Shohei Kawabe

Viscous Property of Granular Material in Drained Triaxial Compression

The viscous properties of a wide variety of reconstituted loose and dense unbound granular materials, including natural sands and gravels, were evaluated by a series of drained triaxial compression (TC) tests at fixed confining pressure. In total sixteen granular materials having different mean particle diameters, D50, coefficients of uniformities, Uc, fines contents, FC, degrees of crushability and particle shapes were newly tested. The viscous properties were quantified basically by many times changing stepwise the axial strain rate and partially by performing drained sustained loading during otherwise drained monotonic loading (ML) at a constant strain rate. It is shown that the viscous properties can be represented by the rate-sensitivity of the stress upon a step change in the strain rate, the decay rate of a viscous stress increment during the subsequent ML at a constant strain rate and the dependency of the residual stress during ML at a constant strain rate. The effects of the particle characteristics on the viscous properties were evaluated by summarising the results from the present and previous studies. As a new and surprising fact, with poorly graded unbound round granular materials, the stress for the same strain during ML at a constant strain rate decreases with an increase in the strain rate.

Effects of Overconsolidation, Cement Stabilisation, and Unsaturation on the Liquefaction Resistance of Urayasu Sand

Following the 2011 Great East Japan Earthquake and its aftershocks, soil liquefaction and associated phenomena have been widely observed at reclaimed lands along Tokyo bay. Enormous amounts of sand boils were erupted in the city of Urayasu. It is known that the fines content of reclaimed liquefiable soils in Urayasu city varies significantly from 10 to 40–50 %. In the present study, the soil sample erupted as sand boils was retrieved from the city of Urayasu, and multiple series of saturated undrained cyclic triaxial tests are conducted to obtain the liquefaction resistance of fines-containing sand and clean sand without fines. The physical effects of overconsolidation as well as the chemical effects of loosely mixed cement stabilisation are especially examined. In addition, a series of unsaturated undrained cyclic triaxial tests are conducted to obtain the cyclic resistance of fines-containing sand as well as clean sand without fines. The effects of fines on the cyclic resistance of unsaturated Urayasu sand are examined. The effects of overconsolidation, loosely mixed cement stabilisation and unsaturation on the liquefaction resistance of Urayasu sand are then compared and discussed in detail.

Use of Swedish Weight Sounding Tests for Detecting Liquefiable Backfills Reclaimed in Iron Sand Mining Pits in Asahi City of Chiba in Japan

Following the 2011 Great East Japan Earthquake and its aftershocks, soil liquefaction and associated phenomena have been observed in various regions on Kanto plain, including Asahi city in Chiba Prefecture, where hundreds of private houses were damaged due to ground failures mainly associated with subsurface soil liquefaction. In the present study, a series of Swedish weight sounding (SWS) tests were carried out at a dozen of sites in Asahi city. It was found that soil liquefaction occurred mainly at areas corresponding to the soil deposits filled back into iron sand mining pits, which had been extensively carried out during the period starting in 1910s and mainly from 1950s to 1970s. The Swedish penetration resistance was found relatively low in the reclaimed deposits and to increase rapidly when it touched upon the underlying natural deposits at the bottom of the reclaimed deposits. With a help of such typical depth-wise profiles, the depth of reclamation is estimated at each location in Asahi city. The soil liquefaction triggering is then discussed with a help of factors of safety against soil liquefaction estimated from SWS test results.