Field Compaction, Soil Mechanics | Soil Mechanics Notes- Agricultural Engineering PDF Download

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)

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

1. What is field compaction in soil mechanics?
Field compaction in soil mechanics refers to the process of increasing the density of soil by removing air voids and reducing its volume. It involves applying mechanical force or pressure to the soil through equipment such as rollers or compactors. The goal of field compaction is to improve the load-bearing capacity and stability of the soil, making it suitable for various engineering and agricultural applications.
2. Why is field compaction important in agricultural engineering?
Field compaction is important in agricultural engineering as it helps create a stable and supportive soil structure for crop growth. Compacted soil has reduced porosity, preventing excessive water drainage and nutrient leaching. It also enhances root penetration, nutrient availability, and water retention, thereby promoting optimal plant growth and higher crop yields.
3. What are the factors influencing field compaction?
Several factors influence field compaction, including soil type, moisture content, compaction energy, compaction method, and compaction timing. Soil type determines the initial density and compactability of the soil, while moisture content affects its plasticity and workability. Compaction energy refers to the force applied to the soil, and the compaction method refers to the type of equipment used. Compaction timing is crucial, as working with wet soil can lead to excessive compaction and damage the soil structure.
4. How can field compaction be achieved effectively?
To achieve effective field compaction, it is essential to follow certain guidelines. Firstly, the soil moisture content should be within the optimum range for compaction, typically around the plastic limit. Secondly, the compaction equipment should be selected based on soil type and project requirements. Thirdly, the compaction process should be carried out in multiple passes, ensuring uniform compaction throughout the area. Lastly, proper quality control measures, such as density and moisture content testing, should be implemented to monitor the compaction progress.
5. What are the potential drawbacks of excessive field compaction?
Excessive field compaction can have negative consequences on soil health and agricultural productivity. It can lead to increased soil density, reducing the soil's ability to hold water and nutrients. The compacted soil may become more prone to erosion and surface runoff, resulting in nutrient loss and reduced water infiltration into the soil profile. Excessive compaction can also limit root penetration and restrict plant growth, ultimately affecting crop yields. Therefore, it is crucial to balance the level of compaction to avoid these drawbacks.
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