Bentonite Handbook

Lubrication for Pipe Jacking

Steffen Praetorius, Britta Schößer

• Publisher: Ernst & Sohn
• Year: 2017
• Print ISBN: 9783433031377
• eBook ISBN: 9783433606537
• Edition: 1
• Topic: Technology & Engineering
• Subtopic: Civil Engineering
• Index: Technology & Engineering

Pipe jacking is a construction process for the no-dig laying of pipes. Successful pipe jacking demands low skin friction between the ground and the jacked pipe. This is achieved with bentonite lubrication. The bentonite slurry fed into the annular gap fulfils several purposes. It stabilises the annular gap by supporting the surrounding ground and reduces friction contact between ground and jacked pipe. The Bentonite Handbook deals comprehensibly with the relevant aspects of annular gap lubrication: starting with the ground conditions, which are of decisive importance for lubrication, through the rheological properties of the bentonite slurry to the technical components of lubrication technology and lubrication strategy. The use of standardised measuring apparatus is described as well as mixing equipment and the automatic lubrication system. Overview tables with calculations and suggested values for bentonite consumption quantities depending on the prevailing ground conditions and the pipe jacking parameters complete the recommendations.

1
Basics

1.1 Basics and technical implementation of bentonite lubrication systems¹⁾

Two basic types of bentonite lubrication systems are differentiated:

• – Interval-controlled bentonite lubrication systems, in which the valves are controlled in a defined sequence.
• – Volume-controlled bentonite lubrication systems (since 2014), in which the valves are controlled according to configured demand along the route; alternatively, the valves can also be controlled in a defined sequence.

Both systems exist both as systems integrated into the control container or as standalone systems.

In general, a lubrication system consists of the parts shown in Fig. 1.1. The first station in the lubrication circuit is the mixing tank, in which the bentonite suspension is dispersed before it is pumped into the storage tank. The bentonite pump supplies the individual lubrication points in the tunnelling machine and in the pipe string.

Fig. 1.1 Principle of construction of the standard Herrenknecht bentonite lubrication system
1: control unit;
2: mixing tank;
3: storage tank;
4: tunnelling machine;
5: lubrication ring;
6: advance pipe;
7: lubrication point;
8: injection fitting;
9: bentonite pump;
10: compressed air supply;
11: control cable;
12: bentonite feed.

In an interval-controlled lubrication system, lubrication cycles are used according to the strategy of the machine driver. A lubrication point (see Fig. 1.2) consists of several injection fittings. The lubrication cycle starts these one after another (e.g. valve 1 – valve 2 – valve 3); thus only one valve is open at any one time. Then the next lubrication point is started.

Generally, normal cycle and extra cycle are differentiated. The normal cycle serves to lubricate the entire tunnel drive. The extra cycle permits in contrast additional control of separately selected lubrication points using the appropriate valves or injection fittings. A larger volume of lubricant can be supplied to the machine using the extra cycle. In addition, each lubrication point sends a feedback signal to the control unit, enabling a check whether the individual lubrication point is actually connected.

In a volume-controlled system, the tunnel length is divided into sections each 1 m long. Each of these sections is assigned a configured ideal quantity of suspension depending on the ground conditions. The lubrication system automatically ensures that the connected lubrication points fill these quantities in the corresponding tunnel sections. The individual components of the lubrication system are basically the same for both systems; they are now described in more detail blow.

1.1.1 Control unit

The control unit is installed in the container or as a stand-alone unit next to the launching shaft. From here, the machine driver controls the tunnel drive and the lubrication cycle. In principle, the machine driver can select each valve in the entire tunnel drive individually. The (maximum) pump pressure is set directly at the pump.

In interval-controlled operation, the control unit enables two different presets for the valve setting. The first method is called “preset quantity”. In this case a defined bentonite quantity is provided, which should be fed through each valve. As soon as the given quantity has been reached, the valve closes and the next valve is opened. The opening time of the valve in this case follows from the flow rate of the bentonite suspension, so a flow meter and pressure measurement unit is required for this control variant, which is connected directly to the control unit. It has the task of recording the flow quantity and sending it to the control unit. For this purpose, a magnetic-inductive flow meter (MID) is often used. This instrument is based on the fact that the suspension flows through a magnetic field and thus induces a voltage, which is recorded by two electrodes.

The second method of valve control is called “preset tim...

Table of contents

• Cover
• Table of Contents
• Title
• Copyright
• Dedication
• Acknowledgement
• Foreword
• List of symbols used
• 1 Basics
• 2 Bentonite and bentonite suspensions
• 3 Additives
• 4 Correct preparation of bentonite suspensions
• 5 Properties of the suspension and measurement processes
• 6 Ground and groundwater
• 7 Bentonite suspensions for annular gap lubrication
• 8 Lubrication technology
• 9 Reporting
• 10 Lists of the required injection quantities
• Literature
• End User License Agreement