CASE STUDIES OF STONE COLUMNS IMPROVEMENT IN SEISMIC AREAS
Soil improvement with stone columns is often implemented in seismic areas in particular as a countermeasure against liquefaction. The efficiency of stone columns can be explained by the compaction effect during their execution, by the reduction of the seismic stress on the soil, and by their draining effect as well. A historical evolution of the first realisations is presented, followed by an inventory of the observed performance of such systems in seismic conditions. Then, recent applications of stone columns combined with pile foundations are presented. Key-Words: seismic area, stone columns, liquefaction, case study, pile foundation.
Physical modelling of vibro stone column using recycled aggregates
Vibro-stone column (VSC) is one of the most commonly used ground improvement techniques worldwide. Its performance depends on the quality of aggregates and interaction with the surrounding soil. The impact of installation methods used and the choice of aggregates to form the columns are still unknown which can result in short and long-term failures. 
 
In this research a primary and three recycled aggregates (RA) which are commonly used in practice were compared in the actual context of the installation and loading of a single column in soft clay. 
 
Two sets of large and small unit cell tests were designed for the study of the short-term behaviour in which the dry top feed method of installation was used on the actual aggregates, despite their unacceptable index tests results. 
 
In both of the unit cell tests, the RAs behaved comparable to the primary source in terms of load carrying capacity and showed that the aggregate index tests results alone should not be considered for the selection of the materials. The particle size distribution and grading of the aggregates were found to be the most important factors affecting the column formation and ultimately its load carrying capacity.
Archaeological Survey of Dangoyama Kofun by 3DGPR
We presented a three-dimensional ground penetrating radar (3DGPR) system for the archeological investigation in a harsh site, where we have to deal with many trees and/or great topographic variations. This system consists of a commercial GPR system with a laser positioning system. With this system, we can move the GPR antenna freely, on which a positioning detector can record accurate position for each GPR data trace. We applied our 3DGPR system at Dangoyama Kofun, a burial mound, in Fukushima prefecture, Japan. A lot of trees and bushes covered the survey area and cannot be cut. We acquired six datasets in two days in this area. We successfully imaged the boundary between the original surface of the burial mound and the covering soil clearly at about 0.3 m depth around the mound. Furthermore, we found some strong reflections appeared at 0.8 m depth in the top area of the mound, which can be from the artificial parts of the burial mound. The results would greatly aid the following archaeological excavation. In addition, we compared the non-interpolated depth slice with interpolated depth slice at same position and demonstrated that the interpolation process on threedimensional GPR data may introduce some artifacts which might mislead our interpretation.