Laboratory tests including triaxial compression tests and brazilian tests and in-situ triaxial tests and in-situ large scale block shear tests were performed to determine mechanical properties of sedimentary soft rock mass composed of mudstone and Sandstone of the Miocene series of the Neogene system with an alternating layered structure. The in-situ test results have been analysed using some mechanical models available in continum mechanics and mechanical properties obtained from laboratory tests. The calculated results indicate that there is a possibility of obtaining the strength and deformational properties of rock mass through the properties measured in laboratory and some mechanical models incorporating the structure of the mass.
In examining the suitability of foundations for nuclear power plant sites, the strength and deformation properties of the rock are usually determined on the basis of laboratory tests and/or in-situ tests.
Since the strength and deformation properties of the foundation rock are greatly influenced by discontinuities such as joints, bedding planes etc., they are usually determined from in-situ tests, and laboratory tests are regared as supple- mentary.
However, in the case of soft rock, the strength and deformation properties are Considered to be largely influenced by the properties of the intact rock rather than the properties and orientations of discontinuities.
The rock of the present study is a sedi- mentary soft rock of the Miocene series of the Neogene system, forming alternating layers of mudstone and sandstone. In the study, an emphasis was placed on investigating into the properties of the soft rock and those of the alternating layered system.
This paper presents the results of the laboratory tests and the in-situ tests on the alternating layered soft rock, and shows that there is a possibility of Obtaining the strength and deformational Properties of rock mass through the Properties measured in laboratory and some mechanical models incorporating the structure of the mass.
The rock mass at the site is a sedimentary soft rock of the Miocene series of the Neogene system, forming alternating layers of mudstone and sandstone. It contains only a few joints together with bedding planes, which are more or less uniformly distributed.
The average thicknesses of the mudstone layers and sandstone layers are 13 cm and 6 cm respectively at the site for the reactor building base mat, with mudstone becoming gradually predominant with depth. The dip angle of the bedding plane is approximately 10°.
The uniaxial compressive strengths of the mudstone and the sandstone are about 10 MPa and 2 MPa respectively.
The mudstone and the sandstone were tested for determining their physical and mechanical properties.
The triaxial compression tests were performed on specimens in their natural state at seven different confining pressure
(Figure in full paper)
The relationship between the confining pressure σ3 and the differential stress (σ1 - σ3) at peak was obtained from the results of the brazilian tests and of the triaxial compression test, and the relationship was approximated using bilinear equations as shown in Fig. 1.