HIGHWAY GUIDE – Page 3 – HIGHWAY GUIDE

Contract Review Procedure

1. Summary
1.1. This procedure defines the process and methods of reviewing contract , and for verifying the project which meets the requirements.
1.2.The contract department is responsible for implementation and management of review activities.

2. Procedure
2.1.Once the contract has been awarded, the Estimating Department generates a “Contract and Specification Review” form which contain the following:
• The contract
• Specifications
• Specific documents and requirements related to production
• General notes
• Project specific work instructions & Circular
• Requirements from the contract or specification that vary will be highlighted, and copies of that will be distributed to the appropriate processing departments.
• Once the designated departments have reviewed the documents, they will sign in the appropriate space, commenting if desired, and return to the QS department. A completed “Contract and Specification Review” sign-off form will demonstrate a complete review.
2.2. Throughout the project, revisions to contract documents will be reviewed with the original Estimate and the Project Coordinator will ensure compliance with the contract documents. The potential cost and/or schedule impacts to the project will be determined based on any changes.
2.3. These subsequent reviews are documented by memo or other suitable means and are routed with a new generated form to any function that is affected by the change to inform and solicit input. The final result’s filed within the job folder.
2.4. The QS department will attach the completed form to the Estimator’s budget sheet(s) and place them in the job folder. The job folder is then furnished to the Project Coordinator for project assignment.
2.5. The Project Coordinator/Vertical head will assign a Job Number to the project and make four copies of the form and re-distribute to all functions.

GIRDER LAUNCHING

Transportation, unloading and erection of the precast prestressed concrete girders shall be done under the direction of experienced engineer he should be present for all stages of girder loading, unloading and erection. We have divided all these process into 7 sections

1.OBJECTIVE:

This methodology describes a detailed procedure for the erection of PSC Girders. Minor changes to the methodology would be adopted to suit the site conditions.

2.SCOPE OF WORK:

The scope of this methodology covers Lifting, Transportation and Erection of PSC Girders for all Flyovers & Bridges.

3.RESPONSIBILITY:

The responsibilities of the entire operation shall be assigned to a Senior Officer of the company who shall take care as an In-charge regarding all

4.MANPOWER:

A) Personnel to be deployed for smooth conducting work
Section In charge-01 No’s
Site Engineer/Site Supervisor-01 No’s
Fore Man-01 No’s
Segment man-02 No’s
Rigman-04 No’s
Kalasi-06 No’s
Crane Operator-2 No’s
Hydra Operator-2 No’s
B) Personnel to be deployed for safety during work

Officer Safety-01 No’s
Supervisor Safety-01 No’s
Marshal Man -02 No’s

5. MACHINERIES :

Modular Trailers with capacity of 60 MT (2 Nos.).
Tyre mounted 180 MT crane with Telescopic or Lattice Boom (2 Nos.)
Tyre mounted mobile 80 MT service crane (1 Nos.)
Pilot van (1 No.)

6.0 CONSTRUCTION METHODOLOGY

6.1 PREPARATION OF SITE AT ERECTION POINT:-

Following points to be ensured:-

The site of erection and the approach to be leveled, dressed and rolled (if required) so that the machineries viz; cranes and trailers move and can be placed on s firm ground in correct position.
Overhead obstruction (if any) to be removed.
Adequate Area lighting to be provided for work at night.
Proper and safe access to be arranged for supervisory staff to climb up to the top of Pier Cap to check correct alignment/ level of girder when erected.
All lifting tackles viz; Slings, D- Shackle, U clamp ropes and temporary packing viz. wooden block etc. to be checked regarding the Quality/ Soundness and kept near site.

6.2 LOADING OF GIRDER AT CASTING YARD:-

Following points to be ensured:-

The girders are to be loaded at the casting yard either by the help of Mobile Cranes.
The site where the girders are to be loaded on to the trailer to be dressed leveled and rolled (if required) for smooth and safe movement of trailers and cranes.
After girder is loaded on to the trailers, the same is to be securely tied at two ends (near support) so that the same doesn’t tilt during transportation.
Girders to be loaded for erection are to be identified and checked carefully regarding length etc. so that there is no mistake regarding the sequence to erection.
The engineer shall check the identification mark, length and finishing of girders before loading on to trailers.
Lifting tackles viz; slings etc. to be checked and sleepers/ packing are to be kept in correct position before placing the girders on to the trailer.

6.3 ERECTION OF GIRDER:-

Before starting erection work the positions of trailer and the cranes are to be ascertained carefully to ensure that during lifting, swinging and placing on to the pier cap is done smoothly.
Before lifting the girders, the Radius and Angle of the crane booms to be checked to ascertain safe lifting capacity during erection.
The outriggers of the cranes must have proper supports/ packing so that during lifting, swinging and placing the girder, cranes remain stable.
Once the girder gets lifted from the trailer, it is to be moved out from the erection site so as to provide adequate space during erection.
The girders thus being erected to be placed directly on the Neoprene Bearing (which are to be fixed prior to erection in correct position and level). In-case the girder cannot be placed directly on the bearing the same is to be placed on Pier Cap on wooden sleepers and shifted to correct location by changing the position of the cranes.
Before removing the slings from the erected girders it is important to temporarily support the girders by the help of proper diagonal supports. When the second girder is erected in position immediate arrangement is to be made to tie two girders at the support and at the middle by proper tie member (i.e. Channels, Angles etc.).
The position of the cranes is to be changed for erection at each girder suitably as required.
Once all girders for one carriageway are lifted and placed in positions, cross diaphragm are to be cast so that temporary ties can be removed.

7.0 SAFETY:–

Safety during lifting, loading, transportation and erection is the most important and primary consideration of the entire operation. The following points need to be checked and ensured:-

Capacity of cranes, trailers, lifting devices and packing (wooden blocks) to be ascertained before use.
The approach for the cranes and trailers both at the loading and erection point must be leveled, dressed and rolled to ensure smooth and safe movement.
During transportation/ movement of cranes all care to be taken to ensure smooth traffic flow on the highway.
A Pilot van with flag/ batten light must escort the cranes and trailers during their movement.
Safety officer along with traffic marshals must be available during the entire operation to ensure safety.
All persons engaged must use P.P.Es viz. helmets, belts, gloves, shoes, jackets etc.

