Concrete can be classified as a brittle material containing many inherent flaws such as some kinds of air voids and microcracks. Due to such heterogeneous characteristics, the failure of concrete is a kind of fracture due to cracking, following a complex process. Consequently, it seems to be necessary that the strength of concrete should be discussed not only from the standpoints of non-cracked body, but also from that of cracked body. At present, it is widely recognized that fracture mechanics is the most useful approach for evaluating the mechanical properties of cracked materials. In the present paper, the applicability of fracture mechanics to cement concrete materials for torrent control dams was discussed. Referring to the method of test for plane-strain fracture toughness specified by ASTM Committee, which was not yet applied in the past investigations of a heterogeneous brittle material, we carried out the fracture toughness tests on single-edge notched cement concrete beams by concentrated flexural loading at midspan. From the experimental data, we found that the stress intensity factor at fracture seems to be approximately constant in spite of the remarkable differences of crack length in the specimens, and as a result, it is noticeably excellent as the practical parameter evaluating the strength of cracked materials as compared with the ordinary ultimate load, even for cement concrete materials.

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The result of the creep test performed in this study shows that the creep deformation of soils is represented by the equation which is the combination of the equation expressing the behavior of a visco-plasto-elastic model and non linear time dependent function, t^α. Then, a new rheological model which consists of a series of the visco-plasto-elastic model and modified Bingham model is proposed to describe the creep deformation of soils.

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