抄録
The objective of this study is to clarify the stress-strain-time relation and strength of porous fine tuff-sandstone obtained from Tainohata zonal layer belonging to Kobe stratum, in terms of effective stress. The stratum which deposited in Miocene Epock of Tertiary Period is distributed around Kobe area where one route of Honshu-Shikoku bridge connections is going to be constructed.
The conclusions obtained through this investigation are as follows:
(1) The fine tuff-sandstone samples are almost fully saturated so that they should be analyzed in terms of effective stress. It is found that Skempton's pore pressure coefficients, B, is 1 and the coefficient at breakage, Af, changes in the range of 0.2-0.5 depending on the reconsolidation pressure.
(2) The layer from which the samples were taken is in overconsolidated state. The preconsolidation pressure is estimated about 25kg/cm2.
(3) One may analyze the rock mass as an ideal elastic continuum up to the strain range of 1.0-1.5%.
(4) The interrelation of the deformation coefficient E50 and the strength is similar to those for alluvial and diluvial clays. The relation, E50=70(σ1-σ3)max is deduced from the results of reconsolidated undrained triaxial shear tests. Both the deformation coefficient and the strength increase with the increase of reconsolidation pressure.
(5) Mohr-Coulomb failure criterion is applicable within the reconsolidation pressure range of 0-30kg/cm2. The effective internal friction angle φ' and the cohesive strength c'are found to be 40°and 4kg/cm2, respectively.
(6) It is necessary to take into account the creep deformation. The creep strength is 70-80% of the strength obtained by constant strain rate shear tests.
