UNITRACC - Underground Infrastructure Training and Competence Center

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

Critical operating condition - condition 4

Critical operating condition - Condition 4

Results from a too low conveying performance of the spiral conveyor.
Solidification of the mud in interaction with the agitating of the cutting wheel, especially in and first in the central region, caused by the excessive pressure in the excavation chamber.
Consequence: sticking of machine parts up to downtime of the machine (condition 5).

(Image: EPB shield with compaction of the mud in the excavation …

Aug 27, 2008

Critical operating condition - condition 5

Critical operating condition - Condition 5

Resulting from condition 4 if the too low conveyor performance of the spiral conveyor is not immediately corrected.
With growing torque and reducing jacking speed the mud warms up increasingly.
Warming increasingly affects the solidification and sticking tendency.
In an extreme case the solidification reaches the entire excavation chamber starting from the centre of the excavation chamber.
Consequence: …

Aug 27, 2008

Critical operating condition - condition 6

(Image: Operating condition when encountering an obstacle (Condition 6) with reference to [Maidl97b] [Image: S&P GmbH])

Critical operating condition - Condition 6: Encountering an obstacle

When encountering an obstacle (e.g. a boulder), the contact pressure force must be increased.
Consequence: control and transfer of the required support pressure from the pressure bulkhead via the mud in the surrounding subsoil is immensely impaired.

(Image: EPB shield …

Aug 25, 2008

SM-V5 - working face with earth pressure support

Aug 27, 2008

Obstacle removal

Obstacle removal in partial excavation

(Table: Obstacle removal in pipe jacking with partial excavation [FI-Steina])

Aug 27, 2008

Obstacle removal

Obstacle removal in full-face excavation

(Table: Obstacle removal in pipe jacking with full-face excavation [FI-Steina])

Aug 27, 2008

Obstacle removal

Obstacle removal in special forms

(Table: Obstacle removal in pipe jacking (special forms))

Aug 25, 2008

Obstacle removal

Aug 27, 2008

(Image: Attention!)

If the method is changed, the principle of supporting the working face during jacking is changed. By doing so the technique-specific limits of application can be shifted and/or extended.

It is distinguished between:

unscheduled change of method by modification
schedules change of method by modification
scheduled change of method by conversion.

[Tunnel01]

In all cases, access is necessary for carrying out the required mechanical …

Aug 27, 2008

Unscheduled change of method by modification

Unscheduled changes of the method by means of modification are carried out from the pipe string or from a specially excavated auxiliary shaft.

(Image: Pros and cons)

Disadvantages of unscheduled changes of the method by modification:

the modification is labour-intensive and time-consuming (might take weeks)
causes high costs due to the delay of the construction project
ground stabilisation measures might have to be taken

(Image: Attention!)

Aug 27, 2008

Scheduled change of method by modification

(Image: Attention!)

An expected or scheduled change of method technology must be taken into account early on in the planning phase.

If modification in the shaft is not possible due to topographical or other reasons, then it is carried out in the protection of a specially built station through the pipe string [Tunnel01].

(Image: Pros and cons)

Disadvantages of scheduled change of method by modification:

modification is labour-intensive and time-…

Aug 27, 2008

Scheduled change of method by conversion

(Image: Attention!) A scheduled change of method by conversion can only be carried out with shield types that are further developed for this purpose.
(Image: Pros and cons) Advantages of scheduled change of method by conversion: conversion can take place in each spot of the jacking route relatively short conversion times if the subsequent material conveying does not have to be changed	(Image: Pros and cons) Disadvantage of scheduled change of …

Aug 27, 2008

Conventional changes of method by conversion

(Table: Conventional changes of method by conversion in pipe jacking [Tunnel01])

Aug 25, 2008