UNITRACC - Underground Infrastructure Training and Competence Center

Shield machines with partial excavation by hand - classification

(Table: Classification of hand shields according to the type of working face support)

May 18, 2020

SM-T1 - working face with natural support

(Image: Attention!)

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.

(Image: Simple hand shield - working face with natural support) (Image: Handshield - working face with natural support)

May 18, 2020

SM-T2 - working face with partial support

(Image: Attention!)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.

(Image: Hand shield with breast plates - working face with mechanical partial support) (Image: Hand shield with benches (Bench shield) - working face with natural partial support) (…

May 18, 2020

Shield machines with partial excavation by hand - area of application

(Image: Attention!)

Shield machines with partial excavation by hand are predominantly used for:

short jacking distances under 50 m
crossings of traffic ways
jacking of an extraordinary cross-section
groundwater-free soil or rock

May 18, 2020

Area of application for soil classes according to DIN 18319

SM-T1 - areas of application:

stable, cohesive soil, i.e. firm-stiff and very stiff cohesive soil (soil class LBM 2 and 3 and/or LBO 2 and 3 according to DIN 18319) with a compressive strength of approx. 1.0 N/mm²
Rock with uniaxial compressive strength ≥ 5 N/mm² (classes FD 2 to 4 and/or FZ 2 to 4)

SM-T2 - areas of application:

loose to densely compacted non-cohesive soil (classes LNE 1 to 3 and/or LNW 1 to 3) with a particle size concentration < …

May 18, 2020

Shield machines with partial excavation by hand

May 18, 2020

(Image: Shield with fixed intalled excavation machine - working face with natural support (SM-T1))

The shield machines with mechanical partial excavation correspond in concept to the design of the hand shield. They feature a mechanized 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.

Examples:

(Image: Principles of support for open shield …

May 18, 2020

Shield machines with mechanically partial excavation - classification

(Table: Classification of shield machines with mechanically partial excavation according to their type of work face support )

May 18, 2020

SM-T3 - working face supported by compressed air

Shield machines with compressed air support (SM-T3) are closed shields based on shield types SM-T1 and SM-T2 in which the working face is pressurized with the flow off compressed air, e.g. "air with a positive pressure of more than 0.1 bar (10 kPa, 1.5 psi) above atmospheric" [ [DINEN12110:2014]] in order that the working chamber (defined in EN 12110 [ [DINEN12110:2014]] as "space in which work is carried out in compressed air") can be kept free …

May 18, 2020

Defintion of compressed air support according to DIN EN 12110

Working chamber:
Space in which work in compressed air is carried out.
[ [DINEN12110:2014]]

Air lock:
Pressure vessel with one or more chambers with access doors, which can be sealed and pressurized with compressed air.
[ [DINEN12110:2014]]

Material lock:
Air lock through which only material or equipment goes into or out of the working chamber.
[ [DINEN12110:2014]]

Personnel lock:
Air lock through which only persons go into or out of the working chamber.

May 18, 2020

Working face supported by compressed air - air locks

(Image: Attention!)

When pipe jacking under air pressure, the working chamber e.g. the region from the working face to the air lock must be made airtight by means of a pressure bulkhead ("equipment which separates spaces with different pressure levels" [ [DINEN12110:2014]]) from the ambient atmosphere.

Types of air locks:

material lock
personnel lock
combined lock

(Image: Longitudinal section of an air lock system in the trailing shield segment with …

May 18, 2020

Arrangement of air locks

The arrangement of the locks is of central importance from a site operation point of view. In principle, three variants with different effects on the size of the working chamber are possible in pipe jacking:

Air lock(s) above or in the starting shaft ("shaft locks")
Moving air lock(s) in the pipe string
Moving air lock(s) in the trailing shield segment

Air lock above the starting shaft ("shaft lock")

(Image: Principle possibilities of arranging …

May 18, 2020

Working face supported by compressed air - area of application

Shield machines with compressed air support are used [Krets72] :

