ML20151H213

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Need to Mitigate Earthquake Hazards to Lifelines, Presented at 880412-15 Meeting in Olympia,Wa
ML20151H213
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Site: Trojan File:Portland General Electric icon.png
Issue date: 04/12/1988
From: Elliott W
PORTLAND, OR
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NUDOCS 8808010187
Download: ML20151H213 (9)
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THE NEED TO MITIGATE EARTHQUAKE HAZARDS TO LIFELINES f?g

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by William M. Elliott, Portland Water Bureau Portland, Oregon 97204 ABSTRACT Most attention and concern regarding earthquakes and the impacts on people have centered on the effects of earthquakes on buildings and structures. The effects on lifeline facilities, those which people rely on for the most basic of human needs, has not received adequate attention. Following the 1971 San Fernando earthquake, it became apparent ~ that the impact of earthquakes on lifeline facilities such as water and sewage delivery systems needed mere attention.

The American Society of Civil Engineers created the Technical Council on Lifeline Earthquake Engineering and several subcommittees to deal with these critical facilities such as water and sewage, power, communica-tions, gas and liquid fuels, and the related topic of seismic risk.

This paper describes the ef forts of the City of Portland, Oregon to deal with 1 seismic risk matters that affect our system and our ability to continue to function under all conditions.

INTRODUCTION The 1971 earthquake in San Fernando, California caused extensive damage to a wide range of lifeline facilities in addition to the building and structure damage which gained national attention such as the collapse of the Veterans Administration Hospital.

Equally important was the near collapse of the lower San Fernando dam which could have affected tens of thousands of people direct-ly and af fected the water supply to the millions that depend on the critical water facilities that pas 4 thecugh this area.

Had there been an additioral af tershock, the flood would have been devastating. The 1906 San Francisco earthquake disrupted water facilities and allowed a fire to ravage the entire city. More c17ser to Portland, windstorms, floods, and other hazards have impacted tla city and have rerulted in a recognition of the fragility of components of the water supply system.

The Portland. Water Bureau has taken steps to address certain of these needs and is looking further for other needs that need to be addressed.

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( The lack of earthquake activity in the Northwest, particularly in the Portland region in recent years, may have created an aura of apathy regarding earth- l quake motion and the devastating ef fect it can have. Further, the emerging t

research on subduction type earthquak?s such as the article by Heaton and Hartzell in the April 10, 1987 issue of Science magazine are beginning to I raise some doubts. The possibility of great earthquakes and the similarity of subduction situations to other parts of the world needs to be discussed among lifeline purveyors and utilities more fully so that steps can be taken, pro-grammed, or budgeted to harden facilities as a normal course of operations.

1 LIFELINES Lifelines are the critical facilities and utilities that bring a modern, urban population those commodities that are urgently needed for life, health, and safety. The American Society of Civil Engineers throsg- their Tecnnical  !

Council on Lifeline Earthquake Engineering recognize the following key life-line functions: i Water and sewage lifelines Electrical power and communications lifelines Gas and liquid fuel lifelines

  • 4 Transportation lifelines I

All of these lifeline systems are critical to meet the human needs of food, shelter, and clothing, but are by no means the only critical needs during a catastrophic emergency. Other needs are functional buildings such as hospi-tals and food distribution centers; bridges for transportation; electrical power plants; port structures; and airports are further examples of critical '

point facilities.

Several of these lifelines are aerially distributed in the form of buried

, pipes or pipes on bridges. For example, in the City of Portland, 40 percent of our installed asset cost is in tha form of buried pipes and long, large diameter pipeline delivery systems. Also, transportation lifelines such as roadways and railway systems extend over long distances and are impacted by

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l ground shaking, subsidence, and other effects of earthquakes. Gas and liquid i

fuel pipelines are generally buried and under extremely high pressures and are also susceptible to disruption. Electrical power systems and communication l systems extend over vast expanses and are networked to provide reliability but are also subject to gross disruption.

AFFECTS ON THE PORTLAND WATER BUREAU The earthquakes of the past in the Portland area have not created great public observable disruptions to service. Occasional rockfalls and disruptions of power to pumping stations and the consequent outage of water have been minor to moderate. However in 1964, a combination of severe weather that created deep snow packs followed by a change in the weather which melted the snow packs quickly resulted in flooding in the region of Oregon and Washington.

