Lessons Learned and Need Lessons Learned and Need for NEES Instrumented for NEES Instrumented

Liquefaction Sites Liquefaction Sites

T. Leslie YoudT. Leslie Youd

Brigham Young UniversityBrigham Young University

Purposes of PresentationPurposes of Presentation

To convince the members of this workshop To convince the members of this workshop that instrumented liquefaction sites are that instrumented liquefaction sites are important and deserves our support important and deserves our support

To urge geotechical engineers in Taiwan, To urge geotechical engineers in Taiwan, Japan and the US to actively identify sites Japan and the US to actively identify sites and seek opportunities place instruments to and seek opportunities place instruments to add much needed instrumental data to the add much needed instrumental data to the liquefaction case history data base liquefaction case history data base

Need for Instrumented Field SitesNeed for Instrumented Field Sites

Past instrumental records provide important Past instrumental records provide important information on pore pressure rise and site information on pore pressure rise and site response response

These records provide field data for These records provide field data for development and verification of empirical and development and verification of empirical and analytical predictive procedures analytical predictive procedures

More instrumental records are needed to better More instrumental records are needed to better understand and model pore pressure understand and model pore pressure generation, ground deformation and ground generation, ground deformation and ground failurefailure

Wildlife Liquefaction Array (WLA)Wildlife Liquefaction Array (WLA)

WLA was instrumented by US Geological Survey WLA was instrumented by US Geological Survey in 1982in 1982

Recorded two earthquakes in 1987: the Elmore Recorded two earthquakes in 1987: the Elmore Ranch (M=6.2), which did not generate significant Ranch (M=6.2), which did not generate significant pore pressures, and the Superstition Hills (M=6.6) pore pressures, and the Superstition Hills (M=6.6) which generated liquefaction at the sitewhich generated liquefaction at the site

WLA is being redeveloped and reinstrumented WLA is being redeveloped and reinstrumented under the NSF Network for Earthquake under the NSF Network for Earthquake Engineering Simulation (NEES) programEngineering Simulation (NEES) program

Wildlife SiteWildlife Site

Regional map showing location of Wildlife site

General setting and recent earthquakes that have shaken the Wildlife site (WLA) (map from Holzer et al., 1989)

Liquefaction Occurrences Near Liquefaction Occurrences Near Wildlife SiteWildlife Site

LiquefactionLiquefaction Effects observed Effects observed followingfollowing six six earthquakes in earthquakes in past 72 Yearspast 72 Years

Wildlife site

Wildlife site

Year Area of effects193019501957197919811987

1950 sand boil that erupted about 1.5 km northwest of Wildlife Site

1982 USGS Array

•The two accelerometers are still functioning and maintained by USGS

•The six piezometers failed sometime after 1987 earthquakes

View of Wildlife View of Wildlife site After 1987 site After 1987

Superstition Hills Superstition Hills EarthquakeEarthquake

Sand boils in the Sand boils in the foreground and foreground and

instrument hut in instrument hut in the background. the background. (USGS photo)(USGS photo)

Wildlife Site

Acceleration and Pore Pressure records generated during the 1987 Superstition Hills earthquake

a.) North-South (NS) motions

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b.) East-West (EW) motions

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A. Predicted and actual ground motions at WLA site from November 24, 1987 Superstition Hills earthquake

B. Pore pressure ratios versus time (after Dobry et al., 1989)

A

BPeakAccel

Pore pressure ratios, ru, range from 0.4 to 0.6

Ru = 1.0

End of strong ground shaking

Reason for continued rise of pore water pressure: Although strong ground accelerations ceased at about 23 sec, ground displacements continued to rise with maximum of 22 cm (peak to peak) at about 35 sec. Cyclic shear strain, as a consequence of ground displacement, generates increased pore water pressures.

Correlation of acceleration and pore water pressure spikes was due to dilatent arrest of ground movement producing a sudden drop of pore pressure and the acceleration spike. Movement then ensued in the opposite direction. These spikes are numbered on the upper plots (Zeghal and Elgamal, 1994)

WLA Site Response – 1987 Superstition Hills Eq

End of strong shaking

Shear stresses were calculated from measured ground accelerations and mass of soil above liquefied layer

•Shear strains were calculated from ground displacements, determined from double integration of acceleration records, and dividing by distance between accelerometers

•Note initial near-vertical stress strain loops that flattened and develop banana-type loops with time

Analysis by Zeghal and Elgamal (1994)

a.) North-South (NS) motions

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b.) East-West (EW) motions

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Predicted and actual acceleration time histories from the Superstition Hills earthquake, WLA site, M = 6.6

Predicted Amax = 0.31 gActual Amax = 0.21 g

a.) from North-South (NS) motions

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b.) from East-West (EW) motions

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Predicted and actual response spectra for Superstition Hills earthquake - WLA site

Short-period (>0.7 sec) spectral accelerations were attenuated

Long-period (> 0.7 sec) spectral accelerations were enhanced

Lessons from 1987 SH EarthquakeLessons from 1987 SH Earthquake Pore pressures continued to rise after strong ground Pore pressures continued to rise after strong ground accelerations ceasedaccelerations ceased

