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HomeMy WebLinkAboutGeotechnical Engineering Investigation Report 01.24.2025rNa■ GivZS�' Ckbl( GEOTECHNICAL ENGINEERING INVESTIGATION SWEETWATER RANCH GUEST CABINS 4894 SWEETWATER ROAD GARFIELD COUNTY, COLORADO gak Prepared for: Beck Building Company P.O. Box 4030 Vail, CO 81658 CTLIT Project No. GS06935.000-125-R3 January 24, 2025 CTL Thom son Inc. Denver, Fort Collins, Colorado Springs, Glenwood Springs, Pueblo, Summit County — Colorado Cheyenne, Wyoming and Bozeman, Montana SCOPE CTLIThompson, Inc. (CTLIT) has completed a geotechnical engineering investigation regarding the guest cabins proposed at Sweetwater Ranch in Garfield County, Colorado. We conducted this investigation to evaluate subsurface conditions at the site and provide geotech- nical engineering recommendations for the planned construction. The scope of our investigation was set forth in our Proposal No. GS 24-0170-CM1. Our report was prepared from data developed from our field exploration, laboratory test- ing, engineering analysis, and our experience with similar conditions. This report includes a de- scription of the subsurface conditions found in our exploratory pits and provides geotechnical engineering recommendations for design and construction of the foundation, floor systems, be- low -grade walls, subsurface drainage, and details influenced by the subsoils. Recommendations in this report were developed based on our understanding of the currently planned construction. We should be provided with architectural plans, as they are further developed, so that we can provide geotechnical/geo-structural engineering input. PROPERTY DESCRIPTION The Sweetwater Ranch property is located west of the intersection of Sweetwater Road (County Road 40) and Sheep Creek Road (Forest Road 8450) in Eagle County, Colorado. The road intersection is about 1,000 feet northeast of the confluence of Sweetwater Creek and the East Fork of Sheep Creek. A property boundary map is included as Figure 1. The property is comprised of an east parcel of approximately 732 acres in Eagle County and a west parcel of about 1,953 acres in Garfield County. Sweetwater Creek flows to the south along the east property boundary. Mason Creek and Morris Creek, which are tributaries to Sweetwater Creek, flow down to the east in the north and south parts of the property, respec- tively. The HMS Relocated Ditch trends south across the property on the west side of the county line. The property is generally comprised of a hummocky terrace that slopes down to the southeast. Steep slopes drop down from higher elevations adjacent to the property boundary at the west and south. The creek channels are incised in the terrace terrain. The east edge of the property is on the valley floor of the Sweetwater Creek drainage. Several reservoirs and ponds BECK BUILDING COMPANY Page 1 of 16 SWEETWATER RANCH - GUEST CABINS CTLIT PROJECT NO. GS06935.000-125-R3 U Looking southwest at Guest Cabin 3 site View northwest across Guest Cabin 4 site PROPOSED CONSTRUCTION CTLIT was provided with schematic design drawings for the Guest Cabins 2 and 4 by Centre Sky Architecture, LTD (dated December 13, 2024). The guest cabins are planned as BECK BUILDING COMPANY Page 3 of 16 SWEETWATER RANCH - GUEST CABINS CTLIT PROJECT NO. GS06935.000-125-R3 SUBSURFACE CONDITIONS Subsurface conditions at the planned locations of Guest Cabins 2, 3, and 4 were investi- gated by directing excavation of six exploratory pits at the approximate locations shown on Fig- ures 3 through 6. GC2-A and GC2-B were excavated for Guest Cabin 2, GC3-A and GC-B, were excavated for Guest Cabin 3, and GC4-A and GC4-B were excavated for Guest Cabin 4. The pits were excavated with a trackhoe on November 18, 2025. Exploratory excavation opera- tions were directed by our engineer, who logged subsurface conditions encountered and ob- tained samples of the subsoils. Graphic logs of subsurface conditions found in our exploratory pits are shown on Figures 7 and 8. Photographs of the exploratory pits and excavated materials are attached as Appendix A. Subsurface conditions encountered in our exploratory pit, GC2-A, for Guest Cabin 2 consisted of about 6 inches of topsoil, 5.5 feet of sandy clay, and 2.5 feet of weathered sand- stone, underlain by competent sandstone. The hardness of the sandstone