Soil Mechanics: Shear Strength of Soil
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Questions and Answers

The ability of soil deposit to support an imposed loading or of a soil mass to support itself is governed by ______ strength of the soil.

shear

Shear strength refers to the resistance along a plane that passes between or along a long particle ______.

surfaces

The problems related to shear strength include the ______ capacity of soil for foundation design.

bearing

Shear strength and related ______ of a foundation is conventionally studied in laboratory by testing samples.

<p>deflection</p> Signup and view all the answers

When the stress applied on soil exceeded the shear strength of soil, the ______ of soil particles upon each other causes change in volume.

<p>sliding</p> Signup and view all the answers

Part of soil may move or get displaced with respect to ______ media when its shear strength is exceeded.

<p>surrounded</p> Signup and view all the answers

The shear strength developed either due to compression or ______ forces.

<p>tension</p> Signup and view all the answers

What is the optimal amount of water for soil compaction?

<p>A little bit of water</p> Signup and view all the answers

What is the primary goal of soil compaction?

<p>To reduce air-void volume in soils as much as possible</p> Signup and view all the answers

What happens when too much water is added to soil during compaction?

<p>Compaction is inhibited</p> Signup and view all the answers

What is the primary purpose of the Standard Proctor Test?

<p>To determine the maximum dry unit weight of the soil</p> Signup and view all the answers

Why is it important to control soil water content during compaction?

<p>To achieve the optimal compaction effort</p> Signup and view all the answers

What is the difference between the Standard Proctor Test and the Modified Proctor Test?

<p>The compaction energy applied to the soil</p> Signup and view all the answers

What is the relationship between compaction energy and soil water content?

<p>Compaction energy increases with increasing soil water content</p> Signup and view all the answers

How is the compaction effort calculated in the Standard Proctor Test?

<p>By using the formula: compaction effort = (number of drops x weight of hammer) / volume of soil</p> Signup and view all the answers

What is the ideal outcome of optimal soil compaction?

<p>Minimum air-void volume</p> Signup and view all the answers

What is the range of optimum water content for sandy silt (sub-base material)?

<p>8-12</p> Signup and view all the answers

What happens to the dry density of the soil when the water content is above the optimum water content?

<p>It decreases</p> Signup and view all the answers

What is the unit of measurement for the compaction effort in the Standard Proctor Test?

<p>lb-ft/ft³</p> Signup and view all the answers

What is the number of times the hammer is dropped onto the confined soil for each lift?

<p>25 times</p> Signup and view all the answers

What is the purpose of dividing the soil mold into three lifts?

<p>To facilitate testing of different soil layers</p> Signup and view all the answers

What is the name of the test developed during World War II by the U.S.?

<p>Modified Proctor Test</p> Signup and view all the answers

How many times is the compaction process repeated from dry to wet?

<p>4-6 times</p> Signup and view all the answers

What is the total number of blows applied to each layer?

<p>25 blows</p> Signup and view all the answers

What is the term used to describe the energy applied to the soil to achieve the desired density?

<p>Soil compaction energy</p> Signup and view all the answers

What is the purpose of the standard Proctor test?

<p>To find the optimal water content for soil compaction</p> Signup and view all the answers

What is the relationship between the void ratio and the degree of saturation?

<p>e = w / (Gs * S)</p> Signup and view all the answers

What is the Zero-Air-Void (ZAV) curve used for?

<p>To represent the fully saturated condition of soil</p> Signup and view all the answers

What is the purpose of finding the Optimum Moisture Content (OMC) in soil compaction?

<p>To optimize the water content for maximum dry density and stability</p> Signup and view all the answers

What is the unit of the compaction energy in the Modified Proctor test?

<p>Foot-pounds per cubic foot</p> Signup and view all the answers

What is the formula for calculating the dry unit weight of soil (γd) during compaction?

<p>γd = γw / (1 + w / c)</p> Signup and view all the answers

What is the primary objective of increasing soil density through compaction?

<p>Increase density, strength, and bearing capacity</p> Signup and view all the answers

What is the process of increasing soil unit weight by reducing soil void ratio?

<p>Compaction</p> Signup and view all the answers

What is the purpose of laboratory work in soil compaction?

<p>To obtain maximum dry density and optimum water content</p> Signup and view all the answers

What is the difference between the Standard Proctor Test and the Modified Proctor Test?

<p>The weight of the hammer</p> Signup and view all the answers

What is the relationship between compaction energy and soil water content?

