pile vs well

8/9/2019 Pile vs Well

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Comparison On Actual Case Study-Pile Foundation v/s Well foundation

OBJECTIVE:

Comparative study of pile foundation and well foundation, in terms ofcost & time by collecting data from the field to help in decision makingregarding appropriate type of deep foundation for bridges. The bridges withpile foundation and well foundation under construction in NW Railway withsame loading standard, span arrangement and depth of foundation havebeen selected for the study.

1. GENERAL

In fairly good soils having sufficient bearing capacities, such as dense sand,hard moorum, soft and hard rocks, it is normally possible to construct bridgefoundations as open foundations and this does not create any problemsexcept the protections works in case the piers are founded in the river bed.

However, at sites where suitable soil strata for constructing the open

foundations are not available, it becomes necessary to go in for pilefoundations or well foundations.

Well foundations had their origin in India and have been used for providingdeep foundations for buildings and bridges. The technique of sinkingmasonry well for water is very old and even today small water wells areconstructed using the same methods as were prevalent centuries ago. Dueto availability of the expertise and skill for the sinking and construction ofwells the well type foundation has been more popular in India. Wellcontinues to be most important type of foundation for bridges in all type ofstrata, particularly in scourable river beds.

Use of pile foundation till recently has not been a popular choice for bridgesin India. In the bridges constructed recently, particularly on the Railways,one can find large number of cast iron/steel screw piles, been driven in toground and even extended above bed level up to the girder bearing level.With the increased loading and horizontal forces caused by newerlocomotives, these are being replaced by well foundation and cast-in-situR.C.C. bored piles. Pile foundation can be used quite economically,particularly, where foundations have to be built very deep or taken throughdeep layers of soil subjected to a minimum of scour.


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2. Well Foundation

Well foundations are commonly used for transferring heavy loads to deepstrata in river or sea bed for bridges, transmission towers and harbour

structures. The situation where well foundation are resorted are as below-

a) Wherever consideration of scour or bearing capacity requirefoundation to be taken to a depth of more than 5 M below groundlevel open foundation becomes uneconomical. Heavy excavation anddewatering problem coupled with effort involve in retaining the soilmakes the open foundation costlier in comparison to other type offoundation.

b) Soil becomes loose due to excavation around the open foundationand hence susceptible to scouring. This is avoided in well foundation

which is sunk by dredging inside of the well.

c) From bearing pressure considerations, a well foundation can alwaysbe left hollow thereby considerably reducing bearing pressuretransmitted to the foundation material. This is very important in soilsof poor bearing capacity, particularly in clayey soils. In other type offoundation, the soil displaced is occupied by solid masonry/concretewhich are heavier than the soil displaced and hence this does notgive any relief in respect of adjusting bearing capacity. However incase of well foundation this is easily achieved because of cellularspace left inside the well.

3. Pile Foundation

Depending upon the type of soil, foundation piles are used in following ways:

a. Bearing pilesb. Friction pilesc. Friction cum bearing piles

The bearing piles are designed as those which transmit the load tofoundation strata directly without taking in to account the frictional resistanceoffered by enclosing soil. The passive earth pressure resistance is taken into account only for the purpose of determining its resistance against thehorizontal force. Such bearing piles are generally taken up to or in to thehard strata, such as mooram, soft or hard rock, hard consolidated sandy orgravelly soil.

Friction piles are those in which the load is transmitted by the pile throughfriction offered by surrounding soil. Such piles can be provided in cohesivesoils not subjected to heavy scour. Friction cum bearing piles designed in

such a way that the load is transmitted both by friction of the surroundingsoil and the bearing resistance of the founding soil at the tip of pile.


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4. Pile Classification By Construction Method

a. Precast Driven Piles These are usually of RCC or pre-stressed

concrete and generally small in size for ease in handling. The mainadvantage of this type of pile is that its quality, in terms of dimension,use of reinforcement and concrete, can be ensured as the piles arecast in a yard under controlled conditions. However care is neededwhile handling, transporting and driving the pile to avoid damages.

