The construction of an underpass in the City of Edmonton required the temporary relocation of the CNR main-line prior to the construction of a permanent bridge. The line was placed close to the underpass excavation which was supported by a tie-back sheet pile wall. Because of the stringent requirements associated with the presence of the railway line, the supports were designed on a conservative basis and observations of tie-back loads were taken over a period of 7 months.This note presents the observations of tie-back loads from January to July, 1977. Following installation in accordance with the design requirements, substantial fluctuations in tie-back load were observed for about 3 months. Then the loads fell off gradually to about 50% of the originally applied values. The variation of the load with time bears a strong correlation with average air temperature and is accounted for by the alternate freezing and thawing of the ground adjacent to the sheet pile wall. The ultimate decline in load is attributed to relaxation of the soil behind the wall during spring thaw. The case history draws attention to special requirements associated with interpretation of earth pressure measurements during winter con struction.
Behavior of a Braced Excavation in Soft Clay and the Undrained Shear Strength for Passive Earth Pressure