made exploratory excavation deeper than 9 feet not practical. GC2-13 exposed 6 inches of topsoil and 2.5 feet of sandy clay, underlain by clayey gravel and sandy clay to the total excavated depth of 10 feet. Subsoils observed in our exploratory pit, GC3-A, for Guest Cabin 3 consisted of about 1 foot of topsoil over sandy clay and clayey gravel to the total excavated depth of 12 feet. GC3-B exposed 1 foot of topsoil, 6 feet of clayey gravel and sandy clay, and 3 feet of weathered sand- stone, underlain by competent sandstone. The hardness of the sandstone made exploratory excavation deeper than 10.5 feet not practical. The subsoils found in our exploratory pit, GC4-A, for Guest Cabin 4 consisted of about 6 inches of topsoil and 1 foot of sandy clay, underlain by clayey gravel and sandy clay to the total excavated depth of 12 feet. Subsurface conditions in GC4-B were 6 inches of topsoil and 7.5 feet of clayey gravel and sandy clay, underlain by competent sandstone. The hardness of the sandstone made exploratory excavation deeper than 8.5 feet not practical. Groundwater was not encountered in our exploratory pits at the time of our subsurface investigation. The pits were backfilled immediately after exploratory excavation operations were completed. BECK BUILDING COMPANY Page 5 of 16 SWEETWATER RANCH - GUEST CABINS CTLIT PROJECT NO. GS06935.000-125-R3 Subexcavation and Structural Fill The overburden soils at this site are relatively heterogeneous. Furthermore, the soils have not been subject to geologic loads and have potential for consolidation when wetted under building loads. We judge the use of footings and slabs -on -grade is reasonable, provided poten- tial for differential building movement is mitigated. To create more uniform support conditions and reduce the potential for differential movement of foundations for the building, we recommend subexcavation of the soils below the bottoms of footings and floor slabs to a depth at least 3 feet. The sub -excavated areas should extend laterally at least 1 foot beyond the edges of footings and slabs. The excavated soils should be replaced with densely -compacted, structural fill. The excavated soils can be reused as structural fill, provided they are screened to re- move rocks larger than 4 inches in diameter, organics, and debris. Import soil needed for struc- tural fill should consist of a clayey sand or gravel with a maximum rock size of 4 inches and 20 to 40 percent silt and clay sized material. A sample of potential import soil for structural fill should be submitted to CTLIT for approval prior to the hauling to the site. Structural fill should be placed in loose lifts of 8 inches thick or less, moisture - conditioned to within 2 percent of optimum moisture content and compacted to at least 98 per- cent of standard Proctor (ASTM D 698) maximum dry density. Moisture content and density of structural fill should be checked by a representative of CTLIT during placement. Observation of the compaction procedure is necessary. Foundation Wall Backfill Proper placement and compaction of foundation backfill is important to reduce infiltration of surface water and settlement from consolidation of backfill soils. This is especially important for backfill areas that will support exterior concrete flatwork, such as patios, walkways, and driveways. The excavated soils can be reused as backfill, provided they are screened to remove or- ganics, debris, and rocks larger than 6 inches in diameter. Backfill should be placed in loose lifts BECK BUILDING COMPANY Page 7 of 16 SW EETWATER RANCH — GUEST CABINS CTLIT PROJECT NO. GS06935.000-125-R3 BUILDING FOUNDATIONS The overburden soils at this site are relatively heterogeneous. Furthermore, the soils have not been subject to geologic loads and have potential for consolidation when wetted under building loads. We judge the use of footing foundations is reasonable for Guest Cabins 2, 3 and 4, provided potential for differential building movement is mitigated. To create more uniform support conditions and reduce the potential for differential movement of foundations for the buildings, we recommend subexcavation of the soils below the bottoms of footings to a depth at least 3 feet. The sub -excavated areas should extend laterally at least 1 foot beyond the edges of the building footprints. The excavated soils should be re- placed with densely -compacted, structural fill in accordance with recommendations in the Subexcavation and Structural Fill section. Recommended design and construction criteria for footings are below. These criteria were developed based on our analysis of field and laboratory data, as well as our engineering experience. Footings Footings should be supported by densely compacted, structural fill that is at least 3 feet thick. The structural fill should be in accordance with recommendations in the Subexcavation and Structural Fill section. 