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HomeMy WebLinkAboutSoils Report 02.07.2018-P�KUMAR Geotechnical Engineering 1 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 14, BLOCK 2, BATTLEMENT CREEK VILLAGE BATTLEMENT MESA 502 BATTLEMENT CREEK TRAIL GARFIELD COUNTY, COLORADO PROJECT NO. 18-7-110 FEBRUARY 7, 2018 PREPARED FOR: KEN PETERSON 1377 EAST 17TH STREET RIFLE, COLORADO 81650 (iustineiabsl @ gmail.com) RECEIVED COMMUNITY DEVELOPMENT TABLE OF CONTENTS PURPOSE AND SCOPE OF STUDY - 1 - PROPOSED CONSTRUCTION - 1 - SITE CONDITIONS - 1 - FIELD EXPLORATION - 2 - SUBSURFACE CONDITIONS - 2 - FOUNDATION BEARING CONDITIONS - 3 - DESIGN RECOMMENDATIONS - 3 - FOUNDATIONS - 3 - FLOOR SLABS - 4 - UNDERDRAIN SYSTEM - 5 - SURFACE DRAINAGE - 5 - LIMITATIONS - 6 - 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 H-P*KUMAR Prniar4 Nn 1 R.7.1 1 !1 PURPOSE AND SCOPE OF STUDY This report presents the results of a subsoil study for a proposed residence to be located on Lot 14, Block 2, Battlement Creek Village, Battlement Mesa, 502 Battlement Creek Trail, 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 accordance with our agreement for geotechnical engineering services to Ken Peterson dated January 12, 2018. An exploratory boring was drilled 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 Building plans for the lot had not been determined at the time of our study. In general, the residence will be one to two story wood -frame construction with an attached garage located roughly in the middle of the lot shown on Figure 1. Ground floors could be structural over crawlspace or slab -on -grade. Grading for the structure is assumed to be relatively minor with cut depths between about 2 to 6 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. SITE CONDITIONS The site was vacant and vegetated with grass and weeds with scattered sage brush at the time of our study. The ground surface is relatively flat with a gentle to strong slope down to the H-PKUMAR Project No. 18-7-110 -2 - northeast. Elevation difference across the proposed residence area is estimated at up to about 5 feet. Some of the nearby lots are vacant. FIELD EXPLORATION The field exploration for the project was conducted on January 16, 2018. One exploratory boring was drilled at the location shown on Figure 1 to evaluate the general subsurface conditions. The boring was advanced with 4 -inch diameter continuous flight augers powered by a truck -mounted CME -45B drill rig. The boring was logged by a representative of H-P/Kumar. Samples of the subsoils were taken with 1% inch and 2 -inch I.D. spoon samplers. The samplers were 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 subsoils. 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. The subsoils encountered, below about 1/2 foot of topsoil, consist of stiff, sandy silt to a depth of about 5 feet underlain by relatively dense, basalt gravel and cobbles in a very stiff, calcareous sandy silt matrix. The basalt gravel and cobble soils probably contain boulders and extended down to the boring depth of 121 feet where practical auger drilling refusal was encountered in the deposit. Laboratory testing performed on samples obtained from the boring included natural moisture content and dry density, and finer than sand size gradation analyses. Results of swell - consolidation testing performed on relatively undisturbed drive samples of the soils are presented on Figures 3 and 4. The test results indicate low to moderate compressibility under conditions of loading and wetting. The sandy silt and sandy silt matrix samples showed a low collapse potential (settlement under constant load) when wetted and moderate compressibility under additional loading after wetting. The laboratory testing is summarized in Table 1. H-P%KUMAR Project No. 18-7-110 3 No free water was encountered in the boring at the