Table 2 Frost protection test for the surrounding rock.

From: Frost protection mechanism based on rubber airbag interlayered composite lining system for cold-region tunnels

Category

Waterproofing test

Thermal insulation performance test

Thermal insulation test

With/without airbag

Without

With

With

With

Airbag thickness (mm)

–

30

30\40\50

30

Internal gas

–

Air

Air, CO2

Air

Test temperature

Temperature –15 °C, Surrounding rock boundary temperature 3 °C

Temperature – 20 °C, Surrounding rock boundary temperature 3 °C

Temperature – 25 °C, Surrounding rock boundary temperature 3 °C

Surrounding rock water content

Seepage state

Saturated state

Initial pressure (kPa)

–

13

13

13

  1. For the waterproofing test, a small number of fine holes were drilled in the inner steel cylinders of both the airbag and airbag-less models to simulate the secondary lining joints.
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