The Cleaner Seas for Sussex project will affect a quarter of a million people on the south coast. Started in the early 1990s as a response to threats of hefty pollution fines for Britain from the EU, it will supplement the old Brighton sewerage system designed by Sir John Hawkshore more than a hundred years ago. It has been severely delayed by environmental factors but the GBP 300M (USD 480M) project is finally nearing completion. Contractor 4Delivery— a JV of Costain, United Utilities and MWH—is undertaking the work for client, Southern Water.

A crucial part of the vision: the linking of the main sewerage works to a long sea outfall at the eastern end of the project is being undertaken at Friars Bay near Peacehaven. This 34-week contract was awarded to Joseph Gallagher. It is valued at around GBP 2.7M (USD 4.4M) but includes the pipe itself, supplied by Costain, which would cost an additional GBP 800,000 (USD 1.3M).

This part of the project will enable treated sewage to be pumped from the treatment plant, down the 1.8m diameter pipe, manufactured by FP McCann, to the 2.5km long sea outfall and then into the sea.

The project
At nearly 1000m in length, the drive is one of the longest in the country. Because of the geography, however, things are made a little more complicated. The drive shaft is located close to the top of the cliffs by the nearby village of Peacehaven, while the section of the long sea outfall that joins onto the end of the tunnel begins some 690m out to sea and around 45m below the start of the drive. According to Ben Green of Southern Water, the floating installation of the outfall broke every harbor procedure ever written.

The drive would be unusual due to its length alone, but to also have a vertical curve with an arc radius of 600m and to be launched at a downward grade of 1:10, the proposal is all the more challenging and impressive.

“The drive has been challenging and unusual, like working two projects at once,” says Martin Brookes, the TBM operator on site. “The grade is so unforgiving that water must not get in. Normally I’d look out the window [at the shaft]—but here? The machine’s capable of flooding after 20m into the drive, and we wouldn’t even see it. This job’s all about picking stuff up along the way, making modifications and adapting—that’s what’s important.”

At the time of T&TI’s visit, the Uncle Mole Super supplied by Iseki had already tunnelled approximately 150m. This is where the choice of equipment comes in to help. As the first drive in Great Britain, or even Western Europe, that has made use of fibre optic machine control in microtunnelling, a massive and reliable data capacity is on hand. This means that many more cameras and detectors can be deployed in the tunnel to monitor the progress and condition of the TBM. According to Paul Wilkinson, the general manager for Iseki Microtunnelling in the UK, the fibre optic technology being used was developed for military communications. Its use here is an example of, as he puts it, “Engineering out the risk.”

Originally intended to be two drives, one from the first shaft at the top of the cliff to the second shaft at the bottom of the cliff, where the machine would be inspected and refitted, no matter the condition of the cutterhead, and then sent a second drive under the sea to the outfall and reception chamber, to await marine recovery.

Now, however, the second shaft will act purely as an inspection and repair access point. The project will be treated as a single drive. This decision was made due to the extreme weather conditions experienced at the shed covering the second shaft. The change is cost neutral, as the site does not require relocation.

“Weather conditions have delayed works by around two weeks,” says Graeme Monteith, contracts director at Joseph Gallagher. “We have had high winds coinciding with spring tides and due to the unusually cold weather and despite draining the system and lagging pumps the slurry tank pipes have frozen overnight, as well as the site being shut down due to heavy snow fall.”

The high winds associated with extreme sea states is the main reason for not relocating the worksite to the second shaft at breakthrough—the high storm tides batter halfway up the cliffs and have in the past ripped the cladding from the shed.

Breakthrough at the second shaft has been achieved since T&TI visited the site. According to Dickie Dexter, tunneling director at Joseph Gallagher, the breakthrough was, “Spot on, in line and level, on 3 February.” He adds, “The machine has performed well in the chalk with only minimal wear and tear on the teeth—approx 20 per cent—but as a precaution we will refurbish the teeth for the 690m section out to sea. The chalk is not ground to a paste and the machine dealt with multiple bands of flints on its way down through the cliff to the lower shaft.”

The machine holed through the cast concrete entry wall, which has an aperture fitted with a rubber ‘sphincter’. Mirroring this on the opposing wall is an exit seal. As T&TI went to press, the refurbishment was underway in the second shaft. Monteith adds, “Interestingly the specially designed lubricant provided a complete cut off of any water pressure in the annulus allowing for a dry reception.”

Treating chalk as rock
Apart from the long drive length, the steep grade, the sharp bend, the howling winds, crushing waves and the groundwater pressure—equivalent to being underneath 40m of water—through the cliffs, there is another risk to the drive. The Uncle Mole Super is a hard rock variant of the regular Uncle Mole. Despite often being treated as a soil, the chalk is hard and self-arching.

This makes it appropriate for the use of a rock capable tunnelling system, though the use of a head loaded with roller discs is generally not used in chalk due to the fear that the roller cutters will not turn and develop flat spots.

Monteith suggested that as this machine has been designed in Japan where chalk or its equivalent is not present, it is possible that this has allowed the designers to take a fresh view and not be influenced by perceived wisdom or urban myths that exist around tool choices in chalk.

