Studies on the Physical Properties and Mechanical Properties of Rocks in Use for Irrigation Dams in Hokkaido

Abstract

Nowadays, we are trying to establish criteria for use of weak rocks for dam construction. The characteristic for compaction and permeability of weak rocks change considerably according to their grain crushing. Generally, weak rocks exhibit low shearing strength compared with hard rocks. Weak rocks in Hokkaido fall under the category of soft sedimentary rocks that were formed during the Neogene period and weathered igneous rocks. They have distinct properties, one of them being the relationship between the mechanical properties and water absorption of the rocks.
In this paper, we summarized the physical and mechanical properties of these rocks, especially the above-mentioned relationship from the data obtained from government irrigation dams. It can be summarized as follows:
(1) It was found that these rocks were characterized by low water absorption and exhibited a great angle of shearing resistance (φd) compared with rocks having high-water absorption. There is a relation between the dilatancy ratio under failure condition and water absorption of the rocks. Also, there is a lineal relation between the dilatancy ratio and internal friction angle (φ0), and 95o turns out great under great dilatancy.
(2) The following equation was devised by using Bishop's equation and transformed to consider the force of grain crushing corresponding to the increment of principal stress.
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Where, W_b is the work of grain crushing, F_B is the grain crushing force ratio (which is dehned in this paper).δ₁ is the major principal stress.δ₃ is the minor principal stress (confining pressure).Δδ is the deviation stress.Δε₁ is the incremental axial strain.Δε_v is the incremental volumetric strain. W_i, is the work of shear slipping.
It was found that there was a lineal relation between FB and the grain crushing index of Marsal (B) on each rock sample. It is able to estimate the grain crushing index (B) from their relative expressions. Furthermore, it gave us an important suggestion for a comparison between the quantity of grain crushing by shearing and the quantity by some else action, slacking, etc. Finally, authors comment it is important for a better understanding of the grain crushing mechanism for making a.decision on the shearing strength of rocks.