This manifested itself in a flood or record at the recently completed Bull Run Dam No. 2 that caused two of Portland's three water conduits to be taken out of service by flood action, undermining, and the breaking of the 1,a rge s t supply pipeline. This event was quickly addressed since men, materials, and i

equipment were available to address the problem immediately.

Subsequently, another emergency affecting the water supply in 1972 resulted when ice bridging at a remote site gave way on the North Fork, one tributary of Bull Run River that undercut a landslide mass, and exposed decomposed volcanic ash materials of colloidal size. This resulted in the entire water system being impacted by material that would not settle out in the reservoirs and lead to a long period of turbid water. The resulting emergency declara-tion by the governor and subsequent repair work using FDAA (now FEMA) grant funds to repair the damage to the natural channel ended up costing in excess of $1 million dollars and lead our thinking to the future development of an emergency groundwater backup system. I Following the emergency repairs in 1972, another grant-funded effort was undertaken to look at the watershed for further disaster causing influences.

This work, the DIMP Project (Disaster Identification and Mitigation Project), l l

had several elements, including the review of the entire watershed for geolo-gic hazards.

The resulting work by Beaulieu in 1974 has helped to focus the 1 l

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Bureau concern to hazardous areas of the watershed. In addition, a hydrologic

( model of the entire watershed using sophisticated computer simulation techni-ques was undertaken and the computer simulation was calibrated to earlier flood events. The computer model was then used to simulate probable maximum flood a; a result of probable maximum precipitation. These flows w,re then simulated over the dams and spillways to check their safety. This work has been reviewed in subsequent years following the installation of hydropower facilities and has been found to still be state-of-the-art in its character .

Additional studies of the condition of facilities and equipment has resulted in capital projects to add emergency power generators and a wide range of other related activities.

The Bureau is undertaking a full hazard assessment review of water facilities this year that may result in further needs being identified for a wide range of hazards, including earthquake. The Bureau added hydropower facilities to the dams in the watershed, and at one location where older distribution reser-voirs exist. The subsequent FERC requiremenr * 'or review have resulted in several dam safety investigations as well as t eps of Engineers' dam safety investigations in 1978.

More recently, the Bureau undertook the review of a large 3-million gallon elevated water storage tank in 1985.

This review of the Denver Tank resulted in a seismic evaluation of several steel water storage reservoirs in 1987. We reviewed the geologic and soils situation, conducted seismic scudies e.nd structural evaluations, and recommended lowering several reservoirs until strengthening and repairs could be made.

This work included the review of eleven surface tanks, nine standpipes, and ten elevated tanks, 30 facilities in total.

EARTHQUAKE ISTENSITY The work of our geotechnical consultants (Cornforth Consultants) and seismic evaluation of the steel water storage tanks noted above resulted in the aware-ness in the i in 500-year c,ent of a maximum credible earthquake (MCE) for these tanks to be a near field event of magnitude 6.0 within ten miles. The 4

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1 far field events of magnitude 7.0 at 55 miles (St. Helens zone) and magnitude '

8.0 at 120 miles (Puget Sound) were not as significant as the near field event. Another project in January 1986 reviewed the liquefaction potential at a large recervoir built in 1911 that holds 75 million gallons of water. '

Reservoir No. 6 is centrally located in the city at a location called the Mt.

Tabor complex and since a small hydrogenerator between two reservoirs of different elevations exist, FERC regulations required a liquefaction study.

The 28-foot high soil embankment was analyzed and our consultant, Derek l Cornforth, engaged Dr. Ignatio Arango and Professor H. Bolton Seed on the analyses. They recommended using a 1 in 5,000 year occurrence interval for high hazard dam structures such as the Mt. Tabor soil embankment. Since the embankment serves as a das for this reservoir, an earthquake of magnitude 6.5 with peak ground acceleration of 0.32 g was selected. Professor Raymond B.

Seed at Stanford performed a finite element study of the horizontal shear stresses on the embankment and the foundation caterials as a part of the liquefaction study. As a result, it was found that the facility is safe under <

rhe stated ear. .akes. .

