240607 BSFD No. 3 - Geotech Supplemental Recommendations.pdf
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- Attached to
- Material Testing and 3rd Party Inspections
- Solicitation number
- RFP_F-BSFD-0000000002
- Issued by
- Gallatin County, Montana
About this file
This document is a supplemental geotechnical recommendations letter from CTL|Thompson, Inc. dated August 30, 2024, addressed to CH SP Acquisition, LLC regarding the South Fork Road Fire Station project in Gallatin County, Montana. The letter provides additional technical details following an initial geotechnical engineering investigation report dated June 7, 2024, specifically addressing seismic design parameters, modulus of subgrade reaction, and lateral earth pressures for foundation and retaining walls. The supplemental recommendations were requested by Anthem Structural Engineers to support the structural design of a Risk Category IV structure.
The technical recommendations include specific engineering specifications such as a recommended modulus of subgrade reaction of 150 pci for floor slabs, and detailed lateral earth pressure tables for both native soils and imported structural fill under static and dynamic seismic conditions. The document provides equivalent fluid pressure values for at-rest and active earth pressure conditions, which are critical for structural design and engineering calculations. The letter is prepared by Leyla Safari, P.E. (Project Manager) and reviewed by James D. Kellogg, P.E. (Principal Engineer), and was distributed via email to multiple recipients including representatives from Lone Mountain Land and Anthem Structural Engineers.
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CTL|Thompson, Inc.
Denver, Fort Collins, Colorado Springs, Glenwood Springs, Pueblo, Summit County – Colorado
Cheyenne, Wyoming and Bozeman, Montana
August 30, 2024
CH SP Acquisition, LLC P.O. Box 160040 Big Sky, MT 59716
Attention: Jon Olsen, P.E.
Subject: Supplemental Geotechnical Recommendations
South Fork Road Fire Station Gallatin County, Montana Project No. MT01140.000-125-L3
CTL|Thompson, Inc. (CTL|T) has performed a geotechnical engineering investigation (report dated June 7, 2024) for the South Fork Road Fire Station planned within Spanish Peaks in Gallatin County, Montana. Subsequent to our report, Anthem Structural Engineers (Anthem) requested additional information regarding design of the structural for seismicity. This letter contains our supplemental geotechnical recommendations.
Seismicity
In the report referenced above, CTL|T estimated seismic design parameters using ASCE/SEI7-16, assuming a Risk Category II for the structure. We understand the structure will actually be designed for Risk Category IV. Analysis of the site with the ASCE Hazard Tool and Risk Category IV does not warrant revisions to the values set forth in the Seismicity section of our report.
Modulus of Subgrade Reaction
Anthem requested that CTL|T provide a modulus of subgrade reaction for design of the floor slabs in the building. In our report, CTL|T recommended the soils below slabs be subexcavated to a depth of at least 3 feet below bottom of slabs and replaced with properly-compacted, structural fill. We recommend that floor slabs conforming to this recommendation be designed for a modulus of subgrade reaction of 150 pci.
Lateral Earth Pressures
For backfill soils conforming to recommendations in the Foundation Wall Backfill section of our report, CTL|T recommends design of the building walls at this site using the lateral earth pressures on the table below. These equivalent fluid densities to not include allowances for sloping backfill, surcharges, or hydrostatic pressures.
LATERAL EARTH PRESSURES FOR FOUNDATION WALLS
Native Soils
Earth Pressure Condition
Equivalent Fluid Pressure
(Static Condition)
Equivalent Fluid Pressure (Dynamic Seismic Condition)
At-Rest 60 65 https://ctlthompson.com/ https://ctlthompson.com/denver https://www.ctlthompson.com/fortcollins https://www.ctlthompson.com/coloradosprings https://www.ctlthompson.com/glenwoodsprings https://www.ctlthompson.com/pueblo https://www.ctlthompson.com/summitcounty https://www.ctlthompson.com/cheyenne https://www.ctlthompson.com/bozeman
CH SP ACQUISITION, LLC 2
SOUTH FORK ROAD FIRE STATION
PROJECT NO. MT01140.000-125-L3
For backfill soils conforming to recommendations in the Site Grading Fill section of our report, CTL|T recommends design of site earth retaining walls at the site using the lateral earth pressures summarized on the table below. These equivalent fluid densities to not include allowances for sloping backfill, surcharges, or hydrostatic pressures.
LATERAL EARTH PRESSURE FOR SITE EARTH RETAINING WALLS
Imported Structural Fill Native Soils
Earth Pressure Condition
Equivalent Fluid Pressure
(Static Condition)
Equivalent Fluid Pressure (Dynamic Seismic Condition)
Equivalent Fluid Pressure
(Static Condition)
Equivalent Fluid Pressure (Dynamic Seismic Condition)
Active 40 55 45 60 Passive 345 345 250 250
We are available to discuss the contents of this letter. Please contact us if you have questions or need additional information.
CTL|THOMPSON, INC. Reviewed by:
Leyla Safari, P.E. James D. Kellogg, P.E.
Project Manager Principal Engineer lsafari@ctlthompson.com jkellogg@ctlthompson.com
Via email: jolsen@lonemountainland.com rhuyette@anthemstructural.com ccasias@anthemstructural.com dhenderson@anthemstructural.com
8/30/2024
8/30/2024 mailto:lsafari@ctlthompson.com mailto:jkellogg@ctlthompson.com mailto:jolsen@lonemountainland.com mailto:rhuyette@anthemstructural.com mailto:ccasias@anthemstructural.com
| 2024-08-30T15:03:49-0700 | |
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