What Happens?
Utility Pipelines Leak
Excerpts From "The REAL Dirt on Liquefaction"
What Happens?

In earthquakes, utility pipelines leak and break. The most vulnerable pipelines are typically those carrying sewage because they are made of the most brittle materials and do not have sealed joints. The next most vulnerable are water pipelines. Some pipelines carrying natural gas are also vulnerable, but utilities such as Pacific Gas & Electric are upgrading and replacing vulnerable pipelines as described below.

Why Does This Happen? Utility pipelines can leak or break due to the passage of earthquake waves through the soil or due to permanent ground displacement (such as faulting, landsliding or liquefaction). Even though areas susceptible to liquefaction are a relatively small percentage of the areas in which pipelines are located, these liquefaction-susceptible areas have contained a disproportionate number of breaks.
What Were the Pipe Damage Statistics in the Loma Prieta Earthquake?

ABAG, in examining pipeline breakage statistics from the Loma Prieta earthquake, concluded that the damage to pipelines in areas mapped as highly susceptible to liquefaction experienced significantly greater damage than areas with lower susceptibility, given similar shaking levels.

First, the number of water pipeline leaks per mile of water pipeline in areas mapped as having high and very high susceptibility to liquefaction was four-to-six times greater than outside of these areas, given equivalent shaking intensities.

Second, the number of leaks per mile of natural gas pipelines was three-to-eleven times greater within the areas mapped as having high and very high susceptibility than outside of these areas, given equivalent shaking intensities. The gas pipeline leaks were predominately in cast iron and other older pipelines that are known to be vulnerable to earthquake effects.
Example of main sewage treatment conduit rupture in the 1995 Kobe Earthquake.
Source - Kobe Geotechnical Collection, Earthquake Engineering Research Center, Univ. of California, Berkeley
 Much of the pipeline damage occurred in areas where no surface expression of liquefaction was observed. Thus, these statistics show increased damage in areas mapped as being susceptible to liquefaction; they do not indicate that the damage was necessarily due to liquefaction. See Appendix C for more information.
  Note that no damage surveys were conducted of sewer lines as a result of the Loma Prieta earthquake, so no data on statistical damage to these facilities are available. However, as stated above, sewer lines probably had more damage than water lines because they are more brittle and do not have sealed joints.
Utilities and the Seismic Hazard Mapping Program of the California Division of Mines and Geology (CDMG)

The following excerpt from CDMG Special Publication 117, Chapter 6 (1997) notes the concern of that organization for pipeline damage in areas subject to liquefaction:

    To date, most liquefaction hazard investigations have focused on assessing the risks to commercial buildings, homes, and other occupied structures. However, liquefaction also poses problems for streets and lifelines- problems that may, in turn, jeopardize lives and property. For example, liquefaction locally caused natural gas pipelines to break and catch fire during the Northridge earthquake, and liquefaction-caused water line breakage greatly hampered firefighters in San Francisco following the 1906 earthquake. Thus, although lifelines are not explicitly mentioned in the Seismic Hazards Mapping Act, cities and counties may wish to require investigation and mitigation of potential liquefaction-caused damage to lifelines.
Pg&E's Gas Pipeline Replacement Program (GPRP)  
Beginning in 1985, PG&E undertook a 25-year, $2.5 billion program, known as the Gas Pipeline Replacement Program (GPRP). As a result of the GPRP, many pipeline upgrades were installed both prior to and following the Loma Prieta earthquake. These upgrades are continuing. The newer pipelines are significantly less vulnerable to earthquake effects, including liquefaction, differential settlement, violent shaking, and ground strain, than the older types of pipe installed 50 - 100 years ago.
Gas pipelines being replaced in San Francisco
Source - W. Savage, PG&E		  

New Guidelines for Pipeline Systems Are Being Developed

In response to the lack of a national code for pipeline systems, the American Lifelines Alliance (ALA) is developing two guideline documents:

    1. on the design of water transmission systems to resist earthquake hazards, including liquefaction, and
    2. an Appendix to the American Society of Mechanical Engineers (ASME) B-31 Piping Codes for the design of better performing buried pipelines in earthquakes, not just water pipelines.
The projects are being funded by the Federal Emergency Management Agency (FEMA) under a cooperative agreement with the American Society of Civil Engineers (ASCE). Both of these documents should be available in early 2001 and will be able to be obtained from ASCE. Contact Thomas McLane, tmclane@asce.org. For further information on ALA, go to - http://www.americanlifelinesalliance.org/

 

ABAG, the Association of Bay Area Governments, is the regional planning and services agency for the nine-county San Francisco Bay Area. The liquefaction hazard map information was last updated by ABAG in October 2003.

jbp 10/16/03