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International Conference and Exhibition on Tunnelling and Trenchless Technology7-9 March 2006, Subang, Selangor, MALAYSIA

MODULAR CONCEPT GUIDANCE SYSTEM FOR FULL COVERAGE OF PIPEJACKING APPLICATIONS

NOD CLARKEHackston, Jürgen Göckel & Manfred Messing

VMT GmbH, Bruchsal Germany

ABSTRACT

In the ever expanding range of pipejacking projects there is currently no automatic guidance system available on the market that gives the optimal and most profitable solution for all applications in the 600mm – 4m+ range.

The current available automatic navigation systems can be divided into: 4 main classes, simple laser with Active Laser Target Unit for shorter drives and for curved and extended distance drives either a gyro compass based system in combination with electronic hose level or a Motorized Laser Theodolite Systems with Active Laser target or an Automatic Traverse Systems.

Choosing the most appropriate system for the project involves detailed knowledge of the alignment geometry, diameter, technical specifications (machine type, advance type), geology, specifications in the tender documents and economic considerations. Typically however any follow on projects that the contractor is awarded will have differing criteria that reduce the effectiveness in the reuse of the initial system.

Having previously supplied the full range of guidance systems VMT GmbH has now created a modular concept system that enables the user to mix and match the necessary components needed to give complete flexibility in the choice of the most effective system for each project.

This paper details of the advantages of this flexible modular based system which enables the job site staff to always work with the same (or with similar), components; monitor display, menu navigation, system editor and handling. Printouts always have the same style format, regardless of which system is used.

In addition to the navigation modules of this system there are also substantial complementary systems which can be easily connected to the SLS-XL. These modules deal with data recording and documentation of all advance processes and cover the requirements that are increasingly included in the tender documents, such as: - Recording and display of pressures and extensions of the interjack stations, steering cylinders and main jacks, Video recording and measurement to the heading face on open face machines, joint gap measurement and full integration to the machine PLC.

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INTRODUCTION

Since its establishment in 1994, systems from VMT GmbH have been responsible for the successful navigation of more than 400 tunnelling projects throughout the world, achieving the desired alignment in association with a wide range of tunnelling machines. The company was set up to supply, from its headquarters in Bruchsal, Germany, tailor-made solutions, services and surveying systems to the international tunnelling industry. Development of specific systems for the guidance of Tunnel Boring Machines in segmentally lined and pipejacked tunnels has been the major focus of the company’s product development strategy to date. Sales and rental of VMT equipment around the world has established the company as a leading Survey Technology Supply Company.

EXISTING SYSTEM COMPARISON

Having developed systems for basic straight line drives, curved bores and extended distance projects, VMT engineers have for some time been aware that no single system currently available offers an automatic measuring system to the pipejacking market that gives the optimal and most profitable solution for all application ranges where navigation is concerned. Each of the common systems used has its special field of application and various strengths and weaknesses.

VMT engineers have defined the requirements for such an optimal system whereby, for a given project, different criteria must be considered including:

Alignment Geometry Bore Diameter Technical Specifications (machine type,

advance type) Geology (homogeneous, inhomogeneous) Specifications in the Tender Documents (measurement interval, additional

measuring equipment) Economic Considerations - Minimizing of down time during the advance

Automatic navigation systems that are currently available can be divided into the four main categories:

1. The Simple Laser – Target Unit Systems2. Laser Theodolite Systems with Automatic Laser Target; 3. Automatic Traverse Systems.4. Gyro based navigation systems in combination with electronic hose levelling

system.

Laser – Target Unit Systems are generally used on short, straight drives in all diameters and advance techniques but can have restrictions on use in compressed air drives. The main advantages of the system are their cost-effective, user-friendly, easy to handle and effective characteristics (laser control takes minimal time). However, the disadvantages

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are that they are suitable only for straight drives, refraction problems can occur on the laser beam, shaft movement can be problematic and the system has a restricted measurement area limited by the screen size of the target.

Figure 1 – Active Laser Target Unit

Laser-Theodolite Systems offer suitability for long-range and curved bores starting from DN1200. There are however restrictions within air pressure advances or when using muck skips. Advantages are that all alignment geometries are achievable, a continuous authentic display of the TBM position is available, control measurement interval of 60 m to 120 m can be used, advance is possible even during system measurement work and the system is very efficient because of this.

Figure 2 – Motorized Laser theodolite on self levelling platform.

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Automatic Traverse Systems on the other hand are designed for use on extended distance drives and alignments with large radius curves and on drives with slurry machines operating without muck skips. Advantages of these systems include: Connection to the shaft and surface network during each measurement; Precise accuracy in plan and elevation; and High efficiency (only a few control measurements are required). However disadvantages can be high cost; numerous installations in a pipeline; a requirement for intervisibility; and interference due to electronics in the pipeline.

