02-EARTH WORK



ROADS-EARTH WORK

Earthwork includes excavation and fill. Excavation is carried out for the construction of roads, buildings and other structures. Road excavation is required where a hill is to be cut to get the design profile of the road, widening the existing road etc. Excavation for structures shall consist of:

  1. Removal of material for the construction of foundations for buildings, bridges, culverts, retaining walls, headwalls, cut off walls, pipe culverts and other similar   structures, in accordance with the requirements of contract specifications and to lines and dimensions shown in the Drawings or as directed by the Engineer.
  2. Construction of the necessary cofferdams and cribs and their subsequent removal.
  3. All necessary sheeting, shoring, bracing, draining and/or pumping for dewatering.
  4. Removal of all logs, stumps, grubs and other deleterious matter and obstructions, necessary for placing the foundations.
  5. Trimming bottom and sides of excavations.
  6. Backfilling and clearing up the site and the disposal of all surplus material.

Fill includes earthwork operations for backfilling the space between the structure and excavation, yard filling at construction sites, construction of embankment etc. Adequate protective measures to see that the excavation operations do not affect or damage adjoining structures. For safety precautions, guidance may be taken from IS: 3764.

EMBANKMENT CONSTRUCTION

  1. All embankments, subgrades, earthen shoulders and miscellaneous backfills shall be constructed in accordance with the requirements of Clause 305 of MoRTH Specifications and in conformity with the lines, grades and cross sections shown in the Drawings or as directed by the Engineer.
  2. The samples of soil brought to site shall be tested to determine the laboratory maximum dry density (MDD) and optimum moisture content (OMC) in accordance with IS: 2720 (Part 8).
  3. If the fill is to be deposited against the face of a slope steeper than 1:4, such faces shall be benched in advance as per Clause 305.4.1 of MoRTH Specifications, before the material is placed.
  4. Embankment construction in waterlogged and marshy areas shall be in accordance with IRC: 34.
  5. Only materials satisfying the density requirements given in table shall be employed for the construction of the embankment and the sub grade.

Sl. No

Type of Work

Maximum laboratory dry density

when tested as per IS: 2720 (Part 8)

1

Embankments up to 3.0 m height, not subjected to extensive flooding.

Not less than 15.2 kN/m2

  1. The selection of materials for the construction of the embankment shall be made after conducting necessary soil surveys and laboratory investigations as set out in IRC:36.
  2. The embankment construction using fly-ash shall be in accordance with IRC: SP 38 Guidelines for use of fly-ash in road construction

  Control tests on borrow material

Sl. No

Test

Code

Minimum Desirable Frequency

1

Gradation*/Sand content

IS: 2720 Part 4

1-2 tests per 8000 m3 of soil

2

Plasticity index

IS: 2720 Part 5

1-2 tests per 3 8000 m3of soil

3

Standard Proctor test

IS: 2720 Part 7

1-2 tests per 3 8000 m3 of soil

4

CBR test on a set of 3 specimens**

IS: 2720 Part 16

One test per 3000 m3 of soil.

5

Deleterious Constituents

IS: 2720 Part 27

As required.

6

Natural moisture content

IS: 2720 Part 2

One test per 250 m3 of soil

*To be done if specification requires it.

**For the purpose of design, unless specified in the Contract.

 Construction

  1. The construction operations of embankment shall be in accordance with the requirements of Clause 305.3 of MoRTH Specifications.
  2. The field dry density shall be determined in accordance with IS: 2720 (Part 28) and the mean of 5 determinations obtained for each compaction condition.
  3. The moisture content of the material shall be checked in accordance with IS: 2720 (Part 2), before the commencement of compaction. If water is to be added, a water tanker fitted with sprinkler arrangement shall be used.
  4. The field moisture content during compaction shall be within 1% above to 2% below the optimum moisture content (OMC) determined in accordance with IS:2720(Part 8).
  5. The finished layer shall be subjected to field density tests as per IS: 2720 (Part 28) and accepted by the Engineer.
  6. If approved by the Engineer, a properly calibrated nuclear density gauge may be used for checking the field densities if the gauge is capable of providing identical test results to that obtained from tests in accordance with IS: 2720 (Part 28).

Compaction requirements for embankment and subgrade.

Sl.No

Type of work / material

Relative compaction as % of max laboratory dry density as per

IS: 2720 (Part 8)

1

Subgrade and earthen shoulders

Not less than 97%.

2

Embankment

Not less than 95%.

