Discussion. Strata Control in Coal Mines.

Abstract

, in presenting the Paper, emphasized the fact that it was a preliminary report upon a research which was still in progress, and said that the Authors hoped to learn from the discussion ways in which the measurements might perhaps be improved.The dynamometer prop shown in Fig. 2 (p. 340) had been abandoned in subsequent work because of the complication involved in having a special type of prop, and ordinary steel props were being used, measurements being made with a strain-gauge. The mercury dynamometer could be used underground because at the coal face the temperature-changes were small, but if it were used at the surface it would act as a thermometer and the readings would be erratic. Mr. F. E. Wentworth-Sheilds expressed the regret which he knewwas felt by all those present that Sir Richard Redmayne, K.C.B., PastPresident Inst. C.E., was unable to be with them that evening, as he had played a very important part in the commencement of the research.At the beginning of the Paper the Authors expressed the view that a discussion of the results so far obtained might be of interest in view of the somewhat similar problems being studied by the Institution Research Committee. He was quite sure that every member of that Committee would agree with that statement, although it could not be said in any sense that the researches overlapped. The problem of the mining engineer was how to support an enormous slab which was over his head, whilst'the problem of the surface engineer was how to distribute his load on that enormous slab. The Committee on Earth-Pressures of the Institution Research Committee had, during the past few years, been studying four main problems. The first was the classification of soils according to their physical and mechanical properties, such as friction and cohesive strength ; the second and third problems were the estimation of the movement of soils under vertical and horizontal loads respectively ; and the fourth problem was the estimation of forces such as arose when slips were formed or landslides took place. In the first research much useful work had been done in different countries, and a technique had been evolved for ascertaining the mechanical properties of different soils, and therefore of classifying them. In regard to the estimation of settlement under vertical load, some very successful work had been done, and a stage-had been reached where it was possible more or less to estimate what vertical movement a given load would produce on a known soil. With regard to the problem of movement under lateral pressure, the work had not gone so