The Portsmouth and Havant WTW & SRC scheme is part of Southern Water‘s US$2.8bn programme of capital projects to achieve compliance with the European Union’s Bathing Water and Urban Wastewater Treatment directives. The Environment Agency required an improvement in the quality and a reduction in the frequency of stormwater overflows following heavy rainfall. The US$142M project, which was completed in summer 2001, included construction of a new wastewater treatment works at Budds Farm to replace the old one, a new and refurbished pumping station at Eastney and refurbished stormwater storage tanks at Fort Cumberland.

Edmund Nuttall were contracted to construct a new transfer tunnel from Budds Farm WWTW to the existing long outfall at Eastney Pumping Station under modified design and build, IChemE (Red Book) Conditions of Contract. Donaldson Associates was Edmund Nuttall’s designer for the project and Halliburton KBR supervised the US$37.4m contract on behalf of the client, Southern Water. The project comprised five shafts, two TBM tunnel drives and two short interconnecting tunnels.

The new scheme in operation

Litter is removed from Portsmouth’s wastewater at Eastney pumping station and the water is then pumped to Budds Farm through a pipeline in the new transfer tunnel. Litter is removed from Havant’s wastewater in a new facility at Budds Farm, where Portsmouth’s wastewater is combined with Havant’s and treated. The treated wastewater from Budds Farm is transferred back to Eastney flowing under gravity through the new transfer tunnel. A new transfer pumping station sends the treated wastewater from Eastney out to sea through the existing long sea outfall. Under storm conditions excess wastewater flows are handled by new stormwater storage tanks at Budds Farm, new fine screening for all stormwater overflows in Portsmouth and Havant and refurbished stormwater storage tanks at Fort Cumberland.

In addition, a new sludge recycling centre at Budds Farm treats sludge created by the new treatment works and from other parts of Hampshire.

Connecting tunnels

The four shafts at Kendall’s Wharf and at Eastney were connected by short lengths of tunnel. At Kendall’s Wharf a 2.85m i.d. tunnel was constructed connecting the two TBM drive shafts. The 60m long, tunnel was excavated with a rotating cutter head mounted on a Bobcat mini excavator. The lining was steel fibre-reinforced wet-mix sprayed concrete with a reinforced cast concrete invert. The tunnel was built within a de-watered chalk block in which the shafts had been sunk. Fifteen de-watering wells had been sunk to a depth of 45m around the shafts and were successful in drawing down the water table to below the level of construction. Progress rates achieved for this tunnel were very good, with the whole drive completed in less than two months.

At Eastney the 8m long connection between the two shafts was constructed using a pipejack. Edmund Nuttall subcontracted this work to Delta Civil Engineering and an Iseki Unclemole Slurry TBM was used to excavate the 1.5m i.d. tunnel.

Main tunnel drives

Two tunnel drives were constructed from the shafts at Kendall’s Wharf using Lovat RME131SE earth pressure balance (EPB) machines. The TBMs were identical with only the arrangement of cutting tools differing for each drive, each had a diameter of 3.36m. The cutting head featured a combination of disc cutters, ripper teeth and scrapers. The machines featured a variety of injection ports on the face and within the cutter head chamber and screw for ground and spoil conditioning. The lining comprised a six-segment precast trapezoidal ring with an i.d. of 2.85m manufactured by Macrete. The segments were 180mm thick and nominally 1m wide.

The first tunnel drive to Eastney began on 27 April 1999 and was completed on 8 December 2000. The 4km drive encountered chalk for the first 70m, the chalk’s flint content varied from 20% to 2% as the drive progressed. The tunnel passed through an interface between chalk and later tertiary deposits, known as the Bullhead Beds, containing large flints and cobbles. The tunnel then passed into firm to very stiff clays of the Reading Beds, which also contained sandy horizons. At around 1.4km the tunnel passed into the London Clay sequence, which comprised four units each with a progressively higher sand content. Each unit was separated by water-bearing sandy layers and limestone bands:

Unit A – firm to very stiff sandy clay with silt and sand horizons and the Bognor Sands, a medium dense to dense silty sand.

