This paper deals with the results of studies on the theoretical analysis of the deformation behavior of rocks, and the actual measurements made during the underground cavity excavation at Okutataragi Pumped-Storage Hydro Project. To initiate the studies, the material properties of rock were obtained by repeated in-situ tests at the proposed location for the projects to define the initial ground stress, rock shear strength, modulus of elasticity, creep deformation ratio, retardation ratio, Poisson's ratio, and rock compressive strength. The material properties thus obtained were used to analyze the extent of rock loose zone, the rock displacement and other fundamental factors for each step of the excavation work by means of a two- or three-dimensional elastic finite element method. To compare the measured data with the analytical calculations, the rock deformeters were installed in such an arrangement as to observe changes with the time of the rock displacement at the cavity arch and side walls, and several concrete strain gauges and reinforcing bar strain meters were also buried in the arch concrete to measure the loads on the arch concrete. The comparison of the calculations and these measurements disclosed the followings; (1) The results or calculations of the analysis could be adequately utilized for designing the rock walls anchored by prestressed steel bars and for maintaining the safety or security control during the construction. (2) The three-dimensional analysis and the results of measurements confirmed that the rock strut or rock mass support method could confine the displacement to about 70 percent of the estimated values of displacement for the construction method without rock strut support. As proposed and adopted at Okutataragi Project, the rock strut was arranged to come in the center of the cavity to house the underground power station and to provide the space for assembling the power equipment, machinery and tools. (3) The horizontal displacement, which was most carefully studied, was 12 to 14mm at the measurement as against 11mm arrived at by the analysis. It follows that the analysis calculation proved to be fairly precise. (4) It is understood that the loads on the arch concrete comes primarily from the horizontal forced displacement arising out of the loose side walls, but not from the ground pressure in the upper direction as has otherwise been assumed. This was proved by the measurement of the maximum concrete compressive stress of 120 to 130kg/cm2 and the calculated estimate of 140kg/cm2 maximum. The estimations and the measurements carried out for this project have proved quite satisfactory. However, several problems have been raised for further reviews and analyses to improve the safety or security of large underground power station structures, such as; (1) Decrease of the rock strength in the loose zones. (2) A method or methods to estimate the effects of rock bolts of prestressed steel bars. (3) Development of more accurate and efficient devices or methods for measuring the initial ground pressure. (4) Improved excavation methods to prevent the rock loose zone from developing or expanding.
The stability of rock masses around a pressure tunnel is influenced by many factors, i.e. the overburden load, the slope of ground surface and the shape of tunnel as well as mechanical characteristics such as strength, deformability and fissuration of the rock masses. When two or more neighbouring pressure tunnels exist, their interactions should also be considered. In this paper, the authors assume that the rock with circular tunnels is a homogeneous and anisotropic elastic body. The stresses and deformations in the neighbourhood of two or more parallel pressure tunnels are calculated by successive approximation using the point matching approach from the exact solution of anisotropic elastic body with a circular opening.
It has been pointed out in the calculation of pressure acting on a tunnel lining that the medium around a tunnel cannot be assumed to be an elastic body even for the first degree of approximation. Since the pressure usually increases with time, time must be considered in its theoretical analysis. In the designing purpose of the lining, however, the maximum pressure rather than the transient pressure change is of importance. The authors have previously proposed a method of calculation of the maximum pressure acting on the lining installed in a viscoelastic isotropic underground medium. The proposed method does not require a time-dependent analysis, but follows exactly the same technique based on the theory of elasticity. The real state of the medium, however, exhibits more or less anisotropic mechanical characteristics, so that the anisotropy must be considered in the calculation. In this paper, the proposed method is extended to the case of an orthotropic viscoelastic medium of Kelvin type, and some numerical results are shown for a circular lining.