More to it, the limitation of length depending upon the capacity of thedriving equipment is a disadvantage as these cannot be taken verydeep except by joining. Generally, the depth over which these areused is restricted to 36 mt.

b. Driven Cast-in-Situ Piles- A steel casing pile with a shoe at thebottom is driven first to the required depth. The reinforcement cagefor the pile is then lowered inside the casing and the pile is concreted.As the concreting of the pile proceeds upwards, the casing iswithdrawn keeping a suitable overlapping length. When such pilesare driven in soft soil and the tube is withdrawn while concreting, itaffects resistance and changes the property of the soil and this alsoaffects the capacity of individual piles. These are not suitable for usein soft soils, in greater depths or where keying with the rock isrequired.

c. Bored cast-in-situ piles In the bored cast-in-situ process, a largerdiameter casing is used. A casing of 3 to 4 m in length is provided ontop of the bore hole which is driven with the help of a bailor. Boringfurther below this casing is carried out by chiselling and the side wallsare kept stable by circulating bentonite slurry inside the bore hole.The boring is continued up to the layer decided for founding thestructure. After reaching the desired founding level, the chisel isremoved, bore-hole flushed, reinforcement cage lowered into thehole, and held in position by tack welding it to the support bars at thetop of the cas ing.

After this, concreting is carried out by using tremie, keeping its endalways below the top level of rising concrete. The concreting iscontinued till a good quality concrete is seen at the top of the borehole. After this, the tremie is removed and when the concrete hasreached the top, the casing pipe on the top is also removed. Thebentonite mix should be periodically checked for its specific gravityand changed as, due to constant use, it can get mixed with the soiland deteriorate in quality. This type of pile can be used even wherethe pile is keyed into the rock as chiselling in the rock can be carriedout more easily. These piles serve as bearing-cum-friction piles. The

diameters of such piles are generally more than 1.0m and can go upto 3.6m or more. They can be used singly or in group and are good


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replacements for well foundations required for bridge piers in riverswith clayey and mixed soils.

d. Bored pre-cast piles In this, as the name itself suggests, a hole is

bored using a casing and a pre-cast pile is inserted into it. Aftersecuring it in position, the casing is withdrawn. A particular processused for bored pre-cast piles is the Benoto process which involves asteel tube being pushed into the soil, turned and reversed usingcompressed air. The tube is in the form of a casing and is driven forthe entire depth after the soil is progressively grabbed from the tube.The process is continued till the tube reaches the pre-determinedlevel. Then the pre-cast pile is lowered inside and held in position.The tube is lifted gradually after filling the annular gap between thepre-cast pile and the soil by grouting.

e. Driven steel piles Steel piles can be circular or in other structuralshapes. The circular ones are made in the form of either welded orseamless piles. Usually steel or cast iron piles used earlier for bridgestructures are of longer diameter and screw type. These were used inpast when loading was less. These piles are suitable for being driventhrough cohesive soil to reach up to the hard strata and to serve asbearing piles. They are not suitable where heavy scour is expectedand for foundation for bridges when foundations are situated wideapart.

f. Driven timer piles Timber piles have been extensively used inAmerica. These have been used in India on the railways andhighways, for temporary bridges. Timber piles are of hard wood, andused in natural form with thin end cut or suitably sized. They are usedmostly as end-bearing piles in clusters. They are normally used inlengths of 12m and extended by splicing for use in deeper channels.The piles protruding above bed/low water level are suitably braced incluster.

