Cities and urban areas around the world are continuously being modernized with infrastructures developed to match increasing traffic flows. As a result, tunneling projects are moving into more challenging conditions such as soil, weak rock and shallow overburden in already developed areas. No matter what challenges a tunneling project is facing, compromises can never be made on safety and economical efficiency. This calls for innovative and reliable methods of ground support.
Settlements from excavation
Tunnel excavation causes stress to the ground that may result in settlements. The effect of settlements is hazardous not only to nearby buildings and structures but also to the people working inside the tunnel. The answer to these challenges is pre-support, a method of pre-reinforcing the formation ahead of the tunnel face to ensure that the excavation can proceed safely until heavier and permanent support structures have been installed.
Pre-support increases stability
Over the last decades, technical developments have led to increased use of different pre-support technologies preventing unwanted accidents and protecting surrounding structures from damage. Some of these methods, such as freezing and jet grouting, are known as both costly and time-consuming, while the method known as pipe roofing is becoming increasingly popular with many economical advantages. The experience gained from several tunnel projects indicates that the pipe roof support method not only increases the stability of the tunnel itself as well as the working face but also significantly decreases the subsidence induced by the excavation. The popularity of this pre-support method has led to many different names. You might recognize it as Umbrella, umbrella arch, Tube umbrella, pipe canopy, fore poling, or pipe roofing.
The principles of pipe roofing
In implementing the method, steel pipes are installed ahead of the tunnel face and arranged like an umbrella or canopy around the excavation line. The umbrella stabilizes and protects the ceiling and face of the tunnel by increasing the load-bearing capacity of the ground. Thanks to the rigidity of the steel pipes, the distribution of loads will be improved and the critical spot will be moved further ahead of the working face. The pipe roof support method is a pre-support concept widely used in conventional tunneling but has also gained interest as a support system for TBM tunnels. This method of supporting potentially unstable ground ahead of the excavation face provides a high degree of flexibility and is easily adapted to the encountered conditions.
Cost-efficient and easy to adapt
Requiring only standard equipment and little training of your operator crew, your investment in employing special machinery or contractors is notably reduced.
By reinforcing the ground ahead of the excavation, the ground is never without support. This means that the installation of regular tunnel support can be carried out more effectively and with increased safety for the operators.
Using the same principles, installation method, and equipment, perforated PVC and steel pipes can be installed for drainage purposes, bringing added value in controlling the groundwater, especially in extreme conditions.
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