In order to quantitatively evaluate the support effect of rock bolts in tunnel practice, first physical model tests were carried out to reveal a functioning mechanism of rock bolts reinforcing the discontinuities of rock joints. Secondly, field measurement results were collected from published data of tunnel projects. They were then analyzed taking into consideration the mechanism of functioning of rock bolts revealed by the physical model test. As a result, it became clear that serious deformation problems such as failure of shotcrete, breakage of rock bolts, buckling of steel ribs, etc., occurring during the excavation of tunnels were closely related to the softening behaviour of rock masses.

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CEM (Contact Element Method) is an effective numerical method for analyzing continuous and discontinuous behavior of the ground. In this paper, a packing method to assemble particle elements has been presented to reduce the time required for modeling the ground by CEM. An analytical compression test method has been proposed. The relationships between input parameters in CEM and output parameters in compression analysis such as strength and deformation parameters have been made clear. By using the above relationships, it becomes possible to determine values of the input parameters from experimental compression test results.

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We monitored AE (Acoustic Emission) in the frequency range from 5 to 100kHz in a porphyrite around an underground powerhouse, measuring 24.0m wide, 46.6m high and 134.5m long at 280m below the surface. Eight AE events could be located and their fault plane solutions were obtained from P-wave radiation pattern. The solutions are consistent with a strike and a dip of the most dominant joint surface, in situ stress state, and displacements measured by a multi-extensometer. These results indicate that fault plane solutions can be applied to assess stability of underground powerhouses excavated at relatively shallow depths, in a similar way to deep mines where the method has been practically used.

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Shaking table tests in a centrifuge have been carried out for dry and saturated deposits of the Toyoura sand which were prepared in laminar container, 74cm long, 34cm wide, and 50cm deep. Model deposits were saturated with either water or silicon oil, and then subjected to sinusoidal input shaking under centrifuge accelerations. Shear moduli and damping ratios were calculated using back analysis for the results of dry and saturated sand model tests. Consequently, it has been found that the shear moduli and the damping ratios of the sand in saturated state is 1.5 times large as same as those of it in dry at the same confining pressure; and dynamic centrifuge model test results of saturated sand can be simulated with a good level of precision on the basis of the shear moduli and damping ratios determined by back analysis.

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Series of centrifugal model tests for rigid box culverts were carried out to investigate the effect of laying flexible materials for reducing the vertical earth pressures acting on the culvert.
The optimum position of installed flexible material to reduce the vertical earth pressure were studied comparing the experimental results with the values of design criteria, Marston-Spangler theory and FEM analysis.
After selecting the best position of installed flexible material, the influence of the other factors such as differential settlements, water content, fill material, for the reduction of the earth pressure, was examined by the another series of centrifugal model tests for a rigid culvert.

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Earth pressures acting on lining of a shield tunnel considerably vary with construction processes such as stress conditions around excavation face and grouting conditions. Precise simulation of the construction process is of essence to examine the pressure development around the lining in a model test. This paper describes the development of a miniature shield machine introduced by high mechatoronics and control technology which can operate under high centrifugal accelerations, simulating the detailed construction processes of shield advancing and tail void formation. The initial set of data demonstrates the significant influence of the construction processes on the final stress distribution around the lining.

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This paper described three-dimensional effects of a support system and its evaluation for NATM. The investigation was carried out by means of three-dimensional FEM analysis considering progress of face. The investigation made it clear that the support effect of rock mass around tunnel was influenced by the difference of rigidity in the installed support system. Based on this result, we proposed a new three-dimensional support system which combines with a heavier support system with a lighter support system. This was regarded as a reasonable support system based on the concept of NATM. Finally, three-dimensional analysis results and the results obtained at the test construction site made it clear that the three-dimensional support system recommended here was useful.

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The fractal is a concept of the statistical self-similarity that has been found in many natural phenomenons. The distribution of the differential settlement may be one of the fractals. Then, the justice of this supposition is examined by using observed data at sites. Also, the feature of the differential settlement as a fractal is revealed. The estimation method of the differential settlement is constituted by applying the feature as the fractal. This method is applied for the estimation of the settlement of a place where the construction is planed in the future, and the applicability is testified by using observed data at the site. At the results, the effectiveness of this method was confirmed.

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In cold regions, ground freezing and thawing is repeated several times at winter season. Recently many studies on soil water migration during ground freezing have been done, but studies on soil water migration during ground thawing is not sufficient now. So laboratory test of unsaturated sandy soil freezing and thawing under closed system condition is treated and soil water migration is observed with γ ray moisture content meter. It became clear that soil water migrated to freezing zone during freezing and thawing, and water flow rapidly to ground surface from subsurface. A numerical analysis is developed to estimate the soil water migration during freezing and thawing using the coupled heat and water flow movement. This methed is useful to predict ground water flow at cold regions.

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It is very important to grasp the groundwater behavior not only on the design of underground structures but on their maintenance. This paper presents an application of multivariate regressive model to the groundwater system including structure, precipitation and other influential factors. First, we describe the modeling by selecting and newly adding manipulated variables with the use of simulated data. Second, we have applied the modeling method to the observed data of the Kikuma Test Plant for underground oil storage. We have also found this method is applicable for the groundwater system including natural factors.

