Sika and Putzmeister Apply Efficient Shotcrete and Concrete at Schmuecke TunnelThe two 1,720 m and 1,729 m-long tunnels are part of the new construction section of the A 71 motorway between Erfurt and Sangerhausen. In total, the section is 7.5 km long and is being constructed by a consortium consisting of building contractors Baresel, Herman Kirchner Hoch- und Ingenieurbau and Alfred Kunz Untertagebau. The construction costs for the project are approximately EUR100 million. Click de/13. Visit www.baresel.de, www.hermann-kirchner.com and www.kunz-gmbh.de Four shotcrete machinesThe prevailing ground conditions mean that a full outbreak would not have been controllable for a tunnel excavation between 105 and 147 cubic metres. The consortium therefore decided to excavate the east and west tunnels using separate crown/side wall blasting and crown/side wall/base blasting drive methods respectively. As the tunnelling work in both tunnels progressed simultaneously from the north and south side, the consortium used four independently operating Sika-PM500 shotcrete machines for the concrete spraying work. Two additional, identically constructed spraying machines were on standby over the period. Visit www.sika.comThe consortium has been well on schedule since the tunnel operation started in December 2005. At the end of November 2006 the semicircular crown profile had already been completely excavated in both tunnels. Different section lengths between 0.8 to two metres were necessary for the headwork as a result of the strongly fluctuating load bearing behaviour of the surrounding mountains. For safety reasons, a total of five emergency galleries, which run in parallel at a distance of 20 metres, connect the two tunnels. Using a Sika-PM500 to secure the side wall drive with shotcrete The pipe length is kept as short as possible - the Putzmeister concrete pump BSA 1408 is therefore located directly in front of the formwork carriage Water level lowered with 35 wellsThe Schmuecke mountain has considerable water resources. The ground at the central area of the two tunnels was so saturated with water that excavation with the chosen drive method would not have been possible. Therefore, a gallery consisting of 35 wells had to be sunk in a depression on the rear of the Schmuecke mountain at depths up to 90 metres for drainage purposes. When work is completed the wells will be restored to their previous state so that natural groundwater conditions can be reproduced in the Schmuecke mountain. Shotcrete shellAs soon as the first cross heading was reached after 140 metres in the crown drive, the consortium began the side wall and base drives. The cut sections also varied significantly from each other, with lengths ranging between two and 12.6 metres as a result of geological conditions (including shell limestone and various types of mottled sandstone). After an initial application of shotcrete to stabilise the rock, a second application of shotcrete shell is applied as a sealant carrier. Due to the very smooth surface (80% of the aggregate granulation measures up to 4 mm, 20% up to 8 mm), the shotcrete shell can be lined directly with fleece and plastic sealing sheeting. On average, the wall thickness of the outer shell is between 20 and 30 centimetres. Approximately 75,000 cubic metres of shotcrete is required altogether for the two tunnels and the four entrances/exits of the Schmuecke tunnel. Of course this challenging project also subjects the six shotcrete machines to natural wear, for example the spray nozzles. Downtime, however, was reduced to a minimum because two of the six shotcrete manipulators were kept available as reserves during the service intervals. Concreting the inner shellBefore the turn of the year from 2006/2007, the placement of concrete began on the north and south sides of the tunnel for the base and the arch in the inner formwork. When doing this, the consortium used formwork carriages and up to four stationary Putzmeister concrete pumps (two BSA 1408 E pumps, a BSA 1405 E and a BSA 1005 E). Visit www.putzmeister.deBefore concreting the arch, a section of the base measuring around 60 metres in length had to be concreted initially to support the arch formwork carriage. The BSA pumps follow directly behind the formwork carriages and are pulled along section by section. The delivery lines are deliberately kept short (max. 10 metres). The respective 12 m-long inner shell blocks made from cast-in-place concrete (C30/37) are constructed in thicknesses ranging from 0.4 to 0.6 metre. The time which the concreting crew requires for placing approx. 135 mcubic metres of concrete for each arch section is around 5 ½ hours and they require around 3 to 3 ½ hours to place the approx. 75 cubic metres of concrete for the base sections. By varying the proportion of cement, the consortium reached an optimum relationship between processability and hardening temperature. The aim is to concrete one base and one arch block per day, per tunnel section. This requires striking times of less than twelve hours in the arch. One of the few wear parts on the Sika/PM shotcrete spraying manipulators is the spray nozzle. This can be replaced within a few minutes Each of the tunnels is concreted in 144 blocks and each block is approved by the site management. The total requirement of concrete for the inner shell is approx. 65,000 cubic metres. The Schmuecke tunnel consortium procures both the shotcrete and the cast-in-place concrete from several mixing works in the region. Work is usually conducted in two 12-hour shifts, seven days a week. This is the only way the schedule can be met. The headwork was concluded in May 2007 and the inner shell is estimated to have been concreted by the end of 2007. Visit www.a71.de 35/07.