Transportation and loading

Rail Haulage

General

Mucking is an integral part of underground tunnel construction. Mucking could be done efficiently by the rail-borne plant, the use of plant should be planned. Factors affecting the choice of the plant are:

• • Gradients;

  • The length of the main haul;

  • The rate of muck removal;

  • Clearance;

  • The total mass of the trains;

  • The need/ no need for  passing points;

  • The size and availability of the haulage system.

Rubber-Tyred Vehicles

In larger tunnels, the rubber-tyred vehicles can be used for material transportation. The vehicles require sufficient space for reversing and making a turn. The operation of reversing is dangerous for pedestrians. Also, the vehicle is risky to use on a ground with a steep slope. Hence, a proper risk assessment should be carried out before using the vehicles in the tunnel.

To operate such vehicles inside the tunnel, the ground should be leveled, and discharging should be carried out on the leveled ground. The vehicle used should be provided with the following equipment, which should be functional at all times:

1. “An audible warning device.

2. Two white front headlights are visible at 60 m.

3. Two red rear lights are visible at 60m.

4. A braking system, preferably fail-safe when the design allows, which can be operated instantaneously by the driver.

5. A parking brake capable of holding the vehicle fully loaded on the steepest slope likely to be encountered.

6. Spray or jets for cleaning windscreens if fitted.“(BS 6164: 23.2).

Crawler-tracked vehicles

Crawler tracked vehicles for the mucking operation should be used where the ground condition is soft. Same general recommendations applied in case of the rubber-tyred vehicles should be used for the crawler tracked vehicles.

Conveyors

Belt conveyors

Belt conveyors can be used to significantly reduce the frequency of traffic movement in tunnels. They can be hazardous while using in a confined space, as they are dangerous in case a  person is working near them. Pinch point occurs at each loading and discharge point, and at any tensioning device that is fitted.

Precautions should be taken on how to deal with the different parts of the belt conveyor. Idlers on the underside of the conveyor should be guarded. Pull cords should be provided on either side of the conveyor and proper inspection should be carried out at regular intervals. Emergency buttons should also be installed constantly to stop the belt in a time of emergency. The machine should be started only from a single point, particularly from the operator’s side. An audible signal should be installed and provided at a safe time interval that can elapse before startup.

Fire resistance belt should be installed on the conveyor with the motor being properly ventilated, and any spillage should be avoided on the motor. In case of emergency, a fire extinguisher should be located in close proximity.

The conveyor sides should be high enough to prevent any spilling over. A gating device should be installed to stop any big piece of removed rock or soil, as potential hazards to the person working or to the machinery itself may arise from these pieces

A proper inspection and maintenance plan of the conveyor system should be laid out, any worn or damaged part should be replaced as soon as possible. The belt should be kept free from any potential build-up, which can affect motor efficiency and cause a risk of spillage (BS 6164: 23.5.1).

Where the spoil is transported out of the tunnel over the conveyor belt, one or more belt weighers should be fitted on the conveyor system (BS 6164: 23.5.2).

For vertical muck conveyance, vertical conveyors should be installed to reduce a considerable lifting operation (BS 6164: 23.5.3).

Slurry Pumping

Slurry pumping comprises a mixture of fluid and excavated material by the tunneling shield. The slurry system should be composed of the minimum of:

• • a mixer to mix the components of the slurry,

  • an injection device to inject the slurry into the tunneling machine,

  • a discharge pump to carry the mixed slurry to the ground, and

  • a pipe network to convey the slurry and a unit (plant) to separate the excavated material and slurry (BS 6164: 23.61.1)

The mixing and slurry pumping system

The material used for the pumping system, such as bentonite or long-chain polymers should be stored in compliance with the manufacturer’s safety data sheets (MSDS). Workers coming in contact with such material should be trained properly. The station should have eyewash facilities near the mixing plant and a facility to change clothes at. The mixing tank should be properly covered to reduce the chances of material splash while working near the mixing machine (BS 6164: 23.6.2).

The slurry system contains high-pressure liquid, the area near the machine should contain warning signs with sufficient data about working near a highly pressurized work area. Where the pumps are operated in confined spaces, special procedures must be followed, and the power supply should be isolated in such work zones. Any maintenance work “permit to work”  system and a suitable lock-off procedure should be enforced to immobilize the plant before carrying out the maintenance work of the machine. In case of an accident, a special monitoring system should be applied to check the power plugs and coupler isolation (BS 6164: 23.6.3)

The Piping networks

The slurry pipe network should be sufficient to withstand the slurry pressure and abrasion caused by the spoil carried back with the slurry. The pipe networks’ support clamps should be strong, and where extra load is anticipated, the clamps should be designed to withstand double the design force. Due to high pressure carrying the pipe, the connections should be suitably designed. 

In case the piping system is open for pipe jacking, there should be a system to minimize the spillage of the contents, as this leads to slipping hazards and contamination (BS 6164: 23.6.4).

Intervention procedures

In case the TBM is equipped with man entry facilities to a normally flooded slurry chamber, personal safety should be ensured at all times and safety procedures should be in place. The following are additional safety measures:

• 1. Compressed air pressure should be maintained on the tunnel face.

  2. A constant watch should be maintained to detect the deterioration of the face.

  3. At the first signs of unfavorable conditions, the crew should be withdrawn.

  4. All personnel should be using harness and fall arrest equipment.

  5. There should be a method in place to remove injured people from the front of the machine.

All the equipment, including the slurry plant, pumping systems, and the TBM should be kept ready to be able to excavate one extra cycle into the undisturbed ground quickly. For this reason, no maintenance should be carried out at this stage (BS 6164: 23.6.5).

