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Bauer Maschinen revolutionises special foundation engineering

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Special foundation engineering devices from the Bauer Maschinen Group are characteristic on a world-scale. They started with the construction and manufacture of earth drilling machines as there were no suitable devices for anchoring holes and bored pile production on the market in around 1970 for their own Bauer foundation engineering company in Bavarian Schrobenhausen.

Therefore, the building contractors at Bauer designed and manufactured the first anchor drill for their own needs and in 1976, the first large diameter heavy-duty drilling rig followed. The machines were originally only intended for use in their own company but in the mid eighties, they moved to open sale as the major construction groups demanded Bauer devices. Since the end of the sixties, special foundation engineering machinery from Bauer has stood for the highest performance, quality and innovations. Bauer Maschinen GmbH designs and manufactures rotary drilling rigs, trench cutters and all associated tools and since 2001, it has been operating independently on the market within the Bauer Group.

When Bauer developed the first trench cutter in 1984, the limits of trench wall technology were expanded significantly. Scarcely any foundation engineering method has changed construction in such a lasting way as the introduction of the trench cutter. The basic concept of wall manufacture is broadly unchanged since the introduction around 60 years ago. A continuous through wall is manufactured from a series of individual rectangular elements. The open, dredged or milled out trench is supported with a thixotropic suspension during excavation. A fluid is designated as thixotropic if the viscosity breaks down during a constant shear over a certain amount of time and rebuilds after suspension of the shear stress. A well-known example is ketchup, which needs to be shaken so that it pours from the bottle. Next, a reinforcement cage made from structural steel is hoisted into the open trench segment. After that, the area is filled with concrete and self-hardening soil concrete using a concreting pipe. At the same time, the rising concrete displaces the specifically lighter supporting suspension. It is pumped up, cleaned and used again to support a new trench. After the concrete has hardened, the cutting of the secondary trenches between the primary trenches and its filling takes place. In order to achieve a connection that is as close as possible between the two trenches, the joint is provided with suitable sealing elements using trench wall grabbers. 40 to 80 metres in depth can be achieved with the method based on excavator buckets. This conventional excavation is difficult on hard ground and impossible on rock. Trench walls can be manufactured in the most difficult ground conditions only by using Bauer trench cutters. Two typical examples of this are the trench wall for the Dhauligangha embankment dam project in the Indian Himalayas and the trench walls for the embankment dam of the Peribonka hydropower station in Canada where hard rock of up to 120 m depth had to be cut into. The cutting machines work at -20 °C as well as at +40 °C. They are successfully used in remote regions in the Arctic circle but also in the vibrant centres of large cities such as Hong Kong, Tokyo, Turin or Moscow.

The Bauer cutting system is made from many independent components which are coordinated with each other according to use, depth and ground type. The main components are: trench cutter, cutting control, twisting mechanism, hose guidance system and carrier.

The core item of the system, the actual trench cutter, is made from a steel frame on the underside of which two hydraulically operated gear cylinders are arranged which rotate around the horizontal axis in opposite directions. Different cutting wheels are assembled on the gears depending on the ground type. Through the rotation of these cutting wheels the ground material is continuously loosened under the cutter, crushed, mixed with the suspension in the trench and fed to a vacuum outlet. In order to be able to wear the strokes occurring during the smashing of large rocks undamaged, there are damping elements installed between the cutting wheels and gears for the protection of the transmission. Close above the cutting wheels, there is a hydraulically operated rotary pump. It continuously carries the suspension concentrated with the cut material upwards and from there on to the processing plant. In soft ground and when using hard suspensions, the capacity of this pump is crucial for the excavation output. Cutting transmission and feed pump are protected against harmful concrete entry using a pressure equalisation system. The output of a cutting machine is dependent on the feeding force, designated by the weight of the cutting machine and the torque of the cutting wheels. Both factors mutually influence each other. In order to achieve an optimal excavation output, the Bauer cutting systems are equipped with a particularly sensitive, electronically controlled feed winch for the control of the contact pressure.

Although the Bauer trench cutters are extremely robustly designed, the hydraulics system and gear cylinders must be carefully maintained. Finally, they should work reliably both at areas at the equator and also in the extreme north of Canada. In the process, the conditions of use could often not be more challenging and the surroundings more adverse to machines. The cutting machines work for example immersed in the supporting liquid (bentonite) up to depths of 150m with a high bandwidth of the operating temperatures and changing pressure conditions. The gears, drive motors and control systems are exposed to extreme contamination and water levels, high temperatures and strong vibrations.

The maintenance of the devices is mostly assumed by the users using a detailed maintenance plan provided by Bauer. Upon request, for example for rented devices, the service will also be assumed by Bauer. However, regardless as to who carries out the maintenance work, Bauer always recommends that an accompanying monitoring of the components filled with oil using OELCHECK lubricant analyses in its machine documentation. In the event of an extended warranty, they are even mandatory. 

The hydraulics systems are operated with 700 to 1,400 litres of mineral oil-based or "bio" hydraulic fluid, depending on the cutting. The oil corresponds to the guidelines of the carrier, whose system it also comes from. The gear cylinders require 30 to 130 litres of synthetic gear oil each. For the hydraulic liquids, the lubricant analyses together with the impurity check mainly serve as an excellent instrument to control the oil change intervals in a condition-based manner. The oil change intervals are fixed for the highly loaded gears. Here, Bauer uses the analyses principally to assess the wear and tear of gears and their components and the functionality of the gaskets. 

In addition, the analyses also always provide important information if irregularities occur. In this way, they also detect the cause for a sudden dark colouration of a hydraulic oil from a trench cutter. In the laboratory, an impurity of the hydraulic oil was discovered through engine oil. Thanks to this information, the Bauer service technicians were able to specifically search for the defect without long delays. The engine oil had entered the hydraulics system through a power take-off in the diesel engine. Once detected, the cause was quickly fixed and the hydraulics protected from possible resultant damage. 

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