System Selection: Tanking and Underground Works

The reasons for tanking and cut and cover trenches solutions

Preventing the ingress of water or damp into underground premises is a problem often faced by building contractors. It needs to be taken into consideration from design stage onwards. The concerns are all the more complex as there are many possible sources of unwanted moisture:
The water table, whose level may vary ( rainfall, or high water levels in neighbouring water courses), causing water to rise above the lowest level of the building underground.
Groundwater runoff against or infiltration into the outer walls of the underground part of buildings. In mountainous regions in particular, underground sources of water can project massive quantities of water against the outer walls of buildings, both above and below ground.
Damp capillary rise, which can lead to water rising up walls up to the level of the residential quarters of a building when in contact with and under the pressure of water-laden soil.
Wind-blown rain on building facades, which can penetrate through the walls and, depending on the building structure, reach the inner surfaces of underground walls under the force of gravity or by capillary attraction.
Condensation of the water vapour contained in moist air in contact with walls that are cold (because insufficiently insulated), in rooms or premises that are insufficiently ventilated.
These situations can be remedied by adequate waterproofing or water-protection systems.
Siplast-Icopal guide proposes definitions of the technical solutions potentially most suitable to each of the above situations.

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Performance requirements

The protection of underground walls against the action of water is a complex matter in design terms. This is because there are many possible sources of water, and many factors liable to play a part in the choice of the right solution. Among these are the hydraulics of underground water, nature of soil, type of foundations, nature and thickness of walls, the intended and actual use of the building interior These factors play a major role in the determination of the type of outer coating required and the associated construction techniques. Many persons are involved and play a critical role.
Among those concerned are:
-Building or project Owner, who must define the nature of the construction and requirements in respect of the presence or absence of damp, and the degree of reliability sought in protection against it.
-The main contractor who is required to determine the nature of the foundation soil and degree of exposure of the building to groundwater, in the light of the known levels of high water, topographical environment and climate.
-The specialised sub-contractor who either alone, or with the main contractor, makes the choice of types of walls.

All these criteria interact. Consequently, the proper protection of underground walls involves the input of skills from all these areas

Tanking Solutions

Tanking with waterproof coating
The waterproof coating consists of an inner film or waterproof coat adhering to its substarate, without any notable resistance to cracking in that substrate. The protective coating is made of water-repellent water or resin-based film coating, or by a mineral-based surface application.
Tanking surrounds the whole of the perimeter of the building directly in contact with groundwater and the connected adjacent inner portions, known as returns. In most cases a topcoat is applied to the tanking coat.
The technical rules governing the design calculation of the structural work (including outer perimeter and possibly returns) are usually determined in local standards.
Tanking with partial waterproofing
Tanking of this kind does not require the application any coating or rendering over it. Accordingly, a degree of permeability to water seepage through the walls is acceptable.
The conditions of use of the premises should make allowance for this partial degree of waterproofing of the building perimeter. Hence facilities should be provided to collect seepage water, provide ventilation etc.
The technical rules for the design and calculation of the structural work in this layout are usually determined in local standards.
Tanking with waterproofing membrane:
The tanking is performed with the Teranap TP Tanking System, a comprehensive system featuring Teranap 431TP,elastomeric bitumen extra wide (2 m or 4 m wide) geomembrane, Parafor M3S covering strip on overlaps and Terasop waterbar for compartmentalization.
The double protection of Teranap 431TP by polyester film surfacing and thick polyester reinforcement allows for looselaid application to the outer surfaces of the structure, withstanding permanent water pressure (up to 7 bars).

Underground solutions

The development of underground works and cut-&-cover trenches responds to the objective of integrating roads more fully into their environment and reducing unpleasant phenomena The solution: the prefabricated membranes.
These membranes combine the advantages of traditional materials like bituminous binders with the advantages of modern materials, in particular, polymers and geotextiles.
Factory-made with rigorous industrial processes, these elastomeric bitumen membranes possess optimised and homogeneous physical and mechanical characteristics. The association of its two components, reinforcement and specific binder, give it complementary performances:
The reinforcement withstands mechanical stresses such as the tensile forces induced by movements and any cracks in the wearing course or in the deck slabs, along with any elongation induced by phenomena of thermal origin or circumscribed forces generated by the traffic.
The binder ensures waterproofing: its considerable elasticity enables it to go along with the movements of the reinforcement without losing its properties. Moreover, its elastic spring back enables it to accommodate the alternating movements of concrete cracks.

Siplast elastomeric bitumen Teranap TP geomembranes provide:
- Excellent resistance to ageing of the Teranap TP geomembrane due to the elastomeric bitumen compound enabling the material to retain its elasticity for extensive periods.
- Teranap TP is highly resistant to puncturing due to its double protection by polyester film surfacing and a thick polyester fabric reinforcement
- The elastomeric bitumen compound of Teranap TP makes the application easier by torching for anchoring and joining works to concrete structures.

Siplast elastomeric bitumen Parafor Pont membranes provide:
Fully-bonded elastomeric bitumen single-layer system for direct application of the overlaid wearing course
Waterproofing of slabs used to cap 'cut & cover' trenches
Speed of application
Allows light jobsite traffic of vehicles, particularly for the laying of the wearing course