Arrangement with a hollow mandrel for introducing drainage ribbons in a subsoil

A method for operating an arrangement for vertically introducing an elongate, flexible element, such as a drainage element, in particular a drainage ribbon, into a subsoil,

• wherein the arrangement comprises a king post and an elongate hollow mandrel that is slideably guided along the king post in its longitudinal direction between a retracted position in which the mandrel extends above the subsoil and an extended position in which the mandrel penetrates the subsoil,
• wherein the elongate, flexible element is fed through the hollow mandrel,
• wherein the mandrel comprises a permanent section and respective replacement section at the end of the mandrel,
• wherein the permanent section comprises a first elongate and hollow mandrel profile and a mandrel drive, and
• wherein the replacement section comprises a second elongate and hollow mandrel profile that is attached to the end of the first mandrel profile, a bottom face at the bottom end of the second mandrel profile, a push bar that is slideably guided inside the second mandrel profile in its elongate direction between a retracted position with respect to the bottom face and an extended position in which it projects downwards from the bottom face, and a spring that biases the push bar towards its extended position,
• wherein the mandrel drive comprises an hydraulic drive cylinder that is mounted to the first mandrel profile, and a drive cable that extends through the hollow mandrel and that is at one end operatively connected with the hydraulic drive cylinder and that is at the opposite end operatively connected with the push bar by means of a releasable coupling,
• wherein the method comprises vertically introducing a series of elongate, flexible elements into the subsoil by penetrating the subsoil with the mandrel and retracting it while leaving the introduced elongate, flexible element behind,
• wherein after introducing the series of elongate, flexible elements the replacement section is separated from the permanent section and the releasable coupling is released, and another replacement section is installed by operatively connecting the drive cable with the push bar by means of the releasable coupling and by attaching the replacement section to the permanent section.