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District 11-0: Geotechnical Engineering Unit
Landslide, Drainage Failures, Shallow Failure Identification and Remediation
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Identification of Failure Types
• Drainage facility failure• Erosion of Shoulder Back up due to sheet flow• Deep failure
– Slip plane (red beds)– Increased overburden pressure– Soils compromised due to oversaturation
• Scour
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Drainage Failure
Lack of maintenance of drainage facilities results in the erosion of fines in the slope.
The failure will continue to chase its way back into the roadway.
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Sheet Flow removing fines in the back up
Prior to channelizing, sheet flow will wipe the fines from a surface.
Typical symptoms are leaning guide rail and a lack of shoulder back up.
Cracking can reflect up into the pavement if the supporting material islost.
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Deep FailureThe slope is pulling away from the roadway.
The weight of gabions andsupporting soil are causing the overburden soil to slide on a clay layer.
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Overburden Sliding on a Clay Layer
Saturated clay layers act like an oil slick for overburden soils/trees/roads to slide down.
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Deep Failure – Toe bulge visible down slope
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Scour
Supporting material at the toe of wall/ slope removed. Results reflected inpavement & leaning walls.
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Scour
Stream removed toe of slope. Compounded with sheet flow removing fines, over steepening of slope results in slope settlement.
Leaning trees and settlement of guiderail are key indicators.
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Typical Repair Details
• Shoulder Backup– Prevents erosion of fines from sheet flow– 1V:1.25H Max Slope
• Rock Slope– Buttressing effect of competent, well drained material– 1V:1.25H Max Slope
• Soil Nails – Creates composite action tying weaker layers into
competent layers• GRS Wall
– 1V:0.5H Max Slope
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Typical Repair Details
• Pile and Lagging Wall• Low-Cost Short Term Fixes
– Block Walls– Gabion Walls
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Typical Shoulder Backup Detail
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Typical Shoulder Back up
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Typical Rock Slope Armoring Details
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Benched Rock Slope Detail
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Typical Rock Slope
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Typical Rock Slope
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Typical Rock Slope
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Typical Soil Nail Repair
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Typical Soil Nail Repair
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Typical GRS
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Typical GRS Wall Repair
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Pile and Lagging Wall
Before
After
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Pile and Lagging Wall - Details
Size in accordance with project specific details.
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Gabion Block Wall
Ensure proper installation to prevent scour.
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RC-43M - Gabions
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RC-58M – Single Faced Barrier Wall
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RC-30M – Combo Pipe