Even the best of concrete construction will show distress if the foundations are inadequate. It is impossible to tell just how much differential settlement at adjacent footings can be tolerated by a rigidly connected frame because so many factors are involved. Only in a pin-connected structure will the distress occur directly above the settlement. But pin-connected structures are practically nonexistent in the concrete field. A rigid frame will span over the soft spot, and failure is more likely at the relatively stable supports. This is simply illustrated by the example of a rigid log being carried by four men- A, B, C and D- positioned so that the load is equally distributed. If A steps into a depression in the ground, he suddenly finds a release of loading, while B is simultaneously more than doubly loaded and may even collapse. This is the probable explanation of some form work failures. For example, in 1958 concrete cylinders were extruded under pressure to act as piers or piles for the support of a five-story concrete office building near Montreal, Canada. The necking of these cylinders from the intrusion of mud as they were extruded so reduced the strength of the support that the building as a rigid mass, tipped 20 inches from the level in the length of 200 feet. The cylinders failed in rapid succession and without warning as the load was transferred from the previous failure. There was nothing wrong with the design but the building still sloped and later was demolished. It was then built on new piers with permanent steel casings. Another example is retaining wall failures. To often, designers copy standard designs without allowing for possible changes in soil conditions and additional pressures. Investigators found that most retaining wall failures in New York were usual after warm spring rains. They concluded that the walls fell because of additional pressure from: (1) the action of ice forming in cavities in back of and under the wall structure; (2) water pressure from the filing of continuous voids; (3) the wedging action of expanding tree trunks and roots.