HomeMy WebLinkAboutGeotechnical Summary letter 05-28-19 Civil Engineering . Geotechnical Engineering , Land Surveying
32 Discovery Drive
ALLIED Bozeman,Montana 59718
ENGINEERING
SFP.CICES,INC. �V=� Ph: (406) 582-0221
_ Fax: (406) 582-5770
May 28, 2019
Chris Budeski
Madison Engineering
895 Technology Blvd.,Suite 203
Bozeman, MT 59718
Re: Geotechnical Summary Letter
Nexus Point—Bozeman,MT
Dear Mr. Budeski:
This letter acknowledges that AESI is working on the geotechnical investigation and report for the
proposed Nexus Point project, located on the south side of Bozeman. The project site is a 20-acre parcel
on the south side of Grace Bible Church. It is bounded on the east by S. 19th Avenue and is legally
described as Lot 1 of Minor Subdivision 235. As of now, we have conducted the fieldwork. Laboratory
testing is underway. We expected the report will be issued in the middle to latter part of June.
EXPLORATIONS AND SUBSURFACE CONDITIONS
Subsurface Explorations
Subsurface conditions were investigated at the site on April 26 and 29, 2019 by Lee Evans,a professional
geotechnical engineer with Allied Engineering. Eight test pits identified as TP-1 through TP-8 were dug
with a large excavator provided by Townsend Backhoe. All pits extended to about the 10-foot depth
and all were backfilled the vertical PVC pipes for future groundwater monitoring. See our field map
(attached)for the approximate test pit locations.
Soil and Groundwater Conditions
The site is generally blanketed by about 9 to 18 inches of topsoil. Underlying the topsoil is native
silt/clay. Beginning at depths of 3.0 to 5.0 feet is cobbly, sandy gravel, which extended to the bottom of
the test pits. The silt/clay in the middle of the site is drier and stiffer; whereas the silt/clay on the east
and west sides is wetter and softer. Groundwater depths were at 4.0 to 6.0 feet on the west side, in the
middle they were at 7.5 to 8.0 feet, and on the east they were at about 3.5 feet.
POTENTIAL GEOTECHNICAL ISSUES
Most likely, all the commercial buildings will be underlain by at-grades. Therefore, groundwater should
not be an issue with respect to the building foundations. Probably the biggest issue will be soft road-
www.alliedengineering.com
Chris Budeski Geotechnical Summary Letter
May 28, 2019 Nexus Point—Bozeman,MT
way subgrade soils on the west and east sides of the site. In this area, we are recommending a high
strength geosynthetic under the pavement section for roadbed stabilization as well as a little thicker
sub-base section.
PRELIMINARY RECOMMENDATIONS
• All buildings can be supported on a conventional shallow foundation that bears on the native
sandy gravel, which underlies the site at depths of 3.0 to 5.0 feet. The native gravel is the
"target" bearing material for all building footings.
• The pavement section in the middle of the site will bear on drier, silt/clay. As a result, we
assume stable subgrade conditions. In this area, we recommend a section consisting of 3" of
asphalt, 6" of base course gravel, 15" of sub-base gravel, which is underlain by a 315 lb. woven
geotextile separator fabric(Mirafi 60OX or equal).
• On the east and west sides of the site, the subgrade soils will consist of wetter, silt/clay. As a
result,we are assuming the subgrade conditions will be unstable. In this area, we recommend a
section consisting of 3" of asphalt, 6" of base course gravel, 21" of sub-base gravel, which is
underlain by a high strength geosynthetic(Mirafi RS580i).
If you have any questions about this geotechnical summary letter, please give me a call at 406-582-0221.
Sincerely,
Allied Engineering Services, Inc. ,
L2- _ S •• pNT,�,�1., .
Lee S. Evans, PE •—s
Geotechnical Engineer LEE SCOTT ••.
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