3(a)

Expansive clays: Subgrade and 500 mm just below subgrade

Not permitted to use such materials.

3(b)

Expansive clays: Remaining portion of the

embankment

90 to 95%.

Field tests for compaction control

Sl.No

Type of test

Frequency

1

Field moisture content as per IS: 2720 Part 2 (Any of the rapid methods for the  determination of the moisture content can also be used)

2-3 tests per 250 m2 of loose material.

2

Embankment

One test per 1000 m2 of compacted area. For the top 500 mm of the embankment (Subgrade), this shall be 2 increased to one test per 500-1000 m2

area.

3

Control of surface evenness of earthen subgrade layer

Measured for every 300 m length using a 3 m straight edge. Permitted undulations 30 nos. of 24 mm or above.

TURFING WITH SODS

Sod or turf consists of grass and the part of the soil beneath it held together by the roots, or a piece of thin material. This work consists of providing and laying of the live sod of perennial turf forming grass on the embankment slopes, verges or in landscaping. The work shall be carried out immediately following the construction of the embankment subject to the weather conditions. The details of materials and construction are given under Clause 307 of MoRTH Specifications.

TURFING BY SEEDING AND MULCHING

This clause describes the requirements for preparing slopes, placing top soil, furnishing and installing seed, mulching material, fertilizer, and netting. The requirements include the type of materials to be used, methods and requirements for installation. The details of materials and construction are given under Clause 308 of MoRTH Specifications.

GROUND IMPRROVEMENT USING PVD WITH SURCHARGE

Using geosynthetic drains viz., prefabricated vertical drains (PVD) with surcharge, weak embankment foundations having problematic sub-soil conditions can be improved to carry the design load of the embankment. The design and construction of PVD with surcharge is carried out as per IS: 15284 (Part 2). The details of materials and installation are given in Clause 314.2 of MoRTH Specifications for Road and Bridge works.

Materials

  1. Geosynthetic drain:  The band drain shall meet the properties specified in table 700-3 of MoRTH Specifications.
  2. Granular sand blanket: After vertical band drains are installed in the subsoil, a blanket of well draining natural or coarse sand conforming to class I grading given in table 300-4 of MoRTH Specifications is provided. The sand blanket of the specified thickness shall be compacted to a density of 75% to 80% of the MDD obtained as per IS: 2720 (Part 8).
  3. Geotextile fabric for separation and drainage: The synthetic geotextile shall meet the requirements given in table 700-1 of MoRTH Specifications (5th revision). Under any circumstance, the paving fabric shall not be subjected to ultraviolet light for more than 14 days.

RAMMED STONE COLUMNS FOR GROUND IMPROVEMENT

  1. Rammed stone columns using non-displacement method of construction is provided for strengthening weak embankment foundations. Due to the high angle of internal friction and stiffness of stone column when compared with that of in-situ weak soil, the majority of the applied load is transferred to the stone column. As a result, lesser load is transferred to surrounding weak soil which leads to reduction in settlement.
  2. The design and construction of this is carried out in accordance with IS: 15284 (Part 2).
  3. The details of materials and installation are given in Clause 314.3 of MoRTH Specifications for Road and Bridge works.

Materials

Grading for crushed stone in stone columns.

IS sieve designation

% passing

75

90-100

50

80-90

38

55-75

20

10-20

12

5-13

2

0-5

  1. A compacted blanket of well draining gravel or coarse sand is to be provided. The sand blanket of the specified thickness shall be compacted to a density of 75% to 80% of the MDD obtained as per IS: 2720 (Part 8). 

 Construction

  1. The rammed stone columns shall be constructed by non-displacement technique of ‘Bailer and Casing Method’ as given in IS: 15284 (Part 1).
  2. The field controls, initial and routine tests, data recording etc shall be carried out as given in IS: 15284 (Part 1).
  3. The ultimate load capacity of single column shall be determined from load tests.

RELATED CODES :

1.         MoRTH           Specifications for Road and Bridge Works, 5th Edition 2013 – published by IRC, New Delhi.

2.         MoRTH           Specifications for Road and Bridge Works, 4th Edition 2001 – published by IRC, New Delhi.

3.         IRC SP: 11      Quality control for the construction of roads and runways.

4.         IRC: 34            Recommendations for road construction in water logged areas.

5.         IS: 3764          Code of safety for excavation work.

6.         IS: 15284        Design and construction of ground improvement – guidelines.

  Part -1:           Stone columns.

  Part -2:           Pre consolidation using vertical drains.

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