Fifth sluice chamber construction, Brunsbüttel

Grouted anchoring of the sluice chamber walls and base

In 2014, PORR Spezialtiefbau secured the contract for an ambitious specialist civil engineering project: the new construction of a fifth sluice chamber at the Elbe-side exit of the Kiel Canal in Brunsbüttel. During the first construction stage, 580 piles of various designs were manufactured. By June 2022, PORR expects to complete the second element of the project, the manufacture of a further approx. 560 jet-grouted uplift piles together with approx. 280 injected uplift piles.

Top engineering skills, both then and now

The German Emperor opened the Kiel Canal in 1895 after a construction period of just eight years. The monumental 98.5-kilometre-long waterway connects the Kiel fjord with the Elbe river. Simply ensuring the entire length of the canal was perfectly symmetrical represented an extraordinary engineering feat for the time. Powerful tide gates were also installed at the canal mouths at Kiel-Holtenau and the Brunsbüttel sluice.

Now more than 100 years old, the two great sluice chambers in Brunsbüttel are in urgent need of repair. To avoid interrupting shipping for an anticipated period of several years, a fifth sluice chamber featuring a working area of 330 metres long by 42 metres wide is under construction on the central sluice island. Everything from the construction team and machinery to the steelwork components, aggregate and cement has to be transported across the water.

Drilled piles up to 64 metres in length

The sluice chamber walls comprise a combination of sheet-pile wall with a reinforced concrete superstructure, while the chamber base is made from anchored underwater concrete. Ramming methods could not be used to create the grouted anchoring required to resist the pressures of earth, water and buoyancy uplift in the soil, due to the risk of damage to the adjacent sluice chambers.

Further complications included the groundwater on the site, which is damaging to concrete, and the expectation of loads of up to 4,000kN. The team chose to apply jet grouting methods, which could be implemented without vibration. The jet-grouted elements improve the durability of the grout body.

The grouted anchoring of the sheet-pile wall consisted of jet-grouted piles in the form of raking piles at a 45° angle, anchored up to 40 metres into the ground. The uplift piles were transported 25m through the water from the pontoon as empty bores, and then drilled 27m into the ground on location. 

Uncharted territory in manufacturing the jet-grouted piles

In the jet grouting method, the soil is cut by a cutting jet and then replaced, with a hardened cement slurry serving as the construction material for the jet-grouted elements. Our innovation in Brunsbüttel: steel supporting elements up to 125mm in diameter were inserted in the jet-grouted columns, which measured a diameter of 1.1m and lengths up to 7.5m. Stump-Franki constructed a special machine to combine the drilling and jetting procedures and implement this plan. Building approvals for this procedure were not available, so exceptional permission was obtained from the Federal Waterways Engineering and Research Institute.

Once the holes (borehole diameter approx. 245mm) were drilled to depths up to 64m, the area of the fixed anchor length was expanded with jet grouting in two operations. Next, the core of each jet-grouted column was replaced with cement slurry (water/cement ratio approx. 0.45) and the supporting element incorporated into the fresh body. Spraying ensured the jet-grouted columns interlocked successfully with the soil. The resultant piles will be highly durable: able to withstand the expected loads of up to 4000kN, even with high concentrations of sulphates and ammonia in the groundwater.