CPT Filter to Estimate the End Bearing of Closed-Ended Driven Piles in Layered Sands-Paper

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The paper presents a CPT-based method for estimating the end-bearing resistance of closed-ended driven piles in layered sands. Because a pile is much wider than a CPT cone, its resistance reflects a smoothed response to soil layers around the tip. The authors apply the Boulanger and DeJong filtering procedure to CPT cone resistance data, using the pile diameter to calculate an equivalent resistance, \(q_p\), for a cone of pile-sized diameter.<br /><br />The method was evaluated against measurements from 19 instrumented pile load tests. The measured pile resistance at a displacement of 10% of the pile diameter, \(q_{b0.1}\), was found to be approximately proportional to the filtered resistance:<br /><br />\[<br />q_{b0.1} \approx 0.5q_p<br />\]<br /><br />This relationship had a coefficient of variation of about 20% and showed little dependence on pile diameter. By comparison, conventional CPT averaging approaches—particularly fixed averaging over 1.5 pile diameters and the Dutch method—could produce greater scatter or unrealistic estimates in layered profiles.<br /><br />The proposed method was also compared with four established CPT-based design methods (ICP-05, UWA-05, Fugro-05, and NGI-05). It gave the most consistent predictions in the test database, with a prediction-ratio coefficient of variation of 0.21 and no evident bias with pile diameter. The authors conclude that filtering CPT data in a manner accounting for layer effects and pile scale provides a more rational and reliable estimate of pile end bearing than the existing methods assessed.

Keywords

CPT-based method

end-bearing resistance

closed-ended driven piles

layered sands

Boulanger and DeJong filtering

cone resistance

pile diameter

instrumented pile load tests

prediction ratio

pile design methods