5. Pile Foundation V/S Well Foundation

a. Well foundations provide a solid and massive foundation for heavyloads as against a cluster of piles which are slender and weakindividually and are liable to get damaged when hit by floating treesor boulder rolling in river bed.

b. Wells provide a large section modulus with the minimum crosssectional area and hence efficient in taking large vertical andhorizontal loads even when the unsupported length is large.

c. Concreting of well steining is done under dry and controlled

conditions and hence quality of work is assured, however samecannot hold good in case of cast-in-situ bored piles where concreting


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is to be done under water or below ground level. Even in case ofprecast piles, the concrete is subjected of heavy stresses duringdriving operation and consequent damages cannot be ruled out.

d. When scour takes place, the piles act as long struts and have to bedesigned for buckling stresses, which are quite heavy due to thebending moments contributed by the longitudinal forces on the bridgedeck due to tractive effort and braking forces.

e. It is difficult to drive the piles through the strata having boulders andtree logs which are frequently encountered in alluvial soil, whereas inthe case of a well foundation there is sufficiently access to removethe obstruction. Quite often the skin friction developed is of muchmagnitude as to prevent further driving of a pile although a firm

stratum has not been reached.

f. The adoption of pile foundations is advantageous over wellfoundations where the soil characteristics and conditions of watertable are such that the phenomenon of blow occurs duringdewatering of the well.

g. Increased mechanization and advent of new machinery have broughtdown the cost of foundation with piles considerably low in comparisonto well. New testing techniques for checking the integrity of piles andinformation about strata through piles have passed or resting have

removed the uncertainty of load carrying capacity of piles to largeextent.

h. Pile foundations have a clear advantage over well foundations interms of speedy construction. Wherever time is the criterion, the pilefoundation is the natural choice.

6. Pile Foundation on N. W. Railway

a. The use of large diameter bored piles for Railway bridges is a recentdevelopment. These piles were first extensively used on Apta-Rohaand Pen-Thal B.G. Railway projects. Foundation with cast-in-situR.C.C. bored piles were adopted for most of the bridges in KonkanRailway Project. This type of foundation was found suitable and usedfor bridging even for perennial rivers and creeks on this alignmentbarring foundations for few navigational spans. Speedy constructionand commissioning of the Konkan Railway project could be possibledue adoption of pile as first choice for foundations.

b. In North Western Railway cast-in-situ bored piles have been adoptedas foundation for most of the bridges in projects which are in

progress. As the soil is predominantly sandy, mixed gravel and hardclayey strata and rivers being seasonal in nature foundation of most


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of the bridges constructed earlier have been open foundation or wellfoundation. In gauge conversion projects foundations of most of thebridges have been retained by doing the strengthening by jacketing offoundations and piers as the governing criterion has been cost

consideration and overall economy. However in all the new projectsof doubling and new lines most of the foundations are either openfoundation or pile foundation. Details of the doubling and new lineprojects and foundation adopted are summarized below-

Sr.No.

ProjectNo. of

Major/ Imp.Bridges

Br. on PileFoundation

Br. onOpen

Foundation

Br. on WellFoundation

1Alwar-Harsauli

Doubling1 1 Nil Nil

2Bandikui-Dausa

Doubling3 1 2 Nil

3Dausa-Jaipur

Doubling7 6 Nil 1

4Jaipur-Phulera

Doubling2 1 1 Nil

5Dausa-

Gangapur NewLine

12 12 Nil Nil

Details of bridges and foundation adopted is enclosed as Annexure-B

From the above details, it can be clearly observed that except one bridgethe foundations of rest of the bridges are either on pile or open. Asexplained earlier, there are very few perennial rivers in NW railway and mostof the drainage system is seasonal in nature. Heavy discharge to the tune ofhigh flood level occurs occasionally after the interval of many years and thattoo is confined to few days period. Discharge pattern is different for riversflowing in North and Central India where heavy floods for a long duration is aregular feature.

7. Case Study- Pile v/s Well Foundation

Dausa-Gangapur City new line projects the Delhi-Jaipur main line to Delhi-Mumbai route. The alignment passes through mainly flat terrain andencounters the hilly terrain of Aravalli range near Lalsot. Strata is mainlysilty/clayey sand. The rock is lying at a varying depth from 30 to 35 mt.

Dausa-Gangapur City alignment is located in same geographical area asthat of Dausa-Jaipur doubling project and hence sub-soil strata of both theprojects are similar. The depth of water table is about 12-15 mt. in both thecases.


