An Schofield

Complementary Shear Stresses in Dynamic Centrifuge Modelling

The semi-infinite extent of the natural soil medium needs to be simulated accurately while attempting to model stress wave propagation or dynamic soil-structure interaction problems on a centrifuge. In this internal report results from two centrifuge tests conducted to study the effects of complementary shear will be discussed. The normal stress at the base of a horizontal sand bed and the shear stress generated at the base of the centrifuge model were generated using Stroud cells (Stroud, 1971). The complc:mentary shear stress along the vertical face of the duxseal boundary was measured by mean:; of a thin duraluminium sheet coated with sand particles and which was fitted with strain guage j at three different levels. It was shown that it is indeed possible to measure the normal and shear stresses at the base of dynamic centrifuge model:; using standard Stroud cells. A simple De Alembert’s analyses suggested that about two-thirds of the shear stress is transmitted into the model and remaining shear stresses would result in a pressure wave generation along the vertical face of the boundary. The complementary shear stress measured by the strain guaged dural sheets agreed satisfactorily with the observed base shear stress magnitudes. The present study lists the specific centrifuge model tests which need to be conducted in future.

Seismic modeling of embankments on saturated soil deposits

Following an earthquake it is important that the transport networks are operable for the use of relief convoys. Following the Northridge earthquake several of the key road networks in the Los Angeles area have become unusable. Kobe earthquake presented a similar problem to the transport networks. Embankments constitute a key element in highways and other transport networks. It is therefore important to ensure the safety of embankments subjected to seismic loading. This paper presents the results of the centrifuge tests carried out as a preliminary investigation into the behaviour of granular embankments founded on loose saturated sand subjected to earthquake loading. It was observed that the embankment settled by considerable amounts during the earthquakes. The post test investigation revealed that gravel had sunk into the sand foundation and there was some lateral spread of the embankment.