Pile vs Well

Comparison On Actual Case StudyPile Foundation v /s We We ll foundation

OBJECTIVE:

Comparative study of pile foundation and well foundation, in terms of cost & time by collecting data from the field to help in decision making regarding appropriate type of deep foundation for bridges. The bridges with pile foundation and well foundation under construction in NW Railway with same loading standard, span arrangement and depth of foundation have been 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 bridge foundations as open foundations and this does not create any problems except 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 pile foundations or well foundations. Well foundations had their origin in India and have been used for providing deep foundations for buildings and bridges. The technique of sinking masonry well for water is very old and even today small water wells are constructed using the same methods as were prevalent centuries ago. Due to availability of the expertise and skill for the sinking and construction of wells the well type foundation has been more popular in India. Well continues to be most important type of foundation for bridges in all type of strata, particularly in scourable river beds. Use of pile foundation till recently has not been a popular choice for bridges in India. In the bridges constructed recently, particularly on the Railways, one can find large number of cast iron/steel screw piles, been driven in to ground and even extended above bed level up to the girder bearing level. With the increased loading and horizontal forces caused by newer locomotives, these are being replaced by well foundation and cast-in-situ R.C.C. bored piles piles . Pile Pile foundation foundation can can be used quite qui te econom econom ically, particularly, where foundations have to be built very deep or taken through deep layers ayers of soil subjected subjected to a m inim inim um of s cour.

1

2.

Well Foundation Well foundations are commonly used for transferring heavy loads to deep strata in river or sea bed for bridges, transmission towers and harbour structures. The situation where well foundation are resorted are as belowa) Wherever consideration of scour or bearing capacity require foundation to be taken to a depth of more than 5 M below ground level open foundation becomes uneconomical. Heavy excavation and dewatering problem coupled with effort involve in retaining the soil makes the open foundation costlier in comparison to other type of foundation. b) Soil becomes loose due to excavation around the open foundation and hence susceptible to scouring. This is avoided in well foundation which is s unk by dredging inside of the well. c) From bearing pressure considerations, a well foundation can always be left hollow thereby considerably reducing bearing pressure transmitted to the foundation material. This is very important in soils of poor bearing capacity, particularly in clayey soils. In other type of foundation, the soil displaced is occupied by solid masonry/concrete which are heavier than the soil displaced and hence this does not give any relief in respect of adjusting bearing capacity. However in case of well foundation this is easily achieved because of cellular space left inside the well.

3.

Pile Foundation Depending upon the type of soil, foundation piles are used in following ways: a. Bearing piles b. Friction piles c. Friction cum bearing piles The bearing piles are designed as those which transmit the load to foundation strata directly without taking in to account the frictional resistance offered by enclosing soil. The passive earth pressure resistance is taken in to account only for the purpose of determining its resistance against the horizontal force. Such bearing piles are generally taken up to or in to the hard strata, such as mooram, soft or hard rock, hard consolidated sandy or gravelly soil. Friction piles are those in which the load is transmitted by the pile through friction offered by surrounding soil. Such piles can be provided in cohesive soils not subjected to heavy scour. Friction cum bearing piles designed in such a way that the load is transmitted both by friction of the surrounding soil and the bearing resistance of the founding soil at the tip of pile. 2

4.

