Title of Presentation CRL C1 Subheading
Groundwater & Settlement Author Monitoring & Contingency Plan Date (GSMCP) Neil Korte Tonkin & Taylor 15 May 2018
Introduction • Part of a comprehensive suite of environmental controls • Objective is to avoid damage to structures and surrounding
infrastructure • Required under the Consent Conditions – 20 working days prior to the start of dewatering • Will be updated during the course of the project to align with changes to construction techniques and environmental conditions encountered
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Progress to Date • Construction works being • • • • • • •
undertaken by DSBJV, started in July 2016 Interior of CPO stripped out D-walls for tunnels installed Jet grouting nearing completion Piles installed across LQS Building underpinning started Monitoring instrumentation in place Excavation for tunnels due to start in July 2018 3
What is required in terms of the consent? • • • •
No more than “slight (aesthetic) damage” to CPO No more than “negligible damage” to surrounding buildings Any damage will be repaired by CRLL/DSBJV if it occurs Groundwater levels adjacent to the tunnel shall not reduce below preexisting seasonal low levels or rise above seasonal high levels measured during the pre-construction monitoring • No long term ground settlement caused by post construction dewatering or long term groundwater mounding • Baseline monitoring 3 months prior to excavation for the tunnels
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How will monitoring be undertaken? • • • •
Automated telemetry system installed by Sixense Real time monitoring of groundwater and survey markers Live reporting to monitoring website Text/email messages to project staff responsible for monitoring when alert or alarm levels are triggered
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What will be monitored? • • • • •
Groundwater levels Ground settlement (surrounding streets) Building settlement (CPO & surrounding buildings) Building condition surveys (CPO & surrounding buildings) Retaining walls
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Groundwater Monitoring
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Ground & Building Monitoring
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Ground & Building Monitoring
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Ground Monitoring
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Building Monitoring
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Alert and Alarm Triggers Used for Groundwater, Ground, Building & Retaining Wall Monitoring
• Alert Levels • Alarm Levels
set as a warning that getting close to max/min levels allowed (~80% of alarm levels) set at maximum/minimum allowable/tolerable levels
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Building Monitoring
ALERT
ALARM
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Building Condition Assessments/Surveys Prior to dewatering
One (completed)
During dewatering
Visual inspection of the surrounding ground and external building façades at least twice weekly
After completion of excavation until completion of dewatering
Visual inspection of the surrounding ground and external building façades at least weekly
After completion of dewatering
One
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Retaining Walls
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Services • Temporarily diverted during construction onto secure structures e.g.
attached retaining wall capping beams which will not be subject to movement • Relocated back to LQS once tunnels are completed and ground survey monitoring shows no settlement
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Monitoring/Reporting • • • •
Monthly reports to Council Graphical plots vs time Any trigger level exceedances Actions undertaken
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Typical actions on ALERT/ALARM – Groundwater, Ground or Building • Council & IBA notified • SQP engaged to: identify causes assess risk of settlement, potential for damage or damage identify mitigation measures/actions provide report to Council • CRLL/DSBJV will implement any recommendations of the SQP/IBA
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Typical actions on ALERT/ALARM ALERT
ALARM
remeasure
stop works
investigate if as expected/cause
investigate cause
review/increase monitoring
remeasure
review triggers
review monitoring, triggers and mitigation
identify mitigation
implement mitigation/additional mitigation
undertake mitigation (if appropriate)
Restart once mitigation undertaken and/or when levels below alarm 19
In the event of damage • CRLL/DSBJV will notify Council & Asset/Building Owners • SQP to prepare a report: describing damage, mitigation to avoid further damage and remediation required • CRLL/DSBJV will undertake repairs
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GSMCP Review • Consult with CLG • Certification by Council by independent peer reviewer Thereafter GSCMP will be reviewed • annually, or • if material change on the project, or • to address unforeseen adverse effects
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