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HomeMy WebLinkAbout1.05 Exhibit E - Geotechnical Engineering Report 5020 County Road 154 Glenwood Springs, CO 81601 phone: (970) 945-7988 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 SUBDIVISION AMI’S ACRES CAMPGROUNDS 50235 US HIGHWAY 6 & 24 WEST OF GLENWOOD SPRINGS, COLORADO PROJECT NO. 25-7- 674.01 MARCH 6, 2026 PREPARED FOR: ANDREW SETTLE AMI’S ACRES CAMPGROUNDS 50235 US HIGHWAY 6&24 GLENWOOD SPRINGS, CO 81601 asettle@cava-capital.com Kumar & Associates, Inc.® Project No. 25-7-674.01 TABLE OF CONTENTS PURPOSE AND SCOPE OF STUDY ....................................................................................... - 1 - PROPOSED CONSTRUCTION ................................................................................................ - 1 - SITE CONDITIONS ................................................................................................................... - 1 - GEOLOGIC SETTING .............................................................................................................. - 1 - FIELD EXPLORATION ............................................................................................................ - 2 - SUBSURFACE CONDITIONS ................................................................................................. - 2 - GEOLOGIC ASSESSMENT...................................................................................................... - 2 - PRELIMINARY DESIGN RECOMMENDATIONS ................................................................ - 3 - FOUNDATIONS .................................................................................................................... - 3 - FOUNDATION AND RETAINING WALLS ....................................................................... - 3 - FLOOR SLABS ...................................................................................................................... - 4 - UNDERDRAIN SYSTEM ..................................................................................................... - 5 - SITE GRADING ..................................................................................................................... - 5 - SURFACE DRAINAGE ......................................................................................................... - 5 - LIMITATIONS ........................................................................................................................... - 6 - FIGURES 1 and 1A- LOCATION OF EXPLORATORY BORINGS FIGURE 2 - LOGS OF EXPLORATORY BORINGS FIGURE 3 - LEGEND AND NOTES FIGURE 4 - SWELL-CONSOLIDATION TEST RESULTS FIGURE 5 – GRADATION TEST RESULTS TABLE 1- SUMMARY OF LABORATORY TEST RESULTS Kumar & Associates, Inc.® Project No. 25-7-674.01 PURPOSE AND SCOPE OF STUDY This report presents the results of a preliminary geotechnical study for the proposed subdivision to be located at Ami’s Acres, 50235 US Highway 6 & 24, west of Glenwood Springs, Colorado. The project site is shown on Figure 1. The purpose of the study was to evaluate the geologic and subsurface conditions and their impact on the project and to develop preliminary recommendations for the foundation design. The study was conducted in accordance with our proposal for geotechnical engineering services to Andrew Settle, dated January 26, 2026. We previously performed a subsoil study for foundation design at the subject site and presented the findings in a report dated January 9, 2026, Project No. 25-7-674. 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 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 foundations. 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 subdivision will consist of an about 100 lot subdivision as shown on Figure 1. The development will consist of single family homes. Private driveways will access the building sites. We assume the residences will be typical of the area and be one to two stories. The development will be serviced with municipal water and sewer systems. If development plans change significantly from those described, we should be notified to re- evaluate the recommendations presented in this report. SITE CONDITIONS The proposed subdivision consists of about 26 acres located in the NWNE and SWNE quarters of Section 6, T6S, R89W of the 6th Principal Meridian. The terrain is moderately sloping generally down to the south-southwest. The elevation ranges from about 5,700 feet to about 5,830 feet in the proposed development area. Vegetation consists of native grass and weeds with scattered scrub oak. There is an existing RV campground in the proposed building area with electrical, water, and sewer hook-ups. GEOLOGIC SETTING The project site is underlain by the Pennsylvanian-age lower member of the Maroon Formation. The Maroon Formation consists of red sandstone with interlayered siltstones. Surficial deposits at the site consist of younger alluvial fan deposits made up of medium dense to dense silty sand and gravel with scattered cobbles and boulders. -2 - Kumar & Associates, Inc.