UNITRACC - Underground Infrastructure Training and Competence Center

Working face with fluid support - hydroshields

(Image: Hydroshield without boring head)

In the rear chamber (pressure chamber) that is separated from the trailing shield segment by a pressure bulkhead, there is a compressed air cushion through which the support pressure at the fluid balanced working face is controlled by means of a compressed air regulating installation.

The most important deviating design feature of hydroshields from the slurry shields is that the excavation chamber is divided …

Aug 26, 2008

Working face with fluid support - hydroshields

(Image: Pros and cons)

Advantages of hydroshields:

The fluid of the pressure chamber forms a cushion volume that, if combined with quick decompression of the compressed air cushion, is able to balance sudden loss of support fluid (approaching of fault zones, permeabilities of the subsoil, cavities, etc.) within a certain scope without a collapse of the working face
Control of the support pressure and the flow volume of the conveying circuit are …

Aug 26, 2008

Working face with fluid support - Mixshields

A mixshield is a fluid supported shield machine for multi-layered, complex geological conditions, especially with high concentration of water and high water pressures. The principle of the hydroshield forms the basis for the mixed shield. It can be driven in slurry as well in a mixshield modes. A bentonite suspension serves as a support of the working face and at the same time as a transport medium. The support pressure is not regulated via the …

Aug 26, 2008

Working face with fluid support - Mixshield

Slurry shield mode

(Image: Principles of the Mixshield with example of changing from a slurry shield to a hydroshield with reference to [FI-Herreb] [Image: S&P GmbH] - Slurry shield mode)

Mixshield mode

(Image: Principles of the Mixshield with example of changing from a slurry shield to a hydroshield with reference to [FI-Herreb] [Image: S&P GmbH] - Hydroshield or Mixshield mode)

Aug 26, 2008

Boring head design and stone crusher arrangement

For working faces with fluid support the following boring heads come into consideration:

cutting wheel
scraper cutting head
rock cutting head

(Image: Attention!)

The decision of the use of a closed, open or closable boring head is influenced mostly by the expected particle size distribution of the soil.

In addition, shields with fluid supported working faces have the possibility to artificially reduce the particle size to suit the conveying system …

Aug 26, 2008

Cone crusher

Cone crusher: Cone-shaped part of a shield machine which is located behind the cutterhead, which is able to crush larger stones for removal due to its special form and rotation [FI-Herreb].

(Image: Converting versions of the EPB UNCLEMOLE - Sketch of the principle of the slurry shield mode with reference to [FI-Isekib] [Image: S&P GmbH])	(Image: Pros and cons) Cone crushers are unsuitable for large jacking lengths and in abrasive subsoil because …

Aug 26, 2008

Jaw crusher

Jaw crusher:
Hydraulically driven part of the shield machine, which is arranged directly before the suction nozzle of the discharge line in the excavation chamber on the shield invert to crush the spoil [Stein05a].

(Image: Jaw crusher with rake arranged on the shield invert)

Areas of application for jaw crushers:

external shield diameters > 2600 mm (due to increased need of space)

Aug 26, 2008

Roll crusher

Roll crusher: A crusher that consists of one or two counterrotating rollers and that is installed directly between rakes and suction nozzle of the discharge line (also called in-line crusher) [Stein05a].

(Image: Dismantled roll crusher (MOCO system [FI-Moco]) of a hydroshield with a shield diameter of 1966 mm [FI-Dywida])	(Image: Pros and cons) Advantages of roll cutters: they are able to chaff torn and chipped wood into hydraulically conveyable …

Aug 26, 2008

Sticking caused by clayey soil

(Image: Possible problems regarding the method technology when jacking in cohesive soils with a high sticking potential with reference to [Sager00] [Image: S&P GmbH])

Aug 26, 2008

Sticking potential of clayey soil

(Image: Indication regions of the sticking potential of clay soils with reference to the plasticity index IP and the consistency index IC with reference to [Thewe99] [Image: S&P GmbH])

Aug 26, 2008

Countermeasures to prevent sticking

Possible countermeasures for prevention of stickiness are:

Use of open spoke cutting wheels (if possible with a rim) instead of closed scraper cutting heads and rock cutting heads with the largest possible removal slots up to the centre in order to present a small adhesion surface and to ensure a possibly unhindered soil entry.
Equipping the boring head with slicing-peeling excavation tools (scraper teeth) in order to prevent a plasticine effect …

