Yoshimichi Tsukamoto

Settlement of Rigid Circular Foundations during Seismic Shaking in Shaking Table Tests

AbstractThe settlements of structures resting on saturated sand deposits are examined in shaking table tests. Two series of tests are conducted to examine the effects of the duration of seismic shaking and the group effects of closely spaced foundations. The models of rigid circular foundations are founded on the surface of saturated clean fine sand, and seismically excited. The settlements of model foundations and the distributions of excess pore-water pressures induced around the model foundations are observed. In one of the test series, the settlements occurring during shaking are found to increase as the durations of shaking increase; however, the settlements occurring after the end of the shaking remain almost the same, regardless of the durations of shaking. The total settlements are, therefore, found to increase as the durations of shaking increase. In the other test series, the settlements occurring during shaking remain almost the same, regardless of the spacing. However, the settlements occurrin...

Integrating use of Swedish Weight Sounding Tests for Earthquake Reconnaissance Investigations

The use of Swedish weight sounding tests has been examined by the authors for a wide range of stability problems of natural and reclaimed soil deposits during earthquakes. The present study is aimed at integrating these studies into one framework and at facilitating the use of Swedish weight sounding tests for future earthquake reconnaissance investigations. The example case history is given to prove the usefulness of subsurface soil profiling by means of Swedish weight sounding tests, and the procedures for determining the undrained shear strength, liquefaction strength and post-liquefaction settlement are examined and described in detail. Swedish weight sounding tests prove to be useful in analyzing the field performance of natural and reclaimed soil deposits during earthquakes.

Small Strain Properties and Cyclic Resistance of Clean Sand Improved by Silicate-Based Permeation Grouting

Permeation grouting has been developed as one of countermeasures against soil liquefaction during earthquakes. This study aims at examining the small strain properties and cyclic resistance of jellied sand improved by silicate-based permeation grouting. In the first part of the present study, the small strain properties and cyclic resistance of jellied sand were examined based on the measurements of propagation velocities of longitudinal and shear waves travelling through triaxial specimens and the results from subsequently conducted undrained cyclic triaxial tests. In the second part, straincontrolled small-amplitude cyclic triaxial tests are conducted using non-contact gap displacement transducers to examine the initial elastic moduli of silicate gel itself and intact sand as well as jellied sand. The roles of the stiffness at small and large strains of silicate gel in increasing the undrained cyclic resistance of jellied sand are discussed in detail.

Centrifuge modelling of jackups and spudcans on drained and partially drained silica sand

Abstract This paper presents selected data and analyses of centrifuge tests of spudcans and 3-leg independent leg jackup models under fully drained and partially drained conditions on medium dense fine saturated sand. Data of single spudcan models show the importance of vertical displacements in terms of ‘hardening’, and for reducing the potential for liquefaction under cyclic loading. Similarity of loadpaths under conditions of zero vertical displacement during loading at different values of vertical settlement is observed. Data of 3-leg jackup tests indicate that, in the absence of scour, a well-seated flat spudcan on medium dense silica sand can provide considerable rotational stiffness which, however, reduces as cyclic load amplitudes increase. An empirical concept of a ‘fixity ellipse’ is developed. Related analytical studies and experimental work on horizontally-skirted spudcans are also briefly discussed.

Development of Rational Soil Liquefaction Countermeasure Consisting of Lattice-Shaped Soil Improvement by Jet Grouting for Existing Housing Estates

The lattice-shaped soil improvement by means of jet grouting is one of the promising methods for soil liquefaction countermeasures. In order to develop a more effective construction method for residential houses, a series of centrifuge model tests and numerical analyses are conducted to see if there would be any more rational shapes of underground soil improvement structures to counter against soil liquefaction. It is found that the ordinary lattice walls with a surface cover would be more effective. The field verification tests are also conducted to examine if the micro machine developed in the present study can be practically used in residential areas.

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.