Table of Contents
Understand the compaction properties of different soils and the most suitable solutions for them.
COMPACTION PROPERTIES OF DIFFERENT SOILS, Paving and Milling Manual
COMPACTION PROPERTIES OF DIFFERENT SOILS
The choice of compaction equipment must take into account several factors.
Some of them are:
type of work and area to be compacted
soil type and water content
the hardness of the underlying layer
The section below discusses the different types of soils and their compaction properties.
Castled (blocks and pebbles)
The castles contain blocks and pebbles, whose sizes vary from a hen’s egg to about 1.5 meters. Rocks, detonated rocks, crushed rocks, or natural materials. Blocks and pebbles are the dominant fractions, although they can also occur in small fractions.
The maximum size of the stones and the granulometry of the rock are determined by the type and quality of the rock and by the detonation procedure of the rock. Primary rocks, such as basalt, gneiss, and granite have high strength, and rock detonation of rocks detonated at a size of 1.0 to 1.5 m has a small number of fines. When limestone or sandstone bedding is done, the maximum size of the stones is smaller and the number of fines can be so great that considerable settlement will occur, in case the earth is not properly compacted.
The maximum allowed particle size is normally two-thirds of the layer thickness. But in terms of compaction, it is an advantage if the maximum size of the blocks does not exceed one-third of the layer thickness. This reduces the risk of rock cracks during compaction.
Vibratory equipment proved to be the most suitable and economical compaction method. Static and impact compaction are not the most suitable for bedding. Vibratory compaction can be used if heavyweights are used.
However, the greater the weight, the greater the risk of cracks.
In the case of bedding, it is necessary to use medium-heavy to heavy-weight vibratory compaction equipment to reorganize the large blocks and achieve the necessary density and stability.
The risk of cracks in the rocks must be observed, which may influence the choice of size, amplitude, and the number of passes of the roller.
Rolling compaction puts extreme stresses on the compaction equipment and therefore it is important to select machines that have been specifically designed for this purpose.
Gravel and sand
Gravel and sand vary in size, ranging from the size of a chicken egg to 0.063mm or, in some cases, 0.075mm. They include fractions from other types of soils, which will affect their compaction properties.
The compaction properties of gravel and sand are influenced by the water content; compaction is most effective when there is ideal water content.
If the fine content is less than 5 to 10%, the soil is considered free draining. In free-draining soils, excess water is drained off during compaction. This means that, in certain circumstances, the compaction work can continue even when it is raining.
If the soil is not free draining, problems are likely to occur if you try to compact the material over the ideal water content. The soil will become elastic and waterlogged. It may be impossible to achieve compaction requirements as the soil becomes saturated with water, as the soil will remain at a lower density than specified.
When the sand and gravel have a uniform granulometry, it is difficult to obtain a high density close to the surface (in the first 10 to 15 cm), due to the shear resistance of the material. The material tends to be pressed behind the compactor cylinder and, consequently, the surface acquires a relatively low density. In practice, this is not of great importance since when compacting in layers, the loose surface on top is compacted as the next layer is worked. Surface relaxation should be considered when performing compaction tests.
As a general rule, all types and sizes of machines can be used in compaction of gravel and sand, except for rollers with legs. The choice will depend on the compaction and capacity requirements.
Medium to heavy vibratory rollers will perform compaction in thick layers, while smaller rollers are more suitable for limited layer thicknesses and volumes.
Silt grain size ranges from 0.063mm to 0.002mm, although these limits may vary somewhat, depending on the soil classification system. It may contain fractions of other types of soils, which will affect its compaction properties.
In pure silt or mixed with coarse-grained fractions, there is little cohesion. With a higher clay content, the cohesion will increase.
As with all fine-grained soils, silt compaction is extremely dependent on water content. For a good compaction effect, the water content should not be very different from the value considered ideal.
At an ideal water content, silt is relatively easy to compact. At a high water content and under the influence of vibration or vehicle traffic, the silt transforms, acquiring a more or less fluid state. Vibratory equipment is the most effective for silt.
The thickness of the layers can be practically the same as those of gravel and sand if the clay content is not very high. If this is greater than 5% (but less than 15%), larger machines and thinner layers will be necessary to overcome the cohesion of the material. In such cases, a crowfoot cylinder can provide better results than a smooth cylinder. In addition, vibratory plates and smooth cylinder compaction rollers can present traction problems, especially when the water content is slightly higher.
