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In these methods, jacking pipes [DINEN12889:2000] [ATVA125:1996] [Scher77a] [Stein85f] are jacked by pressing-in through the subsoil from a starting shaft to a target shaft with the aid of a jacking station or a main jacking station helped by intermediate jacking stations. Jacking in a straight or curved line path is made possible by means of a steerable shield machine positioned at the head of the first pipe. Operation and steering of the shield … |
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Sep 14, 2005 Trenchless Technology for Installation of Cables and Pipelines Shield machines with partial excavation by hand (hand shields) (Image: Open cowl shield with spiral conveyor for spoil removal and hydraulically extendable breast plate for gravel-sand soils without groundwater (external diameter 4280 mm) [FI-Eppin]) Natural support of the working face is always applicable when the existing subsoil is free of groundwater and the working face is a priori stable (working face without support) or is sufficiently supported by a self-forming earth wedge with a natural slope angle.… |
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Sep 14, 2005 Trenchless Technology for Installation of Cables and Pipelines Shield machines with partial excavation by hand (hand shields) With partial support, the surface of the working face is divided into sections and is either supported by means of natural partial support on bench plates (bench (plate) or platform shields) and/or by means of mechanical partial support using breast plates (Bild 9.2.1.1.2). With bench shields, this division into sections has the purpose of reducing the length of the earth wedge and the size of the surface area of the slope [Scher77a]. Depending on … |
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Sep 15, 2005 Trenchless Technology for Installation of Cables and Pipelines Shield machines with partial excavation by hand (hand shields) The use of hand shields is recommended wherever very short jacking distances make the use of mechanical excavation uneconomic due to the high initial investment for the complex machine technology. In trenchless installation they are mainly used for crossing of traffic lanes and jacking distances of less than 50 m as well as for excavating special cross sections such as rectangular or arched profiles with manaccessible cross sections (Abschnitt 3). |
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Hand shields are non-mechanised open shield machines in which the soil at the working face is loosened by hand using auxiliary tools (pickaxe, spades, shovels or pneumatic hammer) (Bild 9.2.1.1) (Bild 9.2.1.1) (Bild 9.2.1.1). The removal of the spoil is carried out with the aid of conveyor belts, transport carts or tracked conveying buckets (dump trucks) (Bild 9.2.1.1).
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Because of their relatively low costs and numerous possibilities for use in soil and rock free of groundwater, open shield machines with mechanical partial excavation enjoy a wide application for jacking lengths up to 1000 m [FI-Herreb]. Water retention measures (open water retention or groundwater lowering) are required when jacking in groundwater (Abschnitt 4.4) (Abschnitt 12.8.2). In the cases in which this is not possible or permissible, a closed … |
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(Image: Open cowl shield with spiral conveyor for spoil removal and hydraulically extendable breast plate for gravel-sand soils without groundwater (external diameter 4280 mm) [FI-Eppin]) Shield machines with special excavation and conveying installations have been developed, and used for special purposes. The features of these excavation tools are that the working face is only partially excavated at some points in the shield, e.g. more or less passively. |
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Shield machines with compressed air support are used [Krets72] :
The limits of use for jacking in compressed air are determined by [Krets72] :
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(Image: Qualitative depiction of compressed air consumption [FI-Baben]) In order to ensure the stability of the working face, a high support pressure as possible is required on the one hand, but, on the other hand, with increasing air pressure, there is the danger that the resulting large pneumatic gradient causes a ground failure at the surface and thus an increasing loss of air in the working chamber (blow out). The increasing loss of air can lead … |
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Compressed air installations for spaces in which work is being carried out by people are subject to special safety demands and require special safety measures in order to protect the personnel from health hazards. Important for these in the Federal Republic of Germany are the:
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(Image: Design and method of operation of the membrane shield method with reference to [FI-Zübli] [Image: S&P GmbH]) In order to expand the area of application of shields with mechanical partial excavation and compressed air supported working face to inhomogeneous soils with a water permeability coefficient k > 10-4 m/s (e.g. sand or gravel with intrusions of cobbles and boulders), shield types have been developed in which the air support is combined … |
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Shield machines with fluid support (SM-T4) … |
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(Image: Closed cowl shield (external diameter 2.0 m) with integrated microtunnelling machine of type AVN 800 B (external diameter 975 mm) [FI-Herreb]) The shield machines with mechanical partial excavation correspond in concept to the design of the hand shield. They feature a mechanised open (SM-T1 or SM-T2) or closed (SM-T3 or SM-T4) shield with a fixed installed excavator for partial excavation of the soil or rock at the working face. The spoil is … |
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Project example - construction of the utility tunnel "Versorgungstunnel Kieler Förde" |
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Shield machines with partial excavation feature an open or closed shield of the models SM-T1, SM-T2, SM-T3 or SM-T4, in which the soil at the working face is partially loosened by means of fluid jets. The spoilfluid mixture is transported hydraulically to the surface. Representatives of these types of shield, which is no longer in use today, are discussed in the following for the sake of completeness. They are:
Flushing … |
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Shield machines with partial excavation feature an open (SM-T1 or SM-T2) or closed shield (SM-T3 or SMT4) and partial loosening of the soil or material at the working face. The spoil is transferred directly or by a conveyor belt, chain conveyor or a spiral conveyor (auger) to the downstream conveying system (belt conveyor, transport cart or conveying bucket). In exceptional cases, the spoil can also be conveyed hydraulically. Shield machines with partial … |
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The cutting wheel is a mostly open designed boring head that does not serve to support the working face mechanically ( Bild 9.2.2.1.1 a and b) (Bild 9.2.2.1.1) (Bild 9.2.2.1.1) (Bild 9.2.2.1.1) (Bild 9.2.2.1.1) (Bild 9.2.2.1.1). Its advantages are in the small cover and thus good accessibility to the working face if desired.
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Scraper cutting heads are nearby, closed, disc-shaped boring heads or cutting wheels with adjustable or fixed supporting plates with soil entry openings that are adapted to suit the size of the maximum particle to be transported Bild 9.2.2.1.2 (Bild 9.2.2.1.2) (Bild 9.2.2.1.2) (Bild 9.2.2.1.2). Besides their excavation function, the mechanical support of the working face becomes important with this boring head variant. Scraper cutting heads have a … |
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Rock cutting heads consist of almost closed, disc shaped basic constructions with usually slot shaped entry openings (removal slots) and are flat with a rounded periphery, slightly coned or almost convex (Bild 9.2.2.1.3) (Bild 9.2.2.1.3) (Bild 9.2.2.1.3) (Bild 9.2.2.1.3) (Bild 9.2.2.1.3) (Bild 9.2.2.1.3). Set into the boring head there are additional carriers for attaching or bearing the roller cutters. So-called removal teeth are situated along the … |
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For shield machines with full-face excavation, special attention must be paid to the ability to change tools without changing the support conditions of the working face. One method of carrying this out in a safe and simple manner underground without withdrawing the machine from the rear of the boring head is the so-called "Backloading system" [Kollm00]. Examples of the fastenings used for the various tools are shown in Bild 9.2.2.1.5, Bild 9.2.2.1.5 |
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Shield machines with full-face excavation are equipped with various boring heads [Arnol93] depending of the subsoil conditions and especially the strength of the soil and rock material. Depending on the design, the boring head, besides excavation, can also undertake an earth pressure balance function. A difference is made between:
The … |
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Shield machines with full-face excavation and natural support of the working face are open, fully mechanised shields (Tabelle 9.2). They are the simplest form of shield machines … |
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