A sports hall was to be built on a site with severe mining subsidence. At ﬁrst sight the economic superstructure solution of a brickwork diaphragm wall was ruled out, since the settlement due to mining would result in unacceptable tensile stresses in the brickwork. The obvious solutions were to cast massive, expensive foundation beams to resist the settlement and support the walls, or to abandon the brickwork diaphragm wall solution in favour of a probably more expensive structural steelwork superstructure.
The problem was economically solved by prestressing the wall to eliminate the tensile stresses resulting from differential settlement.
Composite deep beams
Load-bearing masonry walls built on a soil of low bearing capacity containing soft spots are often founded on strip footings reinforced to act as beams, to enable the footings to span over local depressions. The possibility of composite action between the wall and strip footing, acting together as a deeper beam, is not usually considered. Composite action signiﬁcantly reduces foundation costs with only minor increases in wall construction costs (i.e. engineering bricks are used as a d.p.c. in lieu of normal d.p.c.s, which would otherwise act as a slip plane of low shear resistance). Bed joint reinforcement may also be used to increase the strength of the wall/foundation composite.