The present paper is concerned with the transient states of stresses and deformations around the lined and unlined tunnels during the passage of traveling waves. In the analysis, the tensor code and the finite element method are used and three types of surrounding media are assumed, such as the linear elastic medium, and the elasto-plastic media with yield criteria of von Mises as well as of Drucker. The lining material is assumed linear elastic. The traveling waves discussed are the step-shaped and the bell-shaped. The following results were obtained; (1) The results obtained by the finite element method well coincide with those obtained by the tensor code analysis as well as those by the analytical procedure. (2) The transient maximum stress concentrations are generally lower those under the static loading of the same intensity as the traveling waves. (3) The transient stress concentration due the single half-sinusoidal wave is almost equal to the stress concentration of the steady-state due to the sinusoidal harmonic wave train, so long as the wave length is larger than approximately three times of the radius of circular tunnel. As the wave length decreases, the maximum stress concentration decreases. (4) For the lined tunnel, as the lining becomes stiffer, stresses become higher in the lining whereas lower in the surrounding medium. The rate of increase of the stress concentration factor is slightly less than the ratio of the Young's modulus of the lining to that of the medium. (5) The stiffer the lining is, the smaller the yielded zone becomes. However, the properties of the surrounding media have little effect on the stresses in the lining. (6) A wide yielded zone may be formed in the surrounding medium in the source side of the traveling wave due to the reflected tensile wave from the tunnel.
The objective of this study is to clarify the stress-strain-time relation and strength of porous fine tuff-sandstone obtained from Tainohata zonal layer belonging to Kobe stratum, in terms of effective stress. The stratum which deposited in Miocene Epock of Tertiary Period is distributed around Kobe area where one route of Honshu-Shikoku bridge connections is going to be constructed. The conclusions obtained through this investigation are as follows: (1) The fine tuff-sandstone samples are almost fully saturated so that they should be analyzed in terms of effective stress. It is found that Skempton's pore pressure coefficients, B, is 1 and the coefficient at breakage, Af, changes in the range of 0.2-0.5 depending on the reconsolidation pressure. (2) The layer from which the samples were taken is in overconsolidated state. The preconsolidation pressure is estimated about 25kg/cm2. (3) One may analyze the rock mass as an ideal elastic continuum up to the strain range of 1.0-1.5%. (4) The interrelation of the deformation coefficient E50 and the strength is similar to those for alluvial and diluvial clays. The relation, E50=70(σ1-σ3)max is deduced from the results of reconsolidated undrained triaxial shear tests. Both the deformation coefficient and the strength increase with the increase of reconsolidation pressure. (5) Mohr-Coulomb failure criterion is applicable within the reconsolidation pressure range of 0-30kg/cm2. The effective internal friction angle φ' and the cohesive strength c'are found to be 40°and 4kg/cm2, respectively. (6) It is necessary to take into account the creep deformation. The creep strength is 70-80% of the strength obtained by constant strain rate shear tests.
This paper describes the whole process of rock failure under uniaxial compression in terms several indices of failure. The authors try to characterize the point of strength failure by means of the particular point of diagrams of indices, and to explain the difference between the modes of failure of two rock samples, i. e., Akiyoshi-limestone and Sanjome-andesite. The authors have used the stiffness testing machine (total stiffness=6.8×105kg/cm2) which is stiffened by placing stiff bars parallel to the specimen. After the specimens were loaded to various stages of the failure process, the changes of the indices were measured. The important results obtained are as follows: (1) The permanent strain increases steadily up to the point of strength failure, and then increases rapidly after the strength failure. On the other hand, the elastic strain remains constant even after the strength failure until a macroscopic shear fracture plane appears. (2) Both the elastic strain energy and the energy loss increase steadily up to the point of strength failure. After the strength failure, the elastic strain energy decreases and the energy loss increases rapidly. Thus, the point of strength failure coincides with the follwing point; (i) the point at which the elastic strain energy is maximum, and (ii) the point at which the rate of increase of energy loss is maximum. (3) Porosity increases early even before the strength failure. This suggests that the micro-fractures have initiated before the strength failure. (4) As the failure process proceeds, P-wave velocity in the direction of specimen axis decreases to the final value about 70% of that of the intact sample.
