Trenchless Installation of Utility Tunnels

One technological innovation to optimise cost-effectiveness of tunnelling systems in respective ground conditions is the Herrenknecht TBM 1200 for use in hard rock conditions. The design of a new water pressure system for Slurry-machines improves the advance rates in sticky soil. Another important economic aspect in Microtunnelling is the construction of launch and reception shafts, especially in difficult ground conditions. For this purpose Herrenknecht has developed the VSM range of shaft sinking equipment for shafts up to 8m diameter. To guarantee the compatibility between the machines and the navigation systems, Herrenknecht AG has developed the Universal Navigation System (U.N.S.) as a basic module for three different navigation systems.

1. Working principle for Microtunnelling Machines

Controlled soil excavation and controlled extraction of the soil is necessary in order to prevent soil settlement on the surface. For this reason, safe support of the face during the entire tunnelling is of great importance.

Two different types of face support can be implemented with the flushing circuit procedure. For purely geometric reasons, for machines with a nominal diameter up to 1500 mm (AVN 1500) only the so-called slurry principle can be deployed. In this case, the face is supported by a combination of mechanical and flushing water support. The pressure of the flushing water can be regulated and should be 0.1 to 0.3 bar greater than the predominant groundwater pressure. The mechanical face support is provided via the arms of the cutting wheel. Machines with this construction are also called slurry shields.

For tunnelling with larger diameters in changing and instable soil this form of face support is not stable enough due to the non-homogenous face and the fluctuations of pressure in the conveyor circuit and can result in the face collapsing. The result would be settlement of the ground surface.

To enable microtunnelling even in difficult soil Herrenknecht AG developed micromachines with compressed air support of the face. For years, this technique has been used with excellent success for tunnelling machines with large diameters. Micromachines with a nominal diameter of 1600 mm (AVN 1600) or greater can be equipped with this technique.

2. Major Technologies
2.1 AVN (Slurry) Technology

2.1.1 AVN 250 - 1200

AVN stands for a microtunnelling machine type for automatic pipe jacking with slurry-circuit. It is a no-dig technology to install a pipe underground, in soils with or without groundwater between the launch shaft and the reception shaft. The locations to use this type of equipment is street and highway crossings, railway crossings, river and channel crossings, constructions like buildings, factories, houses, deep locations and areas with groundwater. Open trenches with dewatering and soil stabilisation are not necessary.

These machines are designed as full face tunnelling machines. The cutting wheel can be rotated in both directions. A cone crusher behind the cutting wheel crushes the excavated material into suitable sizes. The soil is mixed with the flushing agent and subsequently transported to the surface through the conveyor pipe by the discharge pump. On the AVN 250-700 machines the flushing agent is conveyed through the centre of the machine by the drive shaft (hollow shaft). Regarding the AVN 800-1200, a suction pipe for removing the flushing agent is installed directly behind the cone crusher.

By quick and simple installation of an extension kit all machines can be extended by one stage. The basic design of this machine enables deployment in soils like silt, cohesive soils and rock. A machine version with a rock cutterhead is only available from ID 400 upwards.

2.1.2 AVN 1200-3000

The Herrenknecht Microtunnelling Machine Department has developed slurry shields and successfully deployed them throughout the world.

With slurry machines the extraction chamber is filled with the support and conveyance medium. The conveyance medium is only introduced to the extraction chamber via the cutting head or the ring chamber nozzles. The conveyance takes place via the conveyor conduit which begins at the conveyor case which is connected in the lower area of the pressure chamber.

The support of the working face is achieved by the combination of the conveyor and feed pumps. Therefore, it is not necessary to use compressed air regulating equipment. When the machine is deployed as a hydroshield, compressed air regulating equipment is used. The pressure compensation between the extraction chamber and the pressure chamber is implemented via the communicating pipes

2.1.3 AVN 1500 – 2000C

The wellknown Herrenknecht AVN "C" – Series, which stands for power pack within the control container (no power pack within the tunnelling machine) has been extended to machines with nominal diameter up to 2000 mm.

The robust and economically priced machines were developed to carry out projects with lengths up to 200 m and are to be connected simply to a "standard AVN – container" with sufficiant rated power (for example: AVN 2000C requires only 132kW). Available are machines for nominal diameters of 1500, 1600, 1800 and 2000 mm.
 

