MS-08-BF

1.0 General

This work shall consist of the necessary excavation & backfilling for foundations of bridges, culverts, retaining walls, head walls, wing walls, drains and other structures.

2.0 Reference

Volume 2: - Technical Specifications: Part I - Standard specifications; Chapter 302, 304 & 705 Part II - Special Provisions; Chapter 302, 304, 705

3.0 Resources

3.1 Material

No. Material Specification

1 Type II embankment material Clause 1708.1 of special provisions & standard specification

2 Type I embankment material Clause 1708.1 of special provisions & standard specification

3 Sub base material Clause 1708.2 of special provisions & standard specification

4 Aggregate Base Course Clause 1701.3 of special provisions & standard specification

3.2 Equipments / Machinery (one unit)

No. Equipment / Machinery Q’ty Remarks1 Backhoe Loader 1 For excavation

2 Tipper / Farm tractor 1 For transporting material

3 Water Bowser 1 For water supplying

4 Rammer 1 For compaction

5 1 Ton Roller 1 For compaction

6 Soil Testing Equipment 1 For checking compaction

3.3 Manpower (One unit)

No. Job Title Q’ty Remarks1 Work Supervisor 1

2 Labour 5

3 Lab Technician 1

4 Lab Helpers 2

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MS-08-BF

4.0 Flow Chart

5.0 Sequence of work

Step 1 - PreparationPrior to commencement of excavation, the limits of excavation shall be set out as shown in drawings by using timber pegs & string. The depth of excavation shall be as shown in the drawings or as directed by the Engineer. If it is necessary, exposed surface of excavation shall be protected by erecting all necessary shoring, shuttering or timber planking. Prior to commencement of backfilling, all loose material and any debris shall be removed from the area to be backfilled. The bottom of the area to be backfilled shall be leveled and compacted to get even surface. Backfilling shall be commenced after 7 days of construction of the concrete or masonry work.

While backfilling work is in progress behind earth retaining structures, 300 mm*150 mm clay puddle shall be placed at the bottom level of the weep holes. 100 mm crushed aggregate backfill shall be placed along the wall and the filter medium of 37.5 mm graded aggregate shall be placed along the sloping face of the aggregate backfill as shown in the construction drawings. The material shall be compacted using a hand tamper.

Step 2 - Placing and Compacting of materialApproved embankment material type I and type II shall be transported and placed in layer not exceeding 225 mm loose thickness. Excavated material shall be used for backfilling if the material confirm to specification. Material shall be spread by means of backhoe loader in larger areas and manually in small areas. The material shall be compacted using rammer / 1 ton roller. After the specified degree of compaction is achieved in previous layer the successive layer shall be placed. This process shall be preceded up to the top of type I embankment material layer. The thickness of the type I material layer shall be 500 mm. Sub base material and aggregate base course material shall be placed on the top of type I embankment material depend on the position of the backfill.

The field density tests shall be carried out in every fill layer to find out the degree of compaction as follows.

The aggregate base course layer shall be compacted to not less than 98% of the maximum dry density of the material as determined by BS - 1377 Test 13 (Modified Proctor) or AASHTO T-180.

The sub base layer shall be compacted to not less than 98% of the maximum dry density of the material as determined by BS - 1377 Test 13 (Modified Proctor) or AASHTO T-180.

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Step 1 – Preparation

Step 2 – Placing and Compacting of material

MS-08-BF The embankment layers shall be compacted to not less than 95% of the

maximum dry density of the material as determined by BS - 1377 Test 13 (Modified Proctor) or AASHTO T-180.

The field moisture content shall be determined by drying out the test pit sample using a gas burner.

6.0 Supervision

Position Responsibilities

Site Engineer Perform the backfilling on the basis of method statement and specifications

Technical Officer All setting out works in accordance with Method Statement and drawings

Work Supervisor Assist to Site Engineer and supervise the work Laboratory Technician

Carrying out of relevant tests in accordance with method statement

7.0 Safety Provision

Warning signs shall be displayed in advance as well as in working area. Working area shall be barricaded with barricading tapes with painted barrels or by placing traffic cones. Traffic warden jackets are to be provided to all flagmen. When a road section is closed at night blinker lights shall be provided at both sides.

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