No preview available
HomeMy WebLinkAboutSoils Report 11.09.2020Kumar & Associates, Inc.® Geotechnical and Materials Engineers and Environmental Scientists An Employee Owned Company 5020 County Road 154 Glenwood Springs, CO 81601 phone: (970) 945-7988 fax: (970) 945-8454 email: kaglenwood@kumarusa.com 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 3, FIRST EAGLES POINT 40 EAGLE RIDGE DRIVE, BATTLEMENT MESA GARFIELD COUNTY, COLORADO PROJECT NO. 20-7-419 NOVEMBER 9, 2020 PREPARED FOR: RUSSELL CARTWRIGHT 35 WILLOWVIEW WAY PARACHUTE, COLORADO 81635 (russccart(x?gniail.cotu) 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- FOUNDATION AND RETAINING WALLS - 4 - FLOOR SLABS - 5 - UNDERDRAIN SYSTEM - 5 - SURFACE DRAINAGE - 6 - LIMITATIONS - 6 - FIGURE 1 - LOCATION OF EXPLORATORY BORING FIGURE 2 - LOG OF EXPLORATORY BORING TABLE 1- SUMMARY OF LABORATORY TEST RESULTS Kumar & Associates, Inc. ® Project No. 20-7.419 PURPOSE AND SCOPE OF STUDY This report presents the results of a subsoil study for a proposed residence to be located on Lot 2, First Eagles Point, 40 Eagle Ridge Drive, Battlement Mesa, 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 Russell Cartwright dated July 27, 2020. Hepworth-Pawlak Geotechnical, Inc. previously conducted a preliminary geotechnical study for development of the subdivision and presented the findings in a report dated November 21, 2003, Job No. 103 680. A field exploration program consisting of an exploratory boring was conducted to obtain information on general the subsurface conditions. Samples of the subsoils obtained during the field exploration were tested in the laboratory to determine their classification 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 residence will be a single -story wood frame structure over walkout basement with an attached garage at the main level. Ground floor 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. SITE CONDITIONS The lot was vacant at the time of our field exploration. The ground surface appeared to have undergone some minor grading probably during the subdivision infrastructure construction. The Kumar & Associates, Inc. ® Project No. 20-7-419 -2 - terrain is relatively flat with a moderately steep slope down to the southwest. Vegetation consisted of scattered grass and weeds. There are scattered basalt cobbles on the ground surface. FIELD EXPLORATION The field exploration for the project was conducted on August 6, 2020. One exploratory boring was drilled at the location shown on Figure 1 to evaluate the 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 Kumar & Associates. Samples of the subsoils were taken with 1'/a 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 foot of topsoil, consisted of relatively dense, silty to very silty sandy gravel and cobbles with boulders down to the depth drilled of 16 feet. The rocks are primarily basalt but, based on our experience in the area, may include some shale blocks. Laboratory testing performed on samples obtained from the boring included natural moisture content and percent finer than sand grain size gradation analyses. The soils were too rocky to obtain undisturbed samples for swell -consolidation testing. The laboratory testing is summarized in Table 1. No groundwater was encountered in the boring at the time of drilling and the subsoils were slightly moist. Kumar & Associates, Inc. ® Project No. 20-7-419 -3 FOUNDATION BEARING CONDITIONS The soils encountered at the site possess low to moderate bearing capacity and should be suitable for support of lightly loaded spread footings with relatively low risk of foundation movement. Some of the shallow fine-grained soils encountered in the First Eagles Point development possess an expansion potential when wetted and, if encountered, will likely need to be removed below footing (and floor slab) areas. DESIGN RECOMMENDATIONS FOUNDATIONS Considering the subsurface conditions encountered in the exploratory boring and the nature of the proposed construction, we recommend the building be founded with spread footings bearing on the natural granular 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. Based on experience, we expect settlement of footings designed and constructed as discussed in this section will be about 1 inch or less. 