Landslide and Slope Stabilization Using Piles And Micro

Report
2014 National RAC and TRB State Representatives Meeting
RP 213: LANDSLIDE AND SLOPE
STABILIZATION USING PILES AND
MICRO-PILES ON THE LRFD
Donald L. Williams, P.E.
Section Head
West Virginia Department of
Transportation – Division of Highways
Research and Special Studies Section
The Research Team
• Principal Investigator:
Mohamed Ashour, Ph.D., P.E.
West Virginia University Tech
• WVDOT-DOH Project Monitors:
Joe Carte, P.E.
Larry Douglass
• Validation of Research Findings:
Tia Como, P.E.
Fairmont State University
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The Problem
1. Landslides are a critical issue in West Virginia.
2. The WVDOT often uses driven, drilled, or micropiles to reduce the potential, or to prevent slope
failures, stabilize bridge embankments, etc.
3. Prior to the RP 213
research, simplified
methods based on
crude assumptions
were used in design.
3
The Problem
4. The major challenge
lies in the evaluation of
lateral loads (pressure)
acting on piles by the
moving soil.
4
The Problem
5. The interaction among piles including the lateral
effective range of pile resistance is very complex.
6. A more sophisticated and proven analysis was
needed to more realistically assess the destructive
effect of the sliding soil mass.
7. The use of piles is a favorable practice, particularly
when rock deposits lie to the ground surface;
however, no effective or practical technique was
available to address this condition.
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The Research Objectives
1. Highlight the limitations of existing procedures
currently used to address slope stabilization using
piles.
2. Provide a design methodology for slope stabilization
using driven/drilled/micro-piles based on limit
equilibrium analysis and the Strain Wedge method.
3. Improve the level of certainty related to the
downslope soil movement (small shoulder slopes
and large slopes) and the induced distributed load
along the stabilizing piles.
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The Research Objectives
4. Incorporate soil and pile properties, and pile
spacing in the analysis of stabilized slopes.
5. Develop the ability to input pre-existing landslide
geometry and to estimate the resulting distributed
driving forces.
6. Assess the shear force and moment developed
along the pile based on the pile type (materials and
dimensions) and the LRFD.
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The Research Objectives
6. Provide a number of case studies and comparisons
to validate and verify the research findings.
7. Establish a Windows-based computer program
(PSSLOPE) and accompanying manual, customized
to meet the needs of the WVDOH, to deal with
small shoulder slips and large slips as well.
8
The Research Product: PSSLOPE
1. Limit equilibrium analysis and
Strain Wedge (SW) model
technique is used to assess
slope stability before and after
using driven piles.
2. Determines the mobilized driving force caused by
sliding soil mass that needs to be transferred via
piles to stable soil layers below the slip surface.
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The Research Product: PSSLOPE
3. Graphic-user interface
facilitates entering the
input data and the
analysis/plot of the
output results.
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Impact of Implementing Results
1. The research provides a reliable LRFD-based design
procedure that is compiled into the PSSLOPE
program for the analysis of pile-stabilized slopes.
2. The use of PSSLOPE will lower the chance of
catastrophic failure and level of risk that the
designers assume by using unreliable techniques
based on questionable assumptions.
3. Designers have the ability to input pre-existing
landslide geometry and to estimate the resulting
driving forces.
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Impact of Implementing Results
4. Cost savings or relief from a possible failure will be
achieved.
5. The tedious manual iterations required in past
practices are no longer necessary.
6. The design methodology demonstrates the
suitability of pile-stabilized slopes; therefore, a
mitigation plan for vulnerable slopes and bridge
embankments can be established based on such
knowledge.
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Impact of Implementing Results
7. The use of the PSSLOPE software has been fully
implemented by the WVDOT-DOH and is currently
in use with great success.
8. Updates to the PSSLOPE software and users
manual are currently in development.
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Thank You
Donald L. Williams, P.E.
Section Head
West Virginia Department of
Transportation – Division of Highways
Research and Special Studies Section
(304) 677-4000
[email protected]
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