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ROBIT -  Pipe Roofing System / Umbrella System is a support system used in loose ground conditions in conventional and mechanized tunneling. It is used to enhance

ground properties to stabilize and reduce risk in tunnel works. It is a method of supporting tunnel by driving pipes ahead of excavation. It is also used in developing the portal sections

and for the re-excavation of collapsed sections in underground works.

Fields of Application

  • Weak Ground Structure

  • Portal Sections

  • Frequently Changing Ground Conditions

  • Re-Excavation of Collapsed Tunnels

  • Urban Tunnelling

The installation of the Pipe Roof System is simple and quick and has the following effects.

  • Reducing the ground loss by creating a boundary of stiff material between the soil and tunnel crore.​

  • Stabilizing the ground in the area of newly excavated and get unsupported excavation round.

  • Distributing loads acting upon the tunnel roof above the freshly excavated round into the in-site ground ahead of the face and the lined tunnel behind the face. Confinement of

  • the tunnel excavation area ahead of the tunnel face.

  • Enhancing tunnel face stability by reducing loads acting upon the tunnel face.

  • Reducing surface settlement.

Pipe Roofing Components

  • Starter Pipe: First Pipe Welded with Ring Bit on one end & female threading on other end, which can be perforated / non- perforated as per the design requirement.

  • Extension Pipe: Male - Female threaded pipe for extension, which can be perforated / nonperforated as per the design requirement.

  • Pilot Bit

  • Drill Rods

  • Grout Plugs / Injection Cap

Threads: Pipe have a trapezoidal thread with double start.

Sizes for Pipe Roofing System: 76.1, 88.9, 101.6, 114.3, 139.7, 159, 168.3   

Types Of Thread Connection

Standard Thread.png

Standard Thread Connection: Male and Female Threads are cut into both ends of each casing pipe. The internal pipe dia and the outer pipe dia always stays constant. To decrease risk of failure at threaded joints, designer should analyse their project requirement for bending load in the tunnel and also design staggered piperoofing system and to stagger the joints, element of 1m and 2m be used in the project. A higher wall thickness pipe be chosen for safe design and avoiding failure due to bending load at thread joints.

Nipple connection: It consists of threaded connection nipple fittings which are pressed and welded into the ends of standard pipes. This connection type provides an elastic design load as well as stiffness properties equal to an un-weakened pipe. The internal diameter of the casing tube is reduced in the threaded portion of the pipe. At the joint area of two casing pipes, there are two welded joints and one mechanical joint. Mechanically, the welding properties shows same strength as an one unit, but practically one needs to take in consideration the welding failure possibility also. Utmost care should be taken during the welding & pressing method and only welding to be done by a certified welder else it may result failure from the welded portion of the nipples on the casing.

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