2 | One of a total of 28 chalice-shaped pillars in the new main station in Stuttgart
Credit/Quelle: Arnim Kilgus, Dez. 2020
2 | One of a total of 28 chalice-shaped pillars in the new main station in Stuttgart
Credit/Quelle: Arnim Kilgus, Dez. 2020
1 Tunnels under Construction
As in previous years, the STUVA also undertook a survey of current tunnelling projects in Germany at the turn of the year 2020/21. The outcome is compiled in tabular form for the month of December 2020 and subsequently assessed. The table follows up its predecessors published for the years 1978  to 2020 . Only tunnels and drain/sewer structures which possess an accessible (walk-in or crawl-in) excavated cross-section, i.e. a clear minimum diameter of 1000 mm or, including the pipe wall, a minimum cross-section of roughly 1 m2, are listed. As in previous years, small trenchless headings, which have been executed in conjunction with main drain construction, the relevant domestic connections and also pipe-jacking operations beneath rail and road facilities, are not included.
The tables for the tunnel projects under construction at the turn of the year 2020/21 are not listed in detail on account of their extent; however, data can be obtained from STUVA’s internet pages . In these tables, the numbering of the tunnel projects indicates the relationship to the data material originating from previous years. Essentially it takes the form of single or double identification letters, a two-digit sequential registration number and a two-digit annual identification number. The identification letters serve to provide a brief assessment of the planned tunnel utilisation, namely:
US⇥Underground, urban and rapid transit rail tunnels
B Main-line rail tunnels
S Road tunnels
V Line and other supply tunnels
A Drain/sewer tunnels
So Miscellaneous tunnels
GS Tunnel modernisation
The identification number US 0120 therefore refers to a tunnel project with the sequential number 1 from the underground, urban and rapid transit tunnels sector, which was included for the first time in the statistics in 2020. The above-mentioned method of identification was selected against the background that the majority of construction sites, especially those from the transportation tunnel sector, run for two or three years or even more. This method of registration has proved itself in order to avoid projects being counted twice and to identify the new construction volume that has to be included. Accordingly, Table 1 shows not only the total construction volume but also, in brackets, the construction volume newly recorded in the year under review. In addition to the details for the turn of the year 2020/21, the figures from the two previous years can also be found there for comparison.
By and large, the tunnel lists on the STUVA internet pages  provide information on the location and ultimate use of the tunnels that are included, their length and cross-sections, and also the soil conditions mainly encountered. The construction method used is explained in brief and the scheduled construction time stated. As far as possible, the clients, designers and contractors are named. Details of constructional or technical aspects of a special nature are also provided for many projects.
When comparing transportation tunnels with supply and disposal tunnels, information on the excavated volumes of the individual schemes makes it possible to estimate the actual extent of the relevant measures in a better manner than mere details relating to lengths. However, the following should be observed when comparing the excavated volume: whereas the excavated volumes for underground construction measures can be determined with certainty, the comparative value for cut-and-cover methods can only be obtained by subtracting the amount of soil required for refilling from the total excavated volume.
Table 1 | Driven length and excavated volume of tunnels under construction at the given turn of the year
Table 1 provides a picture of the overall tunnelling length under construction at the end of the year in question and the related construction volume. For the turn of the year 2020/21, Fig. 1 also contains the driven length and the excavated volume in accordance with the type of tunnel utilisation shown in graphic form.
A general comparison of the figures in Table 1 shows a slight increase in construction activity in the area of transport tunnels with a total of a good 196 km (previous year 191 km). While construction activity on tunnels for regional and long-distance railways is stagnating, tunnel construction activity in the road transport sector is once more showing an increase.
Looking at the data on the excavation volume, a comparison between the traffic tunnels on the one hand and the supply and disposal tunnels on the other hand shows a volume ratio of about 142 : 1 for a length-related ratio of 21 : 1 (cf. Fig. 1).
The question of the completeness of the data obtained from the STUVA survey from contractors and consultants is difficult to assess. In order to ensure greater reliability in this respect, the 2020/21 survey, as in previous years, again contacted the cities engaged in underground, urban and rapid transit construction activities, and also Deutsche Bahn AG. The Federal Ministry of Transport and Digital Infrastructure (BMVI) provided data for federal
trunk road tunnels . Such data is indispensable for the updating of these statistics and provides important additions and corrections. At this point, a special word of thanks goes to the Federal Ministry of Transport and Digital Infrastructure, Deutsche Bahn AG, the other authorities and clients mentioned and the architects and contractors involved, for their assistance in compiling these statistics for tunnelling projects.
