Simplified methods in Soil Dynamics

• Simplified methods still important in Geotechnical Engineering and Soil Dynamics.
• Engineer does hand calculations, develops better feel, verifies computer results.
• Understanding of basic theory is useful including dynamics and wave propagation.
• Equivalent springs and dashpots for shallow foundations on half-space.
• From circular surface foundations to embedded foundations of arbitrary shape.

After a brief description of the main characteristics that define Soil Dynamics and its engineering applications, the role of Simplified Methods is discussed. Despite the current wide availability of powerful computer simulations, it is concluded that Simplified Methods will continue to play an important role in Soil Dynamics as they do in the rest of Geotechnical Engineering. Simplified Methods allow the engineer to conduct calculations by hand or with a minimum computational effort, including parametric variations. In the process, the engineer has the possibility to develop a feel for the physical meaning and relative importance of the various factors, with more personal control of calculations and decisions including use of engineering judgment as needed. A list of simplified procedures proposed by the author is provided, covering systems that range from the free field and earth dams to shallow and deep foundations, subjected to excitations that include both seismic shaking and machine vibrations. Basic understanding of the basic theory and simplifications behind the simplified procedure can be very helpful to engineers, including Dynamics and Wave Propagation concepts. Some of this understanding is developed in the paper, with focus on shallow machine foundations and other dynamic soil–structure interaction applications.The Lecture concentrates on shallow machine foundations on a half-space subjected to dynamic loads in any of the six degrees of freedom of the foundation, and the Simplified Methods that have been proposed over the years to characterize the corresponding equivalent soil springs and dashpots. This includes both frequency-dependent and frequency-independent springs and dashpots. It started with the circular surface foundation which was studied over much of the 20th Century, until the breakthroughs by Lysmer and others in 1966–1971, and continued with the cases of surface and embedded foundations of arbitrary shape that culminated in the two summary publications by Gazetas in 1990 and 1991. The development of these simplified equivalent springs and dashpots for both surface and embedded foundations of arbitrary shape is discussed in some detail, including the contribution of the author in the early part of the process.