The REAL dirt on liquefaction : a guide to the liquefaction hazard in future earthquakes affecting the San Francisco Bay Area

32 Pages·2001·2.4 MB·English

by  Perkins, Jeanne B

SANFRANCISCOPUBLICLIBRARY
IIIIIHillII
3 1223 05956 5623
on Liquefaction
A
Guide to the
Liquefaction Hazard
Future Earthquakes
in
Affecting the
San Francisco
Bay Area
DOCUMENTS
DEPT.
JUL
1 9 2002
ref February 2001
624 .1762
R229
ASSOCIATION OF BAY AREA GOVERNMENTS
LIX
San Francisco PublicLibrary
•
REFERENCE BOOK
Not to be taken from the Library
REAL
The Dirt
on
Liquefaction
A
Guide to the
Liquefaction Hazard
Future Earthquakes
in
Affecting the
San Francisco
J." •
Bay Area
February 2001
ASSOCIATION OF BAY AREA GOVERNMENTS
:
Credits
Principal Report Author:
Jeanne B. Perkins-Earthquake ProgramManager, AssociationofBayAreaGovernments
Support:
DATABASEPROGRAMMING-FredParkinson- Systems Programmer
CARTOGRAPHY and COLOR LAYOUT-Kearey Smith andVicki Rutherford
RESEARCH ASSISTANTS- SusannahBelding, StuartLowe,Michael Smith, andRobert Swierk
ABAG Management:
Eugene Y. Leong-Executive Director
Acknowledgments
ABAG would like to specifically acknowledge Keith Knudsen for his extensive efforts to ensure the
scientific accuracyofthisreport.
ABAG also would like to acknowledge the efforts of the following members of the ABAG
Earthquake Hazard Mapping Review Committee for their thoughtful comments on the material that
forms abasis forthis document.
Earthquake Hazard Mapping Review Committee:
Bill Ward-Committee Chair-Councilmember, CityofHayward
Catherine Bauman-Planner, City PlanningDepartment, Cityand County ofSan Francisco
EdwardBortugno/ ScottMcAfee-Calif. Office ofEmergency Services-Coastal Region
ArrietaChakos-Office ofthe CityManager, Berkeley
TomHolzer/Mike Bennett-Geologists, U.S. Geological Survey
StephanKiefer-Building Official, City ofLivermore
KeithKnudsen- SeniorEngineering Geologist, CaliforniaDivision ofMines and Geology (CDMG)
William Lettis/ John Baldwin-William Lettis & Associates
Dale Marcum/Bill Cotton-Geologist, Cotton, Shires andAssociates
Carl Mortensen-Geophysicist, U.S. Geological Survey
Carol Prentice-Geologist, U.S. Geological Survey
Doug Sandy-AssistantDirector-Disaster Services, AmericanRed Cross-BayArea
William ("Woody") Savage- Sr. Seismologist, Pacific Gas & Electric Company (PG&E)
Richard Scott-Principal EngineeringTechnician, CityofNovato
William Schock-Building Official, Development Services, City ofSan Leandro
Michael Shimamoto-Geologist, Public Works Department, City ofSanJose
Ted Smith- Supervising Geologist, CaliforniaDivision ofMines and Geology (CDMG)
The writing and production ofthis report was funded by Grant Nos. 1434-HQ-97-GR-03048 and
1434-HQ-97-GR-03121 from the U.S. Geological Survey (USGS), as well as by the Association
of Bay Area Governments and William Lettis & Associates, Inc. Any opinions, findings,
conclusions or recommendations expressed in this material are those of the authors and do not
necessarily reflect the views ofthe funding agencies.