Unit B – firm to very stiff silty sandy clay with silt and sand horizons and the Lingula Sands, a dense to very dense silty sand with limestone bands.

Unit C – silt, sand and clay of variable strength and Portsmouth Sands, a dense to very dense silt/sand.

Unit D – silt, sand and clay of variable strength and Whitecliff Sands, a medium dense to very dense silt/sand.

To avoid built-up areas on the surface, the Eastney tunnel contained two curves, of 2,600m radius and 1,000m radius, on its route. The TBM was delivered with disc cutters installed for excavating the flinty chalk at the start of the drive and the Bullhead Beds and were replaced with ripper teeth once the TBM had passed into the clays of the Reading Beds.

The tunnel drive to Budds Farm began on 24 May 1999 and was completed on 18 February 2000. The 3.8km bore was straight and entirely within chalk. This drive was initially considered the more difficult one, as large flints were expected along the route and should excessive wear to the TBM cutterhead occur, recovery from the surface would have been impossible as the drive passed beneath the harbour.

From observations of the behaviour of the chalk/flint matrix when it was being excavated by the roadheader in the Kendall’s Wharf connecting tunnel, this TBM was delivered with an all-ripper-teeth configuration. It was noted that the chalk was sufficiently hard to hold the flint in place while pieces were chipped off the nodules by the road header tool. Over the drive, the flint content of the chalk started at 20%, reducing to a 2% face content at Budds Farm.

TBM production logging system

Both TBMs were equipped with a Lovat data logging system and vast quantities of data were collected on every aspect of the TBM’s operation. However, while the data logging system provided information about what the machine was doing at a given point in time it would not help if the machine was stopped for a reason not associated with the TBM e.g. a derailment of rolling stock in the tunnel, halting production. For this reason a TBM production logging system was developed.

The system was designed to be simple enough to be used as part of the contractor’s regular progress reporting system, without it becoming a chore. The system proforma, developed as a simplified version of the system used on the Channel Tunnel project, would be filled in during the shift to account for every minute of a 12-hour shift. The data would then be fed into a spreadsheet and a weekly summary sheet of the data produced.

A data sheet was produced for every shift on both tunnel drives. Tunnelling activities or non-productive activities were listed down the sheet and the time of day across the sheet. The sheet was marked with a line indicating the activity being carried out during a particular time. In this way all activity in the tunnel was logged for an entire shift.

The system was originally designed for the TBM drivers to fill in, as they would be at the face at all times but the contractor preferred shift engineers to fill in the sheets. The sheets were divided into 15-minute sections. If an activity lasted for a shorter time, the section of the sheet was only partly filled, to represent the actual time taken.

The activities were divided in four main headings that were further subdivided:

  • Production: excavation, grouting and ring building.

  • Planned downtime: probing, planned maintenance, cutter changes, face inspections, cable extensions, other service extensions and survey.

  • TBM downtime: cutterhead, motors, steering rams, shove rams, erector, screw conveyor, segment crane, conveyors, segment magazine, plant modifications, grout plant, ground conditioning, PLC cabinet and ventilation.

  • Other downtime: waiting for skips/segments, waiting for other materials, derailments, clean build area, grouting problems, failure of services, failure of equipment at surface, missing crew, survey, other delays, site closed and missing records.

The completed sheets were submitted to Halliburton KBR’s staff for inputting into the system.

The data presented on the shift report sheets was input into a spreadsheet system with identical activity headings. An activity which was represented on the data sheet as a line across a full section was input as a ‘1’. An activity that lasted for a shorter amount of time was represented as a decimal. In this way the lines representing activities on the data sheet were translated into time periods for each activity, which could then be totalled up on a shift by shift basis.