PLASTIC SHRINKAGE CRACK

In simple way ,when fresh concrete has been placed in forms, concrete undergoes a volumetric contraction while it is in plastic state (before the concrete has set). This is known as Plastic Shrinkage,

Plastic Shrinkage are so-called because they form while the concrete is still plastic, ie has not set. Rapid drying of the surface of the plastic concrete causes it to shrink and crack.They rarely occur near the edges of a slab as at those locations the concrete is usually free to move.It can starts after 30 minutes of concrete pouring or during finishing.Plastic shrinkage cracking rarely impairs the strength of a concrete element.

Main factors affecting plastic SHRINKAGE

The main reason behind plastic shrinkage cracking is considered to be rapid and excessive surface water evaporation of the concrete element in the plastic stage (freshly cast concrete) which in turn leads to the so-called plastic or capillary shrinkage1. Water/cement ratio: Low water cement ratio resulting high strength mixes resulting in early plastic shrinkage crack.2. Additives(Effect of superplasticizer on cracking): Higher doses of SP resulting in early crack. 3. Fines Content: More fines is liable to get plastic shrinkage crack.
4. Depth of the concrete section: Deeper concrete section is less prone to plastic shrinkage cracking

5. Curing measures- Poor or inadequate curing

6. Effect of coarse aggregate content on cracking – Reducing the amount of the coarse aggregate in concrete mix leads to more plastic shrinkage and higher cracking risk.

7. Type of cement – OPC 53 grade cement is very fine grinding and need more water to hydrate & liable to get crack.

Practice To Minimize The Plastic Shrinkage Crack

To minimize the incidence of plastic shrinkage cracking: Dampen the subgrade and formwork , ensuring that any excess water is removed prior to placing concrete.
In hot weather, lower the temperature of the fresh concrete by using chilled mixing water or any suitable method.
Do the concrete work , when temperature is below 35˚ C
Protect concrete surfaces from drying out by gunny bags or suitable means
Commence curing regime promptly after finishing and continue for the specified period.
Revibrate the concrete or use towel with pressing into the concrete and make finish before hardening the concrete.

DETERMINATION OF QUANTITY OF WATER ADDED , FOR REQUIRED COMPACTION OF SUB GRADE & EMBANKMENT

Example: A soil in the borrow pit is at a dry density of 17 kN/ m³ with a moisture content of 10%. The soil is excavated from this pit and compacted in a embankment to a dry density of 18 kN/ m³ with a moisture content of 15%. Compute the quantity of soil to be excavated from the borrow pit and the amount of water to be added for 100 m³ of compacted soil in the embankment.

Ans :Volume of compacted soil = 100 m³ & Dry density of compacted soil = 18 kN/m3

Weight of compacted dry soil = 100 × 18 = 1800 kN. This is the weight of dry soil to be excavated from the borrow pit.

Weight of wet soil to be excavated = 1800 (1 + w) = 1800 (1 + 0.10) = 1980 kN.

Wet density of soil in the borrow pit = 17 (1 + 0.10) = 18.7 kN/ m³

Volume of wet soil to be excavated = 1980 / 18.7 = 105.9 m³

Moisture present in the wet soil, in the borrow pit for every 100 m³ of compacted soil

= 1800 × 0.10 = 180 kN

Moisture present in the compacted soil of 100 m³ = 1800 × 0.15 = 270 kN

Weight of water to be added for 100 m³ of compacted soil = (270 – 180) kN = 90 kN

= 90/ 9.81 m³ = 9.18 kl

METHOD STATEMENT OF PILE CAP

A pile cap is a thick concrete foundation rest on concrete or timber piles that have been driven into soft or unstable ground to provide a stable foundation. It usually forms part of the foundation of a building or structure or it is the uppermost portion of a pile which acts to secure the piles in position and receive and distribute superstructure loads.

In this article we will discuss the method statement of pile cap in detail with the help of following section:

Equipment
Procedure
Safety

1.EQUIPMENT

Excavator
Dumpers
Batching Plant
Transit Mixers
Truck / trailer
Welding Generator
Concrete Vibrators
Concrete Needles
Jack hammer
Compressor
Crane / Hydra
De-watering Pump

* As per site condition above mentioned equipment can be increased or decreased.

2.Procedure

a.SURVEY:

Before commencing excavation, the pile cap area shall be marked on the ground after carrying out survey with reference to control points. After excavation the levels of the pit shall be checked for correctness to the drawings and recorded. Longitudinal and transverse centerlines shall be marked outside the pit for reference for cross checking the pile. The shift of pile shall be recorded by marking the theoretical coordinates of pile on ground and circle of equivalent to pile diameter shall be drawn and shift of actual pile will be measured from theoretical edges of pile. The as built details of the piles shall be recorded jointly. Based on shifted location of pile top, pile Cap / P.C.C. layout shall be marked to ensure minimum 150 mm offset from outer edge of pile. After laying of PCC, the layout of the pile cap shall be marked on it with reference to the reference points to facilitate tying of rebar and erection of shuttering.

b.EXCAVATION:

Shoring shall be provided depending upon the stability of the soil found in the area. Shoring shall be done with the help of old steel plates and props. At road locations the pit shall be excavated to the dimensions providing working space all around the pile cap, to facilitate fixing of steel & erection of shuttering as detailed in the drawings. The last 300 mm excavation shall be carried out manually & leveling course shall be laid down within 36 hrs after completing excavation of last 200 mm depth. Provision for sump shall be made at the comer of the pit to pump out underground water of about 750 mm deep from PCC bottom. Also an earthen drain of about 200 mm width if required shall be provided all around pile cap dimension & it shall be connected with sump to drain off excess rain water/seepage water to ensure that the water table will at least 300 mm below the lowest level of the excavation before laying PCC. The excavated earth shall be then disposed by means of trucks / loaders.