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A. Dausa-Gangapur City New Line

i. (a) Route Kilometre 92.76 KM (Single Line)(b) Standard of Loading MBG with 25 T axle load(c) Block station 08 No

(d) Flag station 05(e) Length of Tunnel 2120 M(f) Important Bridge Nil(g) Major Bridge 12(h) Minor Bridges 77

ii. Bridge span in this project has been standardised to 18.3 M and allthe 12 Major Bridges have been designed with the same span. Superstructures consist of 2 no. PSC girder for the MBG 25 T axle load withRCC deck slabs. Adoption of one span (i.e. 18.3 M) has led to easein construction and development of expertise due to repetitive nature

of job. Similarly 1200 mm dia. cast in situ RCC bored pile has beenadopted for foundation for all the major bridges.

iii. To assess the soil characteristic bore hole were drilled at location ofall the major bridges and it was observed that strata is predominantlymade of silty sand/Clayey sand up to an average depth of 14 M.Thereafter the sub-soil consist of sandy silty clay of mediumcompressibility General ground water table varies from 12-15 Mdepth from the ground surface. Ground water table has beenrecorded during pre-monsoon periods. The post monsoon water tablehas been observed 8-10m depth from bed level of stream.

Preliminary bore logs were done up to a depth of 24-26 m and norock was encountered. However bore well which were dug for waterpurpose it is observer that rock is laying at a depth of about 30 -35 mbelow ground level. Bore log details at Bridge no. 21 at Km 18.40 isenclosed as Annexure-C. Foundation details of Major Bridges aretabulated below-

Foundation Details

Type Depth No. of pile per

Sr.No.

Br.No

Chainage Span SuperStructure

(M) Abutment Pier

1 12 13.407 3x18.3 M PSC Girder Pile 20 12 6










11 68 65.450 3x18.3 M PSC Girder Pile 20 12 612 79 79.795 2x18.3 M PSC Girder Pile 20 12 6


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iv. COST ANALYSIS OF PILE FOUNDATION

(a) For Pier Pile Group With Pile Cap-

No. of Pile per Pier - 06

Depth of Pile - 20 M

Ht. from founding level to top of pier -27.15 M

Dia. of pile -1200 mm

Concrete Mix in Pile - M-35

Concrete Mix in pile cap - M-35

Quantity of concrete per pile - 22.62 Cum

Quantity of concrete in pile cap - 79.87 Cum

Quantity of Reinforcement per pile - 2242 Kg

Quantity of reinforcement in pile cap - 4946 Kg

Length of 8mm steel liner per pile - 1530 mm

Schedule of Quantity and Rate-

S.No.

DescriptionQuantity Unit Rate Amount

1 Earthwork in excavation 124.24 Cum 89.90 10175.00

2 1200 Dia RCC cast in situ Pile 120.00 RM 6363.0 763560.003 RCC M-35 79.87 Cum 2491.0 198956.00

4 Structural Steel 2.00 MT 50250.0 100500.00

5 Reinforcement 18.40 MT 41235.0 758642.00

6 Cement 2017.00 Bags 274.0 552658.00

7 Integrity test of pile 6.00 No 2052.0 12312.00

TOTAL Rs. 23,96,803.00

(b) For Abutment Pile Group with Pile Cap-

No. of Pile per Abutment - 12

Depth of Pile - 20 M

Ht. from founding level to top of abutment -27.15 M

Dia. of pile -1200 mm

Concrete Mix in Pile - M-35

Concrete Mix in pile cap - M-35

Quantity of concrete per pile - 22.62 Cum


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Quantity of concrete in pile cap - 192.62Cum

Quantity of Reinforcement per pile - 2644 Kg

Quantity of reinforcement in pile cap - 18569 Kg

Length of 8mm steel liner per pile - 1530 mm


S.No.

