The Building Research Establishment used an electro-level (E-L) system to monitor the below ground level performance under lateral load of two large diameter (1.5 m and 1.2 m) bored and cast-in-place piles. The piles were also fitted with 5 levels of vibrating wire (VW) strain gauges. The tests demonstrated that the E-L system can be deployed in bored cast-in-place piles at very little cost, or inconvenience to the piling contractor and that detailed information can be obtained on the below ground performance of the pile. Good agreement was found between the lateral head deflections of the piles monitored by surface instruments and calculated from the E-L results. This suggests that the deflected shape of the pile below ground level was accurately determined. Bending strains determined from the E-L results agreed at low loads with those determined from the VW gauges. At higher loads the strains monitored by the VW gauges were considered unrepresentative of the general strain levels in the piles due to the concrete cracking.

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