c.REMOVAL OF LAITANCE:

After excavation the laitance of the piles shall be removed by using Pneumatic Jack Hammers seven days after casting of pile or manually three days after casting of pile. The top of pile after striping shall project 50 mm into the pile cap and reinforcements of pile shall be fully anchored in pile cap as per clause 709.5.2 of IRC: 78:2000. The debris of broken concrete shall be removed from the pit and disposed off to approve dumping sites. Exposed bars shall be straightened & cleaned properly with wire brush.

d. PCC:

After leveling the bottom of the bed, sprinkle some water to keep the soil moist. PCC of Mix M15 or specified in drawing shall be mixed at the centralized batching plant at the casting yard and transported to site in transit mixers. The concrete shall directly pour through chutes from three locations, shall be spread and leveled manually to the specified thickness shown in the drawing. PCC edges shall be projected 100 mm more than that of pile cap as detailed in the drawing to facilitate the fixing of form work and levels of PCC shall be jointly checked & verified. The PCC shall be cured by sprinkling water.

e.REINFORCEMENT

a) Fabrication: For fabrication of reinforcement, BBS shall be prepared as per the “Good for Construction” drawings. The Reinforcement shall be cut using cutting machines or manually as required and bent at Rebar yard. The re-bars shall either be transported to location in trailer / truck or cutting bending may be done at site depending upon the situation.

b) Fixing of Re-bars:

The re-bars shall be manually fixed into its position as shown in the good for construction drawing. Reinforcement of pile cap shall be lapped with the reinforcement of pile. Cover blocks of same grade of concrete in which these are to be embedded shall be provided at spacing of about 2.0 m c/c to ensure uniform cover as specified in the drawing and tied together with GI binding wire. After fixing the pile cap rebar, pier shaft rebar shall be erected. This rebar shall be supported by erecting a suitable staging frame across the width of the pile cap. The rebar cage shall be checked as per checklist given in QA manual and RFI for inspection shall be raised with IE. The rebar, chairs, spacers & laps shall be jointly checked after completion of cage placing. Sufficient chairs and spacers shall be provided to keep the cage in its proper position. After getting the clearance, balance shuttering work will be taken up. Pier dowels shall be hold in position rigidly to prevent it from buckling.

f.SHUTTERING

Shuttering fabricated as per approved drawings shall be placed at locations as per the pile cap dimensions shown in the good for construction drawing. Reinforcement shall be fixed as per the drawing and marking the layout on PCC for pile cap. After completing the fixing of rebar cage shuttering shall be erected & fixed on the layout drawn on PCC. Before fixing, the shuttering area shall be cleaned with wire brush & approved shuttering oil shall be applied on concrete face. After fixing of shuttering it shall be checked as per QA checklist and RFI to be raised for inspection of IE. For preventing leakages from joints, rubber strip/foam strip shall be provided at the joints of shuttering plates. Proper side supports/bracings/tie bars shall be provided to resist lateral pressure of green concrete during pouring.

g.CONCRETING

The required (M-35) grade concrete shall be produced as per the approved concrete design mix from the centralized batching plant and transported by transit mixers to the pouring location. Before pouring concrete, slump of 80 mm to 130 mm shall be checked at pouring location. The concrete shall be placed by concrete pump /placer boom or by direct chutes. Concrete placing commences from one end to another in cascading manner till completion. The drop height of the concrete should not be more than 1.5 m. The concrete shall be vibrated using 60 mm / 40 mm diameter needle vibrators. Concrete cubes shall be taken for testing of compressive strength as per IRC 21 at pouring location. Concreting should be done in such a way that next layer of concrete should be laid before initial set of concrete of previous layer to avoid cold joints. Regular tamping shall be done during & after concreting operation.

h.CURING

Date of concrete shall be written on the concrete surface to ensure curing up to the specified duration after date of casting.

The concrete shall be cured by ponding method. Bunds of cement mortar of lean mix shall be built after the concrete attains final setting time after casting of concrete, these bunds shall be filled with water from approved source. The sides of the pile cap shall be covered with Hessian cloth till back filling is started. Further curing is ensured by keeping the backfill moist with water.

i. BACKFILLING

Immediately after de-shuttering, concrete surface shall be checked jointly and get the approval for backfilling. Back filling with local earth available or excavated material shall be carried out in layers of 250 mm (compacted thickness).(as per MORT&H clause no – 304.3.7)

The compaction shall be done with the help of suitable equipment such as rammer or plate vibrator etc., after necessary watering, so as to achieve a density not less than required field density .

j.MISCELLANEOUS WORKS

After backfilling the damaged roads, if any shall be repaired immediately preferably within 15 days of backfilling as per specification before removing of the barricades, the whole area shall be cleaned after completion of work.

SAFETY:- All safety precautions shall be taken as per safety manual submitted by us. Further the preparatory works shall also be carried out as per Diversion plans separately submitted for construction activities on urban areas.

1.A width of approx.8.00 m (outside to outside of barricading) shall be barricaded along road for purposes of construction of pile caps. This can be increased at specific location with prior approval of Engineer.

2.Suitable reflectors, blinkers, diversion board, painting of barricade etc. shall be done to caution the road users and for their safety. Working space shall be well illuminated during work at night.

3.All site personnel shall wear helmets, safety shoes and other safety devices as required.

4. Proper precautions and safety arrangements shall be used for activities like welding, handling of reinforcement, fixing of formwork, electrically operated equipment etc.

WHAT IS 90th PERCENTILE CBR

The kth percentile is a value in a data set that splits the data into two pieces: If lower piece contains k percent of the data, then upper piece contains the rest of the data means (100 – k) percent, because the total amount of data percentage is 100% where k is any number between 0 and 100 & median will the 50th percentile.