2.1.4 AVN with electical Drive for Rock Microtunnelling

With a total investment of over 600 million Euro the north Spanish city Bilbao reorganizes its urban sewage system. The project ranks among the largest environmental infrastructure measures of spain.

One of the most demanding sections is the production of a 2.5 km long waste water tunnel (1,800 mm ID) in Basauri, a suburb of Bilbao. A joint venture of two Spanish construction companies received the order for this subproject. While the first two sections were still under construction, but did not advance fast enough, the given completion date was endangered.

Herrenknecht AG received an order to deliver a suitable microtunneling system as soon as possible. The available ground surveys showed the geological conditions with dark grey marly limestone with compressive strengths of 60 – 90 MPa.

Herrenknecht choosed an upskinned AVN 1600E with direct electrical main drive, which was originally built for a contractor in the USA and is ideal for rock excavation.

The major advantage of electrical against hydraulic main drives are the more simple basic buildup and the higher degrees of efficiency.

A cutterhead strictly adapted to the geology and a suitable crusher mechanism supplied ideal chip sizes for the disposal of the excavated limestone. The project was completed beginning of May 2003 – almost one month ahead of schedule.

2.1.5 AVN with access to cutting wheel (AVN T-series)

The free centre drive of this machine type makes acces to the tunnel face possible for AVN 1200 (for pipe ID 1200 mm) and larger. This allows removal of obstacles, e.g. sheet piles, steel girders, boulders, etc.. Tunnelling in rock can be extended to previously unimaginable drive lengths of over 500 m due to the fact that it is possible to replace worn cutting tools.

This makes it possible to reduce the number of intermediate shafts which results in a considerable reduction of the construction costs.

On microtunnelling machines with central hydraulic or electric main drives the door is located directly above the drive unit. This arrangement can be implemented from AVN 1600 onwards. For microtunnelling machines with peripheral main drives the door is located in the centre. Due to their robust support these machines were originally constructed for rock tunnelling. This construction can be implemented from AVN 1200 onwards.

Inspection of the tools can be carried out quickly and simply through the opening to the face. It is even possible to remove small obstacles. The replacement of worn cutting tools on the cutting wheel is enabled by means of a special backloading system. Tools can be replaced easily underground from the back of the cutting head without having to pull back the machine.

2.2 The Cone Crusher

In principle, all AVN tunnelling machines can be equipped with a crusher so that the stones and blocks in the pipe route can be broken down to a transportable size.

The installation of the crusher in the immediate area of the cutting head of the tunnelling machine significantly expanded the areas of deployment for pipe jacking in loose rock with grain sizes exceeding 50 mm. Depending on the type of machine being used, the upper limit of the stones which can be handled extends to a grain diameter of up to 40% of the diameter of the cutting head.

The crusher works according to the principle of a "cone crusher". Inside the machine there is an internal cone with crusher strips. The crusher arms on the back of the cutting wheel form the counterpart to these. The stones are broken up between the stationary crusher strips on the internal cone and the rotating crusher arms of the cutting wheel.

2.3 High pressure nozzles for Slurry machines

Microtunnelling machines with slurry circuit, so-called AVN machines manufactured by Herrenknecht, are usually equipped with so-called high pressure nozzles, helping to avoid cohesion of the cutting wheel and material slow-down in the working chamber.

2.4 Low-pressure water system

In case of using tunnelling machines with a large diameter in cohesive soils the high pressure nozzles reach their limits due to the larger cross section of the tunnel face. As a result, advance rates decrease. Equipping tunnelling machines whose outer diameter exceed 1,500 mm with a sufficient number of high pressure nozzles and the corresponding high-performance pumps would be uneconomical for use in such soil conditions.

Herrenknecht has recently developed the so-called low pressure jet system for slurry shields which are deployed in cohesive to extremely cohesive soils or sticky soils. Depending on the diameter of the tunnelling machine four to eight solid jet nozzles are installed in the excavation chamber.

