In building construction, you build into a transparent medium, namely the air. This is naturally not the case in civil engineering and, of course, explorations of the subsoil are carried out prior to civil engineering measures. These can be, for example, so-called trenches, small excavations that are used, for example, to locate or confirm the position of pipes, or soundings with pile-driving probes or drilling equipment. Ultimately, however, these are always spot checks that only provide limited information about the situation between these exploration points. In the intermediate areas, deviating and unexpected situations are regularly encountered.

The list of lurking difficulties is long, starting with pipelines that are not included in any plans, pipelines that are located in a different place than expected or have been laid too high with too little cover, pipelines of unknown owners/operators that are sometimes difficult to identify. Particularly in inner-city areas, there are often unknown and unrecorded cellar vaults that have been built into the public space, or even larger remains of building rubble or concrete. In an old city like Bonn with an eventful history, archaeologically significant relics are also regularly encountered, which require appropriate construction supervision by specialist offices, which is often very time-consuming.

In large parts of the city area, bombs were dropped during the Second World War, which today lead to unexploded ordnance being found underground. Suspected areas must be sampled by the Explosive Ordnance Disposal Service prior to the actual construction work and any finds must be defused, which can lead to delays.

However, natural causes also repeatedly lead to difficulties and obstructions in the construction process, such as boulders, which are individual large stones, or deposits of exceptionally hard rock such as basalt. Changing ground conditions in sometimes confined spaces can also become a problem. The shoring of excavation pits - as the lateral support of pits is called, which prevents soil from falling into the pit - is always adapted to the respective looseness of the soil. If the homogenous area changes during the excavation of a sewer trench, for example, this can lead to problems and delays in the construction process.

The weather can also have an influence on measures. Heat, frost or precipitation can hinder the safe installation of certain construction materials or even make it technically impossible. Unusually high water levels in watercourses can lead to changes in groundwater levels and corresponding influences on construction work, particularly on neighboring properties.

What are the consequences of these difficulties? First of all, any additional work performed by the construction company must be remunerated. If, for example, pipes have to be relocated, the construction company is of course entitled to remuneration. If - because it was not foreseeable - the services involved are not included in the specifications, i.e. no price was offered, a price must be negotiated that is no longer subject to full competition and is therefore often less favorable.

This usually results in an extension of the construction period. This also leads to costs, as the construction company has calculated a certain period of time for the service, e.g. "construction of a trench 50 m long, 3 m deep and 1.0 meter wide". If this period is now exceeded, the so-called overhead costs, i.e. costs for equipment rental or barrier material, for example, are undercovered because costs are incurred for the same service over a longer period. As the building ground risk is the responsibility of the client, i.e. the city, it has to bear the costs. So the saying "time is money" really does apply here.

Overall, delays in civil engineering are highly unsatisfactory both for the client, the city, and for the directly affected residents and people who are restricted in their use of the traffic area. As reputable construction companies earn money by providing construction services and not by standing still, it can generally be assumed that construction work will be carried out as quickly as possible so that a new contract can be executed as soon as possible. If this is not successful, there are reasons for this, such as those mentioned above.

Another aspect should not be neglected: Civil engineering is not an end in itself. The Civil Engineering Department does not carry out construction work because it enjoys building, but to create and maintain the urban infrastructure that serves all residents of the city. It should be understandable that this cannot be done without disruption, especially in the city center.

In addition, the civil engineering department always specifies the "gentlest" construction method, for example by using trenchless construction methods, and also specifies construction times that are as conflict-free as possible (e.g. summer vacations). This is based on an overall economic consideration and not just the economic efficiency for the city or the contractor. More expensive construction methods are also used so as not to place an undue burden on road users.

Last but not least, one decisive factor should also be pointed out: people. The shortage of skilled workers is omnipresent these days. This is particularly true of the technical professions. A shortage of personnel who ultimately have to carry out all these measures - both on the municipal side and on the side of the contractors - has a sensitive impact on the factors mentioned above.

In summary, the following can be stated for civil engineering measures: The Civil Engineering Department of the City of Bonn builds for you!