Harasawa Yoshinobu

Research on methods for evaluating the tensile strength of geomaterials.

Yutaka Fukumoto

In recent years, natural disasters such as earthquakes have become increasingly severe, and damage and countermeasures have become major social problems. The development of cracks in the soil can cause major problems in terms of geotechnical engineering and other aspects. As a prerequisite, it is important to measure and evaluate the tensile strength of the soil that causes cracking. Existing tensile testing machines for geomaterials cannot grip the specimen in parts, so a surface gripping method is used. However, this makes it difficult to fill the frame sufficiently and has frictional effects. Concrete testing machines grip the edges of the specimen so strongly that the geomaterial is destroyed. A new mechanism was therefore considered necessary. In this study, the specimen was covered with a membrane, and the tensile test was carried out using a surface gripping method. Four specimens were used in this study: compacted (blue clay and Kasaoka clay), compacted (Kasaoka clay) and undisturbed specimens. Two methods were used to prepare the specimens: compaction and consolidation. For compaction, a method that allows specimens to be prepared in a single layer without forming layers was used, as existing methods such as five-layer compaction fail when vacuum pressure is applied. From the above, it was found that the peak point appeared later in the specimens made by consolidation than by compaction. For the same Kasaoka clay, the slope and peak point of the graph differ between compaction and consolidation, with consolidation being more gradual. The undisturbed specimens were found to have a longer time from the change in slope to failure than the other specimens. The compaction (blue clay) was found to have a lower overall tensile strength and strain. In conclusion, the objectives of this study, i.e. to establish whether a direct tensile test method for geomaterials using vacuum pressure is feasible, to obtain test results and to define the various conditions, were achieved. Future tasks include collecting data on consolidation and undisturbed samples.