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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.

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Presentation on theme: "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."— Presentation transcript:

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2 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

3 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

4 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)

5 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)

6 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

7 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

8 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

9 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

10 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

11 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

12 Z Soil-Shaft Side Shear Resistance SHORT SHAFT MODELING

13 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 oo nn 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

14 The Basic Strain Wedge Model in Uniform Soil

15 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

16 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)

17 COMPARISONS WITH FIELD TESTS

18 8-ft Diameter Shaft

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20 Las Vegas field test for short shaft

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24 4-ft Diameter Shaft

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26 Southern California field test for short shaft

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28 SHAFT GROUP INTERACTION

29 P-multiplier (f m ) concept for pile group (Brown et al. 1988)

30 PILE GROUP Configuration of the Mobilized Passive Wedges,and Associated Pile Group Interference

31 Horizontal (Lateral and Frontal ) Interference for a Particular Pile in the Pile Group at a Given Depth (in the Strain Wedge Model)

32 Shaft B1 Shaft B2 The Taiwan Test by Brown et al. 2001

33 In order to match the measured data using LPILE, the traditional p-y curves were modified as shown above

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36 SHORT SHAFTS IN LIQUEFIED SOIL

37 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)

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

39 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

40 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)

41 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 )

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

43 TREASURE ISLAND TEST

44 Measured and Calculated Results for Treasure Island Test (CISS of m diameter

45 Measured and Calculated Results for Treasure Island Test (H-Pile)

46 Measured and Calculated Results for Treasure Island Test (CISS of 0.61-m diameter

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

48 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

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

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

51 P-y curves from the SW model program

52 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

53 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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