DescriptionQuantity Unit Rate Amount


2 1200 Dia RCC cast in situ Pile 240 RM 6363.0 1527120.00

3 RCC M-35 192.62 Cum 2491.0 479816.00

4 Structural Steel 4 MT 50250.0 201000.005 Reinforcement 50.297 MT 41235.0 2073997.00

6 Cement 4323 Bags 274.0 1184502.00

7 Integrity test of pile 12.0 No 2052.0 24624.00

TOTAL Rs. 55,15,599.00

v. Time Analysis of Pile Foundation-

Time for each group of pile for pier as well as abutment has beenworked out after considering the total time taken in piling workincluding pile cap for each Bridge individually. As detailed abovethere are total 458 piles out of which 393 piles have been completed.For piling work at a bridge location 2-3 rigs and total 8 rigs weredeployed. The works at 3 bridge locations were taken upsimultaneously. The details of starting the piling work and theprogress achieved bridge wise is enclosed as Annexure-D

First Piling was started at Bridge no. 34 on 18-March-2008. In timespan of 62months a progress of 393 pile have been achieved whichincludes the intervening monsoon period, progress of work was also

badly affected for 20 days due to Gurjer andolan in this part ofcountry. After excluding the andolan period and its consequent effectwhich spanned for about a month the progress of 393 pile can besafely assumed to have been achieved in a 52months which givesan average progress of 72 pile per month. A peak progress of 110piles in the month of May-2008 has been achieved.

(a) Average time taken in drilling of pile

up to 20m depth from cut off level - 18-24 Hrs

(b) Av. Time taken in Cage lowering - 2.0 Hrs

(c) Av. Time taken in lowering of trimmy pipe - 1.0 Hrs

(d) Av. Time taken in Washing of Borehole - 2.0 Hrs


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(e) Av. Time taken in concreting of one pile - 3.0 Hrs

(f) Av. Time taken in excavation & chipping of

pile up to cut off level

(i) For group of 6 Piles - 7 days

(ii) For group of 12 piles - 12 days(iii) For group of 16 piles - 15 days

(g) Av. Time taken in placement of reinforcement

and concreting of pile cap

(i) For group of 6 Piles - 7 days

(ii) For group of 12 piles - 10 days

(iii) For group of 16 piles - 12days

Piling work has been completed at all the bridges except Br.No.12, 68& 79 and casting of pile cap is also completed at Bridge no. 32(2x18.3m) and Bridge No. 35 (5 x18.3 m). Piling and pile cap work,took about 4 months for Br.No.32 while it took about 6 months forBr.35. Br. No 32 which is having 2 abutments & 1 pier foundation,average time per foundation (pile group plus pile cap) works out to be1.33 months while for Br.No.35 which is having 2 abutments and 4pier foundations, average time per foundation works out to be onemonth only.

B. Dausa Jaipur Doubling project-

i. (a) Route Kilometre 61.28 KM (Single Line)

(b) Standard of Loading MBG with 25 T axle load

(c) Block station 10 No

(d) Flag station 01

(e) Important Bridge Nil

(f) Major Bridge 07

(g) Minor Bridges 53

ii. As detailed above there are 7 major bridges. The pile foundation has

been adopted on all the bridges except bridge No. 198 (10x18.3 M)situated at Km 219/1-2 in Bassi-Kanauta block section, this bridge isspanning over Dhoond River and in terms of water way it is thebiggest bridge in this section. This project is a doubling projectrunning parallel to existing Rewari-Jaipur BG track. Spanarrangements are similar to existing bridges. PSC slab has beenadopted for span of 12.2 M while PSC Girder with RCC deck slab hasbeen adopted for 18.3 M span. Pile foundation is with 1200 mm dia.bored cast-in-situ RCC piles while circular well has been adopted atbridge No 198.


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iii. To assess the soil characteristic bore hole were drilled at location ofall the major bridges and it was observed that strata arepredominantly made of Clayey silty sand up to an average depth of14 M. Thereafter the sub-soil consists of silty sand mixed with gravel

& bounders. General ground water table varies from 13-16 M depthfrom the ground surface. Preliminary bore logs were done up to adepth of 30 m and no rock was encountered. Bore log details atBridge no. 198 at Km 219/1-2 is enclosed as Annexure-E.Foundationdetails of major bridges are tabulated below-

Foundation Details

Type Depth No. of pile

Sr.No.

