Bringing two electricity pylons back to vertical with hydraulic jacks

Objective

Two steel lattice pylons on an Endesa overhead medium-voltage line, in the olive groves of Villanueva, had visibly tilted. They had to be brought back to vertical without dismantling or replacing them, by working on their foundations.

Difficulties

• The ground had moved. One of the pylons stood at the edge of an eroded slope that had left part of its footing exposed. The other, on flat ground, had a cracked and undermined concrete base.
• A structure in service. The pylons carry the line’s conductors. The correction had to be gradual and controlled, with no sudden movements.
• Moving a whole footing. To straighten the pylon its foundation had to be rotated, and that needed a fixed point to push against.

Solution

Next to the footings of each pylon, the ground was excavated and reinforced-concrete tie beams were cast to act as reaction. At the larger pylon, the beams are up to 1.50 m wide and 2 m deep.

Single-acting 55 t hydraulic jacks were placed between the beams and the footings, driven by hand pumps and fitted with tilting heads to follow the rotation. The jacks pushed against UPN 240 spreader beams and base plates. As the pylon came back to vertical, its position was fixed with HEB struts.

Once the pylon was level, the gaps between footing and beam were filled with mass concrete, so that the old foundation and the new beams work together.

Result

Both pylons were brought back to vertical without dismantling the line. Their foundations were underpinned and tied by reinforced-concrete beams, with the base finished with a concrete slab.