Lateral Spreading of Pile Foundations During Liquefaction

1. Lateral Spreading of Pile Foundations During Liquefaction Kyle Bickler Eci 281a / Fall 2003 University of California, Davis

2. Pile Foundations • Reasons for Implementing Pile Foundations[1] • Upper soil layers may be too weak to support loads transmitted by the superstructure • Overall soil stratum may be composed of expansive and collapsible soils • Piles resist uplifting forces imposed on the superstructure • Bearing capacity is maintained in the event of ground surface erosion • Piles resist the forces associated with horizontal loading of the superstructure • Basic Theory Behind Pile Design Qu=Qp+Qs • Qu = Ultimate pile load carrying capacity • Qp = Point bearing capacity • Qs = Skin friction

3. Pile Foundations Cont’d • Instances of Pile Foundation Failure • Excessive settlement due to the loss of load carrying capacity • Pile fracture due to excessive horizontal loading of the superstructure • Pile shearing and fracture due to lateral displacement of underlying liquefied soil layer(s) • Scope of this Presentation • To briefly examine the latter instance of failure outlined above • To briefly outline commonly used ground improvement techniques that will minimize or prevent liquefaction induced lateral spreading • To briefly consider the implementation of an underground structural barrier to mitigate the consequences of liquefaction near a free boundary

4. Single Pile Damage Associated With the Lateral Displacement of a Single Liquefied Soil Layer Abdoun & Dobry, 2002

5. Typical Pile Group Damage Associated With Lateral Displacements of Underlying Soil Layers • Figures (a) through (e) show the typical locations of permanent damage to pile foundations as a result of subsurface soil layers liquefying. • Figure (f) demonstrates how appropriate treatments may minimize, if not eliminate entirely, the risk of pile damage associated with differential lateral spreading. Abdoun & Dobry, 2002

6. Main Variations of Liquefaction Induced Ground Displacements • Far from a free boundary • Moderate, to large settlements • Some lateral displacements • Near a free boundary • Moderate, to large settlements • Moderate, to Large lateral displacements Arango, 2002

7. Limiting Ground Displacements of Liquefied Soils • Ground Improvement Methods • Vibration methods • Deep Dynamic Compaction • Deep Soil Mixing • Rock Drains • Excavation & Replacement • Best for improving ground far from free boundaries • Structural Barriers • Underground Pile Barrier • Underground Clay Barrier • Underground Cemented Barrier (through deep mixing) • Best for protecting ground near free boundaries

8. Underground Pile Barrier • Main Principle • Drive a network of staggered piles into the stratum between the ground to be protected and the free boundary • At least 40-50% of the pile length must be embedded in a non-liquefiable layer • Some liquefied material may flow through the spaces between the piles developing passive earth pressures against the pile walls

9. Example of an Underground Pile Barrier Free boundary Protected ground Arango, 2002

10. Main Points • High financial losses are associated with lateral spreading and ground displacements towards free boundaries such as shorelines, river channels, and open trenches[3]. • The fundamental design principals do not safely account for the stresses transmitted to the pile system by the spreading of liquefied earth. • Current practice deals almost entirely with minimizing the risk of excessive ground displacements during liquefaction events .

11. Literature Sources [1] Das, MB. Principles of Foundation Engineering. Pacific Grove: Brooks/Cole Publishing Co, 1999. [2] Abdoun T, Doubry R. Evaluation of Pile Foundation Response to Lateral Spreading. Soil Dynamics and Earthquake Engineering. 22 (2002). 1051-1058. [3] Arango I. Mitigation of Lateral Ground Displacements of Liquefied Soils with Underground Barriers. Soil Dynamics and Earthquake Engineering. 22 (2002). 1067-1073.