Pile Classification By Construction Me thod a. Precast Driven Piles –These are usually of RCC or pre-stressed concrete and generally small in size for ease in handling. The main advantage of this type of pile is that its quality, in terms of dimension, use of reinforcement and concrete, can be ensured as the piles are cast in a yard under controlled conditions. However care is needed while handling, transporting and driving the pile to avoid damages. More to it, the limitation of length depending upon the capacity of the driving equipment is a disadvantage as these cannot be taken very deep except by joining. Generally, the depth over which these are used is restricted to 36 mt. b. Driven Cast-in-Situ Piles- A steel casing pile with a shoe at the bottom is driven first to the required depth. The reinforcement cage for the pile is then lowered inside the casing and the pile is concreted. As the concreting of the pile proceeds upwards, the casing is withdrawn keeping a suitable overlapping length. When such piles are driven in soft soil and the tube is withdrawn while concreting, it affects resistance and changes the property of the soil and this also affects the capacity of individual piles. These are not suitable for use in soft soils, in greater depths or where keying with the rock is required. c. Bored cast-in-situ piles – In the bored cast-in-situ process, a larger diameter casing is used. A casing of 3 to 4 m in length is provided on top of the bore hole which is driven with the help of a bailor. Boring further below this casing is carried out by chis elling and the side walls are kept stable by circulating bentonite slurry inside the bore hole. The boring is continued up to the layer decided for founding the structure. After reaching the desired founding level, the chisel is removed, bore-hole flushed, reinforcement cage lowered into the hole, and held in position by tack welding it to the support bars at the top of the cas ing. After this, concreting is carried out by using tremie, keeping its end always below the top level of rising concrete. The concreting is continued till a good quality concrete is seen at the top of the bore hole. After this, the tremie is removed and when the concrete has reached the top, the casing pipe on the top is also removed. The bentonite mix should be periodically checked for its specific gravity and changed as, due to constant use, it can get mixed with the soil and deteriorate in quality. This type of pile can be used even where the pile is keyed into the rock as chiselling in the rock can be carried out more easily. These piles serve as bearing-cum-friction piles. The diameters of such piles are generally more than 1.0m and can go up to 3.6m or more. They can be used singly or in group and are good 3

replacements for well foundations required for bridge piers in rivers with 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. After securing it in position, the casing is withdrawn. A particular process used for bored pre-cast piles is the Benoto process which involves a steel tube being pushed into the soil, turned and reversed using compressed air. The tube is in the form of a casing and is driven for the entire depth after the soil is progressively grabbed from the tube. The process is continued till the tube reaches the pre-determined level. Then the pre-cast pile is lowered inside and held in position. The tube is lifted gradually after filling the annular gap between the pre-cast pile and the soil by grouting. e. Driven steel piles – Steel piles can be circular or in other structural shapes. The circular ones are made in the form of either welded or seamless piles. Usually steel or cast iron piles used earlier for bridge structures are of longer diameter and screw type. Thes e were used in past when loading was less. These piles are suitable for being driven through cohesive soil to reach up to the hard strata and to serve as bearing piles. They are not suitable where heavy scour is expected and for foundation for bridges when foundations are situated wide apart.

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

5.

Pile Foundation V/S Well Foundation a. Well foundations provide a solid and massive foundation for heavy loads as against a cluster of piles which are slender and weak individually and are liable to get damaged when hit by floating trees or boulder rolling in river bed. b. Wells provide a large section modulus with the minimum cross sectional area and hence efficient in taking large vertical and horizontal 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 same cannot hold good in case of cast-in-situ bored piles where concreting 4

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

d. When scour takes place, the piles act as long struts and have to be designed for buckling stresses, which are quite heavy due to the bending moments contributed by the longitudinal forces on the bridge deck due to tractive effort and braking forces. e. It is difficult to drive the piles through the strata having boulders and tree logs which are frequently encountered in alluvial soil, whereas in the case of a well foundation there is sufficiently access to remove the obstruction. Quite often the skin friction developed is of much magnitude 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 well foundations where the soil characteristics and conditions of water table are such that the phenomenon of blow occurs during dewatering of the well. g. Increased mechanization and advent of new machinery have brought down the cost of foundation with piles considerably low in comparison to well. New testing techniques for checking the integrity of piles and information about strata through piles have passed or resting have removed the uncertainty of load carrying capacity of piles to large extent. h. Pile foundations have a clear advantage over well foundations in terms of speedy construction. Wherever time is the criterion, the pile foundation is the natural choice.

6.