PROCEDURE
1. First of all arrange all values from smallest to largest.
2. Mulitiply the 90 percent with total number of data if multiplied product is not whole number, round them.
3. Rounding number will be the test data.(Smallest to largest) suppose it is 5
4. Then you go until you find the 5th value in the data set . This value will be 90th percentile. Lets take an example ,suppose 4 days soaked CBR for 10 test in percentage is 15.86,10.32,19.08,11.87,23.84,18.73,16.74,18.15,17.27 & 19.32
then simplified solution can be determined as below :

step 1. First arrange with smallest to largest value it will be
10.32, 11.87, 15.86, 16.74,17.27,18.15,18.73,19.08,19.32,23.84
Step 2. Multiply 10 by 90% i.e 10 x .09 = 9
Step 3. Counting from left to right (from the smallest to the largest value in the above CBR set), you go until you find the 9th value in the step 2 data sheet & this value is 19.32, and it’s the 90th percentile for this data set.

PILING METHOD STATEMENT

When the soil intended for the foundation is not capable of supporting a structure , deep foundations are required to transfer the loads to deeper strata. A pile is a slender structural member made of steel , concrete or wood.These days piles are more in trend rather than in well foundation .In this article we will discuss the typical method statement pertaining to pile.We had divided the method statement into 7 sections for easiness

1.Scope of Work

Equipment

Material

Method Statement

Tolerances

Routine Test

Integrity Test

Scope Of Work –This work consist of Pilling work -1200 mm dia. Bored piles Boring and Installation of 1200 mm dia .

Machineries/Equipment The following machineries shall be deployed at each working site.

Rotary rig -3
Augur of 1200 Size -3 Nos.
Drilling bucket of suitable size -3
Cleaning bucket (skip bases) -3
Crane 20 ton capacity -3
Slurry sampler -3
Metallic chain 25 m-3
Steel tape 30 m & spirit level plumb- 1 set at every site of
Jar& bucket and hydrometer – 1 set at every site of
Steel plate circular liner 6 mm thick and 5 m long -2 at every site or as required.
Steel rectangular tank of 20,000 litre capacity each -3 at each site,
Bentonite agitator with 3 HP motor -1 No at each
Flushing pumps 5 HP capacities -2 at each site.
Diesel pump 10 HP standby -1 No
Water tanker -1 No
JCB-1 No
Dumper/Tipper-2
Generator 62 KVA -1
Welding Transformer -2
Tremie pipes 200 mm of different lengths as required for proper concreting.
Hopper 4 M³ capacity with plug at each site.

Material

3.1 Bentonite – The betonite (drilling mud) shall be arranged of approved quality and shall be stored about 30 cms in water tanks , 5% of bentonite by weight of water may be used subject to ensuring appropriate density

Density of suspension =1.05 gm/cc
Silt content = <1%
PH value = 5 -12
Liquid Limit (not less than ) = 400

3.2 Concrete

Grade of concrete = M 35
Slump = 150 -200
Temperature = < 40°c
Minimum cement content = 400 kg./ M³
Maximum size of Aggregate = 20 mm

3.3 Reinforcement

T.M.T bars FE 415/500 shall be used. Reinforcement cage shall be fabricated after cleaning as per approved bar bending schedule.
Stiffeners as show in the drawings. and cover blocks prepared out of non – shrink mortar of approved quality shall be provided and reinforcement shall be tied with 18 SWG binding wire and welding may be done only where necessary after providing suitable lap length. The clear cover of 75 mm shall be kept.

Method Statement

4.1 Layout

The layout of piles shall be carried out with the help of Total Station only.
Grid /axis lines shall be established by total station as shown in the approved drawings and four Nos. reference points for each pile shall be established, in such a way so that these do not get disturbed during piling work.
The ground levels shall be recorded with the help of auto level and the length of the piles shall be evaluated.
The nomenclature of pile group shall be designated clock wise or Anti clock wise with specified location mentioning grid /axis.

4.2 Procedure

The pre-trenching shall be carried out to detect the utility (if any). Manual trenching in transverse and longitudinal direction shall be done near pile location up to about 2 m in depth or as required.
A circular pit shall be dug out for outer dia for steel casing manually for a depth of 1 m. The centre of pit shall be checked accurately from reference points.
Drilling by auger up to depth of casing shall be done.The steel casing shall be fixed with the help of rotary rig collar guide, truly in centre of hole as well as vertical.
The verticality of Kelli bar shall be checked by spirit level in two directions at bucket top level.
The casing shall be checked by plump bob also.
The verticality & levels are seen in cabin of Rotary Rig at Instrument display board.
Beyond casing depth of 5 m the drilling bucket shall be used.
The bentonite shall be mixed in tank mature for at least 8 hrs. before actual use and during feedings it shall be agitated.
The density of bentonite shall be checked during boring.
Verticality and depth shall be recorded as per Rotary Rig panel board.If it is not so, suitable measures shall be taken to rectify tendency of the bore to go beyond the centre point.
The cleaning bucket / skip box shall be used for the last 30 cms depth to achieve required founding level and for cleaning of mud.
The sounding shall be taken by using metallic chain.
The soil strata shall be recorded at every 3 m or at the change of strata.
Soil samples shall be kept for record in polythene bags marking the depth and pile no.
If there are chances of bore collapse, extra liner shall be provided upto a suitable depth.

4.3 Acceptance limits

Verticality – It shall not exceed 1 in 50.
Shift – The resultant shift in any direction from the location designed at cut off level shall not exceed 50 mm and shall be measured at pile cut off level.

4.4 Movement of Rig and Machines

The sequence of concreting of pile would be such that reference pillars are not damaged during movement or rig /machines.