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 well reinforced top and bottom to span local anomalies such as by assuming an unsupported length of at least 12 feet. Foundation walls acting as retaining structures should also be designed to resist lateral earth pressures as discussed in the "Foundation and Retaining Walls" section of this report. Kumar & Associates, Inc. ® Project No. 20-7-419 -4- 5) All existing fill, topsoil, fine grained soils and any loose disturbed soils should be removed and the footing bearing level extended down to the natural granular soils. The exposed soils in footing area 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. 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 50 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. The backfill should not contain topsoil or oversized (plus 6 -inch) rocks. 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 a moisture content near optimum. Backfill in pavement and 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 Kumar & Associates, Inc. ® Project No. 20-7-419 -5 - the side of the footing. Resistance to sliding at the bottoms of the footings can be calculated based on a coefficient of friction of 0.45. Passive pressure of compacted backfill against the sides of the footings can be calculated using an equivalent fluid unit weight of 350 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 a granular material, such as the on-site soils, compacted to at least 95% of the maximum standard Proctor density at a moisture content near optimum. FLOOR SLABS The natural on-site granular soils, exclusive of topsoil, should be suitable to support lightly loaded slab -on -grade construction. The exposed subgrade in slab areas should be evaluated for expansion potential at the time of construction. If potentially expansive soils are encountered, these soils may need to be removed and replaced with compacted granular soils. 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- site granular soils devoid of topsoil and oversized (plus 6 -inch) rocks. UNDERDRAIN SYSTEM Although groundwater 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 Kumar & Associates, Inc. ® Project No. 20-7.419 -6 - seasonal runoff. Frozen ground during spring runoff can also create a perched condition. 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 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 and be covered by filter fabric such as Mirafi 140 or 160N. 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 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, such as sod, and lawn sprinkler heads should be located at least 5 feet from foundation walls. 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. Kumar & Associates, Inc. ® Project No. 20-7-419 7 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 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, Kumar & Associates, Inc. James H. Parsons, E.I. Reviewed by: David A. Young, P.E. JHP/kac Kumar & Associates, Inc. Project No. 20-7-419 30 0 30 60 APPROXIMATE SCALE -FEET Open Space/ Common Area & Utility Basement 20-7-419 Kumar & Associates LOCATION OF EXPLORATORY BORING Fig. 1 ►-- w w 0- 0 - Lai 0 5 10 15 20 BORING 1 EL. 100' ti 24/6, 50/5 20/12 WC=10.2 - 200=58 58/6 WC=4.2 - 200=20 50/2 50/1 LEGEND "i :47 TOPSOIL; ORGANIC SILTY, SAND AND GRAVEL WITH COBBLES, DRY TO SLIGHTLY MOIST, TAN, ROOTS. GRAVEL AND COBBLES (GM); CONSISTING PRIMARILY OF BASALT ROCKS TO BOULDER SIZE, SANDY, SILTY TO VERY SILTY, MEDIUM DENSE TO DENSE, SLIGHTLY MOIST, TAN. DRIVE SAMPLE, 2 -INCH I.D. CALIFORNIA LINER SAMPLE. 11 DRIVE SAMPLE, 1 3/8 -INCH I.D. SPLIT SPOON STANDARD PENETRATION TEST NOTES 1. THE EXPLORATORY BORING WAS DRILLED ON AUGUST 6, 2020 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); -200 = PERCENTAGE PASSING NO. 200 SIEVE (ASTM D 1140). 20-7-419 Kumar & Associates LOG OF EXPLORATORY BORING Fig. 2 Kumar & Associates, Inc. Geotechnical and Materials Engineers and Environmental Scientists TABLE 1 SUMMARY OF LABORATORY TEST RESULTS SAMPLE LOCATION NATURAL MOISTURE CONTENT (%) NATURAL DRY DENSITYPASSING (ncf) GRADATION PERCENT NO. 200 SIEVE ATTERBERG LIMITS UNCONFINED COMPRESSIVE STRENGTH (psf) SOIL TYPE Boring DEPTH (ft) GRAVEL (°�°) SAND (°�°) LIQUID LIMIT (%) PLASTIC INDEX (%) 1 4 10.2 58 Very Gravelly Sandy Silt 7 4.2 20 Silty Sandy Gravel