Performance of Soil Improvement Techniques in Earthquakes

In the last four decades, there has been a steady trend toward the use of ground improvement as a countermeasure against the hazard of liquefaction. It is well understood that sites with ground improvement suffer less ground deformation and subsidence than adjacent, unimproved areas. However, the lack of quantitative performance data has inhibited the development of empirical relationships between site design parameters such as remediation zone depth and lateral extent and site performance parameters such as ground and building settlement for a given level of earthquake shaking. To date, we have compiled over 90 case histories on the performance of improved sites from 14 earthquakes in Japan, Taiwan, Turkey, and the United States. The collection of field case histories, as the first step towards a greater understanding of the performance of improved soil sites during earthquakes, are summarized in this paper. The field case histories cover a wide range of improvement methods, from conventional densification methods like sand compaction piles to less common lateral restraint-based methods such as sheet pile walls or deep soil mixing grids. The collected data indicate that improved sites generally performed well. About 10 percent of the surveyed sites required significant post-earthquake remediation, repair or demolition. Unacceptable performance designations resulted most often for excessive ground deformations in the presence of a severe lateral spreading hazard or because of an insufficient remediation zone depth

Performance of Improved Ground During the 2001 Nisqually Earthquake

Several sites in the Seattle area of Washington incorporated ground improvement as liquefaction mitigation or to increase bearing capacity prior to the 2001 Nisqually earthquake. Facilities with improved ground include an earthen dam, a waste repository embankment, lightweight and large plan structures, and bridge columns and approaches. The sites were improved using vibro-replacement stone columns, vibroflotation, or deep dynamic compaction. All sites performed extremely well, despite evidence of liquefaction and minor structural damage nearby. In this paper, 10 sites are summarized, and the performance of three sites located near liquefied or damaged areas will be described in detail. The detailed sites include a large plan commercial property on liquefiable fill improved to a limited lateral extent, a lightweight tilt-up structure located near evidence of liquefaction at King County International Airport, and an earthen dam with its toe retrofitted using vibro-replacement stone columns

The genetic architecture of the human cerebral cortex

The cerebral cortex underlies our complex cognitive capabilities, yet little is known about the specific genetic loci that influence human cortical structure. To identify genetic variants that affect cortical structure, we conducted a genome-wide association meta-analysis of brain magnetic resonance imaging data from 51,665 individuals. We analyzed the surface area and average thickness of the whole cortex and 34 regions with known functional specializations. We identified 199 significant loci and found significant enrichment for loci influencing total surface area within regulatory elements that are active during prenatal cortical development, supporting the radial unit hypothesis. Loci that affect regional surface area cluster near genes in Wnt signaling pathways, which influence progenitor expansion and areal identity. Variation in cortical structure is genetically correlated with cognitive function, Parkinson's disease, insomnia, depression, neuroticism, and attention deficit hyperactivity disorder