Torsional chear and triaxial compression tests on deformation characters of sands before and after liquefaction

The stress-strain relationships of sand after liquefaction were studied by conducting torsional shear and triaxial compression tests under several conditions. A prescribed number of cyclic loadings were applied first, then a monotonic loading was applied in undrained conditions. The stress-strain curves were affected by the accumulated excess pore pressure ratio and by the severity of liquefaction. The shear and secant modulus decreased to less than 1/1000 due to liquefaction. The shear strain increased more than 10

with very low stress in the liquefied specimen. And, there exists a so called "reference strain at resistance transformation, " which increases with decreases in soil density, severity of liquefaction and fines content, and with increase with confining pressure.(AU)

Shaking table tests on countermeasures against large ground displacement due to liquefaction

Large ground displacements due to liquefaction are classified into two groups: (1) permanent ground displacement along a gentle slope, and (2) lateral flow near banks or seashore. Against the first group, following three categories of countermeasures are seemed to be effective: (1-A) improving the ground in all area by densification to prevent liquefaction, (1-B) strengthening structures to prevent damage, and (1-C) strengthening the ground with walls or steel piles, densification at narrow bands. And, two categories of countermeasures: (2-A) improving the ground and (2-B) strengthening quay walls or retaining walls, are seemed to be effective against the second group. Shaking table tests and some analyses were conducted to study the effectiveness of (1-C) ans (2-B) methods. Based on these tests and analyses, several appropriate methods are proposed.(AU)

Several simulations of buried pipelines during liquefaction

In Japan, everyday life would be seriously affected by damage to the infrastructure resulting from an earthquake, since most lifeline facilities are buried. Given those circunstances, studies of the damage caused to underground structures due to liquefaction have began over the past few years. However, most studies have concentrated on the behavior of buried structures in liquefied ground, with few taking into consideration the process by which the ground is liquefied or the large permanent displacements produced by liquefaction. Accordingly, we have traced the mechanism of damage to lifeline facilities, specifically buried pipelines, with the lapse of time, based on knowledge obtained from past experimental results. We carried out stress analysis on buried pipelines during the liquefaction process and looked for correspondence between the analytical results and the temporally equivalent results of effective stress analysis.(AU)