Safety Risk Analysis and Protective Control of Existing Pipelines Affected by Deep Pit Excavation in Metro Construction

Table 2

Summary of pipeline safety factors in the FE study.

Pipeline safety factor		Effect degree		Effect on regularity
		Effect on horizontal displacement	Effect on vertical displacement
1	Excavating process	General	General	As the pipelines are shallow buried, the initial excavation has a great impact on the pipeline. Therefore, monitoring and management on initial excavating period need to be strengthened to reduce accidents.
2	Soil property around the pipeline	Great	General	The horizontal and vertical pipeline displacement values significantly decreased with soil Young’s modulus Es increased. It illustrates pipeline displacement can be reduced by improving soil property around the pipeline in project.
3	The distance away from pit	Great	Great	The closer the pipeline away from the pit, the larger pipeline displacement values are. The pipeline under the influence of corner effect when the distance from pipeline to pit L is with in the scope of 30 mm (about twice as much as the pit depth).
4	Pipeline burial depth	General	Weak	The underground pipeline displacement values increased with burial depth values h increased (in the situation under discussion).
5	Pipeline property	Weak	General	With Young’s modulus of pipeline decreased, the pipeline is easily damaged by overlarge stress and strain. With Young’s modulus of pipeline increased, pipeline joint is easily damaged by overlarge deformation.
6	Pipeline outer diameter	Weak	Weak	The changes of pipeline displacement values caused by outer diameter changes are quite small.
7	Pipeline thickness	Weak	Weak	The changes of pipeline displacement values caused by thickness of the pipeline changes are quite small.
8	The coexistence of multipipeline	Weak	Weak	The coexistence of multipipeline has small effect on the original pipeline displacement.