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Home My WebLink About18-7-289 (05-22-18) Exc Obs signed.pdf H-P 1 KU mAR5020 County Road 154 Glenwood Springs, CO 81601 Geotechnical Engineering I Engineering Geology Phone: (970)945-7988 Materials Testing I Environmental Fax: (970)945-8454 Email: hpkglenwood@kumarusa.com Office Locations: Denver(HQ), Parker, Colorado Springs, Fort Collins, Glenwood Springs, Summit County, Colorado May 22, 2018 Tina and David Wilson 2609 Davos Trail Vail, Colorado 81657 tinawilsonvail@gmail.com Project No. 18-7-289 Subject: Observation of Excavation, Proposed Additions to Residence, Lot 11, Filing 23, Vail Valley, 1945 Sunburst, Vail, Colorado Dear Mrs. and Mr. Wilson: As requested, a representative of H-P/Kumar observed the excavation at the subject site on May 16, 2018 to evaluate the soils exposed for foundation support. The findings of our observations and recommendations are presented in this report. The services were performed in accordance with our agreement for professional engineering services to you, dated April 23, 2016. Building additions are planned on the northwest and northeast sides of the residence. The northwest addition will be new'living area with a slab-on-grade floor. The northeast addition will be new deck area. The additions have been designed to be supported on spread footings using an allowable soil bearing pressure of 2,000 psf based on a previous subsoil study at the site by Chen-Northern, Inc. dated September 29,1993, Job No. 4 257 93. We have been provided a copy of that report. The existing residence is apparently founded on shallow spread footings with no signs of excessive settlement and distress reported. At the time of our site visit, the foundation excavations were essentially complete and had been cut in three levels from about 4 to 8 feet below the adjacent ground surface. The steps in grade between the excavation levels were about 21/2 to 4 feet. The excavation subgrade was at the same elevation as the existing residence spread footing bearing elevation. The soils exposed in the bottom of the excavations consisted of medium dense, silty clayey sand and gravel with cobbles. The results of a gradation analysis performed on a sample of the granular soils (minus 3 inch Tina and David Wilson May 22, 2018 Page 2 fraction) obtained from the site are presented on Figure 1. No free water was encountered in the excavation and the soils were generally moist. Considering the conditions exposed in the excavations and the nature of the proposed construction, spread footings placed on the undisturbed natural granular soil designed for an allowable bearing pressure of 2,000 psf can be used for support of the proposed additions. There could be some differential settlement with respect to the existing structure which should be considered in the design. Footings should be a minimum width of 16 inches for continuous walls and 2 feet for columns. Any existing fill and all loose disturbed soils in footing areas should be removed and the bearing level extended down to the undisturbed natural granular soils, and the subgrade compacted. Exterior footings should be provided with adequate soil cover above their bearing elevations for frost protection. 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 45 pcf for on-site soil (excluding debris, topsoil and plus 6-inch size rocks) as backfill. A perimeter foundation drain should be provided to prevent temporary buildup of hydrostatic pressure behind the foundation walls and prevent wetting of the lower level. Structural fill placed within floor slab areas can consist of the on-site sand and gravel soils compacted to at least 95% of standard Proctor density (SPD) at a moisture content near optimum. Backfill placed around the structure should be compacted to at least 90% SPD (95% in pavement areas) and the surface graded to prevent ponding within at least 10 feet of the building. Landscape that requires regular heavy irrigation, such as sod, and lawn sprinkler heads should not be located within 5 feet of the foundation. The recommendations submitted in this letter are based on our observation of the soils exposed within the foundation excavations and do not include subsurface exploration to evaluate the subsurface conditions within the loaded depth of foundation influence. This study is based on the assumption that soils beneath the footings have equal or better support than those exposed. The risk of foundation movement may be greater than indicated in this report because of possible variations in the subsurface conditions. In order to reveal the nature and extent of variations in the subsurface conditions below the excavations, drilling would be required. It is possible the H-Pk'KUMAR Project No. 18-7-289 Tina and David Wilson May 22, 2018 Page 3 data obtained by subsurface exploration could change the recommendations contained in this letter. 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. If you have any questions or need further assistance, please call our office. Sincerely, t `ik ii .o 1.-; f a ./ iii- .74 David A. Young, l 32`216 1. r, .Z3 j DAY/kac �°+to ONAL � + attachment Figure 1, Gradation Test Resiilts cc: Evans Chaffee Construction—Mark Jones (mjones@evanschaffee.com) H-PWUMAR Project No. 18-7-289 HYDROMETER ANALYSIS SIEVE ANALYSIS TIME READINGS U.S. STANDARD SERIES CLEAR SQUARE OPENINGS 24 HRS 7 MRS 10a 45 MIN 15 MIN 60MIN 19MIN 4MIN 1MIN a 00 #100 E 0#40#30 16 #10 8 4 3 8" 3 4" 1 1/2" " "6" 8"0 Ammo _- i 90 -a ==�� 10 60 _� _- I ___1____ 20 . • 70 MIIIII. -� 30 60 us E'. �� I 40 50 z IOWI 50 ti -1111140 I 60 ti a -_®__ ES a 30 1 I I 70 I I 20 I I T 1 80 10 I - I 90 0 -_� .001 .002 .005 .009 .019 .037 .075 .150 .300 I .600 1.18 12.36 4.75 9.5 19 38.1 76.2 127 200 00 I DIAMETER OF PARTICLES IN MILLIMETERS 152 CLAY TO SILT SAND GRAVEL - FINE ' MEDIUM COARSE FINE COARSE COBBLES • • GRAVEL 50 % - SAND 31 •% SILT AND CLAY 19 LIQUID LIMIT PLASTICITY INDEX SAMPLE OF: Silty Cloyey Sand and Gravel FROM: Bottom of North East addition area • s' EglE i j SThese test results apply only to the samples which were tested. The d testing report shall not be reproduced, except in full, without the written ori approval of Kumar & Associates, Inc. „q Sieve analysis testing Is performed in accordance with ASTM D422, ASTM C136 e 6 and/or ASTM D1140. "g 18-7-289 H-P- KUii#1AR GRADATION TEST RESULTS Fig. 1