Water Isolation using geosynthetics for a two sub-storey parking in Patras (September 2000)

The photos are from a project in the city of Patras, Greece. The project consists of a two sub-storey parking below an entertainment complex. After the completion of the deep excavation, geosynthetics were used for the water isolation of the excavated area. The Geomembranes used (yellow color), are bonded together with some kind of glue. It is very important that the two parts are perfectly bonded using thermal bonding. This is a very delicate procedure since imperfections in the bonding could lead to water intrusion. Photos of the thermal bonding procedure are provided. Below are briefly described some details in the execution of thermal bonding and Construction Quality Assurance (CQA).

Methods to check the quality of work

• There is a very thin copper wire along the joining. This wire must not have contact with the air if the work is done properly. So at the two-ends of the wire a source (like a battery) is installed. If there is a point were the wire comes in contact with air, then a sparkle comes out and the spot is indicated to restore it.
• A pump presses air between the bonds. If the air pressure falls, this mean that in a place the textiles are not bonded perfectly.

Materials 

In the specific site, three kind of geosynthetics were used (check the photo above) forming a "geocomposite":

• In the outside, in contact with the concrete a tough plastic was used for the protection of the other two PVC (dark green) typically called Geoglass.
• In the middle, a white colored geotextile (Polyfond type) is used to protect the geomembrane.
• On the top, a geomembrane (yellow), is used as a hydraulic barrier.