NEHRP Clearinghouse

Performance of Improved Ground during the Loma Prieta Earthquake.
Mitchell, J. K.; Wentz, F. J.
National Science Foundation, Washington, DC., October 1991, 115 p.
Identifying Number(s)
The Loma Prieta earthquake has provided one of the first opportunities to evaluate the behavior of treated ground that has actually been subjected to significant seismic shaking. A comprehensive evaluation has been made of twelve sites where ground improvement had been used prior to the earthquake. The treatment methods included vibro-replacement using stone columns, sand compaction piles, non-structural timber displacement piles, deep dynamic compaction, compaction grout, and chemical penetration grouting. For each site available information was collected and analyzed with respect to the type of structure or facility, initial soil conditions, the level of ground improvement required, treatment methods considered and selected, construction procedures and problems, level of improvement achieved, shaking at the site during the Loma Prieta earthquake, and performance of the treated ground. At all but one site the treated soil was a man-made fill; at seven, the soil was a hydraulic sand fill. The required depths of treatment were up to about 30 ft in most cases, with treatment to a depth of 40 ft specified for one of them. The maximum peak ground accelerations at the sites ranged from a low of 0.11g to a high of 0.45g. Without exception, there was little or no distress or damage from ground shaking to either the improved ground or to the facilities and structures on it. In many cases, untreated ground adjacent to the improved ground cracked and/or settled, primarily because of liquefaction. In every case studied in which the ground accelerations were great enough that liquefaction of the untreated ground would be predicted to occur, it did occur.
Earthquake damage; Earthquake engineering; Earthquakes; Soil aggregates; Soil dynamics; Soil properties; Loma Prieta Earthquake; Earth movements; Soil compacting; Soil cement; Soil stabilization; Liquefaction