Flexible trench shoring system creates room to manoeuvre. Rectangular sections swiftly inserted

Apr 18, 2006

A high-performance trench shoring system satisfies all the structural prerequisites for the quick and efficient installation of even large-size precast concrete elements. This is something that the civil engineering specialists of Stratebau GmbH experienced for themselves during a construction project in Markt Lappersdorf in Regensburg rural district.

On behalf of the construction department in charge, the company replaced the sewerage and created a stormwater overflow structure during the upgrading of the R 15 road. Contrary to the original invitation to tender, which envisaged casting the stormwater overflow in situ, an alternative proposal involving a "package" of Linear Shoring from Emunds+Staudinger and precast concrete elements was adopted for the project. And this paid off for everyone concerned.

Because of the speed of progress, the nuisance for residents and road users was kept to an absolute minimum – an outcome in which Linear Shoring played a major part. As soon as the base slab had been poured, thus providing the necessary ground support for the shoring system, it was possible to raise the roller units in accordance with Emunds+Staudinger's structural specifications. In this way sufficient space was created for the lowering and trouble-free joining of the roughly 32 tonne rectangular precast concrete sections.

The extensive excavation work in Markt Lappersdorf took place concurrently with the upgrading of the R 15 road in the locality of Kareth. "Because of the heavy traffic, the road surface was no longer up to requirements and its wearing course was in a poor state of repair," explains Dipl.-Ing. Gerhard Bortner of Dr. Blasy – Dr. Øverland Engineers. This is why Regensburg rural district awarded the contract for a new road surface for a class III road conforming to the German road construction guidelines. Since the sewers running beneath the district road were also hydraulically overloaded and seriously damaged in places, the Markt Lappersdorf construction department opted to replace the sewers in the course of the road construction project and modernize the waste water system.

"Lappersdorf has a combined sewerage system carrying both soil and rainwater," Bortner continues. "The existing sewers consisting of vitrified clay and reinforced concrete pipes with nominal diameters of DN 400 were replaced by vitrified clay and reinforced concrete pipes with nominal diameters conforming to the design calculations for the sewerage network." DN 600 vitrified clay pipes and DN 600/900 and DN 800/1200 oval-section reinforced concrete pipes were laid. In addition, the stormwater overflow was replaced by a new stormwater tank.

With a total length of 30 m, the structure has a useful volume of about 150 m3 and is used for retaining heavily soiled waste water from the combined system. The fact that less pollution will enter the River Regen after completion is, in the words of construction department Manager Peter Achatz, Markt Lappersdorf, "a big contribution to water purity". Achatz continues: "Because of the structure, the surging water that picks up deposited soil in the sewers at the start of rain can be stored in the tank and supplied to the sewage treatment plant with a delay." With the old system, this water used to sweep over the stormwater overflow and enter the river.

Package of shoring and precast elements
"According to the invitation to bid, the stormwater overflow was to built of cast-in-place concrete," explains Project Manager Dipl.-Ing. Frank Fenk of Stratebau GmbH. Because of the conditions on site – these included above all the confined space and the traffic situation – the contractor decided to use Linear Shoring from Emunds+Staudinger.

Together with Dipl.-Ing. Markus Gehse, E+S Sales Bavaria, the project management draw up an alternative strategy in advance that envisaged a "package" solution of Linear Shoring and precast concrete elements. And, in the opinion of Project Manager Frank Fenk, this paid dividends.

Linear Shoring also reveals its strengths in the handling sector. The elements of the shoring system can be quickly and easily manipulated during installation and removal. What’s more, it was also possible to feed the 3.75 m, 3.4 m tall and 3 m long precast concrete elements without difficulty under the shoring. Beforehand, a 20 cm thick concrete base slab was poured as the bed for the pipe.

"When the minimum strength was achieved, it was possible to change the position of the roller unit," explains Project Manager Robert Kellner, Stratebau GmbH. "This way sufficient space was created for the subsequent tasks." After a mobile crane had lowered the 32 tonne rectangular sections into the trench, they could be fed with ease beneath the roller units and joined together.

Practicable end-of-trench solution

To secure the ends of the trench, Markus Gehse was also able to propose a practicable solution. “For such engineering projects, we use a corner rail system at the ends of the trench or panels are placed in front of the shoring,” explains Gehse. "If pipes or cables enter the trench from
the ends or in the case of larger widths, the E+S waler girder is used." It is slotted into the profile of the Linear Shoring soldier.

The bottom waler is preassembled together with the components of the shoring system. During installation, the waler slides smoothly into its intended position. It can be height-adjusted at any time and is aligned flush with the end of the Linear Shoring system. When the upper waler is then fitted from the top, the sheet piles can be inserted.

Project Managers Fenk and Kellner were extremely satisfied with project progress. They were extremely impressed by the technical potential and handling of the Linear Shoring system. They were also very happy with the extensive service and advice from E+S. The necessary shoring components – Linear Shoring soldiers, shoring panels and components of the roller units – were brought by a forwarder to the construction site. E+S fitters were than on hand for the preassembly of the first unit.

"At the start of the project, an E+S expert was always on hand to give advice and practical assistance," Kellner recalls. "Our men benefited from this, and progress was quick, enabling us to complete the civil engineering work on time and to the client's complete satisfaction in September 2005."

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