Gyro compass based systems with electronic hose levelling systems however offer navigation for both straight and curved drives with small diameters (starting from DN800) and can be used on compressed air drives. There are restrictions in complex curves and with inhomogeneous geology. Advantages with the system include: Compact construction; No line of sight required; Simple control measurements; Precise elevation data through the electronic hose levelling system and it is applicability to all advance methods. Its disadvantages however are that frequent check measurements are needed (every 30-50m); it is drift dependent; there is no continuous display of the machine position; advance is interrupted during system measurements (approximately 4 minutes each time); Vibrations on slurry advance systems can disrupt measurement and careful handling of the hose levelling system is needed.

SYSTEM DEVELOPMENT

All the guidance systems described in this article use hardware components that are suitable for the rugged environmental conditions experienced during pipejacking and follow the IP65 industrial standard. All the important information for the successful navigation of the drive is clearly displayed on the monitor in real-time and recorded to a database for documentation and post-processing. The Guidance PC can be located in a control cabin on the surface or in the TBM itself, to-date over 190 of these projects have been successfully completed.

The SLS-Basic Guidance System is designed to navigate short straight drives in pipe jacking projects (max. length ~200m). Inside the starting shaft a laser beam is orientated towards the laser target inside the TBM. The horizontal and vertical offset of the laser beam to the centre of the target unit is the measure for the deviation of the TBM to the DTA. A built-in dual axis inclinometer inside the target measures the roll and pitch of the TBM which will be shown on the display of the Guidance PC. The angle of incidence of the laser reference to the target gives the horizontal tendency of the TBM. The vertical tendency will be calculated with help of the pitch angle.

A measuring wheel, which is mounted inside the start shaft on top of the concrete pipes, is made to rotate while pushing the pipes. The rotation is transferred into linear information and indicates the progress of the advance.

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Figure 3 – Schematic of SLS-Basicplus System

The operating principle of the SLS-Basicplus Guidance System is more or less identical to the SLS-Basic with the difference that an electronic hose levelling system is integrated into the system and used for the precise, refraction-free determination of the height of the TBM.

The reference module with integrated height sensor is mounted inside the start shaft. Another height sensor is mounted inside the TBM. Both sensors are connected by a hose line filled with propriety liquid.

The different pressures which are indicated at these two pressure sensors are a precise measure for the height difference between the sensors. The combination of the electronic hose levelling system with the SLS-Basic enables the precise navigation of straight drives up to a length of about 400-500m.

VMT’s SLS-RV guidance system is designed for the navigation of long distance and curved pipe jacks;. The main component of the system is a servo-motorised laser theodolite that is mounted inside the tunnel on a special bracket, which moves along together with the pipeline. The actual position of the laser theodolite is continuously calculated using the known ‘as-built’ position of the already installed pipes.

Figure 4 - Schematic of SLS-RV System

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The calculation principle of this system is based on the theory of the invariance of the pipeline, which means that all pipes must follow the same course as that driven by the TBM.

Even the drift of the TBM will be recognised and will not influence the accuracy of the system calculations. As the complete hardware of the SLS-RV System is installed in the front (first 100 m) of the tunnel, refraction will not influence the measurements for the vertical TBM position.

The intervals for the necessary check measurements the regular calibration of the system depend on the inside diameter of the pipes and the curvature of the DTA, but these are typically between 80 and 100 m.

An automatic measurement cycle is undertaken approximately every 500 mm, by the system to verify the azimuth to the back sight reference target prism and the location of the reference prisms. The measurement cycle can be carried out during the advance and does not require a stand-still of the TBM.

The operating principle of the SLS-RVplus software module is more or less identical to the SLS-RV with the difference that an electronic hose levelling system is used to establish the TBM elevation. A reference module height sensor is mounted in the start shaft with another mounted in the tunnel next to the bracket on which the Laser Theodolite is mounted. The difference in elevation is again found using the measure of the pressure difference between the two sensors. This is used in cases where precise height information is needed where unstable geological and hydrological conditions prevail, causing such anomalies as pipe float which affects the height accuracy of the SLS-RV system.

VMT’s SLS-G system offers a gyro-based guidance platform, which uses a self-levelling, north-seeking gyro compass for the determination of the horizontal position and azimuth of the TBM.

