The Am Bruckhaufen housing estate in Vienna, located on a 6m high embankment beside the River Danube, was not previously connected to the public sewer system.

The contract to remedy the situation presented Hobas with a significant challenge.

Adverse ground conditions, including residual settlement of up to 15cm, had to be contended with and possible gas formation posed great problems.

The task for the Hobas engineers was to provide the housing scheme with a 4km sewer system. The solution was microtunnelling.

A drill equipped with a control unit and an adjustable cutter head was driven horizontally through the soil at the required gradient to the target shafts. Lasers were used to display the exact location and position of the cutting head, which is monitored and remote controlled from above ground.

As a result progress can easily be corrected at any time and the gradient calculated and complied with to a precision of 0.1%.

A crusher behind the drill can break aggregate of up to a third of the drilling diameter. The crushed material is transported hydraulically in a settling basin above ground. Similar to conventional pipe jacking, hydraulic presses control tunnel driving and jack the pipes into the ground at the front end of the drill.

The advantages of the system are obvious. Installing a conventional sewage system by the open cut construction method could have led to different degrees of settlement and thus to cracks and other damage.

This would also have been substantially more expensive than microtunnelling in this special case. In addition, microtunnelling guarantees a long service life because the pipes are designed for jacking pressures and such high loads are never reached under normal circumstances.

Maintenance and inspection is also much easier thanks to the star-shaped connection from each individual house to the mains.

The local residents were also grateful for the minimal disturbance during construction. Indeed, over 95% of households opted to have their sewage pipes laid using microtunnelling.

The glass reinforced polyester pipes used in the Am Bruckhaufen project meet the most stringent specifications and offer benefits compared with conventional pipe systems.

They are highly corrosion-resistant, extremely rugged, lightweight and easy to lay. Such advantages make Hobas pipe systems a realistic solution in areas of sewage, potable and service water, irrigation, power stations and industrial applications.

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