The low pressure nozzles can be piloted in pairs in the cone with the help of an additional booster pump. The jets cut the clay chunks during the excavation and are thus directed that the grill in the excavation chamber does not become clogged. This improves the efficiency of the slurry circuit. The torque of the cutting wheel is reduced, the efficiency, however, is increased, which results in a higher advance rate.

The cross-section of the nozzles of the new low pressure jet system is considerably larger than that of the high pressure jet system, and with variable diameter. The effect is powerful: the volume flow is variable up to 500 l/min and per nozzle. Whereas the traditional high pressure jet system injects the water with 250 – 300 bar pressure into the cone, the low pressure jet system works at a higher volume flow and efficiency with a variable pressure which is less than 10 bar.

250 – 300 bar pressure. The mode of operation is comparable to that of a firehose. The strong water jets enable the necessary “turbulence” in the excavation chamber.

The low pressure jet system offers a considerable advantage regarding water supply. The traditional high pressure nozzles have to be fed with clear water, thus unbalancing the slurry circuit due to the oversupply of water, while the water for the low pressure jet system can be extracted directly from the slurry system. As a result of the fast conveyance the accumulation of fine particles in the slurry water is reduced which is advantageous for the separation. The slurry feed pump, designed to work as booster pump, can handle particles up to 2,0 mm without major impact. For long distance drives an extra pump can be installed directly in the machine or in the trailing tube so as to compensate flow losses.

3. Operation and Guidance

3.1 Control container

The AVN machines are designed as automatic, remote-controlled tunnelling machines. Complete control of the tunnelling machine takes place via the control container which is located either above or behind the launch shaft. The control container is divided into two sound insulated rooms, the machine room with its electrical and hydraulic power pack components and the operation room with all facilities required for operation and control of the tunnelling machine.

3.2 Universal Navigation System (U.N.S.)

Due to modern navigation technologies, remote-controlled Pipe Jacking can be carried out in straight or curved drives, in any tunnel alignment as well as over long distances. High-tech sensor technology ensures high accuracy even in variable tunnel alignments. Depending on tunnel alignment and length, different navigation systems are used for Microtunnelling equipment. To guarantee the compatibility between the machines and the navigation systems, Herrenknecht AG has developed the Universal Navigation System as a basic module. With the modular concept, U.N.S., of the Microtunnelling systems can be equipped with the relevant navigation system quickly and economically. U.N.S. is a basic module for integrated or stand-alone navigation systems.

3.2.1 ELS (Electronic Laser System)

ELS is designed for straight drives and tunnel lengths of around 200m. The max. tunnel length depends on the laser used, as well as on refraction in the tunnel. TBM position and direction determination takes place continuously. The system comprises the ELS target in the TBM and the tunnel laser in the pit.

3.2.2 ELS-HWL (Electronic Laser System - Hydrostatic Water Levelling)

ELS-HWL is an upgrade to the ELS system and comprises additionally the HWL-system. The system is suitable for long, straight drives up to 400m length. The Hydrostatic Water Levelling system supplies altitude data permanently via a reference module, which is mounted in the jacking shaft and via an altitude sensor, which is mounted inside the TBM. The laser is used to determine the exact direction, thus allowing a continuous position sensoring.

3.2.3 GNS-P (Gyro Navigation System for Pipe Jacking)

GNS-P is designed for curved drives of any radius. The system can be used in tunnels with a minimum inner diameter of 800 mm. There are no components installed in the pipe and line-of-sight is not necessary between the components. The north-seeking gyro compass, Northstar24, is permanently mounted inside the TBM. Every 1 to 3 m, it calculates the direction due north as a reference to the machine axis. The HWL-system supplies elevation data permanently. The current position of the TBM is calculated via dead reckoning navigation.

4. New Developments in Microtunnelling

4.1 TBM 1200 for operation in hard ground conditions

Based upon tightened health & safety regulations worldwide, the use of open face machines, where the operation is done within the machine, is becoming more and more restricted. Minimum clear dimensions limit machines in the size range of 1,200 mm internal diameter upwards in emergency situations. The operator is exposed to emergency situations such as cave-in, unexpected groundwater but also difficult working conditions with dust emissions in an often very limited space.

