By Carl Erbrich, Earl & Wright (formerly of Fugro-McClelland). This paper was first published in GE’s January 1991 issue.
This paper describes an assessment of potential liquifaction in soils beneath the Conwy tunnel, north Wales which was carried out by the author.
A numerical model was used to predict the soil-tunnel interaction and the extent of the pore pressure generation due to dynamic earthquake loads.
Parameters for ther model were derived from cyclic simple shear tests carried out by Fugro-McClelland. In order to obtain realistic parameters it was necessary to derive a procedure that was somewhat different to the theoretical approach. This new procedure allowed much greater confidence to be placed in the model predictions than could have been obtained from the theoretical approach.
The results obtained from the numerical model demonstrated that liquefaction was extremely unlikely for the magnitude of earthquake that could be expected in north Wales. Some small permanenet settlements were predicted.