Soil Compaction Techniques and Laboratory Testing, Lecture notes of Geotechnical Engineering

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GEOTECHNICAL ENGINEERING 2A (GTECIA2)

SOIL COMPACTION

KAVEH TAGHIZADEHTEFLISSI

Introduction

➢Compaction is also very important when soil is used as an engineering material, that is the structure itself is made of soil. ➢Such as:

• Earth dams
• Highways
• Airfields
• etc.

Introduction

What is Compaction?

➢The degree of compaction of soil is measured by its dry unit weight. ➢When water is added during compaction it acts as a softening agent on the soil particles. ➢When the moisture content is gradually increased, the weight of the soil solids in a unit volume gradually increases. ➢Optimum moisture content (OMC) is the water content at which the maximum dry unit weight is attained.

General Principle

➢A simple ground improvement technique, where the soil is densified through external compactive effort.

Compaction Curve

Water content Dry unit weight (  )d Optimum moisture content (OMC) d (max) Soil grains densely packed

• good strength and stiffness
• low permeability

➢Increase load bearing capacity ➢Increase stability ➢Reduce soil settlement ➢Reduce soil permeability ➢Reduce frost damage ➢Reduce erosion damage ➢Reduce water seepage ➢Reduce shrinkage

Effect of Soil Compaction

Laboratory Compaction Test

➢The soil is compacted in a mold that has a volume of 944 cm 3 . ➢The diameter of the mold is 101.6 mm. ➢During the laboratory test, the mold is attached to a baseplate at the bottom and to an extension at the top (Figure a). ➢ The soil is mixed with varying amounts of water and then compacted in three equal layers by a hammer (Figure b) that delivers 25 blows to each layer. ➢The hammer has a mass of 2.5 kg and has a drop of 305 mm.

Standard Proctor Test (SPC)

Mold Hammer

➢For each test, the moist unit weight of compaction, g , can be calculated as Where: W=weight of the compacted soil in the mold Vm=volume of the mold ( 944 cm^3 ) ➢For each test, the moisture content of the compacted soil is determined in the laboratory. With the known moisture content, the dry unit weight can be calculated as Where: w(%)=percentage of moisture content

Standard Proctor Test (SPC)

m W V  = (%) 1 100 d w   =

➢For a given moisture content w and degree of saturation Sr, the dry unit weight of compaction can be calculated as ➢when the degree of saturation equals 100 %, the maximum dry unit weight at a given moisture content with zero air voids can be obtained by substituting Sr= 1

Standard Proctor Test (SPC)

1 s w d G e   =

1 s w d s r G G w S   =

1 1 s w w zav s s G wG w G    = =

(%) 1 100 d w   =

Standard Proctor Test (SPC)

Standard Proctor Test (SPC)

➢Moisture content (Wc) ➢Soil type ➢Compaction effort required (Energy) Note: moisture content has a strong influence on the degree of compaction achieved by a given soil, Water is added to lubricate the contact surfaces of soil particles and improve the compressibility of the soil.

Factor Affecting Soil Compaction