Earthquake Engineering Support
Abstract
A large experimental study has been undertaken at the USAE Waterways Experiment Station (WES) as part of the ongoing U.S. Army Engineer Earthquake Engineering Research Program (EQEN) to investigate the behavior of liquefying soil materials. In this study, experiments have addressed the development of excess pore pressure and the onset of liquefaction within a deep soil column using the new large geotechnical centrifuge and earthquake shaker. The approach adopted was to use standard procedures for the assessment of liquefaction resistance to derive values of the strength reduction factor K(delta) from the experimental results, with the object of confirming the validity of the simplified K(delta) approach under high effective overburden stresses. Data of excess pore pressures from the experiments showed the soil column reaching a state of initial liquefaction over a range of depths up to around 20 m (65 ft) under moderate levels of base input shaking, and from this data values of Ka could be derived. As expected, these showed considerable variability, being sensitive to initial assumptions. More significantly, at greater depths, the development of excess pore pressure was capped and despite continued shaking at similar amplitude, the development of excess pore pressure did not reach a sufficient level to cause initial liquefaction. Similar observations have been found in the literature from torsional shear tests. It is concluded that the effects of confining stress and the strain boundary conditions which exist in the soil column in the field are significant in controlling the development of excess pore pressure. In the absence of initial liquefaction, the use of the Ka factor to assess the cyclic resistance of the soil is not considered appropriate.
Document Details
- Document Type
- Technical Report
- Publication Date
- Nov 01, 1999
- Accession Number
- ADA372475
Entities
People
- R. S. Steedman