN, COLORADO 81612 (stawe k @ des ig_nsourceb u i I d.con) TABLE OF CONTENTS PURPOSE AND SCOPE OF STUDY - 1 - PROPOSED CONSTRUCTION - 1 SITE CONDITIONS - 2 - FIELD EXPLORATION _ 2 - SUBSURFACE CONDITIONS - 2 - DESIGN RECOMMENDATIONS - 3 - FOUNDATIONS - 3 - FOUNDATION AND RETAINING WALLS ... - 4 - FLOOR SLABS 5 UNDERDRAIN SYSTEM. _ 6 - SURFACE DRAINAGE - 6 - LIMITATIONS - 7 - FIGURE 1 - LOCATION OF EXPLORATORY BORINGS FIGURE 2 - LOGS OF EXPLORATORY BORINGS FIGURE 3 - LEGEND AND NOTES FIGURES 4-6 - SWELL -CONSOLIDATION TEST RESULTS TABLE 1- SUMMARY OF LABORATORY TEST RESULTS H-PKUMAR Project No 17-7 -896 PURPOSE AND SCOPE OF STUDY This report presents the results of a subsoil study for a proposed residence to be located at Lot 15, Spring Ridge Reserve, Spring View Drive, Garfield County, Colorado. The project site is shown on Figure 1. The purpose of the study was to develop recommendations for the foundation design. The study was conducted in general accordance with our agreement for geotechnical engineering services to Design Source Build dated December 29, 2017. Hepworth- Pawlak Geotechnical previously performed a preliminary geotechnical study for the subdivision development and reported their findings February 26, 2001, Job No. 101 126 and updated the study in a report dated June 22, 2004. A field exploration program consisting of exploratory borings was conducted to obtain information on the 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 subsurface conditions encountered. PROPOSED CONSTRUCTION The proposed residence will be single -story, wood frame construction above a basement level with an attached garage located as shown on Figure 1. Ground floors will be slab -on -grade. Grading for the structure is assumed to be relatively minor with cut depths between about 3 to 8 feet. We assume relatively light foundation loadings, typical of the proposed type of construction. If building loadings, location or grading plans change significantly from those described above, we should be notified to re-evaluate the recommendations contained in this report. H-PeKUMAR Project No 17-7 -896 2 SITE CONDITIONS The residence will be located in the northern part of the building envelope near Spring View Drive as shown on Figure 1. Vegetation consists of grass and weeds. The ground surface slope is gentle down to the southeast with about 3 to 4 feet of elevation difference across the building area. FIELD EXPLORATION The field exploration for the project was conducted on January 10, 2018. Two exploratory borings were drilled at the locations shown on Figure 1 to evaluate the subsurface conditions. The borings were advanced with 4 -inch diameter continuous flight augers powered by a truck- mounted CME -45B drill rig. The borings were logged by a representative of H-P/Kumar. Samples of the subsoils were taken with a 2 -inch I.D. spoon sampler. The sampler was driven into the subsurface materials 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 subsoils and hardness of the bedrock. Depths at which the samples were taken and the penetration resistance values are shown on the Logs of Exploratory Borings, Figure 2. The samples were returned to our laboratory for review by the project engineer and testing. SUBSURFACE CONDITIONS Graphic logs of the subsurface conditions encountered at the site are shown on Figure 2. The subsoils, below about six inches of topsoil, consist of about 9 to 15 feet of very stiff to hard, silty sandy underlain by very clayey sand to sandy clay to the drilled depth of 26 to 41 feet. Laboratory testing performed on samples obtained from the borings included natural moisture content and density and percent finer than sand size gradation analyses. Results of swell - consolidation testing performed on relatively undisturbed drive sample