An Investigation into the Tunnel-Soil-Pipeline Interaction by In Situ Measured Settlements of the Pipelines

Table 4

Preliminary assessment of the effect of ground movement on buried pipeline (Attewell et al. [3]).

Maximum surface settlement (mm)	Brittle materials (gray iron, asbestos cement, and clayware)	Ductile materials (steel, ductile iron, uPVC, and polyethylene)
≤ 10	Pipe stress increase is not significant compared with other causes of stress such as installation, traffic load, and seasonal movement
> 10	The effects of movement should be accessed in detail	_________
> 25	Significant stress increase virtually certain; possible failure of small-diameter pipes	_________
> 50	Possible failure of large-diameter pipes	Significant stress increases likely; the effects of movement should be accessed in detail

Notes. Pipeline failure is defined here as an incident that leads to a significant leak or otherwise requires immediate repair. For brittle materials, depth from pipeline axis to tunnel crown must be greater than twice the tunnel diameter except for tunnels overlain by stiff clay, where this may be reduced to a minimum clearance of one diameter. Minimum tunnel depth to axis level irrespective of diameter is 3.5 m.