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Aug 05, 2008

Modules

Utility Tunnelling: Micro Tunnelling - Part 2

Microtunnelling with soil displacement

In the ACEMOLE PL 30 method (PL = Press-in Long Distance) [ [FI-NTTa]] , the displacement and steering head consists of a closed blunt cylinder that is extended hydraulically for soil displacement and, if required for steering, can be angled a maximum of ± 1.5%. After completing the stroke, the pipe string and the microtunnelling machine are advanced by the jacking station by the amount of the stroke [Matsu96].

(Video: Displacement- and steering …

Aug 05, 2008

Modules

Utility Tunnelling: Micro Tunnelling - Part 2

Microtunnelling with soil displacement

Microtunnelling machines of the HERRENKNECHT AVB type possess a coned displacement and steering head at whose point a rotating three-spoked rim cutting wheel is arranged.

(Image: HERRENKNECHT AVB microtunnelling method with soil displacement [FI-Herreb])

Jan 04, 2010

Modules

Utility Tunnelling: Micro Tunnelling - Part 2

Aug 05, 2008

Modules

Utility Tunnelling: Micro Tunnelling - Part 2

Measures to reduce jacking forces

(Image: Attention!)

In all jacking methods in which the jacking pipes are pressed in with the aid of a jacking station positioned in the starting shaft (e.g. microtunnelling and pipe jacking ), the jacking force required is determined by the penetration resistance encountered by the boring head and the skin friction along the pipe string.

(Video: Operating forces during pipe jacking)

Video: Operating forces during pipe jacking [Image: S&P GmbH]. …

Jan 25, 2005

Modules

Utility Tunnelling: Micro Tunnelling - Part 2

Measures to reduce jacking forces

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.
(Image: Penetration resistance and jacking force)

Aug 05, 2008

Modules

Utility Tunnelling: Micro Tunnelling - Part 2

Measures to reduce jacking forces

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 …

Aug 05, 2008

Modules

Utility Tunnelling: Micro Tunnelling - Part 2

Measures to reduce jacking forces

Overcut:
The annular space around the pipe deliberately created by using a cutting head or shield of greater dimension than the outside dimension of the pipe [DINEN12889:2000].

Overcut:
Half of the difference resulting from borehole diameter and outer pipe diameter (ideally an even annular space around the pipeline) (with reference to [DWAA125:2008]).
(Image: Annular space fluid supported)

Jan 25, 2005

Modules

Utility Tunnelling: Micro Tunnelling - Part 2

Measures to reduce jacking forces

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 …

Aug 05, 2008

Modules

Utility Tunnelling: Micro Tunnelling - Part 2

Measures to reduce jacking forces

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. …

Aug 05, 2008

Modules

Utility Tunnelling: Micro Tunnelling - Part 2

Measures to reduce jacking forces

Method of operation and procedure

In this variant, developed in Japan, the principle of soil removal and soil displacement are combined. A portion of the soil loosened by the cutting head is pressed and compacted through the exit opening into the annular space over the periphery of the shield skin against the borehole wall.

(Image: Combination of soil removal and soil displacement [FI-Isekib] - Boring and steering head with soil exit openings for …

Aug 05, 2008

Modules

Utility Tunnelling: Micro Tunnelling - Part 2

Measures to reduce jacking forces

(Image: Pros and cons)

Advantages of jacking in combination with soil excavation and soil displacement:

  • improvement of the soil parameters of the borehole wall
  • positive influence on the borehole stability
  • positive influence of the load and skin friction
  • reduction of the pore content in the compaction zone; thus the development of the filter cake caused by bentonite suspension is facilitated and the flow off of the lubricant is prevented

Aug 05, 2008

Modules

Utility Tunnelling: Micro Tunnelling - Part 2

Measures to reduce jacking forces

Method of operation and procedure

The method is characterized in that jacking is carried out by means of an endless hose that advances with the jacking and that is contained in a magazine in the trailing shield segment. This soft PVC hose has a thickness of 0.3 mm and envelopes the jacking pipes.
(Image: Jacking with hose envelope - Section through the hose magazine with reference to [Tohym87] [Image: S&P GmbH])

Aug 05, 2008

Modules

Utility Tunnelling: Micro Tunnelling - Part 2

Measures to reduce jacking forces

(Image: Pros and cons)

The advantages of the jacking method with hose envelope can be summarized as follows:

  • Ensuring the water tightness of the pipe string
  • Minimizing the required jacking force
  • Possibility of greater jacking distances
(Image: Pros and cons)

The disadvantage of jacking with hose envelope:

