Study of subcritical crack growth is important in estimating the long-term strength of rock and in ensuring the long-term stability of structures in a rock mass. The long-term strength is affected by the value of subcritical crack growth index (SCGI). However, the effect of environmental conditions on SCGI has not been clarified. In this study, we have estimated SCGI under various environmental conditions on a sample of Kumamoto andesite, using the Double-Torsion method. We show that the SCGI decreased when the temperature is higher in both air and water; the SCGI in water is smaller than that in air. When the relative humidity of the air increased, SCGI tended to be smaller and at 90 % relative humidity was close to the value in water. Under alkali conditions, the SCGI decreased slightly. Using the values of SCGI, the long-term strength was estimated and it is shown that the long-term strength decreased when SCGI was smaller. It is concluded that SCGI and the long-term strength is affected by the surrounding environment, specifically by the temperature and water. To ensure the long-term stability of rock, the control of the temperature and water migration is important.
This paper introduces a new measurement system using digital images for tunnel construction management. This measurement technique that utilizes digital images brings the following benefits compared with conventional techniques. The 3-dimensional deformations and the area-wide distributions of many measurement points can be obtained through simple measurement work. As the image data are all in digital format, real-time monitoring is possible. Measurement involves photographing from a distance only, eliminating the need for sophisticated techniques to improve accuracy as in conventional measurement. The necessary measurement hardware consists of a digital camera and a PC only, which brings down measurement cost. This study first attempts to establish the theoretical framework for using images photographed from any position with a digital camera for measuring any object for which is difficult to set fiducial points, such as a tunnel and reproduce the 3-dimensional displacement of a tunnel with considerable decision. It then goes on to clarify the relation between various measurement parameters and measurement decision and includes experiments to evaluate the performance of the technique that is applied to deformation measurement system of jointed rock masses. As a result, the establishment of a new measurement system featuring simple measurement work and a high degree of decision was found to be possible.
Recently, in Japan, heavy rainfall observed during very short period, so-called Guerilla rainfall, which may be considered as one phenomenon of climate change, has highlighted as one of serious natural hazards that may cause slope failure. It should be considered that in the case of heavy rainfall, slope stability against rainfall heavily depends on amount of rainfall, which infiltrates into subsoil. Therefore, it is very important to develop a method that can clarify amount of rainfall infiltration into subsoil from total amount of rainfall, which is one of dominant factor on slope stability, and investigate mechanism of rainfall infiltration into subsoil. From such a viewpoint, this study discussed field data of surface flow, variation of soil moisture content and variation of pore water pressure monitored at investigated slope, Nakhon Nayok, Thailand.
Rockfall hazard zoning is not simple to achieve in practice. It involves the different factors: rock block shape and size, characteristics of the topography, and the occurrence of rockfall which depends on some triggering events that cause a change in the forces acting a rock block. Rockfall hazard maps are often replaced with figures which show the frequency and the corresponding intensity of a predefined rock magnitude. Some attempts are introducing the results of the three-dimensional numerical modeling to get the objective zoning based on the mechanical parameters (e.g. kinetic energy). In such attempts, it is important to recognize that the mechanical parameters may be affected by modeling of the physical factors mentioned above. The most important role of the three-dimensional simulation is to display the lateral dispersion of trajectories. In this paper, the influence of controlling factors on the dispersion has been evaluated by conducting 3D simulation. Parametric simulations have been performed at different spatial resolutions using sets of synthetic biplanar slopes characterized by mean inclination and local asperities. The results of the lateral dispersion of trajectories are explained with the width of computed trajectories and the fixed distance along the slope surface from the block launch position.
The fluid flow in rock fractures during shearing processes was investigated in this paper considering the evolutions of aperture (void geometry) with shear displacement histories under constant normal stress. The distribution of fracture aperture and its evolution during shear were calculated from the initial aperture and shear dilations measured in the laboratory coupled shear-flow tests. For the fluid flow simulations, three-dimensional Navier-Stokes (NS) and two-dimensional Reynolds (local cubic law) were solved numerically and simulation results were compared.
