MSE Retaining Wall
Design Considerations
by
Marcus Galvan, P.E.
TxDOT Bridge Division
Geotechnical Branch
Wall Selection
CONCRETE BLOCK MSE TEMPORARY EARTH SPREAD FOOTING
Gabions Drilled Shaft Soil Nail
RETAINING
Tiedback Hybrid Walls – WALL
SELECTION
MSE/Soil Nail
CUT/FILL
FILL SITUATIONS CUT SITUATIONS
SITUATIONS
DRILLED SHAFT
MSE DRILLED SHAFT
TIEDBACK
CONCRETE BLOCK MSE WITH SHORING
SOIL NAIL
SPREAD FOOTING SPREAD FOOTING
MSE WITH SHORING
TEMPORARY EARTH WITH SHORING
SPREAD FOOTING
GABION HYBRID – SOIL NAIL/MSE
WITH SHORING
Wall Usage by TxDOT
(August 2010 through September 2011)
Retaining Wall By Type
2% 4% 1%
5%
3%
12%
1%
72%
MSE Conc. Block CIP SN RN DS TB other
Wall Usage by TxDOT
(August 2010 through September 2011)
Wall Type Area (ft2) %
MSE 3,196,417 72
Concrete block (no r/f) 47,791 1
Cantilever drilled shaft 72,286 2
Soil Nailed 146,793 3
Rock Nailed 197,216 5
Tied-back 161,827 4
Spread footing 505,019 12
Other 22,389 1
Responsibility
The Project Engineer (Designer of Record) must
ensure that the retaining wall system (design)
selected for a given location is appropriate.
MSEW Construction Project Development
• External Stability Check by TXDOT or Consultant
– Sliding
– Limiting Eccentricity
– Bearing Capacity
– Global Stability
– Settlement
• Internal Stability Check by Vendor
– Tensile Resistance
– Pullout Resistance
– Face Element
– Face Element Connection
• MSEW reinforcement and wall type is NOT specified at
project bidding stage
MSEW Construction Project Development
• External Stability Check by TXDOT or
Consultant
– Sliding – FS > 1.5
– Limiting Eccentricity – e < B/6
– Bearing Capacity – FS > 2.0
– Global Stability – FS > 1.3
– Settlement
Assumed Soil Parameters (External Analysis)
Short- term Long-term
Material
c (psf) φ (ο) c (psf) φ (ο)
Type A,B,D 0 34 0 34
Reinforced fill
Type C 0 30 0 30
Retained controlled 30 or
750 0 0
backfill fill, PI<30 PI- correlation
Foundation soil controlled 30 or
750 0 0
(Fill) fill, PI<30 PI- correlation
Principal Modes of Failure - External
Principal Modes of Failure - External
MSE WALL STANDARD
External Stability - Sliding
FS – Sliding = V1(Tan (phi))
F1 + F2
105/125 = 0.84 or a 16%
reduction in sliding resistance
Sliding Analysis
Sliding Analysis
But less than 2.04
or 0.84 H
Sliding Analysis
We find that the sliding
analysis is very sensitive
to the unit weight in both
the resisting and driving
zones and to the
coefficient of friction
utilized at the base of the
But less than 2.04 wall.
or 0.87 H
Principal Modes of Failure - External
Soil Characteristics
• Stability of every wall must be evaluated
• Short-term and Long-term conditions (make
sure that the soil strengths used in analysis
are valid for the given soil profile).
Soil Characteristics
If the site investigation and geotechnical analysis
results in design parameters that are different from
those shown on the RW(MSE) standard, minimum
factors of safety for the principle external modes of
failure and a ground improvement strategy is not
employed that would improve strength values to
meet or exceed design parameters shown on the
standard, the design strengths must be
communicated to the wall supplier. This can be
accomplished by plan note or a modified standard
reflecting lower strengths as applicable.
