Dynamic and seismic loading of soils

: Abstract There are many instances where soils experience dynamic loading, either through natural forces or human-induced forces. Although the magnitudes of these dynamic loads are often much smaller than static loads, the cyclic nature of the loading introduces inertial forces that become important and must be considered in geotechnical design. This chapter introduces the concept of dynamic loading of soils and the main characteristics that differentiate dynamic and static loading: loading frequency and loading cycles, and the strain-dependent behaviour of soil. The various methods that can be employed for characterising the dynamic behaviour of the soil are outlined, differentiating those that employ low- or high-strain cyclic loading, both in field measurements and laboratory testing. The theory that captures the dynamic response of the soil to cyclic loading is briefly examined with the main features highlighted. The main factors that influence the dynamic behaviour of soil are explored, with reference to results from the extensive laboratory testing that has been conducted in this area. The phenomenon of 'soil liquefaction' is also highlighted, along with the factors that influence it.