Field Compaction Methods

Compaction is the densification of soil materials by the use of mechanical energy. Soil is compacted by removing air and water from its pore space. There exists a certain amount of moisture that soil can have where a maximum unit weight is obtained. When the soil is compacted to this state it is referred to as the maximum moisture/ unit weight. The maximum Moisture/ unit weight is used exclusively to determine the degree of compaction of the earth back-fill.

Objectives of Compaction:-

·         Increase the shear strength.

·         Increased bearing capacity for foundation support.

·       Reduce compressibility and smaller settlement of buildings and lesser deformation of earth structures. 

·         Reduce permeability, leading to less seepage of water.

·         Improve stability and lower damage due to frost action.

·         Heavy/highway vs. building foundation compaction operations.

·         To reduce the degree of shrinkage and formation of cracks on drying

Compaction method:-

         Compaction efforts may be provided by:

·         Kneading ( Using punching device)

·         Dynamic ( Rollers)

·         Static action ( Mechanical jacks)

Different Types of Soil Compaction Equipment:

          The soil compaction equipment can be divided into two groups:

1.       Light soil compacting equipment’s

2.       Heavy soil compacting equipment’s

1)   Light Soil Compacting Equipment:

                        Rammers                                         Vibrating Plate

Rammers Provide impact load to the soil.            Used for compacting small areas.            This equipment is light and can be hand or machine operated.            Also called a 'trench tamper'            The base size of rammers can be 15cm x 15cm or 20cm x 20cm or more.           Suitable for:           trench back-fill           work in confined areas            Unsuitable for:           large volume work

·       Vibrating plate compactors are used for compaction of coarse soils with 4 to 8% fines.  ·         This equipment is used for small areas. ·         The usual weights of these machines vary from 100 kg to 2 tons with plate areas between 0.16 m2 and 1.6 m2. ·         Suitable for: –        most soils with low to moderate fines content ·         Unsuitable for: –        large volume work –        wet clayey soils

 

1)   Heavy Soil Compaction Equipment’s :-                                                            

                   These compacting machines are used for large areas for use on different types of soils. The heavy compaction equipment is selected based on the moisture content of soil and types of soil. Following are different types of equipment:

    

  1. Smooth Wheeled Rollers:-

●        Smooth wheeled rollers are of two types:

–        Static smooth wheeled rollers

–        Vibrating smooth wheeled rollers

●        100% coverage under the wheel

●        Contact pressure up to 380 KPa

●        Can be used on all soil types except for rocky soils.

●        The most a common use of large smooth wheel rollers is for proof-rolling subgrades and compacting asphalt pavement.

●       Suitable for:

–        well-graded sands and gravels

–        silts and clays of low plasticity

●       Unsuitable for:

–        uniform sands;

–        silty sands;

–        soft clays

            

2.        Sheepsfoot roller:-

●        Sheepsfoot rollers are drums with a large number of projections.

●        Has many round or rectangular shaped protrusions or “feet” attached to a steel drum.

●        Area of each of this projection may range from 25 to 85 .

●        8%  ~ 12 % coverage

●        Contact the pressure is from 1400 to 7000 kPa.

●        It is best suited for clayed soils.

●        Compacting effort:   static weight and kneading.

●       Suitable for:

–        fine-grained soils

–        sands and gravels, with >20% fines

●       Unsuitable for:

–        very coarse soils

–        uniform gravels

 3.     Pneumatic Rubber-Tired Roller:-

                                  

●        Pneumatic rubber-tired rollers are better in many respects than smooth wheel rollers.

●        The former is heavily loaded wagons with several rows of tires.

●        7 to 13 wheels are arranged in two rows.

●        80% coverage under the wheel

●        Contact pressure up to 700 kPa

●        Compacting effort: static weight and kneading.

●        Suitable for: most

–        Coarse

–        Fine soils.

●        Unsuitable for:

–        very soft clay

–        highly variable soils

   4.    Vibratory Rollers:-

●        Vibratory rollers are very efficient in compacting granular soil.

●        Vibrators can be attached to smooth-wheel, Pneumatic rubber-tired, or sheepsfoot rollers to provide vibratory effect to the soil.

●        The vibration is produced by rotating off-centre weights.

    5.   Grid Rollers:-

                                      

●        Grid rollers are used for compaction of weathered rocks, well-graded coarse soils.

●        The main use of these rollers are in subgrade and sub-base in road constructions.

●        As the name suggests, these rollers have a cylindrical heavy steel surface consisting   of a network of steel bars forming a grid with squire holes.

●        50% coverage

●        Masses range from 5-12 Tones

●        Contact pressure is from 1400 to 6200 kPa

●        Compacting effort:  static weight and vibration.

●        High towing speed, the material is vibrated, crushed, and impacted.

●        Suitable for:

–        well-graded sands

–         soft rocks

–        stony soils with fine fractions

●        Unsuitable for:

–        uniform sands

–        Silty sands

–        Very soft clays