Repeated dilatent arrest of lateral ground displacement Repeated dilatent arrest of lateral ground displacement observed observed

Stress-strain properties of softening soil calculated Stress-strain properties of softening soil calculated from site response from site response

Softened layer inhibited transmission of short-period Softened layer inhibited transmission of short-period (T<0.7 sec) strong motions(T<0.7 sec) strong motions

Liquefaction enhanced long-period motions (T>0.7 Liquefaction enhanced long-period motions (T>0.7 sec)sec)

Test of viability of predictive tools Test of viability of predictive tools

Principal InvestigatorsPrincipal Investigators

T. Leslie Youd, BYUT. Leslie Youd, BYU

Jamison Steidl, UCSBJamison Steidl, UCSB

Robert Nigbor, USCRobert Nigbor, USC

The George E. Brown Jr. The George E. Brown Jr. Network for Earthquake Engineering Simulation (NEES) Network for Earthquake Engineering Simulation (NEES)

Phase 2 AwardPhase 2 Award

PERMANENTLY INSTRUMENTED PERMANENTLY INSTRUMENTED FIELD SITES FOR STUDY OF SFSIFIELD SITES FOR STUDY OF SFSI

Cooperative Agreement No. CMS-0217421Cooperative Agreement No. CMS-0217421

Wildlife Liquefaction Array (WLA)Wildlife Liquefaction Array (WLA)

Objectives:

•Provide a simple, well-characterized permanently instrumented field site for study of liquefaction, ground deformation, and ground failure

•Install new accelerometers, piezometers, inclinometers, etc., to monitor liquefaction and induced ground deformation and displacement

•Provide teleobservation and telepresence capabilities for remote monitoring and interaction with site

Reasons for Reinstrumenting WLAReasons for Reinstrumenting WLAMany new and important lessons learned Many new and important lessons learned from old site; more lessons yet to be learnedfrom old site; more lessons yet to be learned

Old site has been disturbed and piezometers Old site has been disturbed and piezometers are no longer functionalare no longer functional

New research opportunities with expanded New research opportunities with expanded instrumentation and greater ground instrumentation and greater ground deformation potentialdeformation potential

Teleobservation and telepresence capabilities Teleobservation and telepresence capabilities provide distributed research and educational provide distributed research and educational opportunitiesopportunities

General view of wildlife area with locations of old and new sites (view looking east southeast)

New SiteNew SiteOld SiteOld SiteAlamo RiverAlamo River

New Site

Old Site

Stream erosion is cutting into bank adjacent to new site generating a free face that should facilitate ground deformation and lateral spread

Alamo

River

Map of wildlife area showing locations of 1982 and new sites

USGS CPT rig conducting soundings at new WLA site

Free face created by incised river

Enlarged view of new WLA site

clay

sand

Wildlife Liquefaction Array (WLA)Cross-section A-A’

Soil Behavior Types Interpreted by USGS from CPT Soundings

River

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Wildlife Liquefaction Array (WLA)Cross-section B-B’ – Soil Behavior Types from CPT Soundings

Riverclaysand

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Wildlife Liquefaction Array (WLA)Cross-section C-C’ – Soil Behavior Types from CPT Soundings

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Enlarged view of new WLA site

CPT 35

Liquefaction resistance of WLA CPT 35: M = 6.5 and various levels of peak ground acceleration (CPT procedure of Youd et al., 2001)

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Enlarged view of new WLA site

Cross section A-A’ showing liquefaction resistance from analyses of CPT data for M = 6.5 earthquakes and Amax = 0.4 g

River

Cross section B-B’ showing liquefaction resistance from analyses of CPT data for M = 6.5 earthquakes and Amax = 0.4 g

River

Cross section E-E’ showing liquefaction resistance from analyses of CPT data for M = 6.5 earthquakes and Amax = 0.4 g

Cross section D-D’ showing liquefaction resistance from analyses of CPT data for M = 6.5 earthquakes and Amax = 0.4 g

1982 SiteNew Site

Cross section C-C’ showing liquefaction resistance from analyses of CPT data for M = 6.5 earthquakes and Amax = 0.4 g

Enlarged view of new WLA site

Expected Contributions to NEESExpected Contributions to NEES

Fully instrumented site to monitor ground Fully instrumented site to monitor ground motions, pore pressures, and ground motions, pore pressures, and ground deformation as liquefaction and lateral deformation as liquefaction and lateral spread develop during future earthquakesspread develop during future earthquakes

Well characterized site from which Well characterized site from which analytical and empirical tools can be analytical and empirical tools can be developed and testeddeveloped and tested

Site where new field measurement tools can Site where new field measurement tools can be tested and calibratedbe tested and calibrated

More instrumented sites are neededMore instrumented sites are needed

To increase the likelihood of timely recording of To increase the likelihood of timely recording of site responses site responses

To increase the number of recorded responses To increase the number of recorded responses availableavailable

To increase the variety of sites and site To increase the variety of sites and site conditions conditions

To increase the variety of earthquake To increase the variety of earthquake mechanisms and magnitudes mechanisms and magnitudes

To speed the development of predictive To speed the development of predictive proceduresprocedures