A crossover should be carried out by trenchless technology when opening a continuous surface trench would generate too high a technical, economic, environmental or social impact. This occurs, for example, at crossings under roads, railroads, rivers, urban areas, protected areas, existing services, critical infrastructures or routes where surface activity needs to be maintained during the work.
In projects of pipe ramming, horizontal directional drilling, Direct Pipe o microtunneling in terrestrial and subway applications, The choice versus open pit excavation depends on depth, length, diameter, geotechnics, water table, traffic, utilities affected, permits, environmental impact and overall project cost.
Situations where a trenchless solution is usually desirable
Crossings under roads, highways or railroads: allows the pipeline to be executed without completely cutting the infrastructure or opening a trench in the platform. At infrastructure crossings, The objective is to reduce service disruptions, safety risks, detours, replacements and operating constraints.
Dense urban areas: on streets with traffic, stores, homes, parking lots, buried utilities or limited space, a trenchless solution reduces occupancy, open trenches, noise, dust, detours and prolonged inconvenience.
River crossings, riverbeds or watercourses: avoids direct intervention on the watercourse, reduces earthworks and can limit hydraulic, environmental and administrative impacts. In these cases, specific solutions can be considered for river and watercourse crossings.
Coastal areas, catchments and outfalls: when the route affects maritime zones, beaches, protected areas or desalination and aquaculture facilities, trenchless technologies can reduce surface and marine impact. It can be applied in submarine emissaries, sea water catchments o crossings of marine protected areas.
Existing infrastructure or services in operation: when there are collectors, supply networks, gas, electricity, telecommunications, tunnels, foundations or critical installations, controlled subway work can reduce interference and keep services active.
High depths or large repositions: above certain depths, open-cut excavation can require complex shoring, pumping, extensive occupations, major diversions and large volumes of excavation and reinstatement. In these cases, a trenchless solution can be more efficient in overall cost and schedule.
Environmentally sensitive environments: when the route crosses areas with environmental restrictions, watercourses, protected areas or areas with occupation limitations, the reduction of surface excavation can be a decisive factor.
When can open pit excavation remain valid?
Open pit excavation can be suitable for shallow routes, areas with sufficient space, low impact on traffic or services, simple geotechnical engineering, short lengths and absence of relevant environmental or administrative constraints.
Therefore, the decision should not be based only on the direct cost of excavation. A comparison should be made of the overall project cost, including traffic, repositioning, permits, detours, pumping, safety, timing, social impact, environmental impacts and risk of interference.
Criteria for comparing the two solutions
Depth and length of crossing: the greater the depth or the more complex the length, the more sense a trenchless solution can make.
Diameter and use of the conduction: sewerage, supply, gas, drainage, outfalls, catchments or other pipelines may have different requirements for slope, tightness, pressure or maintenance.
Geotechnics and water table: the presence of water, unstable ground, boulders, rock, backfill or mixed soils conditions both open excavation and choice of tunnel boring machine.
Impact on the environment: traffic, pedestrians, businesses, buildings, existing services, waterways, railroads, roads and environmentally sensitive areas.
Availability of space for wells: trenchless technologies require vertical pits for driving and microtunneling or entry and exit zones, so implementation should be verified at an early stage.
Permits and operating conditions: administrations, infrastructure owners, network managers and environmental agencies may impose restrictions that favor a trenchless solution.
In practical terms, trenchless technology is usually recommended when it allows maintaining the service on the surface, reducing risks on existing infrastructures, minimizing environmental or urban impacts and improving the overall constructability of the crossing.
Minimum checklist to compare trenchless vs. open pit: plan and profile, depth, length, diameter, geotechnics, water table, traffic, affected services, infrastructures crossed, permits, space for wells, repositioning, environmental impact, time and overall cost.
Request a technical comparison between trenchless technology and open-pit excavation to evaluate the most viable solution according to the layout, terrain and project conditions.
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