Interaction of transport infrastructure with man-made hazards (accidents)
Not only natural hazards but also man-made ones, sometimes simply called accidents, can have a negative impact on transport infrastructure utilization, particularly from the availability and affordability point of views. In this section, not all accidents will be deal with, but only those with some relation to the discussed problem. Many of them, however, are the result of a combination of factors, similarly as for natural hazards.
A classic example is that of a traffic accident. In most cases, it is an isolated traffic problem. However, when there is the collision with a civil engineering structure - such as a biidge pier - the problem is more serious, as the bridge stability will need to be assessed by a structural engineer. Similarly, when the collision is with retaining structure that enables a steeper slope, a geotechnical engineer is responsible for such assessment. The question arises as to whether this type of collision should be part of the design, as one of the design situations. If so, the engineer needs to know the expected frequency of such an accident as a function of energy of the collision with the civil engineering structure. After that, the selected approach is very similar to the design for natural hazards, such as when dikes are designed for a hundred-year flood. Similarly, a civil-engineered structure can be designed for the accident causing additional loading which can be expected with a certain frequency.
In the next sections, three cases will be discussed in more detail. They focus on the decrease of potential negative impacts of subsoil contamination, crashes with animals, and finally fire.
Prevention against subsoil contamination
There are roughly two basic possibilities leading to the potential contamination of subsoil.
The first one is caused by the gradual leakage of fuel and exhaust from various vehicles - cars, trucks, trains etc. - and can be sensitive not only for motorways and railways but also for parking areas and airports. The main aim is focused on the collection of the mixture of potential contaminants with rainwater in a sealed reservoir, Figure 5.35. Subsequent cleaning will allow the discharge of water into a watercourse or its infiltration into subsoil.
For areas with a bituminous carpet or a concrete layer, the surface water will be retained by peripheral drain and subsequently carried to the reservoir by different standpipes. A sealing element on the contact of ballast or sub-ballast with subgrade is preferred for railway lines, e.g. application of geomembrane or bentonite mattresses.
The second source of potential subsoil contamination is caused by a traffic accident of the truck transporting liquid chemicals. A larger amount of liquid chemicals requires a quick solution, for which detail information about chemical composition and about composition
Figure 5.35 Retention ponds during construction and operation
Figure 5.35 (Continued)
of subsoil (ground model) are needed, e.g. particularly the groundwater level and its fluctuation and the permeability of individual layers of ground. In this respect, the BIM process is very useful, both from the position point of view and from that of ground properties. Such quick information can help to conservatively specify the depth which can be contaminated for given time, subsequently excavated and treated off place.
For a more precise approach, an estimation of individual factors influencing contaminant spreading (see Equation (4.7)) is needed. In this case, two advanced methods for the contaminant of spreading can be applied - for unsaturated ground or for seepage along preferential paths - as the subsoil is not homogeneous; it is an environment which includes different preferential paths along which seepage happens much faster (Cislerova et al., 2011).
Prevention against interaction with animals (eco ducts)
Problems associated with negative impacts of crashes of vehicles with animals are getting relatively more attention. Higher speed as well as higher transport density are decreasing the possibility of eliminating potential crashes and are causing more human and material damages, together with the subsequent impact on transport line utilization. The classical approach of constructing fences along the transport lines very often interferes with the demands of environmentalists who prefer the interconnection of both parts for the free movement of various animals. Such a solution involves the construction of communication paths either in the form of biidges or underground passages.
A culvert aqueduct was mentioned already for the diversion of water, particularly for floodwater. For the passage of animals, a new term is now preferred - eco duct. To find a cheaper solution than classical concrete aqueducts, different possibilities are proposed. In principle, they incorporate more ductile structures. For small animals such as frogs, such structures incorporate polyethylene pipes, corrugate pipes and flexible culverts. For larger animals such as red deer or bear, corrugated metal conduits are preferr ed.
For such large eco ducts, it is necessary to pay attention not only to the shape of the corrugated metal conduit (with predominant compression loading) but also to soil compaction. Soil compaction should be symmetrical, preferably at the same time from both sides. The application of soil reinforcement alongside and above conduits can decrease loading (Vanicek and Vanicek, 2008), Figure 5.36. Detailed specification for the design of different types of pipelines or corrugated metal conduits is given in special publications, e.g. Selig (1985) and Moser (2001).
Figure 5.36 Application of soil reinforcement to eliminate asymmetrical loading of corrugated metal conduits
Prevention against fire
The interaction of fir es with transport infrastructure is very sensitive for tunnels, as it can block transport for a relatively long period. Fire mostly occurs because of traffic accidents, but exceptionally as the result of spontaneous combustion of an individual vehicle.
For the transport infrastructure embankment or cut, there are better possibilities from the view of direct reaction to an incurred fire - usually quicker information, better accessibility for the fire brigade. Better possibilities also exist concerning the quick removal of the burned wreck from the main transport line. The direct technical negative impact is mainly attributed to the high temperature of fire, with questionable interaction with the road surface. There is also potential risk that the fire will spread to the surrounding environment, particularly when the vegetation is dry.
Fire is usually combined with the leakage of driving fuel, and therefore the following problems should be taken into account:
- • Outflow of bruning fuels to the drainage system, which can be after that non-functional, especially when plastic tubes are involved;
- • Outflow of burning fuels on the embankment slopes, with negative impact on protection system against surface erosion, such as vegetation or different anti-erosion mattresses, plastic or natural (e.g. coconut matting);
- • Outflow can also penetrate the ground, causing ground contamination - which should be treated in accordance with that offered in section 5.2.1.
The direct impact of fire on soil properties is discussed by Pereira et al. (2019).
Note: For reinforced slopes or reinforced retaining walls, where different geosynthetics are used, the designer usually counts with their protection by soil, at least by few centimetres. The question is if this protection can protect the geosynthetics against failure by high temperature (fire), namely in the case when the protection layer was paxtly washed away.
Briefly speaking, protection of earth structures against fire have to start in the design phase by considering the aforementioned possibilities. The design should guarantee that flammable parts will not have a chance to come into direct contact with fire/high temperature during all the construction and sendee life phases of the designed earth structure.