Equilibrium, strength, strain, dilation and superposition

摘要

Some basic principles of mechanics are considered, using examples to show how they are importantrnto practical design. In most of the cases considered, computer programs have been used to carry outrncalculations, with the user sometimes lacking a full appreciation of the problem or a proper understanding ofrnthe calculation and material model in use. Equilibrium is the fundamental requirement of many engineeringrncalculations, and it is important to ensure that all forces can be transmitted into ground that is able to resistrnthem; computer programs that consider only part of the equilibrium may be insufficient. Modern finite elementrnprograms are easy to use, but it is essential that users cling to a sound grasp of soil mechanics and behaviour, andrnconstantly ask themselves if the model in use is suitable for the current task; in particular dilation is important inrncontrolling the strength of undrained or confined soils. Engineering courses tend to concentrate on stress statesrnand stress analysis; but strain is much easier to observe and sometimes gives important warnings of impendingrnproblems. Finally, the principle of superposition is carefully taught, with emphasis that it only applies in linearrnsituations; but in practice this limitation is often forgotten.