of clay and sand soils, H-P*KUMAR Project No 17-7 -896 -3 - presented on Figures 4-6, generally indicate low to moderate compressibility under conditions of loading and wetting. The samples from Boring 1 at 5 feet and Boring 2 at 5 feet showed low to moderate expansion potential when wetted under light loading. The other two samples showed nil to low collapse potential (settlement under constant load) when wetted. The laboratory testing is summarized in Table 1. No free water was encountered in the borings at the time of drilling and the subsoils were slightly moist. DESIGN RECOMMENDATIONS FOUNDATIONS Considering the subsurface conditions encountered in the exploratory borings, the nature of the proposed construction and our experience in this are with spread footings bearing on the natural soils. a, we recommend the building be founded The expansion potential of the clay samples from 5 feet depth appears to be an anomaly and the expansion potential of the exposed soils should be further evaluated at the time of excavation for possible mitigation measures. The design and construction criteria presented below should be observed for a spread footing foundation system. 1) Footings placed on the undisturbed natural soils should be designed for an allowable bearing pressure of 2,000 psf. Based on experience, we expect settlement of footings designed and constructed as discussed in this section will be less than 1 inch. Additional differential movement of about 1 inch could occur if the bearing soils are wetted and precautions should be taken to keep the bearing soils dry. 2) The footings should have a minimum width of 16 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 H-PkKUMAR Project No 17-7 -896 -4 - 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 lateral earth pressure as described below in the "Foundation and Retaining Walls" section. 5) All topsoil and any loose or disturbed soils should be removed and the footing bearing level extended down to the undisturbed natural soils. The exposed soils in footing area should then be moistened and compacted as needed. 6) A representative of the geotechnical engineer should observe all footing excavations prior to concrete placement to evaluate bearing conditions. FOUNDATION AND RETAINING WALLS Foundation walls and retaining structures which are laterally supported and can be expected to undergo only a slight amount of deflection should be designed for a lateral earth pressure computed on the basis of an equivalent fluid unit weight of at least 55 pcf for backfill consisting of the on-site soils. Cantilevered retaining structures which are separate from the residence and can be expected to deflect sufficiently to mobilize the full active earth pressure condition should be designed for a lateral earth pressure computed on the basis of an equivalent fluid unit weight of at least 45 pcf for backfill consisting of the on-site soils. All foundation and retaining structures should be designed for appropriate hydrostatic and surcharge pressures such as adjacent footings, traffic, construction materials and equipment. The pressures recommended above assume drained conditions behind the walls and a horizontal backfill surface. The buildup of water behind a wall or an upward sloping backfill surface will increase the lateral pressure imposed on a foundation wall or retaining structure. An underdrain should be provided to prevent hydrostatic pressure buildup behind walls. Backfill should be placed in uniform lifts and compacted to at least 90% of the maximum standard Proctor density at near optimum moisture content. Backfill placed in pavement and H -P KUMAR Project No 17-7 -896 -5 - walkway areas should be compacted to at least 95% of the maximum standard Proctor density. Care should be taken not to