Borewell Casing Damage - Rebore? - Advice Required : Hyderabad
Submitted by dps99 on January 25, 2010 - 20:13
My builder has dug a borewell of 4 and half inch size in loose soil area, generally in this area water is struck around 40 ft. The borewell in my case was dug to 260 ft, with 70 ft of casing and the motor kept at 230 ft. Water level is at 15 ft in the well currently. Due to some problems with pumping the motor was being recovered when it got stuck at 60 ft. Fortunately the motor was recovered using chain/block by an expert. He advices that for 15 ft (46 to 60ft) the casing has buckled and will prevent re-insertion of the motor. Also opines that the casing be "expanded" using a borewell machine.
I am looking for guidance regarding what this procedure involves. Or is removal of the casing and addition of new one needed (recasing) ? A few others advice on digging a new borewell, but in my case space restrictions are against that.
What are my options in this case?
What was the cause for the buckling of the pipe? (quality of casing?)
Your valuable suggestions are sought on what further action I should follow.
D. Partha Sarathi
Hyderabad
Comments
1. Borewell Casing Damage
Dear D. partha sarathi,
I am not very familiar with the problems in your area as I usually work only in the Deccan Basalts.
But as most technical problems related to bore wells are common I will try to give you a solution to the problem.
First thing, there is no guarantee that the casing pipe has been pressed at around 60ft. This is only an assumption as the person had to get a chain uplly block to pull out the motor which got stuck while being removed.
The motor may have been stuck due to various reasons-
1) one of the most common reason being that the cable joint kit slips downward and gets lodged between the pump and the bore wall or casing wall. this is usually the case when the pump is manually being lifted
2) there is possibility that something falls down while lifting the pump and this locks the pump
3) Cable gets wound around the pump due to the slack while lifting the assembly causing the pump to get stuck
All I can say that it is really difficult to accept that the casing pipe has got pressed only around 46 to 60 ft- though it is possible but settlement at that level is usually not very common.
I will advice you to try and lower a piece of pipe which has the exact diameter as that of the pump or that fits in the PVC pipe that has been installed as casing in the bore well.
This pipe should be tappred at the lower end and on the upper end too should have a lower diameter pipe supporting it.
Lower this pipe using GI pipeline to the depth of 70ft- if this goes through then there is no constriction and the pump may have been stuck due to any of the above reasons.
IF not see what diameter of pipe fits in this as it will be cheaper to buy a new smaller diameter pump that fits in through this constriction as compared to drilling a new bore or also trying to recase the existing bore well.
Recasign is to try and remove the existing casing and install a totally new casing, while doing this the existing casing tends to break and the bore well has to be cleared of the material that falls in by flushing- it turns out to be more costly than actual drilling of new bore well and there is no guarantee that ti will be successfully executed.
You get a 3 inch (V3 model from Suguna motors) which works as good as the V4 model
If the bore well does not get cleared, you can always think of drilling a new bore well, in some place where the drilling platform could be installed, it probably could be installed on your roof and then drilling done through it...worst case scenario
You coudl install the pump only down to the level it is clear and pump out the water that you get between 15ft to 46 ft...only---
I am really sorry i really cannot do more than this at this stage and with the information passed on by you.
Regards
Anil Lalwani
www.wellwaterworks.com
2. Dear D. Partha
Dear D. Partha Sarathi,
Dug-cum-bore wells are a common occurrence in Andhra Pradesh. Generally, a bore well is drilled at the bottom of dug well in situations where, the water table, over the years, recedes below the dug well depth. In such practices, if the water struck in the bore well is under confined or semi-confined condition, it rises and fills the dug well.
You may consider the feasibility of excavating a small diameter dug well to the desired depth, pull the faulty casing out and then reinstall the motor. Cement casing pipes would prevent collapse of the walls of the dug well
With regards,
Ramesh Athavale
Formerly Director Grade Scientist
National Geophysical Research Institute
Hyderabad
3. Dear Sarathi, The problem is
Dear Sarathi,
The problem is that the casing of the borewell has been damaged at around 60 ft. The option is to construct a new well and the existing well may be utilised for recharge purpose.
With regrads,
D. Chakraborty
Scientist
Central Ground Water Authority (CGWA)
New Delhi
4. Borewell Casing Damage - Rebore? - Advice Required : Hyderabad
Dear Sir,
Two renowned experts have already advised. Still I choose your specific doubts or queries and try to give some practical way out which may or may not be a correct one.
Because your queries are site specific and needs site visit and through understanding of the geohydrology.
By possible guess I try to answer.
I repeat your query here
I am looking for guidance regarding what this procedure involves. Or is removal of the casing and addition of new one needed (recasing) ? A few others advice on digging a new borewell, but in my case space restrictions are against that.
What are my options in this case?
What was the cause for the buckling of the pipe? (quality of casing?)
1. There is no need for drilling a new bore well, not because there is not much space to provide but the Geohydrological set up in your site may or may not yield sufficient yield as we find at every meter in space and depth the behaviour changes. Why to take risk and for a known success one you can spend little more also. I think the cost will be little lessor thaN drilling new bore well or going for dug well to about FORTY or 60 feet with cement steening ring.
2. Ask some efficient driller, who drills 6.5 inches diameter bore and tell him to powder down your casing pipe up to 70 feet and ask him to insert 7 inches dia heavy duty pipe. Please provide a company manufactured, slot pipe between FORTY to 60 feet or even upto 70 feet and enhance the depth of casing to 80 or 90 feet.
In the mean time advise your drilling people to clean the bore well, by the same air compressor.
3. Since you have informed that you get soft formation and water is struck at FORTY feet and below. In your old condition, over the period of recharge and discharge, the ground water flow pressure from that zone might be above resistance of the FOUR inches pvc pipe which may be four or 6 psi per square inches. Now you will get heavy duty pipes more than 8 or 12 depending up on the diameter of the pipe. Please choose pipe or purchase pipe from markets that are located in Sedimentary areas such as Vijayawada or anywhere in east or west Godavery districts. Please take care to provide company made slotted pipe. As yours is a hard rock country there may not be any need for any pebbles, which will get adjusted from the formation itself may be for some period you may get clay and water while starting thepump and after couple of weeks it will get adjusted to the slot diameter.
5. I come to your doubt for the cause for bugling of pipes.
As the formation is brittle or highly weathered, during the fake end of rainy season or during summer your pump suck out water suddenly from the depth. As the hydrostatic pressure head stands at 15 feet may be in summer at 30 feet when you put on your switch of your pump, the water level will started falling quickly during summer and slowly during the rainy season. So when the water level crosses the forty to 60 feet zone, due to natures equilibrium more and more flow from the top forty to 60 feet zone, being more permeable will ENTER into the well mouth. When you stop your motor, with high entry velocity, the ground water flow will enter that particular zone which trickle down to casing end where ever there is opening to enter into the bore. in this process over the period, the colloidal particle associated with ground water will hit and try to dent the casing pipe at depths below forty feet and over the prolonged period, the pipe will give way and bugle. Hence if you provide perforated pipe the ground water will enter directly with less resistance and your pipe will be safe. Much safer is to drill 10 inches dia bore and insert 6 inches dia pipe and pour tiny pebbles in the annular space between bore well end and pipe which has a one inches hollow annular space.
With best wishes,
A. Raja Mohamed Ambalam
Geophysicist
Chennai - bismi1234786@gmail.com ; 09443619352
A. RAJAMOHAMED AMBALAM GEOPHYSICIST COASTAL ENERGY Pvt Ltd, CHENNAI +919443619352
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