Method Statements (Bridge works) Methodology

CONTENTS



1. Introduction

2. Structural Excavation

3. Sub-Surface Investigation

4. Confirmatory Bore Holes

5. Bored cast-in-situ piles using conventional rig

6. Initial Pile load test

7. Pile cap

8. Well Steining

9. Well Sinking

10. Well bottom plug

11. Well cap

12. Sub structure

13. Filter media and backfilling

14. RCC Girder

15. Deck slab

16. PSC Girder and Deck slab

17. Box Girder

18. Fixing of POT / PTFE bearings


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1. INTRODUCTION


1.1 SCOPE

This document outlines the procedure for the method of construction of major items of Bridge works as per approved drawings and specifications of the Project.

The Standard Specifications for Road and Bridge Works of Ministry of Shipping, Road Transport & Highway (MoSRTH) shall be consulted for the details which are not covered in this document.


1.2 FIELD OF APPLICATION

1. Structural Excavation

2. Sub-Surface Investigation

3. Confirmatory Bore Holes

4. Bored cast-in-situ piles using conventional rig

5. Initial Pile load test

6. Pile cap

7. Well Steining

8. Well Sinking

9. Well bottom plug

10. Well cap

11. Sub structure

12. Filter media and backfilling

13. RCC Girder

14. Deck slab

15. PSC Girder and Deck slab

16. Box Girder

17. Fixing of POT / PTFE bearings


1.3. REFERENCES

1. Concessionaire Agreement

2. MoSRTH Specifications for Road and Bridge Works



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2. STRUCTURAL EXCAVATION



2.1 OBJECTIVE:

To out line the procedure for method of Excavation for the construction of foundations for bridges, culverts, retaining walls, headwalls, cutoff walls, pipe culverts and other similar structures to the required dimensions and levels conforming to approved drawings and project specifications.


2.2 CONSTRUCTION EQUIPMENT:

• Excavator

• Dump Trucks


2.3 CONSTRUCTION METHODOLOGY:

The following sequence of activities shall be carried out for execution of structural excavation works:


a After the site has been cleared, the limits of excavation shall be set out true to lines, curves and slopes.

b Excavation shall be taken to the width of the lowest step of the footing and the sides shall be left plumb where the nature of soil allows it. Where the nature of soil or the depth of the trench and season of the year do not permit vertical sides, put up necessary shoring, strutting and planking or cut slopes to a safer angle.

c Normally, open foundations shall be laid dry. Where water is met with in excavation due to stream flow, seepage, springs, rain or other reasons, adequate measures such as bailing, pumping, constructing diversion channels, bunds, depression of water level by well point system, cofferdams and other necessary works to keep the foundation trenches dry when so required and to protect the green concrete against damage by erosion or sudden rising of water level.

d The bottom of the foundation shall be leveled both longitudinally and transversely. Before footing is laid, the surface shall be slightly watered and rammed.

e If there are any slips or slip-outs in the excavation, these shall be removed.

f Near towns, villages and all frequented places, trenches and foundation pits shall be securely fenced, provided with proper caution signs and marked with red lights at night to avoid accidents. Take adequate protective measures to see that the excavation operations do not affect or damage adjoining structures.

g Backfilling shall be done with approved material after concrete is fully set and carried out in such a way as not to cause undue thrust on any part of the structure. All space between foundation concrete and the sides of excavation shall be refilled to the original surface in layers not exceeding 150 mm compacted thickness. The compaction shall be done with the help of suitable equipment such as mechanical tamper, rammer or plate vibrator after necessary watering, so as to achieve a density not less than the field density before excavation.

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3. SUB-SURFACE INVESTIGATION



3.1 OBJECTIVE:

To out line the procedure for method of complete sub-surface investigation of strata in which pile foundations are proposed shall be carried out in advance and by in-situ pile tests conforming to approved drawings and project specifications.


3.2 CONSTRUCTION EQUIPMENT:

• Rig

• Standard Penetration Test Sampler


3.3 CONSTRUCTION METHODOLOGY:

The following sequence of activities shall be carried out for sub-surface investigation:


a At least one bore-hole for every foundation of the bridge shall be executed, depth of the boring shall not be less than:

i) 1.5 times estimated length of pile in soil but not less than 15m beyond the probable length of pile.

ii) 15 times diameter of pile in weak/jointed rock but minimum 15m in such rock.

iii) 4 times diameter of pile in sound, hard rock but minimum 3m in such rock.

b The investigation shall also include location of ground water table and other parameters including results of chemical tests showing sulphate and chloride content and any other deleterious chemical content in soil and / or ground water, likely to affect durability.