General Operating Procedures

A system to identify high pressure on the face of the TBM must be in place, as this can affect the installation of segments with high pressure as well. In such a case, a suitable reduction of the slurry pressure on the face of the TBM should be performed.

In a similar way, high pressure slurry and soil can be discharged into a shaft when launching, and a shaft seal system should be used to prevent it  (BS 6164: 23.6.6).

Slurry Separation

When doing slurry separation using separation plants and settlement tanks, this should be well secured by adequate foundations and supports. Also, tanks should be provided with gratings when there are risks of falls into the tank.

In the separation plants, guards should be installed for all moving plants, a kill switch for shutting down the plant should be found and emergency procedures should be placed in advance.

Where lagoons are used, this should be fenced and properly signed identifying the maximum depth and nature of the contents. Removal of the slurry should be done by the tanker and managed with due recognition of the contents’ nature (BS 6164: 23.6.7).

Personal Protective Equipment

A minimum of eyewash facilities and fluids for cleaning the skin and eyes should be provided at the minimum in case of contamination with slurry. Masks, goggles, and gloves should be part of the basic PPE and protective overalls where necessary (BS 6164: 23.6.8).

Tipping and disposal

When on-site tip or disposal take place, special consideration for the method of construction, drainage, and compaction should be taken. If this is located in the path of future tunnel excavation, the soil should be able to withstand these additional loads.

Properly built roadways using ballast as necessary will allow the stability and traction in vehicles, and dust control should minimize risks to health and the environment.

When driving the vehicles on the road, road regulations and by-laws must be followed such as wheel cleaning procedures.

If the slurry storage facilities are subject to potential flooding, the shafts should be protected above any possible slurry lagoon level (BS 6164: 23.7).

MUST KNOW

Alberta Occupational Health and Safety Code Relevant to the Topic

As according to the Alberta Occupational Health and Safety Code (current as of January 1, 2019) an employer must follow the following:

According to Part 21, Section 292(1)

An employer must ensure that rigging is not subjected to a load of more than

(a) 10 percent of the breaking strength of the weakest part of the rigging, if a worker is

being raised or lowered,

(b) subject to Alberta OHS Code Part 21, Section 292.1, 20 percent of the ultimate breaking strength of the weakest part of the rigging in all other situations unless the manufacturer has fatigue rated the rigging in accordance with CEN Standard EN 1677-1: 2000, Components for slings – Part 1: Forged steel components grade 8, and

(c) subject to section Alberta OHS Code Part 21, Section 292.1, if the rigging is fatigue rated in accordance with CEN Standard EN 1677-1: 2000 and a worker is not being raised or lowered, the maximum load must not exceed 25 percent of the ultimate breaking strength.

According to Part 21, Section 292(2)

Despite AOHS Part 21: 292(1), an employer may use a dedicated rigging assembly designed and certified for a particular lift or project by a professional engineer, but the dedicated rigging assembly must be re-rated to comply with AOHS Part 21: 292(1) before it is used for another lift or project.

According to Part 21, Section 292.1(1)

Subject to section 292, an employer must ensure that rigging components are rated relative to their ultimate breaking strength in accordance with the following safety factors:

(a) running lines    3.5 to 1;

(b) non-rotating hoist lines    5 to 1;

(c) tugger lines/blocks for pulling    3 to 1;

(d) pendant lines/guy lines    3 to 1;

(e) winch lines    2 to 1.

According to Part 21, Section 292.1(2)

An employer must ensure that rigging components or hoisting lines that are used in any towing operation are not used for any hoisting operation.

According to Part 21, Section 293(1)

An employer must ensure that the maximum load rating of the rigging, as determined by the rigging manufacturer or a professional engineer, is legibly and conspicuously marked on the rigging.

According to Part 21, Section 293(2)

Despite AOHS Part 21: 293(1), if it is not practicable to mark the rigging, the employer must ensure the maximum load rating of the rigging is available to the workers at the work site.

According to Part 21, Section 294

An employer must ensure that rigging to be used during a work shift is inspected thoroughly prior to each period of continuous use during the shift to ensure that the rigging is functional and safe.

According to Part 21, Section 295

A worker must not use rigging that does not comply with AOHS Part 21.

According to Part 21, Section 296

An employer must ensure that sharp edges on loads to be hoisted are guarded to prevent damage to the slings or straps of the rigging.

According to Part 21, Section 297(1)

An employer must ensure that wire rope, alloy steel chain, synthetic fibre rope, metal

mesh slings and synthetic fibre slings manufactured on or after July 1, 2009 meet the

requirements of ASME Standard B30.9-2006, Safety Standard for Cableways, Cranes, Derricks, Hoists, Hooks, Jacks and Slings.

According to Part 21, Section 297(2)

An employer must ensure that below-the-hook lifting devices, other than slings, meet the requirements of ASME Standard B30.20-2006, Below the Hook Lifting Devices.

According to Part 21, Section 297(3)

Despite AOHS Part 21: 297(2), an employer may use a capacity data sheet to label a spreader bar with its rated capacity.

According to Part 21, Section 297(4)

Where a capacity data sheet is used in accordance with AOHS Part 21: 297(3), an employer must ensure that the data sheet and corresponding spreader bar are identified by a unique numbering system.