It is necessary to establish the empirical formula on the depth of cut for slot cutting in rocks with high-speed waterjets both in air and in water in order to apply the high-speed waterjets technology to various engineering fields such as tunnelling, pre-cracking around a deep borehole and rock excavation at the sea bottom as well as quarrying rocks.
In this paper, to clarify the effects of standoff distance up to its limit where no cutting occurs and nozzle diameter from 1 to 2 mm on the depth of cut in rocks, systematic experiments were carried out both in air and in water for welded tuff and a comprehensive empirical formula on the depth of cut in rocks was proposed from the test results and those from a previous work.
Main results obtained in this study are summarized as follows:
1) There exists a limit of standoff distance beyond which no cutting occurrs for both in air and in water. The limit of standoff distance increases with both driving pressure and nozzle. diameter, and becomes much smaller in water in comparison with in air.
2) The depth of cut depends on the distance from the limit of standoff distance rather than standoff distance itself.
3) The critical pressure is almost independent of both standoff distance and nozzle diameter.
4) The following formula is proposed as a comprehensive empirical formula on the depth of cut h for slot cutting in rocks both in air and in water.
h=k(1-L/L₀)^γd^βV^-n (p-p_c).
where L is standoff distance, L₀ is the limit of standoff distance, d is nozzle diameter, V is traverse rate, p is driving pressure, p_c is critical pressure, and k, γ, β and n are coefficients which depend on environmental medium and rocks.

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Most big limestone quarries in Japan use an ore pass system with large vertical or inclined ore pass to transport the ore from the bench to the crushing room. Despite their importance in controlling the quality of quarry products, the mixing property and the mechanism of the gravity flow of ore in the ore pass system are not apparent in most quarries. The mixing property is considered to depend on the material properties of the ore, the geometry of the system and also on the mechanism of the gravity flow inside the system.
Based on the observation of the so called “breathing” phenomena of the ore pass in Toumi limestone quarry, a model for the gravity flow considering the bulk density variation through secondary motions of ore and the forming of a local micro arch is proposed. Several phenomena occurring in the ore pass according to the production of ore could be easily explained using this model. Extending this gravity flow model to an inclined ore pass, the possibility is shown that the mixing property of an inclined ore pass may also depend on its length.

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The present paper describes the results of mine fire experiments conducted in an actual size gallery. The main purpose of the experiments was to obtain the fundamental data about temperature distribution downwind of the fire, velocity and pressure variation of the air which are indispensable for taking effective counter measures against the underground fire. The air velocity decreases as the fire burns. The higher the temperature of the fire zone and the initial air velocity, the greater is the decrease in the velocity. The air temperatures decreased nearly exponentially with distance from the fire. The coefficients of air temperature decreasing with distance, as defined by Eq.(2), ranged from 0.007 to 0.01 (1/m) in these experiments. The value increases as the air velocity decreases although the differences involved are relatively small.

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This paper deals with water hammer in coarse solid-liquid two-phase flow in a pipe. Pressure wave velocity decreased with increasing solid concentration because the propagation of pressure wave was obstructed by solid particles in the pipe. On the other hand, maximum surge pressure by rapid shutdown increased as solid concentration increased. This result is owing to the increase of the momentum of mixture with the increase of solid concentration.
Theoretical consideration was made on in-site solid concentration, and Eq.(8) was obtained. By using Eq.(8), equations for pressure wave velocity and maximum surge pressure were derived as Eqs.(14) and (18), respectively. It was found that calculated values were in good agreement with the experiments.

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To consider the experimental results presented in the previous paper, theoretical study has been made on the accumulator behavior of an oil hydraulic breaker. The theoretical results which are compared with the experimental results are as follows:
(1) With respect to the effect of the accumulator gas pressure and volume, the theoretical results agree well with the experimental results except for the conditions that the pressure and volume are small. The optimal values are indicated as that the gas pressure is about 3.43 MPa and the volume is about 0.2 to 0.3l.
(2) The expression to estimate the accumulator gas volume is obtained, and it is a function of a pressure drop ratio of the rear chamber at the forward stroke of piston and effective discharge volume of the accumulator. Various oil hydraulic breakers are given optimal sizes of the accumulators by using the expression.

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The hydraulic gradient in slurry transportation has been practically discussing with the data on the single size particles. However, the most economic conditions are obtained in the case of the slurries mixed of different size particles. While the Wasp's method has been comprehensively used for prediction of hydraulic gradient on the slurries containing various size particles, the authors had already pointed out that the method should provide sufficiently accurate predictions for the hydraulic gradient under the limited transport conditions.
In this paper, the size distribution of materials were estimated with the distribution constant n and basic constant b associated with the specified residue, Rosin-Rammlar's distribution law and median size diameter d₅₀, and the influence of size distribution on the hydraulic gradient in systems were investigated analytically. Moreover, experiments to ascertain the results of the analytical studies were performed using sand particles, whose size laid between 0.42 and 2.83 mm, in transparent plastic recirculating pipeline loops with 25.9 and 31.9 mm diameter.
The principal results of this study may be summarised as follows:
(1) As the distribution constant n deceases at a given basic constant b, the hydraulic gradient decreases at lower mean velocities, whereas it increases at high velocities.
(2) The effect of n value on the hydraulic gradient is dependent not on the pipe diameter and delivered volume concentration, but highly on the median size diameter d₅₀.
(3) The exponent in Durand-Condolios equation for the nonuniform solids tend to be lower than the one for the uniform solids if the median size diameter is selected as the representative diameter of solids of distributed size.

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The adsorption characteristics of Ca, Na⁺ and K⁺ on H-form dickite (a two-layer clay), mainly below pH10, were studied. The results were compared with those for H-form sericite (a non-expanding three-layer clay) and quartz.
The Ca adsorption in the region of weakly acid to neutral pH decreased in the order sericite>dickite>quartz. The Ca adsorption on dickite was more strongly hindered by K⁺ than by Na⁺; whereas for quartz, the effect of these monovalent cations was similar. The saturation adsorption of Ca on dickite increased with pH; on sericite it was constant over the pH range below 10. The negative zeta potential of dickite was reversed at high Ca concentration; as for sericite, the charge reversal was not observed.
The above results show that the mechanism of Ca adsorption on dickite involves some specific interaction in addition to the simple electrostatic one with the negative surface charge and to the exchange reaction with H⁺ which is considered to be the dominant mechanism of the adsorption on sericite.

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Isopiestic measurements for determining water activity at 298 K were extended to the aqueous solutions of H₂S0₄-Mx (SO₄) y (including UO2S0₄, CdSO₄, Li₂SO₄, and Na₂SO₄). The applicability of Robinson-Bower equation, which had been proposed for evaluating water activity in mixed solutions, was examined for these solution systems, and it was found that the water activities calculated by this equation are in good agreement with those experimentally determined. The mean activity coefficients of H₂S0₄ and Mx (SO₄) y in these solution systems were calculated by the McKay-Perring method on the basis of equiwater activity lines. The mean activity coefficients of H₂S0₄ calculated by the McKay-Perring method agreed well with those measured at 298 K by the emf method using a cell consisting of a glass electrode and a Pb0₂-PbSO₄ electrode. The applicability of the Meissner-Kusik method to the aqueous solution of H₂S0₄-CdSO₄ was examined by comparing the mean activity coefficients calculated by this method with those determined by the emf method. The Meissner-Kusik method gives activity coefficients of 20-40 pct higher than those determined experimentally.

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