How to optimize Horizontal Directional Drill (HDD) and Jack Bore Installation Pipeline Projects

Pipeline construction by trenchless methods including horizontal directional drill (HDD) and Jack and Bore have become increasingly prevalent to minimize pavement cuts, maintain surface traffic, and reduce restoration costs.?Some entities, especially railroads, have valid concerns of these installations with regards to inadvertent mud returns during HDD installations and risks for settlement under their facilities resulting from HDD and Jack and Bore projects.

It is critical to consider the HDD or Jack and Bore at the appropriate depth of cover and soil layer. Using software and engineers with experience in the design of HDD’s, analysis of the risk of the inadvertent mud returns and recommendations of mud pressure limits can reduce the chance of these to occur.?

Soil conditions for HDD’s Jack and Bores can also be evaluated to determine if there are concerns that could cause more soils to be excavated from the boring process and that could result in the settlement or collapse of the ground at the crossing.?The performance of engineering studies of the soil or rock layers can determine the collapsing risks during the drilling and installation process of the crossings. This is, in many cases, a recommended approach for early stages.

As part of construction planning, a soil monitoring plan can be developed to understand the soil that is being excavated from beneath key facilities, to verify that an over-excavation is not occurring.?The plan should list the expected soil removal in regular increments, associated with the boring machine capabilities and method for measuring the soil removed from the Jack and Bore excavation, compared to the expected value.?

Geotechnical engineers can also evaluate the soil or rock being excavated, or the amount of ground water that is being extracted from these crossings, to determine if conditions are different from the soil borings and rock cores.?These findings are then evaluated to determine if there are concerns that could affect the crossing to be completed safely as designed.

Another feedback measure gathered during the installation process and typically a required practice for rail crossings, are surveys for elevation monitoring of the crossing area. These are completed to identify any impact to the grade elevation above the bore, particularly for the rails.?These measurements would identify if there are any changes in grade elevation during the construction of the pipeline bore, that could cause a concern.

The above, are all detailed but key considerations that will allow the progression of project completion in safe conditions, for which an investment with the right expertise, will avoid downstream unexpected costs.