Technical focus on inspection and safety 27 May 2015

Some of the highlights among the technical presentations of Day One and Day Two of WTC2015 could be found in the field of maintenance, inspection and safety.

WTC2015 technical presentations

Kouichi Kawakami of Tokyo Metro shared the inspection methods of Tokyo Metro, which has a total tunnel length of 166.8km. “We currently manage a list of 89,000 deformations in our tunnel metro system. Regulations require that we inspect all tunnels visually. This means we had to find a way to streamline the inspections,” said Kawakami. First of all, tablets were introduced to simplify record-keeping and do away with the need to manually enter hand-written notes into a computer. As part of preventive maintenance, a visualisation tool for repair plans was developed.

Most damage to the tunnel walls are small water leaks or cracks, caused by salt water fills of tidal rivers and bay shores. Sacrificial anodes will be used to repair or prevent these damages. “The visualisation tool qualifies which water leaks should be repaired first. It also enables us to draft repair plans to prevent the occurrence and progression of rebar corrosion due to neutralisation.” Mechanised inspections like visible image photography and infrared image photography are used to speed up the process. Beacons are placed at 10m interval to accumulate data. The beacons also calculate the position of an inspector and tell them – through communication with the tablet – when they have missed a deformation.

Dr Götz Vollmann, left, of Ruhr University, Bochum

Sprayed concrete against explosion and fire

Goetz Vollmann of the Ruhr-University of Bochum, Germany, commented on the invention of his research team: a highly ductile sprayed concrete that acts as an effective countermeasure against explosion and fire impacts. The team has developed a fibre-reinforced sprayed concrete, which offers enormous resistance against fire and explosion loads. “For the first time it became possible to spray concrete with an unsuspected fibre content of 140kg/m³ of steel fibers and 3kg/m³ of PP-fibres,” said Vollmann. An air mix was added as the vital ingredient to ensure sufficient workability of the concrete (see TunnelTalk references below).

The sprayed concrete takes into account both explosion and fire hazards and can be pumped underground through small diameter tubes. It was designed, primarily, as a safety measure for application in cross passages, which most times are difficult to reinforce because of their complex geometry. “But I would imagine the concrete can also be used for refurbishment jobs,” said Vollmann. “The only thing still missing is knowledge about the life cycle. Our next research step will be to assess the life span of the concrete we have produced.”

Intelligent lighting control

Pierre Longtin of Nyx Hemera Technologies introduced an innovative lighting control system to save energy and maintenance time. “Most tunnels are over-lit by about 30%,” he said. “And lighting represents roughly half of a tunnel’s operational cost.” The solution of his company is therefore to introduce an intelligent lighting system, which has more lighting stages implemented and individually controls and monitors every light.

TLACS system fitted as part of Carlin Tunnel refurbishment

Longtin highlighted the 500m-long Carlin Tunnel in Nevada, USA, as a test case. When it was refurbished two years ago, an LED-system was installed, which was operated by the intelligent lighting system. “It has nine lighting stages and advanced monitoring with an illuminance photometer in each tunnel zone. Each day it also alternates which lights are on. This way it also extends the life span of the lights,” said Longtin. “The energy savings measured against a ‘non-intelligent’ system is equivalent to 42% a year, and the expected life span is now more than 15 years.”

NetTUN

Thomas Camus, director of the European R&D programme NetTUN that started in 2012, was also present at the conference. Camus gave a status update of the 12 work packages that make up the programme. Among these are projects that seek to predict ground conditions ahead of the TBM face; increasing the lifetime of drag bits; the development of robots which might eventually replace the need for human intervention to replace disc cutters; and a decision support system for tunnel maintenance. Much of the work is now reaching the implementation phase, said Camus. For instance, “field tests for the ground prediction system – which works with seismic waves and radar imagery – are set for mid-June. The disc cutter replacement robot will be manufactured shortly and tested before the end of the year.”

ROBO-SPECT

On Tuesday ITA-COSUF organised a workshop which contained high quality lectures covering the safety and refurbishment of ageing tunnels. One main topic was an automated robot system for tunnel inspection. The ROBO-SPECT automatically scans the tunnel interior for potential structural defects on the surface and inspects and measures radial deformation in the cross section with millimetre accuracy. The project is still under development, but insights on several of the components of the robot were shared.

For instance “the robot arm will be equipped with a computer vision system and ultrasonic sensors to detect and classify defects and cracks,” said one of the developers, Konstantinous Loupos of the Institute of Communication and Computer Systems in Greece. The ideal situation would be a fully autonomous robot, but for the first step, the robot will be wirelessly controlled by an operator at a ground station. This ground station can be located outside the tunnel. The first tests are planned in July this year in the London Underground. Subsequent tests will be held in January 2016 in Greece. “One of the biggest challenges we still face will be lighting intensities, which give difficulties with processing the camera vision data,” explained Loupos.

Assessing behaviour patterns in tunnel fires

At the end of the session, the annual ITA-COSUF safety prize for young engineers was awarded to Karl Friedhoff, researcher at the SP Fire Research Institute in Sweden. As part of his PhD research, Friedhoff carried out an extensive field test that focused on the impact of smoke on the walking speed of evacuating train passengers. In a controlled environment, 100 test subjects were asked to simulate passengers on a train that had caught fire and come to a stop in the middle of a rail tunnel. Smoke filled the entire tunnel and the test subjects were monitored as they tried to find the exits. “One of the most surprising findings was that some people found the exit door, but decided to not use it and continued walking,” said Friedhoff. “When I asked them why, they said that in the smoke, the door looked like the front of a train. Since they were inside a rail tunnel, their instinct told them to move on.”

In the coming weeks Tunneltalk will share more highlights of the technical sessions held at WTC2015.