No abstract

No abstract

In this study, to examine the effects of the fabric anisotropy of sand specimen and the anisotropic consolidation stress on the small strain stiffness, the bender elements test and the cyclic and monotonic triaxial tests were performed on several kinds of reconstituted and undisturbed sand samples. These laboratory test results were compared to the results of in-situ seismic surveys. Test results showed that the shear wave velocity estimated from the Young's modulus on triaxial test is lower than those from bender elements and in-situ tests. In particular, it was remarkably recognized in the sample including coarse materials. Therefore, in the case of a comparison of initial stiffness between the laboratory and in-situ tests, the shear wave velocity should be measured in the laboratory test in the same way as the in-situ test.

In this study, to examine the effect of the fabric anisotropy on elastic moduli (shear and Young's moduli), the bender element, cyclic and monotonic triaxial tests were performed on reconstituted clay specimens with different fabric characteristics. The specimens with the angle between the axial direction of the triaxial specimen and the bedding direction of 0 and 90 degrees were cut from the pre-consolidated clay block. These specimens were isotropically consolidated under several kinds of confining pressures. The shear wave velocities in three different directions (VH, HH, HV-wave) were measured by bender element tests, and the stiffness under wide ranges of strain levels up to failure were measured by cyclic and monotonic triaxial tests. Test results showed that; 1) the shear modulus obtained from the shear wave for propagating and vibrating horizontal to the bedding plane is higher than the others two kinds of moduli, 2) the horizontal Young's modulus at small strain is also higher than the vertical one, 3) the anisotropy of the elastic modulus of clay is larger than that with sand, but becomes lower with the increase in strain level and consolidation stress.

At present, almost all mountain tunnels in Japan are excavated and constructed utilizing the New Austrian Tunneling Method (NATM), which was advocated by Prof. Rabcewicz of Austria in 1964. In Japan, this method has been applied to tunnel construction since around 1978, after which there has been a subsequent decrease in the number of casualties during tunnel construction. However, there is still a relatively high incidence of labour accidents during tunnel construction when compared to incidence rates in the construction industry in general. During tunnel construction, rock fall events at the cutting face are a particularly characteristic of the type of accident that occurs. In this study, we analysed labour accidents that possess the characteristics of a rock fall event at a work site. We also introduced accident prevention measures against rock fall events.

In order to express the mechanical behavior of soft rocks as faithful as possible by Discrete Element Method (DEM), it is important how to determine the parameters. In this study, we proposed a method to determine the stiffness of the sphere element and the parallel-bond from the elastic wave velocities and the parallel-bond strength from the unconfined compression strength (UCS). The specimen used in the experimental tests was the Toyoura sand bonded by a liquid grout in order to simulate a soft rock. The primary and shear wave velocities of the Toyoura sand and the bonded Toyoura sand specimens were measured by the bender element test and then the stiffness of the sphere element and the parallel-bond were calculated by those velocities. The unconfined compression test (UCT) by DEM based on those stiffness could cleverly express the secant Young's modulus of the stress-strain relationship in the experimental UCT. In addition, the UCS provided the parallel-bond strength. Therefore, the main parameters for DEM can be obtained experimentally.

The following study examines a new soil measurement method to achieve simple and reliable slope monitoring to ensure labor safety. The method measures the increase in shear strain in the shallow subsurface of the slope. The target that is measured in the soil using this method is different from that of the conventional methods, which use extensometers and inclinometers. Although the increase in shear strain in the shallow subsurface is considered negligible, this study discusses the potential application of the measurement for detecting the potential threat of slope failure. A mini pipe strain (MPS) meter was developed to measure shear strain in the shallow subsurface of slopes. A full-scale test model of slope failure was constructed via excavation to examine the detectability of the threat of slope failure using an MPS meter. Corresponding to the development of slip surfaces in deep positions, less than 0.5 % of shear strain in the shallow subsurface is clearly observable. Although the inverse of the shear strain rate (1/ν) showed a drastic decrease prior to failure, the slope did not fail immediately; in addition, creep phenomena was observed. An unstable slope may be considered a stable one because of the lag time prior to failure. Identifying the second or third creep could provide a few minutes for workers to escape. Accordingly, the threat of workers being injured by collapsing soil can be reduced by using the proposed method and sensor.

No abstract