For information on ABAG's Earthquake
Program, liquefaction hazard maps by city
and other earthquake impacts, see our
Internet site at: http://quake.abag.ca.gov
ABAG Publication Number: P01001EQK
ABAG Earthquake Program February 2001
ii
Table of Contents
page
Background iv
„
Introduction
1
Figure 1 - Potential Effects ofLiquefaction 1
PART I - What Happens to the GROUND? 2
Figure 2 - Ground Failure Types 2
A - Flow Failure 2
B- Lateral Spread Failure 2
C - Ground Oscillation Failure 3
D - Loss ofBearing Strength 3
E- Differential Settlement 3
PART II - When Does Liquefaction Occur? 4
Figure 3 - A Recipe for Liquefaction 4
Ingredient 1 - "Loose" Sand 4
Ingredient 2 - High Ground-Water Table or Water Saturated 4
Map Plate - Liquefaction Susceptibility for the San Francisco Bay Area 5
Figure 4 - Percentage ofUrban Land Exposed to Various Levels ofLiquefaction Susceptibility..6
Ingredient 3 - Earthquake Shaking 6
Figure 5 - San Francisco Bay Region Earthquake Probability 6
Figure 6 - Liquefaction Hazard Based on Combinations ofModified Mercalli Intensity
and Liquefaction Susceptibility 7
Table 1 - Extent ofUrban Areas Potentially Subject to Liquefaction 8
Figure 7 - Comparison ofLiquefaction Hazard of 1989 Loma Prieta Earthquake with Larger
Bay Area Earthquake Scenarios 9
Loma Prieta Earthquake 9
Entire Hayward Fault 9
Entire Bay Area San Andreas Fault 10
Rodgers Creek Fault 10
PART III - What Happens to Our BUILT ENVIRONMENT? 11
Utility Pipelines Leak 12
What Happens?
Why Does This Happen?
What Were the Pipe Damage Statistics in the Loma Prieta Earthquake?
Utilities and the Seismic Hazard Mapping Program ofthe California Division ofMines and Geology
(CDMG)
PG&E's Gas Pipeline Replacement Program(GPRP)
New Guidelines forPipeline Systems Are Being Developed
Highways, Roads and Airport Runways Buckle 14
What Happens?
Why Does This Happen?
What Were the Road Damage Statistics in the Loma Prieta Earthquake?
Were Airports Affected by Liquefaction in the Loma Prieta Earthquake?
WhatDo We ExpectWill Happen in Future Earthquakes?
Programs forAirports and ofCaltrans
Port and Harbor Facilities Are Damaged 16
What Happens?
Why Does This Happen?
How Vulnerable Were Our Ports in the Loma Prieta Earthquake?
How Vulnerable Was the Port in the Kobe, Japan Earthquake?
How Does the Port ofOakland View Its Vulnerability to Future Earthquakes?
ABAG Earthquake Program iii February 2001
page
Buildings and Other Structures May Be Damaged 18
WhatHappens?
Why Does This Happen?
WhatWere the Building Damage Statistics inthe Loma PrietaEarthquake?
The Seismic HazardMapping Programofthe California DivisionofMines andGeology
The Story ofHydraulic Fill Dams inCalifornia
PART IV - What Can YOU Do Next? 20
Table 2 - Sources ofLiquefaction Hazard and Susceptibility Information Covering All Nine
Bay Area Counties 20
Table 3 - Sources ofLocal Liquefaction Information 21
Table 4 - Components ofa Site-Specific Liquefaction Analysis 22
Table 5 -Techniques for Liquefaction Hazard Mitigation 23
References 25
Technical Appendices (Available only on ABAG's Internet Site)
A- Liquefaction Susceptibility Mapping Approach Al
B - The Process ofDeveloping Liquefaction Hazard Maps Bl
C - Collection and Analysis ofLiquefaction Data from the Northridge and Loma Prieta
Earthquakes CI
BACKGROUND
The purpose ofthis report is to serve as a catalyst for understanding and mitigating
(through avoidance, engineering, planning and response) the liquefaction hazard in the
San Francisco Bay Area. As such, the audience is not the geology or engineering
community, but rather those who work for and with the local governments, utilities,
businesses, and residents in our region.
&
This report is intended to supplement the maps prepared by William Lettis
Associates, Inc. (WLA), the U.S. Geological Survey (USGS), and the California Division
ofMines and Geology (CDMG). It is not a substitute for site-specific advice from a
licensed geologist or geotechnical engineer.
This ABAG report is part ofa collaborative project with WLA and USGS funded by
USGS. As part ofthis collaborative effort, WLA received funding from USGS to
develop new regional consistent maps ofQuaternary deposits (materials deposited in the
last 1.6 million years) (Knudsen and others, 2000).