  • greater installation effort inside the starting shaft

Aug 05, 2008

Modules

Utility Tunnelling: Micro Tunnelling - Part 2

Measures to reduce jacking forces

Method of operation and procedure

Using this technique when microtunnelling with auger spoil removal , the jacking forces for overcoming the penetration resistance (which is difficult to calculate) are introduced through the spiral conveyor guide pipe. When microtunnelling with hydraulic spoil removal, these jacking forces are provided by means of an inner steel auxiliary pipe.
(Image: ENVILINER method of type SH-253 for nominal pipe size DN/ID …

Aug 05, 2008

Modules

Utility Tunnelling: Micro Tunnelling - Part 2

Measures to reduce jacking forces

Method of operation and procedure

The gripper method is a further development of the "jacking with uncoupling of the penetration resistance and skin friction" in which, additionally, the forces to be overcome in skin friction and those to be taken up by the jacking pipes are substantially reduced by breaking them down into equal force components [Isele94].

The separation of the jacking force for overcoming skin friction is carried out with the aid …

Aug 01, 2008

Modules

Utility Tunnelling: Micro Tunnelling - Part 2

Aug 05, 2008

Modules

Utility Tunnelling: Micro Tunnelling - Part 2

Measures taken to remove obstacles

(Image: Attention!)

The term obstacle in trenchless installation must be viewed from a contractual [Liepe02] as well as a technical point of view.
(Image: Obstacle)

From a technical aspect, one differentiates between:

  • Non-removable obstacles

  • Removable obstacles

Aug 05, 2008

Modules

Utility Tunnelling: Micro Tunnelling - Part 2

Measures taken to remove obstacles

Non-removable obstacles must be considered unsurmountable in trenchless technology and can only be bypassed.

Inhomogeneity in the subsoil can be considered removable obstacles.

In this case, the unexpected appearance of these obstacles leads to interruptions in jacking for their removal or, in extreme cases, to the abortion of the jacking work and to the abandonment of the already jacked section [Stein84g].

Examples of obstacles:

(Image: Obstacles - …

Aug 05, 2008

Modules

Utility Tunnelling: Micro Tunnelling - Part 2

Measures taken to remove obstacles

Decide for yourself in the following table whether obstacles listed in the left column can be removed or not removed during tunneling. You will find the solution on the following page.

(Table: Classification of obstacles into the category removable or non-removable [FI-Steina])

Aug 05, 2008

Modules

Utility Tunnelling: Micro Tunnelling - Part 2

Measures taken to remove obstacles

(Table: Classification of obstacles into the category removable or non-removable [FI-Steina])

Aug 05, 2008

Modules

Utility Tunnelling: Micro Tunnelling - Part 2

Measures taken to remove obstacles

(Image: Attention!)

Obstacles can be noticed, for instance, by:

  • Increase of the jacking force

  • Blocking of the boring head combined with an increased registration in the tendency of the microtunnelling machine to roll

  • Reduced jacking performance

  • Acoustic, in the case that a microphone is installed in the boring and steering head

Aug 05, 2008

Modules

Utility Tunnelling: Micro Tunnelling - Part 2

Measures taken to remove obstacles

(Image: Attention!)

In all cases in which procedural and mechanical possibilities of the method used are not sufficient to destroy the obstacle, it must be removed [Stein84h].
(Image: Unmanned techniques)

Access to the obstacle from the outside, i.e. from the ground surface
(Image: Manned techniques)

Access to the obstacle from the inside, i.e. from the excavation chamber

Aug 05, 2008

Modules

Utility Tunnelling: Micro Tunnelling - Part 2

Measures taken to remove obstacles

(Image: Groundwater-free)

Removal of obstacles in soil that is free of groundwater:

  • recovery of the obstacle by
    • large-scale boring
    • sinking of a steel pipe
    • excavation of an auxiliary pit
  • sinking of the obstacle
(Image: Groundwater-bearing)

Removal of obstacles in groundwater-bearing soil:

  • groundwater lowering or blockage and recovery as in soil free of groundwater
  • piped drilling underwater and destruction of the obstacle by means of a chopping …

Aug 05, 2008

Modules

Utility Tunnelling: Micro Tunnelling - Part 2

Measures taken to remove obstacles

(Image: Removal of obstacles by destruction and/or removal from an auxiliary pit)

Aug 05, 2008

Modules

Utility Tunnelling: Micro Tunnelling - Part 2

Measures taken to remove obstacles

Step 1

(Image: Removing obstacles by means of sinking - Creating a cased vertical borehole)

Step 2

(Image: Removing obstacles by means of sinking - Pulling the casing up to the top of the microtunnelling machine with simultaneous jacking)

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