HomeMy WebLinkAbout10_Geotechnical report with groundwater info_02-04-2020 Groundwater Nloidlorin�
Included in this section is a geotechnical summary letter from C&H that states that groundwater
in the surrounding area has been observed to be as high as 3.5 feet below existing grade. The
underground stormwater system has been designed to be above this seasonally high groundwater.
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Engineering and Surveying Inc.
1091 Stoneridge Drive • Bozeman, Montana • Phone(406)587-1115 • Fax(406)587-9768
www.chengineers.com • E-Mail: info@chengineers.com
January 31,2020
Springer Group Archtiects
Attn: Lowell Springer
E-mail: lowell@springergroup.net
Re: Preliminary Geotechnical Recommendations — Lots 2 and 3, Block 2, Cattail Creek
Subdivision Phase 3; Bozeman,Montana(200115)
Dear Lowell,
Per your request, C&H Engineering has provided the following preliminary recommendations regarding
subgrade improvements for the multi-family residential structures to be constructed on the above
referenced property in Bozeman, Montana. The scope of services was to provide subgrade improvement
recommendations for the structure's foundation based on our experience regarding the subsurface soils
and conditions in the project area.
Based on our experience in the area, the subsurface soils consist of an Organic Soil (OL), followed by a
Lean Clay (CL), after which native "pit-run" gravel is present. The depth to gravel is typically 3 to 5 feet
below existing grade. It is recommended that subgrade improvements consist of excavating down to
native "pit-run" gravel and using structural fill to achieve the desired bottom of footing elevation. It
should be noted that seasonally high groundwater has been observed to be as high as 3.5 feet below
existing grade in the surrounding area.
Structural fill is recommended to be 3-inch minus "pit-run" gravel or 3/4-inch minus washed rock. Both
types of structural fill must be placed in lifts(12-inch maximum loose thickness)and be compacted with a
large vibrating smooth drum roller. The 3/4-inch washed rock needs to be compacted to an unyielding
condition and the 3-inch minus "pit-run" gravel shall be compacted to a minimum of 97 percent of its
maximum dry density, as determined by ASTM D698. Additionally, the site may need to be dewatered
prior to beginning placement and compaction of the structural fill if 3-inch minus "pit-run" gravel is used
as structural fill.
Foundation footings may be dimensioned for an allowable bearing capacity of 2,500 pounds per square
foot. If you have any questions or need further assistance with your project, please contact the
undersigned.
Sincerely
Michael J. Welch, P.E.
GAc&h\20\2001115S1PrclnhAaY. '6*6614n,ical Recontmendaitons-Lots 2&3 Block I Cattail Creek Ph 3(200115).doc
Civil/Structural Engineering and Surveying