Construction Issues in Periglacial Environments

Permafrost
1. Melting
  1. Train tracks can be uprooted by thawing of the ground below of by the process of frost heave.
    1. The Qinghai-Xiang railroad in China was constructed to cross a large permafrost area. To prevent heat from the track melting the permafrost and making the ground unstable it was elevated. High bridges were constructed and crushed rock used to insulate the ground.
  2. Roads can buckle as a result of uneven thawing or frost heave.
    1. The use of gravel beds to isolate roads and the permafrost is practiced in permafrost areas to prevent permafrost from melting. Some structures can be up to 3m high.
    2. Roads are painted white to reduce the amount of heat they absorb from exposure to the sun, therefore reducing the melting effect.
  3. Subsurface pipes can be ruptured as the permafrost melts and the ground fluctuates and becomes unstable.
    1. Pipes are placed above ground.
    2. Large transport pipes such as the Trans-Alaska Pipeline are built as separate components therefore if there is movement sections of the pipe can be closedand any potential leak contained.
      1. Sealed tubes of ammonia are placed within stantions. As the ammonia heats up it rises within the tube. Once at the top it is cooled by the passing cold air, it then sinks back to the bottom of the tube. this cooling cycle helps to negate the warming effect of the pipeline.
      2. Pipes are designed to move slightly in accordance to fluctuations in the permafrost layer and to also survive seismic events.
  4. Flooding can occur as the permafrost layer melts. This could create mass flooding or ponding of surface water in depressions.
    1. Preventative measures are in place to prevent permafrost melt and subsequent flooding. Gravel is used as a base as an insulator but also due to its high drainage capacity to prevent excess water ponding.
  5. Subsidence can occur as the ground thaws at different rates and becomes unstable.
    1. Homes and buildings are built on raised steel frames to isolate the heat they generate to prevent the permafrost layer from melting. The gap between the building and the ground allows cool air to negate the heating effect of the building.
  6. Mass Movement can occur as permafrost melts and ground becomes unstable. it can also be a by-product of the addition of eexcess water to the system.
    1. Steps are taken to ensure permafrost stays frozen to reduce the risk of melt induced mass movement.
2. Freezing
  1. The process of frost heave is when groundwater is frozen by the permafrost layer, and expands, effectively heaving the ground above it.
    1. Gravel beds used in construction are also used because of its drainage capacity therefore reducing the amount of water in the sediment and reducing the rick of frost heave.
  2. Subsurface pipes carrying water can freeze.
    1. Many pipes are placed above ground.
    2. Pipes are well insulated to prevent freezing.
  3. The presence of permafrost means the ground is impenetrable due to the ice.
    1. Due to the impenetrable ground many buildings are raised and built on the surface.
    2. In some cases the ground is fully thawed and the building constructed. The heat from the building or the activities taking place ensures that the ground does not re-freeze.
Access
1. Seasonal permafrost melt can create marshland and unstable ground. This can mean some areas become inaccessible as it is impossible to construct roads in these conditions.
  1. In the winter ice roads are constructed to cross these areas.
Resource Extraction
1. Impenetrable ground
2. Drilling for resources can cause permafrost to melt.
  1. Drilling platforms are constructed on concrete plinths to isolate them from the ground. This also helps stabilise the heavy machinery.
  2. Specialised drilling fluid is created with a lower freezing point to prevent problems with extraction.
Climate
1. High Altitude/Thin Air
  1. In the Tibetan plateau the permafrost is at a high altitude therefore posing a risk to workers. To negate this issue many workers were sourced from these areas where they have been pre-exposed to this environment. There are also guidelines in place to ensure safe working conditions and regulated breaks and health checks.
2. Extreme Temperatures
  1. People
    2. Mandatory safety equipment and warm clothing are standard requirements for all construction jobs in extreme temperatures. Regular breaks and warm environments should be available to all employees in the workplace.
  2. Machinery
    1. In extreme temperatures machinery may not perform well. To prevent this specialised equipment is developed such as drilling liquids that have a lower freezing point then normal to ensure smooth running of equipment.
  3. Maintenance
    1. Adverse weather conditions may mean access for maintenance can be restricted. This is solved by providing a high standard of work initially and maintenance work conducted when possible.
Amenities
1. Lack of available extractable freshwater. In areas of permafrost minerals in the groundwater tend to become extremely concentrated in the water above the ice thereofre making it unsuitable for human consumption.
  1. Water is transported into the area. Either by pipes or in bottled form.
  2. In some areas groundwater is available as a result of taliks in the permafrost.
2. Water within pipes can freeze.
  1. Overland pipes
  2. Well insulated pipes.

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Construction Issues in Periglacial Environments

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	Creado por Amy Ward hace más de 9 años