All three methods are used to execute trenchless subway crossings, but each responds to different geotechnical conditions, lengths and levels of accuracy. The microtunnel -Eurohinca's primary method - offers the highest precision and pressure control, especially in complex soils. The horizontal directional drilling (HDD) is more flexible and economical on wide curved layouts, whereas Direct Pipe combines continuous thrust with tunnel boring machine and is ideal for crossings under rivers, sensitive areas or pressurized pipelines.
The microtunnel (microtunneling) is a mechanized excavation technique with a remote-controlled tunnel boring machine (MTBM) that works from an attack shaft and pushes the pipe as it excavates. It allows control front pressure, alignment and slope with millimeter precision, even in complex soils and low water table. It is the most robust option when the crossing passes through urban environments, critical infrastructures or complicated geotechnics. A full explanation of the technology can be found in the article what is microtunneling and what are its main applications?.
The horizontal directional drilling (HDD) is based on pilot drilling followed by one or more reaming. It is very competitive in long and curved crosses, with minor civil works of wells, provided that the ground has sufficient stability. In the page of horizontal directional drilling describes its phases, advantages and typical applications in road crossings, river crossings or buried utilities.
The Direct Pipe combines a microtunnel-like overhead shield with direct pushing of the product pipe in one continuous operation. It is especially interesting for large diameters and crossings under rivers or environmentally sensitive areas, where high watertightness and minimum surface occupation are required. Eurohinca describes this technique on its website at Direct Pipe.
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