A systematic laboratory work on high pressure experimentation at the Geological Survey has revealed that compaction (consolidation) is the most important factor to control mechanical properties of the clastic sedimentary rocks, although there are a great variety in terms of geological age, grain size, and texture in it Hoshino et al, 1972; Hoshino, 1974; Hoshino and Inami, 1977). The specimens have been collected from all sedimentary basins in Japanese archipelago, most of which are composed of considerably thick layers of clastic rocks such as mudstone and sandstone only. The apparatus and method of experimentation was described in Hoshino et al (1972).
The experimental results have clearly shown that porosity n decreases as strength increases in semi-logarithm relation as.
(Figure in full paper)
In Fig. 1, relation between porosity and strength of mudstone is shown. This relation satisfies formula (1). At atmospheric pressure, all deformational behaviors are brittle (black circle). However, at higher confining pressure like 500 kg/cm, mudstone more than 30 % in porosity exhibits visco-ductile (open circle), whereas that less than approximately 30 % in porosity remains brittle. Some specimens ranging 20 or 30 % in porosity show transitional and ductile behaviors (open square). This tendency continues in same way at higher confining pressure up to 1000 and 1500 kg/cm (Hoshino et al, 1972).
The behavior of deformation is classified based on stress-strain relation in experimentation as Fig. 2. Brittle behavior is characterized by noisy fracturing followed by sudden drop of the stress strain curve, while ductile behavior is characterized by successive stress increase after yielding. Transitional behavior is found between brittle and ductile behaviors and identified by nearly horizontal stress strain curve. Visco-ductile behavior has been proposed by Hoshino et al (1972), when they discovers.' a phase of extremely ductile flow after ductile phase. It is characterized by stress-strain relation moving monotonously upwards under constant strain rate. The visco-ductile behavior always appear at higher confining pressure than ductile behavior.
Compressibility is also dependent on porosity (Inami and Hoshino, 1974). Compressibility increases gradually as porosity increases. At less than 10 % in porosity, compressiblity is about 0.002, same as that of quartz and feldspar. However, at around 30 % compressibilty attains 0.002 or 0.001 per kb, which is same value of the poly-molecular compound. Beyond 30 % of porosity compressibility suddenly increases up to 0.03 or 0.2 per kb, which is very close to that of water or alcohol.
(Figure in full paper)
Other mechanical properties such as cohesive strength and equivalent viscosity change from liquid-like to solid-like material at porosity of around 30 % (Hoshino, 1978)
The above results have made it possible to materialize the hypothetical model of compaction (consolidation). From a viewpoint of mechanical evolution of the clastic rocks, process of diagenesis is divided as Fig. 3 (Hoshino and Inami, 1977).
(Figure in full paper)
are amorphous organic materials that are not to able to identify with microscope (Fig. 4).
