Impacts of foundation pit excavation on adjacent railway subgrade and control

Deformation of subgrade and pit observed during construction of foundation pit engineering near a railway are presented. The deformation and control measures are analyzed. The settlement of surface ground and subgrade increase linearly over time during slope excavation, which is up to 12 mm after the slope excavation is completed. Affected by the train load and water leakage, the subgrade settlements increase rapidly during the construction of jet-grouting reinforcement of foundation pit bottom, top beam and concrete strut; and a nearly 50 meters long settlement tank with maximum settlement 95 mm is observed. It is also found that over 60% of subgrade subsidence increment during the construction of aforementioned stages accounts for more than 70% of cumulative settlement. Most of the surface settlement is less than 20 mm, 2.4% of excavation depth. The shape of the ground surface settlement profile within the region of subgrade settlement tank is concave type and the maximum settlement occurs at the subgrade. Two fluid grouting at slope top can effectively control the surface and subgrade settlement and reduce the impacts of subsequent excavation on subgrade. But the grouting construction may cause displacement mutation of slope, especially the lateral displacement towards to the pit, which is harmful to slope stability and railway safety.