trench excavation

The length of the panels to be excavated is generally between 1.5 and 6 m. The order of execution of the panels depends on the excavation system and the type of screen, since they can be executed by the primary-secondary (alternating) or continuous method.

Excavation can be done in three ways:

Reinforcement Placement

The armor "Armor (structure)") must be previously assembled and it is usually recommended that it also be welded. To place it, the reinforcement is lifted with a crane and inserted into the panel. The reinforcement cannot rest on the bottom of the trench, since it would bend, and upon coming into contact with the walls of the excavation it would lose the lateral concrete covering. For this reason, it must be hung from the guide wall, for which some metal element is usually used, and spacers are placed laterally on the reinforcement to avoid contact with the ground.

Placement of joints or lateral formwork

Before concreting, side formwork or joints are placed between the excavated panel and the panel that will be excavated later.

The mission of these joints is to create a tongue and groove between the screens, create a clean surface and help guide the clamshell on the next screen. If not installed, there would be irregularities between the panels, which would lead to leaks that could be unsightly, or even dangerous.

These joints are usually metal tubes (circular joints) or semicircular joints and to a lesser extent triangular joints.

The most used are circular precisely because the water must travel a greater distance from the upper surface to the lower surface of the wall.

In general, circular joints are usually used for depths greater than 15-20 meters since they are easily joined together and are more rigid to receive the push of the concrete.

Semicircular joints are used in smaller screens offering numerous advantages such as the excavation of the next panel without removing the joint (This way it is not contaminated with mud or excavated ground and prevents water from entering the interior of the wall. It also makes it easier for us to make the outer wall thinner (and therefore less wasted space) since the joint can be extracted with the same excavation equipment and hydraulic jacks are not needed that would exert pressure on the guide wall. It also allows, and this is important, the excavation of the corner panels in two units instead of a single one, in terrain such as sand and gravel or large disaggregated drops in the terrain.

Concreting

When concreting, the trench is filled with bentonite sludge.

To prevent the concrete from being contaminated when mixed with these, it is necessary to start the concreting process from the bottom to the top, using a tube called a "tremie pipe". As the density of the concrete is higher than that of the bentonite sludge, it will remain below the sludge, and these can be extracted on the surface.

Once concreting is completed, the top of the concrete is contaminated by sludge. Therefore, it will be necessary to continue concreting until it overflows, extracting the contaminated part of concrete.

Construction of the crown beam

Once all the panels have been made, the crowning beam is built, consisting of a concrete beam that joins the top of all the panels.

But before executing it, the concrete at the head of the panels or screens that could be contaminated by bentonite sludge must be cleaned.

The crowning beam has the mission:

Excavation and milling of the interior enclosure

Once all the previous operations have been carried out, the excavation of the enclosure (generally interior) of the diaphragm wall can proceed.

If it is planned to execute support elements (anchors or props), they are placed as the excavation is carried out.

Diaphragm walls are retaining elements, so they require surface treatment so that they can be seen. This process is called "milling" and consists of roughing the intrados of the diaphragm wall using "milling machines" (circular milling wheels provided with tungsten picks) and which are generally attached to an excavator as an implement. Through this process, a layer contaminated with the soil itself, bentonite sludge and lumps produced by landslides is removed. This process will give the diaphragm wall a better appearance and allows waterproofing systems to be applied. There are three types of commercial finishes for milling diaphragm walls: ROUGH, ROUGH AND FINE[4]​.

Waterproofing

For correct waterproofing of diaphragm walls: it is recommended to mill the internal face exposed to the ground.

trench excavation

The length of the panels to be excavated is generally between 1.5 and 6 m. The order of execution of the panels depends on the excavation system and the type of screen, since they can be executed by the primary-secondary (alternating) or continuous method.

Excavation can be done in three ways:

Reinforcement Placement

The armor "Armor (structure)") must be previously assembled and it is usually recommended that it also be welded. To place it, the reinforcement is lifted with a crane and inserted into the panel. The reinforcement cannot rest on the bottom of the trench, since it would bend, and upon coming into contact with the walls of the excavation it would lose the lateral concrete covering. For this reason, it must be hung from the guide wall, for which some metal element is usually used, and spacers are placed laterally on the reinforcement to avoid contact with the ground.

Placement of joints or lateral formwork

Before concreting, side formwork or joints are placed between the excavated panel and the panel that will be excavated later.

The mission of these joints is to create a tongue and groove between the screens, create a clean surface and help guide the clamshell on the next screen. If not installed, there would be irregularities between the panels, which would lead to leaks that could be unsightly, or even dangerous.

These joints are usually metal tubes (circular joints) or semicircular joints and to a lesser extent triangular joints.

The most used are circular precisely because the water must travel a greater distance from the upper surface to the lower surface of the wall.

In general, circular joints are usually used for depths greater than 15-20 meters since they are easily joined together and are more rigid to receive the push of the concrete.

Semicircular joints are used in smaller screens offering numerous advantages such as the excavation of the next panel without removing the joint (This way it is not contaminated with mud or excavated ground and prevents water from entering the interior of the wall. It also makes it easier for us to make the outer wall thinner (and therefore less wasted space) since the joint can be extracted with the same excavation equipment and hydraulic jacks are not needed that would exert pressure on the guide wall. It also allows, and this is important, the excavation of the corner panels in two units instead of a single one, in terrain such as sand and gravel or large disaggregated drops in the terrain.

Concreting

When concreting, the trench is filled with bentonite sludge.

To prevent the concrete from being contaminated when mixed with these, it is necessary to start the concreting process from the bottom to the top, using a tube called a "tremie pipe". As the density of the concrete is higher than that of the bentonite sludge, it will remain below the sludge, and these can be extracted on the surface.

Once concreting is completed, the top of the concrete is contaminated by sludge. Therefore, it will be necessary to continue concreting until it overflows, extracting the contaminated part of concrete.

Construction of the crown beam

Once all the panels have been made, the crowning beam is built, consisting of a concrete beam that joins the top of all the panels.

But before executing it, the concrete at the head of the panels or screens that could be contaminated by bentonite sludge must be cleaned.

The crowning beam has the mission:

Excavation and milling of the interior enclosure

Once all the previous operations have been carried out, the excavation of the enclosure (generally interior) of the diaphragm wall can proceed.

If it is planned to execute support elements (anchors or props), they are placed as the excavation is carried out.

Diaphragm walls are retaining elements, so they require surface treatment so that they can be seen. This process is called "milling" and consists of roughing the intrados of the diaphragm wall using "milling machines" (circular milling wheels provided with tungsten picks) and which are generally attached to an excavator as an implement. Through this process, a layer contaminated with the soil itself, bentonite sludge and lumps produced by landslides is removed. This process will give the diaphragm wall a better appearance and allows waterproofing systems to be applied. There are three types of commercial finishes for milling diaphragm walls: ROUGH, ROUGH AND FINE[4]​.

Waterproofing

For correct waterproofing of diaphragm walls: it is recommended to mill the internal face exposed to the ground.