What excavation parameters are monitored during tunnel boring with a tunnel boring machine?

Q: What excavation parameters are monitored during tunnel boring with a tunnel boring machine?

Durante una hinca con tuneladora se monitorizan los parámetros que permiten controlar el avance, la estabilidad del frente, la precisión del trazado, los empujes, la gestión del material excavado y la seguridad de la obra. Los más habituales son empuje, par de corte, velocidad de avance, presión de frente, volumen excavado, caudales, presión y densidad de lodos, lubricación, alineación, cota, pendiente, asentamientos e incidencias operativas. Estos datos ayudan a verificar que la excavación avanza dentro de los rangos previstos y permiten detectar cambios de terreno, pérdidas de frente, sobreexcavaciones, aumentos de rozamiento, desviaciones de trazado o riesgos de asentamiento. La interpretación técnica combina datos de producción, geotecnia, guiado, comportamiento de lodos y auscultación.

During a tunnel boring with tunnel boring machine parameters are monitored to control progress, face stability, layout precision, thrust, excavated material management and site safety. The most common are thrust, shear torque, feed rate, face pressure, excavated volume, flow rates, slurry pressure and density, lubrication, alignment, elevation, settlement and operating incidents.

In projects of pipe ramming, microtunneling in terrestrial and subway applications o infrastructure crossings, These data help to verify that the excavation is progressing within the foreseen ranges and to detect changes in terrain, loss of face, over-excavation, increased friction or deviations in layout.

Main parameters to be monitored

Pile-driving thrust:
It measures the force required to advance the pipe and the TBM. An abnormal increase may indicate increased friction, terrain changes, lack of lubrication, partial blockage or the need to check the feed.

Cutting torque:
Indicates the effort made by the cutting head to excavate. Significant variations may indicate geological changes, presence of boulders, rock, abrasive materials or more compact soils.

Forward speed:
Allows comparison of actual production with planned production. If the feed rate decreases without a planned cause, there may be increased ground resistance, mechanical impact, excess thrust or extraction constraints.

Front pressure:
It is key in closed shields, especially in EPB tunnel boring machine o hydro-shield for water-logged terrain. Helps maintain ground stability and reduce the risk of settlement, water ingress or loss of material.

Excavated volume:
It should be consistent with the theoretical tunnel advance. A higher volume than expected may indicate over-excavation, loss of ground or fines entrainment; a lower volume may indicate blockage, compaction or insufficient extraction.

Flow rates, pressure and sludge density:
In hydroshield or slurry circuit systems, flow and return flows, density, pressure, solids separation and behavior of the excavated material are controlled. These parameters are essential to maintain the balance of the front and to manage the excavation correctly.

Lubrication between pipe and ground:
Lubrication consumption, distribution and pressure help reduce friction, control thrust and protect the pipe during driving.

Alignment, elevation and slope:
The topographic tracking and guidance systems allow verifying that the TBM advances within the axis, depth and tolerances defined in the project.

Settlements and auscultation:
In urban areas or under critical infrastructures, surface movements, structures, services, roads, railroads or nearby buildings are controlled.

Incidents and shutdowns:
Shutdowns, tool changes, maintenance, blockages, terrain variations, water ingress, alarms, pressure adjustments and relevant operational decisions are recorded.

How data are interpreted during the work

Parameters are not analyzed in isolation. An increase in thrust, for example, may be related to increased friction, lubrication deficits, terrain changes or a deviation in layout. A variation in face pressure may be associated with changes in permeability, water table or excavated volume. Therefore, the technical interpretation combines production, geotechnical, guidance, mud behavior and auscultation data.

The choice of tunnel boring machine conditions which parameters are more relevant. In an open shield, excavability, feed rate and visible face control will be more important; in EPB, chamber pressure and ground conditioning; and in hydro-shield, the slurry circuit, pressure and solids separation.

What these parameters are used for

Monitoring the excavation parameters allows:

Control the stability of the front.
Detect unforeseen geotechnical changes.
Maintain accuracy of axis, dimension and slope.
Reduce the risk of settlements.
Control thrust and friction.
Adjust lubrication and working pressure.
Evaluate production and yield.
Record incidents for traceability.
Providing quality reports and closing of work.

Minimum checklist of excavation parameters: thrust, shear torque, daily advance, face pressure, excavated volume, flow rates, slurry pressure and density, lubrication, alignment, elevation, slope, settlement, water table, incidents, stoppages and ground changes.

Request a technical review of control and monitoring for tunnel boring with tunnel boring machine (TBM) before executing a crossing, microtunnel or trenchless conduit.