Microtunnelling systems increasingly replace open-face tunnelling machines, which are often chosen for cost reasons. Therefore, Herrenknecht has designed a new machine concept. A combination of practical benefits of an open-face machine and the operational safety of a remote-controlled Microtunnelling system complies with the necessary safety requirements dictated by the legislation. The machine operator can control and supervise excavation and muck transport from the operating container on the surface via video cameras installed in the tunnelling machine. Depending on the geology, the machine can be equipped with soft ground, mixed soil or hard rock cutting wheel. The excavated material is economically removed and disposed via belt conveyor and muck skip.

5. Machine developments for Shaft Sinking

5.1. VSM 8000 Shaft sinking equipment in Kuwait

Currently a huge sewer project in executed in Kuwait using Microtunnelling equipment. Therefore, a large number of launch and reception shafts has to be constructed in various water bearing geological conditions: sand, cemented sand, loam and limestone. The construction of shafts in such conditions is a challenge: the shafts are up to 28 m deep, with internal diameters between 6 and 8 m. The deeper the shaft and the more complex the geological and hydrological conditions, the more difficult shaft construction becomes. The presence of ground water aggravates the conditions considerably. Usually the construction schedule is extremely tight and time is critical.

Herrenknecht’s development engineers have now provided a solution. In co-operation with KBC Greenline, a novel shaft sinking equipment has been developed, to achieve safer and more economical shaft construction, especially below groundwater level in difficult geology.

The shaft sinking equipment consists of two main components: the lowering unit and the shaft boring machine. The lowering unit is anchored firmly to the shaft collar at the surface. The shaft is continuously extended with precast concrete segmental rings which are assembled on the top of the shaft caisson with the help of a crane and fixed to the previous completed ring. The hydraulic cylinders on the lowering unit,dependent on the circumstances encounterd, can push or hold the caisson whilst the cutting boom excavates beneath the cutting edge. The cutting edge is assembled and the first section of concrete shaft is cast in place. The shaft boring machine is attached to the steel plates cast into the concrete.

The shaft is flooded with water to balance the surrounding ground water pressure to avoid cave-in. The underwater excavation of the material is comparable to the mode of operation of a microtunnelling slurry shield. The cutting boom can be turned from the central position through 190° in both directions. The rotating cutter drum, positioned on the cutting boom and equipped with special cutting tools, excavates the material across the entire base of the shaft. The excavation sequences run automatically with specific developped computer programs.

The slurry is pumped to a settlement tanks and/or soil separation system. The whole process of material excavation and extraction is controlled from the control panel in the operating container at the surface.

5.2. VSM 7700 for operation in St. Petersburg

A comparable shaft sinking equipment of the type VSM 7700 (inner shaft diameter up to 7,700 mm) has been designed and built for a challenging project in St. Petersburg. Mid 2005, operation of the equipment will start. In the Russian metropolis connections to existing pipelines and sewers have to be constructed in a depth of 85 m. Working temperatures down to 20° C below zero, the extreme depth of the shaft construction in the multilayer geology and groundwater will demand everything from both the jobsite team and the machine technology. In “Venice of the North” the geology consists of sand and loam with a high water content. Whereas the first layer, reaching a depth of approx. 60 m, contains groundwater, the layer beneath consists of compact, dry, hard loam. Furthermore, geologists expect boulders of up to 2.5 m in the transition zone between soft soil and hard loam.

6. Herrenknecht activities in Middle East

In the late 1980s many cities around the gulf were growing faster than the infrastructure that had already been put in place could handle. Many motorways, large buildings and residential areas were constructed requiring an upgrading of the infrastructure. It was necessary to introduce Microtunnelling to install these new pipelines with minimum disturbance to the traffic flows and local every day life. Another main reason for the success of this technology is the fact that most cities are close to the sea or rivers, causing high ground water tables.

The first large-scale project was awarded in 1991 in Dubai, U.A.E., including 4500 meters of Microtunnelling – at that time, the world´s largest project ever awarded. A significant step was introduced in Abu Dhabi in 1996, stipulating that any pipeline deeper than 6 meters would have to be installed by the no-dig method, and cutting of roads and trees was no longer allowed. Another historically important project is the Greater Cairo Waste Water system where continuously Microtunnelling technology from Herreknecht was and is used.

