PILE GROUP SETTLEMENT ANALYSIS FOR WEAK ROCK FOUNDATION SOCKETS DESIGNED USING A MODIFIED CORELATION FACTOR-PPT Presentation

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The presentation proposes a more suitable design approach for pile groups and barrettes socketed into weak carbonate rock, where conventional correlations can produce highly variable foundation lengths and potentially excessive material use.

Using data from 44 load tests in Dubai, the authors examined rock with unconfined compressive strengths (UCS) of approximately 0.6–3 MPa. Their regression analysis found that ultimate mobilized skin friction is represented by <strong>fs = 0.5√UCS</strong>. The relationship showed a strong fit (R² = 0.879) and was statistically significant. The authors recommend it for piles and barrettes in weak rock within the studied strength range.

The La Maison Tower case study illustrates the design benefits. Applying the revised correlation reduced barrette length in a serviceability analysis from 48 m to 35 m; predicted settlement was about 41 mm, compared with 75 mm for the initial design. Load testing also supported revising the foundation design. The overall optimization reduced concrete use by 23.5%, with estimated savings of 1,255 tonnes of carbon emissions from cement and steel.

The authors also recommend using stiffness values derived from geophysical testing to improve settlement predictions. They report that back-analyzed stiffness values can be three to 15 times higher than values from conventional laboratory testing, and suggest <strong>Es = 0.2Ed</strong> as a practical relationship for estimating static stiffness from dynamic test results.

The presentation concludes that observational methods, advanced testing, and numerical analysis should inform design correlations for large foundations in weak rock. This can avoid reliance on overly conservative methods developed for smaller structures and help optimize foundation performance, material use, and emissions.

Keywords

pile groups

barrettes

weak carbonate rock

ultimate skin friction

UCS correlation

Dubai load tests

settlement prediction

foundation optimization

carbon emissions reduction

geophysical stiffness