ABAG E^i !?<!.• Program iv February 2001
3 1223 05956 5623
Introduction
Liquefaction problems The 1989 Loma Pneta earthquake caused a total of $5.9 billion in
property damage. Most of the damage was due to ground shaking.
in past earthquakes are
However, approximately $100 million of that (1.6%) was due to
not as significant as liquefaction (Holzer, 1998, p.B4). We were lucky. In 1906,
shaking, but can cause liquefaction-related damage to water supply pipelines prevented
extensive damage. containment ofthe fire in San Francisco that destroyed about 500 city
blocks. Thus, liquefaction can be indirectly blamed for 85% of the
total damage to San Francisco in 1906 (Youd and Hoose, 1978).
When the ground liquefies, sandy materials saturated with water can
behave like a liquid, instead of like solid ground. The ground may
sink or even pull apart. Sand boils, or sand "volcanoes," can appear.
Liquefaction can cause ground displacement and ground failure such
as lateral spreads (essentially landslides on nearly flat ground next to
rivers, harbors, and drainage channels) and flows.
Our most vulnerable land falls into two general categories:
1. areas covered by the huge amount of fill poured into San
Francisco Bay since 1845 to transform 77 square miles (200
Liquefaction damage, Marina
District, 1989 Loma Prieta, square km) oftidal and submerged areas into land1; and
California, Earthquake 2. areas along existing and filled stream channels and flood plains,
Source-M. Bennett, particularly those areas with deposits less than 10,000 years old.
U.S. Geological Survey
Overall, shaking does more damage to buildings and highway
structures than liquefaction. But liquefaction damage can be a
significant threat for underground pipelines, airports (especially
runways), harborfacilities, androadorhighwaysurfaces.
Figure 1 - Potential Effects of Liquefaction
Buildings can be damaged Theground shiftingcan
dueto foundation movement cause roadsand sidewalks
and cracking when the to buckle.
underlying soils shift.
Ground-Water^
Tabh
Sand boils may appearat Utility pipelines can
thesurface to indicatethat break, both on theedges
liquefaction has occurred ofand within areasthat
underground. have liquefied.
1 Source offill area - Knudsen and others, 2000.
ABAG Earthquake Program February 2001
1
PART What Happens to the GROUND?
I -
How Does the Ground When ground liquefies and "fails," it may cause damage to our built
Fail? environment. These failures take the form of:
flows;
lateral spreads;
ground oscillations (or movement ofthe surface layer of ground
separately from the underlying liquefied layers);
loss ofbearing strength (to hold up buildings or hold tanks and
pipes underground); and
Figure 2 -
settlement and differential settlement.
GroundFailureTypes
The following diagrams illustrate some ofthese effects.
In a flow failure, large amounts of soil can
quicklytravelmanyfeet.
Ground
Before
Earthquake Typically, "flows" occur on slopes ofmore than 3
degrees, while "spreads" are on less steep slopes
(EERI, 1994). Thus, this type ofground failure is a
type of landslide.
Failed
Ground
A-Flow Failure (modifiedfromYoud,1992)
In a lateral spreadfailure, a layer ofground at
the surface is carried on an underlying layer of
liquefied material over a nearly flat surface
towarda riverchannelorotherbank.
Ground BeforeEarthquake
Damage occurs to the surface layer when it is
moved, including fissures and scarps. The surface
deformation can damage building foundations and
underground utilities, as well as result in increased
pressure on retaining walls. Engineers can
7~, -2SL sometimes make rough estimates of the potential
movement distance of a lateral spread. Data from
FailedGround the 1906 San Francisco earthquake show that some
lateral spreads moved about 30% of the thickness
B - Lateral Spread Failure (modifiedfromYoud,1992)
of the saturated loose materials that liquefied
(Pease and O'Rourke, 1998).
AEAG Earthquake Program 2 February 2001
When the ground is almost completely flat,
liquefaction can still cause problems. When an
underlying layer liquefies, the soil on top decouples,
allowing it to oscillate back andforth, and up and
Ground BeforeEarthquake down, in a different way than the surrounding
ground. Large cracks can occur, and sections ofthe
groundbangagainstone another.
Ground oscillation occurred in the Marina District of
LiyUIHED San Francisco during the 1989 Loma Prieta earthquake,
and resulted in extensive sidewalk, road, and pipeline
damage.
