The Direct Pipe technology (DP) is one of the great “no-dig” techniques that allow the laying of pipelines open air trenchless. The DP enables the installation of steel / polyethylene pipes by advancing the pipeline in the ground through a Pipe Thruster together with the drilling process carried out by the cutter head with hydraulic spoil. The DP can be considered a laying system that combines the positive aspects of Microtunnelling technologies (MT) and Horizontal Drilling (HDD). With this method the pipe is installed in a single step without the use of additional piping and without requiring large volumes of mud for the temporary support. Unlike the MT, where the thrust force is applied to each segment in reinforced concrete in the starting shaft, in the Direct Pipe the thrust force is applied through the Pipe Thurster (PT) directly on the previously positioned pipe on the slider way, with full lengths or individual strings, similarly to the HDD. The Thurster is anchored to a structure and transfers its leverage by clamps, for friction, without damaging the coating; then it pushes the cutter head into the ground through the sealing ring. The connection lines necessary to the functioning of the machine are pre-installed inside the pipe, then linked through flexible lines to the grit chamber and the control cabin. The typical diameters are 42″, 48″ and 56” but also other dimensions like 26” and 60” are possible, while the maximum distances vary in function of the diameter and geology from 300m to 1500m.
The excavation is carried out similarly to the MT technology:
- hydraulic evacuation of spoil material
- excavation by closed-shield with balanced pressures
- use of cutter head according to the characteristics of the grounds
- shield guide through action on guiding cylinders
- guidance system with determination of the continuous position.
The main advantages provided by the Direct Pipe technology are:
- reduction to minimum values of the risk of failure due to ground conditions
- high guarantees of hole support thanks to the permanent presence of the pipe
- cutter head equipment adapted to the soil characteristics
- the rock is crashed on the front, ground into the cone and transported through spoil lines, eliminating the presence of cuttings in the hole
- large bending radii can be guaranteed thanks to high accuracy of installation, avoiding overvoltage and high feed forces due to inadmissible radii of curvature
- site area on the starting side only
- temporary modest area only for the recovery of the drilling shield on the arriving side
- minimum volume of excavation
- minimum use of sludge
- very short times of excavation thanks to the possibility of pushing continuously
- installation of large diameters without casing pipes
- thrust management in several sections.