Numerical Assessment of the Response of Piles in a Piled Raft System due to Tunneling in Clayey Soil-Paper

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The study uses three-dimensional finite-element analysis in PLAXIS 3D to examine how side tunneling in clay affects piles in an existing 2 × 2 piled-raft foundation. The model represents a loaded raft and four piles near a shield-driven tunnel, with soil modeled using the Mohr–Coulomb constitutive model. After validation against published field measurements and numerical results for a single pile, the model is used to compare pile behavior before and after tunneling.<br /><br />Tunneling causes the front and rear piles to respond differently. The front pile experiences greater lateral deflection and a substantial increase in axial load, while the rear pile is less affected. Vertical movement changes only modestly, increasing by about 1.5 mm. Tunneling also alters pile bending moments: the front pile’s head moment shifts from −59 to 50 kN·m, while the rear pile’s maximum moment reaches 95 kN·m near its lower end. These findings show that tunnel location and pile position within a piled raft influence structural response and should be considered in foundation assessments near tunneling works.<br /><br />The analysis is limited to a dry-soil, side-tunneling scenario. The authors recommend further investigation of other tunnel configurations, undrained conditions, and consolidation effects, including pore-water-pressure measurements.

Keywords

finite-element analysis

PLAXIS 3D

side tunneling

clay soil

piled-raft foundation

pile behavior

axial load

lateral deflection

bending moment

tunnel-soil interaction