A hyperbaric treatment In a closed-shield tunnel boring machine, this is necessary when access to the excavation chamber, cutting head, or face under pressure is required to inspect, clean, repair, or replace tools without compromising ground stability or face pressure. This is only considered when it is not possible to resolve the issue from the surface, from inside the machine under atmospheric conditions, or using non-pressurized procedures.
In projects of pipe ramming, microtunneling o infrastructure crossings, hyperbaric interventions may be necessary in tunnel boring machines EPB closed shield o hydro shield when water pressure, permeability, or low stability of the face prevent the chamber from being safely opened to atmospheric pressure.
In what situations might it be necessary?
Hyperbaric therapy may be considered when treatment is needed for:
| Situation | Reason for the procedure |
|---|---|
| Changing Cutting Tools | Wear on discs, tines, scrapers, or guards in abrasive terrain |
| Cutting Head Inspection | Check for damage, blockages, wear, or the entry of foreign material |
| Removal of pins or blocks | Obstacles that cannot be broken up or removed using the planned system |
| Camera Cleaning | Clay buildup, clogging, clay balling, or adhered material |
| Repair of Front-End Components | Damage to tools, mounts, openings, seals, or protective covers |
| Checking for Blockages | Loss of performance, increased torque, partial blockage, or excavation anomalies |
| Handling Hydraulic Incidents | Need to maintain pressure due to the water table, sand, gravel, or permeable soil |
In all cases, the procedure must be technically justified and compared with lower-risk alternatives.
Why Doesn't the Chamber Open at Atmospheric Pressure?
In a closed shield, the chamber maintains a pressure that helps stabilize the face. If it is depressurized uncontrollably in saturated, permeable, or unstable ground, the following may occur:
- Sudden influx of water.
- Fine-particle drag.
- Loss of ground.
- Frontal instability.
- Surface settlements.
- Local landslide.
- Damage to nearby services or infrastructure.
- Risk to personnel and the machine.
Therefore, in the presence of significant hydraulic pressure, sand, gravel, unstable soils, or sensitive crossings, the work must be carried out while maintaining pressure conditions compatible with the stability of the face.
How to Determine Whether Hyperbaric Treatment Is Necessary
The decision is based on a technical and HSE assessment. The following are reviewed:
1. Status of the tunnel boring machine
Cutting torque, thrust, feed rate, energy consumption, blockages, tool wear, vibrations, chamber pressure, flow rates, and performance of the extraction system.
2. Site Conditions
Geotechnical engineering, water table, water pressure, permeability, grain size distribution, risk of boulders, abrasiveness, face stability, and the presence of cavities or seepage.
3. Risk of depressurization
An analysis is conducted to determine whether the chamber can be opened at atmospheric pressure without compromising the front. If this is not feasible, hyperbaric intervention or prior ground treatment is considered.
4. Available Options
Before taking action, the following are evaluated: operational adjustments, site preparation, system flushing, reducing the rate of advance, parameter changes, surface treatments, or access via a well, if one exists.
5. Employee Safety
The procedure requires specific protocols, qualified personnel, medical supervision, hyperbaric chambers, airlocks, communication systems, rescue teams, an emergency plan, and exposure limits.
What HSE requirements must be met?
A hyperbaric procedure is not a routine maintenance operation. It must be planned as a safety-critical activity.
You should consider:
- Approved Intervention Procedure.
- Specific risk assessment.
- Trained and authorized staff.
- Locks system or hyperbaric chamber.
- Control of pressure and exposure times.
- Compression and decompression protocol.
- Medical or health supervision in accordance with applicable regulations.
- Ongoing communication.
- Adequate lighting and ventilation.
- Emergency and rescue teams.
- Atmosphere Control.
- Record of Intervention.
- Coordination with the construction manager and the HSE coordinator.
For construction projects under roads, railways, waterways, urban areas, or critical infrastructure, this planning must also be coordinated with monitoring, alert thresholds, and a contingency plan.
Risks of Hyperbaric Treatment
The main risks are:
- Risk to workers due to pressure.
- Accidents during compression or decompression.
- Communication or rescue failures.
- Water ingress or loss of pressure.
- Frontal instability.
- Exposure to hazardous gases or atmospheres.
- Limits on working hours.
- Difficulty with bowel movements.
- Damage to equipment during the intervention.
- Delays due to setup and recovery.
- Additional costs for specialized personnel and auxiliary equipment.
For this reason, the design objective should be to minimize the likelihood of intervention through thorough geotechnical characterization, appropriate selection of the tunnel boring machine, cutting head, tools, site preparation, and maintenance plan.
How to Reduce the Likelihood of Intervention
To reduce the risk of needing hyperbaric treatment, it is recommended that you:
- Accurately identify abrasiveness, bowls, blocks, and mixed fronts.
- Select the appropriate cutting tools.
- Provide abrasion-resistant protection.
- Control clogging or clay balling in EPB.
- Properly size the circuit and the sludge treatment plant in the hydro-shield system.
- Monitor torque, thrust, pressure, flow rate, feed rate, and wear.
- Establish cleaning and maintenance procedures.
- Design wells or access points if the project allows for it.
- Adjust the path to reduce critical areas.
- Anticipate contingencies starting with the RFQ phase.
The choice of tunnel boring machine and the cutting head are crucial for reducing unplanned interventions.
Information Needed to Review the Project
To assess whether a hyperbaric intervention may be necessary, the following information should be provided: type of tunnel boring machine, diameter, driving length, depth, overburden, geotechnical conditions, water table, water pressure, permeability, grain size distribution, abrasiveness, planned bores or blocks, type of cutterhead, installed tools, extraction system, chamber pressure, torque logs, thrust, advance rate, flow rates, energy consumption, incidents, accessibility to the chamber, maintenance procedure, environmental sensitivity, monitoring, HSE restrictions, and emergency plan.
Request a Technical Review of the Risks Associated with Hyperbaric Intervention in Closed-Shield Tunnel Boring Machines Before closing a geotechnical, cutting head, maintenance, or RFQ documentation case.
Español 
English 
Français 