What is well sinking operation?
Well sinking operation involves lowering of well by dredging in the dredge hole with the help of plate grab in the case of soft strata like sandy silt, soft clay, sandy clay, dense sand etc. Levels and alignment of well shall be checked periodically at every 0.5m of sinking.
What happens when a well sinks suddenly?
This sudden well sinking is very dangerous, and the well may crack and which is very difficult to repair. If sand blowing is on one side of the well, tilt will take place.
What are the difficult situations in sinking of well foundations?
• A list of difficult situations, which engineers normally encounter during sinking of well foundations, is presented. • The problems like the formation of hump inside the dredge hole or wells cracking due to sand blow, or in a stiff clay layer wells becoming stationary and not sinking down are quite common situations.
How do you sink a well by hand?
A sinking method is a specific way of sinking a well. Wells may be dug by hand, drilled with hand tools, or drilled with motorized equipment. Hand-dug wells are sunk by digging a hole as deep as is necessary to reach water. is code for well sinking?
What do you mean by sinking of wells?
Well sinking consisted of five stages: (1) digging through the soil horizon, (2) breaking through the highly weathered zone, (3) blasting through the consolidated rock, (4) constructing the well curb and pump platform, and (5) placing the pump.
What is well Steining?
Well Steining: Steining is a wall or shall type of structure made up of RCC, and which helps to transfer the load to the curb. It serves as an enclosure for excavating the soil for the penetration of the foundation well.
How do you check the tilt and shift of a well foundation?
The maximum tilt allowed in case of well foundation is 1 in 60. The shift in well foundation should not be more than 1 % of depth of sunk. Beyond the above limits, well foundation is considered as dangerous and in such a case, remedial measures to rectify shifting and tilting should be followed.
What is well curb?
1A frame or masonry border round the mouth of a well. 2A circular frame on which the lining of a well is built (now rare).
Why sand is filled in well foundation?
Sand Filling – Sand filling provide stability of well, reduce tensile stress produced by bending moment and distributes the load of super structure on to the bottom plug. Sand filling relieves load to steining to some extent.
How is well foundation sunk?
Well sinking operation involves lowering of well by dredging in the dredge hole with the help of plate grab in the case of soft strata like sandy silt, soft clay, sandy clay, dense sand etc. Levels and alignment of well shall be checked periodically at every 0.5m of sinking.
What is tilting and shifting of wells?
Sinking of wells usually encounters difficulties in the form of tilting and shifting of wells. Tilting is the deviation of the vertical alignment of the well and shifting is the deviation from the horizontal alignment. Tilting and shifting are associative; shifting occurs if tilting is large and uncontrolled.
What are the causes of tilts and shifts?
Shifting & tilting occur generally during the sinking phose of well foundations. If proper care is not taken they can cause problems which may lead to the weakening of the stability of foundations. 1) The outer surface of the well curb and steining should be regular & smooth.
What are the precaution to be cared for during sinking of well?
The following precautions should be taken during well sinking. Outer surface should be regular and smooth. Radius of the curb should be 2 to 4 cm larger than the radius of the steining. Cutting edge should be of uniform thickness and sharpness.
Is well foundation a deep foundation?
Well foundation is a type of deep foundation which is generally provided below the water level for bridges.
Why well foundation is used?
Well Foundation is used to provide greater stability to a structure in the circumstances where the velocity of water is high and the depth of water is higher than 5 to 6 m and where no other type of foundation can be used.
What are the types of well foundation?
Shapes of Well Foundations:Circular.Twin circular.Square/Rectangular.Double D.Hexagonal/Octagonal.
What is the aim of a well sinking?
The verticality should be maintained. The aim of the well sinking is to sink the well vertically and at the correct position. The following precautions are to be taken as far as possible.
Where to jett a well?
Jett on the high side of well. Excavate under cutting edge by dewatering or by divers.
How deep can a well be excavated?
Allow the well to remain vertical. Up to a depth of 1 m , excavation underwater can be made manually. When the depth of water exceeds 1 m excavate by Jhams or grabs. When well goes on sinking skin friction increases and weight of well decreased due to buoyancy.
What is well sinking operation?
Well sinking operation involves lowering of well by dredging in the dredge hole with the help of plate grab in the case of soft strata like sandy silt, soft clay, sandy clay, dense sand etc. Periodic monitoring of Tilt and Shift in Well Foundation is necessary.
How is well sinking done?
Well sinking is done in two different ways open sinking and pneumatic sinking. When open sinking does not help much due to hard strata pneumatic well sinking may be adopted. Well sinking operation involves lowering of well by dredging in the dredge hole with the help of plate grab in the case of soft strata like sandy silt, soft clay, sandy clay, dense sand etc. Levels and alignment of well shall be checked periodically at every 0.5m of sinking. Well Sinking operation shall preferably be non-stop under skilled supervision.
