Three-point-bending test under the constant load was conducted on Sanjome-andesite to investigate the time dependency of crack extension of Mode I. Crack length was calculated from the crack mouth opening displacement using the unloading compliance method.
After the loading, the crack extension rate continuously decreases at first while the stress intensity factor increases. Thereafter, the crack extension rate takes its minimum, and then accelerates toward the final failure. In the last region where crack extension rate accelerates, it was found that the crack extension rate α can be expressed as
α=Kⁿ/A
where K is stress intensity factor and A is a constant. This equation has the same form with that obtained by the double torsion tests.
The mathematical model of crack growth proposed by Okubo et al. is
(Δα)=Kⁿ·(C1·(Δα)^-m+C2)
where Δα is the crack extension, and C1, C2 are constants. It was found that the equation can be applicable through the tests carried out in this study including the first region where the crack extension rate decreases.

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Stress-induced cracks in granite obtained from the double-torsion test and three-point bending test were observed with the aid of optical microscope, and crack paths were classified into two types, transgranular cracks (T) and intergranular cracks (I). Transgranular cracks were subdivided according to their association with individual mineral grains. Intergranular cracks are subdivided according to neighboring minerals. Thin section analysis shows that in spite of the extensive range of crack velocities the T/I ratio changes little and the stress-induced crack path tends to propagate along relatively weak portions because of strong heterogeneity around the crack tip. Furthermore, in order to know the scaling of crack path roughness, power-spectra of all data were calculated as the function of spatial frequency. Each spectrum is approximately linear in log-log space and the fractal dimensions calculated from the slopes in spatial frequency-power-spectrum diagrams have ho definite tendency associated with the crack velocities.

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Discontinuities (we call them “joints” ) play a major role in mechanical and hydrological properties of rock mass. We can usually observe them using exploration drifts or boreholes. However, our ability of observation is limited to a certain extent. Hence, it is difficult to estimate joints properties in the whole rock mass.
We studied joint properties in Kurihashi grano-diorite and Ganidake diorite in the Kamaishi mine. These data were used to build a database for the estimation of rock mass properties. In this paper, at first we explain joints database. Next, based on this database, we try to simulate joint distribution in large-scale rock mass. The joints were modeled by a probability model of joints in rock mass, using results that have been obtained by the scanline method. Finally, we also discuss the anisotropy of rock mass permeability.
The following is the summary of this study.
A the oretical estimation suited well with the joint observation by borehole-TV, in Kamaishi site.
Distribution characteristic of filling width was expressed by an exponential function.
Using the discrete probability of the pole of each joint, we calculated the orientation tensor of the permeability tensor. On the orientation, the result agreed with the crosshole permeability test result.

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The DSCA (Differential Strain Curve Analysis) which was proposed by Strickland and Ren in 1980 was applied to measure in-situ stress in the Kan-etsu 2nd tunnel. The basic assumption of the DSCA is that microcracks will be generated in a rock specimen by the stress relief when it is taken from borehole and the microcrack density is related to the earth stress. The object of this study is to validate this method. The overburden of the boreholes from which test specimens were taken was about 800m. Fourteen test pieces were carefully formed into a cubic shape with a side length of about 30mm. Total number of 18 foil strain gages were attached to each test piece, and hydro-static pressure up to about 50 MPa was applied on the test piece. The directions of principal strains were calculated using the outputs of 18 strain gages as a function of hydro-static pressure. From the relations between hydro-static pressure and principal strain, the directions of in-situ principal stresses were estimated. As a result, azimuths of principal stresses estimated from fourteen samples had almost the same tendency, although the dips of those were divided into two groups of different tendency. The ratio of the maximum, intermediate and minimum principal stress was estimated using both Strickland and Ren's method and Dey and Brown's method. The ratio estimated by the former method was 1.00: 0.69: 0.42 while the latter gave the ratio of 1.00: 0.64: 0.45. Finally, these results estimated from DSCA were compared with another method such as hydraulic fracturing method or stress relief methods. There were no apparent contradiction between these results.

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Characteristics of crustal-stress distribution are necessary to study phenomena relating to tectonic activity. Analysis of the factors influencing this distribution has been rarely conducted. One of the reasons for this is in-situ stresses have not been adequately measured. Another reason is data measured in each site reflect the site's geological and tectonic conditions in a complex way. In-situ stress data which are regionally and vertically dense have been obtained in hard (granitic) rocks around the Kofu basin and near Mt. Tanzawa. This makes it possible for us to compare stress distributions between hard and soft rocks. Some of our sites located in hard rocks show a fluctuating stress distribution with depth. One other site shows that stress increases with depth monotonously as in soft rocks. Log data from each site suggest that this difference of stress distribution is under the influence of lithological heterogeneity. However, a linear relationship between shear stresses and effective normal stresses is obtained. The frictional coefficient changes in each site depending on each geological and tectonic setting. This suggests that the yielding caused by the frictional sliding of microfractures controls the stress distribution in hard rocks, as similarly observed in soft rocks.

