Building Design and Construction Handbook - Merritt - Ventech!

6.64 SECTION SIX
FIGURE 6.26 Local shear foundation failure, which is a transitional phase between
general shear and punching shear failures. (Adapted from A. B. Vesić, ‘‘Bearing
Capacity of Deep Foundations in Sand,’’ Highway Research Record, no. 39.)
1. There was an overestimation of the shear strength of the underlying soil.
2. The actual structural load at the time of the bearing capacity failure was greater
than that assumed during the design phase.
3. The site was altered, such as the construction of an adjacent excavation, which
resulted in a reduction in support and a bearing capacity failure.
A famous case of a bearing capacity failure is the Transcona grain elevator,
located at Transcona, Manitoba, Canada, near Winnipeg. Figure 6.27 shows the
October 1913 failure of the grain elevator. At the time of failure, the grain elevator
was essentially fully loaded. The foundation had been constructed on clay that was
described as a stiff clay. Note in Fig. 6.27 that the soil has been pushed up on only
one side of the foundation, with subsequent tilting of the structure.
6.6.1 Bearing Capacity for Shallow Foundations
As indicated in Table 6.2, common types of shallow foundations include spread
footings for isolated columns, combined footings for supporting the load from more
than one structural unit, strip footings for walls, and mats or raft foundations constructed
at or near ground surface. Shallow footings often have an embedment that
is less than the footing width.