JP Singh and Associates in association with Mohamed Ashour, Ph.D., P.E. Gary Norris, Ph.D., P.E. March 2004

1. 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

2. 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

3. P P 4 ft 4 ft K1 K2 Effect of Structure Cross-Sectional Shape on Soil Reaction (Not Considered in LPILE) Laterally Loaded Pile as a Beam on Elastic Foundation (BEF)

4. As presented by Terzaghi (1955) and Vesic (1961) L C B Footing q per unit area H Rigid Footing, Kr =  0.5q Flexible Footing, Kr = 0 Kr =  q Kr = 0 (1-2s) EP H3 Kr = 6 (1-2P) Es B3 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)

5. EI 0.1 EI The traditional p-y curve (in LPILE) does not account for the pile/shaft EI variation Based on the Strain Wedge Model Analysis

6. 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

7. 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.

8. 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

9. Yo Yo Yo Deflection Pattern Linearized Deflection Linearized Deflection h = 0.69 Xo Xo > h > 0.69 Xo Xo h = Xo Xo   Deflection Pattern  Zero Crossing  Zero Crossing Zero Crossing Short Shaft L/T  2 Intermediate Shaft 4 > L/T > 2 Long Shaft L/T  4 L = SHAFT LENGTH T = (EI/f )0.2 f = Coefficient of Modulus of Subgrade Reaction Varying Deflection Patterns Based on Shaft Type

10. Pv Mo Po • LARGE DIAMETER SHORT SHAFT • Elements Required to • Analyze the Large • Diameter Shaft: • Vertical side shear • Sand, Clay, C- Soil, Rock T z S o i l - S h a f t S h e a r R e s i s t a n c e p • T-Z Curve • Sand, Clay, C- Soil, Rock y S o i l - S h a f t H o r i z o n t a l R e s i s t a n c e • Tip Resistance • Material Modeling N e g l e c t e d w i t h L o n g S h a f t s • Soil Liquefaction T i p R e a c t i o n D u e t o S h a f t R o t a t i o n F i g . 2 . A M o d e l f o r A L a t e r a l l y L o a d e d D r i l l e d S h a f t ( S h o r t o r I n t e r m e d i a t e )

11. Pv Mo y o Po o FP Fv v FP Fv FP Fv v Mt Ft Vt T SHORT SHAFT MODELING Z S o i l - S h a f t S i d e S h e a r R e s i s t a n c e

12. Qo X Vert. Shear Stress distribution  Loading Direction q Shaft Cross Section Sheared soil layers Deformations in soil layers around an axially loaded shafts X Shear Stress,  T-Z curve o n Shear Stress, T n + m Distance Zn + m QT zn Shaft zmax ro rn rn + m Shaft Vertical Displacement, Z Displacement, z Vertical Shear Stress Shaft Cross Section

13. Ashour and Norris UNR The Basic Strain Wedge Model in Uniform Soil

14. 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

15. 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)

16. COMPARISONS WITH FIELD TESTS

17. 8-ft Diameter Shaft

19. Las Vegas field test for short shaft

23. 4-ft Diameter Shaft

25. Southern California field test for short shaft

27. SHAFT GROUP INTERACTION

28. P-multiplier (fm) concept for pile group (Brown et al. 1988)

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

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

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

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

35. SHORT SHAFTS IN LIQUEFIED SOIL

36. 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 < 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)

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

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

39. Post-liquefaction stress-strain behavior of partially liquefied sand (Duc < s3c and. Ru <1) Post-liquefaction stress-strain behavior of completely liquefied sand (Duc = s3c and Ru =1) Deviator Stress, sd d = 2 Sr Axial Strain, e xo • Fig. 1 Subsequent undrained stress-strain behavior of sand that has experienced partial or complete liquefaction (employed in S-Shaft)

40. 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)

41. 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

42. TREASURE ISLAND TEST

43. Measured and Calculated Results for Treasure Island Test (CISS of 0.324-m diameter

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

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

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

47. 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 )

48. API (Pmult = 0.3) p-y Curve at 1.5 m Below Ground (0.61-m Diameter CISS )

49. API (Pmult = 0.3) p-y Curve at 2.3 m Below Ground (0.61-m Diameter CISS )

50. P-y curves from the SW model program