Date, Time and Place: 22 August 2013, 0900 hrs, Pier 1 The Embarcadero, San Francisco Presented by: Nick Rogers, Mike Jacka, Kate Williams, Sjoerd van Ballegooy and Rick Wentz, Tonkin & Taylor International Ltd Presented to: Workshop on Liquefaction Assessment, Disaster Risk Reduction and Community Resilience
Canterbury New Zealand Earthquake Sequence 2010-2011 Lessons from Christchurch
Mikes Story Riding the Road to Recovery and Increased Resilience
Technical Inputs For Recovery Planning Longer-term need for good technical information for recovery Where to rebuild? How to rebuild? How to manage future risk?
Where to rebuild?
Red Zones There is area-wide damage, which requires an area-wide solution An engineering solution would be technically difficult, disruptive, not timely, nor cost effective A government offer to purchase the properties
Liquefaction & Lateral Spread Observations Most damage due to shaking not liquefaction. Damage usually only minor. 1/3 major foundation repair or beyond economic repair 1/3 minor foundation repair or re-level 1/3 cosmetic or no damage Beyond economic repair House damage
Where To Rebuild? Govt Red Zone Decisions Observed liquefaction damage after September 2010 CBD
Where To Rebuild? Govt Red Zone Decisions Observed residential foundation damage excluding Red Zone CBD
Where To Rebuild? Govt Red Zone Decisions Observed liquefaction damage after February 2011 CBD
Where To Rebuild? Govt Red Zone Decisions Observed liquefaction damage excluding Red Zone CBD
Where To Rebuild? Govt Red Zone Decisions Observed residential foundation damage CBD
Where To Rebuild? Govt Red Zone Decisions Observed residential foundation damage excluding Red Zone CBD
Ground Surface Elevation (LiDAR) LiDAR Survey Pre September 2010
Change in Ground Surface Elevation Height Difference (2003 to Post June 2011)
Observations Red Zone has generally sustained the most severe damage from liquefaction is theoretically vulnerable to damage from liquefaction at lower levels of shaking (i.e. higher frequency return period events) is theoretically the most vulnerable to damage from liquefaction at higher levels of shaking (i.e. higher frequency return period events) The red zone land is not being rebuilt on which makes the rebuild in Canterbury much simpler (geotechnically).
Green Zones There are no significant technical issues which prevent rebuilding in these areas Land and building damage can be repaired on an individual basis as part of the normal insurance process In some cases, properties may be assessed by insurance companies as not economic to repair, but still able to follow normal process
Green Zones How to make the normal individual process more efficient?
23-Jun-2011: 130,000 homes require an engineer Developing the TCs Evolution
Foundation Technical Category 1 (TC1) Future land damage from liquefaction is unlikely For new or rebuilt foundations: Ground settlements (from liquefaction) expected to be within normal tolerances Standard foundations (NZS 3604) are acceptable, subject to shallow geotechnical investigation.
Foundation Technical Category 2 (TC2) Liquefaction damage is possible in future large earthquakes For new or rebuilt foundations: Shallow geotechnical investigation required Standardised suspended timber floor or enhanced slab foundations likely suitable
Foundation Technical Category 3 (TC3) Liquefaction damage is possible in future large earthquakes For new or rebuilt foundations: Deep geotechnical investigation required (and/or assessment of existing information) Specific engineering input required for foundation option selection/design
Foundation Technical Categories Purpose: Starting point for repair or reconstruction of damaged foundations Guide to the level of site investigation and who should do this Will lead to a variety of outcomes, irrespective of TC Reflect the variability of Canterbury soils, NOT a liquefaction or land hazard map
Foundation Technical Categories Objectives: to direct the engineering resource to where it is needed most provide an appropriate level of overall foundation resilience throughout the building stock
28-Oct-2011: 30,000 homes in TC3 Developing the TCs Evolution
How to rebuild?
Observations : Land The envelope of land in the TC2 / TC3 zones: has generally sustained considerably less damage from liquefaction than red zone is theoretically not vulnerable to damage from liquefaction at lower levels of shaking (i.e. more frequent events) is theoretically slightly to moderately vulnerable to damage from liquefaction at higher levels of shaking (i.e. less frequent events).