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4. CONFIRMATORY BORE HOLES



4.1 OBJECTIVE:

To out line the procedure for the method of execution of confirmatory bore holes conforming to approved drawings and project specifications.


4.2 CONSTRUCTION EQUIPMENT:

• Conventional soil drilling machine including accessories

• Water Pump

• Electrical Generator


4.3 CONSTRUCTION METHODOLOGY:

The following sequence of activities shall be carried out for execution of confirmatory bore holes:


a The Borehole point’s location will be the location of the foundation of the particular bridge structure and the no. of such bore holes and its exact location will be as decided by the Engineer.


b Confirmatory Bore holes will be executed on land based method by deploying rotary drilling equipment.


c After the finalizing of the bore hole location the casing will be driven up to the collapsible strata by drilling and hammering the casing tube.


d Further drilling will be done with Bentonite Mud Circulation up to the head rock level. The depth of the exploration will be at least 1.5 times the minimum depth of the foundation.


e Undisturbed samples will be collected ensuring that their moisture content and structure do not get altered during the recovery of the sample. Undisturbed Samples will be collected as per IS 2132 in reusable open drive thin walled MS tubes of 100 mm diameter tube. The undisturbed samples are waxed at both ends immediately after collection, numbered and labeled properly for identification.


f The standard penetration test sampler will be as per IS 2131. The driving weight of 63.5 Kg weight is provided with suitable arrangement for controlling the height of fall as 75 cms. In Standard Penetration test the blow counts for every penetration of 15 cms, up to the total penetration of 45 cms are recorded. The standard penetration test blow count, “N” is reckoned as the total number of blows for the second and third penetration increments adding to 30 cms. The “N” value is indicative of the relative density of cohesion less soils and consistency of cohesive soils.


g The sample retrieved from Standard penetration test spoon was inspected for visual identification of strata. The samples are preserved in polythene bags, duly numbered and N values mentioned for proper identification.


h The field records shall contain details of bore location, the elevation of the ground surface with respect to permanent bench mark, elevation of the water table, upper boundary of each of the successive soil strata encountered, general information regarding the soil type obtained by visual inspection, the value of resistance obtained by means of standard penetration test.

I Proper care shall be taken in handling and labeling of the samples.


4.4 OBSERVATION SHEET:


CONFIRMATORY BORE HOLES


Bridge No. Date of Execution:

Bore Hole No. Method: Rotary Drilling.

RL: Working Tech: Land based method.

GL:


Depth

(m) Visual Soil Description Graphic Log Samples Penetration Test N value

Depth (m) Type No. 15 cms 30 cms 45 cms


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5. BORED CAST-IN-SITU PILES USING CONVENTIONAL RIG



5.1 OBJECTIVE:

To out line the procedure for the method of construction of bored cast-in-situ piles conforming to approved drawings and project specifications.


5.2 CONSTRUCTION EQUIPMENT:

• Heavy piling tripod

• Reciprocating / Centrifugal pumps

• Bentonite mixing plant

• Boring accessories and tools

• Concreting accessories

• Electrical Generator

• Welding transformer / Gas cutting sets


5.3 CONSTRUCTION METHODOLOGY:

The following sequence of activities shall be carried out for construction of bored cast-in-situ pilling works:


a Pile points will be established on ground from the approved established survey station by using total station based on the approved drawing.


b Bored Cast-in-situ piles can be executed in any of the following two methods

1. Percussion method

2. Rotary Method


c Shift and center the piling tripod over the pile point established on the ground.


d Normally temporary casing pipe will be pitched / installed by making a naked borehole of about 1 meter to 1.5 meter in the ground of the pile location and drive the temporary casing up to the required depth by hammering and boring either by conventional piling rig or by rotary drilling equipment.

