types of tube wells & its construction

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A CONCEPT ON TUBEWELL A CONCEPT ON TUBEWELL CONSTRUCTION CONSTRUCTION

By :- R.B.RoyBy :- R.B.Roy

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IntroductionIntroduction

In the state of Jharkhand more than In the state of Jharkhand more than 90% of rural population depends for 90% of rural population depends for their drinking water on different types their drinking water on different types of Tube wells situated in their vicinity; of Tube wells situated in their vicinity; therefore being a DW&SD Engineer therefore being a DW&SD Engineer you must have good knowledge about you must have good knowledge about HP. I hope all of you have seen some HP. I hope all of you have seen some types of tube well and also used it.types of tube well and also used it.

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Tube wellsTube wells

Tube well is nothing but a form of deep Tube well is nothing but a form of deep well as its name indicate a hole is drilled well as its name indicate a hole is drilled or bored into ground by driving with auger or bored into ground by driving with auger or bit by hand or by machinery and in this or bit by hand or by machinery and in this hole a tube or pipe is inserted. Pipes may hole a tube or pipe is inserted. Pipes may be blind or perforated or screen.be blind or perforated or screen.

They may be constructed in soft They may be constructed in soft unconsolidated soil or hard soil i.e. rocky unconsolidated soil or hard soil i.e. rocky formation. formation.

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It may be shallow or deep.It may be shallow or deep. It may be termed as bored well or It may be termed as bored well or drilled well.drilled well.Their size may range from Their size may range from 25mm to 900mm in diameter.25mm to 900mm in diameter.The geological condition dictate two The geological condition dictate two general type of well construction. general type of well construction. A well that taps an aquifer of A well that taps an aquifer of consolidated rock consists basically of consolidated rock consists basically of a cased portion, usually extending a cased portion, usually extending through the loose overburden material, through the loose overburden material, and an open borehole in the below.and an open borehole in the below.

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A well that taps an aquifer of water A well that taps an aquifer of water bearing sand must necessarily be bearing sand must necessarily be provided with a casing through the provided with a casing through the overburden materials and a well overburden materials and a well screen in the aquifer properly.screen in the aquifer properly.

To draw water from it a suitable To draw water from it a suitable pump is installed as per requirement pump is installed as per requirement and available discharge to suit our and available discharge to suit our demand.demand.

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These are the distinct These are the distinct operation in construction of operation in construction of

tube wells.tube wells. Site selection:-Site selection:- A tube well should be so A tube well should be so

located that it is accessible for pump repair, located that it is accessible for pump repair, cleaning, treatment, testing and inspection. The cleaning, treatment, testing and inspection. The top of the tube well should not be within the top of the tube well should not be within the basement. When adjacent to a building, the well basement. When adjacent to a building, the well should be at least 100cm outside any projection. should be at least 100cm outside any projection. It should be located on highest ground It should be located on highest ground practicable and must be on a ground higher practicable and must be on a ground higher than nearby source of pollution. The ground than nearby source of pollution. The ground surface/ platform at the tube well site should be surface/ platform at the tube well site should be built up so that the surface water will drain built up so that the surface water will drain properly.properly.

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The minimum distance from a tube well to possible source of pollution should be large enough to prevent subsurface flow or seepage of contaminated water reaching the well. Recommended minimum distance from various types of pollution sources are as below:-Cesspool receiving raw sewage :- 30mSeepage pit or drain field :- 25mSeptic tank or tightly joined sewer :- 15mThese distance are meant to be guides to good practice and may be changed as soil condition requires. They should be applied only where the soil has a filtering capacity equal to, or better than that of sand.

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Boring / DrillingBoring / Drilling

There are numerous methods of There are numerous methods of boring/ drilling tube wells and boring/ drilling tube wells and each method has advantages each method has advantages related to ease of construction, related to ease of construction, cost factors, character of cost factors, character of formations to be penetrated; well formations to be penetrated; well diameter and depth, sanitary diameter and depth, sanitary protection and intended use of the protection and intended use of the well it self.well it self.

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Some of the Boring / Drilling methods are as below:-Percussion method:- This is oldest and standard method of constructing tube well in hard rock, also known as cable tool method. In this method a hole is drilled by alternate raising & dropping a drill bit or auger stem or string tools either by manually or by power. While falling, the bit breaks the rock in to small pieces which is removed by means of a sand pump or bailer, after wetting the pulverized material by water.