In soil types where the lowering of the groundwater is not to be recommended on technical, ecological or economic reasons
In regions where the lowering of the groundwater could cause damaging subsidence
For jacking under waterways
For stabilizing the working face

May 18, 2020

Working face supported by compressed air - limits of application

The limits of use for jacking in compressed air are determined by [Krets72] :

The pressure permitted by the compressed air ordinance [ELEXV97] of maximum 3.6 bar (360 kPa, 52.2 psi)
The air permeability of the subsoil
The minimum cover depth above the crown of the pipe (assessment of blow-out safety)
Economics, which can only be achieved with longer jacking lengths due to the high investment costs
The time and costs due to persons and materials …

May 18, 2020

Definition blow-out

Blow-out:
A blow-out is the abrupt escape of compressed air out of the working chamber through loosened or remoulded subsoil when working under compressed air. In this case, it refers to the sudden escape (also blowing-out) of the supporting compressed air on the surface of the site or the water bed [DS853].

In general, there are two types of blow-outs [Baben99]:

Gasometer blow-out
Erosion blow-out

(Image: Types of blow outs with reference to [FI-…

May 18, 2020

Gasometer blow-out

The gasometer blow-outs occurs as a result of the formation of a compressed air store in stratified soil and occurs especially in inter-bedded soils or with an insufficient cover depth between the surface and the crown of the pipe [FI-Baben].

(Image: Types of blow outs with reference to [FI-Baben] [Image: S&P GmbH] - Gasometer blow out)

May 18, 2020

Erosion blow-out

An erosion blow-out is caused by so-called flow channels (air paths) of natural origin (e.g. ice age erosion channels, fissures in the rock mass) or of artificial origin (e.g. insufficiently sealed or filled investigation boreholes, fountains or possibly also release borings for preventing gasometer blowouts, etc.) [Baben99].

In this case, the flow process of the air is no longer continuous and the air flowing through the flow channels displaces the …

May 18, 2020

Work under compressed air

(Image: Attention!)

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.

(Table: Staying and decompression times for working in pressurized areas)

May 18, 2020

Shield machines with mechanical partial excavation

May 18, 2020

SM-V1 - working face with natural support

Working face with natural support

(Image: Shield machine with full-face excavation - working face with natural support (SM-V1))

Shield machines with full-face excavation and natural support of the working face are open, fully mechanized shields. They are the simplest form of shield machines with full-face excavation and require a stable working face.

Most frequent areas where shield machines with full-face excavation and natural working face support are used:

groundwater-free, …

May 18, 2020

SM-V1 - working face with natural support

Working face with natural support - procedure

The subsoil loosened with the aid of the tool-equipped cutting wheel, is transferred by a conveyor belt, scraper belt or a spiral (auger) to a downstream conveying installation (transport cart, tracked conveying bucket or conveyor belt).

The operating and steering of the shield machine are carried out directly at the site by a machine operator who has a continuous view of the working face.

(Image: Open shield machines with cutting wheel and natural …

May 18, 2020

SM-V1 - working face with natural support

May 18, 2020

SM-V2 - working face with mechanical support

Working face with mechanical support

(Image: Shield machine with full-face excavation - working face with mechanical support (SM-V2))	Shield machines with full-face excavation with mechanical support of the working face (also called scraper cutting head shields [Tunnel98]) are open fully mechanized shields. The support of the working face is achieved by means of an almost fully closed cutting wheel covered with excavation tools and called scraper cutting head.
Predominant areas …

May 18, 2020

SM-V2 - working face with mechanical support

Working face with mechanical support - procedure

The spoil enters through the soil entry openings and is transferred by a conveyor belt, scraper belt or a spiral (auger) to a downstream conveying installation (transport cart, tracked conveying bucket or conveyor belt).

The soil entry openings are either fixed [Akker01] or variably adjustable with closable sectors [FI-Lovata].

(Image: Open shield machine with scraper cutting head and mechanical support of the working face - Variably adjustable …

May 18, 2020