After 1996, Microtunnelling was rapidly spreading over the Middle East with jobs in Kuwait, Lebanon, Saudi Arabia, Iran, Bahrain and Qatar.

6.1 Deep Microtunnelling in Abu Dhabi

As the population of the emirate Abu Dhabi is increasing, the surrounding desert is developed on a large scale to support the necessary infrastructure. The Abu Dhabi Municipality is currently investing in such development, the Mussafah district, close to Abu Dhabi City, being one of these areas. More than 40km of Pipe Jacking with Microtunnelling technology have been recently tendered in this district, contractor Al Jaber Tunnelling & Mechanical Works Establishment (AJTM) being awarded one of the sections of works, section 803C with an estimated value of 8.7million USD. Consultant engineers in this project was A.C.E. residing in Lebanon. A Herrenknecht EPB 2000 Microtunnelling machine has been in operation in for this project.

The works to install a 3.3km long tunnel in different diameters entail some of the deepest Microtunnelling jobs ever undertaken in the Gulf States at depths up to 24m. ’Trenchless Pipe Jacking was the only possibility to implement a project in such depth in an economical and efficient manner’, so Adnan El-Kaissi, manager of the microtunnelling division of AJTM. AJTM went to the start line with three different Herrenknecht machines.

The most challenging part of this sub-project was the installation of 2km of main water pipeline using an EPB 2000 machine. Temperatures of more than 50 degrees Celsius together with extreme saline soil conditions required the use of GFK jacking pipes. Shaft installation under the high ground water conditions presented an extremely difficult challenge, the same conditions being much less of a challenge by virtue of the use of EPB Pipe Jacking techniques.

6.2 Safe Airport Tunnelling in Dubai

In Dubai, a leading industrial and economic centre in the United Arab Emirates, huge efforts are being undertaken to develop Dubai International Airport into the largest airport in the region. Under the "Dubai International Airport Expansion Project", more than 4,000m of tunnel for Surface Water Drainage and Service Ducts have been completed by Al Naboodah Engineering Services L.L.C..

Four remote-controlled Microtunnelling machines from Herrenknecht are in operation to construct, expand and improve the underground infrastructure in diameters from 600 to 2000mm (AVN 700, AVN 1000, AVN 1200 & AVN 1500) Under extremely restricted conditions, the live taxiways and aprons have been tunnelled under with as little as 4m overburden. With Herrenknecht Pipe Jacking equipment tunnelling under these busy airport access ways without any disturbance to the tens of thousands of passengers arriving and departing every day.

6.3 Large Pipe Jacking in Cairo

Extraordinary Pipe Jacking was done in El Gabal El Asphar, a district near Cairo. The Herrenknecht AVN 3200 with an outer diameter of 3,960 mm was in action on this project. From one launch shaft, four tunnels of 300m length each had to be driven. In two opposed directions, two parallel tunnels are built with only 2 m space between. This so-called „contract 19“ is executed by the Egyptian construction company Arab Contractors. Within „The Great Cairo Waste Water Project (C.W.O.)“ the new sewer system will transport a peak quantity of sewage flow of 15.05 m³/sec –1.3 x 10 m³/day from the existing distribution chamber in El Gabal El Asphar area to the inlet of the pumping station by gravity through the two 600 m tunnels. Whereas the first design intended to use open-trench method requiring two rectangular concrete shafts with dimensions of 3.5 x 3.0 m, Arab Contractors studied different alternative methods for the execution of the project. The studies included hydraulic requirements according to the average and peak flow in both normal and emergency operation. In order to reduce impact on surrounding buildings and infrastructure and to achieve maximum economic advantage, Arab Contractors and consultants final decided to go for trenchless technology with tunnelling equipment from Herrenknecht.

So far, the first two drives have successfully been completed. The slurry system for soil conveyance was able to handle the predominantly stiff clay. Due to the automatic lubrication system to reduce friction between soil and pipes, installed interjacking stations did not have to be used to complete the 300m long drives. Taking benefits from the first experience gained on the first drive, performance is constantly improving. Contrary to initial criticism, the machine performs within requested time schedule and helps to increase general trust in trenchless technology.