Page 134 - Pipeline Risk Management Manual Ideas, Techniques, and Resources

Risk variables and scoring 511 11
Table 5.6 Possible categorization of natural hazards Construction activities near or in the pipeline right of way may
produce slopes that are not stable and could put the pipeline at
Cutego?y Subrategoy Specific Events risk. These activities include excavation for road or railway
cuts, removal of material from the toe of a slope, or adding sig-
Geotechnical On-ROW instability Landslide nificant material to the crest of a slope. Given that maintenance
Soil erosion
Liquefaction activity involving excavation could potentially occur without
Off-ROW Landslide engineering supervision, standard procedures may be war-
Rockslide ranted to require notification of an engineer should such condi-
Debris flows tions be found to exist.
Tsunami In soil sliding analyses, a pipeline experiences axial and
Volcano bending loads depending on the direction of sliding movement
Fault rupture with respect to the pipe axis. Axial strains in the pipeline are
Hydrotechnical Scour caused by soil sliding normal to the pipe axis. If the sliding
Channel degradation movement is 90 degrees to the pipe axis, the pipeline will pre-
Bank erosion
Encroachment dominantly experience tensile strain with small compressive
Avulsion bending strains present at the transition zones of the liquefied
and nonliquefied soil sections. If the sliding movement is 45
Source: Porter, M., and K. W. Savigny, "Natural Hazard and Risk degrees to the pipeline, both compressive and tensile axial
Management for South American Pipelines," Proceedings of IPC strains increase significantly due to the combination of axial
2002: 4th International Pipeline Conference, Calgary, Canada, and bending loads.
September 2002.
Impact loadings are also possible, especially involving rock-
slides and above ground pipeline components. An evaluation
for rockfall hazards to railroads has identified some key
creep are the more well-known downslope movement phenom- variables to assess. These are shown inTable 5.7. An evaluation
ena. Another movement involving freezing, thawing, and grav- methodology like this is readily modified to be applicable to
ity is solifluction, a cold-regions phenomenon distinct from the pipelines.
more common movements [93]. Some available databases provide rankings for landslide
Landslides can occur from heavy rain, especially on slopes potential. As with soils data, these are very coarse rankings
or hillsides with heavy cutting of vegetation or loadings from and are best supplemented with field surveys or local
construction or other activities that disturb the land. Slides can know ledge.
also be caused by seismic activity. Landslide displacement of
pipe can cause structural damage and leaks by increased exter- Soils (shrink, swell, subsidence, settling)
nal force loading if the pipeline is buried under displaced soil.
Landslides can happen offshore also, with rock fall damage to Effects that are not slope oriented include changes in soil vol-
pipeline possible. ume causing shrinkage, swelling, or subsidence. These can be
Slope issues can be an important but often overlooked aspect caused by differential heating, cooling, or moisture contents.
of changing pipeline stability. Slope alterations near, but out- Sudden subsidence or settling can cause shear forces as well as
side. the right of way by third parties should be monitored. bending stresses.

nrinil.ral slope Pipe position after
slope failure-this
displacement has added
bending stresses to the
pipeline
Original
position A- Slope profile
,\ '--- after slow

failure of 2L /
\
/
.---
Line
slope
/
Figure 5.5 Sudden slope failure over pipeline.