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Open shields: Open shields do not have a pressure-tight seal between the working face and the subsequent pipe string. They are characterized by relatively good access to the working face and easy-to-use machine technique. (Image: Hand shields - Overall view of a hand shield (external diameter 2098 mm) [FI-Nishi]) (Image: Open shield) (Image: … |
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May 18, 2020 |
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May 18, 2020
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May 18, 2020 Depending on the in-situ subsoil, the following excavation machines are usually utilized in these shield machines:
(Image: Shield machines with mechanical partial excavation - working face with natural support with reference to [FI-Herreb] [Image: S&P GmbH]) (Image: Shield … |
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May 18, 2020
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(Image: Attention!) In order to excavate the soil or rock at the working face, the boring head must be equipped with excavation tools adapted to the geotechnical conditions. The following excavation tools are available:
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Pick bits are blunt tools inserted at right angles to the working face and usually have a square shape. Their purpose is the loosening of non-cohesive soils such as gravel, sand and silt, including the numerous intermediate variants, from their natural positions. Cohesive soils are kneaded if pick bits are used [Maidl94]. |
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Round shank cutter bits are manufactured in different designs and geometries to suit the ease of breakout ability of the rock. They are used for destructive excavation mostly in rock that is easily to difficultly excavated. (Image: Wear when using a shield machine with fixed installed boom cutting machine with an axial cutting head while jacking pipes DN/ID 1600 in rock with uniaxial compressive strengths up to 200 N/mm2 ("greywacke") and a jacking … |
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Roller cutters are used as disc cutters, milled tooth roller cutters or TCI roller cutters and are borne to be axially rotatable. They destroy rock and intruding boulders in soil. (Image: Types of roller cutters [FI-Palmie] - (Tungsten carbide) Insert roller cutter) (Image: Types of roller cutters - Triple disc cutters) (Image: Types of roller cutters - Triple disc cutters) (Image: Types of roller cutters - Triple disc cutters) (Image: Installed roller … |
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Centre cutters are excavation tools arranged in advance in the centre of the boring head in order to release the pressure in the centre of the working face during boring and especially in cohesive soils such as clay and silt with low to high plastic properties to counteract sticking of the boring head. |
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(Image: Pros and cons) Backloading: The advantages of the backloading system:
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The soil mechanically loosened at the working face is transported into a suspension chamber through corresponding inlets. The suspension chamber is constantly supplied with water or a bentonite suspension by means of a feed pipe inside the pipe string. Over a second line (discharge line) the solid-fluid-mixture of soil and water/bentonite suspension is constantly absorbed and is transported to the ground surface. (Image: Hydraulic soil conveying) (… |
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May 18, 2020 Today, the installation of gas, water and wastewater pipelines is still predominantly carried out using open trenches. In view of the numerous disadvantages associated with this method, it is imperative that trenchless pipeline construction be considered much more strongly in the future than it has been to date as an alternative in the planning and construction of sewers and pipelines. This module deals in detail with the procedure and the various components. Emphasis is placed on the different types of shield machines, excavation tools, separation systems, the control and steering station, injection/grouting agent and soil extraction and reprocessing. After completing this module, you will have a sound knowledge of:
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