GROUND SETTLEMENT IN SIMI VALLEY FOLLOWING THE NORTHRIDGE EARTHQUAKE

Significant differential settlements were observed on a flat, undevelo ped, generally silty but highly stratified alluvial site in eastern Si mi Valley, Calif., due to groundshaking from the 1994 Northridge earth quake. The observed settlements were due to both liquefaction of soil beneath the ground water table and dry shaking of loose soils above it . A nearby strong motion recording station provided highly reliable gr ound motion data for analysis. Extensive cone penetration tests (CPT) along with occasional seismic cones (SCPT), Rat plate dilatometer test s (DMT), and soil sampling were performed. Previously developed method s were adopted for converting the CPT data to equivalent Standard Pene tration Test blow count (SPT-N) values for establishing liquefaction p otential and predicting settlement. Site specific calibration of CPT d ata was performed to establish a correlation between CPT readings and the percentage of fines. Contours of predicted ground settlement agree d very well with the location and the observed differential settlement s along a ground fissure that developed shortly after the earthquake.