Soil compaction properties
A summary of the compaction properties of fine-grained (cohesive) and coarse-grained (non-cohesive / granular) soils.
They are relatively easy to compact, especially by vibration, and have a high bearing capacity. Free draining soils are not susceptible to ponding and freezing.
Fine granulation materials
The water content and, consequently, the climatic conditions are important for the compaction results. They must be compacted in relatively thin layers.
Maximum allowable content of fines in free-draining soils: 5 to 10%
Soils have different densities, depending on whether they are found in situ, loose, or compacted. The thickness of the compacted layer is always mentioned in the project of new structures.
Soil volume can be defined under different conditions
- in the natural state (in situ)
- in a loose state (not compacted)
The table below shows the relative volumes of the different types of soils.
Clay is formed by the smallest existing particles, with approximate sizes of 0.002 mm. The clay content of 15% is sufficient for the soil to exhibit the properties of clay, provided that cohesion and apparent cohesion are the main resistance factors. The effect of cohesion depends on the clay content, the size and format of the grains, and also on its mineral composition. This can vary greatly between two different clays with the same particle size distribution curve but with different grain formats and mineral compositions.
Clay requires relatively high compaction stress (compared to coarse-grained soils). Vibratory goat-foot rollers are quite suitable for compacting clay. They are capable of transmitting the high pressures and breaking forces necessary to compact the material in the ideal water content or just below it.
Here, the compaction efforts are the highest possible. Layer thicknesses are normally limited to 15 to 40 cm, depending on the size of the machine. Tamping-type rollers are also suitable for compacting clay. They are quite inexpensive on large embankment areas. In these cases, the clay is put in layers of 15 to 30 cm.
It is not advisable to work with clays whose water content is above the ideal, since this soil will present an excessively elastic behavior.
Cohesive soils cannot be compacted when their water content is high. Stabilizing the material using limestone is one of the ways to improve the compact ability and stability of the material. The limestone is spread on the surface and mixed with the material, using a rotary mixer. The limestone binds with some of the water and, over time, also creates a chemical bond that substantially increases the strength of the clay.
Vibratory goat-foot rollers are generally the best option for compacting stabilized materials.
Undercoat and base
The undercoat and base are selected materials and must be within the specified limits of a grading curve. The main fraction is made up of gravel. In certain countries, relatively high amounts of fines are allowed in the undercoat; however, it loses its free-draining properties.
Underlayers and underlays typically have high compaction specifications, requiring greater compaction stress than fill materials for the same layer thickness. Vibratory equipment is most effective on sub-layers and bases, while impact compaction is not adequate.
In some cases, where the base is thin (less than 10 to 15 cm), static rollers can be used. They are especially suitable if you want to avoid the relaxation of the material. A base should always be finished with a few static passes before starting the coating work.
Sometimes the sublayers and bases can be composed of granular materials mixed with cement, fly ash, or even bitumen. This is done to increase the load-bearing properties of the material. The stabilized underlayment material is often laid using a paver, to obtain the best possible uniformity.
What are the different types of compaction of soil? ›
The method of compaction is primarily of four types such as kneading, static, dynamic or impact and vibratory compaction.What are compaction properties of soil? ›
What is compaction? Soil compaction occurs when soil particles are pressed together, reducing pore space between them (Figure 1). Heavily compacted soils contain few large pores, less total pore volume and, consequently, a greater density. A compacted soil has a reduced rate of both water infiltration and drainage.What is the best soil for compaction? ›
"The soils easiest to compact are soils with spheric and smooth particles," he continues. "Soils with irregular particles are more difficult to compact but, on the other hand, they have a larger bearing capacity."What are at least four properties of soil affected by compaction of soil? ›
Experimental studies have shown that the soil compaction results in increase in the soil strength, bulk density, volumetric water contents, and field capacity while decrease in total porosity, soil aeration, water infiltration rate, and saturated hydraulic conductivity.What are the 4 factors affecting compaction? ›
- Nature and type of soil, i.e. sand or clay, grading, plasticity.
- Water content at the time of compaction.
- Site conditions, e.g. weather, type of site, layer thickness.
- Compactive effort: type of plant (weight, vibration, number of passes)
- TYPE OF SOIL. The type of soil has a great influence on its compaction characteristics. ...
