Page 137 - Pipeline Risk Management Manual Ideas, Techniques, and Resources

5/114 Design Index
Perform site-specific geomorphic studies for specific cross- Low 10 pts
ings. These studies may suggest mitigation measures (if any) None 15 pts
to address scour. Unknown 0 pts
Perform studies to address the issue of uplift of the pipeline
at high-velocity rock bed crossings. High Areas where damaging soil movements are common or
can be quite severe. Regular fault movements, landslides, sub-
The flood flow velocities for a crossing can be estimated sidence, creep, or frost heave are seen. The pipeline is exposed
using cross-sections derived from the best available mapping, to these movements. A rigid pipeline in an area of less frequent
flow rates derived from region-specific regression equations, soil movements should also be classified here due to the
and channel/floodplain roughness values derived from a review increased susceptibility of rigid pipe to soil movement damage.
of vegetation from photography or site visits. Active earthquake faults in the immediate vicinity of the
Upstream and downstream comparisons can be made to pipeline should be included in this category.
identify any significant changes in stream flow regime or
visual evidence of scour that would warrant a site-specific geo- Medium Damaging soil movements are possible but rare or
morphic study. unlikely to affect the pipeline due to its depth or position.
Potential impact by foreign bodies on the pipeline after a Topography and soil types are compatible with soil movements,
scour event can be considered, as well as stresses caused by although no damage in this area has been recorded.
buoyancy, lateral water movements, pipe oscillations in the cur-
rent, etc. The maximum allowable velocity against an exposed Low Evidence of soil movements is rarely if ever seen.
pipe span can be estimated and compared to potential veloci- Movements and damage are not likely. There are no recorded
ties, as one means of quantifying the threat. episodes of structural damage due to soil movements. All rigid
The potential for wind erosion, including dune formation pipelines should fall into this category as a minimum, even
and movement, can also be evaluated here. when movements are rare.

Evaluating land movement potential None No evidence of any kind is seen to indicate potential
threat due to soil movements.
The evaluator can establish a point schedule for assessing the
risk of pipeline failure due to land movements. The point scale Unknown In keeping with an "uncertainty = increased risk"
should reflect the relative risk among the pipeline sections eval- bias, having no knowledge should register as high risk, pending
uated. If the evaluations cover everything from pipelines in the the acquisition of information that suggests otherwise.
mountains ofAlaska to the deserts ofthe Middle East, the range
of possible point values should similarly cover all possibilities. Mitigation
Evaluations performed on pipelines in a consistent environ-
ment may need to incorporate more subtleties to distinguish the Initial investigation and ongoing monitoring are often the first
differences in risk. choices in mitigation of potentially damaging land movements.
As noted, public databases are available that show relative Beyond that, many geotechnical and a few pipeline-specific
rankings for landslides, seismic peak ground accelerations, soil remedies are possible.
shrink and swell behavior, scour potential, and other land A geotechnical evaluation is the best method to determine
movement-related issues. These are often available at no cost the potential for significant ground movements. In the absence
through government agencies. However, they are often on a of such an evaluation, however, the evaluator should seek evi-
very coarse scale and will fail to pick up some very localized, dence in the form of operator experience. Large cracks in the
high-potential areas that are readily identified in a field survey ground during dry spells, sink holes or sloughs that appear dur-
or are already well known. ing periods of heavy rain, foundation problems on buildings
nearby, landslide or earthquake potential, observation of soil
Scoring of land movement movements over time or on a seasonal cycle, and displacements
of buried structures discovered during routine inspections are
It is often advantageous to develop scoring scales for each type all indicators that the area is susceptible. Even a brief survey of
of land movement. This helps to ensure that each potential the topography together with information as to the soil type and
threat is examined individually. These can be added so that mul- the climatic conditions should either readily confirm the opera-
tiple threats in one location are captured. Directly using the rel- tor's experience or establish doubt in the evaluator's mind.
ative ranking scales from the available databases, and then Anticipated soil movements are often confirmed by actual
supplementing this with local information, can make this a very measurements. Instruments such as inclinometers and exten-
straightforward exercise. someters can be used to detect even slight soil movements.
The threat can alternatively be examined in a more qualita- Although these instruments reveal soil movements, they are not
tive fashion and for all threats simultaneously. The following necessarily a direct indication of the stresses induced on the
schedule is designed to cover pipeline evaluations in which the pipe. They only indicate increased probability of additional
pipelines are in moderately differing environments. pipe stress. In areas prone to soil movements, these instruments
can be set to transmit alarms to warn when more drastic
Potential for significant (damaging) soil movements: changes have occurred.
High 0 pts Movements of the pipe itself are the best indication of
Medium 5 pts increased stress. Strain gauges attached to the pipe wall can be