Br.No

Chainage Span SuperStructure

(M) Abutment Pier

1 178 192.028 4x12.2 M PSC Slab Pile 20 15 8

2 195 213.720 4x18.3 MPSC

GirderPile 20 16 6

3 197 215.620 2X12.2 M PSC Slab Pile 20 12 6

4 198 219.200 10X18.3 MPSC

GirderWell 20 - -

5 200 221.090 3X18.3 MPSC

GirderPile 20 12 6

6 212 233.905 2X12.2 M PSC Slab Pile 20 12 6

7 215 237.953 3X12.2 M PSC Slab Pile 20 12 6

iv.COST ANALYSIS OF WELL FOUNDATION

(a) For Pier -

Type of well - Circular

Depth of Well - 19.07 M

Ht. from founding level to top of Pier -26.82 M

Dia. of well - 7.3 M

Thickness of wall - 1.5 M

Depth of well curb - 2.5 M

Concrete Mix in well curb & cap - M-35

Concrete Mix in well staining - M-25

Quantity of concrete per well M-25 - 550.00 Cum

Quantity of concrete per well M-35 - 100.00 Cum

Quantity of concrete in well capM-35 - 99.90 Cum

Quantity of Reinforcement per Well - 11022 Kg

Quantity of reinforcement in Well cap - 11890 Kg

Quantity of structural steel per well - 10000 Kg


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S. No. Description Quantity Unit Rate Amount


2 Sinking of Well 3213.00 Cum 813.50 2613775.00

3 RCC M-25 550.00 Cum 2330.00 1281500.00

4 RCC M-35 199.90 Cum 2491.00 497951.00



7 Cement 6377.00 Bags 274.00 1747298.00

TOTAL Rs. 76,00,529.00

(b) For Abutment -

Type of well - CircularDepth of Well - 19.07 MHt. from founding level to top of abutment -25.82 MDia. of well - 8.5 MThickness of wall - 1.6 MDepth of well curb - 2.5 MConcrete Mix in well curb & cap - M-35Concrete Mix in well staining - M-25Quantity of concrete per well M-25 - 666.00 CumQuantity of concrete per well M-35 - 146.00CumQuantity of concrete in well capM-35 - 139.40 CumQuantity of Reinforcement per Well - 12072 KgQuantity of reinforcement in Well cap - 20910 KgQuantity of structural steel per well - 11000 Kg


S.No.

Description Quantity Unit Rate Amount


2 Sinking of Well 4356.00 Cum 813.50 3543606.00

3 RCC M-25 666.00 Cum 2330.00 1551780.00

4 RCC M-35 285.40 Cum 2491.00 710931.00



7 Cement 8100.00 Bags 274.00 2219400.00

TOTAL Rs. 99,56,239.00


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V. Time Analysis Of Well Foundation-

The work on first abutment was started in the month of January-2008and well curb was placed on 31-January-2008. Subsequently work on

other abutments and piers were also taken up by deploying total 6no.of Diesel engine driven winches and other equipments. Sinking ofwells on one abutment and 4 no of piers have been completed. Thedetail progress of sinking of wells are tabulated below-

ConcreteQuantity

Well staining RemarksS.No.

Abutment/ Pier

No.WellsteiningM-25

BottomPlugM-35

Started completed Totalduration

1 A-1 666 146 31.01.2008 WIP /60%

2 A-2 666 146 13.02.2008 05.08.2008 6 MonthBottom

plugging notstarted

3 P-1 550 100 10.06.2008 WIP / 50%

4 P-2 550 100 07.06.2008 WIP / 80%

5 P-3 550 100 05.06.2008 WIP / 80%

6 P-4 550 100 11.05.2008 WIP / 65%

7 P-5 550 100 24.02.2008 01.09.2008 6 MonthBottom

plugging notstarted

8 P-6 550 100 06.03.2008 WIP / 65%

9 P-7 550 100 24.03.2008 24.08.2008 5 Month

Bottom

plugging notstarted

10 P-8 550 100 06.04.2008 12.09.2008 5 MonthBottom

plugging notstarted

11 P-9 550 100 04.05.2008 27.09.2008 5 MonthBottom

plugging notstarted


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Average time taken in various activities connected with sinking of wellfoundation has been worked out from progress register maintained atsite. The details of time taken on an average on various activities areas below-

Sr.No.

