Swelling and slaking of soft rocks have close relationships with the extrusion of tunnel wall, rapid weathering of cutting slope, landslide and so on. So it is important to grasp the characteristics. However, becsuse of the facts that much time has to be put in the experiment and it is difficult to lay hold of the properties quantitatively, experiments and surveys have not been made sufficiently. The authors have proposed some simple and rapid tests to solve this problem(Kojima et al 1977). We can divide the factors which govern swelling and slaking of soft rocks into two different types. One is the internal factors based on the rock itself, and the other the external ones such as moisture content in rocks. In the former factors, latent possibility of swelling and slaking determined by the grain size distribution of rock itself and species of clay minerals, and extent of compaction are important, especially in soft rocks, special considerations have to be given to so called extent of solidification based on texture and cementation of grains. In simple and rapid test, these factors can be expressed by the following variables.

Latent possibility of swelling WA; it is absorbed water content of the powder which is made by deciccating and pulverizing samples and it can be considered to show the swelling capacity of material itself removing solidification by pulverization. WA is the important index proterties which indicate the extent of swelling without affected by species of clay minerals as shown in Fig. 1.

Extent of compaction yd; it is dry density of "artificially compacted mud" which is made by compacting the powder described above to the density of intact Fig. 1 Change in swelling strain of artifcially compacted mud with WA. WA governs the affection of clay minerals and clay content in and it represents the maximum extent of swelling removing solidification by pulverization.

(Figure in full paper)

Solidification ISL; it can be expressed by slaking index described later. And the latter factors can be expressed by water saturation rate Sw and overburden P. We reported on changes of swelling strain in relation to these conditions in the previous paper (Kojima 1978).

The purpose of this paper is, as the first step to clarify swelling and slaking.characteristics, to understand how swelling strain AV/Vo and slaking change by the internal factors and to derive the experimental formulae to estimate these quantities by simple and rapid tests.

Expression for extent of slaking

The simple and rapid method to determine extent of slaking is to put dry rock fragments into the water and rank them from A to E by observation of their breakage (Kojima 1978). ISL in Fig. 2 can be expressed as follows.

where WSL is moisture content of the rock fragments by absorption after some cycles of drying and wetting in the slaking test. And WSL1 expresses maximum absorbed moisture content by the first cycle of submersion.

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