In the following, the results of the survey as of December 2020 are evaluated more thoroughly in various ways in order to obtain an up-to-date overview of tunnelling in Germany.
This year, the main activities relating to inner-urban rail tunnelling (table section US) once again are taking place in Munich, where some 15.3 km of urban and underground tunnels are under construction at the turn of the year 2020/21. It should be noted that preparatory construction work is still in progress on the second main S-Bahn line and that the tunnelling work had not yet begun at the time of the survey This is followed by Stuttgart (5.4 km) and Karlsruhe (4.7 km). Further tunnel projects, each less than 3 km long, are under construction in Hamburg, Nuremberg, Frankfurt am Main and Düsseldorf.
3 | Construction methods of current German tunneling projects
The length-related proportion of underground construction methods with regard to inner-urban rail tunnel construction amounted to 21.9 km at the end of 2020, accounting for about 67% of the total national construction volume for underground, urban and rapid transit rail systems (79% the previous year). Of this total, a good 19% was accounted for by shotcreting methods (20% the previous year) and roughly 48% by shield driving (60% the previous year). Fig. 3a provides an overview of the percentages accounted for by the various tunnelling methods. In this context, the diagram in Fig. 4a shows the length-related proportion of construction methods in underground, urban and rapid transit rail construction during the last 20 years.
4 | Methods applied for transportation tunnel construction during the last 20 years, related to driven length
The main-line rail tunnels listed in table segment B largely relate to DB Netz AG tunnelling works in and around Stuttgart. Of the tunnelling projects currently being implemented (a total of 116 km), almost 51 km are accounted for by the major project “Stuttgart 21 rail hub” (Fig. 2) and some 57 km by the new Wendlingen–Ulm rail route. Further 8 km of main-line tunnels
are being constructed in conjunction with the upgraded/new Karlsruhe–Basle section. Currently, 32% of main-line tunnels are built by the conventional method, whereas tunnel boring machines (TBMs) are applied for 63% of the driven volume (please see Fig. 4b).
5 | Course of awards in tunnel construction during the last 20 years, related to driven length
Road tunnel construction (section S of the table), like the two other transportation tunnel segments, has been subject to pronounced commissioning fluctuations in recent years. This can be derived from the award curve in Fig. 5 and, above all, from the block diagram showing the length-related shares of the modes of transport in the award volume in Fig. 6. About two thirds of all road tunnels are built by underground methods (see Fig. 4c). In this connection, shotcreting predominates in the majority of cases as far as underground construction projects are concerned.
6 | Transportation tunnel construction during the last 20 years: Contract-related and length-related proportions concerning the mode of transport
In the V and A sections of the table, relating to supply and disposal tunnels, only those of larger diameter – as initially explained – are listed. The smallest cross-sections dealt with are roughly 1.0 m in diameter, the largest around 3–4 m. All supply and disposal tunnels recorded at the turn of the year are constructed underground. In the case of waste disposal tunnels, pipe-jacking continues to dominate as it has in previous years. Furthermore, in compiling drain/sewer statistics, it should be pointed out that only major collectors are featured here. The considerably greater part accounted for by drains with smaller cross-section, mostly driven close to the surface by means of cut-and-cover, is not listed here, as this is generally not classified as tunnelling.
Table 2 | Regional distribution of the transportation tunnels under construction at the turn of the year
Table 2 and Fig. 7 provide details of the regional distribution of ongoing tunnelling projects. At present 69% of the volume of tunnels being built nationally on the transportation tunnel sector is accounted for by the federal state of Baden-Württemberg.
7 | Length-related classification of transportation tunnel projects under construction according to federal states (please see Table 2), with the number of registered transportation tunnel projects given in brackets
If one compares the newly obtained driven lengths and excavated volumes at the turn of the year for transportation tunnels based on the statistics of recent years, this provides a revealing picture of just how contracts are awarded. In this connection, Fig. 5 clearly shows the important influence of the DB’s upgraded/new lines and displays the continuing fickleness on the part of public authorities in awarding new tunnelling contracts. With regard to main-line tunnels, following a steep increase in awarding contracts (mainly on account of the commissioning of “blocks” for the DB upgraded/new lines) the resultant years experienced an equally pronounced dip (please refer to Fig. 6). The awards curve (Fig. 5) indicates that a minimum level of awards is currently being established again. The annual „production rate“ is thus falling to an average of about 25 km/year over the course of 20 years.
