Hydraulic fracturing is now widely used for in-situ tectonic stress measurements. With this technique, the stresses are calculated using equations derived through considerations on crack initiation and crack growth in the tectonic stress field. One of these equations is the so-called breakdown equation which relates the crack initiation pressure to the in-situ stress. However as demonstrated by many laboratory hydrofrac experiments published before, breakdown pressures predicted by the classical breakdown equation do not always agree with the experimental data. To resolve this problem, the mechanics of hydraulic fracture initiation have been investigated by comparing laboratory experiments with theoretical predictions based on the fracture criterion. In this criterion, it is assumed that failure occurs from a wellbore when the maximum principal stress at some fixed distance ahead of the wellbore reaches the tensile strength of the rock. Laboratory hydrofrac experiments were carried out on cubical rock specimens uniaxially loaded. Prior to fracture, the pressurizing fluid may penetrate into the surrounding rock and thus perturb the stress field by increasing the interstitial pore pressure around the wellbore. In order to avoid this effect due to fluid penetration, the experiments were 'carried out by using wellbores jacketed with plastic tubes. Results show that the breakdown pressures predicted by the classical breakdown equation are fairly lower than the breakdown pressures obtained experimentally. On the other hand, the pressures predicted based on the fracture criterion perfectly agree with the experimental data independently of the various conditions of experiments, i. e., the load, the wellbore size and the rock type.

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A new method, Equivalent Volume Defect Method (EVDM), to estimate the deformability of jointed rock is proposed. Equivalent Volume Defect (EVD) is theoretically defined in this paper as its effect on the deformability is equivalent to the effect of joint. Basing on EVD concept, stress/strain relationship of jointed rock is simply formulated as it can be treated in a framework of continuum mechanics.
A stress/strain relationship of the elastic body which contains many cracks is theoretically analyzed in consideration of mechanical interaction of cracks. It is made clear that EVD is determined by the length and the orientation of each crack, and the effective elastic compliance of the body is expressed as a function of EVD and intrinsic elastic moduli of the body. Furthermore, a numerical procedure for Finite Element Analysis based on EVDM is presented.
In order to examine the proposed method for its validity, model calculations have been performed. The result obtained by EVDM agrees fairly well with that by Displacement Discontinuity Method, hence it is confirmed that EVDM gives a good approximation for deformation behavior of jointed rock.

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In order to know the applicability of high-speed waterjets technology to the engineering fields such as slot cutting from the wall of a deep borehole for hydraulic fracturing and geothermal energy extraction, drilling of a borehole and excavation of rocks under the sea, it is necessary to clarify the effect of high ambient water pressure on the depth of cut in rocks.
In this paper the depth of cut of Shirakawa welded tuff under high ambient water pressure up to 20 MPa was systematically investigated using a conventional tapered nozzle with the maximum driving pressure of 98.1 MPa.
Main results obtained in this study are summarized as follows: 1) Although the depth of cut decreases rapidly with ambient water pressure, it reaches an almost constant value at a certain ambient water pressure. The maximum depth of cut at the ambient pressure of 19.7 MPa was 32.2 mm for the welded tuff when driving pressure was 98.1 MPa. Accordingly it can be said that the high-speed waterjets could be applied to rock cutting in deep water. 2) An empirical formula on the depth of cut under ambient water pressure was proposed. The term which expresses the effect of ambient water pressure for the region where ambient water pressure affects the depth of cut is independently added to the empirical formula which was already proposed by the authors. 3) The cavitation errosion plays a predominant role when cavitation number is less than 0.05 and specific energy becomes minimum when cavitation number is less than 0.01 for the welded tuff.

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Equivalent Volume Defect Method (EVDM) is one of useful methods to estimate the deformation behavior of discontinuous materials but its application is limited in the open crack problem. In this paper, EVDM is expanded as it can apply to the closed crack problem.
Deformability of the elastic body which contains a single closed crack is analyzed in consideration of frictional sliding on the crack surface. It is made clear that Equivalent Volume Defect for a closed crack is expressed as a function of the crack length, the crack orientation, the frictional coefficient on the crack surface and the applied stress. Based on this expression, the elastic compliance of the solid which contains closed cracks is simply evaluated in the same manner as that of open cracks.
To examine the applicability of the proposed method, model calculations are carried out. The results obtained by the proposed method agrees fairly well with that by Displacement Discontinuity Method, hence it is confirmed that the proposed method gives a good approximation for deformability of the materials which contains closed cracks. Furthermore, EVDM can also apply to the deformability analysis of the material which contains both of open and closed cracks.

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For the purpose of more effective underground communication, UHF radio wave propagation along underground gallery was discussed both experimentally and theoretically. From the experimental results, it became clear that the higher frequency bands, i. e. more than 500 MHz, were favorable for underground use by the reason of the lower propagation loss. To establish the propagation model of UHF radio wave theoretically, both the simple geometrical image source method and the characteristic equation method were discussed to allow for gallery conditions such as timbering methods, cross sectional area and others. Reasonably good agreements were observed between experimental results and theoretical calculation which is based on the simple geometrical image source method.

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A hydrochloric waste etch at a printing plant contained 176g/l of Fe³⁺, 44g/_l of Fe²⁺, 40g/l of Ni, 0.3 g/l of Co, 0.8g/l of Mn, and the pH of the 1: 10 dilution of it was 1.2. The selective removal of iron ion as iron hydroxide from it was investigated in order to recover Ni, Co and Mn.
At first, the precipitation behavior of various metal ions in the artificial waste etch that contained 2.2 g/l of Fe³⁺, 0.4 g/l of Ni, 3 mg/l of Co and 8 mg/l of Mn was examined using sodium hydroxide, calcium hydroxide and calcium carbonate as a neutralizing reagent. The coprecipitation of Ni, Mn and Co with ferric hydroxide was observed when sodium hydroxide or calcium hydroxide was added. However, calcium carbonate caused ferric ion to precipitate with less coprecipitation of other metal ions. It could be explained in terms of low solubility of calcium carbonate and the buffer effect of desolved carbon dioxide.
When the 1: 10 dilution of the hydrochloric waste etch was aerated for 30 minutes using a Denver type flotator after adding 50 g/l of calcium carbonate, iron ion was precipitated selectively. In this case the filtration rate was very low, but the addition of sodium sulfate with calcium carbonate reduced the filtration time and increased the volume of the filtrate.

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The chemical compositions of iron-saturated mattes have been measured at 1473 K. The vapor pressures of sulfur have been determined experimentally over the Cu-Fe-S mattes by equilibrating them under the H2-H2S gas mixtures. Based on the present work and also literature data, a single equation has been established which provides excellent descriptions of sulfur partial pressures over the entire Cu-Fe-S matte compositions including the Fe-S and Cu-S binary systems as well. This simple function facilitates the ternary Gibbs-Duhem integrations for determining the Cu and Fe activities in mattes. The Fe and Cu activities in the matte-saturated alloys, which are required as initial conditions for the Gibbs-Duhem integrations, have been established by using quasichemical solution models. The Raoultian activities of FeS and CuS_0.5 have been presented for the metal-saturated mattes as well as the pseudobinary FeS-CuS_0.5 mattes.

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