Pile Foundation on N. W. Railway a. The use of large diameter bored piles for Railway bridges is a recent development. These piles were first extensively used on Apta-Roha and Pen-Thal B.G. Railway projects. Foundation with cast-in-situ R.C.C. bored piles were adopted for most of the bridges in Konkan Railway Project. This type of foundation was found suitable and used for bridging even for perennial rivers and creeks on this alignment barring foundations for few navigational spans. Speedy construction and commissioning of the Konkan Railway project could be possible due adoption of pile as first choice for foundations. b. In North Western Railway cast-in-situ bored piles have been adopted as foundation for most of the bridges in projects which are in progress. As the soil is predominantly sandy, mixed gravel and hard clayey strata and rivers being seasonal in nature foundation of most 5

of the bridges constructed earlier have been open foundation or well foundation. In gauge conversion projects foundations of most of the bridges have been retained by doing the strengthening by jacketing of foundations and piers as the governing criterion has been cost consideration and overall economy. However in all the new projects of doubling and new lines most of the foundations are either open foundation or pile foundation. Details of the doubling and new line projects and foundation adopted are summarized belowSr. No. 1 2 3 4 5

Project Alwar-Harsauli Doubling Bandikui-Dausa Doubling Dausa-Jaipur Doubling Jaipur-Phulera Doubling DausaGangapur New Line

No. of Major/ Imp. Bridges

Br. on Pile Foundation

Br. on Open Foundation

Br. on Well Foundation

1

1

Nil

Nil

3

1

2

Nil

7

6

Nil

1

2

1

1

Nil

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 bridge the foundations of rest of the bridges are either on pile or open. As explained earlier, there are very few perennial rivers in NW railway and most of the drainage system is seasonal in nature. Heavy discharge to the tune of high flood level occurs occasionally after the interval of many years and that too is confined to few days period. Discharge pattern is different for rivers flowing in North and Central India where heavy floods for a long duration is a regular feature.

7.

Case Study- Pile v/s Well Foundation Dausa-Gangapur City new line projects the Delhi-Jaipur main line to DelhiMumbai route. The alignment passes through mainly flat terrain and encounters the hilly terrain of Aravalli range near Lalsot. Strata is mainly silty/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 as that of Dausa-Jaipur doubling project and hence sub-soil strata of both the projects are similar. The depth of water table is about 12-15 mt. in both the cases.

6

A. Dausa-Gangapur City New Line i.

(a) (b) (c) (d) (e) (f) (g) (h)

Route Kilometre – 92.76 KM (Single Line) Standard of Loading – MBG with 25 T axle load Block station – 08 No Flag station – 05 Length of Tunnel – 2120 M Important Bridge – Nil Major Bridge – 12 Minor Bridges – 77

ii. Bridge span in this project has been standardised to 18.3 M and all the 12 Major Bridges have been designed with the same span. Super structures consist of 2 no. PSC girder for the MBG 25 T axle load with RCC deck slabs. Adoption of one span (i.e. 18.3 M) has led to ease in construction and development of expertise due to repetitive nature of job. Similarly 1200 mm dia. cast in situ RCC bored pile has been adopted for foundation for all the major bridges. iii. To assess the soil characteristic bore hole were drilled at location of all the major bridges and it was observed that strata is predominantly made of silty sand/Clayey sand up to an average depth of 14 M. Thereafter the sub-soil consist of sandy silty clay of medium compressibility General ground water table varies from 12-15 M depth from the ground surface. Ground water table has been recorded during pre-monsoon periods. The post monsoon water table has been observed 8-10m depth from bed level of stream. Preliminary bore logs were done up to a depth of 24-26 m and no rock was encountered. However bore well which were dug for water purpose it is observer that rock is laying at a depth of about 30 -35 m below ground level. Bore log details at Bridge no. 21 at Km 18.40 is enclosed as Annexure-C.  Foundation details of Major Bridges are tabulated belowSr. Br. No. No 1 2 3 4 5 6 7 8 9 10 11 12

12 21 28 29 32 34 35 38 39 40 68 79

Chainage

13.407 18.414 23.350 24.043 28.125 28.615 30.080 32.222 32.600 34.030 65.450 79.795