To position this temporary casing with exact pile location two reference points are to be fixed on the ground approximately perpendicular to each other from the center point of the pile. Normally these reference points will be distanced from the casing with the conventional measurement.


e Pile boring can be done either of the two following methods

1. Direct Mud Circulation Method (DMC Method)

2. Reverse Mud Circulation Method (RMC Method)


1. Direct Mud Circulation Method

In DMC method boring will be done with the help of conventional piling rig i.e. heavy tripod coupled with power winch and an attachment of DMC rods and chisel. Chisel is normally 75mm lesser than the diameter of the pile. This reduction of diameter is for limiting the over breakage of the sides of the borehole which happens due to the oscillation of the chisel fitted to the long length of the DMC rods. With the help of the chisel boring will be done. In the process of boring bentonite slurry (drilling mud) will be continuously fed/injected in the bottom of the borehole through DMC pipes. Due to the penetration of the chisel and continuous flow of bentonite slurry soil will get agitated and the agitated soil will come out from the borehole along with the overflowing bentonite slurry. This forms the borehole.


2. Reverse Mud Circulation Method

In this method boring will be done either by Percussion or by Rotary method. In percussion method the bored material will be bailed out by suction either by bailor or by pumps

In rotary method bored material will be directly scooped out either by augur or by bucket.

In both the methods bentonite slurry is pumped at the top of the borehole.


f After reaching the final level boring is stopped and bentonite slurry is fed for some more time to allow the floating material to come out and the bentonite coming out reaches the standard specific gravity.

The reinforcement cages that are already made as per the design were lowered in suitable lengths and the pieces will be joined together by tack welding.


g Before concreting the borehole has to be flushed again with bentonite slurry to remove any sediment material left within the bore hole. After flushing tremie pipes will be lowered up to the bottom of the borehole for concreting. On top of the tremie pipe suitable capacity funnel is to be fitted. Before the first pour the funnel neck is covered by a metallic cover and it is removed after sufficient concrete has been poured into the funnel. This ensures that first pour concrete displaces the bentonite slurry and gives sufficient embedment to the tremie pipe. Likewise concrete is to be built up to the required level i.e. above the cutoff level to clear off the contaminated top concrete mixed with bentonite and at each stage crosschecks will be done so that the minimum embedment of the tremie pipe is ensured. The laitance will be chipped off at a later stage so that sound concrete is ensured at the cutoff level.

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6. INITIAL PILE LOAD TEST



6.1 OBJECTIVE:

To out line the procedure for the method of Initial Pile load test conforming to approved drawings and project specifications.


6.2 CONSTRUCTION EQUIPMENT:

• Hydraulic Jacks

• Pressure gauge and Dial gauges

• Datum bar


6.3 CONSTRUCTION METHODOLOGY FOR INITIAL VERTICAL PILE LOAD TEST:

The following sequence of activities shall be carried out for Initial vertical pile load test:


The pile head should be chipped off to natural horizontal plane till sound concrete is met. The projecting reinforcement should be cut off or bent suitably and the top surface finished and leveled with plaster of paris or similar synthetic material where required. A bearing plate with a hole at the center should be placed on the head of the pile for the jacks to rest.


The test should be carried out by applying a series of vertical downward incremental load each increment being of about 20% of safe load on the pile.

The reaction may be obtained from the following:


i. Kentledge placed on a platform supported clear of the test pile in case of load test below under–pinned structure, the existing structure if having adequate weight and suitable construction may serve as kentledge. The center of gravity of the kentledge should generally be on the axis of the pile and the load applied by the jack should also be coaxial with this pile.


ii. Anchor piles with center-to-center distance with the test pile not less than three times the test pile shaft diameter subject to minimum of two meters. If the anchor piles are permanent working piles it should be ensured that their residual uplift is with in limits. Care should be exercised to ensure that the datum bar supports are not affected by heaving up of the soil.


Settlement shall be recorded with minimum 2 dial gauges for single pile and 4 dial gauges of 0.01mm sensitivity for groups, each positioned at equal distance around the piles and normally held by datum bars resting on immovable supports at a distance of 3D from the edge of the piles where D is the pile stem diameter of circular piles.


The safe load on a single pile for the initial test should be least of the following:


i. Two-thirds of the final load at which the total displacement attains a value of 12mm unless other wise required in a given case on the basis of nature and type structure in which case, the safe load should be corresponding to the stated total displacement permissible.

ii. 50% of the final load at which the total displacement equals 10% of the pile diameter in case of uniform diameter piles and 7.5% of bulb diameter in case of under reamed piles.


6.4 SUMMARY SHEET FOR INITIAL VERTICAL PILE LOAD TEST:

1. Location :

2. Diameter of Pile :

3. Founding Level :

4. Cut-off Level :

5. Length of Pile :

6. Reinforcement Details :

7. Grade of Concrete :

8. Mix Proportion by Weight :

9. Design Load :

10. Test Load (2.5 x Design Load) :

(The reaction to be made available for the test should be 25 % more than the final test load proposed to be applied.)

