Deformation monitoring of an adjacent subgrade consisting of lightweight foam concrete in a loess region

Constructing a subgrade adjacent to an existing railway in loess regions is problematic, resulting in construction difficulties, constraints, and impacts on the existing line. We obtained monitoring data in different construction stages to analyze the deformation of an adjacent subgrade consisting of lightweight foam concrete. The results show that the vertical deformation of the subgrade increased and decreased at each monitoring point. The vertical deformation of the left line increased and decreased, whereas the right line exhibited secondary increase followed by a decrease. Uplifting changed three times in two stages during the construction of the screwed cast-in-place piles. The deformation was inversely proportional to the distance from the existing line, and the impact on the existing subgrade was more significant in the initial stage. The uplift deformation increased and decreased as each row of high-pressure jet grouting piles was installed. The most significant influence on the existing line occurred at 1/3–2/3 from the top of the piles. The additional deformation of the existing subgrade was significant on both sides and small in the center. The displacement rate was low initially and then increased sharply with the height of the filling layer as the lightweight foam concrete was poured and the graded crushed stone was added. • Deformation mechanism of adjacent subgrade consist of foam lightweight concrete in Chinese loess region. • The uplift changed slowly, rapidly, and slowly as the screwed cast-in-place piles were installed in two stages. • The uplift deformation increased and decreased during the construction of the high-pressure jet grouting piles. • The additional deformation at each monitoring point increased with the filling height of the subgrade during track construction.