THE INFLUENCE OF PHASE ON THE CALCULATION OF PSEUDO-STATIC EARTH PRESSURE ON A RETAINING WALL

Centrifuge modelling tests show clearly the phase change in lateral acceleration in the backfill behind a retaining wall as shear waves propagate from the base of the model towards the ground surface. However, design calculations for the dynamic lateral earth pressure on a retaining wall which use a pseudo-static approach assume that the backfill experiences a uniform acceleration throughout. Researchers have agreed that the total lateral earth pressure calculated using this approach is approximately correct, but have disagreed over the distribution of the dynamic increment of pressure. The Paper presents an analysis which takes into account a finite shear wave velocity in the backfill, thus allowing for the phase change in a prototype structure. The phase change does not have a significant influence on the magnitude of the total earth pressure, but it has a marked effect on the distribution of the dynamic increment. The resultant pressure is seen to act at a point above one third of the height of the wall. The maximum dynamic earth pressure and the peak bending moment on the wall are approximately in phase with the acceleration at mid-depth, and therefore this acceleration may be the most appropriate value to use for design. The effect of a non-uniform shear modulus distribution is considered, as is the effect of amplification of acceleration on the distribution and magnitude of earth pressure. Amplification of acceleration has an influence similar in character to the effect of increasing the acceleration coefficient in a uniform acceleration field. Centrifuge model test data analysed using this approach show good agreement if the amplification of motion is taken into account. © 1990, Thomas Telford Ltd. All rights reserved.