CIVIL ENGINEERING AND MINING PROJECTS—RECONCILIATION OF DESIGN PHILOSOPHIES

The conduct of scientific experiments at DUSEL will require excavation of large openings at a considerable depth below the surface. The laboratory-module excavations will have footprint dimensions about 66 x 328 feet (20 meters [m] x 100 m) and the excavation of the large cavity to host the water Cherenkov neutrino detector will have a diameter greater than 180 feet (55 m) and height of approximately 240 feet (80 m), including the crown of the excavation. Construction of such openings in a high-rock-stress environment, at a depth of 4,850 feet (1,478 m), requires combined experience in design and construction of large civil engineering underground facilities and deep mines. Experience in civil engineering is fundamental to secure a high level of stability of large caverns and minimal disturbance to rock due to the blasting. Experience in mining is indispensible when it comes to excavations at considerable depths where a high-rock-stress field dominates the behavior of the rock mass. Combination of the mining and civil engineering experiences requires reconciliation of differences in their respective approaches to design and construction.

The first aspect differentiating mining and civil engineering projects is the issue of “design life” or “stand-up time.” In mines, the object is to get the underground excavations to stand up just long enough for the ore to be extracted: in underground civil engineering projects, the underground excavations must be stable, without any rockfalls, for at least the life if the project, which may be a hundred years or more.An important difference is also the concept of maintenance. In mines, there is a tolerance for rockfalls (within the limits of mine safety) as there are mining equipment and personnel on hand who can easily stabilize any area of the mine. In civil engineering projects, there is little or no tolerance for rockfalls when the project is in service due to the safety hazard, conduct of scientific experiments and, especially because there is no mining equipment on hand to undertake stabilization work.

Reconciliation of these differing design philosophies is of particular importance for DUSEL’s project, which involves construction of the large excavations applying civil engineering standards in a deep mining environment.