Performance of EVA-Based Membranes for SCL in Hard Rock

Abstract

The bonded property of multi-layered sprayed concrete tunnel linings (SCL) waterproofed with sprayed membranes means that the constituent materials will be exposed to the groundwater without any draining or mechanically separating measures. Moisture properties of the sprayed concrete and membrane materials are therefore important in order to establish the system properties of such linings. Ethyl-vinyl-acetate based sprayed membranes exhibit high water absorption potential under direct exposure to water, but are found to be significantly less hygroscopic and exhibit lower sorptivity (water absorption rate) than sprayed concrete. This material behavior explains the relatively dry in situ condition of the membrane that was observed. Measured in situ moisture content levels of the membrane material in tunnel linings have been found to vary within the range of 30-40 % of the maximum water absorption potential, and show a decreasing trend over the first 4 years after construction has been completed. A model for the mechanical loading, moisture condition and thermal exposure of the membrane and the resulting realistic parameters to be tested is presented. Laboratory testing methods for the membrane materials are evaluated considering possible loads, moisture and freezing exposure. Material testing of membrane materials was conducted with preconditioning to realistic moisture contents and under different temperature conditions including relevant freezing temperatures for tunnel linings. The main effects of the in situ moisture condition of the tested membrane materials are favorable tensile strengths in the range of 1.1-1.5 MPa and low risk of freeze-thaw damage. The crack bridging capacity of the tested membranes is found to be sensitive to temperature. With membrane thicknesses in the range of 3-4 mm, crack bridging capacity up to 4-6 mm opening of the crack width at 23°C and approximately 1 mm opening at -3°C was measured for the tested membranes. No significant reduction of the tensile bond strength could be demonstrated after 35 freeze-thaw cycles with -3°C minimum temperature at the membrane location in the lining. Further work is required to verify the performance of the SCL system under exposure to high hydrostatic pressures and the effects of long term mechanical exposure.

Interface parameters of composite sprayed concrete linings in soft ground with spray-applied waterproofing

“…Table 1 Lining and interface loading scenarios for different SCL tunnel configurations Field measurements by Holter and Geving (2015) on an SCL tunnel in rock with spray-applied waterproofing found the moisture content of the membrane to vary between 30% and 40%, determined by the moisture properties of the concrete and the membrane, as well as the interfaces between the two materials. Further research by Holter (2016) suggested that high moisture content in the membrane may affect its mechanical properties, e.g. reduce its tensile strength.…”

Conditions on the Application of Sprayable waterproofing Membrane in Tunnels under Sulfate Attack Environments

“…The case histories indicated that the sprayed membrane can cope with crack widths equal to its thickness [1]. The recent case studies [10] gave similar results.…”

“…The properties of sprayed-on waterproofing membrane is strongly related to the composition of the mixtures of the waterproofing membrane. The recent results [10] shows that the membrane products with low polymeric content (e.g., below 70 %) exhibit low elasticity and are likely unsuitable for tunnel waterproofing purposes.…”

Simulating composite behaviour in SCL tunnels with sprayed waterproofing membrane interface: A state-of-the-art review

“…one partially or fully saturated due to water coming through cracks in the primary lining, has considerably lower compressive, tensile and shear stiffness and strength than a 'dry' membrane, i.e. one exposed only to the ambient atmospheric environment without direct contact with water [39]. This will theoretically cause a waterproofing membrane interface that was originally bonded to degrade to unbonded, resulting in significant change in load sharing between the primary and secondary linings.…”