overcompact the backfill or use large equipment near the wall, since this could cause excessive lateral pressure on the wall. Some settlement of deep foundation wall backfill should be expected, even if the material is placed correctly, and could result in distress to facilities constructed on the backfill. The lateral resistance of foundation or retaining wall footings will be a combination of the sliding resistance of the footing on the foundation materials and passive earth pressure against the side of the footing. Resistance to sliding at the bottoms of the footings can be calculated based on a coefficient of friction of 0.35. Passive pressure of compacted backfill against the sides of the footings can be calculated using an equivalent fluid unit weight of 300 pcf. The coefficient of friction and passive pressure values recommended above assume ultimate soil strength. Suitable factors of safety should be included in the design to limit the strain which will occur at the ultimate strength, particularly in the case of passive resistance. Fill placed against the sides of the footings to resist lateral loads should be compacted to at least 95% of the maximum standard Proctor density at a moisture content near optimum. FLOOR SLABS The natural on-site soils, exclusive of topsoil, can be used to support lightly loaded slab -on -grade construction. The expansion potential and need for sub -excavation to remove expansive clay soils should be evaluated at the time of excavation. 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 at Least 50% retained on 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- H-P%KUMAR Project No 17-7 -896 -6 - site soils or imported relatively well graded granular soils 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 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. An impervious membrane, such as 20 mil PVC should be placed below the drain gravel in a trough shape and attached to the foundation wall with mastic 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 he 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 he 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 H-PKUMAR Project No 17-7 -896 -7 - inches in the first 10 feet in paved areas. Free -draining wall backfill should be covered with filter fabric and capped with about 2 feet of the on-site finer graded 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 limit potential wetting below the building from landscape 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 borings drilled at the locations 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 borings 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 so that 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 H-P*KUMAR Project No 17-7 -896 _g - of excavations and foundation bearing strata and testing of structural fill by a representative of the geotechnical engineer. Respectfully Submitted, H -P KUMAR Steven L. Pawlak, P. Reviewed by: Daniel E. Hardin, P.E. SLP/kac H-PMKUMAR Project No 17-7 -896 1 - PROPERTY LINE aw —� as• y1b { 4 a� - C F N. 1 Li • { 91,9/16" BORING x BUILDING ENVELOPE I4-- �� 15 0 15 30 APPROXIMATE SCALE -FEET i011 1 1 1 7-7-896 H -P- KUMAR LOCATION OF EXPLORATORY BORINGS Fig. 1 BORING EL L 100' / / / 1 ROBING EL. 97' �/ / 2 — _ L //T 42/12 /� 38/12 _ — , _ —5 K/ // 5 //] 38/12 / //� 41/12 — / WC=8.3 / WC=6.9 _. — / / DD=120 DD=124 — — / /f / / / y / / / / 10 L / //_j 28/12 / / 24/12 10— // WC=7.2 WC=5.6 — DD=120 / DD=115 — // —200=71 // —200=61 / / — / / / / — 15 18/12 15 32/12 / WC=5.2 J — /` ✓/ DD=110 - - /f // — _ / / / / — 20 / / 20 4.1/ — / 24/12 WC=4.9 / 22/12 — w w- 1 / / D0=115 / /w— �— / // —I - w / �/ w 0— / —O —25 25 — /'1 17/12 /115/12 — / WC=7.4 WC=12.0 - - / DD=123 DD=119 _ / —200=65 —200=79 f _ — // _ — 30 30 — / /r-26/12 _ / / — / / — — / / — 35 // 35 _ / / ._ / / — / _ / — / _ / — 40 / — 71 20/12 40 45 45---. 