All about civil construction knowledge- PARAM VISIONS

Concreting in water-logged foundation pit./How to do concreting work for a foundation in water?

 The foundation area gets filled by the water due to the following 2 reasons.

a. Due to rainwater: 

If the RL of the foundation site is lower, the water gets accumulated in the area from the surrounding catchment area. The rainwater is a temporary problem & they subside or drain out in the coming season.

b. Due to the water table:

If the level of the water table is above the foundation level, we have to deal with the situation by following certain methods, to maintain the quality of the foundation.

Now, let us understand the different methods or procedures to be followed while making the concreting work in the water-logged foundation area.

1. Working season:

If the construction work is not within the timeframe, the best way is to start the foundation work in the summer season. 

The water table sinks to the lower level in the summer season. This helps to save extra costs required in dewatering & labor.

2. Creating a sump:

Create a sump of 2' 🇽 2' size at the lowest level of the foundation area. The depth of the sump should be 2 to 4ft., depending upon the flow or percolation of water within the ground. 

The location of the sump should be selected in such a way that it does not fall within the positioned foundation pit area.

Pumping out the water at regular intervals helps to maintain the water table below the strata base & the foundation laying becomes less tedious.

 3. Partial work:

The digging of the pit should be done partially or in batches depending upon the concreting capability. The water table softens the soil & the excavated pit collapses due to rising water. 

Part by part working reduces the re-excavation of collapsed soil & saves in our budget.

4. Soil stabilization:

If the soil strata get loose or soft due to the water table, we should stabilize the strata for further work. A layer of lime & sand mixture works better in handling loose soils. Spread the dry mixture over the foundation base & compact them by using a rammer.

5. Laying boulders:

We should use boulders of a specified size to lay over the strata & to maintain the required SBC. The base level of the foundation PCC gets raised within the water, without compromising the load-bearing capacity of the soil.

The boulder should be rammed within the loose soil to embed densely into the soil bed. Any leftover voids should be filled by the murum (construction soil) or coarse aggregates. 

6. Dewatering:

Create a sump at the lower corner of the footing pit. Pump out the excess water continuously by using a water pump. While concreting, you should take care that the water level should not rise above the concrete level.

 Dewatering should be done until the concrete sets or hardens. Usually, 90 to 120 minutes of pumping is enough, as the concrete hardens within those time period. 

Keep a standby water pump in a ready position. If the running pump fails, handling the situation becomes difficult as we cannot leave the footing work incomplete in water-logged areas.

7. Concrete mix:

For the PCC bed work, we can use a stiff concrete mix. The concrete absorbs the water from the strata when we lay the foundation bed.

Add 10% extra cement to the concrete mix to maintain the safer designed strength. Any absorbed excess water weakens the concrete strength & adding extra cement helps to keep up the concrete grade.  

Out of all these 7 methods, follow those procedures, whichever is applicable to your site conditions.

👀  To go through all types of construction-related procedures & checklists, click here.

Thank you for going through this article. Have a good day 😄.


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