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Consolidated undrained triaxial tests were performed on a diatomaceous soft rock to investigate the effect of a single joint with different inclinations on the residual strength characteristics.
Measurements of the stress strain behaviour show that the residual strength of intact rocks (no joint) coincides with that of precut rocks having a single joint and the strain softening behaviour is influenced by the magnitude of consolidation pressure. The residual strengths of overconsolidated intact and precut specimens are little affected by the rate of strain and in the comparisons of the rate of creep strain, there is no significant difference between the intact and the precut specimens.

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Coal fly ash discharged from thermal power plants has increased and been disposed for reclamation. We investigated a reclaimed ground in which coal fly ash may be included, and found that its ground profile and properties of strength, void ratio and others show irregular variations with depth. We clarified that the properties of fly ash may be influenced by the process of reclamation and that the improvement of the ground can be successfully achieved by means of dynamic compaction with sand piles or reduction of shear deformation with cement mixing columns to provide effective resistance to liquefaction during earthquakes.

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A bearing capacity test on granular assemblies of aluminum rods and it's numerical simulation by DEM were performed. Based on the comparison between these results, it is concluded that DEM can be what is called “numerical model ground”. To investigate the mechanism of sandbag-like reinforcement numerically, firstly, a distinct element modeling for the reinforcement was proposed. Then, numerical compression tests on wrapped granular assemblies and a bearing capacity test of model ground with the sandbag-like reinforcement were performed. On the basis of the results, the mechanism that the reinforced granular mass behaves as a rigid body due to the nature of granular materials of being dilative and frictional was made clear.

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A series of centrifuge model tests with a reduced model by factor of 1/13.3 was perfonned using undistiubed block samples of naturally deposited sand, to attempt direct comparisons of bearing capacity and failure mechanism with an in-situ loading test. It was found that centrifuge models predicted ultimete bearing capacities to be 60-70% of a corresponding prototype, and elastic defonnations close to the prototype. It was also seen that in the centrifugal models, clear slip lines were not developed, and settlements at yield load were much larger than those observed in the prototype. Furthermore, it was indicated that the bearing capacity and the failure mechanism on the naturally deposited sand were strongly affected by the stress level and the soil structure.

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In the study of fracture mechanics of soil, the influence of the particle rotations are usualy ignored. But their influence cannot be ignored on shear strength. To study the mechanism of granular materials, the Distinct Element Method (DEM) are used commonly. In DEM, the particle rotations are considered, but some details, as the peek strength, are not well-simulated. In this paper, we decompose the sliding and rotational relative displacement from the tangential dispacement at the particle contact. Then we install the effect of moment (couple stress) transfer at the particle contacts into DEM. Biaxal tests are done and the results shows the effect is sufficient and the validity of the new DEM.

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The strength characteristics of the weathered serpentine which was sampled in various parts of Japan were examined by the triaxial and ring shear tests. The angle of shear resistance of the weathered serpentine was divided broadly into two main groups. One group has φ′, φ_r of about 30°. It was confirmed by the X-ray analysis that these weathered serpentines were composed of an antigorite and chrysotile. Another has φ′ less than 30° and the drop of the angle of shear resistance to φ_r from φ′ is remarkable. These weathered serpentines involve a chlorite, talc and montmorillonite.

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In hydraulic fracturing for stress measurement, the direction of cracks due to fracturing follows the direction of the maximum compressive stress. To identify the direction, the sonde is usually removed after hydraulic fracturing, and then the other sonde is inserted into the borehole and traces of the cracks are obtained. Thus, this method takes a lot of time when a borehole becomes deep. To solve the problem, we get an idea to measure AE (Acoustic Emission) events accompanied with hydraulic fracturing and determine the crack direction. We developed a test sonde mounting four AE sensors in a cross section normal to the axis of the sonde. Using the sonde, the feasibility in determination of the crack direction is investigated. It is found that the sonde could be used practically with some improvements clarified from this investigation.

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In this paper upper bound calculations and centrifuge lateral loading tests on piles were carried out to estimate the stability of clay around piled bridge abutments subjected to backfilling and obtain the relationship between lateral resistance (p) and displacement of pile (y). An attempt was also made to predict the lateral load acting along the pile at the failure of clay by combining the results of the upper bound calculation and the observed p-y relation. It was found that the calculated backfill height and lateral load at the failure of the clay compared well with the results of centrifuge model tests which had been previously conducted by the authors.

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Design methods of thickness, such as Koerner's method, Co-energy method and elastic method proposed by authors, with which geomembrane deforms without any failure in case of differential settlement of subgrade soils are reviewed and meanings of factors of safety, F_s, emploied in design are discussed from a view point of elastic theory. As a result, it is found that F_s or elongation of geomembrane embedded in ground is related to square of F_s for strength, that F_s for thickness coincidence with those for Co energy and for elongation and that stiffer geomembrane, larger overburden pressure or higherfrictional coefficient need thicker thickness.

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Borehole extensometers are used to measure displacements in rock mass surrounding an underground excavation. Although a conventional multi-rod extensometer enables one to measure relative displacement changes at multiple points in a borehole, the monitoring to measure the position of each end of the rods is carried out by using a manual dial indicator readout or multiple electronic displacement sensors.
A newly developed extensometer has the mechanism to measure each displacement by a single displacement sensor. The adoption of a laser displacement sensor and its rotational position control make it possible to realize the production of an economical and high-accuracy extensometer and the monitoring system. The verification test of the device in a laboratory showed the accuracy of 0.2mm or less with the standard deviation. The results also demonstrate that the device and its measuring system have no measuring errors derived from its mechanical structure and are fully applicable for the efficient and economical monitoring of rock mass behaviour in the field.

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