Mixing and grouting systems made by Häny are being used to construct the new Alstetten – Zurich Main Station - Oerlikon cross-city underground link in Switzerland. In contract section 3 (Weinberg Tunnel) they are being employed for grouting the target block zone as well as to carry mortar for backfilling on the TBM.
Grouting on a cement basis represents a tried and tested measure for stabilising and securing the subsoil and excavated areas. Such injections place high demands on planners and contractors as well as on the mixing and grouting equipment. As a consequence the right choice of machines – the mixing, grouting and registration units for instance – have an important part to play for carrying out grouting projects.
In recent years mixes for grouting material have been further developed, optimised and made more environmentally-friendly, something that has also led to technical adjustments for the mixing and grouting equipment. The Häny AG from Jona/CH is a leading supplier of mixing and grouting systems.
Mixing, Pumping and Registering
The mixers are of great significant for cement-based grouting. They prepare the grouting material consisting of various components in such a way that it obtains its desired, specific properties. Ideally high-speed mixers are employed to prepare cement-based mixes and suspensions. In this way complete hydration of the cement particles can be assured and the formation of clumps avoided. Stable, homogenous mixes can be produced using such mixers – mixes which do not tend to precipitate and scarcely demix in groundwater.
An efficient pump belongs to a grouting system, which can grout various types of material – from thin suspension to “pappy” mortar – in accordance with the guiding values (maximum pressure and quantity).
A further, important element for modern grouting technology is data processing. The grouting or throughput quantity and the pressure course are registered. This registration on the one hand permits the grouting measures carried out to be checked and analysed and on the other provides detailed and invaluable comparisons relating to other grouting measures. Data processing can be undertaken manually or by means of a special unit. For this purpose units are used, which check all essential parameters, process them digitally and facilitate speedy and precise evaluation with the computer.
Modern grouting systems are compact and can be assembled and transported in standard containers. In this way the systems remain mobile and require few operating staff.
Target Block Grouting for the Zurich Weinberg Tunnel
The “Südtrakt” shaft is located directly in front of the Main Station (east side), into which the TBM coming from the Limmat side will subsequently drive. The shaft is excavated within diaphragm walls down to a depth of some 24 m. In order to stabilise the tunnel zone immediately in front of the shaft for the TBM entering (increase in strength, reduction of permeability) this zone – known as the target block – is grouted from the shaft by specialists from the Implenia Bau AG. Injections are executed both within and without the tunnel cross-sectional area in a 1.5 x 0.75 m grid over a 17 m long section of tunnel. Cement suspension as well as soft gel is used for grouting purposes. Grouting is undertaken in a series of steps via sleeve injection pipes with double packers. The quantity and pressure course for each injection stage is precisely registered, documented and evaluated. Similarly double packers are used for undercutting the “Südtrakt” from the shaft in the direction of the Main Station.
The mobile grouting system supplied by Häny for grouting the target block is installed in a container in front of the Main Station and embraces a mixer (HMC 600 with weighing control, output up to 10 m³/h), 4 powerful pumps (plunger piston pumps ZMP 610), an agitator (HRW 800) and a registration unit (HFR).
Transporting Grout on the TBM
A further installation shaft is located at the Wehntaler-Hof-wiesenstraße crossing in Oerli-kon (“Brunnenhof” shaft) for the new 5 km long, s-shaped Wein-berg Tunnel. The TBM starts from this shaft and moves towards the Main Station. A further grouting pump (ZMP 725) and an agitator (RHW 800) are installed on its back-up system. Here the pump “only” fulfils the task of delivering the grout (cement mortar 0 to 4 mm) into a container set up further forward on the back-up. From there the grout is used to backfill the base area below and behind the steel shield.