TECHNICAL | WATERPROOFING/BTSYM WORKSHOP
Performance 100%
Validation Simulation 50% End of service life
Here, it is important to note that a thin geotextile
serves as a membrane protection and should not be used as a drainage layer. Depending on the quality and amount of groundwater, sintering or clogging may occur behind the geotextile which would impede the design life of the product. The membrane is then mounted, and the seams
Service life 0 years 41 years 100 years
welded. Similar to a joint, the weld may act as a weak point if it is incorrectly sealed or there is insufficient overlap. The number of joints can be reduced by using bigger sheets and it is crucial to carry out a quality check of the weld by either seam testing with compressed air or by using a vacuum bell. This then allows them to become the strongest part. The second line of defense in waterproofing is
achieved through different ways. The system can either be compartmentalised with sections being split into 150m2
zones, using control sockets or injectable Above: Graph showing
comparison of lab testing (‘Simulation’) against sampling (‘Validation’) of recent sampling of PVC membrane from 1970’s Reussport Tunnel, Switzerland
TBM excavations) and cut-and-cover tunnels.
Specific to the UK, the BS8102:2009 (Code of Practice for Protection of Below Ground Structures Against Water from the Ground) provides excellent guidelines via its Design Flowchart and additionally it also provides crucial guidance in considering both the buildability and repairability of the proposed waterproofing system.
CONSTRUCTION While designing is key in ensuring you have chosen the right system for your project, installation is just as crucial in ensuring that the system functions successfully. By showcasing some excellent photography, while passing around samples of materials she was speaking about, Sarah provided the young engineers with a step- by-step overview of how waterproofing is installed. This would provide engineers overseeing the works with an understanding of what to keep an eye out for. The installation of the tunnel lining commences with
Below:
BTSYM waterproofing workshop
PHOTO CREDIT: BTSYM
substrate preparation with the section elasticity modulus of the membrane being specified based on the evenness of the shotcrete. This is followed by installation of the drainage layer using disc fixations.
waterbars at joints. In addition to explaining the basic concepts behind waterproofing, Sarah also presented a slide pack which went through the detailing of different joint sections, covering waterproofing at cross-passages, penetration sealing systems, D-wall connections, pile head solutions, and waterbars as well. The most important component of successful
construction is a trained and confident workforce. Training of the workforce or provision of waterproofing specialists is an option provided by Sika. As engineers, to ensure quality control of the waterproofing, it is important to carefully plan the installation procedure for waterproofing systems while keeping in mind the site conditions and weather conditions. It is important to define the daily work phases. Make sure that the completed daily work phases are watertight with special focus on the seams. If the site is exposed to wind then ensure there is no wind uplift and, in general, the sheets should be protected against works being carried out on site as well as foot traffic. The workshop concluded with the topic of
innovation and here Sarah presented: SikaProof A+, which is a hybrid bonding layers that forms a dual bond with concrete, through polymer-modified cementitious bonding, thereby providing a watertight basement structure; and, SikaProof T, which is a two- layer composite membrane combined with existing single EBA sheet layer and a cement filled material layer. Site photos were then available once again to study,
showing the young engineers some truly fantastic images of works in tunnels from different countries, such as Switzerland, Italy, the United Arab Emirates, and Qatar. Overall, the workshop was an excellent start to the workshops provided by BTSYM for the 2022-23 period. The young engineers were exposed to both the design and construction, providing less experienced engineers with a good understanding of the basic concepts and more experienced engineers with resources to further explore waterproofing and understand all the different options that are available.
14 | December 2023
Initial testing
Real life site
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