They are used for varying conditions of sub-strata where suitable load-bearing soils exist at shallow depths below the effects of frost and general weathering. They are particularly economic where the side of the excavation can be used as a shutter and where a suitable depth of mass can be accommodated to disperse the load without the need for reinforcement. The general assumption for load dispersion is as mentioned previously i.e. a 45° spread through the mass concrete (see the typical example shown in Fig. 9.11).
Fig. 9.10 Shallow mass concrete pad.
Fig. 9.11 Load spread on mass concrete pad.