9 Type B (structurally integral) protection
NOTE For water and water vapour resistance, Type 8 protection relies upon the design and the materials incorporated into the external shell of the structure itself.
Schematic illustrations of Type B protection are given in Figure 2b).
Structures providing Type B protection should be constructed of reinforced concrete or structural steel and designed in accordance with the relevant part of BS EN 1992 or BS EN 1993 respectively.
Concrete structures containing a waterproof admixture should be considered as having a lower degree of water/vapour transmission when the design of the concrete mix and casting of the structure is adequately supervised and the admixture is assessed and certified (see 22.214.171.124).
Service entries are particularly vulnerable to water penetration; where they cannot be avoided, they should be carefully detailed, incorporating sealing, to minimize the risk of water ingress.
9.2 Materials for structurally integral protection
NOTE 1 Reinforced concrete structures may be designed and detailed specifically to minimize water ingress with no additional protective measures. Concretes meeting minimum design requirements for structural use and durability in the ground, and properly placed and compacted, are likely to have good resistance to the transmission of water in liquid form. A degree of resistance to water vapour transmission is also achieved dependent on section thickness.
The pattern of any seepage encountered is often associated with poor joints, cracks or other discontinuities such as service penetrations.
The following factors are considered as being of particular importance in achieving a water-resistant concrete structure and thus should be taken into account:
- a) the design of the structure (general and detailed), and the specification of materials;
- b) the quality of workmanship in preparing and placing concrete;
- c) curing;
- d) site organization;
- e) the condition of the formation, i.e. the formation should be clean with no running water;
- f) material storage;
- g) the close-fitting of formwork, the fixing of reinforcement(s) and the preparation of joints.
Crack widths in concrete should be controlled by using the appropriate design, mix specification, detailing, construction supervision and curing (especially in relation to temperature).
NOTE 2 For guidance on limiting crack widths, see BS EN 1992 and CIRIA publication C660 .
The effects of residual moisture ingress (water or water vapour) may be minimized by the provision of appropriate internal environmental design and control mechanisms.
When selecting applied internal finishes, advice should be sought from the manufacturer. Moisture content and relative humidity should also be considered in accordance with BS 8204-1.
126.96.36.199 Reinforced and prestressed concrete (in-situ or precast)
Structures in reinforced or prestressed concrete should be designed and constructed in accordance with BS EN 1992.
188.8.131.52 Concrete containing waterproofing admixtures
COMMENTARY ON 184.108.40.206
There is a range of products, generally categorized as waterproofing admixtures, which seek different ways to increase the inherent resistance of concrete to water and water vapour. As the mechanisms used by each product to achieve these aims are quite diverse, it is not possible in this British Standard to give specific guidance on their use.
Waterproofing admixtures are specified in BS EN 934.
Manufacturers should be consulted as to the performance of a specific waterproofing admixture in reducing the risk of water penetration through a crack, possibly under considerable hydrostatic pressure. Potential seepage locations, such as penetrations and joints, would typically be addressed by design (e.g. waterstops; see 220.127.116.11).
Where the waterproofing admixture has been assessed and certified by a UKAS-accredited body or a European Technical Approval body, certification information should be referred to for guidance on use and the extent or limitation of technical benefit.
Waterproofing admixtures should be used in conjunction with other waterproofing components supplied by the same manufacturer, e.g. waterstops, sealants.
COMMENTARY ON 18.104.22.168
The principal types of waterstops can be classified as the following.
- a) Passive sections:
- 1) rubber or flexible polyvinyl chloride (PVC) extruded profiles cast into the concrete on both sides of the joint, either at the concrete surface or mid-depth of the concrete section, to form a physical obstruction to water transmission;
- 2) steel water bar strips placed mid-depth of the concrete section to form a physical obstruction to water transmission.
- b) Active or hydrophilic strips or crystallization slurries:
- 1) preformed profiles of materials or sealant composition applied to the concrete joint at depth in the section. The materials swell or give rise to crystal growth on contact with water providing an enhanced obstruction. They can used as a sole material or in a composite product with passive waterstop sections;
- 2) post-injected systems.
- c) Permeable hose or other sections that are fixed to the construction joint surface before casting the second pour, to facilitate the injection of a specialist sealing resin into the joint, when required.
Waterstops should be used to provide enhanced resistance to water transmission at joints in the concrete structure, e.g. at construction or day-work joints, services or other penetrations (see Figure 2). The positioning of the waterstop(s) (external and/or internal) should be appropriate for the method of construction and the level of risk. Particular attention should be given to the use of waterstops at movement joints (see 8.1.3).
The specifier should be satisfied that waterstops have been tested and certified for the application, service conditions and groundwater chemistry proposed.
Where centre-bulb waterstops are used, robust methods of fixing should be used to keep the components in place during concreting operations. Correct orientation should be provided to facilitate adequate compaction of the concrete around any internal components and to avoid creating paths for subsequent water ingress.
