The stress around undeground openings is much affected by the state of stress in the ground in which the openings are made.The present paper describes the results of investigation in the stress distributions around a vertical shaft, an inclined shaft and a drift, taking into account that the ground is in threedimensionalstress state.
First the general method of experimental analysis of stress around a shaft or a drift is discussed, paying special attention to the evaluation of indeterminate stresses. Secondly, the stress around a shaft or a drift with a square or a rectangular cross section having rounded corners is found by two-dimensional and threedimensional photoelastic experiments.The results obtained are illustrated, from which the influence of the state of stress in undisturbed ground upon the stress around a shaft or a drift is discussed.

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The effects of thrust, perccussion, rotation of bit and interval of blow on rotary-percussive drilling mechanism are descrived in this paper.
Sample is put on the drop test apparatus under certain prestress. After the blow is made by dropping weight, penetration of bit and cross-section of crator is measured and then bit is rotated 180 degree. From the above mentioned experiments, the following results are obtained.
1) Penetration of bit is proportional to the prestress, but percussion affects penetration much more than prestress in this case.Also, mixed action of thrust and percussion is observed as shown in Fig.4.
2) Shape of the cross section of crator is getting sharp with increasing thrust.
3) Volume of the crator is growing with increasing blow energy.
4) The role of thrust is very important in rotating the bit.Namely, when the bit is rotated with overbalanced thrust, the cutting depth is increased linerly with penetration of bit to the sample.
5) When the bit is continuously rotated several rounds statisticaly, penetration rate per round is increased with the increasing thrust and blow energy, but is decreased when the interval of blow is prolonged.
6) Rotation torque has maximum value when the bit is rotated 360.degree under certain thrust and blow.
7) Energy consumption is getting much more linerly with increasing thrust, but when the interval of blow is prolonged, energy consumption is decreased.

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The effect of various concentration of Cl-on the anodic corrosion of pure and silver-containing lead anodes was studied.The anode potential increases with increasing the amount of chlorine present in the electrolyte ranging from 20 to 320mg/l. The amount of anode slime produced is not too much affected by the presence of Cl- up to about 40mg/l; above this amount it tends to decrease unless the silver content of lead anode exceeds 0.5%.The distribution of lead in cathode'zinc at each concentration of chlorine ion is almost uniform as to the silver-containing lead anode, while the maximum lead content is found in upper part of cathode with pure lead anode.The mean lead content of zinc deposit considerably increases with increasing the amount of chlorine with pure lead anode.
When the chlorine content in the solution is below 80mg/l, the lead content of cathode is not practically affected by varying the silver content of lead anode. Above this concentration the mean lead content of zinc deposit increased in the Pb-Ag anodes containing 0.20% and 0.51% Ag.

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