- TYPE OF COMPACTOR. ...
- LAYER THICKNESS / THICKNESS OF LIFT. ...
- NUMBER OF ROLLER PASSES. ...
- MOISTURE CONTENT. ...
- CONTACT PRESSURE. ...
- SPEED OF ROLLING.
Compaction reduces the voids present in the soil hence permeability also reduces. At a particular density, for the same soil sample, permeability is more for soils which are compacted to dry of optimum than those compacted to wet of optimum.What is soil compaction in civil engineering? ›
Soil compaction is the process whereby soil is mechanically compressed through a reduction in the air voids. It is measured in terms of the dry density or amount of solid matter in unit volume. Soils range in dry density from about 140 lb. per cubic foot for coarse-grained gravels and sands to about 90 lb.What does it mean to have 95% compaction? ›
95 percent compaction means that the soil has been compacted to 95 percent of the possible density of the soil through compactive efforts. Maximum dry density, along with optimum moisture content, is determined in the laboratory and provides the target for field compaction.What soil type is most vulnerable to compaction? ›
Clayey and silty soils are most susceptible to compaction because their particles hold more water for longer than sands or loams. As a result, clay soils remain in a plastic state, sometimes for the whole year, which means they will compress and shear when a load is applied to them.
What is the acceptable percentage of compaction? ›
In general, a compaction between 80 and 85 percent of the standard Proctor maximum dry density optimizes slope stability with vegetation development and growth.What is the solution for soil compaction? ›
The following practical techniques have emerged on how to avoid, delay or prevent soil compaction: (a) reducing pressure on soil either by decreasing axle load and/or increasing the contact area of wheels with the soil; (b) working soil and allowing grazing at optimal soil moisture; (c) reducing the number of passes by ...What are the four different properties of soil which can be improved through compaction? ›
The primary goal of compacting a soil is to enhance certain desirable properties such as compressibility, water absorption, and permeability, as well as increase soil strength, bearing capacity, and change in swelling and shrinkage characteristics.What are the 7 soil properties? ›
Soil physical properties include texture, structure, density, porosity, consistence, temperature, and color.Which property of soil is improved by compacting the soil? ›
The most direct effect of soil compaction is an increase in the bulk density of soil.What are compaction parameters? ›
The most important point on the compaction curve is the optimum compaction point in which two important parameters, maximum dry unit weight ( dmax) and optimum water content (wopt), are obtained, and they represent compaction behaviour (Figure 1).What are the names of the four compacting methods? ›
- Static Pressure. Static pressure is the most basic form of compaction. ...
- Manipulation. Manipulation,also sometimes referred to as kneading,acts to compress materials at a greater depth. ...
- Impact. ...
Scientists attribute soil formation to the following factors: Parent material, climate, biota (organisms), topography and time.What is the meaning of 98% compaction? ›
95% compaction is just 95% of the Proctor density, whereas 98% compaction is 98% of the Proctor density. If the Proctor density is 100 (let's ignore units here), and the percent compaction is 95, that means that the soil that was just packed has a density of 95.Which methods can be used to determine compaction quality in the field? ›
Compaction Using Drop Hammer Methods Drop hammer methods are the test methods most commonly used for establishing the compaction characteristics of soils and aggregates in the laboratory.