Steel piles in either sheet or tubular form may be used as the permanent structural wall in cases where the pile clutch interlock system between individual sections can be adequately sealed. Soldier piles formed from H or I sections may also be used with suitable lagging.
Steel structures should be designed and constructed in accordance with BS EN 1993-5.
Sections should be formed of structural steel of a weldable grade conforming to the following standards, as relevant:
- a) BS EN 10248 for hot rolled steel sheet piles;
- b) BS EN 10249 for cold formed steel sheet piles;
- c) BS EN 10210 for hot finished hollow sections; or
- d) BS EN 10219 for cold finished hollow sections.
NOTE BS EN 10248 also covers special interlock sections, which are produced to allow hollow sections to be connected together or to intermediate sheet piles.
9.3 Embedded retaining walls
Construction for deep structures may be either top down or bottom up, or a combination thereof. The construction method should, as dictated by the ground conditions and site constraints (including the proximity of buildings on adjacent sites), determine the use and type of embedded piled walls, which may be of concrete or steel pile, or diaphragm walls.
For all types of embedded retaining wall, the requirements for water resistance should be clearly specified, e.g. by using the ICE's Specification for piling and embedded retaining walls  or equivalent guidance. In particular, the acceptability of running or dripping water (seepage) and the extent to which any damp areas are tolerable should be considered and specified, as appropriate for the required grade of waterproofing protection (see 6.2.3).
NOTE 1 Embedded retaining walls provide a degree of integral protection, although the number of joints and difficulties controlling their construction can lead to a risk of a greater quantity of water penetration, compared with a cast in form wall, and this needs to be allowed for in the overall design strategy.
For all embedded retaining walls, whether concrete or steel, the joint between the base slab and the wall should be precisely detailed to achieve structural continuity consistent with the design. This junction should be viewed as a three-dimensional arrangement (see also 4.3.1), such that all potential water paths can be identified and detailed. The joint should be carefully detailed and waterstops should be attached to, and follow, the profile of the wall in accordance with the manufacturer's instructions.
NOTE 2 Grouting tubes may also be installed within a clean flush joint so that remedial grouting can be undertaken, if necessary. Attempts to install grout tubes that maintain intimate contact with convoluted joints might be unsuccessful; in this situation, a hydrophilic strip bonded to the joint with adhesive might be more suitable (see also Clause 11).
9.3.2 Concrete retaining walls
Piled and diaphragm retaining walls should conform to the general requirements of BS EN 1992.
NOTE 1 The water penetration through well-formed walls using these techniques is normally limited to, and controlled by, the vertical joints rather than the flow through the concrete elements and there is thus little benefit in designing concrete piled and diaphragm walls in accordance with the higher tightness classes specified in BS EN 1992-3.
Where secant pile retaining walls are used, specialist advice should be obtained as to the appropriate system and construction method for the project.
NOTE 2 The joints between diaphragm wall panels can be enhanced by the incorporation of water bars, where the performance requirements justify it. Such water bars can be effective at restricting water ingress via transverse flow through the wall section but further attention might be necessary to deal with water flowing up the wall joints inboard of the water bar location.
9.3.3 Steel retaining walls
The performance level of water tightness should be specified. This may be achieved by the application of an appropriate sealing system(s) to the clutch interlocks, using one of the following systems:
- a) active (hydrophilic) systems, pre-applied or, if essential, applied under shelter and tightly controlled conditions on site; or
- b) passive (hot-installed bituminous product) systems; or
- c) welded clutches.
The system selected should be able to provide the specified performance and be consistent with the method of installing the piles.
The manufacturer's instructions should be followed to achieve the necessary resistance to seepage.
NOTE 1 In some instances, welded clutches might be used in addition to the systems specified in a) and b).
For integral protection, sheet pile interlocks should be welded or sealed with a hydrophilic material in accordance with BS EN 12063. Sealing welds along the interlock should be capable of accommodating any movement that might take place. The welding process should be selected to suit the environment to which the welds are exposed and the site conditions in which welding occurs.
NOTE 2 Steel sheet pile interlocks can be seal-welded after installation to provide watertight structural walls.
The connection to the base slab should cater for any uplift forces in addition to providing a robust barrier to water ingress. Horizontal sealants should be provided at the junction between the base slab and the perimeter wall using active or passive methods.
Where possible, sheet piles should be shop-welded and subsequently driven in sets of two or three, thus reducing the extent of site welding required. If welding is undertaken on site, only the exposed length of the sheet piles is treated. Appropriate working conditions need to be provided and the piles should be driven within acceptable deviations to form the joint.
NOTE 3 Failure to prepare the surfaces appropriately increases the risk of porosity in the welds, with reduction in the degree of water resistance over time.
NOTE 4 Guidance on welding is given in BS EN 1011 and BS EN ISO 15614-1. Further guidance is also given in the ICE's Specification for piling and embedded retaining walls  and BS EN 1993-5.