Cost effective solution

Published 9/3 at 15:38

Possibly the largest retention basin in Austria is currently being built in Triestingtal (Lower Austria) with engineers from the company PORR being given the task of installing a diaphragm wall along the centre line of the dam during the construction phase.

For this project, it was decided to try a KSI injection attachment from the German manufacturer Kemroc fitted to a modified excavator.

In the future, when the Triesting, a river flowing through south eastern Wienerwald in Lower Austria, floods after heavy rains, people living around Fahrafeld in the district of Pottenstein should find themselves better protected from the flood waters. A massive water retention basin is being built there for this purpose. With a capacity of 725,000 m³, the basin is intended to protect the community and the infrastructure. The construction company PORR is currently building a dam, approximately 10m high, to hold the flood water. The dam consists of two side sections about 1,300m long with the basin located between the riverbed and railway lines. The sides are connected to one another with a transvers dam about 150m long. The main structural element of the dam is a diaphragm wall made of a soil-cement mixture which is firmly anchored into the solid rock below the dam.

Under the topsoil, the local geology consists of various layers of loose rock lying on a bed of compact limestone. To create a sturdy diaphragm wall in this material, the specialists at PORR decided to use equipment they had not tried before. They chose to use a KSI injection excavator attachment designed and manufactured by Kemroc. The attachment has a long blade with a cutting chain that can grind its way down through the earth and rock. It can then mix the broken material with a cement suspension pumped via hoses from a semi mobile mixing plant. When hardened, the soil cement mixture produces a dense, structurally sound, impermeable structure.

By October 2020, PORR was halfway through the first phase of construction of the retention basin. The southern section of the dam running alongside railway tracks had been completed together with the soil cement diaphragm wall which had been constructed using a large excavator with the KSI mixing attachment. Wear on the blade chain for the 1,300m length of diaphragm wall was extremely low. Only 25 cutter teeth had to be replaced on the excavator attachment. 

In the next phase of construction, the actual dam, which is about 10m high, is being built up stage by stage. The soil-cement diaphragm wall will then be installed while working from the top of the dam. It will connect to the existing diaphragm wall located in the overburden below. For this section, the big brother to the KSI 5000 will be used, namely the KSI 10000 with an impressive 10m long mixing blade. PORR is confident that this machine will also perform satisfactorily when mounted on one of its excavators and provide a cost effective alternative to other, more expensive civil engineering methods.

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