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Field Compaction, Soil Mechanics Agricultural Engineering Notes | EduRev

Agricultural Engineering : Field Compaction, Soil Mechanics Agricultural Engineering Notes | EduRev

The document Field Compaction, Soil Mechanics Agricultural Engineering Notes | EduRev is a part of the Agricultural Engineering Course Soil Mechanics Notes- Agricultural Engineering.
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Introduction

The laboratory compaction test gives an ideal that what compacted dry unit weight to be achieved in field. Generally in the field, 90 % - 95% of laboratory obtained dry unit weight is attained. The amount of compaction achieved in the field depends on the thickness of the layer, type of roller used, pressure intensity applied on the soil, number of passes of the roller. Depending upon the type of soils, compaction can be done by vibration, rolling or ramming. Roller can be smooth wheel roller, sheepsfoot rollers and pneumatic rubber rollers.

1. Compaction of Cohesion less Soil

In case of cohesionless soils, vibration is the most effective method of compaction. Best results can be obtained when the frequency of vibration is near to the natural frequency of the soil to be compacted. The vibrating equipments can be hydraulic type or dropping weight type.

2. Compaction of Cohesive Soil

In case of moderately cohesive soils, compaction can be done in layers to get best possible results. The compaction is done by roller. For silts of low plasticity, pneumatic rollers are preferred. In case of soils with moderate plasticity, sheepsfoot rollers are preferred.

The types of equipment used for compaction of various soils are reported in Table 16.1 (Ranjan and Rao, 2000):

Table 16.1: Type of equipment used for compaction of different soils

 Soil type Equipment Use Sands Vibratory rollers Embankments for oil storage tanks Sand, silts, clay Pneumatic rubber rollers Base, Sub-base, embankments for highway, airfield Clay Sheepsfoot rollers Core of the earth dam Crushed rock, gravel, sand Smooth wheeled rollers Road construction All soils Rammer Fills behind the retaining walls, trench fills

The field compaction can be expressed by relative compaction which is the ratio of dry unit weight [ $\gamma$ d(field)] of soil in filed and maximum dry unit weight [ $\gamma$dmax] of soil in laboratory. Thus,

${{\rm Re}\nolimits} lative\;compaction = {{{\gamma _{d(field)}}} \over {{\gamma _{d\max }}}}$                     (16.1)

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