Aug 25, 2008

SM-V4 - working face with fluid support

Aug 27, 2008

Working face with earth pressure support

(Image: Shield machine with full-face excavation - working face with earth pressure support (SM-V5))	Shield machines with earth pressure supported working face, also called Earth Pressure Shields or EPB (EPB = Earth Pressure Balance) shields, are closed shields in which the earth and water pressures at the working face are balanced with the aid of the soil excavated by the boring head in the pressure-controlled excavation chamber.
Predominant areas …

Aug 27, 2008

Working face with earth pressure support - structure of the shield machine

(Image: Earth pressure balance shield of type EPB 1500 (external diameter 1830 mm) with transport cart with reference to [FI-Herreb] [Image: S&P GmbH] - Longitudinal and cross sections)

Aug 27, 2008

Control of the support pressure

(Image: Attention!)

The support pressure is indirectly monitored by the speed of rotation of the spiral and the variably adjustable opening cross-section of the discharge slide gate between the auger and the discharge pipe (A cladding tube at the end of the spiral conveyor with an opening for the discharge of the conveying medium [Herre01]) and thus the conveying quantity of the spiral conveyor as well as the jacking speed, is regulated with the …

Aug 27, 2008

Demands on the subsoil and mud

(Table: Demands on the subsoil and mud for the use of earth pressure balance shields )

Aug 27, 2008

Conditioning

(Image: Possibilities of foam conditioning - Sketch of principle - Test run of a shield machine DN/ID 1500 in the works [FI-Herreb])

If the consistency of the excavated soil is insufficient, or if the application limits of the shield machines are be extended to non-cohesive and inhomogeneous soils, the preferred area of application of EPB shields, then the soil must be artificially conditioned. Suitable additives for this are:

Water
Suspensions based …

Aug 27, 2008

Foam conditioning - mode of action

(Image: Mode of action of foam conditioning)

Aug 27, 2008

Foam conditioning - limits of application

From a process point of view, the limit of application of an EPB shield with foam conditioning is reached when one of the following cases occur:

Application limit of an earth pressure balance shield with foam conditioning - case 1:

By injecting a highly viscous foam, no sufficient support pressure can be created.
Causes: particle distribution is too coarse or compactness of the soil is too low
Consequence: foam only escapes through the working …

Aug 27, 2008

Earth pressure balance shield - critical operating conditions

(Image: Attention!)

Critical operating conditions of an EPB shield can occur even through small deviations of balance conditions, with excavation chamber overpressure as well as with under-pressure.

What may be the causes of critical operating states?

(Image: Question)

What may be the consequences of critical operating states?

(Image: Question)

Aug 27, 2008

Earth pressure balance shield - critical operating conditions

(Image: Attention!)

Critical operating conditions of an EPB shield can occur even through small deviations of balance conditions, with excavation chamber overpressure as well as with under-pressure.

Causes of critical operating states:

operating errors of the shield machine
too late adaption to changing subsoil conditions

Consequences of critical operating conditions:

crown collapse
subsidence
break into the open
machine downtime

Aug 27, 2008

Earth pressure balance shields - operating conditions

(Table: Operating conditions of the earth pressure balance shield [FI-Steina])

Aug 27, 2008

Critical operating condition - condition 2

(Image: EPB shield with incomplete filling of the working chamber with danger of caving (Condition 2a) with reference to [Wilms95] [Image: S&P GmbH])

Critical operating condition - condition 2a

results from a too high soil removal
the upper area of the excavation chamber is not filled
correction via change of the torque of the spiral conveyors
danger: crown collapse with corresponding subsidence at the ground surface

(Image: EPB shield with hardened material …

Aug 27, 2008

Critical operating condition - condition 3

Critical operating condition - Condition 3

Results directly from condition 2a or also after longer downtimes.
The excavation chamber is incomplete and the upper area is filled with water.
Danger: water enters the area of the spiral conveyor and causes liquid to muddy consistencies of the mud.
Pressure-balancing function of the spiral conveyor cannot be maintained.
Increased danger of crown collapse up to breaks into the open.

(Image: EPB …

Aug 27, 2008