2. Footings on densely compacted, structural fill can be designed for a maximum net allowable soil bearing pressure of 3,000 psf. The weight of backfill soils above the footings can be neglected for bearing pressure calculation. A 1,000 psf increase in this bearing pressure is acceptable when using the alternative load combination of IBC 2015, Section 1605.3.2 that include wind and earthquake load. 3. A friction factor of 0.35 can be used to calculate resistance to sliding between concrete footings and the structural fill. 4. Continuous wall footings should have a minimum width of at least 18 inches. Foundations for isolated columns should have minimum dimensions of 30 inches by 30 inches. Larger sizes may be required, depending upon foundation loads. 5. Grade beams and foundation walls should be well -reinforced. We recommend re- inforcement sufficient to span an unsupported distance of at least 12 feet. BECK BUILDING COMPANY Page 9 of 16 SWEETWATER RANCH - GUEST CABINS CTLIT PROJECT NO. GS06935.000-125-R3 of floor coverings and building to moisture. A properly installed vaper retarder (10 mil minimum) is more beneficial below concrete slab -on -grade floors where floor coverings will be sensitive to moisture. The vapor barrier/retarder is most effec- tive when concrete is placed directly on top of it. A sand or gravel leveling course should not be placed between the vapor barrier/retarder and the floor slab. CRAWL SPACE CONSTRUCTION The schematic design drawings indicate that crawl space areas may be constructed be- low parts of the main -level floors in the guest cabins. The required crawl space height depends on the materials used to construct the floor system above the crawl space. Building codes nor- mally require a clear space of at least 18 inches between exposed earth and untreated wood components of the structural floor. Utility connections, including water, gas, air duct, and exhaust stack connections to ap- pliances on structural floors should be capable of absorbing some deflection of the floor. Plumb- ing that passes through the floor should ideally be hung from the underside of the structural floor and not laid on the bottom of the excavation. Control of humidity in crawl spaces is important for indoor air quality and performance of wood floor systems. We believe the best current practice to control humidity involves the use of a vapor retarder or vapor barrier (10 mil minimum) placed on the soils below accessible subfloor areas. The vapor retarder/barrier should be sealed at joints and attached to concrete foundation elements. It may be appropriate to install a ventilation system that is controlled by a humidistat. FOUNDATION WALLS Foundation walls that extend below -grade should be designed for lateral earth pressures where backfill is not present to about the same extent on both sides of the wall, such as in basements and crawl spaces. Many factors affect the values of the design lateral earth pres- sure. These factors include, but are not limited to, the type, compaction, slope, and drainage of the backfill, and the rigidity of the wall against rotation and deflection. For a very rigid wall where negligible or very little deflection will occur, an "at -rest" lateral earth pressure should be used in design. For walls that can deflect or rotate 0.5 to 1 percent of wall height (depending upon the backfill types), design for a lower "active" lateral earth pressure BECK BUILDING COMPANY Page 11 of 16 SWEETWATER RANCH — GUEST CABINS CTLIT PROJECT NO. GS06935.000-125-R3 below the slabs, the gravel layer should be below the barrier. The pipes should convey water to perimeter drain collector pipes. Water collected should be discharged via positive gravity out- lets. The foundation wall drain concepts are shown on Figures 11 and 12. SURFACE DRAINAGE Surface