Underground Excavation

Itasca has performed analyses for some of the largest and most important underground caverns in the world, including the main detector hall for the Superconducting SuperCollider project in the U.S. as well as the Large Hadron Collider for the European Centre on Nuclear Research (CERN). In both cases, there were severe constraints on allowable ground movements during and after construction.

The work for CERN was a cooperative effort between Itasca offices in France and Spain and EdF-CNEH, a department of the French Electricity Authority. The major difficulty in the CERN project was representation of the three-dimensional geometry and construction phases of the entire structure, including several pre-existing structures and future caverns, shafts and chambers. The construction phases not only impact the excavation, but also support placement. First, shotcrete was applied to new excavations and later supplemented with the final concrete lining. One key to understanding the behavior was to allow realistic interactions between the various concrete structures and between the structures and the rock. A non-linear constitutive behavior whose properties varied with location was assigned to the rock-structure interface.

• In the normal direction, only compressive stresses were allowed, so the concrete liner could potentially pull apart from the rock.
• In the shear direction, the maximum force was limited by friction.

Other large excavations have included analysis of the stacked-drift support for the Rio Piedras subway station in Puerto Rico. The Rio Piedras Station was excavated in alluvial material for which Itasca made estimates of water inflow during construction. Itasca has worked on several hydroelectric underground powerhouses in India and Colombia (Guavio and Sogamoso). The Indian Society for Rock Mechanics and Tunneling Technology awarded a prize to a paper co-authored by Itasca personnel, which described a 3DEC analysis of several Indian powerhouses.

Itasca worked directly with a local rock engineering consulting firm to design the Viikinmäki underground sewage treatment plant in Helsinki. The plant was housed in eight parallel caverns totaling one million cubic meters of excavation. All the chambers were located at shallow depth and required special reinforcement, designed by Itasca, where the rock cover thinned. In Helsinki, Itasca worked with the same firm to study the stability and reinforcement for an underground car park, an underground library and a surface excavation for a bus terminal directly above a subway station in the city center.

Itasca also consulted with the owner of large frozen-food storage facility located in a former room-and-pillar limestone mine in Kansas City. The owner needed to know the effects of raising the temperature of the facility above freezing. For this problem, Itasca performed coupled thermo-mechanical analysis to show what would happen over time as the air temperature inside the facility was raised.