tunnelling tips! drilling and blasting in dense urban areas
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Tunnelling Tips! Drilling and blasting in dense urban areas
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It’s a common practice Drilling & blasting is common practice in cities such as Hong Kong due to the large volume of tunnelling work.
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Is it really better to blast?
Blasting methods are proven to be more effective at removing hard rock than mechanical excavation.
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Think before you drill… There are many considerations & hazards that you must be aware of when using this method in highly dense areas.
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Know what you’re up against.
Know your challenges
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• Proximity - close to many sensitive receivers
• Potential impacts on the community
• Possible constraints on contractors
Know your challenges
• Higher level of confidence required for approval authorities
• Needs of the community vs rising construction costs
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Be a step ahead know your hazards
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• Ground-borne vibrations • Fly rock • Dust and fumes • Air overpressure • Explosives handling
Are you aware of the Sensitive receivers?
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• Temporary excavation support • Public utilities • Retaining walls and cut slopes • Natural terrains • Existing building structures • Piled Foundations • Historic buildings
Prepare before you blast
Prepare before you blast
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Address your hazards & sensitive receivers by making the appropriate considerations…
Take action
Prepare before you blast
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Ensure monitoring and control measures are in place before you drill & blast
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Vibration monitoring procedures and inspections are to be put in place
Reduction of air overpressure needs to be considered
Physical protection measures are essential
Prepare before you blast
Take action
• Explosives delivery and handling procedures
are to be drawn up
• Public notification and traffic management needs to be appropriately planned
• Site supervision must be arranged
• Blasting Assessment Report (BAR) needs to be written
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Take action
Prepare before you blast
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Prepare before you blast Ensure Vibration Prediction work and Monitoring procedures are ready to go
This validates design predictions & ensures PPV limits are not exceeded
This involves… • Setting vibration limits
• Predicting vibrations acting at sensitive receivers
• Limiting explosive charge weight
• Measuring and recording vibrations
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Prepare before you blast
Take action
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Prepare before you blast
Know your limits
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Prepare before you blast
The vibration equation?
Write it up
Write it up Contractor’s Blasting Assessment Report
This report demonstrates that the blasting works are feasible without exceeding the impact criteria of nearby sensitive receivers. In this report, you will:
• Identify the location and condition of sensitive receivers
• Propose allowable vibration limits • Estimate allowable charge weights • Examine possible hazards and adverse
consequences • Propose protection measures and safety
procedures to ensure that the hazards are controlled
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Write it up Blasting Method Statement (BMS)
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The contractor will also need to prepare a Blasting Method Statement (BMS) with specific detail of work sequence, blast design, protective measures, monitoring and contingency plans.
Blasting Assessment Report (BAR) needs to be approved by the Mines Division of the Civil Engineering and Development Department (CEDD) before going ahead.
Get it approved
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Measure up
Measuring the vibrations
You need a minimum of monitoring stations for each blast (MTR projects)
6
What you need
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Measuring the vibrations What you need
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Use a Vibrograph (velocity seismograph) to measure and record PPV and amplitude of ground motion
AAA trigger system
Measuring the vibrations What you need
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• Alert • Action • Alarm
Contact: Jack Muir Associate – Transport [email protected] Nick Bedford Senior Civil Engineer – Transport [email protected]
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