Numerical Simulation of Size Effects of Laboratory Pressuremeter Tests

The pressuremeter test (PMT) measures in situ soil properties under the original stress state with minimal disturbance. However, interpreting PMT data for constitutive parameters remains reliant on empirical correlations, and a key challenge is the poorly understood size effect arising from the equipment dimensions.‌ This study aims to systematically quantify such size effects to provide a scientific basis for optimizing the design of laboratory PMTs. A series of 36 PMT simulations were performed using the ‌finite element method (FEM), incorporating the Duncan–Chang E-B hyperbolic model. Six cylindrical soil models of diameters ranging from 0.6 m to 2.4 m were established for both sand and clay, under three overburden pressures (200 kPa, 1000 kPa and 3000 kPa). The radial stress, strain distributions and borehole wall displacement were systematically analyzed. The analysis reveals that the size effect originates from the truncation of the radial strain integration path. In all cases, borehole wall displacement increases with model diameter, characterized by a steep rise for diameters below 1.2 m and a plateau for those above 1.2 m. Although clay produces larger displacements than sand, and higher stress produces larger displacements than lower stress, the identified pattern remains robust. Considering both the displacement–diameter relationship and practical cost constraints, an optimal equipment diameter of 1.2 m is recommended.