Pipe jacking or microtunneling may not be feasible, or may require an alternative solution, when the combination of geometry, geotechnical engineering, water table, available space, construction interferences and risks exceeds the technical or economic limits of the method. Feasibility does not usually depend on a single factor, but rather on the interaction between the route, terrain, diameter, length, manholes, surroundings, and required tolerances.
In a preliminary review, Eurohinca is analyzing whether the conflict can be resolved by pipe ramming, microtunneling in terrestrial and subway applications, Direct Pipe or another trenchless technology. When constraints are critical, it may be necessary to modify the alignment, expand the geotechnical investigation, change the excavation method, or redesign the shafts.
Factors that may jeopardize viability
Incompatible geometry of the route: Excessive lengths for the planned system, radii of curvature that are too tight, gradients incompatible with the guide system, extreme depths, or alignment and dimensional tolerances that are difficult to ensure with the available information.
Insufficient or unfavorable geotechnical conditions: lack of boreholes, highly variable ground conditions, the presence of boulders, highly abrasive rock, mixed soils, cavities, anthropogenic fill, fractured zones, or abrupt changes in material. These factors can affect the stability of the cutting face, tool wear, the required thrust, and excavation performance.
High water table or high water pressure: the presence of high-pressure water, highly permeable soil, or the risk of water inflow into the tunnel face or shafts. In these cases, it may be necessary to consider closed-shield solutions, such as EPB tunnel boring machine o hydro-shield for water-logged terrain.
Lack of space for wells and auxiliary equipment: lack of sufficient space to drill launch and reception wells, install jacking frames, store pipes, position cranes, manage drilling mud, or ensure safe access. The sizing of the vertical pits for driving and microtunneling It is one of the critical factors affecting feasibility.
Interference with existing infrastructure or services: proximity to foundations, tunnels, sewers, sensitive pipelines, roads, railroads, waterways, or active networks. In the infrastructure crossings, feasibility depends on depth, spacing, tolerances, monitoring, and the acceptable level of risk.
Environmental, urban, or administrative restrictions: construction projects in protected areas, riverbeds, coastal areas, densely populated urban environments, and areas subject to restrictions regarding noise, vibrations, traffic, operating hours, permits, or easements. These restrictions do not always make a project unfeasible, but they can affect the method, timeline, and cost.
Forces or stresses that are not compatible with the pipe: When the length, soil-pipe friction, depth, or soil conditions generate thrusts that exceed the allowable limits for the pipeline, it may be necessary to review the design, add intermediate stations, change the pipe material, or modify the construction method.
Disproportionate construction or economic risk: Even if a solution is technically feasible, it may not be advisable if the level of uncertainty, contingencies, auxiliary processes, anticipated downtime, permits, or total cost outweighs the benefits compared to other alternatives.
How Can Viability Be Restored?
In many cases, a pile driving or microtunneling project that was initially deemed unfeasible can be made viable by adjusting the alignment, modifying the depth, expanding the geotechnical investigation, changing the type of tunnel boring machine, redesigning the shafts, dividing the crossing into sections, or comparing alternatives such as horizontal directional drilling o Direct Pipe.
The key is to conduct an early technical review—before finalizing the design or putting the project out to bid—to identify the factors that affect constructability and avoid costly changes in later phases.
Minimum checklist for identifying risks of unviability: plan and profile drawings, diameter, length, depth, radii of curvature, geotechnical data, water table, affected utilities, space for manholes, infrastructure crossed, permits, environmental restrictions, and required tolerances.
Request a Preliminary feasibility study for pipe jacking or microtunneling before finalizing the route or preparing the request for proposals.
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