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Rotary DrillingRotary Drilling

Rotary drilling process are of two types:-Rotary drilling process are of two types:- Direct Circulation Drilling:- This method is suitable Direct Circulation Drilling:- This method is suitable

for drilling small diameter deep wells in soft to for drilling small diameter deep wells in soft to medium alluvial formations. In this method a heavy medium alluvial formations. In this method a heavy walled drill pipe which extends to the surface to the walled drill pipe which extends to the surface to the bit rotated by mechanical means and as the bit is bit rotated by mechanical means and as the bit is turned drilling fluid usually bentonite mixed with turned drilling fluid usually bentonite mixed with water or suitable material is circulated under water or suitable material is circulated under pressure which lubricates and cool the bit, carries pressure which lubricates and cool the bit, carries the cutting in suspension to the surface and plaster the cutting in suspension to the surface and plaster the wall of the hole to prevent caving in.the wall of the hole to prevent caving in.

Reverse Circulation Drilling:-The reverse circulation Reverse Circulation Drilling:-The reverse circulation method is same as above except water is pumped up method is same as above except water is pumped up through the drilling pipe rather than down through it.through the drilling pipe rather than down through it.

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Down-the-Hole (DTH) Hammer Down-the-Hole (DTH) Hammer DrillingDrilling

This method is used for fast and economical This method is used for fast and economical drilling of bore up to 200mm in medium to drilling of bore up to 200mm in medium to hard rock formations. In this method down the hard rock formations. In this method down the hole pneumatic hammer is used at the lower hole pneumatic hammer is used at the lower end of the drill piped and combining the end of the drill piped and combining the percussion and rotary actions. This method percussion and rotary actions. This method utilizes compressed air for the rapid impacting utilizes compressed air for the rapid impacting action given by the hammer to the bit; thus action given by the hammer to the bit; thus crushing the formation in to small chips which crushing the formation in to small chips which are flushed out through the annular space are flushed out through the annular space between the bore & drill pipes by the up between the bore & drill pipes by the up coming air pressure. This is most commonly coming air pressure. This is most commonly used method in the state.used method in the state.

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Water Jet BoringWater Jet Boring

A water jet is used for boring the well which A water jet is used for boring the well which implies that a drilling bit with nozzels is implies that a drilling bit with nozzels is attached to the drill pipes at the bottom attached to the drill pipes at the bottom through which water is pumped at high through which water is pumped at high pressure. The water on its return flows pressure. The water on its return flows through the annular space between the bore through the annular space between the bore and the drill pipe and brings the cutting along and the drill pipe and brings the cutting along with it to the surface. Casing pipe is with it to the surface. Casing pipe is simultaneously used to avoid caving in. This simultaneously used to avoid caving in. This method is useful in sandy formation. method is useful in sandy formation.

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OTHER METHOD OF DRILLINGOTHER METHOD OF DRILLING

Drilling by combination rigDrilling by combination rig Auger DrillingAuger Drilling Hand boring by Dheki processHand boring by Dheki process Hand drilling using force & lift pump Hand drilling using force & lift pump

combined with reverse circulationcombined with reverse circulation Core drillingCore drilling

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Installing/ inserting casing Installing/ inserting casing and / or Housing and/ or screen and / or Housing and/ or screen

pipespipes General:- Well casing is used to prevent caving General:- Well casing is used to prevent caving

in of surrounding soil in to the well or bore hole. in of surrounding soil in to the well or bore hole. The upper portion of the casing used for The upper portion of the casing used for housing the pumping equipment, is called housing the pumping equipment, is called housing pipe. The casing may be temporary housing pipe. The casing may be temporary and is removed on completion of the well (drive and is removed on completion of the well (drive pipe) or it may be a permanent part of the pipe) or it may be a permanent part of the structure. The length and diameter of the structure. The length and diameter of the casing pipe is selected on the basis of static casing pipe is selected on the basis of static water level, drawdown, discharge expected water level, drawdown, discharge expected from the pump and the size of the pump to be from the pump and the size of the pump to be installed.installed.

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Casing PipeCasing Pipe Casing pipes may be of MS tubes with plain end or Casing pipes may be of MS tubes with plain end or

screwed (confirming to IS 4270 : 1992) where tubes screwed (confirming to IS 4270 : 1992) where tubes are required to be galvanized the zinc coating on are required to be galvanized the zinc coating on the tubes shall be in accordance with IS 4736 : the tubes shall be in accordance with IS 4736 : 1986/ 1239 : 1990(for GI), or UPVC tubes 1986/ 1239 : 1990(for GI), or UPVC tubes (confirming to IS 12818 : 1992). (confirming to IS 12818 : 1992).

