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Morwell Land Movement: Public Information Sessions

Photograph of earth moving machinery on a site

 

19 August 2011

Doug Sceney – Director Earth Resources Regulation
Anne Bignell – Acting General Manager Mine Stability

More information about the Morwell Land Movement

Background, what happened?

  1. Heavy rainfall event on February 5, 2011
  2. Movement observed in the northern wall of the Hazelwood Mine.
  3. As a result of the movement, cracks appeared across the mine batter, the surface of the Princes Freeway and at the end of Hazelwood Road.
  4. VicRoads closed a section of the Princes Freeway running between the mine and the township of Morwell.
  5. The former DPI urgently commenced investigations with the assistance of Professor Tim Sullivan - The Chair of the Technical Review Board (TRB).

February 2011

Sinkholes and evidence of new cracks were observed in the MMD and on the northern batter and along its toe. Appearance of cracks from the batter crest that continued done the batter. Cracks appearing in the embankment wall of the Ash Retention Pond. Evidence of significant movement of a large block of coal.

Public Safety Concern and Princes Freeway Close

Screenshot of Latrobe Crime Watch News Special Update Edition - March 2011 and images showing the location of cracks and land movement and the route that over dimensional vehicles must use. The full article can be accessed via the link below.

View the Latrobe Crime Watch News Special Update - March 2011

Area of Concern

Aerial photograph of major areas of concern – the complexity of the situation became apparent from early on. The areas are: Tennis Courts, Houses near the mine, Princess Freeway, Morewell Main Drain, HARA, HARE, Waste Dump and Northern Batters.

Who has been involved in the response?

  1. An Emergency Management Team (EMT) was formed - led by Victoria Police and including DPI, VicRoads, Latrobe City Council, IPH, SPAusnet, Gippsland Water and DHS.
  2. An Inter-Departmental Committee (IDC) was also established within Government to coordinate a whole-ofgovernment approach.
  3. EMT has recently been wound up as we transition into recovery/rehabilitation/remediation - no longer considered to be in an emergency situation.
  4. DPI will lead the Morwell Recovery Team (MRT).

Developing the Geotechnical Model

Review of Large Data Sets:

  • Ground Movement Pins - Vectors of Movement
  • Groundwater Level - Patterns and Trends
  • Horizontal Drain - Flow and Chemistry
  • Stability Analysis – Modelling
  • Aquifer – Flows and Water Levels
  • Historical Deformation
  • Historical Mine Operational Activities

Monitoring Locations

Monitoring points were established and monitoring frequency dramatically increased in the mine area and in the Morwell Township. This enabled data to be acquired and subsequently analysed over time for trends.

Northern Batter Horizontal Bores

One of the major remedial activities included drilling about 50 horizontal drains along the face of the northern batter. Purpose of these drains is to take out the water to relieve the pressure in the coal cracks. There are no drains under Morwell residential areas.

Vectors June 2009 to March 2011

Analysis of new monitoring data and historical monitoring data shows that movement in Morwell north of the Freeway is towards the north and the centre of Morwell. Movement south of the Freeway is towards the mine.

What has been managed by DPI since February?

  1. An extensive system of highly sensitive water and movement monitors has been set up both inside and outside the mine.
  2. The drilling of 50 horizontal drain holes to release water from the area of instability has been completed.
  3. Real-time monitoring to immediately identify any further movement has been installed both at the freeway and within the mine.
  4. A risk assessment workshop and report have been completed that quantified the risk to public safety and the results that the proposed actions would have in reducing that risk to a safe level.
  5. A land movement survey of the residential area adjacent to the site has been recently done.
  6. Two independent reviews have been completed - a review of public safety issues and a peer review of all technical advice received.
  7. A scenario workshop to establish and manage protocols for any emergency situation has taken place.
  8. An aerial survey of the affected area has been undertaken.
  9. A feasibility study has been undertaken by IPH into further earthworks and other remedial works to limit future movement at the site, as a long term project.
  10. IPH and DPI have been working to reach agreement on the redesign and specifications of the drain.
  11. The Government has committed $2million to assist IPH beginwork to line the main drain which passes through the area of instability.

Ground Movement Mechanism

Natural Phenomenon

  • Rainfall
  • Inherent Cracks and Joints in Coal formed into Coal Blocks
  • Brown coal sensitive to water pressure due to low bulk density

Mechanism of Ground Movement

  • Rain water infiltrates into coal cracks (e.g sinkholes in MMD)
  • Water pressure in coal cracks initiate movement of coal blocks and ground movement.
  • Ground movement creates surface cracks which allows more water to infiltrate into coal and further ground movement.

To break the cycle we have to manage the water

Then …

  • When movement was first detected the potential impact and severity of the event was not clearly understood.
  • However there were sufficient fears regarding the risk to users of the Princes Freeway at Morwell and to residents to the north of the Princes Freeway to close the freeway and place the community on alert.
  • The geotechnical model was yet to be developed but it was apparent that water entering the mine batters was the cause of the mine batter instability and that there was a likelihood that the mine batter would collapse.
  • Morwell Main Drain (MMD) which was identified as a potential source of water and as such presents an ongoing risk to the mine batters.

Now …

  • We have the benefit of a significant monitoring database and real-time monitoring.
  • Further development and refinement of the geotechnical model that explains ongoing movement.
  • More confidently anticipate the response of the mine batter to rainfall events.
  • This improved understanding has resulted in a reassessment of the risk to public safety

Government Decision

Public safety risk re-assessed based on improved understanding

Arrow facing down

Government Decided for Conditional Opening of Freeway
In time for September School Holidays

Arrow facing down

Complete Remedial Works of MMD to Stop Creation of Sink
Holes and Leakage of Water into Coal Cracks

Arrow facing down

Government will Decide for Un-Conditional Opening of Freeway

Arrow facing down

Conditional opening of Freeway?

  • Until the Morwell Main Drain (MMD) is remediated there is concern about how much water it will allow to enter the mine batters during a high rainfall event.
  • Should a high rainfall event occur before works on the MMD are complete then the Freeway may be closed for inspection and while monitoring data is reviewed.

What Happens Next?

  1. It is expected that the freeway will be open to traffic, weather permitting so that VicRoads can complete remaining works, before the September school holidays
  2. The monitoring of ground movement around the mine and the freeway area will continue after the road reopens
  3. Around the clock monitoring of the freeway continues.
  4. Work continues to finalise the longer-term solution for the use and design of the Morwell Main drain
  5. Freeway may have to be temporarily closed, to allow for inspection and monitoring to occur, if a high rainfall event occurs.

Future On-Going Works - Mine

(the next months/years ?!)

  • Continue with Monitoring Activities and Analysis
  • Review of Mine Operational Activities
    – Aquifer depressurisation
    – Rehabilitation of northern batters
    – Surface Drainage of northern batters
    – HARA operations
    – Buttressing – is it feasible?
    – Horizontal drains maintenance?
  • Implement Long Term Ground Stability Works

Questions?

There was a question/discussion time at the end of this information session