01.06.2011
Emunds + Staudinger / Krings aids the search – at a depth of 14.5 meters
Extra-Deep Linear Shoring – highly versatile at great depth
When a garage owner arrived at his business premises in Essen one Monday in January, he could hardly believe his eyes. Two of his cars had been swallowed up by a huge, 9-meter diameter crater.
The crater 4 m deep
Since Essen is the mining city of the Ruhr district, the crater was not unrealistically thought to be caused by subsidence due to mining. However, the district government’s mining supervisory authority was pretty quick to rule out mining as the cause.
Ground works specialist Klaus Stewering GmbH from Borken was then entrusted with the search for the cause. “We first had to secure the area around the crater as the surface had subsided by 4 meters. Although the garage is located in a commercial estate, there was a road with a residential building not far away that had to be protected,” says Dipl. Ing. Theo Heitkamp, Managing Director of Klaus Stewering GmbH, describing the situation as he found it.
“We found out relatively quickly that the cause – a burst drain shaft – had to be located deep in the ground. Immediately adjacent to the crater is a pump shaft 1 meter in diameter and another shaft in the shop behind it with a dry weather pump for a depth of 13 meters. Whether the drain shaft being searched for was also at a depth of 13 meters was not clear, however. We now had to decide which shoring system would make it possible to secure an unusually deep pit economically and quickly and would be versatile enough at the same time to enable us to search for the problem at different depths.”
Crater Drawing: K. Stewering GmbH
The solution selected was Extra-Deep Linear Shoring from Emunds+Staudinger/Krings, a business unit of ThyssenKrupp Bauservice GmbH, with whom the contractor had successfully completed an earlier ground works project at great depth. The innovative system is a modified shoring method based on the well-known and proven Linear Shoring system. Two Linear Shoring units are combined and complement each other after installation while ensuring the required load discharge at depths of up to 14 meters.
Extra-Deep Linear Shoring combines the advantages of proven Linear Shoring to yield a high-performance and innovative shoring system for the protection of ground works at great depth. It is based on conventional Linear Shoring. In the first step, a module of this shoring system consisting of Linear Shoring soldiers, panels and roller units is installed in the ground. Then a second module is inserted inside the already installed module. Thanks to a new design and system components, the second module serves as the inner module nesting within the outer module. It operates entirely on the principle of the inner and outer shoring panels of Overlapping Linear Shoring on which, thanks to the sliding of the inner against the outer panel, the friction between the steel and the soil is minimized. The inner module consisting of soldiers, panels and roller units slides against the already installed outer module without friction between the steel and the soil – an advantage that saves labor and time during installation and particularly during the extraction and pulling of the individual shoring elements.
In their final installed state, the two shoring modules are mutually complementary. Their components are of the same length and withstand the soil pressure totally independently of one another.
In addition, the roller units of the Linear Shoring System can be height-adjusted at the various stages of the project in accordance with the manufacturer’s structural analysis. This way sufficient work space is created for the insertion of large-diameter pipes or drains, for example.
For the current project, one bay of Linear Shoring was installed for a depth of up to 6 meters and one bay of Extra-Deep Linear Shoring for the targeted final depth of max. 13 meters, each with a width of 4 meters. This all had to be done relatively quickly because of the severe impairment of drainage, as up to 700 l/s of waste water are fed through the drain once per month.
The first step – two bays of shoring are installed
After this, a third bay of Extra-Deep Linear Shoring was added. For the continuation of the project, the first bay of Linear Shoring was lowered to 7 meters depth for the vacuum pump. Thanks to the system’s huge versatility, the second bay of Extra-Deep Linear Shoring was then lowered to a depth of 14 meters for the new pump shaft.
In his search for the causes of the subsidence, the ground works contractor was finally successful at a depth of 13 meters. The drain found there was severely damaged. The escaping water had washed away the soil and eventually caused the surface of the ground to cave in, creating a crater.
The second step – one bay of Linear Shoring down to 6 meters deep and two bays of Extra-Deep Linear Shoring down to 13 meters
In the third bay, the depth was then extended again to 14.5 meters, because this was to serve as the pit for excavation of a tunnel for the replacement of the sewer under the adjacent buildings.
The height-adjustable roller units also made it possible to install the new pump shaft 2 meters in diameter in the pit without any great difficulty.
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