MS black tubes shall be externally coated with a MS black tubes shall be externally coated with a bituminous solution or any other protective bituminous solution or any other protective anticorrosive coating as per standard specification. anticorrosive coating as per standard specification. All the pipes should be marked with following All the pipes should be marked with following details:- details:-

Nominal size, length of tube, manufacturers trade Nominal size, length of tube, manufacturers trade mark, inspecting agency inspection mark with other mark, inspecting agency inspection mark with other marks as per direction of supply order.marks as per direction of supply order.

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All the UPVC casing pipe shall be marked All the UPVC casing pipe shall be marked with CM or CS (to denote medium well with CM or CS (to denote medium well casing & shallow well casing pipe), casing & shallow well casing pipe), nominal diameter in mm, inspecting nominal diameter in mm, inspecting agency inspection mark with other agency inspection mark with other marks as per direction of supply order.marks as per direction of supply order.

Diameter and wall thickness is selected Diameter and wall thickness is selected as per requirement.as per requirement.

Screen pipes:- MS, UPVC, Brass, Fiber Screen pipes:- MS, UPVC, Brass, Fiber glass copper wire, galvanized steel wire glass copper wire, galvanized steel wire and stainless steel various types of and stainless steel various types of screen pipes are available in the market screen pipes are available in the market to suit our specific requirement to suit to suit our specific requirement to suit the strata condition.the strata condition.

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Present Scenario in our Present Scenario in our departmentdepartment

In our department normally two types of tube wells In our department normally two types of tube wells are constructed as spot water source now a days are constructed as spot water source now a days known as Drilled tube well in rocky area & Gravel known as Drilled tube well in rocky area & Gravel packed tube well in alluvial soil area. However in packed tube well in alluvial soil area. However in some area old TARA Pump may also be found with some area old TARA Pump may also be found with Ordinary Shallow HP & Special HP tube well.Ordinary Shallow HP & Special HP tube well.

Drilled Tube well:- It is drilled with DTH mounted rig Drilled Tube well:- It is drilled with DTH mounted rig machine and we use UPVC casing pipe of CM class machine and we use UPVC casing pipe of CM class having nominal bore diameter 125mm confirming having nominal bore diameter 125mm confirming to IS 12818 : 1992 (latest revision). Its average to IS 12818 : 1992 (latest revision). Its average depth is 50 to 55m and average casing depth is 50 to 55m and average casing consumption is 12 to 15m. Some times GI casing of consumption is 12 to 15m. Some times GI casing of 125mm nominal bore diameter is also in use, where 125mm nominal bore diameter is also in use, where insertion of casing is required hammering. insertion of casing is required hammering.

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DRILLING OPERATIONDRILLING OPERATION The drilling operation for construction of bores for The drilling operation for construction of bores for

tube wells should be carried out by the DTH tube wells should be carried out by the DTH Mounted Rig Machine as mentioned below -Mounted Rig Machine as mentioned below -

The boring in the over burden should be continued The boring in the over burden should be continued through the rock at least up to 25 cm, so that casing through the rock at least up to 25 cm, so that casing pipes can be properly embedded in the rock.pipes can be properly embedded in the rock.

Boring through rocks shall be 115mm diameter and Boring through rocks shall be 115mm diameter and total depth from the ground level of the bore shall total depth from the ground level of the bore shall be average 55/50 meter on completion of drilling. be average 55/50 meter on completion of drilling. The bore shall be flushed till it gives sufficient clear The bore shall be flushed till it gives sufficient clear water. The yield should not be less than 1000 liters water. The yield should not be less than 1000 liters per hour for acceptance as successful bore.per hour for acceptance as successful bore.

The diameter of the bores in the over burden shall The diameter of the bores in the over burden shall be sufficient for insertion of 125 mm dia casing be sufficient for insertion of 125 mm dia casing pipes with sockets leaving sufficient annular space pipes with sockets leaving sufficient annular space for grouting the casing pipesfor grouting the casing pipes..

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If even after a depth of 60 mtr from the If even after a depth of 60 mtr from the ground level bore remains dry or if the yield is ground level bore remains dry or if the yield is found to be less than 1000 liters per hour, the found to be less than 1000 liters per hour, the bore will be declared unsuccessful, bore will be declared unsuccessful, but if it is but if it is detected that after increasing the depth detected that after increasing the depth beyond 60m the bore became success beyond 60m the bore became success extra depth may be allowed subject to extra depth may be allowed subject to condition that bore must be made condition that bore must be made success and extra depth does not cause success and extra depth does not cause increase in average sanctioned increase in average sanctioned estimated depth beyond limit.estimated depth beyond limit.

