Abstract
The rice-field area in the western section of the city of Kumamoto, was buried under a layer. of mud 30 cm thick on the average, by the overflow of the River Shirakawa in the afternoon of June, 26, 1953.
Owing to ill drainage, this area had been under water for one week or more, maximum depth being calculated to 300cm. The author investigated the cracks in those sheets of mud.
The terrain of the area had been as i t was when wheat, the alternate crop of rice, was harvested, with 80cm intervals between 40 to 42cm furrow (Fig. 2). The inclinations found on the surface of the mud were, from over furrow to the groove, 2 to 10 degrees.
The cracks were various in form. They could be assorted into five patterns (Fig. 3). Pattern E was seen where rice had been planted and harvested. The widths of cracks are here put into four grades (Figs. 4 and 5) in each pattern. Cracks of the four of patterns (A-D) were to be found around each of numerous centers.
In perpendicular sections, clayey ingredients are plenty at the top. Drying being quicker atop, cracks are found to have started at the surface as the mud began to contract and cohere; the gaps are widest at the top.
The greater part of the mud over the area is judged to have settled in the first several hours of the inundation, the rest being added in the following week when the area was under water. It was observed that cracks of the first and second grades of width had first took place, while the mud was considerably wet, starting at the top, grades 3rd and 4th following them as drying went on.