Span

3x18.3 M 3x18.3 M 5x18.3 M 2x18.3 M 2x18.3 M 2x18.3 M 5x18.3 M 2x18.3 M 5x18.3 M 2x18.3 M 3x18.3 M 2x18.3 M

Super Structure

Type

PSC Girder PSC Girder PSC Girder PSC Girder PSC Girder PSC Girder PSC Girder PSC Girder PSC Girder PSC Girder PSC Girder PSC Girder

Pile Pile Pile Pile Pile Pile Pile Pile Pile Pile Pile Pile

Foundation Details Depth No. of pile per (M) Abutment Pier 20 12 6 20 12 6 23 16 6 23 16 6 21 12 6 22 12 6 22 16 6 24 12 6 23 16 6 20 9 6 20 12 6 20 12 6 7

iv. COST ANALYSIS OF PILE FOUNDATION (a) For Pier Pile Gr oup W ith Pile CapNo. of Pile per Pier Depth of Pile Ht. from founding level to top of pier Dia. of pile Concrete Mix in Pile Concrete Mix in pile cap Quantity of concrete per pile Quantity of concrete in pile cap

- 06 - 20 M -27.15 M -1200 mm - M-35 - M-35 - 22.62 Cum - 79.87 Cum

Quantity of Reinforcement per pile

- 2242 Kg

Quantity of reinforcem ent in pile cap

- 4946 Kg

Length of 8mm steel liner per pile

- 1530 mm

Schedule of Quantity and RateS. Description No. 1 Earthwork in excavation

Quantity Unit

2 3

1200 Dia RCC cast in situ Pile RCC M-35

4 5

Structural Steel Reinforcement

6 7

Cement Integrity test of pile

Rate

Amount

124.24 Cum

89.90

10175.00

120.00 RM 79.87 Cum

6363.0 2491.0

763560.00 198956.00

50250.0 41235.0

100500.00 758642.00

274.0 2052.0

552658.00 12312.00

Rs.

23,96,803.00

2.00 18.40

MT MT

2017.00 Bags 6.00 No TOTAL

(b) For Abutment Pile Group with Pile CapNo. 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

8

Quantity of concrete in pile cap

- 192.62Cum

Quantity of Reinforcement per pile

- 2644 Kg

Quantity of reinforcem ent in pile cap

- 18569 Kg

Length of 8mm steel liner per pile

- 1530 mm

Schedule of Quantity and RateS. Description No. 1 Earthwork in excavation

Quantity Unit 299.63 Cum 240

Rate

Amount

89.90

24540.00

RM

6363.0

1527120.00

2491.0

479816.00

50250.0 41235.0

201000.00 2073997.00

2

1200 Dia RCC cast in situ Pile

3

RCC M-35

192.62 Cum

4 5

Structural Steel Reinforcement

4 50.297

6

Cement

7

Integrity test of pile

MT MT

4323

Bags

274.0

1184502.00

12.0

No

2052.0

24624.00

Rs.

55,15,599.00

TOTAL v. Time Analysis of Pile Foundation-

Time for each group of pile for pier as well as abutment has been worked out after considering the total time taken in piling work including pile cap for each Bridge individually. As detailed above there 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 were deployed. The works at 3 bridge locations were taken up simultaneously. The details of starting the piling work and the progress achieved bridge wise is enclosed as Annexure-D First Piling was started at Bridge no. 34 on 18-March-2008. In time span of 6   ⁄ 2 months a progress of 393 pile have been achieved which includes the intervening monsoon period, progress of work was also badly affected for 20 days due to Gurjer andolan in this part of country. After excluding the andolan period and its consequent effect which spanned for about a month the progress of 393 pile can be safely ass umed to have been achieved in a 5   ⁄ 2 months which gives an average progress of 72 pile per month. A peak progress of 110 piles 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 (b) Av. Time taken in Cage lowering (c) Av. Time taken in lowering of trimmy pipe (d) Av. Time taken in Washing of Borehole