On designing and performing underground excavation works it is desirable to measure the initial rock stress as one of fundamental data. Recently in the field of mining and civil engineering the rock stress is being measured by the stress relief technique. On the other hand, the tectonic movements, particularly the direction of stress and the strain rate, have been clarified by geological and geophysical investigations. The present paper first describes the method for estimating the tectonic stress. Subsequently, it mentions the fact that the initial rock stresses measured at the sites of Shintakasegawa and Okutataragi underground power stations are connected closely with the tectonic stresses in the respective districts. From these investigations, it has been found that the axis of the maximum rock stress nearly coincides with that of the maximum tectonic stress. Though the experiences in determining rock stress have revealed that the stress obtained varies from one point to another and that the accuracy is not high, it may be concluded that the rock stress measured is reliable to some extent.
The observations on secular changes of the crustal movements by means of extensometers and water-tube tiltmeters have been carried out in a tunnel of the former Tokaido railway at Otsu. The strain elements (main strains and areal strains) have been obtained from these observations of the extensions in the three azimuths and the vertical directions. And the recent changes of these elements for the period 1970 to 1973 have been compared with the mean variation in the whole period from 1961 to 1973. The azimuths of the main strains in the recent period are equal to those of the mean values, but the magnitudes in absolute value of these strains are different from those of the mean values. The constancy in the azimuths of the main strains corresponds well with those of the main stresses of the earthquakes and the crustal movements in this district obtained by the triangulations. The observations of the same components at the departed points on a same azimuth have been carried out simultaneously, and the development of the crustal movement has been detected. The ground tilting has been determined by means of the water tube tiltmeters at 2 points in the tunnel. It seems that the directions of these tiltings have close correlation with the topography around the observatory. The inclination around the observatory has amounted to 0.5 second for about twenty years. According to the observation by means of the recording type tiltmeter, it seems that the magnitudes and phases of the annual tiltings depend very much on the level down of the ground water in the tunnel. It seems also that the timing of anomalous changes of the tiltings correspond to that of the frequency of the felt earthquake. It was also found that many earthquakes have occured during the wet seasons in this district.
This report describes the effect of liquid honing on the fatigue strength of piano wires. In this investigation, wires with diameter of 2, 3, 4 and 5mm were used. They were liquid honed under six different conditions with three sizes of glass beads, and then tested with a rotating bending fatigue tester. The results obtained are summarized as follows: (1) The surface of the liquid honed wires was smooth and dull with fine depressions. (2) The improvement in fatigue strength of liquid honed wires increased as the wire diameter decreased; it was 30% for 5mm diameter wire, and 40% for 2mm diameter wire. (3) To obtain maximum fatigue strength, the optimum condition of liquid honing was different for each wire diameter, i. e. the honing intensity should be kept modest for small diameter and stronger for large diameter. (4) The fatigue strength of wire is considered to be increased, mainly by the residual compression stress appearing on the honed surface layer.
A coil spring made of the wire with a diameter larger than 4mm, is generally subjected to shot peening to improve its fatigue strength. The authors have previously investigated the effect of liquid honing using glass beads on the fatigue strength of piano wires, and obtained the experimental results showing that liquid honing was effective to improve the fatigue strength, for example, by 30% for the wire with 5mm diameter. In order to make clear the effects of liquid honing and shot peening on the wires with various diameters, the rotating bending fatigue strength of shot peened piano wires were studied. And the results were compared with the data for liquid honed wires. The results obtained are as follows: (1) The optimum condition of shot peening to improve fatigue strength was different for each wire diameter, i. e. the modest degree of peening was suitable for small diameter but the stronger for large diameter. (2) In case of the wire with a diameter less than 5mm, the fatigue strength of the liquid honed wire was higher than that of the shot peened wire. However, in case of the wire with a diameter larger than 5mm, the shot peening was estimated to be superior to the liquid honing.