Scholarly record

PREDICTION OF BEARING STRENGTH OF WEAK FLOOR STRATA WITH REGARDS TO PLATE SIZE EFFECTS

D. Kumar, S.K. Das

Abstract

A simple method for determination of bearing strength of weak floor strata in underground mines has been evaluated based on physical modeling approach, with regards to plate loading test conducted on simulated floor strata. This paper presents plate size effect on floor bearing strength of coal measures strata. Plate loading tests were carried out for varying size and shape of footing plates. The analysis was made for model scale footing. The load exerted by the plate on the floor strata was assumed to be uniformly distributed. From the scale model test it is found that the floor bearing strength (Bs) decreases considerably with increase of footing plate size for all the shape of footing plates. The experimental results strongly support the earlier field investigation findings depicted by Yu and Chug et al (1992). For the same plate size of different shapes, square plate offers maximum bearing strength and minimum settlement. For a smaller d/t ratio the ultimate bearing strength is the maximum. A sharp decreasing trend in ultimate bearing strength is observed with an increase in the said ratio up to 1. A further increase in d/t ratio shows a very small decreasing trend in ultimate bearing strength. It is further found that with the increase in plate size the floor bearing strength decreases considerably but at the same time plate settlement also decreases. Hence the optimum plate size must be chosen to provide maximum bearing strength without causing a floor punching. In other words the optimum base area of any underground roof support system should be selected to bear the maximum load without floor punching.

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