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Guideline 836.4107 – Building in water protection areas

1. Scope and principles

The guideline "836.4107 Construction in water protection areas" is a continuation of the previously applicable regulation "836.0509 Water protection and soil protection". The new guideline takes into account the advancing state of the art and the further developed legal basis. Thematically, this guideline is related to guideline "836 Planning, constructing and maintaining earthworks and other structures".

The module is to be applied to the construction and upgrading of railway lines in water protection areas. It serves to protect water and soil from harmful contamination that may occur as a result of scheduled rail traffic and accidents. This guideline is necessary because special considerations that are not covered by general regulations must be taken into account in the construction and operation of rail transport facilities. This also applies to the upgrading of railway lines, especially in water protection areas.

The guideline is an internal DB Netz regulation and supplements federal and state water laws. The aim of all regulations is to protect all water bodies from harmful effects. The catchment areas of public water extraction facilities, drinking water reservoirs and state-approved mineral springs are subject to special protection. This special protection is reflected in the designation of water protection areas. This is determined on the basis of the Water Resources Act (WHG) and the respective state water protection ordinance.

Water protection areas (according to WHG) are divided into different zones:

Zone 1 describes the catchment area of the drinking water extraction point. Zone 2 is the inner protection zone and Zone 3 is the outer protection zone. Depending on the location and extent, Zone 3 can be further subdivided into Zone 3 A as the inner area and Zone 3 B as the outer area.

2. Hazards to water bodies

The railway transport system can pose various threats to groundwater. These include, in particular, the construction of railway transport facilities and the building materials used in this process. The same applies to maintenance and repair work. In addition, railway traffic itself can pose threats to the subsoil and groundwater.

The hazards posed by rail transport can be differentiated in terms of their duration and frequency of occurrence as follows:

• permanent impacts (e.g. train traffic)
• temporary impacts (e.g. construction sites)
• exceptional impacts (e.g. daily events, accidents)

There are numerous sources of pollutants that pose a potential hazard. However, not all of these sources have to occur at the same time, and their effects can also vary.

The most common sources of pollution are listed in the figure below:

In addition to the source of pollution, the potential hazard that can be derived from it is also significant. This depends on various factors. Above all, the volume of traffic plays a major role. A less frequented line with exclusively passenger traffic normally poses a significantly lower risk than a heavily used mixed-traffic line with trains travelling at widely varying speeds. It also matters whether the route section is open track or whether it is a shunting yard or storage area for rail vehicles.

The extent to which groundwater may be at risk is also influenced by hydrogeological conditions. The permeability and thickness of the layers above the saturated soil zone play a major role here. The lower the permeability and the greater the thickness, the greater the protective effect of these overlying layers.

The aforementioned aspects ultimately determine the protective and sealing measures to be taken.

3. Protective and sealing measures

A three-stage classification is used for this purpose. This classification is analogous to the regulations for road construction (RiStWag) with the structure Stage 1 (soil/technology), Stage 2 (technology/soil) and Stage 3 (technology).

Classification depending on the protection requirement and the protection zone:

• Level 1: no concentrated seepage
• Level 2a: Avoidance of infiltration, drainage pipes without special measures
  (protective layer made of KG 1, water drainage with appropriate drainage systems)
• Level 2b: Avoidance of infiltration, largely impermeable drainage pipes
  (protective layer made of KG 1, targeted water drainage with largely impermeable drainage systems)
• Stage 3a: Prevention of infiltration without measures on cut slopes
• Stage 3b: Prevention of seepage with measures on cut slopes

A matrix linking track load (potential hazard), the protective effect of groundwater cover and water protection zones (legal requirements) can be used to determine the level of protection required.

The appropriate protection and sealing measures must then be implemented in relation to the local conditions of the track section in question within the water protection area. The following overview clearly shows that various measures are absolutely necessary, unnecessary or not applicable (because they are insufficient).

