Soil Movements in Deep Excavations Made in Mexico City: Wall Displacements, Bottom Heave and Surface Settlements

Deep excavations in Mexico City induce three characteristic ground movements: horizontal displacement of the retaining wall, bottom heave and settlement of the adjacent ground surface. This paper compiles 100 deep excavation projects; for the 20 cases with field measurements, ranges of maximum horizontal wall displacement are established as a function of excavation depth, geotechnical zone, wall type and support system. Because none of the cases included bottom heave or surface settlement measurements, these movements were studied numerically with the Hardening Soil model with small-strain stiffness, using a model of the crossing of Lines 8 and 9 of the Mexico City Metro calibrated against measured wall displacements; the bottom heave and settlement results are numerical predictions not verified against field measurements. The two-dimensional parametric study shows that, when the excavation width exceeds its depth H, the maximum bottom heave occurs at about H from the wall rather than at the centre, and that the bottom heave at the centre decreases as the width increases. The finite element surface settlement profile is reproduced more closely by the method of Hsieh and Ou than by that of Clough and O’Rourke. Numerical methods remain the only tool to analyse the three movements jointly.