4.3. Non-Displacement Method

Now let us discuss, the non-displacement method. The commonly adopted mechanism or a methodology is the auger boring we are going to discuss about this in this lecture.

The non-displacement method is a construction technique used when pouring concrete for piles without significantly disturbing the surrounding soil. This technique typically involves auger boring, where a rotating drill bit (auger) is used to create a hole in the ground. The process minimizes the displacement of soil, helping to maintain the surrounding structure of the ground.

Think of this method like using a straw to drink a smoothie. You insert the straw into the drink without causing much agitation or spilling. Similarly, in the non-displacement method, the auger carefully removes soil to create space for the pile without moving the surrounding earth too much.

This picture clearly shows you how the auger boring is done. First, you set up the rig, then you can say this is the auger bore, it has a spiral or the helical drilling bit at the bottom which can be rotated by the motor and it is usually accompanied by a casing.

The auger boring setup includes a rig that holds the drilling apparatus securely. The helical bit at the end of the auger digs into the soil as it rotates. Casing, typically a steel pipe, is placed into the hole simultaneously to support the sides and prevent the soil from collapsing during the boring process.

Imagine using a corkscrew to remove a cork from a wine bottle. The twisting motion of the corkscrew pulls the cork out while the bottle maintains its shape. The auger operates similarly, extracting soil while keeping the newly created hole structured and intact.

So, the placement of the casing and the boring is done together. Casing is nothing but a steel pipe, it will act like a formwork it will act like a formwork.

As the auger creates a hole in the soil, the casing is installed to secure the sides of the hole. This casing not only prevents cave-ins but also acts as a formwork for when concrete is poured, ensuring the pile maintains its shape and structural integrity.

Think of making a sandcastle with a mold. As you pour wet sand into the mold (similar to the casing), it holds the shape of the castle. Once you remove the mold, the sandcastle stays intact. The casing allows the concrete to remain in shape while it sets, similar to how a mold does for sand.

Then with the help of the supporting equipment like crane, as I told you for the pile driving mechanism we need loads of supporting equipment. Like the crane to lift your casing, to lift reinforcement cage and to place the tremie pipe, for all these things we need the supporting equipment.

After the casing is set and the reinforcement is placed, a crane is utilized to support the lifting and positioning of these heavy elements. Once everything is aligned, concrete is poured into the casing using a tremie pipe method, which allows for precise placement at depth maximizing the pile's stability. After the concrete hardens, the casing can be removed for reuse.

Imagine constructing a tall cake using a circular cake mold. You would lift and hold the mold while the batter (concrete) goes in, ensuring the mold helps the cake hold its shape as it bakes. Once cooled, you can take off the mold and have a perfectly shaped cake ready to serve.

So, this method we can recommend basically for the clay soil. So, basically for the clay we should not use displacement method the driving method cannot be used for the clay terrain.

Auger boring is particularly suitable for clay soils because it prevents significant soil displacement that could occur with other methods, such as driving. In clay, displacing the soil can lead to increased pore water pressure which can weaken the surrounding structure. Using the auger minimizes this risk by carefully removing soil rather than forcing it out.

Consider digging in a beach with dry sand versus wet mud. If you try to push soil out of the wet mud, it becomes soggy and unstable. But using a gentle digging tool (like an auger) allows you to carefully remove the material without causing a mess, making it easier to work with.

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