DETERMINATION OF THE
UNDRAINED SHEAR STRENGTH
OF FINE GRAINED SOILS
Short Term Analysis
• TEXAS CONE PENETROMETER
• UNDRAINED TRIAXIAL TESTING
• IN-SITU VANE SHEAR TESTING
• DIRECT SHEAR TESTING
Texas Cone Penetrometer - TCP
DETERMINATION OF THE
UNDRAINED SHEAR STRENGTH
OF FINE GRAINED SOILS
• TEXAS CONE PENETROMETER
• Revised Correlation for blow counts less than
15 blows/12”, CTR Research Project 0-5824
Su= 300 + 60(blow count)
TRIAXIAL TESTING
ADVANTAGES DISADVANTAGES
• Long history of use in • Test and Equipment are
engineering practice expensive
• Soil sample is retrieved • Test is complicated
• Principle stresses are known
• Need a fair amount of soil
• Stresses can be varied to for testing
simulate the burial
conditions in the field • Results can vary due to:
- End restraint conditions
- Sample disturbance
IN-SITU VANE SHEAR TESTING
ADVANTAGES DISADVANTAGES
• Rapid, simple, and inexpensive test • No sample is recovered
• Long history of use in engineering • Limited to soft to medium stiff fine
practice grained soils
• Reproducible results in • Results can be affected by roots,
homogeneous fine grained soils shells, gravel, sand seams, and
• Minimal soil disturbance lenses
• Yields the peak and residual
undrained shear strength of fine
grained soils
SHORT TERM GLOBAL STABILITY
ANAYLYS BASED ON APPROPRIATE
SHEAR STRENGTH
FS = 1.45
C = 2000 psf, C = 750 psf,
φ = 34o
φ = 0o
C = 1000 psf, φ = 0o
C = 1200 psf, φ = 0o
C = 2000 psf, φ = 0o
DETERMINATION OF THE
DRAINED SHEAR STRENGTH
OF FINE GRAINED SOILS
Long Term Analysis
• Consolidated Undrained TRIAXIAL Test
with Pore Pressure measurements.
• P.I. Correlation
CU TRIAXIAL TESTING
ADVANTAGES DISADVANTAGES
• Long history of use in • Test and Equipment are
engineering practice expensive
• Soil sample is retrieved • Test is complicated
• Principle stresses are known • Testing Takes Time.
• Stresses can be varied to • Need a fair amount of soil
simulate the burial for testing
conditions in the field • Results can vary due to:
- End restraint conditions
- Sample disturbance
CU Triaxial Test Results
Phi = 29 degrees
Cohesion
Intercept = 2.3 psi
(330 psf)
P.I. Strength Correlation
• ADVANTAGES DISADVANTAGES
• Quick • Correlation, does not take
• History of use in into account secondary
engineering practice structure of materials.
• Various studies have • Indirect measure of soil
contributed to the shear strength.
correlation charts. • Uncertainty in correlation.
• Cohesive component is
unknown.
P.I. Strength Correlation
Long Term GLOBAL STABILITY
ANAYLYS BASED ON APPROPRIATE
SHEAR STRENGTH
FS = 1.35
C = 2000 psf, C = 50 psf,
φ = 34o
φ = 30o
C = 60 psf, φ = 29o
C = 70 psf, φ = 30o
C = 2200 psf, φ = 0o
Principal Modes of Failure - External
OTHER CONSIDERATIONS
POOR PREPARATION
OF RETAINING WALL
FOUNDATION SOILS
MSE Wall
W/Fill
and Ground
Improvement
Foundation Settlement
Ground Water Table
Wall Drainage
Special Design Considerations
• Ground Improvement
– Remove and Replace
– Stone Columns
– Rammed Aggregate Piers
Pile Supported
Embankment
Stone
Columns/Geopiers
MSE Wall Select Backfill
Geosynthetic
Reinforcement
Stone Columns
Remove and
Replace/Wick Drains
Remove and Replace – Reinforced Pad
CONCLUSIONS
• TxDOT has designed and constructed numerous MSE retaining
walls.
• In spite of the increased usage, TxDOT has had relatively few
retaining wall failures.
• The design and planning phase of retaining walls is critical and
must address the actual site conditions, including soil and loading,
that the wall will be subjected to.
• If values in the analysis of the wall (i.e. friction angle for both the
retained and foundation soils) are less than that shown on the
RW(MSE) standard and do not result in a ground improvement
that would positively impact these values, the designer of record
should include the soil strength information in the plan set for use
by the wall supplier.
QUESTIONS?
Ground Conditions
• Soil Shear Strength
– Short Term, C and phi
– Long Term, C’ and phi’
• Ground Water Table
• Necessary Fill
• Necessary Cut
MSE Principal Modes of Failure
LOSS OF MSE BACKFILL
LOSS OF MSE BACKFILL
Obstructions
Obstructions
Incomplete connection
with locking rod.
Soil reinforcing mat is rotated
by wedging to the back of
panel. This prevents bearing
of the grid to the locking rod
allowing potential of
movement on the right side
of the panel.
Photo 1
Obstructions
Omitted
Reinforcement
P.I. Strength Correlation
Design Considerations
vs
Special Design Considerations
TEW WALL
Dissimilar Earth
Reinforcement
TEW WALL
