Pipe Roofing
Settlements from excavation
Tunnel excavation causes stress to the ground that may result in settlements. To address these challenges, pre-support is used, 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
Technical developments have led to an increase in different pre-support technologies, preventing unwanted accidents and protecting surrounding structures from damage. Some methods, such as freezing and jet grouting, are recognized as both cost and time consuming, while the method known as pipe roofing has become increasingly popular because of its many economic advantages. Experience gained from tunnel projects indicates pipe roofing support not only increases the stability of the tunnel itself as well as the working face, but also significantly decreases subsidence induced by the excavation. The popularity of this pre-support method has led to many different names: umbrella, umbrella arch, tube umbrella, pipe canopy, fore poling, or pipe roofing.
The Symmetrix system components
– A pilot bit drills the center part of the hole and transfers the impact energy to the ring bit.
– A ring bit set, which is an integrated ring bit and casing shoe, welded to the front of first pipe, known as the starter pipe. The ring bit, which is connected to the pilot bit through locking mechanism, drills the void needed to advance the pipe into the ground simultaneous to drilling.
A COMPLETE PIPE ROOFING PACKAGE FROM Sigricare
Straightness
In pipe roofing applications, maintaining straightness is crucial from both design and economic perspectives. The Symmetrix system, with its centric design and smooth drilling process, has demonstrated a consistent ability to produce exceptionally straight holes.
Internal Flushing
The TerraRoc Symmetrix system is ingeniously designed to utilize a flushing medium, primarily water, to transport drill cuttings from the bit face back inside the pipes. This feature is particularly beneficial when drilling in poor or unconsolidated ground conditions, as it enables the drilling of pipes without causing any disruption to the surrounding ground.
Efficiency and Productivity
Symmetrix systems can drill at high speed in virtually any ground. Customers can rest assured that the pipes will be installed successfully and efficiently independent of the encountered ground formation. The easiness to unlock and lock the pilot bit from the ring bit set also adds to the high productivity offered by the Symmetrix system.
Less Torque
The Symmetrix systems advances the pipes by impact energy simultaneously to drilling a hole slightly larger than the outer diameter of the pipes. This means, the pipe is not rotated while drilling, requiring less torque than alternative solutions. Customers can thereby utilize relatively small drilling rigs.
Pipe Roof System – range
Sigricare offers systems with pipe diameters ranging from 76.1 to 139.7 mm and wall thickness ranging from 6.3 to 10.0 mm.
Pipe quality and steel grade
Pipes or casings in the TerraRoc Pipe Roof standard assortment are made of high-quality, first-hand steel pipes longitudinally welded with removed welding seam. This ensures a completely round shape and good straightness along the pipe. Steel grade and other characteristics are shown in below table.
Steel grade and properties
Note: Other Steel Grades can be provided upon request.
| EN 10025 | DIN 17100 | Yield min. (N/mm2) | Tensile strength (N/mm2) | Elongation min. (%) | C max | Mn max | P max | S max | Si max |
|---|---|---|---|---|---|---|---|---|---|
|
S355 |
St 52-3 |
355 |
490 – 630 |
22 |
0.2 |
1.6 |
0.035 |
0.035 |
0.55 |