What are the factors that you would consider in selecting compaction equipment? ›
“Factors include the width of the area to be compacted, the final density required, the grade of the area to be compacted, the type of asphalt mix, as well the type of materials that lay below the lift being compacted.What do the properties of a soil under compaction depend upon? ›
Explanation: The properties of soil under compaction depend upon the water content, amount of compaction, and the type of compaction. Explanation: Compaction has a great effect on soil properties, such as strength and stress-strain characteristics, permeability, compression, swelling, and water absorption.What is the standard for soil compaction? ›
Typical compaction requirements for a project may range from 90% to 95% of standard Proctor for non-structural areas to 98% or more of modified Proctor for heavily loaded pavements.What are the requirements for soil compaction in the field? ›
If no well-defined peak in the moisture density curve is observed, the soil should be compacted with significant water, e. g., corresponding to 50 to 75 percent saturation or the maximum amount of moisture that can be retained.How do you compact soil for building construction? ›
For large fill areas, rolling is the fastest, most efficient compaction method. Hand-held compactors can be used in smaller areas and for places that larger mobile equipment can't reach. For granular soils, vibrating plate compactors work best. Rammers or impact type machines are used for cohesive soils.What is compaction and what are the factors affecting compaction? ›
Compaction of soil is a process of densification of soil by displacing air from the pores by applying external stress on soil at different moisture content. Factors Affecting Compaction of Soil – Effect on Different Soil Types. Effect of Water Content on Compaction of Soil.Can you achieve 100% compaction? ›
Because conditions in the field do not match the ideal conditions in a laboratory, the target compaction is scaled to a percentage of the dry density determined in the lab. This can range from 90 percent to over 100 percent.Can relative compaction exceed 100%? ›
In fact, relative soil compaction test results over 100% do not necessarily mean over-compaction because the relative compaction is based on the maximum dry density of the soil obtained by the Proctor test and this does not necessarily refer to absolute maximum dry density.What does 100% compaction mean? ›
In case the compaction test results indicate values exceeding 100%, it only means that the in-situ compaction is more than that being carried out in laboratories which is treated as the basic criterion for satisfactory degree of soil compaction.How does soil texture influence compaction? ›
Soil texture impacts compaction as well. Coarse textured soils (sands) are considered less susceptible to compaction than fine textured soils (clays), although a dry clay soil can actually resist compaction better than a dry sand soil.
Which soil texture ranges are most vulnerable to structural damage and compaction? ›
In general, soils with fine textures (silt and clay), low organic matter contents, high porosity and weakly aggregated structure are more susceptible to serious compaction.Which soil type has the highest compressive strength? ›
Type A Soils i. Type A Soils are cohesive soils with an unconfined compressive strength of 1.5 tons per square foot (tsf) (144 kPa) or greater. Examples of Type A cohesive soils are often: clay, silty clay, sandy clay, clay loam and, in some cases, silty clay loam and sandy clay loam.What is improper compaction? ›
Improper consolidation or compaction of concrete
Bugholes are formed when small pockets of air or water are trapped against the forms. A change in the mixture to make it less “sticky” or the use of small vibrators worked in the form has been used to help eliminate bugholes.
Rolling is the fastest and most efficient compaction method for large fill areas. In small areas where large equipment can't reach, hand-held compactors can be used. Vibrating plate compactors are best for granular soils. For cohesive soils, rammers or impact type machines are recommended.How do you achieve proper compaction? ›
Tamping rammers or jumping jacks, vibratory plate compactors, rollers, and more can all be found at job sites around the world to compact various soils. With these pieces of equipment, two different types of force, static force and vibratoryforce , can be utilized to achieve proper compaction.What are some examples of compaction? ›
Rainforests, dry forests, sand dunes, mountain streams, lakes, rivers, oceans, beaches, and deltas are just a few examples of where compaction, and eventually cementation, can occur.What is an example of soil compaction? ›
What is Compaction? Soil compaction – Decrease in soil volume and porosity, or increase in soil bulk density, due to mechanical stress on soil, for example, from traffic of agricultural machinery. Compaction can also occur naturally.What are the two basic types of compaction? ›
Almost all types of building sites and construction projects utilize mechanical compaction techniques. These different types of effort are found in the two principle types of compaction force: static and vibratory.What are the principles of compaction? ›
Proctor noted that compaction is a function of four variables: (a) dry density, pd; (b) water content, w; (c) compactive effort; and (d) soil type. Compactive effort is a measure of the mechanical energy applied to a soil mass.Which type of compaction is very effective in thick deep layers of soil? ›
But dynamic compaction, as opposed to conventional shallow compaction of controlled fill, is a process of densifying soils at significant depths by applying a large impact energy at the ground surface.
What are compaction characteristics? ›
Soil compaction involves a densification and a relative variation of physical and mechanical characteristics of soils. Evaluating laboratory compaction parameters such as maximum dry density (MDD) and optimum water content (OWC) is a very important task to control field compaction for all earth-works structures.How do you find the compaction factor of soil? ›
3.7 Calculate percent relative compaction by dividing the dry density of the material from the test site by that material's moisture density relation curve's maximum dry density, and multiply by 100%.What are solutions for soil compaction? ›
For smaller areas, you can work in organic materials like compost, peat moss and other organic materials. Gypsum is another amendment that can be used for loosening compacted soil. Earthworms are another way to improve soil compaction.