FailedGround
C - Ground Ocillation Failure This type of failure can become a lateral spread if the
(modified fromYoud, 1992) ground shakes long enough.
When soil liquefies, it becomes "weaker."It may lose
its capacity to support buildings, particularly large
buildings with poorly designed foundations. In
addition, underground tanks and pipelines can
"float"upwards, sometimes allthe wayto the surface.
The "classic" example of a bearing strength failure
happened as a result of the 1964 Niigata, Japan,
earthquake where several four-story apartment
buildings tilted spectacularly.
Ground BeforeEarthquake FailedGround
D - Lossof Bearing Strength Less well publicized, but more common, are problems
(ResultinginTilted Buildingand "Floating"Tanks) with underground tanks at gasoline stations where the
(Youd,1992) tank may rise enough to break connections between the
tank and the pipes leading into and out ofit.
Another common problem is settlement as soil
compacts and consolidates after the ground stops
shaking. Engineers can estimate the expected extent of
settlement. Settlement can range from 1% - 5% ofthe
liquefiable layer. In very loose sands, it can be as large
as 10% ofthe thickness ofthe saturated loose materials
— that liquefy (Tokimatsu and Seed, 1984). Although
SettledGround small uniform changes are typically not damaging, the
r4 r^-r" soil can settle unevenly. This problem, called
Non-liquified
///// differential settlement, occurs when the layers that
///// Soil
#'//////LIQ/UIFI/ED /#/////X- liquefy are not of a uniform thickness, a common
problem when the liquefaction occurs in artificial fills,
particularly fills that have been placed during different
E - Differential Settlement times and using different techniques. Thus, using the
10% settlement estimate for loose materials, if the
liquefying layers are 10 feet different in thickness,
differential settlement ofa foot can be achieved.
ABAG Earthquake Program 3 February 2001
PART When Does Liquefaction Occur?
II -
The "Official* Liquefaction has been defined as "the transformation ofa granular
materialfrom a solidstate into a liquefiedstate as a consequence of
Definition
increasedpore-waterpressure" (Youd, 1973, p.l).
But what does this mean? Where do we expect liquefaction to occur?
The "recipe" below lists the three ingredients necessary for damaging
liquefaction to occur.
A
Figure 3 - Recipe forLiquefaction
Damaging liquefaction can only occur Ingredient 1 - The ground at the site must be
under very specialcircumstances. "loose" - uncompacted or unconsolidated sand
and silt without much clay or stuck together
-
There must be all ofthese ingredients
but even ifall arepresent, damaging Ingredient 2 - The sand and silt must be
liquefaction, or even liquefaction, does "soggy" (water saturated) due to a high water table
not necessarily occur. Even if
liquefaction occurs, thegroundmust Ingredient 3 - The site mustbe shaken long and
move enough to impact our built hard enough by the earthquake to "trigger'''
environment.
liquefaction.
INGREDIENT1- First, the soil in the area must be loose (that is, uncompacted or
"Loose"Sand unconsolidated) sand without much clay or stuck together. A general
map predicting the location ofthese materials can be made based on a
specific type ofgeologic map showing the materials deposited in the
last two millionyears-or Quaternary geologic maps.2
INGREDIENT2- Second, the ground must be saturated with water (or below the
High Ground-Water ground-water table). This information can be collected from well
logs, or interpreted given the topography.
Table or Water Saturated
These two ingredients are built into the regional map of areas
Liquefaction susceptible to liquefaction on the facing page (Knudsen and others,
Susceptibility Mapping 2000). Information on liquefaction in past earthquakes is used to
check and verify the assignment of various geologic units to
liquefaction susceptibility categories. Our experience in past
earthquakes is that maps ofthis type are fairly accurate at predicting
general areas where damage to pipelines and roads is heavier, given
equivalentlevels ofshaking-the thirdingredient.
" These Quaternary maps are often supplemented with soil boring data, analysis ofstandard penetration test (SPT)
blow counts, and analysis ofcone penetration test (CPT) resistances (Power and Holzer, 1996, p.2; Knudsen and
others, 2000, pp.3-4).
ABAG Earthquake Program 4 February 2001