Weekly summary sheet

The data entered into the spreadsheet system was automatically totalled and then presented in a graphical format. These graphics could be used as a tool by contractor and supervisory staff to ascertain whether there were areas in the tunnel production system that were affecting overall productivity and needed attention. On the Portsmouth Transfer Tunnel project, data for the whole of the Budds Farm drive was collected. The system was not put into place until early June 1999 and therefore much of the setting up process for the Eastney drive was not recorded. Continuous records for the Eastney drive were taken up to May 2000, prior to an incident in this tunnel (T&TI, July 2000) which delayed and affected production to completion.

Production database

Now that the tunnel drives have been completed the data collected over 18 months of tunnel production can be collated together and analysed for the benefit of future projects. The data may be presented in many ways, and several plots are discussed here to compare each drive.

Weekly data for the Budds Farm and Eastney tunnels have been brought together on two bar graphs. The data gives an edited view of the information collected for the two drives. The data collected suggests that, apart from TBM downtime, the two drives were very similar. The Eastney TBM was less reliable when compared with the Budds Farm machine and this is confirmed when comparing the edited overall plots for both of the tunnel drives.

Production figures only tell half a story, however, as because of the differing ground conditions on the drives the Eastney TBM had to work longer and harder than the Budds Farm TBM. Production figures only give an indication of how long the machine is in operation. They do not indicate how productive the machine is. It is interesting to note that production figures for the Eastney TBM initially improved once the Budds Farm drive had been completed and resources were concentrated on the one drive.

Excavation and ring building times

The graph for the Budds Farm tunnel shows that ring build and excavation times improved as the drive progressed. Generally, once past the ‘learning curve’ average excavation times of 10 minutes and average ring-building times of 20 minutes were obtained.

Ring-building times for the Eastney drive compare well with the Budds Farm drive. This is not surprising in view of the identical segment-handling equipment on each TBM. It is surprising that ring-building times improved significantly once the Budds Farm drive was completed. What is different is that the Eastney TBM had to mine for twice the time of the Budds Farm TBM, with mining cycles lasting up to an average 40 minutes but generally over 20 minutes. There is a significant increase in mining times during periods when the TBM was passing through an interface zone between strata.

Operating an EPB machine is difficult in mixed face conditions. The local geology in the area of the project has a very shallow dip, which has the effect of prolonging interfaces and therefore these mixed face conditions. Operators found it difficult to balance face pressures and screw conveyor pressures, resulting in significant increases in mining time. Once the machine hit a full face of one material, mining times improved.

Mining times were relatively high in the Reading Beds because of several reasons. Part of the Eastney TBM’s unreliability was due to repeated breakage of the torque linkages between cutterhead and stationary shell. The Reading Beds were very hard and dry, and propulsion pressures needed to sustain reasonable progress may have attributed to this problem. TBM drivers were therefore instructed to limit propulsion pressures, which in turn reduced torque but increased mining times.

The dry nature of the Reading Clay also created problems with mining cycles and the behaviour of material in the spoil chamber and screw conveyor. Prolonged experimentation with ground conditioning foams seemed not to improve the situation but it appears the addition of water alone aided production. Production times improved as the drive moved into the wetter, sandier London Clay units.


The exercise to log TBM production times on this project has been successful. The value of the data to future projects comes from the accuracy of the raw data collected. It is therefore important that the person assigned to the task of record keeping is present in the tunnel during the whole shift; missing records do not improve the accuracy of the data collected. For this reason the contractor’s staff, present in the tunnel for the whole shift, as part of their day to day duties, are the most suited to keeping these records.

It was originally thought that data for the two tunnel drives could be compared, given the rare opportunity to study two tunnel drives driven simultaneously from the same point. The differing nature of the geology on the two drives and the unreliable nature of one of the TBMs has made this difficult. However, it has been shown that collecting detailed production data using a simple manual logging system can be used as an effective tool during the life of a tunnelling project for site-based decision-making processes. The collected database of information can be utilised for production and programme decision-making processes on future projects, particularly with similar machines.

Related Files
Figure 3: an edited view of the average excavating and ring building times on the Budds Farm Tunnel.
Figure 4: An edited view of the average excavation and ring building times onthe Eastney Tunnel
Figure 1: Map of the Langstone Harbour area
Figure 2: Weekly data for the two tunnels