Italian Invention Patent
n ° PR2010A000069 of August 24th
Inventor Guazzi Giuliano
GENERAL DESCRIPTION
It is possible to provide the prefabrication of trunks consisting of a number of bars (depending on the spaces available and the usable means of lifting) previously prepared with the slides described below.
The launching of the pipeline can take place both by pushing the trunk exerted with a work vehicle positioned at the tail of the trunk, and by towing these inside the microtunnel, using a shooting device placed at the arrival post.
Considering a classic conformation of the tunnel with vertical curve, and given the possibility (due to the reduced friction coefficient) that the tube could continue to advance when the pull (or thrust) stops, it would be necessary to provide static restraint systems.
A restraint system consists of the same work vehicle which can also exert a thrust effort on the trunk: this will ensure control of the progressive advance of the string in dynamic conditions. In addition to this, a clamp with side stop wings at the tail of the string guarantees safety in static conditions.
The presence of a clamp will also aim to stop the tube advancement at the end of each pull, positioning it for the welding connection.
SLIDES FOR MICROTUNNEL
Once the microtunnel is completed, it is necessary to insert a conduit for the transport of liquids or gas. In order to avoid direct contact between the tunnel and the pipe to be launched, a series of slides, usually made of steel and equipped with sliding blocks, are to be fixed to the pipe.SLIDE DESIGN AND PLANNING
The patented slide provides a roller system in order to significantly reduce the friction coefficient (which from sliding friction becomes rolling friction) and consequently decrease the pulling forces of the pipeline inside the tunnel.The slide provides the optional possibility of shaping the upper shell so as to also allow the fixing of the secondary pipes, allowing the launch/threading of the main and secondary pipes in a single solution.
The advantages of the proposed solution consist in the considerable reduction of the pulling efforts and the fact that it is no longer necessary to have personnel enter the tunnel to fix the secondary pipes or to lubricate the bottom of the tunnel (with the obvious consequent lighting problems, air exchange, etc.)
This solution can be used for various pipes of any type (32-inch Guazzislit, 36-inch Guazzislit, 42-inch Guazzislit, 48-inch Guazzislit, 56-inch Guazzislit or with multi-pipe configuration), modifying the slide to adapt it to the diameter and mass of the pipe to be launched, at the diameter of the tunnel in which to insert it.
The slides will be installed at a maximum center distance of 15m and cannot be positioned at the restoration points of the pipe bar coating (welding joints and previously repaired points). The shells constituting the slides will be tightened by means of a torque wrench (tightening torque according to the calculation report) and between the shells and the pipe will be a layer of elastomeric material (usually SBR) of thickness to be verified during the project.
The slides can only be painted externally, maintaining the internal part of the closing shells in bare steel to ensure the transmission of the pulling forces.
Experimental tests have shown that the maximum friction coefficient during the shooting operations was equal to 0.06, while the minimum coefficient (detected during the movement) was equal to 0.02. For the dimensioning of the pulling elements, the friction coefficient is cautiously considered equal to 0.10, while for the retention of the pipeline, the coefficient used in the calculations is equal to 0.00 (in favor of safety).
LAUNCHING OF THE FIRST TRUNK PIPELINE
The pipeline section, with previously mounted saddles, will be slowly and evenly lifted by the vehicles and transported along the track, avoiding contact with the ground.
Once the clamp has been secured to the restraint at the tail of the trunk, the coordinator will give the command to begin the trunk launch operation.
During the push-pull phase, all the lifting will be done with the tube in the same direction and with the same speed towards the entrance of the tunnel.
The first launching operation will be completed when the batting tail at the end of the string rests on the tunnel entrance; the rear end of the tube will be positioned so as the second trunk can be welded to the first.
LAUNCHING OF THE SECOND TRUNK PIPELINE
The connection will then be welded between the first and the second trunk on which the structures for retention have previously been prepared. After checking the welding and restoring the coating, the stop plate will be positioned at the tail of the new string.
Then the lifting and launching will take place according to the procedure described in the previous paragraph.
The launching operation of the second section is considered completed when the rear end of the string reaches the welding position (clamp on the surface from the first concrete segment to the tunnel entrance).
Once the thrust force cannot counteract the friction that the saddles exert on the bottom to contrast the movement, in order to continue the launch, it is necessary to pull the pipe using the winch.
In the same way, all subsequent strings are launched.
CONCLUSION OF THE LAUNCHING
Launching operations are common from the second trunk onwards. The towing operation is considered completed once the ends of the tube reach the preset positions.
VERIFYING PROBLEMS RELATED TO A POSSIBLE ROTATION OF THE COLUMN INSIDE THE TUNNEL
The possibility of rotation of the string inside the tunnel is, however, a reduced possibility since no twisting action is exerted on the pulling head, since the pulling device exerts only tractive effort without any rotary motion of the bars. Considering the barycentre position of the duct-saddle system is in the lowest possible position, the trunk will always tend to return to the position of minimum potential energy (corresponding to the central position in the tunnel).
In any case, the possible rotation of the trunk will be monitored at the end of the launching of each single string.
If it is found that the log inserted is not perfectly positioned in the center of the tunnel, two guides (fixed on the concrete of the bottom of the tunnel) made up of 18m-long L-shaped steel sections will be installed inside the tunnel at the initial part, so as to constitute a curve for the realignment during the subsequent launching phases, as indicated below. The guides will remain in place for the entire duration of the launching and will not be removed.
STRUCTURAL CONTROL
The slide and collar are supplied with a finite element structural control, of which some extracts are reported.