“Loaded with a mixture of specially designed tungsten insert protected roller cutters and rippers the TBM has shown itself capable of advance rates of up-to 160mm /min,” says Monteith. “With the slurry machine, rather than an EPBM fitted with conventional rippers, less work is done by the cutters themselves, meaning less wear. The cutter head design proved to be very successful indeed with only around 20 per cent wear being evidenced on the discs following inspection at the promenade shaft.”

Six jacking stations will be employed along the drive, but that is just a formality, according to Monteith. “We’re putting six in, but we don’t expect to use that many, if any at all. Costain, using Joseph Gallagher’s specialist labour has completed a 450m drive in these conditions on the same contract without using a single one and we have just completed 300m with jacking loads of around 200t out of an installed capacity of 1,200t.”

The TBM and all site equipment is connected to the National Grid, no generators are used to power the works. The site draws approximately 1MVA of power.

Gyroscope
“The gyroscopic system is situated in the machine and measures many variations every second so it can plot where it is moving all the time,” says Dexter. “It continually feeds this information back to a PC screen in the driver’s cabin so he can constantly see position and alignment of the machine compared to the theoretical. The information is plotted against the known alignment for the tunnel, which in our case involved a vertical curve—not something attempted often anywhere, microtunnels mostly being straight and occasionally incorporating a horizontal curve.

“The gyro works by interacting with the constant rotation of the earth to know the bearing it is on all the time, and uses this to compare with [the direction] required as well as inclination.

It has the advantage of not needing a laser in the shaft bottom but it needs constant reminding exactly where it really is as small distance errors creep in with time and that can make a large difference on a curve.

The Joseph Gallagher site engineers involved with the project check it every two days, about 25m, and we have the European supply company attend site about every 10 days for a secondary check. They bring with them high-accuracy gyro theodolite to make the job easier.”

Lubricant
Mudtech provided most of the construction chemicals. A ‘super lubricant’ called SeaJack was used during tunnelling. It is designed to be resistant to the dehydrating effects of salt water. The lubricant has performed extremely well having provided a total cut-off of ground water in the annulus and achieving extremely low jacking loads on the first part of the drive. There is every indication, according to Monteith, that if the current conditions prevail the full 1,000m of the jack could be installed just using the main jacking station within the drive shaft.

Slurry separation plant
“The key to successful slurry tunnelling in chalk revolves around the tunnelling system being able to firstly mine the ground effectively, and then separate the excavated material from the slurry quickly and efficiently, returning the slurry to as close to clean water as possible, re-using the slurry reservoir without having to dispose of slurry,” says Monteith. “If any one part of the process is going to cause issues in terms of cost and delay then in chalk it is the separation plant. It is for this reason that I chose to combine the stateof- the-art plant designed by Manvers Engineering in one package, hiring the plant and operator from Barhale Construction and obtaining the expertise in separation plant chemicals from Mudtech. Utilising the specially formulated ‘Chalk Floc’ to dose a single Baioni 47L Centrifuge this plant is capable of supporting up-to six pipes or 15m of advance per shift.”

Removal of spoil
Vast amounts of sodden chalk cake the site and, when asked about it, site workers all reply with the same: ‘it gets everywhere’. The high water content is the real issue however. When loaded onto trucks, the transportation vibration causes the water to rise to the top of the load and slosh around, representing a severe risk to the driver and other road users if the trucks have to break or swerve suddenly. This was a costly problem, as trucks could only be loaded halfway, causing massive inefficiencies. The solution was found in ‘DryAdd’ a superabsorbent that can retain water up to 400 times its own weight and, when added to spoil in a measure of 0.5-1 per cent of the total load, means that full truck loads can be taken from the site. “It’s a good investment – an GBP 40 (USD 65) bag saves about GBP 250 (USD 400) in transport costs,” says Monteith.

Recovery
The Cleaner Seas for Sussex specialist offshore contractor, Land and Marine Engineering, which used to be part of Costain, will handle the recovery of the TBM as part of a GBP 10M (USD 16M) overall contract. A reception pit has been dug with dimensions of roughly 13.5m x 8m x 8m and filled with a granular material—a sea-dredged ballast gathered by a small dredging unit from a designated area near the Isle of Wight. The TBM will push clear of the tunnel, into the pit at which point certain vital electrical components will be removed from the machine.

The TBM’s watertight doors will shut, and a positive air pressure will be applied inside the mole, then the cleared tunnel will be flooded and the ballast removed from the semi-buoyant TBM. “The current proposal is then for a surface support vessel to assist divers in attaching floatation tanks to bring the TBM to the surface,” says Robert Blakebrough, project manager at Costain. “This operation has been done before, but is by no means common. We are currently applying for permission to operate the undersea drive on a 24-hour shift, whether we get this or not will decide the number of months until the recovery operation can go ahead.”

After recovery, the Uncle Mole Super will be sent off to excavate the Prague sewer in the Czech Republic, and then the Riyadh sewer in Saudi Arabia.


Breakthrough of the TBM into the promenade shaft The pipejack connects the main wastewater works with the long sea outfall The drive shaft in the main worksite at the top of the cliffs The promenade shaft awaiting arrival of the TBM, exposed to the elements at the bottom of the cliffs Paul Wilkinson of Iseki next to the electronics clean room Graeme Monteith (left) and Robert Blakebrough explored the site with T&TI