Bi-layer diaphragm walls: Parametric study of construction processes

The bi-layer diaphragm wall is a new type of slurry wall, designed to improve watertightness and to counter leakage problems. These walls consist of two bonded concrete layers: the first, a conventional Reinforced Concrete (RC) diaphragm wall and the second, a sprayed Steel Fibre Reinforced Concrete (SFRC) layer with a waterproof additive. Here, we analyse and quantify the influence of different construction process parameters on the effectiveness of the bi-layer diaphragm wall technique. Thirty numeric simulations were conducted with an uncoupled structure-section analysis, placing special emphasis on the SFRC layer contribution. The results show that, in all cases, the main flexural strength is provided by the RC layer, with a secondary flexural contribution (between 8% and 15%) by the sprayed SFRC layer. Using satisfactory spraying sequences (detailed herein), a reduction in the steel reinforcement of the RC layer can be obtained in every structural configuration and construction sequence, reaching a maximum percentage reduction of 7.0% of the total bending reinforcement. The displacements are almost completely governed by the thickness of the first layer, and a minor reduction (less than 7.3%) is obtained, when the second layer is included.