time of drilling and the subsoils were slightly moist. FOUNDATION BEARING CONDITIONS Based on our experience in the area, the sandy silt soils expected to be encountered at shallow cut depths tend to compress when wetted, and the underlying basalt gravel and cobble soils typically have relatively low compressibility. Lightly loaded spread footings bearing on these soils can be used for foundation support of the residence with some risk of movement and building distress, primarily if the bearing soils become wetted. Sources of wetting include excessive irrigation near the foundation, poor surface drainage adjacent to foundations and utility line leaks. The compressibility potential of the bearing soils should be further evaluated at the time of construction and the need for sub -excavation of collapsible soils for mitigation purposes. A deep foundation system to extend the bearing down into the dense, coarse granular soils could be used to provide a low risk of building settlement and distress. Presented below are recommendations for a spread footing foundation bearing on the natural soils. If recommendations for a deep foundation system are desired, we should be contacted. 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 the upper natural fine-grained sandy silt soils or basalt gravel and cobble soils with some risk of movement. Precautions should be taken to prevent wetting of the bearing soils. 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 1,500 psf. Footings placed entirely on the underlying basalt gravel and cobble soils can be designed for an allowable bearing pressure of 2,500 psf. Based on experience, we expect initial settlement of H-P%KUMAR PrniArt Nn 1A-7-1111 -4 - footings designed and constructed as discussed in this section will be about 1 inch or less. Additional movement on the order of 'h to 1 inch could occur if the bearing soils were to become wetted. 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 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 50 pcf. 5) The topsoil and any loose disturbed soils should be removed and the footing bearing level extended down to the undisturbed natural soils. The exposed soils in footing areas should then be moistened and compacted. 6) A representative of the geotechnical engineer should 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 movement if the subgrade were to become wetted as discussed above. Removal and replacement of a depth (typically 2 feet) of the upper natural silt soils below the slab in a moistened and compacted condition could be done to reduce the risk of slab movement. The compressibility potential of the slab subgrade soils and need for sub -excavation and replacement should be further evaluated at the time of 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 H-P-*KUMAR Project No 1A-7-1 1 0 -5 - 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 sand and gravel road base should be placed beneath floor slabs for support and 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 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 soils devoid of topsoil and oversized (plus 6 inch) rocks. UNDERDRAIN SYSTEM If the ground -level finished floor elevation of the residence is at or above the surrounding grade, a foundation drain system is not required. 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 also create a perched condition. An underdrain system is not recommended around shallow crawlspace area to help limit the potential for wetting below the shallow footings. We recommend below -grade construction, such as retaining walls 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 least 1 foot below lowest adjacent finish grade and sloped at a minimum 1% to a suitable gravity outlet or sump. 