Category Archives: Sub soil water

Footings : Levelling Course & Water Logging :

Dear Friends ,

Let us solve the query of one of the readers today.

This is the query :

1

In fact , there are two queries here :

  1. When do we use Plain Concrete in a footing ?
  2. Ground Water seepage during excavation ?

Let us solve these queries one by one.

First query is about the Plain cement Concrete .

Please have a look at the section of the Footing as given in the RCC drawing :

The PCC is marked here with Red :

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Now have a look at the base of a pit . This is how the surface shall be at the base of the excavation :

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It shall be very clumsy to lay the rebars on such a muddy surface. Right ? Thats why we provide a certain thickness of plain cement concrete here . This concrete is also known as the ” LEVELLING COURSE “.

So the Levelling course is a layer of Plain cement concrete which is given so that we get a good working surface for laying the footing properly. 

Now have a look at the leveling course laid on a site :

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Next step is to lay the Rebars of the Footings :

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Parallely , the shuttering for the footing is also fixed on the Levelling course.

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Now we do casting of the Footing so that it becomes the RCC footing .

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Hope the first query is clarified.

Now second query pertains to the Water logging during excavation.

You can have a condition like this on the site :

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So what do we do in such a case ?

Simple.

We have dewatering pumps and take out the water before laying the Levelling course :

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There might be a case like this also :

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So now , may be we shall have to wait for a dry spell so that this water either gets absorbed in the soil below or is evaporated.

In a situation , when the excavated pit is not completely dried, it shall not be possible to lay the plain cement concrete in the mud.

What do we do then ?

In such a case , we shall have to do Boulder solling so that we get a good ,

solid working surface .

Look at the stake of Boulders which are also known as Rubble or Stone :

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These boulders , when laid in the base of a pit , shall look like this :

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After this , the levelling course is laid in plain cement concrete. This is followed by the RCC footing.

Hope both the queries are clarified now.

Thank you for asking the queries .

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