2 Planned Tunnelling Projects (Future Requirements)
The results of the survey relating to confirmed tunnel projects and those due to be awarded in the near future are naturally of special interest to the construction industry and consultants. Table 3 shows the commissioning period starting in 2021.
Table 3 | Driven length and excavated volume of the tunnels projected at the turn of the year (future requirement)
Examination of the data in Table 3 clearly indicates that the planning volume for transportation tunnels remains at a high level. A slight increase in the planning volume compared to the previous year can be observed for underground, urban and rapid transit tunnels.
Among the listed projects, Hamburg takes the lead with a good 44 km of planned tunnelling, ahead of Munich with a good 42 km. Leipzig is engaged in pre-planning 7 km and Frankfurt am Main is planning around 6 km of tunnel for regional transport. Further tunnelling activities involving less than 3 km are foreseen in the cities of Berlin, Dortmund and Stuttgart.
The planned volume of main-line rail tunnels has increased again in comparison to the previous year. Approx. 30 % of the volume is accounted for by the new/upgraded Leipzig–Prague rail line (approx. 27 km). A further 23 km is accounted for by tunnels already approved as part of the new/upgraded Karlsruhe–Basel rail line. Further tunnels are planned in the course of the new Rhine/Main–Rhine/Neckar line (18 km), the Nuremberg–Fürth rail line (8 km), the new/upgraded line Nuremberg–Marktreditz (6 km) and the Siegen–Hagen rail line.
Compared to the previous year, the planned volume of projected road tunnels has decreased moderately again – on account of the German state’s revamped planning requirements, the scheduled volume had already dipped considerably in previous years.
The roughly 109 km of planned road tunnels listed in Table 3 have at least generally reached the planning approval stage. This applies principally to the tunnels on federal trunk roads, i.e. those for whose construction the federal government is responsible.
Technical details relating to the tunnels contained in Table 3 are available from the relevant detailed tables . Essentially, these are structured in the same manner as the statistics on tunnel projects which are in the process of implementation, as presented in section 1. The same approach was selected to identify and differentiate the individual tunnel projects. However, the letter “Z” has been added to make quite clear that the tunnel construction scheme in question is a “future” one. As a consequence, no details are provided concerning the responsible construction companies, whereas these can be found in the statistics on current tunnel projects.
Generally speaking, as far as assessing the detailed data relating to future tunnel projects is concerned, it must be observed that alterations can occur during the planning approval and award stages, above all, due to special proposals, relating primarily to the tunnelling method. Various clients have expressly pointed this out. Alterations can of course, also result with respect to the probable starting and completion dates for projects.
It is also of interest for the construction industry and the consultants involved to be aware of the regions for which implementation of the planned tunnel projects is mainly scheduled. Table 4 and Fig. 8 show the relevant details, categorised by federal states.
Table 4 | Regional distribution of the transportation tunnels projected at the turn of the year (future requirement)
8 | Length-related classification of planned transportation tunnels according to federal states (please see Table 4), with the number of registered transportation tunnel projects given in brackets
3 Current and Future Tunnel Modernisation Plans
To an increasing extent, partial and complete refurbishing schemes are now being scheduled for old rail tunnels in the years ahead. Generally speaking, such measures call for special organisational and logistical provisions, particularly if these projects are to be implemented without causing disruption to rail traffic as such . Recent examples of this are provided by the complete renovation of the Frauenberg and Kupferheck tunnels on the Nahe valley line between Bingen and Saarbrücken as well as the Langenau and Hollerich tunnels on the Lahn valley line between Wetzlar and Niederlahnstein at Nassau. These lines were originally opened in 1860 and 1862 respectively. Over the next 20 years, a further 91 tunnels totalling almost 51 km in length will be comprehensively modernised in addition to the around 5 km already being tackled.
Refurbishing measures are becoming more essential for road tunnels as well, on the one hand to preserve the basic substance and on the other hand to meet the changed operational and safety requirements. This can e.g. involve replacing the concrete for the inner lining or subsequently adding an evacuation or rescue tunnel . At the time of the survey, roughly 4 km of road tunnels were in the process of being redeveloped or retrofitted. A comprehensive modernisation of a further 9 km or so of road tunnels is currently planned. Details on ongoing renovation schemes are compiled in the table section “GS” or “ZGS” relating to scheduled renovations .