Activity Av. Time Taken

A Well Curb 3.0 M

1 Placing of cutting edge 3 days

2 Structural steel fabrication 5 days

3 Reinforcement cutting, bending & placing 6 days

4 Welding of outer Plate 3 days

5 Concreting of one Lift of 1.5 meter

without Pump 2 days

with Pump 1 day

6 Casting of Next 1.5 m complete 8 days

7 Sinking in sandy soil @ 0.5 m/day (0-3M) 6 days

Total time 34 days

B Well Steining 17.0 M

1 Casting of 2 lift (1.35 x2=2.70m) complete 6 days

2 Sinking in sandy soil @ 0.3 m/day (3-5.7M) 9 days

3 Casting of Next 2 lift (1.35 x2=2.70m) complete 6 days

4 Sinking in sandy soil @ 0.3 m/day (5.7-7.0M) 4 days


6 Casting of 2 next lift (1.35 x2=2.70m) complete 6 days






12 Casting of 2 next lift (1.35x2=2.7m) complete 6 days


Total time 146 days


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The bottom plugging, filling with sand and well cap have not beendone on any of the wells whose sinking have been completed hencetherefore data of actual time for these activities are not available.However considering the quantity of concreting involved in bottom

plug and well cap the probable time for these activities can be asbelow-

C Bottom Plugging & sand filling

1 Excavation in bottom plug 20 days

2 Concreting 2 days

3 Sand filling 2 days

Total time 24 days

D Well Cap

1 Excavation 3 days

2 Reinforcement cutting, bending & placing 6 days

3 Concreting 1 day

Total time 10 days

Total time taken in sinking of one well including bottom plugging and

well cap comes to 214 days (Approx. 7 Months). From the progresschart of well sinking given above a total of 6 month has taken place forsinking of well of A-2 & P-5 while 5 month period has taken in case ofP-7,P-8&P-9.

8. OBSERVATIONS

(a) Cost of well for pier is observed to be more than three times the cost

of pile group for pier. On an average, time of construction for pilegroup including pile cap works out to be one month while for well itcomes to 6 months.

(b) Cost of well for abutment is observed to be more than 1.8 times thecost of pile group for abutment. On an average, time of constructionfor pile group including pile cap works out to be 1.5 month while forwell it comes to 7 months.


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9. CONCLUSION

Worldwide there is an increasing trend for adopting piles for bridgefoundations. With the help of pile foundation, the construction of bridges is

much faster. As per a study conducted, typical Indian bridges cost about40% more than bridges being constructed in US and Europe. Main reasonfor higher cost is the time overrun in Indian Scenario due to uncertaintyassociated with the well foundation mainly adopted for river bridges. Pilefoundations on the other hand require less time for construction.

The larger diameter bored piles which are being adopted in the constructionof bridges are reaching the dividing line between piles and small wells. Withthe help of state-of-the-art equipments and technique available, pilefoundations are proving economical even for large span bridges. Though itis true, selection of foundation does not depend solely on economics but

criteria of serviceability, durability and importance of link particularly incontext of Railways are also governing factors.

Foundation systems for bridges are usually selected based on its ability tocarry the load, on the anticipated structural integrity of the foundation duringits service life, and on economics. Techno-economics of deep foundationdepends on depth of foundation, span configuration, scour depth and subsoil conditions etc. Hence well and pile foundation is not to be viewed ascompeting but complementing technologies for bridge foundation.

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pile vs well

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