Abstract: Lateral displacement control is an important factor for evaluating subgrade deformation during expressway construction period. This paper analyses the settlement deformation observation data of the soft ground distributed along the Suining-Ziyang expressway in Sichuan province, and researches the soft ground treated by PVD and gravel pile in Southwest China.Through observed data, we discuss the variation rules of subgrade lateral deformation(y) and depth(z), maximum lateral deformation increment(△ym) and surface settlement increment(△SD) and average lateral deformation(Sy) and surface settlement(Sf). The research shows that:（1）According to the Boussinesq’s formula and measured data, y-z curve is roughly S-shaped under embankment load area; y varies greatly near surface, but the maximum lateral displacement remains steady with load increasing; The depth of maximum lateral deformation does not related to embankment height but to soil property. (2) During filling period and precompression period, soft ground treated by PVD both produce large lateral deformations; the deformation of each period accounts for 50% of total displacement. The depth of maximum lateral displacement is 1.0-1.5 m from surface. (3) The lateral displacement of soft ground treated by gravel pile during filling period accounts for 75%-80% of total displacement which is much less than that treated by PVD; and the depth of maximum lateral displacement is 2.5-3.5 m from surface. (4) In consolidation stage, the value of △ym/△SD、Sy/Sf is 0.15-0.30 and 0.10-0.20 respectively of soft ground treated by PVD, 2-4 times greater than the early filling; while 0.10-0.15 and 0.03～0.05 respectively of soft ground treated by gravel pile. The variations of every stage are almost equivalent.

Key words: soft soil subgrade, characteristic of lateral deformation, maximum lateral deformation increment, average lateral deformation, Boussinesq equations