The Strépy-Thieu boat lift

As long ago as the 19th century, the link between the Meuse and Scheldt basins by means of a navigable waterway proved essential for the transport of coal and, in general, for the economic development of the province of Hainaut. The construction of the canal du Centre was decided by the Law of 4 August 1879. The canal, opened to shipping in August 1917, was designed for barges of up to 300 tonnes. In 1963, modernisation work started in order to bring the canal up to the European 1350 tonne standard. But how could the 70 m difference in level between La Louvière and Thieu be overcome? The previous canal overcame this drop by means of 2 locks and 4 hydraulic lifts each rising 16 m, and brought into service between 1888 and 1919. To replace the six old structures, and taking account of the lie of the land, the solution of a vertical lift compensating a 73 m drop was ultimately adopted. The "steering" of the whole project was carried out by the General Directorate for Waterways Infrastructure, with the cooperation of the Technical Supervision Division for the geotechnical studies. The Electricity, Electromechanics, Computer and Telecommunications Division was responsible for the mechanical, oleohydraulic and electromechanical parts of the lift:

Two independent counterweighted lifts

The structure consists of two independent counterweighted lifts. Each one comprises a mobile cage which travels vertically between the upstream reach and the downstream reach. The mass of each water-filled cage is balanced by 16 suspension counterweights and 8 control counterweights, connected to the cage by a system of steel cables (112 suspension cables and 32 control cables).

Overall view (December 1999).
Overall view (December 1999).

A cage/counterweight subsystem is set in motion by means of 8 winches. Each of these has a "low speed" (LS) reduction gear, driving 2 drums onto which the control cables are wound. A synchronisation loop connects the LS reduction gears to 4 high speed (HS) reduction gears driven by 4 electric motors.

In the centre, a low-speed reduction gear with, on either side, the drums of the control cables with their brakes, and the drums of the counterweight cables.
In the centre, a low-speed reduction gear with, on either side, the drums of the control cables with their brakes, and the drums of the counterweight cables.

The cages and the reaches of water are fitted with vertical gates allowing a cage to be connected with the reach of water opposite which it is located. This equipment is supplemented by watertight seals between the cages and reaches of water, and the lifting mechanics of the vertical gates between them.

The vats and the levels are provided with vertical lift gates.
The vats and the levels are provided with vertical lift gates.
Unique structure

Although the operation of the two cages is completely independent, the boat lift has a unique structure in order to give the whole unit sufficient rigidity and low vulnerability to deformation. In essence, the concrete structure consists of a watertight monolithic floor, a central tower, extending over the whole length of the lift, and the central zone of the slab at level 131.15 m forming the mid-point of the floor of the machine room. The two side sections of this floor consist of metal girders supported on metal columns on one side and the central floor on the other.
The machine room for manoeuvring the cages is located in the upper part of the tower. In the centre of the roof of the machine room is a twin-column structure on which the sides of the roof and the facades are supported. The solutions adopted were guided by the concern to make the system isostatic. The total mass of the whole building is approximately 200,000 tonnes. The overall dimensions are 117 m high, 130 m long and 81 m wide. Each canal bridge consists of 4 aerial spans of 42 m, resting on the central lift tower, on three piers and an abutment with the canal upstream. The mass of one span is 420 tonnes. The piers and the abutment are made of reinforced concrete.

Double gates

Each of the gates of the canal bridges is duplicated by a guard gate to prevent the upstream reach being emptied accidentally in the event of an incident on one of the lifts. The cages are made of a welded construction, with the longitudinal rigidity provided by two box girders 8 m high. These box girders are connected together by braces in the form of a double T, approximately 2.9 m apart, which support the stiffened base.

Each door of the channels bridges is doubled of a door of guard.
Each door of the channels bridges is doubled of a door of guard.

Between the braces, there are two rooms housing the instrumentation necessary to power and control the electrical and oleohydraulic equipment located on the cage.

Overall view of one of the two machine rooms.
Overall view of one of the two machine rooms.

Mechanical equipment

General principles

The masses of the cage and the water that it contains are balanced by 8 suspension counterweights and 8 control counterweights. Balancing of the cage for average operating conditions (cage filled with 3.75 m of water) has proven the most economic solution: the motor torque to be developed by the mechanisms may change direction from one manoeuvre to the next, and even during the course of a manoeuvre (variation of the imbalance due to the weight of the cables). So connections between the winches and counterweights are essential.
In addition, the terminal gear of the speed-reduction gears can only bear a reduced overload. The winches are linked together by a rigid synchronisation loop, and the spread of the torque between the various winches at the input to the winches is undefined. So the torque transmitted by each winch must be controlled and limited at the output.

