Site liquefaction and remediation

Two free-field downhole array seismic are now available to document the underlying siteliquefaction response mechanisms. records of acceleration and pore pressure at the Wildlife Refuge (Imperial County, CA, USA) reflected liquefaction during the 1987 Superstition Hills earthquake. In 1995, liquefaction at Port Island (Kobe, Japan) was documented by a four accelerometer down-hole array during the Hyogoken-Nambu earthquake. Using these record, the associated shear stress-strain response is identified and employed as a guideline for development of liquefaction cournter-measure techniques. A number of these tecniques are discussed in view of the identified response mechanisms. (AU)

Construction of stress-strain histories from recorded dynamic response

Instrumental centrifuge laminated box experiments generate acceleration and LVDT displacement histories along the model height. These histories are employed to directly construct the associated dynamic stress-strain histories. Soil shear response at different elevations is explored. Soil strenght during liquefaction and lateral spreading is revealed at different elevations along the model height.(AU)

Engineering aspects of the October 12, 1992 Egyptian earthquake

On october 12, 1992 a moderate earthquake Mb = 5.9 (Ms = 5.2) occurred about 18 km southwest of the center of Cairo and resulted in significant damage to numerous old and/or poorly constructued structures. Soil liquefaction associated with the occurrence of large sand-boils was observed close to the epicenter. In this study, the earthquake characteristics, along with typical examples of induced damage, are discussed. The observed liquefaction mechanisms provide valuable information on the seismic response of Nile deposited alluvial soils. Such soils constitute much of the inhabited area of Egypt.(AU)

Engineering evaluation of permanent ground deformations due to seismically-induced liquefaction

A study is presented on the engineering evaluation of permanent lateral ground deformation associated with liquefaction and lateral spreading during earthquakes. Newmark's rigid sliding block model is used as main analytical technique, based on the reasonable assumption that generally the deformation occurs during shaking in the downhill direction of the ground surface slope. The study involves laboratory tests, analitical work, and comparisons with case histories and field observations. It culminates with a simplified method to predict lateral deformation using regional attenuation relations for peak ground acceleration and velocity. The laboratory work includes two series of tests. In the first series, drained and undrained cyclic triaxial experiments at different frecuencies on clean, medium dense Ottawa sand were used test a basic assumption of Newmak's method. It is concluded that the method can be applied to dry sand but not to saturated medium dense sand, due to their dilative character and to the shape of their dense stress-strain curves, which do not exhibit the strenght plateau required by the method(AU)