Monitoring and Controlling the Canning Town Flyover Above Crossrail Tunnel Boring Machine

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"By choosing to use NI’s platform for this project we were able to minimise installation time which was a key factor, considering that the major part of the installation took place under engineering hours for railway which are tight."

- Aris Nikolarakos, Mabey Hire Ltd

The Challenge:
Providing a high precision monitoring and hydraulic control system for the Canning Town Flyover, while ensuring the Docklands Light Railway service remained unaffected by the Crossrail development beneath.

The Solution:
Implementing a system to monitor and control the structure using the CompactDAQ which provided high sampling rates and accuracy and allowed valuable measurements to be made as well as the integration of a high precision hydraulic system. This combination provided a unique system that enabled us to successfully complete this challenge.

Author(s):
Aris Nikolarakos - Mabey Hire Ltd
David Holland - Mabey Hire Ltd

Company Background

Since the foundations of Mabey Hire in 1923, we have built a reputation as a UK market leader in the design, supply and execution of temporary propping and jacking solutions, and bridge building and have worked extensively in structural and civil engineering. Our capability in this field is based on highly developed modular shoring and jacking systems combined with our specialist engineers and site teams, a fusion that remains unrivalled in the UK.

Our Monitoring and Control division, ‘Mabey LIVE Instrumentation’, specialises in real-time monitoring solutions. The team is comprised of a unique combination of experienced engineering and installation teams, Specialist Structural, Instrumentation and Software Engineers. We use the latest equipment to implement integrated hydraulic control and high accuracy monitoring systems to offer cost effective and practical solutions.

 

Introduction

The Crossrail tunnel boring machine was planned to pass beneath the southern sections of the Canning Town Flyover, which is a 330m long viaduct that forms part of the Docklands Light Railway. The flyover provides an elevated route to carry the Poplar to Becton line over the Stratford and Poplar to Woolwich Arsenal lines. It combines precast concrete and steel structures to support the rails with substructures made of reinforced concrete. The original design of the flyover implemented provisions in the design to facilitate the removal of the bridge bearings and the use of jacking to control the relative deck movements.

 

Figure 1: Crossrail Tunnel Boring Machine

 

Mabey LIVE Instrumentation was brought in to design, install and operate a monitoring and control system to minimise the effects of the tunnel boring machine on the viaduct as it passed beneath. Ground movements adjacent to the structure were monitored before, during and after tunnelling operations until they were no longer significant. To implement the system, we replaced the permanent bearings with temporary, hydraulically adjustable bearings, and monitored and accounted for the bridge’s substructure movements during the passage of the tunnel boring machine to maintain the superstructures position.

 

Application

Based on the severity of works taking place in the area and the importance maintaining an uninterrupted service on the Docklands Light Railway and the nearby London Underground Railway, a strict design interface statement was in place over the monitoring and control scheme. The design interface statement detailed a 0.25mm movement tolerance on the viaduct in any direction.

In order to satisfy such a demanding specification, which required a reliable, accurate and failure resilient design, we selected National Instruments products for our data acquisition equipment. Other systems where considered for this project, however we settled on the National Instruments platform based on the simplicity and flexibility offered by their products. The versatile and modular nature of the CompactDAQ platform championed this family of products for our project. The scalability of the system as the project progressed, along with the cross-compatibility of the equipment, allowed installation to become easier and faster.  The main benefit for us was the seamless integration between LabVIEW and the NI hardware chosen for this project.

Our engineers used LabVIEW to create a comprehensive program that acquired data, converted raw measurements into the required engineering units and integrated third party products. We created an all in one software solution. Our engineers developed a unique user interface for presenting the measurements in a graphical and tabular form. Projects Engineers were able to find the required measurements and get a visual representation fast, making interpretation easier.

 

Technology

With NI’s CompactDAQ modules we performed high accuracy measurements at variable sampling rates for each of the sensors installed on the structure. The monitoring system supported two sampling rate modes. The first provided readings at a 100Hz rate over the baseline period and the second was using a 1 kHz sampling rate which was used over the jacking mitigation works as well as over the period of the adjacent tunnel boring operations. The data produced over the full project every second was 600,000 readings based upon 200000 raw readings taken from all the sensors utilised.  

A National Instruments CompactDAQ 9184 Ethernet chassis was installed on each of the 12 piers. This minimised the quantity of cable that we would traditionally install on such a scheme and allowed a ring network to be formed to add redundancy to the system. All chassis were reporting to the main control computer using two Ethernet cables that carried measurements from the whole of the structure and covering the full length of 330m between the outer piers.

 

Figure 2: Tunnel Machine

 

The Monitoring and Control System for each concrete pier consisted of:

80 + Linear potentiometers (100mm range – 0.01mm accuracy)

25 Dual-axis servo-inclinometers (±5° range – 0.001° accuracy)

70+ Pressure sensors (0-700 Bar range – 1.75 Bar accuracy)

12 Digital level (0.3mm accuracy)

 

Linear potentiometers allowed engineers to observe:

Vertical movement of the concrete and steel decks relative to the concrete pier below

Longitudinal relative movement between the piers and the deck

Transverse relative movement.

 

The dual axis servo-inclinometer and digital level instruments allowed engineers to observe:

Rotation of each pier in free space

Vertical movement of each pier relative to a reference point, which was strategically positioned outside the zone of influence of the tunnel boring machines.


Pressure sensors allowed engineers to observe:

Force applied to the steel and concrete precast deck sections by the hydraulic jacks

Cross-reference potential movement due to increased pressure.

 

The viaduct was “floated” on hydraulic jacks at the bearing locations on each pier. The permanent bearings were removed and temporary articulation was designed and installed using structural steel. We used an NI 9265 analogue output module to integrate the instrumentation installed at each pier with a total of 60 hydraulic cylinders and a bespoke synchronised hydraulic control system. Using this module, we were able to control the load from each of the hydraulic jacks providing high assurance to our customer. The total settlement that was observed over the completion of the project was 15mm over the Southern abutment. The twist induced was maintained within the tolerances described in the design interface statement.

 

Figure 3: Bridge Area Diagram

 

We used our LabVIEW program to present measurements from the physical sensors installed on each pier and the analysed data presenting differential and relative movements. The program was also used to present virtual sensors along with a summary of all the readings regarded in the projects. We could then confirm that the jacking operations were carried out within the tolerance and avoid any disruptions to over ground, ground or underground work activities.

 

Figure 4: Bridge Monitoring Graph

 

Final Thoughts

By choosing to use NI’s platform for this project we were able to minimise installation time which was a key factor, considering that the major part of the installation took place under engineering hours for railway which are tight. We reduced the installation cost and time due to the cross-compatibility and scalability of the system. Having finished this project, we are now able to reuse this equipment for our future monitoring schemes, providing equally high reliability and accuracy.

Following the completion of the intense and demanding 3-year project, we complied with the performance specification for the monitoring and jacking works as set out by the design interface statement. Strict compliance to the requirements of this statement was achieved ensuring timely execution of works, without interruption to the operation of Docklands Light Railway, London Underground Railway and the Crossrail tunnelling operation. This project has enhanced our reputation and takes the technology provided by the group into the 21st century.

 

Author Information:
Aris Nikolarakos
Mabey Hire Ltd
United Kingdom
Tel: 07786074903

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