Observations: Buildings Modern slabs on grade houses performed worse than older houses on suspended timber floors Complex shaped houses performed worse than rectangular houses Heavy houses performed worse than light weight houses
Distribution of the residential construction types in the three main New Zealand urban centres Construction Types Auckland Wellington Canterbury based on 2011 portfolio data Region Region Region Unknown 15.2% 13.7% 12.4% Light Wood Frame 47.3% 64.0% 23.2% Light Wood Stud Walls w/ Brick Veneer 21.7% 8.8% 28.6% Masonry 8.7% 5.9% 12.2% Other 7.0% 7.3% 23.6% Light Metal Frame 0.03% 0.30% 0.02%
When would you like to pay? Well Being Post-event: cost too great Pre-event: cost too great.. What are the objectives?. What is sustainable? $ Risk Mgmt
Aligning Performance Objectives: seeking an appropriate level of resilience Event Frequency Building Code Objective Guidance Performance Objective Serviceability Limit State 25 years Low probability of loss of amenity Little or no structural damage; any damage is readily repairable Ultimate Limit State 500 years Life safety Life safety; habitable and repairable damage where practical
Guidance Documents
Rebuilding Resilience Strategy TC1 Timber & Concrete Floors Existing (+ nominal mesh) TC2 Stiffened slabs and timber floors TC3 Enhanced foundations and/or ground Improvement
How To Rebuild? Foundation Guidance A range of standard foundation repair & rebuild options for enhanced resilience
Increased Resilience The repair of the building damage will result in reduced vulnerability of the future building stock in Canterbury: Fewer masonry chimneys More enhanced foundations in TC3 More lightweight homes in TC3 Much less unreinforced masonry No rebuilding on the most vulnerable land Future development is migrating to less vulnerable soils in the west
Readily-Repairable Accepting future minor, readily-repairable damage in moderate earthquakes is a key concept Continue to function remains habitable Minor damage to structure re-levelling floors using standard procedures Some damage to fabric and lining minor cracking at junctions and corners 36
A Pool Of Shared Technical Knowledge Canterbury Geotechnical Database: 13,000 post-eq geotechnical investigations to date
Predicting land performance Scientific literature presents methodology for predicting liquefaction triggering Earthquakes in Christchurch and elsewhere show these methods appear generally suitable to predict occurrence of liquefaction But prediction of occurence is not the end point Need to understand the consequences at the ground surface for buildings and infrastructure Not all liquefaction is consequential
How to go from this... Predicting land performance... to this?
Liquefaction Vulnerability and LSN LSN=10 LSN=30 Crust Liquefying soils Non-liquefying soils Liquefying soils Crust Liquefying soils Crust Liquefying soils LSN=50 Non-liquefying soils Non-liquefying soils Non-liquefying soils Increasing vulnerability to the liquefaction hazard
LSN 0-20 Little or no expression of liquefaction, minor sand boils, minor damage to homes. LSN 20-40 Moderate expression of liquefaction, undulations and cracking of ground surface (there are occasional instances of severe damage. LSN 40+ Widespread severe damage, extension expression of liquefaction, severe settlement of buildings and damage to services.
Liquefaction Vulnerability and LSN
Liquefaction Vulnerability and LSN
CPT analysis for 3 example sites TC2 TC3 Red Zone
Example CPTs - damage trends 80 70 Sep-10 Jun-11 Dec-11 Feb-11 Red Zone 60 50 Damage LSN 40 30 TC3 TC2 20 10 0 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 Peak Ground Acceleration (g) at Magnitude 7.5
Ground Improvement Trials Ground improvement using: Rammed aggregate piers Rapid impact compaction Compaction grouting Permeation grouting Horizontal soil-mix beams Performance testing using: T-Rex shaker in-situ liquefaction CPT testing Crosshole geophysical testing Blast-induced liquefaction
Ground Improvement Trials Exhumed horizontal soil-mix beam Proof-load testing...
Where to from here? Implement enhanced repair/rebuild solutions to improve resilience & habitability in future EQ Ground improvement trials downsize/innovate to provide GI techniques suitable for homes Share learnings from Christchurch with other communities at similar risk around the world Better consideration of consequential effects from land damage in catastrophe loss modelling Then do something about it to reduce the risk!
Thank You