HomeMy WebLinkAboutFile Documents.315 E Hyman Ave.0011-2023-BCOM (4) CTLTHOMPSON
March 16, 2023
Gravity Haus
315 E. Hyman Avenue
Aspen, CO 81611
Attention: Grady Huff
Subject: Preliminary Design Parameters for Water Quality Vault
AspenHaus
315 E. Hyman Avenue
Aspen, Colorado
Project No. GS06759.000-125
CTLIThompson, Inc. (CTLIT) has been retained to perform a geotechnical
engineering investigation for the AspenHaus project located at 315 E. Hyman Av-
enue in Aspen, Colorado. The scope of our services was generally described in
our Proposal No. GS 23-0009 which includes drilling one exploratory boring south
of the existing building. The site is currently not accessible to drilling due to per-
mitting and access restrictions. Prior to our subsurface investigation, we are
providing preliminary recommendations for design of the water quality vault and
anticipated infiltration rates of the subsoils based on information from nearby
sites. Prior to construction of the vault, we will need to verify the assumptions in
this letter by drilling an exploratory boring at the site.
A new water quality vault is planned in the courtyard area in the center of
the building. Plans for the new vault were not available at the time of this letter.
We understand the vault will be approximately 8 feet wide by 10 feet long. The
bottom of the new vault will be about 5 to 6 feet below the top of the basement
slab elevation. This would likely be at least 6 feet below the elevation of the court-
yard area. We should be provided with plans for the vault when they are devel-
oped so that we can revise our recommendations, if necessary.
In the opinion of CTLIT, the primary geotechnical concern with the water
quality vault construction is undermining and/or destabilizing the existing building
foundation during excavation. Our subsurface information and experience from
nearby sites indicate the subsoils at the site will classify as Type C, pursuant to
OSHA standards governing excavations. Unbraced excavation slopes in Type C
soils should be no steeper than 1.5 to 1.0 (horizontal to vertical). For a 6-foot-
deep excavation, this would result in a slope that extends 9 feet laterally from the
vault perimeter.
We suggest that the contractor consider pre-shoring of the vault excava-
tion. An appropriate technique would be to install micropiles around the perimeter
of the vault. This would significantly reduce the volume of excavated soils, as well
CTLIThompson, Inc. RECEIVED
Denver, Fort Collins, Colorado Springs, Glenwood Springs, Pueblo, Summit County—Colo,[a l
4/ 10/2023
Cheyenne, Wyoming and Bozeman, Montana U
ASPEN
BUILDING DEPARTMENT
as subsequent backfill. Typically, micropiles for this type of application are de-
signed by specialty design-build contractors. For preliminary design, we anticipate
micropile lengths of about 15 feet. This should be re-evaluated once we are able
to drill the exploratory boring at the subject site.
Our subsurface and laboratory data from nearby sites, and our experience
in the Aspen Core area, indicate the natural soils contain less than 20 percent silt
and clay size material. CTLIT judges that a hydraulic conductivity rate (k) of 0.034
to 0.0034 ft/sec for the silty gravel soils anticipated at the site is appropriate for
preliminary design. We judge this hydraulic conductivity (k) correlates to a vertical
percolation rate faster than 3 inches per hour (i.e., 20 mins/inch).
We are available to discuss the contents of this letter. Please contact us if
you have questions or need additional information.
Respectfully submitted,
CTLITHOMPSON, INC.
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Ryan R. Barbone, P.E. ;w 61683 in:
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Via email: grady(a�gravityhaus.com
RECEIVED
ASPENHAUS c /10/2023
315 E.HYMAN AVENUE
PROJECT NO.GS06759.000-125
ASPEN
BUILDING DEPARTMENT