687-23-101_Repair_Exterior_Features_Geotech Memorandum.pdf
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- 687-23-101 CON Repair Exterior Features
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- 36C26026R0033
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This is a geotechnical memorandum prepared by GDM of Oregon, a Service-Disabled Veteran-Owned Small Business, dated February 29, 2024, documenting soil conditions at the Jonathan M. Wainwright VA Medical Center in Walla Walla, Washington for the Exterior Improvements Project. The site is characterized by loamy and silty soils with areas of clay and sandy loam, typical of the region's agricultural prominence. Soil composition includes three primary layers: a topsoil layer rich in organic material with limited structural bearing capacity; subsoil layers of loam, silt loam, and clay loam offering moderate to high bearing capacities but presenting shrink-swell challenges in clay-rich areas; and underlying strata of bedrock or gravel deposits providing good bearing capacity for deep foundations. Groundwater levels fluctuate seasonally based on local precipitation and proximity to rivers/streams, with potential impacts on excavation and foundation design due to soil saturation and hydrostatic pressure concerns.
The memorandum identifies three primary geotechnical challenges: soil stability issues from seasonal volume changes in high clay content areas, erosion and sediment control requirements during construction, and seismic considerations for compliance with local building codes. Preliminary recommendations specify that a detailed geotechnical investigation is not recommended; instead, ASCE-7 should be used to determine seismic parameters based on Site Class D requirements with 1500 PSF bearing capacity. Foundation designs should employ an underpinning system to level and restrain buildings, with helical piers as an alternative option. The memorandum emphasizes comprehensive erosion and sediment control measures and effective stormwater management, noting that most foundation damage results from inadequate gutters, downspouts, and water conveyance systems. The assessment was prepared by Adam Goddin, PE (WA PE #46,941).
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GDM of Oregon A Service‐Disabled Veteran‐Owned Small Business
GEOTECHNICAL MEMORANDUM
Date: 02/29/2024
From: Adam Goddin, PE; Engineer
Subject: Soil Conditions at Jonathan M. Wainwright VA Medical Center;
Walla Walla, WA
To: Eric Shreve, RA; Project Architect
This memorandum provides an overview of the known soil conditions at the site of the Jonathan M. Wainwright VA Medical Center; Walla Walla, WA It aims to outline general soil characteristics, potential geotechnical challenges, and preliminary considerations for future construction or development projects at this location. More specifically, the Exterior Improvements Project.
Site Description The area is characterized by its varied topography and the presence of local river/streams, which may influence local soil conditions and groundwater levels.
Soil Composition The soil in Walla Walla, Washington, generally consists of loamy and silty soils, with areas of clay and sandy loam. These soil types are indicative of the region's agricultural prominence and can vary significantly in terms of drainage properties and load-bearing capacities.
1. Topsoil Layer: The uppermost layer is typically rich in organic material, with a depth that varies across the site. This layer is important for vegetation but has limited structural bearing capacity.
2. Subsoil Layers: Below the topsoil, the subsoil layers consist primarily of loam, silt loam, and clay loam. These layers can offer moderate to high bearing capacities but may present challenges in terms of shrink-swell potential, especially in areas with significant clay content.
3. Underlying Strata: Bedrock or denser soil layers, such as gravel or sandy deposits, may be present at varying depths. These layers generally provide good bearing capacity and are critical for deep foundations.
Groundwater Conditions Groundwater levels in the area can fluctuate seasonally and are influenced by local precipitation patterns and proximity to local river/streams. The presence of groundwater near the surface can impact excavation works and foundation design due to potential issues with soil saturation and hydrostatic pressure.
Geotechnical Challenges
Soil Stability: Areas with high clay content may experience significant seasonal volume changes, leading to potential soil heave or settlement.
Erosion and Sediment Control: Due to the site's topography and soil types, erosion control measures will be critical during construction to prevent sediment runoff and protect water quality.
Seismic Considerations: While not in a primary seismic zone, seismic considerations may need to be addressed in the structural design to comply with local building codes.
Preliminary Recommendations
1. Geotechnical Investigation: A detailed geotechnical investigation, including soil borings and laboratory testing, is not recommended. Use ASCE-7 to determine seismic parameters based on Site Class D Requirements. Use 1500 PSF for bearing.
2. Foundation Design: Foundation designs should consider the variability in soil conditions, with special attention to areas with high clay content or shallow groundwater levels. Recommend using an underpinning system to level and restrain buildings. See attached engineering drawing. Helical piers may also be used.
3. Erosion and Water Management: Implement comprehensive erosion and sediment control measures, along with effective stormwater management practices, to protect soil stability and water quality during and after construction. Most of the damage caused to the foundations is by a lack of gutters, downspouts, and conveyance.
Conclusion The soil conditions at the Walla Walla, WA VA Medical Center present both challenges and opportunities for future development. A thorough understanding of these conditions will be crucial in ensuring the stability and longevity of any structures on this site.
Please feel free to contact me for further details or clarification regarding this preliminary assessment.
Respectfully Submitted, Adam Goddin, PE
WA PE #46,941
541-380-1237 agoddin@gdm-ae.com
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