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

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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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Laterally Loaded Pile as a Beam on Elastic Foundation (BEF) P P K1K1 K2K2 4 ft Effect of Structure Cross-Sectional Shape on Soil Reaction (Not Considered in LPILE)

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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) q per unit area B C L q 0.5q K r = K r = 0 Rigid Footing, K r = Flexible Footing, K r = 0 Footing H (1- 2 s ) E P H 3 6 (1- 2 P ) E s B 3 K r = As presented by Terzaghi (1955) and Vesic (1961)

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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 EI 0.1 EI

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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 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. P-y curve (i.e. modulus of subgrade reaction, E s ) is the key factor in the analysis of laterally loaded piles

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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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h = 0.69 X o XoXo Zero Crossing X o > h > 0.69 X o XoXo Zero Crossing h = X o Deflection Pattern Linearized Deflection YoYo YoYo YoYo Deflection Pattern Long Shaft L/T 4 Intermediate Shaft 4 > L/T > 2 Short Shaft L/T 2 L = SHAFT LENGTH T = (EI/f ) 0.2 f = Coefficient of Modulus of Subgrade Reaction Varying Deflection Patterns Based on Shaft Type

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z T y p Soil-Shaft Horizontal Resistance Soil-Shaft Shear Resistance Tip Reaction Due to Shaft Rotation Fig. 2. A Model for A Laterally Loaded Drilled Shaft (Short or Intermediate) Neglected with Long Shafts LARGE DIAMETER SHORT SHAFT Elements Required to Analyze the Large Diameter Shaft: Vertical side shear Sand, Clay, C- Soil, Rock T-Z Curve Sand, Clay, C- Soil, Rock Tip Resistance Material Modeling Soil Liquefaction PoPo MoMo PvPv

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Z Soil-Shaft Side Shear Resistance SHORT SHAFT MODELING

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Deformations in soil layers around an axially loaded shafts QoQo QTQT Sheared soil layers Loading Direction q X X Vert. Shear Stress distribution Shaft Cross Section Shaft Vertical Displacement, Z Shear Stress, T T-Z curve oo nn Shaft roro rnrn r n + m Displacement, z z max Distance n + m znzn Z n + m Shear Stress, Vertical Shear Stress Shaft Cross Section

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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 group (one row) with/without cap effect Shaft classification (short / intermediate/long) and varying cross section 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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8-ft Diameter Shaft

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Las Vegas field test for short shaft

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4-ft Diameter 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 (f m ) 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 P mult < 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 R u (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. 1Corrected blowcount vs. residual strength (Seed and Harder, 1990)

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Pile Deflection, y Soil-Pile Reaction, p Measured p-y Curves at Treasure Island Test (Rollins and Ashford) Upper Limit of S r using soft clay p-y curve Lower Limit of S r API Procedure Comparison between the actual p-y curve in liquefied soil and the currently used ones

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Post-liquefaction stress-strain behavior of completely liquefied sand ( u c = 3c and R u =1) Axial Strain, Deviator Stress, d Post-liquefaction stress-strain behavior of partially liquefied sand ( u c < 3c and. R u <1) xoxo d = 2 S r 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 (a max ) and the magnitude of the EQ to evaluate the excess porewater pressure (R u ) induced by cyclic loading 2.Pile/Shaft properties 3. Soil properties: Effective unit weight of soil (N 1 ) 60 (i.e Relative density, Dr) Angle of internal friction ( ) Sand grain roundness parameter ( Percentage of fines Axial strain in sand at 50% strength, 50% Uniformity coefficient (C u )

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Peak Ground Acceleration (a max ) = 0.1 g Earthquake Magnitude = 6.5 Induced Porewater Pressure Ratio (r u ) = 0.8 - 0.9 Soil Profile and Properties at the Treasure Island Test

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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. 1Corrected blowcount vs. residual strength (Seed and Harder, 1990)

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API (P mult = 0.3) p-y Curve at 0.2 m Below Ground (0.61-m Diameter CISS ) The SW Model is the only program to predict the concave-up p-y curve at Treasure Island Test

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API (P mult = 0.3) p-y Curve at 1.5 m Below Ground (0.61-m Diameter CISS )

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p-y Curve at 2.3 m Below Ground (0.61-m Diameter CISS ) API (P mult = 0.3)

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P-y curves from the SW model program

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Peak Ground Acceleration (a max ) = 0.3 g Earthquake Magnitude = 6.5 Induced Porewater Pressure Ratio (r u ) = 1.0 Mt. Pleasant Site (Cooper River Br) Soil Profile and Data Input Soil Profile and Properties at the Cooper River Bridge Test

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Lateral response of shaft MP-1 at Mount Pleasure test site (Cooper River Bridge ) Induced r u in the field = 1.0, r u = 1

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