In the centre, a low-speed reduction gear with the rigid synchronisation loop (orange); either side of the speed reduction gear, a lifting drum with its braking system.
In the centre, a low-speed reduction gear with the rigid synchronisation loop (orange); either side of the speed reduction gear, a lifting drum with its braking system.

With a single counterweight for control and suspension, the spread of the weight between the control and suspension cables could vary in proportions such that the overloads might cause irreparable damage to the terminal gear of the speed-reduction gears. So it was necessary to separate the two functions clearly.
The control counterweight travels freely in a housing located inside the suspension counterweight. The mass of the control counterweight was calculated so that the minimum traction power in each control cable of the cage should never be lower than 100 kN.

Counterweight and hoisting and suspension cables; to the right, start of the canal bridge.
Counterweight and hoisting and suspension cables; to the right, start of the canal bridge.

In the machine room, the mechanisms are divided into 8 groups, each consisting of 2 rows of 7 suspension idler pulleys, 2 hoisting drums equipped with their own locking brake and a low-speed reducing gear. The choice of spooling diameter of the hoisting cables was the result of a compromise between the lifetime of a cable and the cost of manufacture of the drums and pulleys. The diameter of the drums and pulleys (4800 mm) remains compatible with the manufacturing possibilities, and in combination with an 85 mm diameter cable, it allows a number of cables per cage limited to 144.

Suspension mechanisms

Each suspension counterweight is connected to the cage by means of two sheets of 7 steel cables. These cables are attached directly to the counterweight by means of cable lugs, passing through idler pulleys 4800 mm in diameter, and leading down to the cage.
The connection between the counterweight and the cage creates a high level of redundancy, which necessitates the use of a system for spreading the load between the cables. This system consists of oleohydraulic jacks fitted between the end of each cable and the corresponding fixing lug of the cage. The jack piston rod is fitted with a tension handle, enabling the length of the connection to be adjusted. An anti-roll system prevents the rotation of the cable on its own axis, the tension handle or the jack piston road completes the systems.

Each counterweight of suspension is connected to the vat via two tablecloths of 7 Hoisting cable jacks.
Each counterweight of suspension is connected to the vat via two tablecloths of 7 Hoisting cable jacks.
Hoisting cable jacks of a cage.
Hoisting cable jacks of a cage.

The uniform distribution of the load between the cables is obtained by interconnecting, in parallel, the 500 upper sections of the jacks in groups of 7. Interconnecting the suspension jacks of a counterweight actually forms an oleohydraulic spreader beam.
The counterweights are made from a metal carcass, attached to suspension lugs, submerged in a mass of ballasted concrete with a density of approximately 3. As they move between the metal columns, the counterweights are guided vertically on each side by means of 4 spring-mounted rollers. A fixed mechanical stop limits the longitudinal movement of the counterweight. Inside the central tower, the counterweights are sheltered from the wind, and are not guided.

Control mechanisms

Machine room: at the end, on the left, the hoisting drum, to the right the 7 suspension idler pulleys.
Machine room: at the end, on the left, the hoisting drum, to the right the 7 suspension idler pulleys.
Internal view of a low-speed reducing gear during a maintenance operation.
Internal view of a low-speed reducing gear during a maintenance operation.
Metal cables

These cables are of 85 mm nominal diameter, of the Nuflex type, made of 18 strands of 26 Lang extruded zinc-plated steel wires. For the control and the suspension of the 2 cages, the construction of the lift required the use of 36.7 km of cables. That length is subdivided into 224 sections of 98 m for the suspension, 64 sections of 116.2 m for the control of the cages, and 64 sections of 13.7 m for the counterweights.

Metal Cable.
Metal Cable.
Securing devices

At the extreme positions of the travel of the cage, the docking manoeuvres impose a series of movements. In addition, whatever problems may occur with an item of equipment, the cage must be secured. Long-lasting stoppages are also provided for, downstream, for maintenance operations, or repairs to a serious fault. These various functions are carried out by 8 securing systems, 4 upstream and 4 downstream.