drainage is critical to the performance of foundations, floor slabs, and concrete flatwork. Surface drainage should be designed to provide rapid runoff of surface water away from the residence. Proper surface drainage and irrigation practices can help control the amount of surface water that penetrates to foundation levels and contributes to settlement of soils that support the building foundation and slabs -on -grade. Positive drainage away from the buildings foundation and avoidance of irrigation near the foundations also help to avoid excessive wetting of backfill soils, which can lead to increased backfill settlement and possibly to higher lateral earth pressures, due to increased weight and reduced strength of the backfill. We recommend the following precautions. 1. The ground surface surrounding the exterior of the guest cabins should be sloped to rapidly convey surface water away from the building in all directions. We recommend a constructed slope of at least 12 inches in the first 10 feet (10 percent) in landscaped areas around the buildings, where practical. 2. Backfill around the foundation walls should be moisture -treated and compacted pursuant to recommendations in the Foundation Wall Backfill section. 3. We recommend that the guest cabins be provided with roof drains or gutters and downspouts. The drains or downspouts should discharge well beyond the limits of all backfill. Splash blocks and/or extensions should be provided so water dis- charges onto the ground beyond the backfill. We generally recommend against burial of downspout discharge pipes. 4. Landscaping should be designed and maintained to minimize irrigation. Plants placed close to foundation walls should be limited to those with low moisture re- quirements. Irrigated grass should not be located within 5 feet of the foundations. Sprinklers should not discharge within 5 feet of foundations. Plastic sheeting should not be placed beneath landscaped areas adjacent to foundation walls. Geotextile fabric will inhibit weed growth and allow some evaporation to occur. BECK BUILDING COMPANY Page 13 of 16 SWEETWATER RANCH - GUEST CABINS CTLIT PROJECT NO. GS06935.000-125-R3 than the amount tested in accordance with ASTM C1012/C1012M and meeting the criteria in section 5.5.1 of AC 1332-20. E) Water-soluble chloride ion content that is contributed from the ingredients including water aggregates, ce- mentitious materials, and admixtures shall be determined on the concrete mixture ASTM C1218/C1218M between 29 and 42 days. Superficial damage may occur to the exposed surfaces of highly permeable concrete. To control this risk and to resist freeze thaw deterioration, the water-to-cementitious materials ratio should not exceed 0.50 for concrete in contact with soils that are likely to stay moist due to sur- face drainage or high-water tables. Concrete should have a total air content of 6% +/-1.5%. We recommend foundation walls and grade beams in contact with the subsoils be damp -proofed. CONSTRUCTION OBSERVATIONS We recommend that CTLIT be retained to provide construction observation and materi- als testing services for the project. This would allow us the opportunity to verify whether soil conditions are consistent with those found during this investigation. If others perform these ob- servations, they must accept responsibility to judge whether the recommendations in this report remain appropriate. It is also beneficial to projects, from economic and practical standpoints, when there is continuity between engineering consultation and the construction observation and materials testing phases. GEOTECHNICAL RISK The concept of risk is an important aspect of any geotechnical evaluation. The primary reason for this is that the analytical methods used to develop geotechnical recommendations do not comprise an exact science. We never have complete knowledge of subsurface conditions. Our analysis must be tempered with engineering judgment and experience. Therefore, the rec- ommendations presented in any geotechnical evaluation should not be considered risk -free. We cannot provide a guarantee that the interaction between the soils and the proposed guest cab- ins will lead to performance as desired or intended. Our recommendations represent our judg- ment of those measures that are necessary to increase the chances that the buildings will per- form satisfactorily. It is critical that all recommendations in this report are followed. BECK BUILDING COMPANY Page 15 of 16 SWEETWATER RANCH - GUEST CABINS CTLIT PROJECT NO. GS06935.000-125-R3 iLEGEND: 00 1 APPROXIMATE LOCATION OF PROPERTY BOUNDARY APPROXIMATE LOCATION OF COUNTY UNE t= — ® NOTE: SATELLRE IMAGE FROM MAXAR (COPYRIGHT 2022) BECK BUILOM COMPANY Property Protect No. G508935.000-125-R3 Boundary 7 R0. 