JP Singh and Associates

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COMPUTER PROGRAM S-SHAFT FORLATERALLY LOADED
LARGE DIAMETER SHORT SHAFTS IN LAYERD SOIL
JP Singh and Associates in association
with Mohamed Ashour, Ph.D., P.E. Gary Norris,
Ph.D., P.E. March 2004
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Workshop Objectives

• Why should we use the S-SHAFT program?
• Concepts employed in the S-Shaft program
• Implementation of the S-Shaft with bridge
  foundations
• Capabilities of the S-Shaft program
• Program validation and WSDOT example problems
• Program demonstration
• Future work in the next phase

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Effect of Structure Cross-Sectional Shape on
Soil Reaction (Not Considered in LPILE)
Laterally Loaded Pile as a Beam on Elastic
Foundation (BEF)
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Effect of the Footing Flexural Rigidity (EI) on
the Distribution of the Soil Reaction (Effect of
pile/shaft on soil reaction, i.e. p-y curve,
which is not accounted in the LPILE p-y curve)
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The traditional p-y curve (in LPILE) does not
account for the pile/shaft EI variation
Based on the Strain Wedge Model Analysis
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Pile/shaft-head condition, which is not
considered in the traditional p-y curve (LPILE)
has been proven experimentally and shown below
by the SW model
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A COMPARISON BETWEEN THE SW MODEL AND LPILE
COMPUTER PROGRAM
P-y curve (i.e. modulus of subgrade reaction, Es)
is the key factor in the analysis of laterally
loaded piles
S-SHAFT (SW Model) p-y curve is based on the
concept of triaxial test and effective stress
analysis, and local site conditions. p-y curve
is a function of pile properties such as pile
head fixity, bending stiffness, pile head
embeddment, and pile cross-section shape.
LPILE Semi-empirical p-y curve based on one full
scale field test (Mustang Island test for p-y
curve in sand, Sabine River test for soft
clay). p-y curve accounts for only the pile
width (no pile properties). The p-y curve is
unique in the same soil and for the same pile
width.
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S-SHAFT (SW Model) p-y curve for liquefiable
soils (completely and partially liquefied
soils). P-y curve for large diameter short
shaft P-y curve is affected by the nonlinear
behavior of pile material (varying
EI). Mobilized group interaction with no need
for assuming any P-multiplier.
LPILE No p-y curve in liquefied soil. It is
just a reduction factor based on soil residual
strength P-y curve for slender long piles
Varying EI has no effect on the p-y
curve. Empirical P-multiplier with pile group.
A number of correction factors
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Varying Deflection Patterns Based on Shaft Type
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Pv

• LARGE DIAMETER SHORT SHAFT
• Elements Required to
• Analyze the Large
• Diameter Shaft
• Vertical side shear
• Sand, Clay, C-? Soil, Rock

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• T-Z Curve
• Sand, Clay, C-? Soil, Rock

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• Tip Resistance

• Material Modeling

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• Soil Liquefaction

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SHORT SHAFT MODELING
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Vertical Shear Stress
Shaft Cross Section
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Ashour and Norris UNR
The Basic Strain Wedge Model in Uniform Soil
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Program Capabilities

• Analysis of short shafts under lateral and axial
  loads based on soil-shaft-interaction in sand,
  clay,
• c-? soil and rock
• (deflection, moment, shear force, line load and
  excess water pressure)

• p-y curve based on soil and shaft properties
• Effect of nonlinear behavior of shaft
• material on the p-y curve
• Vertical side shear resistance
• p-y curve in liquefied soil

• Mobilized t-z curve and shaft base resistance

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Program Capabilities

• Shaft classification (short / intermediate/long)
• and varying cross section

• Shaft group (one row) with/without cap effect

• Isolated shaft-head or shaft group stiffnesses
  matrix
• (K11, K22, K33, K44, K55, K66)

• Shaft Axial response (Load vs. Settlement)

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COMPARISONS WITH FIELD TESTS
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Las Vegas field test for short shaft
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Southern California field test for short shaft
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SHAFT GROUP INTERACTION
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P-multiplier (fm) concept for pile group (Brown
et al. 1988)
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PILE GROUP
Configuration of the Mobilized Passive
Wedges,and Associated Pile Group Interference
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Horizontal (Lateral and Frontal ) Interference
for a Particular Pile in the Pile Group at a
Given Depth (in the Strain Wedge Model)
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Shaft B1
Shaft B2
The Taiwan Test by Brown et al. 2001
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In order to match the measured data using LPILE,
the traditional p-y curves were modified as
shown above
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SHORT SHAFTS IN LIQUEFIED SOIL
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Current Available Procedures That Assess the
Pile/Shaft Behavior in Liquefied Soils (Using
the Traditional P-y Curve) 1. Construction of
the p-y curve of soft clay based on the
residual strength of liquefied sand presented
by Seed and Harder (1990) 2. The use of
random Pmult lt 1 to reduce the stiffness of the
traditional p-y curve of sand 3. Reduce the unit
weight of liquefied sand with the amount of Ru
(Earthquake effect in the free-field ) and then
build the traditional p-y curve of sand based on
the new value of the sand unit weight.
(proposed by Brown based on Cooper River Test)
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Fig. 1 Corrected blowcount vs. residual strength
(Seed and Harder, 1990)
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Comparison between the actual p-y curve in
liquefied soil and the currently used ones
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Fig. 1 Subsequent undrained stress-strain
behavior of sand that has experienced partial or
complete liquefaction (employed in S-Shaft)
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Input Data Utilized in the SW Model Procedure
(S-SHAFT) 1. Peak ground acceleration (amax)
and the magnitude of the EQ to evaluate the
excess porewater pressure (Ru) induced by
cyclic loading 2. Pile/Shaft properties 3.
Soil properties Effective unit weight of
soil (N1)60 (i.e Relative density, Dr)
Angle of internal friction (f) Sand grain
roundness parameter (r) Percentage of
fines Axial strain in sand at 50 strength,
e50 Uniformity coefficient (Cu)
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Soil Profile and Properties at the Treasure
Island Test
Peak Ground Acceleration (amax) 0.1
g Earthquake Magnitude 6.5 Induced Porewater
Pressure Ratio (ru) 0.8 - 0.9
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TREASURE ISLAND TEST
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Measured and Calculated Results for Treasure
Island Test (CISS of 0.324-m diameter
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Measured and Calculated Results for Treasure
Island Test (H-Pile)
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Measured and Calculated Results for Treasure
Island Test (CISS of 0.61-m diameter
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Fig. 1 Corrected blowcount vs. residual strength
(Seed and Harder, 1990)
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The SW Model is the only program to predict the
concave-up p-y curve at Treasure Island Test
API (Pmult 0.3)
p-y Curve at 0.2 m Below Ground (0.61-m Diameter
CISS )
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API (Pmult 0.3)
p-y Curve at 1.5 m Below Ground (0.61-m Diameter
CISS )
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API (Pmult 0.3)
p-y Curve at 2.3 m Below Ground (0.61-m Diameter
CISS )
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P-y curves from the SW model program
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Soil Profile and Properties at the Cooper River
Bridge Test
Peak Ground Acceleration (amax) 0.3
g Earthquake Magnitude 6.5 Induced Porewater
Pressure Ratio (ru) 1.0
Mt. Pleasant Site (Cooper River Br) Soil Profile
and Data Input
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Induced ru in the field 1.0
, ru 1
Lateral response of shaft MP-1 at Mount
Pleasure test site (Cooper River Bridge)