What is dredging done uniformly over?
The dredging shall be done uniformly over the dredge hole area.
Why is a controlled sump maintained below the well curb?
The controlled sump shall be maintained below the well curb to avoid sudden and excessive sinking of well.
What happens when sand gushes inside a dredge hole?
The sand from outside gushes inside dredge hole, and there is the sudden sinking of well.
How far should abutment wells be excavated?
For abutment wells having a high bank on one side of the well, sufficiently large-sized pit shall be excavated leaving about 6.0m-8.0m clear distance around the well.
What is acute when such situation happens when the well has reached its design depth?
Problem is acute when such situation happens when the well has reached its design depth since the bottom plug cannot be done without some sump.
What are the problems engineers usually encounter during sinking of well foundations?
19. CONCLUSION. • A list of difficult situations, which engineers normally encounter during sinking of well foundations, is presented. • The problems like the formation of hump inside the dredge hole or wells cracking due to sand blow, or in a stiff clay layer wells becoming stationary and not sinking down are quite common situations. • In several cases, how these problems were overcome and what were the solutions adopted are explained. • Thus, it was observed that, atmost care should be taken while analysing and designing well foundation with the help of appropriate data and adoption of correct detailing.
When two wells sunk near each other, should they be sunk alternately?
8. Precautions. • When two wells sunk near each other, they should be sunk alternately. • Least possible area must be disturbed in vicinity. • In sinking of dumb bell shaped well, excavation must be done simultaneously. • Dredged material must not be accumulated near well. • In sinking of two wells through sand, timber logs are provided between steining. • Care must be taken when cutting edge approaches junction of strata.
What are the measures for ease of sinking?
18. General Measures for Ease of Sinking. Appropriate choice of cutting edge and adoption of proper detailing. • The "Angle iron" cutting edge works well when the well passes through alluvial soil strata without any hard obstruction. • A "V type" cutting edge is more appropriate in meeting various obstructive situation provided correct detailing is adopted . • The inclined plate should be stopped about 25 mm above the bottom tip of vertical plate. Adequate no. of Borelogs must be taken in the location of each well. • Presence of very large boulder covering a part of the well at some depth in the bridge over Brahmaputra at Jogighopa. • Similar type of problems including sudden change of bed profile are encountered in various rivers in India.
Where did well foundations originate?
3. HISTORY • They had their origin in India. • It have been used for 100 of years as a deep foundation for important buildings and structures. • Well foundations are used since Mughal period (TAJ MAHAL is the best example). • They were used for the first time for irrigation structures at Ganga canal at Roorkee. (middle of 19th century) • In towers of Howrah bridge, wells of size 24.8x53.5m were used and sinking depth was 31.4m below gnd level. (largest in India) • Many other such examples are Rajendra Pul,Mahanadi bridge etc. • In spite of excellent development of technology on well foundations there are still some areas where engineers face difficulty while sinking of wells.
What are the benefits of a well foundation?
4. Benefits of Well Foundation • Provides massive and solid foundation. • Possible to sink well through boulders,logs of wood found at depth. • Large section modulous with minimum cross sectional area is advantageous. • The strata through which well passes is known exactly. • Well raising and steining is done in steps so foundation level can be varied. • Economical to provide it for unstable soil mass .
What is the leading edge of a well?
The lowermost portion of the well curb is leading edge.
How deep should a well be?
Allow the well to stay vertical up to a depth of 1 meter, the excavation might be manually below water.
What are the different types of well foundations?
Types of well foundation: Open caisson or well: The top and bottom of the caisson are open throughout construction, it can have any shape in its plan. Box Caisson: It is open on the top, however, close on the bottom. Pneumatic caisson: It consists of a working chamber at the bottom of the caisson, which is kept dry underwater under pressure thus ...
What are the advantages of a well foundation?
Advantages of Well foundation: 1 Larger diameters might be extended to larger depths. 2 Similar to piles they are shorter. 3 If the soil (rock) with a large bearing capability is between 3-7 meters, it may be very effective. 4 If the load is not very large, however, the upper 3-7 m soil is not suitable and it may be applied effectively. 5 The price of construction is comparatively low on the bed level or lower side.
Why is water pressure acted upon the parts of the sub-structure situated between the water level and the maximum sco?
The water pressure because of the flow of water is acted upon the parts of the sub-structure situated between the water level and the maximum scouring level.
Is concrete finished below seawater?
Since the concrete provided is finished below concrete under seawater, this may not be satisfactory. If a block of boulder or log is encountered, the progress of the work is slowed. Cleaning and inspection on the ground of the caisson may be very tough, sometimes not possible.
