HomeMy WebLinkAboutSubsoils Report Addendum 11.07.23November 7, 2023
Andover Management Group
333 East Main Street, Suite 300
Louisville, KY 40202
Attention: Dan Kunau
Subject: Geotechnical Engineering Investigation - Addendum
214 Center Drive
(a.k.a. Parcel 218506100042)
Garfield County, Colorado
CTLIT Project No. GS06693.001-125
CTLIThompson, Inc. (CTLIT) performed a geotechnical engineering investigation regard-
ing 214 Center Drive (a.k.a. Parcel 218506100042) in Garfield County, Colorado. Subsequent to
our report, we were asked to prepare this addendum. This letter provides geotechnical engi-
neering recommendations and design criteria for earth retaining walls, seismic design, and
belled pier foundations.
Site Earth Retaining Wails
We understand site earth retaining walls are included in the current plans for the project.
Earth retaining walls must be designed to resist lateral earth pressures. Many factors affect the
values of the design lateral earth pressure. 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
may be appropriate.
For backfill soils conforming with recommendations in the Foundation Wall backfill sec-
tion of our report that are not saturated, we recommend design equivalent fluid densities of at
least 45 pcf and 60 pcf for the "active" and "at -rest" conditions, respectively. Passive earth pres-
sure calculated with an equivalent fluid pressure of 300 pcf is appropriate for this site, provided
backfill in front of the retaining wall footings will not be removed during the lifespan of the struc-
tures.
Surface water from precipitation and landscape irrigation is likely to infiltrate backfill
placed adjacent to site earth retaining walls. This water can cause reduced backfill strength and
result in hydrostatic pressures on the retaining walls. Drains should be constructed behind the
bases of the footings for the walls.
CTLIThompson, Inc.
Denver, Fort Collins, Colorado Springs, Glenwood Springs, Pueblo, Summit County — Colorado
Cheyenne, Wyoming and Bozeman, Montana
The earth retaining wall drains can consist of 4-inch diameter, slotted, PVC pipe en-
cased in free -draining gravel. A prefabricated drainage composite should be placed adjacent to
the backs of the walls. Care should be taken during backfill operations to prevent damage to
drainage composites. The drains should discharge via gravity outlets or weep holes.
Seismic Design Parameters
We expect the proposed buildings will be considered Risk Category 11, pursuant to the
2021 IBC. The soil and bedrock are not expected to respond unusually to seismic activity, and
they have low susceptibility to liquefaction. Pursuant to the ASCE/SEI 7-22 and our subsurface
information, we judge that Site Soil Class D is appropriate for seismic design. In our opinion, the
developer should consider retaining a geophysical consultant to assist with evaluation of the
seismic site soil classification of the site. We consider the seismic criteria on the table below to
be appropriate for use in structural design at the site.
Table 1
Seismic Criteria
- SS
i 0.32
S1
0.057
SDS
0.24
SDI
0.083
SMs
0.36
SM1
0.13
TL
4
PGAM
0.2
VS30
260
Seismic Design
Category
B
Belled Piers
We understand that the client anticipates that two of the one-story, metal buildings
planned for the site will be subject to significant uplift forces. The client desires belled pier foun-
dations for these buildings to resist the uplift. Our subsurface information indicates that the soils
below the site are generally sandy clay soil that is medium stiff to very stiff with some very soft
zones. Gravel and cobble soil is below the sandy clay, but the elevation is not consistent. The
gravel/cobbles are deeper than 30 feet at some locations. Design and construction criteria for
belled piers are below.
Belled piers should be designed for a maximum allowable end bearing pressure
of 3,000 psf. Skin friction should be neglected.
ANDOVER MANAGEMENT GROUP Page 2 of 3
214 CENTER DRIVE
CTLIT PROJECT NO. GS06693.001-125
2. Piers should be reinforced full-length. Reinforcement should extend into the
grade, beams and foundation walls. Additional reinforcement may be required
depending on structural analysis.
3. The belling tool should be used immediately upon completion of drilling the
straight -shaft portion of the pier. The belling tool should be used to its full capaci-
ty. Casing should be available on -site to prevent caving of soils into pier holes.
4. Piers should be carefully cleaned prior to placing concrete. Concrete should be
on -site and placed in the pier holes immediately after the holes have been drilled,
cleaned and observed. We recommend concrete with a minimum slump in the
range of 5 to 7 inches to reduce possibility of voids in the belled portion of the
pier.
5. Installation of drilled piers should be observed by a representative of CTLIT to
verify subsoils are as anticipated and to observe the contractor's installation
technique.
We are available to discuss the contents of this letter. Please contact us if you have
questions or need additional information.
CTLITHOMPSON, INC.
f
Ryan R. Barbone, P`^
Division Manager
ANDOVER MANAGEMENT GROUP
214 CENTER DRIVE
CTLIT PROJECT NO. G506693.001-125
Reviewed by:
�C/
mes D. Kellogg, P. a,
Principal Engineer
ikellooa@ctlthomi2son.com
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