Earthquakes: Planning for disaster response

Curt Edwards, P.E.
Vice President
Psomas
San Diego, California
Member, APWA Emergency Management Committee

Background
Over the last 40 years, a great deal of information related to damage of public works facilities has been collected and documented by the American Society of Civil Engineers (ASCE) Technical Council on Lifeline Earthquake Engineering (TCLEE). This includes data on all "lifelines" such as water systems, sewer systems, seaports, airports, electrical systems, telecommunication systems, gas and liquid fuel systems, hospitals and emergency response. This report will highlight some of the more relevant conditions related to water, wastewater and roads.

Earthquake Hazards - Soil Interactions
Strong shaking during an earthquake creates surface movements which cause obvious damage to unanchored above-grade facilities. However, what seems to cause even greater damage are the soil conditions that the utilities are constructed on. Depending on conditions, ground shaking can be amplified by "soil effects" increasing damage over those utilities constructed on different soil types.

Liquefaction of soils results in the soil losing its bearing capacity causing movement and foundation support failures for any at-grade or buried structures. This condition can also cause subsidence and lateral spreading. In addition, earthquake shaking can cause landslides in unstable areas. Utilities on or in the path of these earth movements will be impacted. Lastly, faulting or surface cracking directly in the fault zone can cause significant damage to ridged facilities subjected to vertical and horizontal displacements. Design and construction of public works facilities in earthquake zones need to consider both the strong motion of the earthquake and the secondary effects of site conditions which can increase the vulnerability of those facilities.

Three-foot horizontal offset caused extensive pipeline repairs.

Water/Sewer System Vulnerabilities
For buried pipelines, soil conditions govern. Pipelines constructed in stable soils are only subjected to the strong shaking. This can result in some pipe movement in the trench causing joint compression, lateral offsets and increased joint stresses. For fragile pipelines, such as PVC, these additional stresses can be enough to cause the pipeline to crack. For those pipelines placed in areas subject to faulting (surface cracking due to earth movement), lateral spreading, liquefaction and landslides, the vulnerabilities are greatly increased. These movements can cause pipeline joints to separate, pipes to shear, and otherwise render the piping systems unusable. In areas of high groundwater, liquefaction in areas with gravity sewers has caused the pipelines and manholes to float to grades that cannot be readily restored.

Pipeline interfaces with other structures are also weak points during strong motion events. Pipes entering structures, such as tanks and treatment plant basins, can shear due to differential movement between the large structure and the smaller pipeline. Rigid pipeline interfaces at bridge abutments and hanger-supported pipelines under bridges have also been subject to failure.

Water and sewer facilities also have tanks and reservoirs that contact large quantities of water. This water, when subjected to earthquake movements, can also move generating great forces against the containment structures and typically fragile equipment (i.e., weirs, baffles, instrumentation). These strong movements can also cause above-grade tanks to move, severing connecting piping.

Water sloshing lifted this tank off the ground causing pipeline separation and elephant foot failure. Note emergency bypass.

In addition to bulk water movement, multiple failures in pressure water systems (pipe breaks and unanticipated pump shutdowns) can result in pressure surges (water hammer) that can affect appurtenances that otherwise were not impacted by the earthquake.

Most water and sewer systems have treatment plants, pumps and other electrically operated equipment that is especially critical after an earthquake. Most earthquakes cause immediate power outages that can last many days. If there is no emergency power available, critical facilities cannot operate impacting many people and businesses. Even if emergency power is available, quite often they are never subjected to fully-loaded operation for extended periods. As a result, generators often fail when they are most needed. Providing refueling of the generators has also proven to be difficult after an earthquake directly impacting extended generator performance.

  Unrestrained repair fittings could fall.

Lastly, unanchored equipment, pumps, control panels, storage racks and piping can move during an earthquake causing pipeline separation, panel connections to break, panels to tip over, and collateral damage to nearby anchored equipment. In addition, unrestrained overhead cabinet doors, storage bins and rafters can allow contents to fall, either damaging equipment or injuring personnel.

In addition to the obvious vulnerabilities, facilities that were constructed under previous codes can be vulnerable to damage during design earthquake events.

 

Emergency Response Interactions
Many critical lifeline utilities share common utility corridors. As a result, damage to one utility can cause collateral damage to one or more others. As such, repair and response times can be increased. In addition, emergency responders for one facility may not know of the damage to another and actually hinder recovery efforts. Some typical interactions are shown below:

Primary Damage Mode                  Collateral Damage Modes
Water Main Break                               Road Washout, Sewer Washout, Dry Utility Washout
Road/Bridge Damage and Closure      Pipeline and Conduit Failures, Inability to Reach Damaged Utilities
Water Storage Tank Failures              No Water Available for Fires, People or Businesses
Sewer Facility Failures                        Water Contamination
Electrical Failures                                Water Supply Interruptions, Pollution From Failed Sewer Facilities

Lessons Learned - Recommendations

  • Initial post-earthquake recovery efforts focus on people, relocation and relief.
  • Utility buildings can be the hidden "weak link."
  • Typically, engineered facilities perform well. They certainly reduce repair and recovery efforts.
  • Site effects (soil issues) can cause unforeseen damage.
  • Agencies should have an emergency response manual and conduct long-duration emergency simulations. These simulations should include power outages and a full test of communications systems.
  • The emergency training should also include simulation of the interactions between law enforcement, fire and public works to educate all parties on the needs and objectives of each group.
  • Simulations should consider bypass and detour routes.
  • Utility systems should be designed for redundancy so that damaged systems can be isolated.
  • Agencies should maintain adequate materials, parts and fuel inventories.
  • Mutual aid agreements with other utilities are beneficial.
  • Flexible connections between utilities and structures and anchoring equipment reduce failure rates.
  • Utilities in seismic areas should conduct earthquake vulnerability assessments.

Curt Edwards, P.E., is a Vice President at Psomas in the company's San Diego office. He is a member of APWA's Emergency Management Committee and is the Chairman of the ASCE Technical Council on Lifeline Earthquake Engineering, Earthquake Investigation Committee. He can be reached at (858) 576-9200 or cedwards@psomas.com.

Psomas is a leading consulting engineering firm offering services in water resources, planning and entitlements, land surveying and mapping, construction management, environmental, geographic information systems, land development engineering, and transportation to private sector, municipal/local agency, state and regional agency and federal agency clients.