Mechanics related to soft fractured weathered rock were directly related to the stability of dams, tunnels, natural slope, cut, crack or deposit, and a ground power-house, bridge foundation, large cable tower foundation, foundation of nuclear power house, and much research has been conducted in this respect. And at this symposium, with these themes, active discussions and very valuable presentations were conducted.

In concluding this scientific session, I would like to review the scientific papers submitted.

Session I

Session I dealt with the ensuring property on weak rock. And as to the strength and deformability, the rock mechanics, when we consider ensuring property of materials for design parameters, difference between mechanical properties of rock and the rock mass causes questions. In weak rock, this issue is not as serious as that in hard rock. Yet, in rock mass with thin fractured areas for cracks, this may present problems.

Shear strength and deformability of rock with weak plane, assessment of rate effect with laboratory tests were discussed. In-situ strength lies in between peak strength and residual strength. Strength of rock back-calculated from the rock slope cannot be expressed by Mohr-Coulomb theory. These were discussed in some papers.

An attempt was made to relatively homogeneous soft rock and weathered rock to apply concept of critical state used in soil mechanics. Applications of multiple stage triaxial test, and the property change In the process of material fracture under load, and other very interesting points were dealt with.

At 1–2 Session, rheological property was dealt. Time dependency of rock or rock mass is expressed as rheological property. Under a constant stress state, creep phenomenon in which the deformation continues to increase with time, is seen in rock material. And when deformation is maintained constant, stress decreases with time. This relaxation phenomenon is accepted.

In a wide sense, dynamic properties may be classified into a field of rheology; the calculation of stability of rock foundation, opening or slope, needs long term strength. And this issue has been dealt with.

Many papers were presented on creep test in weak rocks. And many kinds of rocks such as porous stuff, coal, semi-consolidated rock, mudrock, oil shale, sandstone, were referred in this connection.

Constitutive equation is established to predict long-term strength and deformability. This type of test is time-consuming, and at the same time, money-consuming, since proof of temperature control is required. Many tests were conducted in spite of all these difficulties. Based upon time-dependent characteristics of creep and relaxation, proposal was made which reads: "Earth pressure on tunnel lining can be predicted." Rheological behaviour of rock mass, as dam foundation, was investigated by the repeat plate loading test. And this was compared with analytical solution by F.E.M.

Four papers were submitted in relation of rock mass with order, and the properties of soft rock, as filled in material and an application to the programme of the safety - the rock stability was attempted.

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