4.5 Clearing of Bore Hole and flushing

The reinforcement cage duly welded at joints shall be lowered by crane. The cage shall be kept at the requisite level by suspending from collar.
Cleaning of the bore hole shall be done by the circulation of bentonite slurry of 1.05 gm/cc under high pressure through tremie pipe, which shall be kept max 150 mm above the bottom of bore.
During flushing the bentonite slurry shall be agitated and sufficient quantity of Bentonite Slurry shall be available.
This process shall be continued till the slurry at the bottom is of density 1.10 gm/cc .However care shall be taken to avoid bore collapse due to excessive flushing.
The slurry sampler shall be used to take the sample from bottom of the bore.
Concreting shall not be done, if density of bentonite slurry from bottom is more than 1.10 gm/cc.
The bentonite slurry carried out from bore, shall be pumped to next container so that the mud settles down.
The dugout earth and muck shall be removed immediately, and disposed off at approved disposal areas.
There shall be no over flow of slurry on road of working space.

4.6 Concreting

Concreting under water shall be placed in on continuous operation by tremie pipe So that concrete entering the tremie pipe shall not get mixed with the slurry.
The tremie pipe of minimum 200 mm dia with water tight joints using rubber seal shall be kept 200 mm above bottom of hole with attached hopper of 0.4 M³ capacity duly held by crane of 20 T capacities.
The approaches for movement of transit mixers shall be kept clean with suitable ramp near bore for easy pouring of concrete.
The 3 nos. of transit mixers shall be sufficient to maintain continuity of concrete, so that there shall be no interruption. The rate of pouring concrete shall be approximately 6M³ /hour.
First charge of concreting shall be done by using a stopper at the bottom of funnel. Stop shall be kept in such a way that it can be removed with least resistance.
The tremie pipe bottom shall be done by using a stopper at the bottom of funnel.
Pieces of tremie pipe shall be removed as per calculated depth of concrete. It shall be ensured that the end of the tremie pipe should always be in concrete to avoid slurry and muck mix with concrete.
If the delay during concreting is more than 2 hrs Cement slurry shall be used for mobilizing concrete inide the tremie pipe.If concrete pouring is delayed due to any reason.
The bentonite slurry shall be re-circulated to avoid settlement of suspended particles of earth. The sounding shall be taken after each load of concrete.
The slump test and concrete cubes shall be casted from each transit mixer as specified for concrete work.
The actual quantity of concrete if less than 10% of theoretical consumption shall be immediately reported to EIC.
The length of concrete above cut off level shall be at least 1.00 m.

4.7 Removal of guide casing

Casing shall be extracted by smooth pull and push movement.
Precaution shall be taken that concrete and reinforcement are not disturbed.

4.8 Breaking of pile head

The breaking of extra concrete shall be done after a minimum of 7 days of concreting.
The breaking can be done by pneumatic jack hammer or manually as per Direction of Engineer in charge.
The pile shall be cut off as indicated on drawing
The exposed reinforcement shall not be damaged while breaking the pile head concrete.
All dismantled material shall be disposed off at approved disposal areas.
The height for 150 mm above cut off level shall be chipped off manually to avoid damage to pile.

Tolerances

Variation in diameter + 50 mm -10 mm
Variation from vertical -1 in 50
Variation in final position of head in plan =50 mm
Variation in level of top of pile +25 mm

Routine Test

General arrangements for routine vertical test shall be made according to IS 2911 (P-IV).
Routine load test shall be carried out for 1.5 times of working load to determine the Safe load on pile.Safe load on pile shall be 2/3 of the load at which settlement is 12 mm.
The pile to be tested shall be selected by Engineer in Charge from any working pile groups.
The pile shall be tested after concrete achieves designed concrete strength.
Datum bar made out of MS Channels of size 125 mm shall be fixed on both side of the main girder such that the clear distance between the supports is at least a distance of 3D (D being dia of pile ) from the edge of the pile. Care shall be taken to ensure that the Datum bars do not get disturbed during loading.
Breaking of false concrete shall be done upto a level 50 mm above cut off level. The pile head shall be build up using non – shrink mortar.
The sub grade shall be built upto required level by properly compacting. approved kentledge arrangement shall then be placed in position,
Placing of base slab and concrete blocks upto required width and level shall be carried out.
Bottom and top plate shall be placed over jack and stool packing packing plate if required shall be used to fill the gap between main girder and jack
Placing main girder over concrete blocks after maintaining required gaps for settlement of secondary girders.
Level and weld the kentledge wherever necessary concrete fill shall be done in gap of concrete block and base girders.
Loading of blocks shall be done in layers as per drawing upto required test load plus 25% extra.
Concrete block in alternate layers shall be secured with 16 mm Ф wire rope and turn buckle after erecting scaffoldings.
Adequate precaution shall be taken for safety of adjacent traffic viz placing caution boards, barricades, blinkers, flags etc.
Four nos. dial gauges (deflect meters) shall be fixed from datum bar at four corners of the pile head. The least count of these shall be 0.001 mm
All the pressure gauges, dial gauges shall be tested and calibrated before use.
Increment of load shall be @ 20% of design load .
Increment of test load and displacement in each stage of load shall be maintained till rate of displacement of pile top is either 0.1 mm in first 30 min. or 0.2 mm in the first Hour or till 2 hrs which ever occur first.
The final load of 1.5 times the design load shall be maintained for 24 hrs.
The load shall be released and rebound shall be recorded.

Integrity Test

Pile integrity test shall be carried with electronic analyzer.
The test shall be carried out by approved agencies.
The test shall be carried out on 10% of working piles.
Records shall be submitted with recommendation.

METHODOLOGY FOR PRESTRESSING

The technique of precasting is eminently suited to bridge girder for quicker construction and minimum interference to traffic below the bridge. The girder my be cast in a central plant or in a temporary yard established near the work site. Girder upto about 40 meter can be precast in a single piece transported to site by means of truck cranes.In this article we will discuss pertaining to stressing and prestressing of girder methodology.

