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

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The paper evaluates a modified method for designing pile and barrette groups socketed into weak carbonate rock, focusing on both load capacity and settlement. Traditional correlations between rock unconfined compressive strength (UCS) and shaft friction vary widely and were often based on smaller foundations or different geological conditions, leading to conservative designs.

The proposed correlation, developed by back-analysis of 44 high-capacity load tests from 18 Dubai sites, estimates ultimate shaft friction as <strong>fs = 0.52√UCS</strong> for weak carbonate rock with UCS values of approximately 1–3 MPa. The authors recommend validating this factor with preliminary bi-directional load tests; where testing is unavailable, they advise using a more conservative factor of 0.4.

The method was assessed through a case study of the La Maison tower in Dubai. A three-dimensional PLAXIS model analysed a barrette group redesigned with 35 m barrettes, compared with the original 48 m design. Ground stiffness was represented by a secant modulus equal to 0.2 times the small-strain modulus derived from geophysical testing. The revised design produced a predicted maximum settlement of 40 mm, within the adopted 80 mm serviceability limit.

The study concludes that combining the revised friction correlation with appropriate stiffness parameters can enable shorter foundations while meeting settlement requirements. For La Maison, the broader design optimization saved about 7,466 m³ of concrete and 586 tonnes of steel, with an estimated reduction of approximately 4,170 tonnes of CO₂ emissions. The authors recommend project-specific ground characterization, suitable finite-element group-settlement analysis, and load-test validation to support safe and more sustainable foundation designs.

Keywords

pile foundation

barrette groups

weak carbonate rock

shaft friction

unconfined compressive strength

load tests

settlement analysis

PLAXIS modeling

Dubai foundation design

sustainable foundation optimization