If the boring in the over burden is done up to If the boring in the over burden is done up to the depth of 30 meters and further boring is the depth of 30 meters and further boring is not possible due to adverse and unsuitable not possible due to adverse and unsuitable geological condition the bore shall be geological condition the bore shall be declared unsuccessful.declared unsuccessful.

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After completion of the boring the After completion of the boring the bore should be developed & washed bore should be developed & washed by means of air compressor for a by means of air compressor for a minimum period of 30 minutes to minimum period of 30 minutes to give clean potable water.give clean potable water.

The contractor should maintain strata The contractor should maintain strata chart in the prescribed format for chart in the prescribed format for each tube wells, and submit “Strata each tube wells, and submit “Strata Chart” at the time of preparation of Chart” at the time of preparation of bill to the Engineer-in-charge; bill to the Engineer-in-charge; otherwise payment will not be made.otherwise payment will not be made.

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LOWERING OF CASING PIPELOWERING OF CASING PIPE Casing pipes should be properly Casing pipes should be properly socketedsocketed or or

welded to ensure continuous length (leak welded to ensure continuous length (leak proof joint) and lower through the over burden proof joint) and lower through the over burden to reach at least 25 cm in side the rock. The to reach at least 25 cm in side the rock. The length of casing pipe should be such that at length of casing pipe should be such that at least 30cm should remain projected above the least 30cm should remain projected above the ground level after completion of drilling work ground level after completion of drilling work at site. The top of the casing pipe shall have at site. The top of the casing pipe shall have to be capped by 125 mm dia GI cap till the to be capped by 125 mm dia GI cap till the hand pump is installed over the bore.hand pump is installed over the bore.

The casing shall have to be lowered in such a The casing shall have to be lowered in such a manner that it remains vertical so as to manner that it remains vertical so as to ensure installation of deep well hand pump ensure installation of deep well hand pump and accessories properly and without and accessories properly and without difficulty.difficulty.

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GROUTINGGROUTING

After fixing or lowering the casing After fixing or lowering the casing pipe in proper position the grouting pipe in proper position the grouting around the casing pipe is done with around the casing pipe is done with Cement & Bentonite solution for Cement & Bentonite solution for sanitary sealing of bore well. If it is sanitary sealing of bore well. If it is not done then the bore may be not done then the bore may be polluted through seepage from any polluted through seepage from any nearby pollution source if any.nearby pollution source if any.

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GPTGPT Gravel Packed Tube Well:- It is either Gravel Packed Tube Well:- It is either

constructed with Reverse Circulatory constructed with Reverse Circulatory Rig Machine or Manually or by Rig Machine or Manually or by Combination Rig Machine suitable for Combination Rig Machine suitable for drilling in Rocky formation as well as drilling in Rocky formation as well as alluvial formation and 125mm UPVC CM alluvial formation and 125mm UPVC CM class casing pipe and screen pipes is class casing pipe and screen pipes is used. Its average depth is 38m except used. Its average depth is 38m except in some area of Ranchi, Gumla & in some area of Ranchi, Gumla & Lohardagga district, where depth goes Lohardagga district, where depth goes up to 60m.up to 60m.

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GPTGPT

Normally GPT is constructed in Alluvial formation Normally GPT is constructed in Alluvial formation where water yielding capacity of aquifer is less. where water yielding capacity of aquifer is less.

Boring Operation :- Boring Operation :- The boring operation for The boring operation for construction of gravel packed T/W should be construction of gravel packed T/W should be carried out by means of Reverse Rotary Rig carried out by means of Reverse Rotary Rig Machine or Water Jet Plant satisfying the Machine or Water Jet Plant satisfying the following conditions: following conditions:

The diameter of the bore shall be minimum The diameter of the bore shall be minimum 250mm.250mm.

The bore shall be vertical.The bore shall be vertical. The soil sample shall be collected and observed The soil sample shall be collected and observed

carefully at regular intervals of each 3 meters carefully at regular intervals of each 3 meters and whenever any change in strata is and whenever any change in strata is encountered, the sample should be collected and encountered, the sample should be collected and its corresponding depth from the ground level its corresponding depth from the ground level shall be noted.shall be noted.