® Project No. 25-7-674.01 FIELD EXPLORATION The field exploration for the project was conducted on February 3, 2026. Four 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 Kumar & Associates. Samples of the subsoils were taken with a 2-inch I.D. spoon sampler. The sampler was 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 of the subsoils. 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. Below a pavement section or about ½ to 5½ feet of gravelly sand and silt fill, the subsoils consist of medium dense to dense, silty sand and gravel. The silty sand and gravel transitioned to silty sand at a depth of about 18 feet in Boring 4. A 2½ foot thick layer of sandy silt and clay was encountered beneath the fill in Boring 3. Drilling in the medium dense granular soils with auger equipment was easy to difficult and practical auger drilling refusal was encountered in Boring 1 at a depth of 15½ feet. Laboratory testing performed on samples obtained from the borings included natural moisture content and density and finer than sand size gradation analyses. Results of a swell-consolidation testing performed on a relatively undisturbed drive sample from Boring 1, presented on Figure 4, indicate low compressibility under light loading and natural moisture conditions and moderate compressibility under increased loading after wetting. Results of gradation analyses performed on small diameter drive samples (minus 1½ inch fraction) of the natural coarse granular soils are shown on Figure 5. 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. GEOLOGIC ASSESSMENT Geologic conditions that would make the proposed development infeasible were not identified in the proposed building areas. Potential geologic hazards at the site are alluvial fan hazards (hydrocompressive soils), slopes greater than 30 percent, corrosive soils, and mudflow/debris flow. We understand that Tetra Tech has evaluated the potential mudflow/debris flow hazard and provided recommendations for mitigation of the hazard. Alluvial Fan Hazards (Hydrocompressive Soils): The hydrocompression potential of the soils was evaluated as part of this study. The soils exhibit low compressibility under light loading and natural moisture conditions and moderate compressibility under increased loading after wetting and the foundation recommendations presented below should adequately mitigate the hazard. -3 - Kumar & Associates, Inc.® Project No. 25-7-674.01 Slopes Greater Than 30 Percent: There are minor areas of slopes greater than 30 percent within the proposed development area. Most of these slopes are man-made and will be graded flatter than 2H:1V as part of the project grading. No signs of slope instability such as bulging, ground cracks, or seepage were observed within or adjacent to the proposed development area. The potential steep slope hazard will be mitigated provided the recommendations presented in the ‘Site Grading’ section below are followed. We have reviewed the proposed grading plan by EV Studio dated January 13, 2026, and it is our opinion that the proposed grading is feasible from a geotechnical perspective and will mitigate the potential steep slope hazard. Corrosive Soils: The alluvial fan soils are mildly corrosive to concrete. Concrete with Type I/II cement is typically used in the area and should be used for buried concrete at this site for corrosion protection. PRELIMINARY DESIGN RECOMMENDATIONS FOUNDATIONS Considering the subsurface conditions encountered in the exploratory borings and the nature of the proposed construction, we recommend the buildings 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 granular 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 up to around 1 inch and mainly from wetting the bearing soils. 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 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. 5)All existing fill, topsoil and any loose or disturbed soils should be removed and the footing bearing level extended down to the relatively dense 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 45 pcf for backfill consisting of -4 - Kumar & Associates, Inc.® Project No. 25-7-674.01 the on-site granular soils. Cantilevered retaining structures which are separate from the residences 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 35 pcf for backfill consisting of the on-site granular 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 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. Backfill should not contain organics, debris or rock larger than about 6 inches. The on-site granular soils can be used for backfilling foundation walls and retaining structures. Subsurface drainage recommendations are discussed in more detail in the "Underdrain System" section of this report. Imported [free-draining] granular wall backfill should contain less than 5% passing the No. 200 sieve and have a maximum size of 4 inches. 