The use of electro-levels on laterally loaded precast driven piles at Stretton

During pile testing at the site of a new bridge near Stretton the Building Research Establishment carried out trials to determine whether electro-levels (E-Ls) installed in a tube, driven as close as possible to a pile that was subsequently loaded laterally, could be used to monitor the pile's below ground deflected shape. The results showed that the pile head deflection calculated from the E-L results agreed reasonably well with the deflection monitored by conventional above ground movement measuring systems. Bending strains deduced from the rotations monitored by the E-Ls suggested that the pile failed as the result of the formation of a plastic hinge, or hinges at a load of 60 to 66 kN. Use of Broms design chart confirmed that this was a reasonable estimate of the ultimate lateral capacity of the pile. It is considered that the method provided meaningful information on pile performance and with further development would offer an inexpensive way of instrumenting commonly used piles that would otherwise by very difficult to instrument.