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Jointed rock mass surrounding underground excavations, whose tensile strength is almost negligible, can only be competent with the help of several arching actions. One of these actions is that of a linear arch formed in the jointed rock beams in the immediate roof of a cavern.
The rock mass outside the ground arch is mechanically stable. But the rock mass between the ground arch and the immediate roof where the stress, normal to the excavation wall surface, becomes relatively low is mechanically unstable. In case of a self supporting excavation, the rock inside this unstable area is supported by the linear arch formed in the rock beams in the immediate roof. The span that gives an equilibrium between the dead weight of the unstable area and the bearing strength of the rock beam, is the critical span of the self supporting excavation.
To investigate the supporting mechanism of such linear arch, model experiments have been performed using rock beams of plaster-cement mixture. According to the results of experiments, simple but effective idea to explain the supporting mechanism of laterally stressed jointed rock beam is proposed. Also the effect of lateral stress to the bearing strength of the rock beam is clarified.
The following procedure to estimate the critical span of an underground cavern based on the idea of a linear arch formation was also considered. 1) Evaluate the shape of the ground arch to obtain a value for the possible load operating on the rock beam under several stress conditions using FEM analysis. 2) Calculate the relationship between the span of the rock beam of particular thickness and its bearing strength. 3) Estimate the critical span of the cavern, comparing 1) and 2), for various conditions.

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The coupled boundary element-characteristics method is successfully applied to thecut slope problem. The elasto-plastic behaviour of drained homogeneous rock slopes of slope angle greaterthan 50 degrees has been analyzed to investigate the failure mechanism and premonitory phenomena. Rock massis assumed, in the present analysis, to be a dilatant Mohr-Coulomb material with weight, and the associated flow rule is used to compute the displacement within the plastic zone. Firstly, analyzing the boundary between the elastic zone and the passive plastic zone, it is clearly shown that the initial lateral stress, as well as the gravity, plays an important role in determining the depth of plastic zone downward from the toe of slope, and the high lateral stress results the tension failure in upper slope surface and the growth of plastic zone downward from the toe of slope. Secondly, from the analysis of displacement and plastic strain within the plastic zone, it is clarified that a small depth of plastic-zone downward from the toe of slope is always associated with the concentration of plastic shear strain on a slip line through the toe of slope. The angle between the slip line and the slope surface generally coincides with the fracture angle of rock, and this analytical result is compatible with the sliding of a wedge-shaped territory observed by the centrifuge experiment. Moreover, it is analytically clarified that the expansion of plastic slope surface is mainly associated with the dilatancy on the slip line, which finally grows into the slide plane, and such a dilatant behaviour is available for the prediction of subsequent progressive failure.

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In an abandoned coal mine, a test tunnel has been newly driven in the massive sandy-shale rock mass from the main roadway located at a depth of 365m from the surface, and several in-situ measurements and laboratory tests have been conducted. The Barton's Q-value to classify the rock mass was evaluated to be 11.1, which means there will be little problems accompanying the excavation and maintenance of the cavern. It should be noticed, however that the physical properties of the rock are sensitive to the water content due to some clay minerals contained in it. Therefore, sufficient countermeasures should be taken into account when designing the cavern.
Three types of test using boreholes were conducted to know the resistability for pressure and the stiffness of the rock mass. It was confirmed that the pressurized hole, when its surface is sealed, behaves elastically for the pressure up to 16 MPa and has a fatigue limit of more than 4.6 MPa. However, for unsealed condition, small value of 8 MPa was recorded as the breakdown pressure when the pressurized area was intersected by the fractures.