1 LEGEND: C m APPROWATE LOCATION OF CXPMWIORY PR NOTE-. WE ORAWMN BY 13LUECKEH ASPEN Guesl Coan � Gveak Co6'n J IF Proposed Ba;K AW Upper .tN�..� sMacs No, pS6FS975.DO6-125.143 Buildings PiQ- s ❑ 30 60 SCALE: 1' - 50' LEGEND: GC3-A APPROXIMATE LOCATION OF I] EXPLORATORY PIT NOTE: BASE DRAWING BY BLUEGREEN ASPEN (DATED DECEMBER 3, 2024) I / o �319 o. \ GC3-A t Propo}sed BECK BUILDING COMPANY L� V es} SWEETWATER RANCH - GUEST CABINS Cabin 3 CTL.ir PROJECT NO. GS06935.000-125-R3 Fig. 5 GC2-A GC2-B EL. 7728 EL 7718 7730 — GUEST CABIN 2 FLOOR EL 7726 7725 7720 n16 7710 7705 GC3-A GC3-B EL 7782 EL T772 7785 7780 r GUEST CABIN 3 J. FLOOR EL 7777 7775 4 7770— 7765 7760 SUMMARY LOGS OF EXPLORATORY PITS GC4-A GC4-B EL. 7775 EL 7768 a 7765 d la 9-10%i� sr-1 FIG.7 ner t1 xo cs ssem+ m Li HYDROMETER ANALYSIS SIEVE ANALYSIS 25 HR- 7 HR. TIME READINGS U.S. STANDARD SERIES CLEAR SQUARE OPENINGS 45 MIN. 15 MIN. 60 MIN. 19 MIN. 4 MIN. 1 MIN. '200 '100 '50 '40 '30 '16 '10 '8 -4 3/8" 3/4" 11/5" 3" $'6" 8" 0 100 10 90 80 20 ^_ LD70 30 Z -- -- - - - - -- - _ - aL60 40 z - U50 _ 50 r; K - - LU — 60 a -, - -. 30 - — - 70 _ — — 80 20 — - � 10 90 - 100 .001 0.002 .005 .009 .019 .037 .074 .149 .297 .590 1.19 2.0 2.38 4.76 9.52 19.1 36.1 76.2 12152200 0.42 - DIAMETER OF PARTICLE IN MILLIMETERS CLAY (PLASTIC) TO SILT (NON -PLASTIC) SANDS GRAVEL FINE MEDIUM COARS I FINE COARSE I COBBLES Sample of CLAY, SANDY (CL) From GC2-A AT 5 FEET GRAVEL % SAND 13 % SILT & CLAY $7 % LIQUID LIMIT % PLASTICITY INDEX % HYDROMETER ANALYSIS I SIEVE ANALYSIS 25 HR. 7 HR. TIME READINGS U.S. STANDARD SERIES CLEAR SQUARE OPENINGS 45 MIN. 15 MIN. 60 MIN. 19 MIN. 4 MIN. 1 MIN. '200 '10D '50 '40 '30 '16 '10 '8 '4 3/8" 3/4" 1M." 3" 5"6" Ir 100 10 —t— — - - - -' 80 20 -_----- -- - - —_ —_ 30 13 ZO 13 40 00 Ir U60 — — = 50 LU — — --- - _ - - — _- a40 60 70 30 -- - — —!— - 80 20 go 10 — - 100 - - 0 .001 0.002 .005 .009 .019 .037 .074 .149 .297 .590 1.19 2.0 2.38 4.76 9.52 19.1 36.1 76.2 12152200 0.42 DIAMETER OF PARTICLE IN MILLIMETERS CLAY (PLASTIC) TO SILT (NON -PLASTIC) SANDS GRAVEL FINE MEDIUM COARS FINE COARSE COBBLES Sample of CLAY, SANDY (CL) From GC3-A AT 6 FEET BECK BUILDING COMPANY SWEETWATER RANCH - GUEST CABINS PROJECT NO. GS06935.000-125-R3 GRAVEL 10 % SAND 31 % SILT & CLAY 59 % LIQUID LIMIT % PLASTICITY INDEX % Gradation Test Results FIG.9 SLOPE PER OSHA COVER ENTIRE WIDTH OF - GRAVEL WITH NON -WOVEN GEOTE MLE FABRIC MIRAFI 148N OR EQUIVALENT). SLOPE 2-3' BACKFILL PREFABRICATED DRAINAGE COMPOSITE (MIRADRAIN 6000 OR EQUIVALENT) ATTACH PLASTIC SHEETING TO FOUNDATION WALL 1!JR1Ln1L" 8' MINIMUM I� OR BEYOND 1:1 SLOPE FROM BOTTOM OF FOOTING (WHICHEVER IS GREATER) 4-INCH DIAMETER PERFORATED RIGID DRAIN PIPE. THE PIPE SHOULD BE PLACED IN A TRENCH WITH A SLOPE OF AT LEAST 1/8-INCH DROP PER FOOT OF DRAIN. ENCASE PIPE IN 1/2" TO 1-1/2" SCREENED GRAVEL EXTEND GRAVEL LATERALLY TO FOOTING AND AT LEAST 1/2 HEIGHT OF FOOTING. FILL ENTIRE TRENCH WITH GRAVEL SUP JOINT PVC DRAIN NETWORK EMBEDDED IN WASHED CONCRETE AGGREGATE NOTE: THE BOTTOM OF THE DRAIN SHOULD BE AT LEAST 2 INCHES BELOW BOTTOM OF FOOTING AT THE HIGHEST POINT AND SLOPE DOWNWARD TO A POSITIVE GRAVITY OUTLET OR TO A SUMP WHERE WATER CAN BE REMOVED BY PUMPING. Foundation Wall Drain BECK BUILDING COMPANY Concept SWEMWATER RANCH - GUEST CABINS Project No. GS06935.000-125-R3 FIg. 11 am rn co z 0 F- a J O U) z O U U W Q U ❑ z w J a Ld w a LL a 0 0 0 w z ❑ w of D a w J J w Soils exposed in Guest Cabin 2 — Pit A Soils excavated from Guest Cabin 2 — Pit A BECK BUILDING COMPANY A-1 SWEETWATER RANCH - GUEST CABINS CTLIT PROJECT NO. GS06935.000-125-R3 Soils exposed in Guest Cabin 3 — Pit A Soils excavated from Guest Cabin 3 — Pit A BECK BUILDING COMPANY A-3 SWEETWATER RANCH - GUEST CABINS CTLIT PROJECT NO. GS06935.000-125-R3 Ll Soils exposed in Guest Cabin 4 — Pit A Soils excavated from Guest Cabin 4 — Pit A BECK BUILDING COMPANY A-5 SWEETWATER RANCH - GUEST CABINS CTLIT PROJECT NO. GS06935.000-125-R3