-

18-24 2.0 1.0 2.0

Hrs Hrs Hrs Hrs 9

(e) Av. Time taken in concreting of one pile (f) Av. Time taken in excavation & chipping of pile up to cut off level (i) For group of 6 Piles (ii) For group of 12 piles (iii) For group of 16 piles (g) Av. Time taken in placement of reinforcement and concreting of pile cap (i) (ii) (iii)

For group of 6 Piles For group of 12 piles For group of 16 piles

-

3.0

Hrs

-

7 days 12 days 15 days

-

7 days 10 days 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 for Br.35. Br. No 32 which is having 2 abutments & 1 pier foundation, average time per foundation (pile group plus pile cap) works out to be 1.33 months while for Br.No.35 which is having 2 abutments and 4 pier foundations, average time per foundation works out to be one month only. B. Dausa – Jaipur Doubling projecti.

(a) (b) (c) (d) (e) (f) (g)

Route Kilometre – 61.28 KM (Single Line) Standard of Loading – MBG with 25 T a xle load Block station – 10 No Flag station – 01 Important Bridge – Nil Major Bridge – 07 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 is spanning over Dhoond River and in terms of water way it is the biggest bridge in this section. This project is a doubling project running parallel to existing Rewari-Jaipur BG track. Span arrangements are similar to existing bridges. PSC slab has been adopted for span of 12.2 M while PSC Girder with RCC deck slab has been 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 at bridge No 198.

10

iii. To assess the soil characteristic bore hole were drilled at location of all the major bridges and it was observed that strata are predominantly made of Clayey silty sand up to an average depth of 14 M. Thereafter the sub-soil consists of silty sand mixed with gravel & bounders. General ground water table varies from 13-16 M depth from the ground surface. Preliminary bore logs were done up to a depth of 30 m and no rock was encountered. Bore log details at Bridge no. 198 at Km 219/1-2 is enclosed as Annexure-E . Foundation details of major bridges are tabulated below-

Sr. Br. No. No

Chainage

Span

Super Structure

Foundation Details Type Depth No. of pile (M) Abutment Pier Pile 20 15 8

1

178

192.028

4x12.2 M

PSC Slab

2

195

213.720

4x18.3 M

PSC Girder

Pile

20

16

6

3

197

215.620

2X12.2 M

PSC Slab

Pile

20

12

6

4

198

219.200

10X18.3 M

Well

20

-

-

5

200

221.090

3X18.3 M

Pile

20

12

6

6

212

233.905

2X12.2 M

PSC Girder PSC Girder 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 Depth of Well Ht. from founding level to top of Pier Dia. of well Thickness of wall Depth of well curb Concrete Mix in well curb & cap Concrete Mix in well staining Quantity of concrete per well M-25 Quantity of concrete per well M-35 Quantity of concrete in well capM-35 Quantity of Reinforcement per Well Quantity of reinforcement in Well cap Quantity of structural steel per well

- Circular - 19.07 M -26.82 M - 7.3 M - 1.5 M - 2.5 M - M-35 - M-25 - 550.00 Cum - 100.00 Cum - 99.90 Cum - 11022 Kg - 11890 Kg - 10000 Kg 11

Schedule of Quantity and RateS. No.

Description

Quantity

Unit

1

Earthwork in excavation

155.41 Cum

81.90

12728.00

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

5

Structural Steel

10.00

MT

50250.00

502500.00

6

Reinforcement

22.912

MT

41235.00

944776.00

7

Cement

274.00

1747298.00

Rs.

76,00,529.00

6377.00 Bags

TOTAL (b) For Abutment Type of well Depth of Well Ht. from founding level to top of abutment Dia. of well Thickness of wall Depth of well curb Concrete Mix in well curb & cap Concrete Mix in well staining Quantity of concrete per well M-25 Quantity of concrete per well M-35 Quantity of concrete in well capM-35 Quantity of Reinforcement per Well Quantity of reinforcement in Well cap Quantity of structural steel per well

Rate

Amount

- Circular - 19.07 M -25.82 M - 8.5 M - 1.6 M - 2.5 M - M-35 - M-25 - 666.00 Cum - 146.00Cum - 139.40 Cum - 12072 Kg - 20910 Kg - 11000 Kg

Schedule of Quantity and RateS. Description No. 1 Earthwork in excavation

Quantity

216.83 Cum

81.90

17758.00

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

5

Structural Steel

11.00 MT

50250.00

552750.00

6

Reinforcement

32.982 MT

41235.00

1360013.00

7

Cement

274.00

2219400.00

Rs.