4. Planning examples

Here are a few planning examples:

Example 1 – Mineral sealing (level 2a) – Key design features:

• Consisting of KG 1 material (low water permeability)
• Thickness is determined by the design of the protective layer system in accordance with Module 4101 (minimum thickness 20 cm)
• Protective layer made of KG 1 over separating and filter element in accordance with AF 3.4 of DBS 918 039 on the subgrade
• for multi-layer structures via KG 2
• Compaction degree of D_Pr ≥ 1.0
• Water permeability of k_f ≤ 1×10^-6 m/s
• No covering required

Below are images (source: GEPRO/Dresden) of the installation of a mineral protective layer:

Example 2 – Mineral waterproofing (level 3a) – Principles:

• Only in the edge area outside the outer pressure area according to Module 836.2001
• Possible: ZFSV – temporarily flowable self-compacting backfill materials (= liquid soil), in particular as dense pipe supports, with proof of erosion resistance and greening, also suitable for embankments
• Can be economical and sensible as a qualified soil improvement for sufficient reduction of permeability in the case of cohesive soils
• Compaction degree of D_Pr ≥ 1.0
• Minimum thickness of 40 cm
• Covered with at least 40 cm of soil (or, above the qualified soil improvement, a 30 cm protective layer KG 1)• Layer structure in accordance with RiStWag / ZTV E-StB 09
• Object-specific verification of low water permeability of k_f ≤ 1×10^-7 m/s as part of a suitability test

Note: not yet in regular practical implementation.

Example 3 – Plastic sealing membrane – KDB – (Level 3a) – Principles:

• Dimensioning of the protective layer system in accordance with Module 836.4101
• KDB in accordance with application case 3.12 of DBS 918 039 with valid HPQ
• in conjunction with protective non-woven fabric according to application case 3.13 below and above KDB
• below the KDB, as an alternative to protective fleece, a water-permeable layer of sand or gravel sand at least 10 cm thick
• Covering of the KDB with a protective layer of KG 1 or KG 2 at least 20 cm thick

Between 2011 and 2015, several excavations were carried out at various locations in the DB Netz AG rail network to examine the condition of the plastic sealing membranes installed there after 15–20 years of use. The results of all investigations confirmed that the materials used were in almost new condition.

Example 4 – Geosynthetic clay liner – GTD – (Level 3a) – Principles:

• Design of the protective layer system in accordance with Module 836.4101
• GTD in accordance with application case 3.11 of DBS 918 039 with valid HPQ
• without additional protective nonwovens
• under fixed track only in the edge area
• Coverage at least 30 cm KG 1
• The laying surface must be free of sharp objects and individual grains > 3 cm
• with additional protective layer under the GTD use of round-grained material with a maximum grain size of 32 mm

Note: no use of hydraulic binders above and below the GTD

During the excavation of geosynthetic clay liners, a very good state of preservation with almost no signs of ageing was also found. There is nothing to prevent their use for further decades.

5. Overview of planned changes, effects

In principle, cost changes arise from:

• the requirement or elimination of case-specific approvals with UiG by DB Netz headquarters and with ZiE by the Federal Railway Authority (EBA)
• the designation of new protective measures as alternative construction methods
• the reduction of the necessary structural protection measures by taking into account the actual route-specific protection requirements, and
• modification of construction methods, in particular by reducing the layer structure.

6. Conclusion

Updating the guideline module increases safety in the planning of sealing measures.

On the one hand, the risk of planning errors is reduced and the time required for planning and construction preparation is shortened. On the other hand, it is to be expected that fewer additional requirements will be imposed by authorities if reference can be made to a currently valid set of rules.

As a result, construction costs and construction cost risks can be significantly reduced.

Standards / regulations

• Water Resources Act (Act on the Regulation of Water Resources; Water Resources Act – WHG, last revised on 31 July 2009, Federal Law Gazette I p. 2585; last amended by Art. 2 G of 4 December 2018 I 2254, 2255, Federal Law Gazette 2018 Part I No. 43, issued in Bonn on 11 December 2018)
• FGSV Forschungsgesellschaft für Straßen- und Verkehrswesen e. V. (Road and Transportation Research Association); Earthworks and Foundation Engineering Working Group; RiStWag 16 – Guidelines for Structural Engineering Measures on Roads in Water Protection Areas, 2016 edition, Cologne 2016
• FGSV Research Association for Road and Traffic Engineering; Earthworks and Foundation Engineering Working Group; ZTV E-StB 09, Additional Technical Contract Conditions and Guidelines for Earthworks in Road Construction, 2009 edition, Cologne 2009