Curling Construction on Isolated Ground Pillars and Walls

We tend to assume that the pressure in foundations with rectangular footing that are widely spread in construction operations is distributed among ground capacities of some frusta. According to Requirements 5.1.2 of the set of rules 22.13330.2011 on “Foundations of Buildings and Structures” it is necessary to prepare deformation forecasts of the latter and there are only 5 cases (5.1.3) when strength forecasts have to be prepared on top of that.

The initial data for forecasting are usually defined in the laboratory by means of special instruments that are called stabilometers. It would be logical for these tools to test specimens of frusta but frusta are mostly pillared shapes, cylinders in particular, that are enclosed with a thin rubber membrane. These specimens are placed in a chamber made of clear plastic and are subjected to edging with fluid and rod end pressure at the top. There is a specific feature typical of testing samples with strabilometers. The matter is that side fluid pressure affects the specimens horizontally.

Stabilometers can specify the parameters of strain-stress distribution (SSD) but the specifications are not reliable to be used for real designing of earth foundations only because they do not have cylindrical structures. However, if one draws conventional vertical planes in the body of a frustum along the perimeter of its foundation base, in the end one gets a non-isolated prism-like pillar with sideways force affecting it. Direction-wise this force differs from the one the test specimen receives. Acting at an angle to the horizontal planes the sideways force of the nonisolated pillars forms a new frustum. Provided the foundation receives maximum pressure, its inclining plates are the reason why the underlying subsoil flees the foundation. Therefore, with solid earth foundations it would be necessary to lay the foundation at certain depths in order to prevent the soil from getting onto the surface.

Non-isolated pillars could be isolated if, for instance, they were separated from the surrounding bodies with slide faces. Then the stress state of the foundation grounds would be of a combined nature.

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TEXT : VICTOR IRKHIN, constructing engineer, inventor