Soil Compaction by Cyclic Loading: Ins and Outs

Clay soils are well known in Civil Engineering for their capability to generate excess pore pressure when loaded. As shear strength and settlements are widely influenced by the range of the excess pore pressure and its dissipation, its prediction reveals itself very important. Cyclic loading is a special case encountered in different and various situations as floods, tide or filling and emptiing of a silo. All these loadings are function of time, have low frequency and often conduct to a stationary state. This paper deals with the excess pore pressure: its amplitude, its out of phase, its relation with soil parameters, geometry of the problem and loading conditions. An analytical solution is proposed, validated by experiments. Principal results are to explain the conditions for which amplitude of excess pore pressure is upper than amplitude of loading, and to discuss the importance of compressibility of pore fluid by comparison with compressibility of soil.