Water Water everywhere !

Overview:

From a trivial trickle of water in the foundation pit to flooding in excavated pits to under water concreting , a construction person interacts with water in different challenging situations.
This article brings to you the various situations where water has to be properly dealt with on the construction sites.

RAIN WATER ACCUMULATED ON THE BASEMENT RAFT which is causing only slight inconvenience.

1.Water from subsoil is trickling in the foundation pit :
This is a tricky issue because if there is water in the pit it is difficult to pour concrete in the raft of footing.
In such situation make a small sump pit in a corner and put the suction of thede-watering pump in this sump.

Keep the casting team ready and as soon as water level in the pit comes below the raft level, start the concrete.
It is advised to keep the Water /cement ratio less than 0.4 so that mixing of pit water in the concrete do not make it more fluid. In simpler words make a dense concrete since there is already water in the pit.

WATER ACCUMULATED IN THE LIFT PIT . Not presently disruptive.It is indicative of the fact that waterproofing has not been carried out around the pit. — WATER ACCUMULATED IN THE LIFT PIT .
Not presently disruptive.It is indicative of the fact that waterproofing has not been carried out around the pit.

2.Surface rain water flooding in the pit :
If the PCC & Raft are already completed we just have to wait for dry spell for binding the column cage ,shuttering and casting it.
However, if both PCC & Raft are pending then take actions as per case no 04.

RAIN WATER ACCUMULATED IN THE EXCAVATED PIT. FURTHER PROGRESS IS HAMPERED. — RAIN WATER ACCUMULATED IN THE EXCAVATED PIT.
FURTHER PROGRESS IS HAMPERED.

3. Water from subsoil trickling in Pile bore :
This can happen in any season of the year. During pile boring ,Bentonite slurry can be used to stabilize the sides.Concreting can be done after removal of water by injecting compressed air.Use ofTremie is must for depositing concrete in the pile.

PILING BY THE HAMMER METHOD.Observe the muck is being cleaned from the dead weight . The yellow colour is due to the bentonite powder. — PILING BY THE HAMMER METHOD.Observe the muck is being cleaned from the dead weight .
The yellow colour is due to the bentonite powder.

4. Water filled up in mass excavation just before the leveling course:

This can become quite serious issue in case water has also started scouring the sides of the pit.
To avoid further collapse of soil inside pit , provide strutting to the weak sides.
Put couple of de-watering pumps .
When the water has almost drained out carry out rubble soling on the pit bottom to make it level & workable.
Complete the leveling course with PCC now.Complete the raft & columns at war level.

LOOK AT THE MASS EXCAVATION FLOODED WITH RAIN WATER ( On the right side ) — LOOK AT THE MASS EXCAVATION FLOODED WITH RAIN WATER
( On the right side )

5.Other liquids flowing in the pit:
Sounds interesting no ?
In one of the industrial projects , we came across a situation when concentrated hydrochloric acid started oozing out from the sides of the pit.
On inquiry we found that acid storage tanks were erected in the front yard of that company. The spillage was collected in the basin.The acid used to get a direct underneath passage from basin up to the location of the expansion on the rear side.

CONCENTRATED HYDRO-CHLORIC ACID OOZING OUT FROM AN OPEN PIT. The acid was to be neutralized using chemicals ,then excavated then only work continued. — CONCENTRATED
HYDRO-CHLORIC ACID OOZING OUT FROM AN OPEN PIT.
The acid was to be neutralized using chemicals ,then excavated then only work continued.

6.Underwater concreting in open foundation( river or sea ):
In case the sub strata is such that an open footing has to be done below the water we have two conventional methods:
6.1 By using caissons:
Caisson is a specially designed reinforced concrete pipe of diameter larger than the foundation to be cast.

The steps are as follows:
1.Shift the caisson to location of the foundation.
2.Sink it vertically under water so that one end firmly penetrates in the silt.Heights of caisson is made such that the other end of this pipe is slightly above water level.
3. Start de-watering from the caisson
4.Complete the excavation in the caisson .
5. Complete the foundation work.
6. Back-fill the caisson with suitable material . caisson permanently remains in this location. This becomes a portion of the pier.

7.Proceed to next location.

6.1 By using cofferdam:

Cofferdam is a temporary bund or dam created around the location of the proposed foundation.

The steps are as follows:

1.Construct a cofferdam around the proposed location for the foundation .it may cover either one or more foundations depending upon the distance between the piers.

2. Start de-watering from the cofferdam
3. Complete the excavation within the cofferdam
4. Complete the foundation work.

5. Remove the cofferdam

6. Proceed to next location.

Note : You would have observed that Caisson stays in the same place whereas the Cofferdam is dismantled and removed.

7. Underwater concreting for Pile foundation ( river or sea ):

As you know Piling shall be resorted at a location where the sub-strata is not sufficiently hard at shallow depths and when it is not practically feasible to excavate at a deeper level. Pile could be either bearing type or skin friction type.

Under water, the Piling has to be essentially done with rotary cutters which are mounted on a Rig.

The Rig is taken to the desired location through ship .The ship is anchored in water at given location while the boring operation is going on underwater.

Underwater concreting is done with the help of tremie. Tremie is a funnel or hopper and is connected to a sufficiently long pipe. At the lower end of the pipe , a valve is fitted which does not allow the pipe to flow out of the pipe .The valve is operated through remote control from the ship. the concrete is carried out in transit mixer over a carrier ship upto the desired location.