After some interesting negotiations and detailed discussion with Trenchless Technology (FE) Pte Ltd from Singapore, the mortars and machinery were sent off to Singapore in March.

In Singapore the protection of the environment is assuming increasing importance, especially to avoid sources of fresh water being tainted by seawater or wastewater.

Surveys by the Public Utilities Board in Singapore confirm that the wastewater network, dating in part from colonial times, is in serious need of rehabilitation. Due to the extremely high volume of road traffic during the night, the Singapore authorities had to opt for repairing the sewer system rather than laying a new one. Many of the countries sewers fill with seawater at high tide because of the considerable damage. Therefore, any engineering operations in the sewers must take place while the water level is falling.

The M-Coating process developed by HERMES Technologie is ideal for just such cases, said the company. The process can use short windows of opportunity to repair shafts due to its fully automated routines in conjunction with early strength dry mortars.

Training the team

As in previous cases in Asia and elsewhere, HERMES Technologie set great store on training a ‘local team’ right from the first renovation operations.

Once the materials and equipment arrived, theoretical training on the M-Coating process was delivered together with Trenchless Technology (FR).

The team that was assembled, including one foreman and three specialist operators, showed commitment and willingness to learn.

The project

Although it seemed advisable to start the rehabilitation procedures at night or early in the morning because of the high volume of traffic and the high temperatures, the first rehabilitation started around 10 am. Once the initial preparations were complete and just as the work was about to begin, the tide came in. The team then had to seal off the incoming water with balloon-plugs and pump it out.

Once the shaft was cleared of water, the walls were thoroughly cleaned robotically using the TSSR. The TSSR works at 380 bar and 24 litres per minute, at a distance of 5–15 cm from the shaft wall. After cleaning, an inspection of the shaft revealed a 5 mm hard shell-like coating. Areas of leakage were obvious, and old packer holes pointed to previous injection with artificial resin. Behind the ‘shell’ lurked cement plaster and an unknown soil mixture.

In order to obtain a perfect repair the visible coating was removed back to the original shaft wall. The TSSR was used once more for a final cleaning. In the shaft’s 20 mm thick, reinforced concrete cladding, approximately 40 holes were found. These were plugged with ERGELIT-10SD. The stabilising injection which was planned was postponed until the next day because of the rising tide.

The following day began with the use of the remote-controlled TSSR to remove the dirt which had built up overnight from the restaurants and fast food stalls connected to the sewer, which discharge a great deal of grease.

Next, the shaft was stabilised with an injection of ERGELIT-Kbi. In order to seal the very small cracks that were present, and to speed up the subsequent coating operation, ERGELIT-10F was rubbed into the shaft wall.

In spite of the fact that the temperature had topped 49 degrees Celsius – a tough test for mortar mixers, hosepipes and pumps – the shaft coating began. The dry mortar used for the project was ERGELIT-KS 1. A 10 mm thick coating was applied in a single operation, with the robotic centrifuge motor being lowered and raised in the shaft. A second coat of mortar was sprayed to a thickness of 40 mm, which together with the original 20 mm cladding gave a rehabilitated sewer shaft wall of 70 mm. According to the client’s spokesman, this was structurally satisfactory for this section of concrete road, exclusively used by light and sporadic traffic.

Immediately after the material had bonded and the equipment had been removed from the shaft, water flooded into the pipe, which made it unnecessary to keep the surface damp, as would otherwise have been essential given the temperature.

The rehabilitation equipment was then moved to the next shaft. Work on a five metre deep shaft began around midnight as the dense afternoon traffic made further work impossible. The vertical shaft wall varied in diameter from 1.2 to 1.4 metres. Thanks to the newly trained Singapore team the thorough cleaning and subsequent robotic coating of the lower part of the shaft wall was completed in the early hours of the morning.

The shaft served as a test site for the new M-Coating team to demonstrate to the client. After a perfectly executed TSSR cleaning cycle, the team succeeded in applying a superb coating to the upper part of the shaft, using ERGELIT-KS1 supplemented with ERGELIT-KS2b. However, due to the heat, in the middle of operations the mortar supply hose suffered a blockage. The event showed that the team must consider equatorial temperatures when preparing and supplying the grout. However, the team’s calm reaction showed that one week’s training – in this case led by HERMES proprietor, engineer Rainer Hermes – can mean a good level of competence. Mr Hermes explained to the water and wastewater operating authority representatives that he was actually rather pleased to have the chance to train the new team to deal with such a problem.

With the co-operation with Trenchless Technology (FE) HERMES said they have set a bench mark for a new rehabilitation technique for the remaining 1001 shafts in Singapore.