<p>Compaction energy increases with increase in soil water content</p> Signup and view all the answers

How is the compaction effort calculated in the Standard Proctor Test?

<p>By counting the number of blows per lift</p> Signup and view all the answers

What happens to the dry density of the soil when the water content is above the optimum water content?

<p>It decreases</p> Signup and view all the answers

What is the unit of measurement for the compaction effort in the Standard Proctor Test?

<p>Foot-pounds per cubic foot</p> Signup and view all the answers

Why is it important to control soil water content during compaction?

<p>To achieve optimal density and strength</p> Signup and view all the answers

What is the ideal outcome of optimal soil compaction?

<p>Maximum dry density and strength</p> Signup and view all the answers

What is the primary purpose of the Standard Proctor Test?

<p>To determine the maximum dry density of soil</p> Signup and view all the answers

What is the difference between the Standard Proctor Test and the Modified Proctor Test?

<p>The weight of the hammer</p> Signup and view all the answers

What happens to the dry density of the soil when the water content is above the optimum water content?

<p>It decreases</p> Signup and view all the answers

What is the unit of measurement for the compaction effort in the Standard Proctor Test?

<p>lb-ft/ft3</p> Signup and view all the answers

What is the range of optimum water content for sandy silt (sub-base material)?

<p>8-12%</p> Signup and view all the answers

What is the purpose of controlling soil water content during compaction?

<p>To achieve the maximum dry density of soil</p> Signup and view all the answers

What is the term used to describe the energy applied to the soil to achieve the desired density?

<p>Compaction energy</p> Signup and view all the answers

What happens to the water films around soil particles as the water content increases?

<p>They start to replace soil particles in the mold</p> Signup and view all the answers

What is the purpose of the Optimum Moisture Content (OMC) in soil compaction?

<p>To achieve maximum dry density</p> Signup and view all the answers

What is the relationship between compaction energy and soil water content?

<p>Increased water content requires less compaction energy</p> Signup and view all the answers

What is the difference between the Standard Proctor Test and the Modified Proctor Test?

<p>The compaction energy applied</p> Signup and view all the answers

What happens to the dry density of the soil when the water content is above the optimum water content?

<p>It decreases linearly</p> Signup and view all the answers

What is the unit of measurement for the compaction effort in the Standard Proctor Test?

<p>Foot-pounds per cubic foot</p> Signup and view all the answers

Why is it important to control soil water content during compaction?

<p>To achieve optimal dry density</p> Signup and view all the answers

What is the primary purpose of the Standard Proctor Test?

<p>To determine the optimum water content for soil compaction</p> Signup and view all the answers

What is the difference between the Standard Proctor Test and the Modified Proctor Test?

<p>The Modified Proctor Test uses a heavier hammer</p> Signup and view all the answers

What happens to the dry density of the soil when the water content is above the optimum water content?

<p>It decreases</p> Signup and view all the answers

What is the relationship between compaction energy and soil water content?

<p>Compaction energy increases with increasing water content</p> Signup and view all the answers

What is the purpose of finding the Optimum Moisture Content (OMC) in soil compaction?

<p>To achieve the maximum compaction of soil</p> Signup and view all the answers

What is the unit of measurement for the compaction effort in the Standard Proctor Test?

<p>ft-lbs/ft³</p> Signup and view all the answers

What is the primary objective of increasing soil density through compaction?

<p>To increase the stability of soil structures</p> Signup and view all the answers

What is the purpose of drawing the Line of Optimum in soil compaction?

<p>To identify the optimum water content for soil compaction</p> Signup and view all the answers

What is the difference between the Standard Proctor Test and the Modified Proctor Test?

<p>The Modified Proctor Test uses a heavier hammer</p> Signup and view all the answers

What happens to the dry density of soil when the water content is above the optimum water content?

<p>It decreases</p> Signup and view all the answers

What is the term used to describe the energy applied to the soil to achieve the desired density?

<p>Compaction energy</p> Signup and view all the answers

What is the relationship between compaction energy and soil water content?

<p>Compaction energy increases with decreasing water content</p> Signup and view all the answers

What is the primary objective of increasing soil density through compaction?

<p>To decrease the soil's void ratio</p> Signup and view all the answers

What is the purpose of laboratory work in soil compaction?

<p>To determine the soil's optimum water content</p> Signup and view all the answers

What is the primary goal of determining the Optimum Moisture Content (OMC) in soil compaction?

<p>To achieve the maximum dry unit weight</p> Signup and view all the answers

What is the relationship between the void ratio and the degree of saturation?