PIPELINES The Portland Water Bureau has a continuing interest in how earthquakes would affect the f acilities of the Bureau and our critical mission of supplying water to the people of Portland and those who rely on us for water. The Bureau is in the midst of conducting a hazard assessment study, and as part of

- that ef fort, has submitted a grant application under the National Earthquake Hazards Reduction Program to describe the seismicity and earthquake hazards I confronting the service area and to understand more fully the earthquake I effects on various pipelines. Loss algorithms will be developed to describe earthquake intensity versus expected loss for the pipeline networks and for  !

concentrated facilities such as pump stations and tanks. Dr. Leon Wang of Old Dominion University will be involved with this work as well as Don Ballantyne of Kennedy /Jenks/Chilton Engineers in the review of concentrated facilities and the expected effects of earthquakes. The unique feature of this grant proposal is that we intend to look not just at water facilities but at the  !

sewage fac'ilities operated by the City of Portland. i J l 1

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LIFELINE PURVEYORS MUST BE INVOLVED It is evident from my work in emergency planning and discussions with other utilities that there is a general lack of emergency planning and very little plan exercising, and a general lack of recognition for the potential impacts of earthquakes in our area. In order to foster an awareness and interest in changing this situation, it will be necessary to catch the attention of high officials'in all of these key lifeline areas. Toward that end it would be helpful to have ways and means of communicating and keeping interest at a reasonable level such as video tape presentations and investigations of earth-quakes and their impacts. A great deal of liter ture is available as noted in the ASCE Annotated Bibliography. Other presentations such as salk-throughs of facilities with experts to discuss damage would be helpful. In addition, workshops and working groups to heighten awareness of all that shouid be concerned over the next several years will be crucial to the success of any earthquake mitigation efforts.

When the USGS began talking about the possibility of Mt. St. Helens erupting, there was little concern because no volcano had erupted in recent memory.

However, following the May 18 event at Mt. St. Helens, a greater credibility has been placed on USGS concerns. Now that the Survey is raising our concerns about the possibility of large and great earthquakes in the Northwest, it is an appropriate time to explore and implement those communications devices that would lead to fresh looks at all of the lifeline utilities that are so criti-cal to us in our modern urban existence.

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l BIBLIOGRAPHY i

1. Beaulieu, J. D., 1974, Geologic Hazards of the Bull Run Watershed, Multnomah and Clackamas County, Oregon, State of Oregon Department of Geology and Mineral Industries, Bulletin 42.
2. Cornforth Consultants,1985 FERC Dam Safety Review, Mt. Tabor Reservoir No. 6.
3. Cornforth Consultants, 1986, FERC Dam Safety Review, Bull Run Dam No. 2.

4 Elliott, William M., 1985, Take That First Step... Start Your Emergency Plan Now:, Paper 2A-5, In Proceedings of the Distribution System Sympo-etum, American Water Works Association, Seattle, Washington, September 8-11, 1985, pp. 53-64

5. Snyder, G. M., et al, 1987, Earthquakes Will Not Damage this Bridge, in ASCE Civil Engineering magazine, September 1987, pp. 54-56.

An account of the use of lead / rubber base isolation bearings as a retrofit to lessen the impact forces on a bridge that carries a critical 116-inch diameter water pipeline. The bridge and pipe will now be able to with-stand the magnitude 7.5 earthquake with a PGA of 0.40g.

6.

Swan Wooster Engineers, 1985, Denver Tank Scismic Analysis, includes seismic studies by Cornforth Consultants.

7.

TCLEE, 1980, Annotated Bibliography of Lifeline Earthquake Engineering, prepared by the Technical Council on Lifeline Earthquake Engineering of the American Society of Civil Engineers, with expanded sections on life-lines for water and sewage; gas and liquid fuels; transportation; electric power and communications; and seismic risk.

8.

URS Corporation, 1987, Seismic Evaluation of Steel Water and Storage Facilities, includes geotechnical report by Cornforth Consultants.

9.

Woodward-Clyde Consultants, 1986, FERC report on Safety Inspection Bull Run Dam No. l.

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