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In-situ measurement of rock deformation was carried out at Hiraki Mine. Two extensometers were installed from an opening which was excavated 30 meters above an experimental tunnel before the exavation and two set of extensometers were also installed around a periphery of the tunnel. Displacement of rock around the tunnel was measured before, during and after the excavation of the tunnel. It became clear that the rock around the tunnel was deformed elastically, but asymmetrically.
The change of rock deformation around an opening with the advance of face was calculated using a three dimensional finite element method under three different stress conditions. Then we discussed the possibility to introduce two dimensional finite element analysis to evaluate three dimensional problem. The inner pressure was applied at the periphery of an opening, then was reduced with the advancement of a face. Results showed that we can practically use a two dimensional finite element method with a sufficient accuracy.
This technique was applied to evaluate the deformation of the experimental tunnel at Hiraki Mine. It was found that (1) rock deformation can be calculated by elastic analysis except the area close to the surface of the tunnel where rock damaged by blasting, and (2) asymmetrical deformation around the tunnel was occurred mainly because of the inhomogeneity of rock mass.

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In this paper, a new method named two points method is proposed to determine the three dimensional stress state over the thickness of the tunnel lining and also the external forces acting at its back surface. It is found that every stress component distributes linearly on the direction perpendicular to the surface of the lining when the ratio R/H larger then 8, where H is the thickness and R the average radius of the lining. Utilizing this characteristics, stress distribution along an arbitrary line perpendicular to the lining can be known by measuring the stress states at two points along its line. It can be recommended that one of the two points should be positioned on the inside surface and the other in the middle section of the lining.
To measure the stresses at these two points the stress relief method is applied. For the second measuring point, a modified Leeman's method is applied and the corresponding observation equations as shown in Eq.2 are derived based on a numerical stress analysis.
In order to verify the reliability of this newly proposed method and to find out every possible factors affecting the results, some laboratory tests were conducted and satisfactory results were successfully obtained.

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The blasting vibration in advance of a working tunnel was observed in a existing tunnel, that is active and crosses above 20m distant from the surface of the working one, and in rock which is not affected by the tunnel.
Vibration caused by blasting has an important effect upon underground structures. The dynamic response of the structures caused by blasting vibration is characterized by the combination among their supports and the condition of rock around the tunnel. It is expected that the vibration mode is variable according to a relationship between the natural rock and the weak one which is influenced by excavation, that is, the plastic state is generated in rock at the circumference of the tunnel.
Boundary element method was employed for examining the possible effects of a wide range of ground conditions. The magnification factor, which is defined as the ratio of the observed amplitude at the wall of tunnel to the input at same frequency, increases according to the decline of elastic wave velocity in the loosened zone and the growth of the thickness.

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The behavior of the loosened zone around rock caverns plays an important role in the mechanical stability of rock pillars during construction and after completion. The authors have carried out the laboratory and in situ experiments to investigate the failure mechanism of the rock around the caverns and the monitoring technique of the occurrence and progress of loosened zones by acoustic emission (AE) measurements.
This paper describes the results of these experiments and discusses the available procedures to predict the initiation of the loosening of the rock mass by the indicators “count rate (the rate of occurrence of AE per minute or hour)”, “AE energy (the square of amplitude of AE)” and “m-value” (the ratio of amplitude to count rate of AE).
(1) As the results of comparison between AE measurements by laboratory triaxial test and in situ rock shear test, the loosening of the rock mass is considered to be strongly affected by the presence of preexisting fractures.
(2) As the results of AE measurements by in situ rock shear test and during tunnel excavation, it is clarified that the decrease ratio of m-value and the increase ratios of count rate and AE energy for the heavily jointed rock mass show smaller figures than those of the intact rock mass.
(3) The decrease ratio of m-value and the increase ratios of count rate and AE energy could be appropriate indicators for the determination of the criteria for the judgement of occurrence of loosening based on the relationship between three AE parameters mentioned above and the seismic wave velocity.

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The Peak Particle Velocity (PPV) of ground motion induced by blasting have been mainly used as one standard scale against the effect of surrounding structures. In recent years, however, the blast vibration is tend to be evaluated from the point of public disturbances by using the Vibration Level (VL). The VL have been derived based on the response of human body against the acceleration of ground motion. On the other hand, Japan Meteorological Agency (JMA) seismic intensity scale have been being used to evaluate the intensity of earthquake motion. The seismic intensity is determined mainly by the feeling of human body at lower scale range and the influence on surrounding objects or structures at higher scale range both with the qualitative expression.
In this study, the relation between the PPV and the VL of ground motion induced by blasting is discussed firstly and then, the relation between the JMA seismic intensity and the VL of earthquake motion is also investigated. To allow for human response against frequency range, two empirical equations have been derived for frequency range of four to eight Hz and eight to 90 Hz respectively.
As a conclusion of discussion, it was found that the vibration degree due to blasting can be evaluated by using the JMA seismic intensity scale. This results show the possibility that the vibration degree is qualitatively understood by JMA seismic intensity scale which is decided through VL.

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