99,56,239.00

TOTAL

Unit

8100.00 Bags

Rate

Amount

12

V. Time Analysis Of Well FoundationThe work on first abutment was started in the month of January-2008 and well curb was placed on 31-January-2008. Subsequently work on other abutments and piers were also taken up by deploying total 6 no. of Diesel engine driven winches and other equipments. Sinking of wells on one abutment and 4 no of piers have been completed. The detail progress of sinking of wells are tabulated below-

S. No.

1

Abut Concrete ment Quantity  / Pier Well Bottom Started No. steining Plug M-25 M-35 A-1

666

146

31.01.2008

Well staining completed

Remarks Total duration

WIP /60%

2

A-2

666

146

13.02.2008

05.08.2008

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

8

P-6

550

100

06.03.2008

6 Month

Bottom plugging not started

6 Month

Bottom plugging not started

WIP / 65%

9

P-7

550

100

24.03.2008 24.08.2008

5 Month

10

P-8

550

100

06.04.2008 12.09.2008

5 Month

11

P-9

550

100

04.05.2008 27.09.2008

5 Month

Bottom plugging not started Bottom plugging not started Bottom plugging not started

13

Average time taken in various activities connected with sinking of well foundation has been worked out from progress register maintained at site. The details of time taken on an average on various activities are as belowSr. No.

A

Activity

Av. Time Taken

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

5

Sinking in sandy soil @ 0.2 m/day (7.0-8.4M)

7 days

6

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

6 days

7

Sinking in sandy soil @ 0.2 m/day (8.4-11.1M)

14 days

8

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

6 days

9

Sinking in sandy soil @ 0.12 m/day (11.1-13.8M)

22 days

10

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

6 days

11

Sinking in sandy soil @ 0.1 m/day (13.8-16.5M)

27 days

12

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

6 days

13

Sinking in sandy soil @ 0.1 m/day (16.5-19.07M)

27 days

Total time

146 days

14

The bottom plugging, filling with sand and well cap have not been done on any of the wells whose sinking have been completed hence therefore 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 as belowC

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

Exca vation

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 progress chart of well sinking given above a total of 6 month has taken place for sinking of well of A-2 & P-5 while 5 month period has taken in case of P-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 pile group including pile cap works out to be one month while for well it comes to 6 months. (b) Cost of well for abutment is observed to be more than 1.8 times the cost of pile group for abutment. On an average, time of construction for pile group including pile cap works out to be 1.5 month while for well it comes to 7 months.

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9.

CONCLUSION Worldwide there is an increasing trend for adopting piles for bridge foundations. With the help of pile foundation, the construction of bridges is much faster. As per a study conducted, typical Indian bridges cost about 40% more than bridges being constructed in US and Europe. Main reason for higher cost is the time overrun in Indian Scenario due to uncertainty associated with the well foundation mainly adopted for river bridges. Pile foundations on the other hand require less time for construction. The larger diameter bored piles which are being adopted in the construction of bridges are reaching the dividing line between piles and small wells. With the help of state-of-the-art equipments and technique available, pile foundations are proving economical even for large span bridges. Though it is true, selection of foundation does not depend solely on economics but criteria of serviceability, durability and importance of link particularly in context of Railways are also governing factors. Foundation systems for bridges are usually selected based on it’s ability to carry the load, on the anticipated structural integrity of the foundation during its service life, and on economics. Techno-economics of deep foundation depends on depth of foundation, span configuration, scour depth and sub soil conditions etc. Hence well and pile foundation is not to be viewed as competing but complementing technologies for bridge foundation.

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