Three-dimensional numerical analysis of excavation-induced deformation in an asymmetric irregular deep excavation in coastal soft soil and comparison with monitoring data

Deformation control during deep excavation in coastal soft-soil areas is an important geotechnical engineering issue. Pre-vious studies have focused mainly on regular and symmetric excavations, while the spatial distribution of deformation around asymmetric excavations with irregular plan geometries remains insufficiently understood. This study investigates the asymmetric deep excavations for the Hexi working shaft and the Line A sea-entry section of the Sanya River Estuary Passage Project. Laboratory triaxial tests were conducted to determine the shear strength parameters of the sand and silty clay. A three-dimensional staged-excavation model was then developed in ABAQUS to simulate excavation-induced ground surface settlement and diaphragm-wall deformation. Numerical results at selected monitoring points were compared with field measurements and SBAS-InSAR observations. The results show that excavation-induced ground deformation is dominated by settlement and exhibits distinct stage-dependent, cumulative, and spatially non-uniform characteristics. A well-defined settlement trough develops outside the retaining structure, with computed final settlements of −5 to −16.5 mm at the near-excavation ground monitoring points. The numerical model predicts horizontal diaphragm-wall movement predominantly towards the excavation. On the eastern side, the principal high-displacement zone develops at or below the current excavation level and shifts downward as excavation progresses. The maximum horizontal displacement reaches 31.5 mm on the eastern side, compared with 16.4 mm on the western side. The predicted vertical wall movement is dominated by settlement, although local heave of 6.4 mm occurs on the eastern side, whereas settlement reaches 21.5 mm on the western side. These results indicate pronounced deformation asymmetry between the two sides. At the selected wall-top and ground surface comparison locations, the numerical results agree with the field measurements and InSAR observations in deformation trend and stage-dependent characteristics, with final differences of 0.3–2.4 mm. The developed three-dimensional model therefore provides a reasonable representation of the excavation response of an asymmetric irregular deep excavation in coastal soft ground.