REFERENCE DOCUMENTS/CODES/DRAWINGS

1.MORT&H 5th Revision
2. IS: 14268 Stress Relieved Low Relaxation 7 Ply Strands for Prestressed Concrete.
3. IS: 210 Grey Iron Casting – specification
4. BS: 970 Specifications for Wrought Steels for Mechanical & Allied Engineering Purposes.
5. IRC: 18-2000 Design Criteria of Prestressed Concrete Road Bridges (Post-tensioned Concrete)
6. Relevant Prestressing Drawings (Latest Revisions)
7. Specifications Related to Prestressing Work

PRESTRESSING MATERIALS

• High Tensile Strands
Following are the properties of 12.7 mm Ø Low Relaxation High Tensile Strands. Oiled strand shall be used –

Nominal Area of Strand – 98.7 mm 2
Minimum Breaking Strength – 183.7 KN
Nominal Weight of Strand – 0.775 kg/mtr.

• SHEATHING PIPES

We are giving typical sheathing pipe , use pipe as per your project specification
84 mm ID & 98 mm OD & 2 mm thick HDPE sheathing pipes for 19 DP13
75 mm ID & 90 mm OD & 2 mm thick HDPE sheathing pipes for 12 DP13
51 mm ID & 64 mm OD & 2 mm thick HDPE sheathing pipes for 7 DP13
Sheathing duct shall be made up of HDPE of thickness (2.3 mm ± 0.3) mm with following properties –

• Approved 19 DP 13,12 DP 13 & 7 DP 13 Live end Anchorage System(Use Project approved brand)

The precast segment will be cast in casting yard. After curing is over, the segment will be shifted to the respective position and will be assembled with the help of launching girder. The high strength epoxy will be used for gluing two segment together and it will be stressed by high tensioned bar. After final stressing, temporary stress will be released

Tube Unit (Anchor Cone)

The basic raw material for manufacture of tube unit is gray cast iron. It allows the transfer of prestressing force from the bearing plate to the concrete. The Tube Unit is embedded in concrete and can be easily fixed to the MS cone box by means of bolts and nuts. The design of Tube Unit allows uniform flaring of H. T. Strands while stressing and free access to the injection of grout.
Anchor Head (Bearing Plate)

The basic raw material for manufacture of bearing plate is Steel casting / forged steel. The conical holes facilitate the seating of wedges and holding the strands in stressed condition.

Wedges
The basic raw material for manufacture of wedges is alloy steel. The individual high tensile strands passing through the bearing plate is anchored by the wedges. The 3 segments of the wedges are held together around the strand by means of special wire circlips for better functioning, easy placement and storage

Prestressing and Grouting is broadly divided into following activities, viz.,

1. Layout & Profiling of the cables/sheathing.

2. Fixing of tube unit/end block.

3.Concreting

4. Cable cutting and threading.

5.Fixing of Bearing plate & Wedges.

6. Stressing.

7. Cutting and end Sealing.

7. Grouting.

1. LAYOUT & PROFILING OF SHEATHING PIPES

After completion of alignment of bottom shuttering & bottom reinforcement of girder, layout & Profiling of cables shall be carried out in following steps :

• Layout of cables is carried out as per given ordinates & related reference drawings.
• After all ordinates are plotted, tie bars of 10 mm. dia. shall be installed as per ordinates to place the sheathing pipe wherever required. Installation of sheathing pipe is carried out over the tie rods.
• Sheathing pipe shall be supported in the bottom by tie rods & shall be cross bound using double binding wire. It should be ensured that the sheathing pipes are fixed firmly in position so as to prevent displacement during concreting by weight of concrete, vibration or by floatation.
• Connect the sheathing with the help of couplers provided at the end of each pipe.
• Sealing of sheathing joints will be done using PVC tapes. It will be ensured that no joints are remaining unsealed.
• Cable profile shall be checked. Vertical ordinates shall be check from soffit of the bottom shutters. Horizontal ordinates shall be check from the face of the side shutters, which has been already checked for verticality or as in drawing.

2. FIXING OF TUBE UNIT

• Fixing of tube unit shall be carried out after installation of end shuttering plate.
• Fix tube unit to End plate with the help of 4 nos. of bolts.
• Bursting reinforcement shall be fixed according to the drawing.
• Connecting the tube unit to sheathing pipe.
• Joint shall be sealed with the help of PVC tape.
• The face of the tube unit shall be truly perpendicular to the axis of the cable and about 1.5 m of cable before trumpet should be in straight alignment.
• After the fixing of tube unit and cable layout, insert the HDPE pipes Or HTS Strand inside all ducts to avoid the damage of sheathing pipe & ingress of cement slurry inside the duct at the time of concreting.

3. CONCRETING

• Although concreting is not a part of stressing but it has very important role in successful completion of stressing of structure.
• It shall be noted that the needle vibrator is not placed directly on sheathing pipe, which may damage the sheathing pipe.
• HDPE pipe Or HTS Strands in all the cables should be moved in both directions during the period of concreting.
• More attention should be given while concreting in the end block portion. Adequate compaction of concrete to be ensured to avoid any kind honeycombing.

4. CABLE CUTTING & THREADING

After completion of concreting & removing end block shuttering, cable threading shall be done.
• H. T. Strands shall be threaded manually.
• For cutting strands, a portable grinding wheel shall be used.
• H. T. Strands shall be cut as given in drawings, considering site conditions & gripping length of jack.

5. FIXING OF BEARING PLATES & WEDGES

• Fixing of bearings plates & wedges is done before stressing. It is ensured that the tapered holes in bearing plates & wedges are free of rust.
• Insert the strands into the tapered holes provided in the bearing plate.
• Install the wedges over the strands and push them with a pipe into the tapered holes of the bearing plate.

