Various initial experiments were carried out on Neogene mudstone in order to work out a standard test method for physically and mechanically testing the inferior properties of soft rock. As a result, it has been found that the specimen's pre-emersion drying temperature, length of drying and initial water content etc. have a strong influence on the slaking and swelling properties of this mudstone.


On a procede à divers tests initiaux sur les marnes neogènes afin d'etablir un methode de test standard pour analyser physiquement et mecaniquement les proprietes d'inferieur de la roche molle. En consequence, on a decouvert que la temperature de sechage du specimen de pre-emersion, la duree de sechage et la teneur initiale en eau etc., ont une grande influence sur les proprietes d'extinction et de foisonnement des marnes.


Recently, with the remarkable development of the Japanese economy, many large scale civil engineering works such as dams, roads and tunnels have been carried out. However, because of the broken and weak rocks and of the complicated geological structure unique to Japan, in the construction of such large scale civil engineering works, many geotechnical problems must be overcome. Soft rock is one aspect of these problems. The soft rock that is so widely distributed in Japan consists mainly of tuffaceous-agrillaceous sedimentary rocks deposited on Neogene "green tuff geosyncline". With regard to the special features of these sedimentary rocks, the problems are not only the lack of strength but also the shrinkage and expansion resulting from drying and wetting which causes a further reduction of strength and slaking. Therefore, where large scale works are to be constructed on such rock, it is necessary to fully understand the physical and mechanical properties of the soft rock underlying the foundations and to decide whether the ground is suitable for construction, before design and construction. However, the current methods employed for the investigation of soft rock are those used to investigate hard rock or soil, and the problems and points regarding the properties of soft rock can therefore hardly be covered. Thus, in order to clarify the various physical and mechanical properties of soft rock and to develop a standard test method to measure such properties, some new testing apparatuses are presented here together with various experiments which have been carried out.

The particular features of mudstone are the swelling and slaking phenomena, both resulting from soaking after drying. The degree of dryness is regarded as the basic factor in the occurence of these phenomena. Based on these ideas, physical and mechanical tests and immersion inferiority tests were carried out on mudstone of various dryness, and the following is a report of these tests.


The samples were taken from mudstone of the shimajiri group of the Neogene period which are widely distributed in the whole of the southern part of Okinawa Island, Southwest of Japan.

The samples were taken from unweathered strata in an exploratory tunnel 30 – 50 m below the surface.

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