ABSTRACT
This chapter focuses on design and selection of two-leg shields. Shields installed in the United States since the early 1990s have been of the two-leg design. There are many positive advantages for employing an over-rated shield support. All theories developed for support capacity determination relate to static loading and do not account for the fact that shields are moving with the longwall face. A complete shield support design consists of four elements: the amount of roof and lateral loads to be supported, structural design and testing of the shield itself, determination of floor load distribution, and fatigue life span. Certain types of powered supports are best suited for certain types of roof and/or floor behaviors and vice versa. For two-leg shields, the selection of the dimensions of shield elements should take into account the expected interactions among roof, support, and floor. The recommended shield design procedures represent the elements that need to be considered for a complete shield design.