6. STRESSING

Prestressing of the girder is done as required by the system of prestressing and design. Following points will be observed while carrying out the stressing operation.
Only trained and experienced personnel, under the guidance of technical Staff, should perform stressing & grouting.
• The required strength of the girder concrete as mentioned in drawings/specifications shall be ensured by cube testing before starting the stressing work.
• Stressing of cables shall be done as per the sequence mentioned in the drawings/specifications.
• The first stage stressing shall be done after the concrete achieves 35 Mpa strength or 10 days after casting, whichever is earlier. In the first stage two cables shall be stressed viz. cable no. 1 & cable no.2 or as shown in the drawing.
• In the second stage stressing balance two cables i.e. cable no. 3 & cable no. 4 shall be stressed after the concrete achieves 45 Mpa strength (28 Days strength ) or 21 days after the casting, whichever is later
• Elongation mentioned in the drawings must be modified for actual value of modulus of elasticity ‘E’ and the area of c/s of strands ‘A’ of the cables as per the results unless otherwise mentioned in the drawings/specifications.
• Actual pressure shall be calculated after applying Jack efficiency factor.
• Stressing shall be done using Multi-pull jacks only.
• Stressing shall be done from both ends, care will be taken to achieve almost equal readings of elongation at both the ends in each step of increment of pressure.
• Readings will be taken preferably at incremental steps of 50 kg/cm2 up to the final pressure.
• After locking the wedges the pressure in the jack will be released very slowly to avoid transfer of prestressing force by impact.
• In every cable instantaneous slip of anchorages must be recorded. It will be within limits prescribed by the designer or by the prestressing agency.
• The pressure applied and elongation achieved will match within the prescribed limits. Normally, the limit is 5% of pressure and elongations.
• No person will be allowed to stand behind the anchorages in any circumstances during the process of tensioning.

6.1 THE FOLLOWING STEPS SHOULD BE PREFERRED FOR JACK MOUNTING

Fix the bearing plates at both the ends of the tensions.
Insert the bearing collar & fix it on tube unit with the help of screws.
Insert the lock-off plate as per the orientation the bearing plate.
A rigid runaway beam (ISMC/ISMB) structure shall be made at the end of the bridge girder from where the Jack is to be suspended by means of a chain pulley block. The arrangement will give full flexibility of movement of Jack both transversely and longitudinally.
Push the Jack over the strands. The axis of the Jack must coincide with the tendon axis. Insert the strand in to the Jack.
Apply “wax” inside the holes of pulling plate as well as outside of master grip.
Install the 3-piece wedge (master grip) over the strand into the pulling plate inside the rear of the Jack. Push the grips with a piece of hollow hammering pipe to seat tightly inside the pulling plate holes.
Ensure all connection of Jack with pump is correct and flexibility of hose pipe for movement of the Jack at the time of stressing.
It is important that the supporting chain or hook shall be slackened off as soon as the Jack starts to carry load, but they must be ready to support the Jack again when the pressure is released.
Locking pressure should be maintained approximately 70-80 % of the stressing pressure.

7.0 CUTTING AND END SEALING

Cutting should be carried out after checking the 24 hrs. slip loss. Strand should be cut approximately 40 mm. from the face of bearing plate. End sealing should be done with the help of GROUT CAP or Epoxy & cement Mortar (Mounting the ends) .

7.1 GROUT CAP :

The advantages of using Dynamic Grout Cap are used for speedy grouting and saving of sealing material i.e. cement mortar.

7.2 FIXING OF GROUT CAP

The stressed strands are cut to the required length i.e. 40 mm. from the face of bearing plate.
On the inner surface of cap, grease should be applied.
‘O’ ring should be placed in the slot provided along the periphery of the cap, which maintains the pressure and prevents the leakage of grout.
Grout cap is fixed by 4 nos. of allen key bolts by keeping the air vent nut in top position.

GROUTING

Neat cement slurry should be filled in the annular spaces between sheathing duct & high tensile (H.T.) steel/strands.

8.1 OBJECTIVES OF GROUTING :

1.To protect the steel against corrosion.

2.Effective bond between the Prestressing steel and concrete.

8.2 MATERIALS FOR GROUTING :

(A) CEMENT:

Ordinary Portland cement should be used for the preparation of the grout. I. The cement shall have no false setting phenomenon and shall be at a temperature less than 40 °C at the time of production of grout. The cement should be free from chemical impurities like chloride and sulphate, which leads to corrosion of steel.

(B) WATER:

Clean potable water, free from impurities shall be used. Sea or Creek water shall be strictly avoided.

(C) ADMIXTURE :

While designing grout mix , we are using Sika (Intraplast N 200) 0.4 % by weight of cement). to reduce shrinkage of grout.

8.3 WATER – CEMENT RATIO

Choose Water-cement ratio as low as possible , consistent with workability. This ratio should not normally exceed 0.45. We are keeping 0.39 as per site condition.(Can select W/C ratio as per your convenient)

8.4 GROUT TEMPERATURE

Generally, the temperature of the grout must be 25 °C. It is likely to change depending upon the site conditions. When the ambient temperature during the day is likely to exceed 40 °C, grouting shall be done in the early morning or late evening hours.

8.5 TESTS ON GROUT MIX

The characteristics of the grout are determined on the grout itself or on samples made from the grout in accordance with the following.

Fluidity
Bleeding
Volume Change

8.6 GROUTING PROCESS

Following points will be observed while doing the grouting.

Grouting of cables shall be done as early as possible, after completion of stressing.
All cables that are to be grouted shall be cleaned thoroughly with water & compressed air.
The grout mix is prepared in the agitator by thoroughly mixing it for 1 min.
The agitator must be placed at a height such that mortar can flow directly in top second tank placed beneath the outlet of agitator.
Before flowing in to the second tank mortar must be passed through a 2 mm. mesh screen so as to eliminate impurities and lumps which otherwise cause choking of the pump at the time of grouting process.
Connect the suction hose of grout pump to the second drum.
Operate the pump to drain off water from the pump and hoses.
Allow discharge of a small quantity of grout from delivery hoses to check the correct functioning of pump.
Connect the delivery hoses to the tube unit’s grout inlet opening and begin grouting.
Ensure that there is always enough grout in tank so that air is not sucked in to the pump.
When the grout flows out of the dead end tube unit’s grout opening, open the air vent nut of the grout caps of both the ends.
Block the outlet of the other end after being assured that the air has been completely bleeded and the duct is filled with grout.
Close the air vent nut and operate the pump until the desired pressure is achieved.
After the design pressure is achieved, stop the pump and maintain the pressure of 3-5 Kg/cm²for 1 min. and close the valve of inlet connector.
Release the pressure in hose. The pump runs idle and returns grout to the tank.
Clean the grout pump & agitator with clean water to z avoid clogging.