This paper presents direct shear test results for single jointed granite and mortar specimens to investigate effects of long-term load holding on mechanical and hydrological properties of rock joints. From the test results, it was confirmed that shear strength increased and permeability decreased for mortar specimens through three days load holding. For granite specimens, however, significant change was not confirmed on mechanical and hydrological properties through up to twenty days load holding due to smallness of confining pressure compared with the strength of granite and shortness of load holding. Relationship between the time of shear holding (th) and the growth of shear strength during shear holding (Δτ) was examined for mortar specimens. When tn was shorter than 106sec, Δτ increased in proportional to the logarithm of th as Dieterich's log-linear model, which explains the time-dependency of Δτ as increase of contact area of fracture surface due to asperity creep. When th was about 106sec, however, Δτ was larger than the value predicted by the Dieterich's log-linear model. This result implies growth of adhesion driven by chemical action at contact area of fracture surface such as pressure solution and precipitation.
In this study, a new Distinct Element Method (DEM) code had been developed, and a series of rock test simulations, such as uniaxial compression test, uniaxial tension test and Brazilian test are performed to investigate the effects of particle number and size distribution on macroscopic mechanical properties of rock models. Each simulation result was in good agreement with actual experimental results conducted by previous researchers, and the findings obtained from this study can be summarized as follows. The variation of calculated values of macroscopic mechanical properties decreases with increasing the number of particles. When the number of particles is 10000 or more, stable results are obtained as a rock test. Moreover, macroscopic mechanical properties of rock model, such as uniaxial compressive strength, Young's modulus and uniaxial tensile strength are significantly affected by porosity of the rock model. Since small particles fill the space among large particles, the porosity of the rock model decreases with increasing the maximum/minimum radius ratio of the particles, and particles are densely packed in the rock model. When the particle is closely arranged, the displacement of each particle is restrained with the adjacent particles even if the bond between particles breaks. As a result, the macroscopic mechanical properties of rock model increase greatly.
A relation of diffusion and seepage is discussed on the basis of mass conservation law for porous media saturated with a multi-component solution. Note that both phenomena have independently treated in the classical theory of porous materials. In the seepage problem we shed light on a physical implication of seepage velocity. In the diffusion problem we show sorption can be introduced on concepts of a source term, a distribution factor or an equation of adsorption isotherm.
CFRP (Carbon fiber reinforced plastics) exhibit superior mechanical properties, and are recently applied to large structural materials using the VaRTM (Vacuum assisted Resin Transfer Molding) method. In the vicinity of the resin inlet of this method, and at the joint of CFRP structures, it is pointed out that the disorder in fiber orientation often occurs. In this study, therefore, the effect of local off-axis fibers array on the tensile properties of unidirectional CFRP was basically investigated. An experimental device for making a local off-axis fibers array on a CFRP lamina was newly developed, and various unidirectional CFRP laminae were prepared by changing the fiber orientation angle and the size. The results show that the tensile strength of CFRP laminae with off-axis fibers array decreases with increasing the fiber orientation angle and the length, and depends on the degree of fiber bundle waving. On the other hand, Young's moduli of the CFRP lamnae show an almost constant value, which is relatively close to that of CFRP lamina without off-axis fibers array. Finally, Young's moduli and tensile strength of the CFRP laminae were analyzed from a proposed composite model with an off-axis fibers array, and its validity was discussed.
We have designed mechanically induced long period fiber grating (LPFG) in which the grating length can be changed to any value up to 16cm as we desire. Measurement of the dependence of the transmission spectrum on the grating length showed that the spectrum became sharper as the grating length was increased until about 10cm, and beyond this length the sharpness of the spectrum remained almost the same.
Risk based maintenance (RBM) was applied as a method to optimize maintenance strategy of a shipyard dock. While in steel plant structures, the application guidelines of RBM have been published, the procedure for concrete structures is not considered. The maintenance strategy of concrete structures has been planed as a traditional way to repair the most damaged area with given priority. In the RBM, the risk is expressed by a matrix with the qualitative or quantitative multiplication of likelihood and consequence on damaged concrete structures. In the present study, in order to clarify the effectiveness of RBM on concrete structures, the procedure was developed on maintenance planning of a concrete dock. Finally, it is concluded that the RBM could be applicable to concrete structures with degradation assessment by the Markov chain model, and reasonable decrease of the life cycle cost on repair.