The tunnel sealing experiment: An international study of full-scale seals

Abstract

The Tunnel Sealing Experiment (TSX), a major international experiment, demonstrating technologies for tunnel sealing at in situ full-scale, was conducted at Atomic Energy of Canada Limited’s Underground Research Laboratory (URL). The objective of the experiment was to demonstrate technologies for construction of bentonite and concrete bulkheads, to quantify the performance of each bulkhead and to document the factors that affect the performance. It was not the purpose of the experiment to demonstrate an optimized bulkhead. Two bulkheads, one composed of low-heat high-performance concrete and the other of highly compacted sand-bentonite material, were constructed in a tunnel in unfractured granitic rock at the URL. The chamber between the two bulkheads was pressurized with water to 4 MPa in a series of steps over a two-year period. The ultimate pressure is representative of the ambient pore pressures in the rock at a depth of 420 m. The first phase of the TSX was conducted at ambient temperature (15 °C) while a second phase involved heating the pressurized water between the bulkheads with temperatures ultimately reaching 65 °C near the upstream face of both bulkheads. Instrumentation in the experiment monitored parameters that are important indicators for bulkhead performance. Seepage was measured at both bulkheads and any other leakage points from the tunnel to maintain a water balance. At 4 MPa pressure in the tunnel and ambient temperature the clay and concrete bulkheads had seepage rates of 1 mL/min and 10 mL/min respectively. Heating caused the concrete bulkhead to expand by a maximum of 0.2 mm, further reducing seepage to 2 mL/min. Heating did not affect the seepage rate at the clay bulkhead. The paper provides an overview of the project.