11. Kentledge Load :

(Separate calculation sheets will be provided for each location depending upon the actual load required for the specific case)

12. Hydraulic jack :

a) Ram Diameter :

b) Ram Area :

c) Jack Capacity :

13. Pressure Gauge :

14. Increments :

(20 % of the safe load)

15. Micrometers / Dial Gauges :

16. Gross settlement :

17. Rebound :

18. Net Settlement :

19. Date of Commencement :

20. Date of Completion :






6.5 OBSERVATION SHEET FOR INITIAL VERTICAL PILE LOAD TEST:

Date Sl No Time Percentage of Load Applied Load applied Pressure gauge reading Dial Gauge Reading Average Settlement Gross Settlement Rebound

From To A B


6.6 CONSTRUCTION METHODOLOGY FOR INITIAL HORIZONTAL PILE LOAD TEST:

The following sequence of activities shall be carried out for Initial horizontal pile load test:


The test may be carried out by introducing a hydraulic jack with gauge between two piles under test or the reaction may be suitably obtained otherwise .If it is conducted by jack located by between two piles, the full load imposed by the jack shall be taken as the lateral resistance of each pile . The loading should be applied in increments of about 20 percent of the estimated safe load.


The next increment should be applied after the rate of displacements nearer to 0.1 mm per 30 minutes.


Displacements shall be read by using at least two dial gauges duly checked and calibrated for 0.01 mm sensitivity spaced at 30 cm and kept horizontally one above the other on the test pile and the displacement interpolated at cutoff level from similar triangles where cutoff level is unapproachable and for approachable cutoff level, how ever, one dial gauge placed diametrically opposite to the jack shall directly measure the displacement. Where it is not possible to locate one of the dial gauges in the line of the jack axis, then two dial gauges may be kept at a distance of 30 cms at a suitable height and the displacement interpolated at load point from similar triangles


The safe lateral load on the pile shall be taken as the least of the following:


a) Fifty percent of the final load at which the total displacement increases to 12mm;

b) Final load at which the total displacement correspond to 5mm; and Load corresponding to any other specified displacement as per Performance requirements.


6.7 SUMMARY SHEET FOR INITIAL HORIZONTAL PILE LOAD TEST:

1. Location :

2. Diameter of Pile :

3. Founding Level :

4. Cut-off Level :

5. Length of Pile :

6. Reinforcement Details :

7. Grade of Concrete :

8. Mix Proportion by Weight :

9. Design Load :

10. Test Load (2 x Design Load) :

11. Hydraulic jack :

a) Ram Diameter :

b) Ram Area :

c) Jack Capacity :

12. Pressure Gauge :

13. Increments :

(20 % of the safe load)

14. Micrometers / Dial Gauges :

15. Gross settlement :

16. Rebound :

17. Net Settlement :

18. Date of Commencement :

19. Date of Completion :

6.8 OBSERVATION SHEET FOR INITIAL HORIZONTAL PILE LOAD TEST:

Date Sl No Time Percentage of Load Applied Load applied Pressure gauge reading Dial Gauge Reading Average Settlement Gross Settlement Rebound

From To A B



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7. PILE CAP



7.1 OBJECTIVE:

To out line the procedure for the method of construction of Pile cap conforming to approved drawings and project specifications.


7.2 CONSTRUCTION EQUIPMENT:

• Excavator

• Form work accessories

• Generator

• Welding transformer / Gas cutting set

• Batching plant

• Concrete pump / Crane and bucket

• Water pump


7.3 CONSTRUCTION METHODOLOGY:

The following sequence of activities shall be carried out for construction of Pile cap works:


a The location of the pile cap is marked on the ground using a Total Station from the

reference coordinates already fixed.


b Earthwork Excavation shall be taken up as per the approved Earth Work Excavation Methodology.


c PCC bottom level is to be achieved. Concreting of the leveling course will be done and the top surface made true to level.


d Pile chipping will be done with the help of jack hammers not earlier than seven days of pile casting.


e Reinforcement tying of the Pile Cap as per the approved drawing will be done for the Pile Cap. Laps are provided in staggered manner wherever required.


f After the placing of formwork, Concreting will be done ensuing proper compaction. The top surface is made true to level.


g Dewatering shall be done wherever necessary for laying concrete.


h Proper curing arrangement shall be made.

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8. WELL STEINING



8.1 OBJECTIVE: