What are the risks involved in driving under roads or railroads?

Q: What are the risks involved in driving under roads or railroads?

Ejecutar una hinca bajo carreteras o ferrocarriles exige controlar el riesgo de asentamientos, pérdida de terreno, desviaciones de trazado, interferencias con servicios existentes, entrada de agua, vibraciones, limitaciones de gálibo, condicionantes de explotación y permisos del titular de la infraestructura. Los riesgos principales son la deformación de la plataforma, la pérdida de estabilidad del frente, la identificación incompleta de servicios afectados, las desviaciones de alineación o cota, el arrastre de finos por presencia de agua y las restricciones operativas impuestas por el gestor de la carretera o ferrocarril. Para reducirlos se requiere una revisión técnica previa del trazado, geotecnia suficiente, selección adecuada de tuneladora, diseño de pozos, control de empujes, auscultación de la plataforma y seguimiento continuo de parámetros de excavación.

Execute a drive under roads or railroads requires special control of the risk of settlements, loss of land, deviations in the route, interference with existing services, water ingress, vibrations, gauge limitations, operating conditions and permits from the infrastructure owner. The objective is to install the pipeline while maintaining structural safety and continuity of service on the surface.

This type of work is usually solved by pipe ramming, microtunneling in terrestrial and subway applications or other trenchless technologies in order to avoid prolonged cuts, open excavations or direct impact on road and rail platforms.

Main technical risks

Settlements on the platform:
This is one of the most sensitive risks. A loss of ground at the front, over-excavation or inadequate pressure control can lead to deformation of the roadway, track, ballast, embankment or nearby structures. On railroads, even small movements may require specific monitoring controls.

Loss of stability of the front:
Stability depends on geotechnics, water table, depth, cover and excavation method. In poorly cohesive, saturated or variable soils, it may be necessary to work with closed shields, such as EPB tunnel boring machine o hydro-shield for water-logged terrain.

Interference with existing services:
Drainage, pipelines, fiber optics, power, signaling, sanitation, water supply or other critical networks may coexist under roads and rail corridors. An incomplete identification of affected services may condition the layout, the shafts and the construction method.

Alignment or elevation deviations:
The crossing must maintain the projected position to respect gauges, coverages, slopes, safety distances and final connections. For this reason, topographic control, guidance system and continuous progress monitoring are required.

Water ingress or fines entrainment:
In embankments, areas with drainage, nearby watercourses or high water table, water can cause instability, loss of material or seepage into the shafts. Hydrogeology should be analyzed before selecting the TBM and face control system.

Operating conditions:
The owner of the road or railroad may require work windows, auscultation, vibration limitations, hourly restrictions, emergency plans, topographical controls, prior technical documentation and validation of the construction procedure.

How to reduce these risks

Mitigation begins prior to the work with a technical review of the layout, sufficient geotechnics, identification of affected utilities, definition of shafts, calculation of thrust, selection of TBM and control plan. At infrastructure crossings, This preliminary phase is critical to demonstrate the constructability of the crossing and to anticipate owner constraints.

During execution, the usual controls include alignment and elevation monitoring, thrust logging, face pressure, excavated volume, torque, daily advance, platform monitoring, settlement control, well inspection and incident management. The intensity of these controls depends on the type of infrastructure, depth, terrain, diameter and client/management requirements.

Warning signs before bidding

Before closing the design or preparing an offer, it is advisable to check if they exist:

Insufficient geotechnics under the platform.
High water table or permeable soil.
Reduced coverage between the pile driving and the roadway.
Critical services not located.
Limited space for attack and reception wells.
Embankments, drains or nearby structures.
Restrictions of the owner not incorporated into the project.
Very demanding settlement or alignment tolerances.

If several of these factors appear, it may be necessary to adjust the route, modify the depth, extend the geotechnical campaign, change the type of TBM, reinforce the monitoring or study alternative solutions.

Minimal checklist to study a pile-driving project under road or railroad: crossing plan and profile, depth, diameter, length, cover, geotechnical, water table, affected utilities, infrastructure owner, operating restrictions, well spacing, existing drainage, settlement tolerances and monitoring requirements.

Request a technical review for crossings under roads or railroads before closing the route, preparing the bidding process or coordinating permits with the infrastructure owner.