Location

Chicago, Illinois

Session Start Date

4-29-2013

Session End Date

5-4-2013

Abstract

At a retail development site in Southington, Connecticut, a multi-tiered Mechanically Stabilized Earth (MSE) retaining wall system was constructed in the early 1990’s to facilitate development of the site. Specifically, the retaining wall system constructed consisted of a sloped structure with three tiers of MSE wall that was approximately 56-feet tall at its highest point. The MSE walls within the slope were spaced approximately 30 to 40 feet apart horizontally, were between six and nine feet in height, and ranged in length from about 375 feet to 1,325 feet. Overall, grades on the slope ranged from about elevation 225 feet at the top to about elevation 163 feet at the fire lane at the base of the slope. The graded portions of the slope between the MSE walls had an inclination of about 2H:1V. Subsurface conditions at the site generally consisted of up to about eight feet of granular fill on the slope in the areas disturbed by the initial grading activities underlain by medium dense to dense coarse to fine sand with varying proportions of silt and gravel. Based on borings conducted at the top of the slope during remedial construction, the sand layer extends to at least elevation 145 feet, or about 15 to 20 feet below the base of the slope. Groundwater was not encountered in any of the borings conducted or during the construction phase. Due to the lack of available information regarding the freeze-thaw effects on the modular block facing at the time of construction, the impact of this behavior was not properly considered in the original design. Consequently, less than 20 years later, freeze-thaw effects deteriorated the majority of the facing to the point where the overall stability of the wall was in question. Specifically, facing block failure was leading to localized raveling of soils and creating erosion zones at the face of the wall. If left unchecked, these areas of erosion would have continued to extend deeper into the slope, compromising the integrity of the MSE structures, and thereby the overall slope. Several options were evaluated to achieve a cost efficient design to stabilize the walls and slope. Conceptual designs were developed and included 1) a single 25-foot tall MSE wall with a reinforced slope in front of the existing wall system and 2) a proposed tiered wall scheme. The selected design concept included a 15-foot tall large block Stone Strong gravity wall in front of the bottom tier and a 10-foot tall Stone Strong gravity wall in front of the center portion of the middle tier of the existing retaining wall system. The remainder of the upper slope was significantly regraded. Re-construction of the wall was completed between November 2008 and August 2009. This paper describes the investigation, design, and construction methodologies that were implemented to provide an economical solution to this unique issue and mitigate long-term wall stability issues.

Department(s)

Civil, Architectural and Environmental Engineering

Appears In

International Conference on Case Histories in Geotechnical Engineering

Meeting Name

Seventh Conference

Publisher

Missouri University of Science and Technology

Publication Date

4-29-2013

Document Version

Final Version

Rights

© 2013 Missouri University of Science and Technology, All rights reserved.

Document Type

Article - Conference proceedings

File Type

text

Language

English

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Apr 29th, 12:00 AM May 4th, 12:00 AM

Reconstruction of a Deteriorating, Tiered, MSE Wall Structure in Connecticut

Chicago, Illinois

At a retail development site in Southington, Connecticut, a multi-tiered Mechanically Stabilized Earth (MSE) retaining wall system was constructed in the early 1990’s to facilitate development of the site. Specifically, the retaining wall system constructed consisted of a sloped structure with three tiers of MSE wall that was approximately 56-feet tall at its highest point. The MSE walls within the slope were spaced approximately 30 to 40 feet apart horizontally, were between six and nine feet in height, and ranged in length from about 375 feet to 1,325 feet. Overall, grades on the slope ranged from about elevation 225 feet at the top to about elevation 163 feet at the fire lane at the base of the slope. The graded portions of the slope between the MSE walls had an inclination of about 2H:1V. Subsurface conditions at the site generally consisted of up to about eight feet of granular fill on the slope in the areas disturbed by the initial grading activities underlain by medium dense to dense coarse to fine sand with varying proportions of silt and gravel. Based on borings conducted at the top of the slope during remedial construction, the sand layer extends to at least elevation 145 feet, or about 15 to 20 feet below the base of the slope. Groundwater was not encountered in any of the borings conducted or during the construction phase. Due to the lack of available information regarding the freeze-thaw effects on the modular block facing at the time of construction, the impact of this behavior was not properly considered in the original design. Consequently, less than 20 years later, freeze-thaw effects deteriorated the majority of the facing to the point where the overall stability of the wall was in question. Specifically, facing block failure was leading to localized raveling of soils and creating erosion zones at the face of the wall. If left unchecked, these areas of erosion would have continued to extend deeper into the slope, compromising the integrity of the MSE structures, and thereby the overall slope. Several options were evaluated to achieve a cost efficient design to stabilize the walls and slope. Conceptual designs were developed and included 1) a single 25-foot tall MSE wall with a reinforced slope in front of the existing wall system and 2) a proposed tiered wall scheme. The selected design concept included a 15-foot tall large block Stone Strong gravity wall in front of the bottom tier and a 10-foot tall Stone Strong gravity wall in front of the center portion of the middle tier of the existing retaining wall system. The remainder of the upper slope was significantly regraded. Re-construction of the wall was completed between November 2008 and August 2009. This paper describes the investigation, design, and construction methodologies that were implemented to provide an economical solution to this unique issue and mitigate long-term wall stability issues.