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Home My WebLink AboutFile Documents.100 Dean St.0056-2021-BCHO (7) irCTL I THOMPSON INCORPORATED July 29, 2020 Timber Ridge Corporation, A Condominium Association do Aspen Resort Accommodations 600 East Hopkins Avenue, Suite #203 Aspen, CO 81611 Attention: David Ellis, President Subject: Preliminary Geotechnical Consultation Timber Ridge Condominiums 100 East Dean Street Aspen, Colorado Project No. GS06471.000-145 This letter presents our preliminary geotechnical consultation for founda- tion supports for new decks and exterior deck stairways on the Timber Ridge Condominiums building at 100 East Dean Street in Aspen, Colorado. A vicinity map with the site location is shown on Figure 1. The purpose of our consultation was to develop opinions about subsurface conditions at the site and provide pre- liminary geotechnical engineering criteria for design and construction of the new structures. Our scope was set forth in our Proposal No. GS 20-0139. Site Conditions The Timber Ridge Condominiums building is located at 100 East Dean Street in Aspen, Colorado. East Durant Avenue borders the property at the north. South Garmisch Street is to the west. Multi-family residential buildings are south and east of the subject property. The existing condominium building on the site is a three-story structure. The existing building footprint is shown on Figure 2. A photograph of the existing building exterior is below. imixii, - .-- A,,ci L.,, ;, iN - \tle4(</ Existing conditions on north side of building % `f)) QGN, P'` 6;le -—-4.r,, 234 Center Drive I Glenwood Springs, Colorado 81601 Telephone: 970-945-2809 Fax: 970-945-7411 ON Proposed Construction Proposed improvements include removing and replacing the existing exte- rior stairways and decks on the south side of the building. The decks on the north side of the building will be replaced. Proposed stairway and deck improve- ments are shown on Figure 3. The new stairs towers will require new foundation. The decks will require strip footings adjacent to the building. Subsurface Conditions The existing building, trees, utilities, and City of Aspen right-of-way restrict access for equipment needed to excavate exploratory pits to investigate subsur- face conditions below the proposed improvements. For this initial geotechnical engineering consultation, we developed recommendations based on our site ob- servations, subsurface conditions encountered during our geotechnical investiga- tions at nearby sites, and excavation observations during construction of the ad- jacent One Aspen buildings. Our experience indicates that natural soils below the Timber Ridge Con- dominiums property consist predominantly of silty gravel with a large percentage of cobbles and boulders to depths of at least 60 feet. The near-surface soils may be comprised of fill and natural clayey sand. Foundation backfill is likely to be encountered near the building. The free groundwater table below the site is likely deeper than 30 feet. When the contractor begins construction, our representative should be called to observe conditions exposed in excavations to verify our assumptions about subsurface conditions. Excavations We anticipate that excavations for the proposed project at this site can be accomplished using conventional, heavy-duty excavation equipment. Sides of excavations must be sloped or braced to meet local, state and federal safety reg- ulations. The soils will likely classify as Type C soils based on OSHA standards governing excavations. Temporary slopes deeper than 4 feet and above ground- water should be no steeper than 1.5 to 1 (horizontal to vertical) in Type C soils. Contractors are responsible for site safety and providing and maintaining safe and stable excavations. Contractors should identify the soils encountered an ensure that OSHA standards are met. .12 Subexcavation and Structural Fill '` $ '1' s'44* 0 Foundation backfill may be encountered in excavations for stru�\ rie tures. To reduce potential for differential settlement, we recom at eA ng QG�' ` backfill be subexcavated to a depth of 2 feet below bottom of foun ations re- GJ & placed with densely-compacted, structural fill. A CDOT Class 6 aggregate base `cDQ ,' TIMBER RIDGE CORPORATION `� TIMBER RIDGE CONDOMINIUMS ,\V PROJECT NO.GS06471.000-145 �V� course or similar soil should be imported for use as structural fill. The structural fill soil should be placed in 8-inch thick loose lifts, moisture-conditioned to within 2 percent of optimum moisture content and compacted to at least 98 percent of standard Proctor maximum dry density (ASTM D 698). Our representative should be called to observe conditions in the subexcavated areas prior to place- ment of structural fill. We should check density and moisture content of structural fill during placement. Footing Pad Foundations We anticipate that the natural soils at depths greater than 2 to 3 feet con- sist of natural gravel with cobbles and boulders. Foundation backfill soils of un- known composition and density are likely present at the locations of supports for the proposed structures. In our opinion, footing pad foundations are appropriate for the stairway and deck structures. The footing pads can be supported by the undisturbed, natural gravel, cobbles and boulders with low risk of potential move- ment and damage. If foundation backfill is encountered at planned footing pad elevation, we recommend subexcavation of 2 feet of the existing fill and replace- ment with densely-compacted, structural fill as discussed in the Structural Fill section. Footing pad foundations for the stairs and decks can be designed for a maximum allowable bearing pressure of 2,000 psf on the natural gravel soil or densely-compacted, structural fill. The gravel soil at this site, and structural fill of the recommended composition, are not frost susceptible. Ice lenses can form be- tween shallow footings and the underlying soils during freezing and thawing cy- cles. Positive surface drainage is important to prevent infiltration of water that can subsequently freeze. The City of Aspen should be consulted whether any frost protection will be required. Backfill The excavated natural soils can be reused as backfill adjacent to footing pad foundations. Particles in excess of 3 inches in diameter should be excluded from the backfill soils. Backfill should be placed in 8-inch thick loose lifts, mois- ture-conditioned to within 2 percent of optimum moisture content and compacted to at least 95 percent of standard Proctor maximum dry density (ASTM D 698). Our representative should be called to check density and moisture of backfill. Surface Drainage A‘<°' etc) Performance of the foundations will be influenced by the moisture, n - le tions existing within the near-surface soils. The risk of wetting found�t on is rO can be reduced by properly planned and maintained surface drains ' is criti0� cal that surface drainage be designed to provide rapid runoff of wa ` way f\9> G\'�'` the building and proposed structures. `1 ',tie �Q QP TIMBER RIDGE CORPORATION 3OCD TIMBER RIDGE CONDOMINIUMS PROJECT NO.GS06471.000-145 Limitations Our subsurface information and project experience from nearby sites was used to develop the geotechnical engineering recommendations in this letter. These recommendations are contingent upon our observations of the subsoils at the site when the excavation contractor is on-site to begin construction. This consultation was provided in a manner consistent with that level of care and skill ordinarily exercised by geotechnical engineers currently practicing under similar conditions in the locality of this project. No warranty, express or im- plied, is made. We are available to discuss the contents of this letter. If you have questions or need additional information, please call. CTL I THOMPSON, INC. 4..ZD Vor,P,e- c) R E g:*4 James D.Kellogg �.••� f�, Jul 29 2020 8 22 PM rL1S473 -"q `11L,v` CS AP. gt If James D. Kellogg, P.E. . ' Division Manager 38208 ti k: • J DK:ac or- til trrr:r�' James D. Kellogg Jul 29 2020 8:23 PM ‘<> el,O (4 kr), */ „gyp N/# CD TIMBER RIDGE CORPORATION \O TIMBER RIDGE CONDOMINIUMS ,\`V PROJECT NO.GS06471.000-145 �V 1 T 0 1500 1000 NOTE: SATELLITE IMAGE FROM GOOGLE EARTH SCALE: 1' = 1000' • 77 r �h 11t 7 t 'f e0 it e k 't',1 .� • t {�ye`�°- p .1:, p R f .. Fi .,_d2 7 �4-''' Sl }I- r�i'.. 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