The aims of the excavation and characterisation phase of the Gas Migration Test (GMT) were:


  • Evaluation of EBS following the gas test;
  • Determination of sand/bentonite properties
  • Detection of gas- and water-flow paths;
  • Assessment of the construction methods used;
  • Evaluation of interface properties (concrete silo/buffer concrete joint, instrumentation arms, risers);
  • Assessment of concrete silo performance and interaction of concrete and bentonite/sand effects
  • Recalibration of instrument


The excavation and characterisation of the silo was carried out in a series of eight steps (explained in greater detail in the sections shown in the side menu above):

Step 1: Depressurisation of GMT Cavern.

Step 2: Cutting through the concrete plug.

Step 3: Removal of backfill from GMT Cavern.

Step 4: Investigations from top of Layer 12.

Step 5: Removal of sand/bentonite by layers to top of concrete silo.

Step 6: Investigations in Layers 8 and 7.

Step 7: Removal of Layers 6-5.

Step 8: Restoration of GMT site.