The traditional method to consolidate the side material of the body of the dam used two hydraulic cylinders, one compressing the sloped side and the main horizontal cylinder compressing the floor.

This traditional system is hazardous because the compaction cylinder was working at the edge of the dam with the consequential risk of fall. This risk increases as the dam grows in height.

In the Brazilian ITA dam we adopted a method for placing an extruding machine over the compacted layer that was topographically aligned with laser. The ridge aligned with the slope of the dam this machine produces is usually called “kerb”.

This machine can produce between 50 and 70 m of kerb per hour. After one hour the kerb has taken enough set to allow placing the next layer of fill (usually 3 to 4 m in width).

Working with this machine, it would be necessary four men, the first one operating the machine, another one loading concrete into the machine and the remaining two controlling the material to be extruded by the machine. The required equipment is completed with a 6 cu. m ready mix lorry, a concrete plant, and the topographical equipment (may be used either laser or optical equipment).

Results produced by this system are much better than the traditional system reducing material losses, and allowing having a wider working road on the top of the dam, avoiding interferences with other tasks being carried on there. And above all it makes safer the work to be performed.

This technology is simple and economic, and nowadays it is being used in most of the dams built all over the globe.

The slipforming of plinths was performed for the first time in 1990 at the XINGO POWER STATION in Sergipe state, Brazil.

The former method of making plinths with fixed forms was expensive both in handwork and materials, being particularly difficult the zone of the form where the copper seal is placed.

A modular slipform able to withstand the pressure while concreting was created to solve that problem, which can easily changed to be reused in the following stages. It is possible to perform 6 to 7 m per day working two 12 hours shifts. Both quality and finishing of the concrete executed are better and costs and execution time are reduced.

Basically, the system consists in the carefully execution of the following stages:

1) Leveling of floor (rock excavation) as precisely as possible with an additional width of 0.5 m each side.

2) Continue placing the anchoring irons, injection pipes and / or blockouts and the reinforcement, as indicated in drawings.

3) After such preparations, the plinth form can be mounted. It consists in a modular metallic latticework that can be assembled in different configurations according to the needs, including also the possibility of reversing elements to work with the same modules both in the left and right sides of the dam. This form can be adapted to the different widths of the plinths. The panels used to form the flat faces of the concrete have a width of 1.2 m and those forming the head, where the copper seal is placed are 2.5 m in width. This allows the concrete in such parts to remain a longer time in the form.

The plinth form is supported by two wheeled bogies situated in the ends, each one with two wheels. To execute plinths of variable thickness, the height of such supports can be changed. The wheels of the form run over a 10/12 cm I beam which also supports the hydraulic jack that propels the form. These jacks have two sets of teeth, one at the front and the other at the rear, that work alternatively gripping the I beam. This hydraulic system allows an easy and vibration-less sliding of the plinth form at the speed of 25 cm to 40 cm per hour. The I iron must be adequately attached to the concrete regularization floor to support the weight of the form and the sliding forces.

4)The start of plinths and the junction of plinths of different section must be executed with fixed forms. Is important the precise placement of the form and the reinforcement, taking care also to use the length of splicing indicated in the project drawings.

To obtain the water-tightness of the project, a copper joint is placed between each pair of adjacent slabs. The copper joint must be placed over a smooth and flat surface, to be executed with mortar.

This mortar pad also supports the sideform.

Is usually 55 to 60 cm width and 3 to 5 cm thick.

The mortar is prepared with 1 part of cement by 3 parts of sand.

Is important to be careful with the level of this supports to avoid form distortion and to maintain the slab thickness complying with tolerances.

We have developed a trolley apt to carry men and materials in order to help the execution of the mortar pads. This trolley is moved by a special winch designed to guarantee its precise placement, giving also absolute safety to the personnel as the working place is an enclosed area with rails that allow the fixation of safety belts. The mortar pads are hand-made with the material carried to the working place by the trolley or sent down with 10” PVC tubes.

Once executed the pads, the copper joint must be placed over them. To avoid damaging the copper joints during transportation, those are manufactured in place. We have developed a machine apt to use copper plate coils of up to 200 m in length (depending on the thickness specified in the project). This allows fabricating long joints in a single piece, bettering water-tightness and reducing the number of costly welds to be performed.

The machine can be placed level or slightly inclinated to make joints to be used between plinths and slabs or supported by a structure that has the same inclination of the face of the dam when making the joints between slabs. The structure has been designed to take little width at the top of the dam, a place which is often much congested.

The machine is powered by an electric motor fitted with electronic speed control that allows to have the required speed in any situation.

The following step is to place the slab’s reinforcement. To simplify the usually risky job of placing steel in place, we have developed a trolley apt to carry to the place preassembled steel mats of up to 8 ton weight.

First, the reinforcement mats are assembled in panels having the size indicated in the project drawings (usually 12 x 15 m) and stacked placing in the bottom position the one to be placed in the topmost position.

Supports are to be placed on the face of the dam in the adequate locations to keep the reinforcement at the height over the slab indicated in the drawings.

When the place is ready, with the help of a crane the trolley is placed on the face of the slab and a winch with enough power to raise and lower when loaded it is placed at the top of the dam.

Reinforcement mats are placed on the trolley with the aid of a crane and are carried to its final location. The first one is carried by the trolley to the bottom of the slab and securely fastened. The process is repeated with the following ones, which are also carried down and fastened each one to the former mat.

Using this system it is possible to place one mat in an hour with the personnel working in complete safety.

The first sliding form developed by BRASTEQ was the one used in Foz do Areia dam in Paraná State, Brazil between 1977 and 1981.

Basically the form is constituted by an upper and a lower platform. The upper platform is over the face form and is used by the drivers of the form and the workers vibrating the concrete.

Two I beams form the main frame of the form, which is lifted by a pair of hydraulic jacks and climbs guided by two rails. Over the rails there are two safety nuts that support the form while the jacks are operated to raise it.

The width of the face form is 1 m and it is made out of steel modules.

In the attached photograhs can be seen a form with improvements added after the additional experience obtained in the works of Segredo, Aguamilpa, Xingó and Messochora.

In the first jobs, the boards used to form the sides of the dam slabs had individual supports but later we took to support these forms with the reinforcement of the adjacent slabs, as shown in the photographs.

The form has been designed to withstand the tensions generated when the support separation is more than the usual slab width of 15 m, taking into account the situations produced when the rails are more separated.

From the structural analysis performed, can be concluded that the deformation of the structure is less than 1/1000 of the free span, complying with the standards.

The jack tooth boxes are manufactured with high tension steels even if the actual stresses don't exceed 300 Kg/sq. cm.

We have also developed a concrete conveyor trolley that goes in front of the form and allows a better distribution of concrete when required because of the characteristics of the job.

Any slipform may need one or two sideforms that also are giving the slipform the right height.

It is important to have in mind that the final alignment of the upper face of the slab may vary as a consequence of the settlement suffered by the fill after its construction.

Because of this, the sideforms must follow the true line of the dam, keeping the slab thickness specified in the project.

Deviations can be compensated adjusting the face form by means of control screws.

Rails, forms, side closings and complementary material are transported to the place of assembly using boxes on skids operated by winches of 2,5 to 5 ton capacity.

As the gross weight of the form is less than 8 ton, we suggest the use of a crane to move it from one slab to the next. Once a slab is finished it is also possible to lower the form to the level of the next start over the rails used for the slipforming.

Our form is able to execute the starter slabs either if are slightly inclinated or if are strongly inclinated together with the main slab, avoiding the cost and delays caused by a cold joint.