The five kinds of slaking tests, which were made up the various combinations of drying, submergence and freezing processes, were carried out on the parent rocks of sedimentary mudstones. Also, for the parent rocks, undrained triaxial compression tests were under ultra-high pressure condition. Furthermore, by using the coarse gravels of sedimentary mudstone produced due to the effect of slaking in-situ, the triaxial compression shear tests were carried out on the compacted air-dried and saturated Specimens with the four different gradations in the range of particle size 0.84 mm – 19.1 mm. Based on the test results, the slaking and triaxial shear properties of sedimentary mudstones were investigated.


The sedimentary mudstone is classified into the soft rock. In general, it is crushed due to the effect of slaking. Then, in order to deal with the geotechnical problems in practical such as the settlement, the slope stability and the bearing capacity of mudstone ground, the fundamental studies on not only the slaking and mechanical properties of parent rocks but also geotechnical properties of crushed mudstone due to the slaking must be performed.

In this paper, the five kinds of slaking tests and the triaxial compression shear tests were carried out on the parent rocks of tertiary sedimentary mudstone, and the geotechnical properties of parent rocks were investigated. After the slaking and compression shear tests, the measurements of pore diameter distributions were carried out. By using the crushed mudstone due to the effect of slaking in-situ, the strength and particle crushing properties of compacted coarse gravels were also discussed.


The samples used in this investigation are three kinds of tertiary sedimentary mudstones with physical properties shown in Table 1. The sample A and B are parent rocks of sedimentary mudstones, and as shown in Photo. 1, the sample C is crush-sample A and B were taken from the depth of 0.5 m – 1.0 m below the ground surface by using core cutter. The parent rocks show high water content more than 20 % and ignition loss (Li) of about 10 %, which is defined as the ratio of the mass lost by heating at the temperature of 800 °C to the total dry mass. The sample C at the air-dried condition in the field is sieved by using sieves in the four different gradations shown in Fig. 1. The measured results of pore diameter distributions for the three kinds of mudstones, which are obtained with porosimeter apparatus, are shown in Figs. 2 and 3. The curves of pore diameter distributions are different each other and the amounts of pore volume per unit dry mass (Σv p) up to diameter p 0.0035 μm tor sample A, B and C are about 0.254 ml/g, 0.156 ml/g and 0.180 ml/g, respectively. However, as can be seen in Fig. 3, the range of pore size for three samples is approximately less than 0.2 μm.

(Photo in full paper)

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