Influence of Consolidation Shear Stresses and Relative Density on Threshold Strain and Pore Pressure during Cyclic Straining of Saturated Sand

A cyclic strain approach to pore pressure buildup and liquefaction during earthquakes of saturated choesionless soils has been proposed and developed. One of the key findings has been the existence, for every potentially liquefiable site and sand layer, of a 'threshold ground surface accelerati...

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Bibliographic Details
Main Authors: Dyvik,R, Dobry,R, Thomas,G E, Pierce,W G
Format: Report
Language:English
Subjects:
Consolidation(Soils)
CYCLES
DENSITY
LOADS(FORCES)
LPN-CWIS-31666
PORE PRESSURE
SAND
SATURATION
SHEAR STRESSES
Soil Mechanics
STRAIN(MECHANICS)
THRESHOLD EFFECTS
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Summary:A cyclic strain approach to pore pressure buildup and liquefaction during earthquakes of saturated choesionless soils has been proposed and developed. One of the key findings has been the existence, for every potentially liquefiable site and sand layer, of a 'threshold ground surface acceleration,' a sub t, below which there is no pore pressure buildup. The value of a sub t is mainly a function of two soil parameters: the 'threshold shear strain' of the sand, gamma sub t, and its maximum shear modulus, G sub max. The existence of a sub t has been detected by several researchers in a number of laboratory studies. Also, the existence of gamma sub t and its range of values for quartz sands has been predicted from simple particulate mechanics considerations. The work presented herein was performed at RPI and constitutes an extension of the experimental study by Ladd and focuses on the effects of anisotropic consolidation and of very low relative densities on gamma sub t and on the rate of pore pressure buildup at cyclic strains slightly above gamma sub t. Two sands, Montery No. 0 sand and Banding Sand, were tested and the results are reported herein. The effect of anisotropic consolidation is important because NC sands in the field are typically anisotropically consolidated, and also because any attempt to extend the cyclic strain approach to earth structures and slopes must necessarily consider the effect of consolidation shear stresses. Testing very loose sand, D sub r = 20 percent, is important because very loose sand deposits in the field are usually the most susceptible to pore pressure buildup and liquefaction during earthquakes.