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 feet deep. SURFACE DRAINAGE Providing proper grading and drainage around the building will be critical to limiting subsurface wetting and adequate performance of the structure. The following drainage precautions should be observed during construction and maintained at all times after the residence has been completed: H-P%KUMAR PrniRnt Nn 1IL7-11n -6- 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. 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. 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 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 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 H-P%KUMAR Prniart Nn 114-7-1111 -7 - 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. Respectfully Submitted, H -P - HCl! MAR Steven L. Pawlak, P.E. Reviewed by: Daniel Hardin SLP/kac H-PkKUMAR Project No. 18-7-110 7-,-- - - _ _ 4.4_ ,----- l 11 1__ rite LOT 13 ! / \ rc,pF I r \ ...,...--(( \ BORING 1 t\\\\ SLOT 14 \\\ t E1.0 t \ \ \ op\- V\ • LOT 12 \ \ _- \\\ �I- t1 \ - i ■ \ \ 9q 30 0 3[] &u APPROXIMATE SCALE -FEET 18-7-110 r H- 3 SKU MAR LOT 15 LOCATION OF EXPLORATORY BORING Fig. 1 0 --5 — 10 15 BORING 1 19/12 WC=3.4 DD=97 29/12 WC=12.4 DD=82 LEGEND 1 TOPSOIL; ORGANIC SANDY SILT, FIRM, BROWN. SILT (ML); SANDY, STIFF, SLIGHTLY MOIST, LIGHT BROWN LOESS. GRAVEL (GM -GC); SILTY, SANDY, COBBLES AND PROBABLE BOULDERS, MEDIUM DENSE TO DENSE, SLIGHTLY MOIST, GRAY -BROWN, BASALT ROCK, CALCAREOUS. DRIVE SAMPLE, 2 -INCH I.D. CALIFORNIA LINER SAMPLE. DRIVE SAMPLE, 1 3/8 -INCH I.D. SPLIT SPOON STANDARD 50/3 PENETRATION TEST. 19/12 DRIVE SAMPLE BLOW COUNT. INDICATES THAT 19 BLOWS OF A 140 -FOUND HAMMER FALLING 30 INCHES WERE REQUIRED TO DRIVE THE SAMPLER 12 INCHES. t PRACTICAL AUGER REFUSAL. NOTES 1. THE EXPLORATORY BORING WAS DRILLED ON JANUARY 16, 2018 WITH A 4 -INCH DIAMETER CONTINUOUS FLIGHT POWER AUGER. 2. THE LOCATION OF THE EXPLORATORY BORING WAS MEASURED APPROXIMATELY BY PACING FROM FEATURES SHOWN ON THE SITE PLAN PROVIDED. 3. THE ELEVATION OF THE EXPLORATORY BORING WAS NOT MEASURED AND THE LOG OF THE EXPLORATORY BORING IS PLOTTED TO DEPTH. 4. THE EXPLORATORY BORING LOCATION SHOULD BE CONSIDERED ACCURATE ONLY TO THE DEGREE IMPLIED BY THE METHOD USED. 5. THE LINES BETWEEN MATERIALS SHOWN ON THE EXPLORATORY BORING LOG REPRESENT THE APPROXIMATE BOUNDARIES BETWEEN MATERIAL TYPES AND THE TRANSITIONS MAY BE GRADUAL. 6. GROUNDWATER WAS NOT ENCOUNTERED IN THE BORING AT THE TIME OF DRILLING. 7. LABORATORY TEST RESULTS: WC = WATER CONTENT (%) (ASTM D 2216); DD = DRY DENSITY (pcf) (ASTM D 2216). 18-7-110 Kumar & Associates LOG OF EXPLORATORY BORING Fig. 2 •C CONSOLIDATION - SWELL 1 —1 — 2 — 3 — 4 — 5 — 6 these tell Mulls oppy nny le the— eaeyue 1411.ea. TM lee newt alien nal be eeprodi ted. c.o.! In kn. Anew the .ellen eppvle! of N..ncd end Mien Wes, it, Seen Cwuecderen et/fenced In accordance .8A ATT/4 18-7-110 SAMPLE OF: Sandy Silt FROM: Boring 1 ® 2.5' WC = 3.4 %, DD = 97 pcf ADDITIONAL COMPRESSION UNDER CONSTANT PRESSURE DUE TO WETTING 1.0 APPLIED PRESSURE - 1SSF 10 1 O H-P-KLJMVIAR SWELL -CONSOLIDATION TEST RESULTS Fig. 3 CONSOLIDATION - SWELL -10 SAMPLE OF: Calcareous Sandy Silt Matrix FROM: Boring 1 ® 5' WC = 12.4 %, DD = 82 pcf 111.1. 1111 .ntdo op* o.p In Ne lompl.. IO IM. 100 1.s/r1 e.Krl .hyl .el W eeproy.Mdk btlrt i. Wit r4.1.1 IM .rll}ae epprpl01 01 Name, anti Mw[1oIM No. S4.0 C.n14WW:on Lea Snip fc.lamtar In aCOI0.140 .11h FS1Y o—a.ls. ADDITIONAL COMPRESSION UNDER CONSTANT PRESSURE DUE TO WETTING 18-7-110 1.0 APPLIED PRESSURE - KSF HI -P-• KUMAR 10 100 SWELL -CONSOLIDATION TEST RESULTS Fig. 4 H-PKUMAR TABLE 1 SUMMARY OF LABORATORY TEST RESULTS Project No. 18-7-110 SAMPLE LOCATION NATURAL NATURAL PERCENT UNCONFINED GRADATION ATTERBERG LIMITS MOISTURE DRY GRAVEL SAND PASSING LIQUID PLASTIC COMPRESSIVE BORING DEPTH CONTENT DENSITY °�°� NO. LIMIT INDEX STRENGTH ft % Pc 1 (%1 % P SIEVESF) 1 2' 3.4 97 5 12.4 82 SOIL TYPE Sandy Silt Calcareous Sandy Silt Matrix