HDD by Intersection Technique (Case Study): A Novel Approach

Horizontal Directional Drilling (HDD) is a trenchless construction technique used extensively in the installation of pipeline carrying hydrocarbons, water, sewage, cables etc., across obstructions where conventional trench and lay method or jacking-boring method cannot be suitably applied. HDD technique also minimises the impact of installation activities in densely populated and ecologically sensitive areas. HDD technique, however, has its inherent shortcomings which render it unsuitable in many real-world scenarios. The torque available at the mud-motor for driving and steering of the drill is fairly reduced for long length crossings. Also, maintaining the directional control of the drill bit becomes increasingly difficult for such long crossings. These shortcomings can be overcome using “Intersect Technique” by utilising electromagnetic steering technology for precise real-time tracking, wherein pilot holes are drilled from both ends using two separate drilling arrangements. On reaching the predefined intersection range, a virtual handshake between the drill bits is achieved. Thereafter, the primary rig continues the bore to the end of the design path to reach at the secondary rig side. The present case study discusses at length the execution of HDD crossing of 18”- 2523 metre multi-product pipeline alongwith 6” CS conduit for OFC of M/s BPCL across the Thane-Vashi Creek in Mumbai, India. The length of the crossing combined with the presence of numerous pipelines of various operators made the execution of this pipeline crossing by “Intersection Technique” as the most suitable methodology. The pipeline was laid at an average depth of 15 m below the lowest creek bed level in geology which primarily included weathered basalt rock. The pilot hole for the crossing was completed utilising ParaTrack® drilling guidance and tracking system.

Development of Filling Material with Fly Ash and Slag as Lubricant in Pipe Jacking Under Acid Sulfate Soils

The pipe jacking method is relatively reasonable among trenchless construction methods.For the application of this method, the acid sulfate soils have negative impacts on filling materials (one of the cement materials) injected into the tail-void which are over-cutting areas formed to reduce the friction between the pipes and the surrounding soils. In thisstudy, the application of fly ash and slag is discussed to minimize the effect of sulfur acid to filling materials. As the results of the experiments, the addition of fly ash and slag can control the gelling time and prevent the reduction of uniaxial strength of filling materialsunder the acid sulfate soils. In addition, the filling materials added slag lowered frictional resistance compared to that of fly ash. Fillingmaterials with the lower frictional resistance are preferred to apply for the smooth pipe jacking constructions. Therefore, filling materials added slag would show better performance than that of fly ash under the acid sulfate soils due to its lower frictional resistance.

Trenchless construction of Phase IIIA District Cooling System (DCS) by TBM pipejacking and hand-dug tunnelling on Kai Tak Development : Part II – The challenges

This paper discusses the challenges of constructing 1.75 km of concrete sleeve pipelines with diameters of 1,200mm, 1,500mm and 2,800mm using slurry operated Tunnel Boring Machines (TBMs) for installing District Cooling System (DCS) pipelines in highly variable ground conditions within the Kowloon Bay area. It covers the problems encountered, solutions provided, and recommendations made. Various construction techniques are also discussed including: running two TBMs in parallel from a jacking pit for the near simultaneous construction of two pipelines; enlarging the lower section of a receiving pit by the caving method to receive the TBM which entered the pit at an oblique angle, for turning inside the pit for removal after skin-off of the TBM; construction of a hand-dug tunnel from a receiving pit to receive three TBMs one at a time in a triangular configuration to suit site constraints. This paper should be read together with Part I which is entitled “Design and Construction Considerations” published in 2017.