Zuluf Downstream Pipelines Project

Execution & Technical Scope

Trenchless Engineering Services Co. Ltd was awarded the Horizontal Directional Drilling (HDD) crossing of a 42" steel pipeline beneath the Dhahran–Jubail Highway, as part of the Zuluf Downstream Project awarded by Dynex. The crossing has a length of 525 m and a design depth of approximately 20 m below the highway. The main technical challenge was the sabkha zone along the alignment — a very loose, unconsolidated formation highly prone to borehole collapse, making it difficult to maintain a stable, open hole for a large-diameter pullback. Two earlier attempts by other agencies failed to complete the installation. The scope was then awarded to Trenchless Engineering as a third attempt. To manage the ground conditions, the crossing was drilled with a 500-ton Herrenknecht HDD rig, reamed up to a final size of 54" to accommodate the 42" carrier pipe, using specially formulated drilling mud additives to stabilise the sabkha formation throughout drilling, reaming and pullback. Antibuoyancy measures were also incorporated to counter the buoyant forces acting on the pipeline during installation. Trenchless Engineering completed the installation successfully on the first attempt, after two previous failures at the same location — demonstrating the company's capability in large-diameter HDD through difficult ground and its ability to recover critical crossings where others could not succeed.