17-7-896 H-PUMAR LOGS OF EXPLORATORY BORINGS Fig. 2 LEGEND / // / TOPSOIL; ORGANIC SANDY SILTY CLAY, FIRM, MOIST, DARK BROWN. CLAY (CL); SILTY, SANDY, VERY STIFF TO HARD, SLIGHTLY MOIST, BROWN, LOW TO MEDIUM PLASTICITY. SAND AND CLAY (SC—CL); SILTY, SCATTERED GRAVEL, MEDIUM DENSE/VERY STIFF, SLIGHTLY MOIST TO MOIST WITH DEPTH, RED—BROWN. RELATIVELY UNDISTURBED DRIVE SAMPLE; 2—INCH I.D. CALIFORNIA LINER SAMPLE. 42/12 DRIVE SAMPLE BLOW COUNT. INDICATES THAT 42 BLOWS OF A 140—POUND HAMMER FALLING 36 INCHES WERE REQUIRED TO DRIVE THE CALIFORNIA SAMPLER 12 INCHES. NOTES 1. THE EXPLORATORY BORINGS WERE DRILLED ON JANUARY 10, 2018 WITH A 4—INCH DIAMETER CONTINUOUS FLIGHT POWER AUGER. 2. THE LOCATIONS OF THE EXPLORATORY BORINGS WERE MEASURED APPROXIMATELY BY PACING FROM FEATURES SHOWN ON THE SITE PLAN PROVIDED. 3. THE ELEVATIONS OF THE EXPLORATORY BORINGS WERE MEASURED BY HAND LEVEL AND REFER TO BORING 1 AS ELEVATION 100', ASSUMED. 4. THE EXPLORATORY BORING 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 BORING LOGS REPRESENT THE APPROXIMATE BOUNDARIES BETWEEN MATERIAL TYPES AND THE TRANSITIONS MAY BE GRADUAL. 6. GROUNDWATER WAS NOT ENCOUNTERED IN THE BORINGS AT THE TIME OF DRILLING. 7. LABORATORY TEST RESULTS: WC = WATER CONTENT (%) (ASTM D 2216); DD = DRY DENSITY (pc f) (ASTM D 2216); —200= PERCENTAGE PASSING NO. 200 SIEVE (ASTM D 1140). 17-7-896 H-P5t- PMAR I LEGEND AND NOTES Fig. 3 1 CONSOLIDATION - SWELL n... nal ruulla .ppy -Ny b n. IL"'n;produeril....p n. 143, •1P0.1 1*4 Ip41ae worm, p Kwner #4 a.wcIalw, Me. i.P1 C .a.v uan Wag t&vTy 0-4N y in W*4. •M A71u 0-.'1.0. SAMPLE OF: Sandy Silty Clay FROM: Boring 1 ® 5' WC = 8.3 %, DD = 120 pcf EXPANSION UNDER CONSTANT PRESSURE UPON WETTING L 1 0 APPLIED PRESSURE - KSF 10 100 17-7-896 H-PAIKUMAR SWELL -CONSOLIDATION TEST RESULTS Fig. 4 CONSOLIDATION - SWELL —J J CONSOLIDATION 3 2 0 —1 —2 SAMPLE OF: Very Silty Clayey Sand FROM: Boring 1 ® 20' WC = 4.9 %, DD = 115 pcf ADDITIONAL COMPRESSION UNDER CONSTANT PRESSURE DUE TO WETTING 10 APPLIED PRESSURE — KSF 10 100 17-7-896 H-P%'KUMAR 10 100 SWELL -CONSOLIDATION TEST RESULTS ' Fig. 5 SAMPLE OF: Sandy Silty Clay FROM: Boring 2 © 5' WC 6.9 %, DD = 124 pcf I ........... EXPANSION UNDER CONSTANT PRESSURE UPON WETTING _......L__ _ _ . - -. ii 17 I - Thr.. het Feuer Fury .ny to m. seryl.. Wick. Tel. Pelting r part lew. nal be rproeueee, nett to uly .Wewthy ..FC., Pomo.* el e.ew - R..oetl.s. Pee- L... C er•b"" *.me.wn itie t �' eccardgete �lh L . __.. --_ - I{ 17-7-896 H-P%'KUMAR 10 100 SWELL -CONSOLIDATION TEST RESULTS ' Fig. 5 CONSOLIDATION - SWELL 1 0 —1 2 — 3 — 4 — 5 —6 17-7-896 H -P KUMAR SWELL -CONSOLIDATION TEST RESULTS Fig. 6 SAMPLE OF: Very Silty Clayey Sand FROM: Boring 2 r.,, 15' WC = 5.2 %, DD = 110 pcf _ T —r—.. �C ADDITIONAL COMPRESSION UNDER CONSTANT PRESSURE DUE TO WETTING ,t 11 shwa N.Inaw ppy may is IM asa,pr.a !nue. to (Woo saa t 046 nal M 661643636664. 66666.1 in I. tlmnmd !M •.M46 dpm.a.0 ml I tailor and /asocials.. Inc. Sall anwfidoliion !,slap padanned in accordance with iaf D-4345. ..._�_.._�«_ 1 0 APPLIED PRESSURE — KSF 10 10[ 17-7-896 H -P KUMAR SWELL -CONSOLIDATION TEST RESULTS Fig. 6 H-PKUMAR TABLE 1 SUMMARY OF LABORATORY TEST RESULTS Project No. 17-7-896 SAMPLE LOCATION NATURAL MOISTURE CONTENT (%I NATURAL DRY DENSITY (pc GRADATION PERCENT PASSING NO. 200 SIEVE ATTERBERG LIMITS UNCONFINED COMPRESSIVE STRENGTH (PSF) I SOIL TYPE BORING DEPTH (ft) GRAVEL (%) SAND (%) LIQUID LIMIT (%) PLASTIC INDEX (%) 1 5 8.3 120 r Sandy Silty Clay 10 7.2 120 71 Sandy Silty Clay 20 4.9 115 Very Silty Clayey Sand 25 7.4 123 65 Very Silty Sandy Clay 2 5 6.9 124 Sandy Silty Clay 10 5.6 115 61 Very Silty Sandy Clay 15 5.2 110 Very Silty Clayey Sand 25 12.0 119 79 Very Silty Sandy Clay