Contiguous piling & diaphragm walls
The use of contiguous / secant piling and diaphragm wall construction techniques to construct retaining walls is common in large commercial basement projects and often an efficient and cost-effective solution. The nature of these construction techniques is such that the only practical option is to apply waterproofing systems to the internal face of the retaining wall in order to reduce the risk of groundwater ingress between the piles.
Safeguard offers a choice of systems for waterproofing these types of basement retaining wall. These are:
- Oldroyd cavity drainage system
- Drybase Tanking Range
- A combination of these two systems
Choosing which system to use will depend on a number of factors including site conditions, drainage options, and personal preference. Typical waterproofing methods using both systems are described on this page. To discuss specific projects, contact our technical department on 01403 210204 or submit an enquiry.
Oldroyd Cavity Drainage System
Figure 1: Type C basement waterproofing system using Oldroyd Xv 20 Cavity Drainage Membrane
This system allows water to permeate through the basement retaining wall, but redirects it away from the internal wall of the basement towards a sump or other suitable discharge point. For this type of application, a cavity drainage membrane with a large stud size such as Oldroyd Xv 20 is usually preferred in order to cope with the higher potential flow rates required for larger basement projects.
This type of waterproofing system can be used on contiguous / secant piling as well as diaphragm walls. In accordance with BS 8102:2009 the structure should offer primary resistance, regulating the volume of water entering the basement, in order not to exceed the drainage capacity of the system. However, from a waterproofing perspective, contiguous piles are not, and should not be considered as a tight structure. Therefore, relying solely on the application of a cavity drainage system on the piles is not recommended.
Other suggestions on how to improve the water tightness of retaining walls can be found in the ICE publication, “Specification for Piling and Embedded Retaining Walls” [1]
Drybase Cementitious Waterproofing Slurries
Figure 2: Type A basement waterproofing system using Drybase Crystalline Active Waterproofing Slurry
When applied to concrete retaining walls, Vandex waterproofing slurries create an impervious barrier, blocking the passage of groundwater into the basement. Because the types of basement retaining wall described on this page are constructed from concrete, Drybase Crystalline Active Tanking Slurry is usually selected as the waterproofing slurry. Drybase Crystalline Active Tanking Slurry is specifically designed for the waterproofing of concrete and offers a higher coverage rate than other Drybase waterproofing slurries, making it an economic choice.
When waterproofing diaphragm walls, Drybase Crystalline Active Tanking Slurry is simply sprayed onto the internal face of the wall. When waterproofing contiguous or secant piling, the Drybase waterproofing layer is typically sandwiched between a layer of shotcrete and a poured concrete internal wall (see Figure 2)
This method of waterproofing is dependent on the strength of the underlying piles and the tolerances between them than the Oldroyd method (see Figure 1). It should only be used in conjunction with reinforced concrete as shown in the diagram above.
Combined Waterproofing System
Figure 3: Combined Type A & Type C basement waterproofing system
Combined waterproofing systems are often desirable when waterproofing basements. BS 8102:2009 “Code of practice for protection of below ground structures against water from the ground” suggests that “combined protection” should be considered where the assessed risks are deemed to be high (e.g. permanently high water table) or the consequences of failure are high. NHBC Chapter 5.4 states that where Grade 3 protection (BS 8102:2009) is required, and below ground wall retains more than 600 mm, measured from the lowest finished floor level, the waterproofing design should include a combination of two types of waterproofing systems. Therefore, Drybase and Oldroyd systems are usually combined (see Figure 3).
A wide variety of combination systems can be specified depending on the type and quality of the retaining wall. For example, in certain situations it would be possible to omit the reinforced concrete wall from the example above. For further details, please contact our technical department on 01403 210204 or submit an enquiry.
[1] “Specification for Piling and Embedded Retaining Walls 2nd edition” Institution of Civil Engineers – ISBN: 9780727733580