Large rock falls in scale such as sliding, toppling and buckling have occurred frequently in the slope of columnar joint structure in welded tuff at Sounkyo Gorge in Hokkaido. In this work, the fracture mechanism of sliding was elucidated by considering theoretically the crack propagation problem along a columnar joint and the crack propagating behaviors had been monitored over two years by the acoustic emission method.
Practically, the reaction on an outside column was determined on the basis of the observational results of the internal temperature gradient.Moreover, the stress intensity factor caused by the reaction was calculated by applying the formula on a double cantilever beam. From this calculated results, it was seen that the crack propagated along a columnar joint corresponding to a decrease in the fracture toughness caused by stress corrosion or an increase in the temperature gradient.The sliding of column is generated by a decrease in the cohesive area due to the crack propargation.
The acoustic emission activity due to the crack propagation fluctuated in response of the seasonal changes of rock temperature and reached the peak in June when the temperature gradient became steepest. This seasonal fluctuation of the acoustic emission activity proved the validity of the theoretical consideration on the crack propagation along a columnar joint.

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The authors examine the variability of the distribution of the fracture trace length in some objective districts. Further, we elucidate the influence of the geological factors (the rock type, the age of rock mass and the geological processes of fracturing) on the fractal characteristics (the fractal dimension and the intercept of the fractal distribution).
On ten objective districts dominated by the shear fractures, the fracture trace length was investigated. Four objective districts were governed by the sedimentary rocks (slate, sand stone etc.). Five objective districts were granitic area. Another objective district was covered by andesite. Further, four objective districts investigated to the tension fractures were one dominated by the cooling joints in granite, the other dominated by the cross joints in alternation of sand and mud stone, the other two dominated by the sheeting joints in granitic rocks.
The results are surmmarized as follows:
1) The frequency distribution of the scan grid, in which fractures longer than a certain length l are numbered N, shows the log-normal distribution. The standard deviation δ of log N calculated from the average fractal distribution curve has the range of 0.16 to 0.29.
2) The fractal dimension Dl of fracture trace length is influenced significantly by the geological processes of fracturing, particularly, the difference of the tension and the shear fractures. The tension fractures affected by the geological boundary do not seem to have the fractal property.
3) From the measured data, the fractal dimensions Dg of fracture pattern are 1.5-2.0 regardless of the geological factors.
4) The C-value (the intercept of fractal distribution) for the igneous rock increases with the age of rock mass.
5) The variability of fracture distribution is reduced by the classification of the fractal characteristics because the variability is affected by the multi-fractal property of the fracture system. The measuring method is also another main cause of the variability among the different scales.

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The flow mechanism of groundwater in granite areas, especially that of deep cyclic water, was elucidated in our earlier paper by conducting geological and topographical analyses of the relationship between fracuture systems and their permeability. Futhermore, fracture systems were classified into six series (A to F) based upon small fault and fracture analyses. The A1, A2, D and F1 series are associated with the type of faults characterized by low permeability and the C1, C2 and F2 with those typified by high permeability. The quality of groundwater is also indicative of the regional flow system because of a relatively high sodium and bicarbonate concentrations and high pH value of the water.
To verify these earlier results, water catchment boring by the collectorwell method, analysis of fractures in recovered core samples, and analysis of the quality of water were conducted. The C2 type faults, striking ENE and dipping southward, are interpreted to act as impermeable barriers. The quality of waters in this type of faults suggests that there is a regional flow system of waters, because these waters are characterized by a relatively high temperature, high sodium and bicarbonate concentrations and high pH value. The total discharge of groundwaters into a bore hole from the C2 type faults amounted to 1800 m³/day. Such a large amount of discahrge is explainable if groundwater in the fault system is under a confined condition.
The geological profile of faults and rock body was analyzed in detail by employing the electrical prospecting method with dipole-dipole array. The method of research as described here has a wide applicability to groundwater analyses in other areas whose foundation is a granite rock body. The stable supply of water is obtainable in such a hard-rock area where hydrogeological conditions similar to those observed in this study are widely developed.
In the southern Abukuma plaleau, there are many springs whose presence suggests the existence of a regional groundwater flow system. These springs are situated at a site lying lower in altitude than the surrounding area. Such a finding gives a possibility that a sufficient supply of water can be exploited from this regional flow system in future. The present study clearly demonstrates that a combined analytical method of aerial photograph interpretation, field observation, electric prospecting and water quality analysis provides a reliable information deciphering the flow of groundwater in a block mass.

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A small three-component seismic sonde has been developed for precise observation of acoustic emissions occurring during underground excavation.The sonde is 400 mm in length, 51 mm in diameter and it weighs 2.7 kg.Its frequency characteristics were measured up to 2 kHz in a sweep test and an impulse test.
The results of two tests agreed well and showed that frequency characteristics of the longitudinal axis and the lateral axis parallel to the locking direction are flat to 700 Hz and have a resonance at 800 Hz. The region above 800 Hz, the alterations are within 10 dB in amplitude and within 90 degrees in phase. The freqency characteristics of the lateral axis perpendicular to the locking direction is flat to 200 Hz and has resonances at 380 Hz and at its harmonic frequencies.

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