Location

New York, New York

Session Start Date

4-13-2004

Session End Date

4-17-2004

Abstract

An area in south-east Iowa is notorious for landslides in both cut slopes and embankments. Most of the failed slopes have been modified to lower slope angles as attempted remediation; however in many instances the failure reoccurred. The dominant soil in the cuts and used for borrow material is Kansan age glacial till, while the underlying bedrock is Pennsylvanian shale of the Des Moines series. The till contains significant amounts of the underlying bedrock. In an effort to gain insight into the cause of these failures, an embankment with extensive failures in Monroe County was studied. One slide selected for intensive study was at a 2V:1H slope and 8 meters high. The slide was 16 meters in length. The failure zone was essentially parallel to the original surface at a depth of 0.75 meters. Average strength parameters used in stability analyses produced factors of safety that indicate that failure should not have occurred. X-ray diffraction tests indicate a slightly broader montmorillonite peak in surface soils compared to interior embankment soils, which may indicate the presence of intracrystalline moisture and perhaps a different exchangeable cation in the failure zone soil. This subtle difference could account for a lower shear strength in the soil at the surface of the embankment. It is interpreted that the most likely cause of failure is the reduction of cohesion near the embankment surface after construction. If the reduction of strength is due to weathering and saturation leading to the subsequent swelling of the montmorillonite is the cause of failure, then remediation such as flattening the slope would be ineffective. The use of other soil strengthening techniques such as the use of geosynthetics, minipiles, or chemical stabilization would provide better, long term stability.

Department(s)

Civil, Architectural and Environmental Engineering

Appears In

International Conference on Case Histories in Geotechnical Engineering

Meeting Name

Fifth Conference

Publisher

University of Missouri--Rolla

Publication Date

4-13-2004

Document Version

Final Version

Rights

© 2004 University of Missouri--Rolla, All rights reserved.

Document Type

Article - Conference proceedings

File Type

text

Language

English

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Apr 13th, 12:00 AM Apr 17th, 12:00 AM

Landslides in Shale-Derived Glacial Till

New York, New York

An area in south-east Iowa is notorious for landslides in both cut slopes and embankments. Most of the failed slopes have been modified to lower slope angles as attempted remediation; however in many instances the failure reoccurred. The dominant soil in the cuts and used for borrow material is Kansan age glacial till, while the underlying bedrock is Pennsylvanian shale of the Des Moines series. The till contains significant amounts of the underlying bedrock. In an effort to gain insight into the cause of these failures, an embankment with extensive failures in Monroe County was studied. One slide selected for intensive study was at a 2V:1H slope and 8 meters high. The slide was 16 meters in length. The failure zone was essentially parallel to the original surface at a depth of 0.75 meters. Average strength parameters used in stability analyses produced factors of safety that indicate that failure should not have occurred. X-ray diffraction tests indicate a slightly broader montmorillonite peak in surface soils compared to interior embankment soils, which may indicate the presence of intracrystalline moisture and perhaps a different exchangeable cation in the failure zone soil. This subtle difference could account for a lower shear strength in the soil at the surface of the embankment. It is interpreted that the most likely cause of failure is the reduction of cohesion near the embankment surface after construction. If the reduction of strength is due to weathering and saturation leading to the subsequent swelling of the montmorillonite is the cause of failure, then remediation such as flattening the slope would be ineffective. The use of other soil strengthening techniques such as the use of geosynthetics, minipiles, or chemical stabilization would provide better, long term stability.