In selected pipe joints inductive position sensors are installed to supervise the joint gaps. At least three sensors are mounted and calibrated in each measurement joint. As a general rule, two or three measurement joints are aligned one after another. The inductive position sensors project to the interior of the pipe radially about 8 cm and have a length of about 35 cm. An additionally required box with the side lengths of 32 cm x 32 cm projects …

The jacking resistances consist of:

• Jacking resistance due to point resistance at the working face with and without the influence of groundwater (loses importance with growing jacking length).
• Resistance due to friction between the outer surface and the subsoil (skin friction).
• Additional radially directed guiding forces between the pipe and the subsoil due to curved jacking and steering errors.

Skin friction is determined by:

• radial stress of the pipe as a consequence of earth pressure

• the friction coefficient

The skin friction, which is decisive for a dimensioning of the main jacking station and the jacking pipes, can basically be influenced by an overcut and by filling the overcut with lubricant and support medium.

(Image: T.B.K. system [FI-TBKa] - Injection medium (Polymer drilling fluid consisting of polymer and water)) (Image: Annular …

Curved jackings and steering errors frequently induce additional, radially directed guiding forces between the pipe and the subsoil. These forces increase the frictional resistance.

Since this resistance is dependent on the longitudinal force in the pipe string, it increases in the course of the jacking.

The effect of repeated steering errors is particularly disadvantageous, because the single resistances do not sum up, but lead to disproportionate …

Thus, besides the creation of an overcut and the lubrication and support of the associated annular gap from DN/ID 800 (32 in), intermediate jacking stations can be installed from DN/ID 500 (20 in) for sectional or cyclical jacking of the whole pipe string in order to reduce the jacking force.

New developments in past years have aimed at, among other targets, reducing the individual forces connected with jacking still further and making them more calculable. …

Modern alignment of jacking spans poses constantly increasing requirements for jacking pipes. Looking back to recent years, it is apparent that jacking lengths are getting longer and longer while narrow curves are becoming more and more frequent. Even complicated curve combinations, partly with multiple S- or three-dimensional curves, are no longer a rare sight in calls for tenders.

Conventional pipe joints with pressure transfer rings made of wood …

The amount of water in the hose is dimensioned depending on the project in such a way that the maximum possible jacking force is achieved while ensuring the necessary deviation ability. CoJackHydra allows for significantly higher jacking forces than conventional pressure transfer rings, especially in tight curves or in curve combinations (S-curves) in the jacking alignment.

Visual description of the steering procedure:

1. Higher permissible jacking forces particularly in curves

• Increase of jacking velocity (rarer use of interjack pipes (Intermediate Jacking Stations))
• Reduction of the number of interjack pipes (Intermediate Jacking Stations)
• Higher reserves of force

2. Better angular deflection of the pipe joints

• More flexible line path in planning (strong curvatures, S-curves)
• Higher pipe lengths
• Higher jacking lengths
• Omission of building pits
• Smaller effects …

The hydraulic joint is supplied as single or multiple circumferential closed rings. The position is fixed without drilling or gluing to the pipe end. There must be no recesses or bevels on the inside of the jacking pipe or on the concrete edges of the pipe end. Any recesses on the pipe end faces must not extend to the inner or outer surface of the pipe. This also applies to the concrete on the steel collar to avoid leakages.

The pocket for receiving …

The earth structural stability analysis includes:

• Assessment against hydraulic ground failure during construction of the shaft before the introduction of the base for cut off groundwater

• Assessment of buoyancy security after the introduction of base for cut off groundwater

• Assessment of the earth bearing for introducing the jacking force into the subsoil behind the installed abutment.

The first two assessments that only apply to the shafts reaching …

The jacking resistances consist of:

• Jacking resistance due to point resistance at the working face with and without the influence of groundwater (loses importance with growing jacking length).
• Resistance due to friction between the outer surface and the subsoil (skin friction).
• Additional radially directed guiding forces between the pipe and the subsoil due to curved jacking and steering errors.

Skin friction is determined by:

• radial stress of the pipe as a consequence of earth pressure
• the friction coefficient

The skin friction, which is decisive for a dimensioning of the main jacking station and the jacking pipes, can basically be influenced by an overcut and by filling the overcut with lubricant and support medium.

(Image: T.B.K. system [FI-TBKa] - Injection medium (Polymer drilling fluid consisting of polymer and water)) (Image: Annular …