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 0.45. Passive pressure of compacted backfill against the sides of the footings can be calculated using an equivalent fluid unit weight of 375 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 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, are suitable to support lightly loaded slab-on-grade 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 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 -5 - Kumar & Associates, Inc.® Project No. 25-7-674.01 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 vegetation, topsoil and oversized rock. UNDERDRAIN SYSTEM Although free water was not encountered during our exploration, it has been our experience in mountainous areas 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 rigid PVC 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 ½% 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 1½ feet deep. SITE GRADING The risk of construction-induced slope instability at the site appears low provided the buildings are located as planned and cut and fill depths are limited. Cut depths for the building pads and driveway access should not exceed about 10 feet. Fills should be limited to about 10 feet deep, especially where they encroach steep downhill sloping areas. Structural fills should be compacted to at least 95% of the maximum standard Proctor density near optimum moisture content. Prior to fill placement, the subgrade should be carefully prepared by removing all vegetation and topsoil. The fill should be benched into the portions of the hillside exceeding 20% grade. The on- site soils excluding oversized rock and topsoil should be suitable for use in embankment fills. SURFACE DRAINAGE The following drainage precautions should be observed during construction and maintained at all times after the residences have 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. Free-draining wall backfill should be covered -6 - Kumar & Associates, Inc.® Project No. 25-7-674.01 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. PAVEMENT SECTION We understand asphalt pavement is proposed for the proposed roadways. Traffic loadings for the roadways were not provided and are assumed to be relatively light and consisting of mainly passenger vehicles and occasional delivery truck traffic and fire trucks. The subgrade soils encountered at the site are generally low plasticity sandy silt and clay to silty sandy gravel (A- 4(1)), which are considered a relatively poor to fair support for pavement sections. Imported fill may be needed for the roadway construction in soft subgrade areas. The import soil should be a sand and gravel soil with a minimum Hveem stabilometer ‘R’ value of 50. Based on our experience, an 18 kip EDLA of 20, a Regional Factor of 2.0 and a serviceability index of 2.0, we recommend the minimum pavement section thickness consist of 3 inches of asphalt on 8 inches of base course. The asphalt should be a batched hot mix, approved by the engineer and placed and compacted to the project specifications. The base course and subbase should meet CDOT Class 6 specifications. All base course, subbase and required subgrade fill should be compacted to at least 95% of the maximum standard Proctor density at a moisture content within 2% of optimum. Required fill to establish design subgrade level can consist of the on-site soils or suitable imported granular soils approved by the geotechnical engineer. Prior to fill placement the subgrade should be scarified to a depth of 8 inches, adjusted to near optimum moisture and compacted to at least 95% of standard Proctor density. In soft or wet areas, the subgrade may require drying or stabilization prior to fill placement. A geogrid and/or subexcavation and replacement with aggregate base soils may be needed for the stabilization. The subgrade should be proofrolled. Areas that deflect excessively should be corrected before placing pavement materials. The subgrade improvements and placement and compaction of base and asphalt materials should be monitored on a regular basis by a representative of the geotechnical engineer. Once traffic loadings are better known, we should review our pavement section recommendations. 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. Kumar & Associates Kumar & Associates Kumar & Associates Kumar & Associates Kumar & Associates Kumar & Associates TABLE 1 SUMMARY OF LABORATORY TEST RESULTS Project No. 25-7-674.01 SAMPLE LOCATION NATURAL MOISTURE CONTENT NATURAL DRY DENSITY GRADATION PERCENT PASSING NO. 200 SIEVE ATTERBERG LIMITS AASHTO SOIL CLASSIFICATION SOIL TYPE GRAVEL SAND LIQUID LIMIT PLASTIC INDEX BORING DEPTH (ft.) (%) (%) (%) (pcf) (%) (%) 1 2 1.9 101 22 Silty Sand and Gravel 9 3.3 112 36 Very Silty Sand and Gravel 2 2 3.8 104 45 Gravelly Sand and Silt 3 2 4.6 94 52 27 6 A-4(1) Slightly Gravelly Sandy Silt and Clay 9 3.6 114 37 Very Silty Sand and Gravel 4 2 2.9 104 32 Silty Sandy Gravel Fill 9 5.3 85 46 Silt and Sand 1* 9 1.1 128 28 Silty Sand and Gravel 14 2.4 115 Very Silty Gravelly Sand 19 2.6 131 41 Very Silty Gravelly Sand 2* 9 2.3 115 32 Silty Sand with Gravel 14 5.6 102 33 Silty Sand with Gravel *Boring drilled for previous study dated January 9, 2026, Project No. 25-7-674.