8.7 END PROTECTION OF ANCHORAGES

Tendons shall be protected against corrosion by a plug at each end to prevent passage of air. After grouting is over the anchorages will be protected for corrosion as under –

Clean the exposed anchorage parts for rust and dirt with wire brush manually.
Clean the surface with cotton waste & apply a coat tar epoxy (solvent free araldite)

9 SAFETY PRECAUTIONS

9.1 Safety Precautions While Concreting

Although concreting is not a part of prestressing, it plays a vital role in successful stressing of structure. Following points should be considered while concreting

Main contractor should ensure that vibration is to be supervised. It should be noted that needle is not directly placed on sheathing pipe, which may damage the duct & thereby blocking the path of strands.
The portion of the end block of the girder should be properly concreted. Weak concrete leads to puncture of tube unit & hence stressing should be done only if concrete is capable of taking the load.
It should be ensured that the bursting reinforcement in the end block zone is adequately & properly installed.

9.2 Safety Precautions While Stressing

Very large forces are introduced into the tendons during stressing and the equipment is under high hydraulic pressure. Hence, careful working can avoid accidents.

Only trained and experienced personnel, under the guidance of Dynamic technical Staff, should perform stressing.
The equipment, especially the high pressure hoses and the adaptors must be in perfect condition. Damaged hoses must be replaced immediately.
Jack should never be handled by hoses.
Stressing should be done according to specified data. The allowed maximum pressure should never be exceeded.
During stressing, nobody should be allowed behind or underneath the jack, since failure of a strand can cause fatal accidents.
For stressing close to traffic areas, the jack must be secured by ropes or chain hoist.
All bars, wires and strands should be stored carefully. Ensure that they are not damaged in any way and should be checked for rust and corrosion before they are used.
Care should be taken while handling coils of high tensile steel strand as they may ‘whip back’ with force, if not securely bound.
Hogging of the girder during stressing operation should be observed & recorded.

9.3 Safety Precautions While Grouting

Protective glasses must be worn during grouting operation.
Do not start the pump while valves are closed, it may cause damage to the pressure gauge.
Place the grout tank preferably at the same level of grout pump.
In case of a longer stoppage (more than 5 min), ensure that the grout does not get set in the pump, if necessary empty the grout and flush the pump with water.

DETERMINATION OF SAFE BEARING CAPACITY OF SOIL WITHOUT PLATE LOAD TEST

In this article we will discuss with example on ‘How to calculate safe bearing capacity of soil on site ,when unit weight of soil , depth of foundation , width of foundation C & ɸ (Phi) value is given ? So what is bearing capacity of soil ? in simple way , bearing capacity is the load carrying capacity of the soil & bearing capacity after applying the factor of safety (FS) is called safe bearing capacity of soil. This vale is used for design of foundation. We can understand it with following example.

Q. A foundation in a sand is 5 metres wide & 1.5 metres deep. Considering factor of safety 2.50 what will be safe bearing capacity if the unit weight of sand is 1.9 gm/cc and angle of internal friction is 30 ˚. How does it compare with safe loading capacity for surface loading.

Ans: From chart ɸ = 30 ˚ Nc =37.2 , Nq = 22.5 , N ү = 19.7 , C=0 , Y= 1.9 t/m³ , b= 5 m , d=1.5 m
Safe bearing capacity =1 /F [ c Nc + ү. d (Nq – 1) + ½ ү b Nү] + ү .d

= 1/2.5 [ 0 x 37.2+1.9 x 1.5 (22.5-1) + 1/2 x 1.9 x 5 x 19.7] + 1.9 x 1.5

= 1/2.5 [ 0 + 1.9 x 1.5 x 21.5 + 0.5 x 1.9 x 5 x 19.7) + 2.85

= 1/2.5 [ 0 + 61.28 + 93.58] + 2.85

= 1/2.5 X 154.86 + 2.85

= 64.79 t/m²

If surface loading is there then d ( depth) will be zero then Safe Bearing Capacity

= 1/2.5 [½ үb Nү]

= 1/2.5 [ ½ x 1.9 x 5 x 19.7] = 1/2.5 x 92.63 = 37.052 t/m² hence we see that loading capacity of the foundation is 1.75 times more than surface loading capacity

METHOD OF TEST FOR MEASUREMENT OF SPREAD OF BINDER FOR PRIME COAT & TACK COAT

The layer between Bituminous Course and Crushed Aggregate Base Course (WBM & WMM) is called Prime Coat. Its purpose is to bind the loose aggregates of (WBM & WMM) so that it can be prepared for subsequent construction activity of laying bituminous layer.

The thin layer between two bituminous course is called Tack Coat. The purpose of Tack Coat is to form a bond between two bituminous layer. There is certain specification mentioned in any project for rate of application of Prime coat & Tack coat.

For measuring that application rate of Tack Coat & Prime Coat , we shall have a Aluminium or any other suitable light tray with dimension 200 mm(L) x 200 mm(B) x 20 mm(H) . A set of three plates are essential for this test.

Procedure :

1. Weigh all the three trays & numbered them.
2. Place these trays along the road in path at 10 metre interval between wheels of distributor.
3. Now pass the distributor .
4. After distributor crosses a length of 50 metre , remove the tray.
5. Immediately without losing time , weigh them to the first place of decimal.
6. Fill all readings into the format.
Take the average of them & compare with the specification. If more are less result is obtaining , adjust the speed of distributor .

Reference : IRC 2008

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