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GPT contGPT cont.. Once the water yielding strata is Once the water yielding strata is

encountered the sample should be encountered the sample should be carefully observed and its depth carefully observed and its depth from G.L. shall be recorded from G.L. shall be recorded carefully and after boring in water carefully and after boring in water bearing formation up to a depth of bearing formation up to a depth of 7/10 meter the boring process 7/10 meter the boring process shall be stopped.shall be stopped.

Bentonite solution should be used Bentonite solution should be used if necessary to avoid caving.if necessary to avoid caving.

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Lowering Of Casing Pipes Lowering Of Casing Pipes And Screen PipeAnd Screen Pipe

After completion of boring the lowering chart should be After completion of boring the lowering chart should be designed according to strata condition encountered. designed according to strata condition encountered. Lowering chart should be designed in such a way that Lowering chart should be designed in such a way that the ribbed screen pipe must be placed in the water the ribbed screen pipe must be placed in the water bearing formation. The ribbed screen pipe should be bearing formation. The ribbed screen pipe should be placed in the bottommost portion of casing pipes or 1 placed in the bottommost portion of casing pipes or 1 to 3 m above blank pipe for settling of sand) with its to 3 m above blank pipe for settling of sand) with its open end suitably plugged with well plug. Five center open end suitably plugged with well plug. Five center guides is also placed at regular intervals spanning the guides is also placed at regular intervals spanning the whole length of the pipe and ribbed screen pipe with whole length of the pipe and ribbed screen pipe with one guide each at the top and the bottommost ends of one guide each at the top and the bottommost ends of the pipes, ensuring that the pipe is placed at the center the pipes, ensuring that the pipe is placed at the center of the bore.of the bore.

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Lowering Of Casing Pipes And Lowering Of Casing Pipes And Screen Pipe cont.Screen Pipe cont.

The annular space of bore must be filled The annular space of bore must be filled immediately with approved quality ‘Pea’ immediately with approved quality ‘Pea’ gravel (3 to 6mm) up to 10 M below ground gravel (3 to 6mm) up to 10 M below ground level after lowering of the pipe assembly and level after lowering of the pipe assembly and from G.L. up to 10 m Below ground level by from G.L. up to 10 m Below ground level by sticky clay to prevent contamination from sticky clay to prevent contamination from surface.surface.

. To disinfect the bore a little bleaching . To disinfect the bore a little bleaching powder should be mixed with “P” gravel. After powder should be mixed with “P” gravel. After surrounding the bore with gravel developing surrounding the bore with gravel developing should be started with the help of water jet should be started with the help of water jet and air compressor till clear water discharge and air compressor till clear water discharge takes place in adequate quantity.takes place in adequate quantity.

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Development Of BoreDevelopment Of Bore After of completion of boring, lowering of pipes, After of completion of boring, lowering of pipes,

ribbed screen pipe and surrounding the tube ribbed screen pipe and surrounding the tube well with ‘Pea’ gravel the bore should be well with ‘Pea’ gravel the bore should be developed and washed by means of air developed and washed by means of air compressor or water jet or combination of both compressor or water jet or combination of both to give sand/ silt free clear adequate drinking to give sand/ silt free clear adequate drinking water. The discharge of bore should not be less water. The discharge of bore should not be less than 1000 liter per hour. than 1000 liter per hour.

If water is not found clean and discharge is If water is not found clean and discharge is found less than 1000 liter, the bore shall be found less than 1000 liter, the bore shall be declared un successful. declared un successful. The plain & screen The plain & screen pipes are used of UPVC of 125mm nominal pipes are used of UPVC of 125mm nominal diameter.diameter.

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Testing for maximum yieldTesting for maximum yield After completion of boring and After completion of boring and

developing the bore shall be tested developing the bore shall be tested for the maximum yield and drawdown for the maximum yield and drawdown with the help of 90with the help of 9000 free flowing “V” free flowing “V” notch method and such record should notch method and such record should

be kept for office recordbe kept for office record..

8

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Installation of suitable Installation of suitable pump.pump.

At present IM II Deep well Hand Pumps At present IM II Deep well Hand Pumps are used in the department for both are used in the department for both types of Tube wells i.e. DT & GPT. types of Tube wells i.e. DT & GPT. However so many However so many types of Pumps types of Pumps are are available in market.available in market.

The The Deep well IMII HP Deep well IMII HP must be must be confirming to IS : 9301 - 1984 confirming to IS : 9301 - 1984 specification latest amendment.specification latest amendment.

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Pump InstallationPump Installation

types of tube wells & its construction

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