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

2nd International Scientific Conference - SGEM2002, www.sgem.org, SGEM2002 Conference Proceedings/ ISBN: 954-918181-2, June 9-15, 2002, 35- 48pp

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.