Clamping mechanisms.
Clamping mechanisms.
Oleohydraulic unit

The jacks of the locking brakes on each cage hoisting winch are controlled by an oleohydraulic unit consisting of two identical motor pump units, each of which powers a jack. The lock manoeuvring jack unit of each securing device downstream is fitted with two identical motor pump units which normally function in parallel. The control of the securing jacks upstream, the suspension and control cables is carried out by 4 oleohydraulic units located in pairs in 2 rooms installed under the bottom of the cage. One unit powers the jacks relating to one quarter of the cage, or two corresponding hoisting winches and the securing device upstream.
The control and suspension jacks have the specific feature of moving very little, but they must remain completely watertight. This objective was achieved by nickel-plating and chrome-plating of the piston rods, and use of a Teflon piston/cylinder seal. Tests showed the great consistency of manufacture. The maximum stress in the cylinder is 310 N/mm², under a test pressure of 335 bar.

Guidance of the cages

The cage is guided only from the central tower quarter-way and three-quarter way along its length. Each guide rail forms an assembly consisting of:

This is provided, upstream and downstream, by means of runner rollers fitted in pairs on articulated bogies, supported by a rigid chassis. Each transverse guidance system consists of two runner rollers and two counter-runners. The runners, fitted in pairs on an articulated bogie, transfer the forces towards the tower. The chassis of the bogie rests on 6 springs.
Manoeuvring the gates

The ends of the cages and the reaches of water upstream and downstream are closed off by 3 groups of gates per cage:

The raising of the cage/reach gates occurs in several stages:
In the down position, the gate rests on two runners located on its upper section. The role of these runners is to enable horizontal movement of separation imposed by the link rods. The hoisting winch has the specific feature of only having a single drum to raise the two suspension hangers. The hoisting motor, which is asynchronous, is powered by the cycle converters of the cage hoisting winches. Nominal power is 300 kW. There is no mechanical locking provided for when the gates are in the up position, but a locking brake (disk brake) is installed on the drum.
The doors of the levels and those of the vats are equipped with a device deadening the possible shocks of the boats, being able to stop a barge of 2000 T charged and launched to 5 km/h.
The doors of the levels and those of the vats are equipped with a device deadening the possible shocks of the boats, being able to stop a barge of 2000 T charged and launched to 5 km/h.

The reach gates and those of the cages are fitted with a device to absorb any impacts from boats, which can stop a 2000 t loaded barge travelling at 5 km/h. The leaf of each gate is fitted with systems to keep the cage/reach watertight, and to empty out the water between the gates.

Electrical equipment

The boat lift of Strépy-Thieu consists of a range of items electrical equipment that can be subdivided into five categories:


Distribution

The boat lift of Strépy-Thieu is powered by an aluminium cable of a cross-section of 3x400 mm². The HV connection is designed for a power of 10 MVA at a nominal voltage of 10500V. The short-circuit power of the network is 500 MVA.

The computers and microprocessors which carry out the monitoring and control functions are supplied with 220 V/50 Hz current, from the network of rectifiers/batteries/inverters which also serves the emergency generator system with 24 VDC. The emergency generator, consisting of an alternator of 1800 kVA and a hydraulic turbine, switches on in the event of a breakdown of the network, to allow an ongoing manoeuvre to be completed.
Group of electrical distribution cabinets.
Group of electrical distribution cabinets.
Power equipment


Speed regulator cabinet for asynchronous motor.
Speed regulator cabinet for asynchronous motor.
Low voltage equipment

The management of the structure, which includes the regulation of the manoeuvring of the cages and gates, is broken down into two levels: the upper level (NHS) and lower level (NHI). The NHS is charged with the display, the control interface, the surveillance of the coherence of the redundant information of the NHI and the testing of redundant controls, in order to detect any fault. The NHI is designed to meet the requirements of system safety and availability and carries out the functions of control of the equipment and safety controls. The NHI consists of groups of 3 redundant automatic control systems, and critical actions have to be validated by at least 2 systems out of 3. These automatic control systems are known as decentralised control units (UCD). Per cage, 3 UCDs are installed in the computer room and 3 UCDs are installed in the electrical room under the cage. The various units of the NHS and the NHI communicate with each other.

The dialogue tools consist of graphical screens using an imaging software.
The various types of images enable:
The control desk
The control desk
Auxiliary equipment

- the emergency hydroelectric generator,
- waterway signalling,
- the cage-mounted fire extinguishing system,
- the half-gantry cranes in the machine room.
The following equipment completes the installation :
- three passenger lifts and two goods lifts,
- lighting equipment for the inside of the tower, for the cages and for the approaches to the structure,
- fire detection and extinguishing equipment in rooms and technical premises,
- telephony, intercom and utility television equipment,
- access monitoring and anti-intrusion equipment,
- conventional electric equipment for building premises (distribution panels, indoor lighting, heating, plugs, etc.).

Big Projects