There has probably never been more focus on the working environment than now. Construction sites are regularly closed down temporarily due to lack of signing, fencing, use of dangerous machinery and general lack of tidiness on the streets. Many more incidents are reported due to the focus on personal safety, but also the industry attitude and policy, that it is in fact correct to report an accident, however minor it might seem at the time.

In general one could conclude that the spin offs are safer sites and much fewer incidents annually involving on-site construction personnel. There is however still much to be hoped for when it comes to equipment safety and responsibility taken for that by various producers in the pipe rehabilitation industry.

Hydrostatic pipe bursting is a well-known and approved pipe rehabilitation method. Regardless of the machine brand and the differences in design, the method of how the old pipe is replaced is based on the same principals.

General method
One or more hydraulic rams are mounted in a horizontal frame, providing the pull or push thrust needed for pipe-bursting. A gripping mechanism, attached to the horizontal cylinders, holds on to a steel rod that is either screwed or linked together with it. The gripping system may be a mechanical linkage or hydraulic according to the brand.

Mechanical systems operate by a one-way, non-positive grip, which does not control the rods in case of a mechanical rod failure.

The hydrostatic system operates by having a constant positive grip around or behind the steel rod during the pullback. This system provides complete rod control in case of a mechanical rod failure.

Using a known force the machine pulls, via the steel rods, a ‘bursting tool’ through the ground, breaking the existing pipe and inserting a new product pipe. The amount of pulling force varies with machines pulling at up to 400 tones force is available.

Reported incident
On the 27 June 2008 a machine operator of contractor GWhite & Son Ltd, UK, subcontracting to Enterprise, had his leg broken. The incident was reported and filed as Health and Safety Executive incident report ref 02213856. The injured person was, at the time of the accident, standing behind and operating a pipe-burster.

Due to a mechanical failure in which one of the connecting rods broke, the remaining rods shot backwards out through the back of the machine, hitting and breaking the operator’s leg on impact.

Nearly a year went by without any serious steps taken to analyse the accident. What actually happened on the 27 June 2008, could it happen again and what can be done to prevent this?

On 21 May 2009 some of the biggest trench less construction companies in England sponsored and organised a pipe bursting safety test to specifically focus on the topic of safe pipe-bursting machines.

Equipment from the three main suppliers and producers of pipe-bursting machines were rented or borrowed for the event. These were:
• The 400G Grundo burst distributed by TTUK in England and rented from A-Plant;
• The Hammerhead Hydro burst HB5058 produced by the Earth Tool Company in US, and rented from UMole in the UK;
• A T45 hydrostatic Pipe burster on loan from the producer, Scandinavian No-Dig Centre, Denmark, and distributed in the UK by TA Drilling Enterprise.

The three rigs were set up in parallel lines, connected to the hydraulic power pack of each, and with 18m of 4-in. (100mm)- diameter ductile iron pipe lined up in front to ‘burst’. Each then had its bursting rods inserted, with a rod from each machine adapted (drilled and tapped to take a 20- mm M20 bolt). The bolt, having known shear strength, was fitted through a steel disc larger than the outside diameter of the pipe, so this disc acts as an obstruction or anchor plate.

Each unit pressed 20m of rods through the ductile iron pipe, to the end, and the first rod fixed at the opposite end, 20m from the machine. The test method is that when pressure is applied by the normal rig operation a load is exerted onto the shear bolt as the rods are pulled back. The pressure is built up until the bolt snaps. When the bolt snaps the energy is transferred to the rods resulting in a reaction. This reaction was to be viewed during the demonstration.

Pre-demo trials
Four tests were conducted with each of the three rigs prior to the demonstration. This was to observe the reaction effect and the set up so that the demonstration was safe for the invited personnel. Scandinavian No- Dig had previously performed several tests in Denmark and had set out a method statement with a safe procedure for this demonstration.

The demonstration, as the trails, was held in front of client, contractor and manufacturer representives in Whetstone, Leicester, England. The results of the demonstration mirrored the trials virtually the same for each machine.

A test was done with each rig using a 25-tonnef bolt. The bolt strength was reduced to 10 tones. The results were the same but the strain on each machine was reduced. It was then decided to conduct the demonstration with a 10-tonnef bolt for safety reasons.

During the testing it was noted that, when the bolt snapped, the pipe moved away from each rig approximately 300mm. To overcome this action and simulate a buried pipe an excavator was used to butt up the pipe to the bursting machine to prevent any lateral pipe movement.

Four tests were completed of the Hammerhead Hydro burst from U Mole plus the demonstration. Each resulted in the rod ejecting from the rear of the rig to a distance varying from 600mm to 1000mm. The maximum was achieved during the demonstration.

Four tests were completed of the Tracto-Technik Grundo burst from TTUK, plus the demonstration. The result showed that the minimum distance the rod was ejected was 1500mm and the maximum was 2500mm.In the demonstration the ejection was 2000mm.

Scandinavian T45
Four tests were completed plus the demonstration. All the results were virtually identical. The rod was held within the machine with zero ejection but the whole rig moved from a minimum of 40mm to a maximum of 60mm. The lateral movement of the rig during the demonstration was 50mm.

The three pipe-bursting rigs on test laid out in parallel Tracto-Technik QuickLock bursting rods and anchor plate Adapted bursting rod with bolt connector and anchor plate Anchor plate connector and a sheared bolt Demonstration attendees discuss the issues