Underground service galleries offer a solution to the chaos of services existing beneath the streets of our cities. Nevertheless, the limitations imposed by the regulations of the services make their use technically impossible for all of them, reducing their usefulness.
In response to this tendency, underground buildings offer an intermediate situation between the continuous gallery and trench installation, permitting the registration and control of the key points of service networks without the need for work to be done along their whole length. Therefore the main advantages compared to galleries are:
- Much lower cost: The costs of a continuous gallery are high, maintenance costs being especially so, as they are not taken on by the service companies.
- Ease of construction: The installation of a continuous gallery involves the excavation of the whole road under which it is to be installed, with the resulting inconvenience and complications arising from land containment, effects on nearby foundations, etc. However, the installation of prefabricated underground buildings is extremely fast, with a temporary, isolated excavation which has far less affect on the environment.
- Watertightness and waterproofing: The watertightness requirements of visitable enclosures raise long term problems in galleries made using prefabricated frames. Joint sealing systems are very sensitive to relative movements between modules, necessitating continuous maintenance in those zones with differential settlements. Moreover, the appearance of water leaks in a gallery in use is difficult to solve, involving high costs. In contrast, prefabricated underground buildings are completely watertight, as guaranteed by the immersion tests.
- Control of access: Galleries present a public safety problem because of the difficulty of control of access and use of the installation, which has several entry or exit points. On the other hand, underground buildings are completely independent, without any possibility of this incorrect use of the building.