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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