Improper Backfilling of Structures

To

The Concessionaire

Subject: Improper Backfilling and poor workmanship working of CD structures- Reg.

Dear Sir,

Time and again, we would like to highlight the following deficiencies in your ongoing CD structure construction works

Backfilling are never being taken up as per Appendix-6 of IRC-78-2000/Clause 2907 of MoRT&H, inspire of our several verbal and written instructions.

It has been a standard practice of your EPC either not to provide weep holes where required at all or they are not being done as per the requisite.

The workmanship of the work for the CD structures are very poor (Honeycombs, lack of line and grade).

Now, you are being finally instructed to rectify your works with immediate effect else we will be forced to issue NCPNs.

This is for your information and necessary action.

Thanking you,

The Concessionaire

Subject: Providing & Laying of filter media (600 mm thick)and back filling behind the Abutment & Return wall and poor workmanship of at structures of Sec-1- Reg

Dear Sir,

In spite of repeated verbal and written instructions we had given to you, till date there are no actions taken for the compliance for these from your end. Again the same faulty things going on repeating for the new structures

Following are our observations in chainagewise.

1. At Ch.1+100 the work of super structure was in progress, but till date no choked weep holes are being cleared, also partial backfilling have been done without filter media.
2. At Ch.5+995 and 6+029 super structure work was nearly completion but backfilling have been done, without laying of 600 filter media.
3. At Ch.26+795 RHS super structure work is completed but till date no finishing has been taken up, resulting improper line and grades, creating unaesthetic look for the Structure

So, you are instructed to comply the above structured defects immediately

Thanking You,

Backfilling as per Appendix_6 of IRC-78 (FILLING BEHIND ABUTMENTS, WING AND RETURN WALLS of Structures)

A. FILLING MATERIALS

The materials to be used for filling behind abutments and other earth retaining structure, should be selected with care. A general guide to the selection of soils is given below

B. LAYING AND COMPACTION

• Laying of Filter Media for Drainage

• The filter material shall be well packed to a thickness of not less than 600 mm

• Shall place the material with smaller size towards the soil and bigger size towards the wall

• It provided over the entire surface behind abutment, wings or return walls to the full height.

• Note: Filter materials need not be provided in case the abutment is of spill through type.

C. Density of Compaction

• Densities to be aimed at in compaction shall be chosen with due regard to factors, such ast he soil type, height of embankment, drainage conditions, position of the individual layers and type of plant available for compaction.

• Each compacted layer shall be tested in the field for density and accepted before the operations for next layer are begun.

D. EXTENT OF BACKFILL

The extent of backfill to be provided behind the abutment should be as illustrated in Fig. 1

E. PRECAUTIONS TO BE TAKEN DURING CONSTRUCTION

• The sequence of filling behind abutments, wing walls and return walls shall be so controlled that the assumptions made in the design are fulfilled and they should clearly be indicated in the relevant drawings.

• For example,if the earth pressure inf ront of the abutment is assumed in the design, the front filling shall also be done

• simultaneously along with the filling behind abutment, layer by, and in case the filling

• behind abutment before placing the superstructure is considered not desirable, the filling behind abutment should also be deferred to a later date.

• In case of tie beam and friction slabs, special care shall be taken in compacting the layer underneath and above them so that no damage is done to them by mechanical equipment.

• Special precautions should be taken to prevent any wedging action against structure, and the slopes bounding the excavation for the structure shall be stepped or strutted to prevent such wedging action.

• Adequate number of weep holes not exceeding one metre spacing in both directions should be provided to prevent any accumulation of water and building up of hydrostatic pressure behind the walls. The weep holes should be provided above the low water level.

The cross drainage work space trenches shall be backfilled immediately after the pipes have been laid and the joint material has hardened.

About the material:

• The type of backfill soil shall be clean, free from boulders, large roots, excessive amounts of sods or other vegetable matter, and lumps.

• Moreover it shall be approved by the supervision consultant or Engineer.

Backfilling Procedure:

• Backfilling upto 300 mm above the top of the pipe shall be carefully done.

• The soil thoroughly rammed, tamped or vibrated in layers not exceeding 150 mm.

• Particular care being taken to thoroughly consolidate the materials under the haunches of the pipe.

• Approved pneumatic or light mechanical tamping equipment can be used.

• Filling of the trench shall be carried out simultaneously on both sides of the pipe in such a manner that unequal pressures do not occur.

At higher embankments:

In case of high embankment, after filling the trench upto the top of the pipe in the above said manner, a loose fill of a depth equal to external diameter of the pipe shall be placed over the pipe before further layers are added and compacted.