Figure 5 - Schematic of SLS-G System

Calculations using this system are based on the principle of the “dead-reckoning” which means that it is assumed that the TBM will move exactly along the direction which is defined by its axis. The difference between the direction along which the TBM is moving

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and the axis of the TBM is called drift. This drift will influence the calculations of the SLS-G.Check measurements for system calibration must be carried out every 40 m in order to determine the TBM drift and reduce its influence to a minimum by pre-setting this value for further calculations. The TBM elevation is precisely determined using the integrated electronic hose levelling system. Provided the hose levelling system is correctly handled, it is not normally necessary to do check measurements for the height. The horizontal position of the TBM will be updated after each gyro measurement; the vertical position is updated continuously. During the gyro measurements, normally after each 1m advance, the machine has to be stopped for about 4 minutes.

VMT GmbH has always advised clients on which navigation system is most suited to their requirements and it was out of this service that engineers looked at combining the available options into a single common platform. By purchasing a basic module with it’s hardware components and SLS-Basic operating module for short, straight advances, the optional leasing or purchase of further navigation and complementary modules for special projects could be offered as and when required, giving a cost effective and very flexible overall solution.

Figure 6 – North-seeking Gyro Compass

The SLS-XL Range

Now known as the SLS-XL navigation range, the combined single platform offered by VMT means that project staff always work with the same or very similar components. Monitor display, menu navigation, system editor and handling interfaces do not change so operators do not have to adjust to different systems.

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Figure 7 – Common display style for SLS-XL range.

In this way data printouts always have the same format, regardless of which system combination is used and this can mean a smooth transition from one system to another with continuous data recording in the same format, identical printouts and the same visualization.

Such a range also offers high flexibility, with the most suitable and cost effective system being used for every project, whilst freeing the client from a commitment to one style of navigation system. This also brings with it practical advantages such as reduced cabling with only one data line being necessary through the pipe.

The basic module of the SLS-XL consists of the basic hardware components and the Navigation module of the SLS-Basic.

Figure 8 – SLS-XL Modular Structure

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In addition to this basic module the complementary systems are easily connected to create the required SLS-XL configuration.

These modules deal with data recording and documentation around all advance processes and cover all requirements that increasingly appear in tenders for pipe jacking construction such as the recording and display of pressures and extensions of the interjack stations, steering cylinders and main jacks.

Figure 9 – Ram pressure & Extension module

Video observation and recording of pictures of the heading face on open face machines in order to receive a qualified documentation of the ground conditions. A network-compatible camera controls the works at the open heading face. The pictures will be sent to the PC and recorded on the hard disc for documentation. The file name of each picture includes date, time and actual chainage of the advance. In this way areas with difficult geological conditions for example can be clearly assigned and proven afterwards.

Figure 9 – Video Observation Face

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Heading Face Distance Module for the observation of the depth of penetration of the shield in the ground on open face machine. A laser distance meter is mounted in the cutting head of an open face shield and measures continuously the distance to the heading face.

Figure 10 – Heading Face distance module

As soon as a pre-defined limit is exceeded, a warning will be shown on the system monitor. The measured distances will be recorded in a file for subsequent documentation.

A Joint Observation Module is also available that observes joint movement between the pipes in order to adjust the jacking forces to changing static loads at the pipe faces. This is designed to avoid damage to the pipes during the jacking process.

Figure 11 – Schematic of Joint Observation Module

It is VMT’s belief that with the new SLS-XL range modular navigation concept the user will be able to individually configure the necessary components that allow each pipejack to reach its target successfully and economically, giving flexibility to both customer and project specific requirements by allowing optimal configuration of the components. Although differing hardware components may be used, the ‘recognition factor’ for the operating personnel will be very high, thanks to the common system and software philosophy, eliminating many of the pressures that come to bear when changing from one known system to another unknown one.

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CONCLUSIONS

By combining the experience gained from the creation and supply of a range of guidance systems to over 400 projects including approximately 320 individual pipejacking drives totalling 135,000m, VMT engineers have been able to create a modular range of components for use on the complete range of pipejacking applications on all types of machine from any manufacturer as a cost effective solution for accurate navigation throughout the world.

REFERENCES

Broomfield, J. Complex Pipejack Alignment in South Korea. No-Dig International Nov / Dec 2003

Clarke-Hackston, N. Guidance for Extended Distance & Curved Pipe Jacking Applications. Presented at the Microtunnelling Short-course. Feb 9-11 2000. Colorado School of Mines, Boulder, CO, USA

Clarke-Hackston, N. Guiding the way Forwards. Tunnels & Tunnelling International, April 2003.

Großkopf, J. & Fischer, A. 2004 Good cooperation leads to success. Gute Zusammenarbeit führt zum Erfolg April 2004

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