<p>They are inversely proportional</p> Signup and view all the answers

What is the purpose of the Zero-Air-Void (ZAV) curve?

<p>To represent the fully saturated condition of the soil</p> Signup and view all the answers

What is the formula for calculating the dry unit weight of soil (γd) during compaction?

<p>γd = γw / (1 + w/c)</p> Signup and view all the answers

What is the primary objective of increasing soil density through compaction?

<p>To increase the bearing capacity of the soil</p> Signup and view all the answers

What is the purpose of laboratory work in soil compaction?

<p>To simulate field conditions in the laboratory</p> Signup and view all the answers

What is the difference between the Standard Proctor Test and the Modified Proctor Test?

<p>The amount of compaction energy applied</p> Signup and view all the answers

What happens to the dry density of the soil when the water content is above the optimum water content?

<p>It decreases</p> Signup and view all the answers

What is the unit of measurement for the compaction effort in the Standard Proctor Test?

<p>foot-pounds per cubic foot</p> Signup and view all the answers

What is the unit of measurement for the compaction effort in the Standard Proctor Test?

<p>lb.ft/ft3</p> Signup and view all the answers

What is the primary difference between the Standard Proctor Test and the Modified Proctor Test?

<p>The number of blows applied to each layer</p> Signup and view all the answers

What happens to the dry density of the soil when the water content is above the optimum water content?

<p>It decreases</p> Signup and view all the answers

What is the purpose of the Standard Proctor Test?

<p>To determine the optimum water content for soil compaction</p> Signup and view all the answers

What is the range of optimum water content for sandy silt (sub-base material)?

<p>8-12%</p> Signup and view all the answers

What is the term used to describe the energy applied to the soil to achieve the desired density?

<p>Compaction energy</p> Signup and view all the answers

What is the purpose of controlling soil water content during compaction?

<p>To achieve the maximum dry density of soil</p> Signup and view all the answers

What happens to the dry density of the soil when the water content is at the optimum?

<p>It becomes maximum</p> Signup and view all the answers

What is the purpose of the Standard Proctor Test?

<p>To determine the optimum water content for soil compaction</p> Signup and view all the answers

What is the primary purpose of the Standard Proctor Test?

<p>To determine the optimal water content for compaction</p> Signup and view all the answers

What is the effect of increasing compaction energy on soil density?

<p>It increases soil density</p> Signup and view all the answers

What happens to the dry density of soil when the water content is above the optimum water content?

<p>It decreases</p> Signup and view all the answers

What is the difference between the Standard Proctor Test and the Modified Proctor Test?

<p>Compactive effort</p> Signup and view all the answers

What is the purpose of controlling soil water content during compaction?

<p>To achieve the optimal density</p> Signup and view all the answers

What is the difference between the Standard Proctor Test and the Modified Proctor Test?

<p>The compaction energy applied</p> Signup and view all the answers

What is the unit of measurement for the compaction effort in the Standard Proctor Test?

<p>ft-lbs</p> Signup and view all the answers

What is the purpose of controlling soil water content during compaction?

<p>To achieve maximum density</p> Signup and view all the answers

What happens to the water films around soil particles as the water content increases?

<p>They become thicker</p> Signup and view all the answers

What is the unit of measurement for the compaction effort in the Standard Proctor Test?

<p>ft-lbs/in³</p> Signup and view all the answers

What is the term used to describe the energy applied to the soil to achieve the desired density?

<p>Compaction energy</p> Signup and view all the answers

What is the range of optimum water content for sandy silt (sub-base material)?

<p>8-12%</p> Signup and view all the answers

What is the unit of measurement for the compactive effort in the Modified Proctor Test?

<p>lb-ft/ft³</p> Signup and view all the answers

What is the purpose of drawing the Line of Optimum?

<p>To determine the optimum water content for compaction</p> Signup and view all the answers

What happens to the dry density of the soil when the water content is below the optimum water content?

<p>It increases rapidly</p> Signup and view all the answers

What is the difference between the Standard Proctor Test and the Modified Proctor Test?

<p>The compactive effort applied</p> Signup and view all the answers

What is the term used to describe the energy applied to the soil to achieve the desired density?

<p>Compaction energy</p> Signup and view all the answers

What is the purpose of controlling soil water content during compaction?

<p>To achieve the maximum dry density of the soil</p> Signup and view all the answers

What is the effect of entrapped air on the compaction curve?

<p>It shifts the curve to the right</p> Signup and view all the answers

What is the purpose of finding the Optimum Moisture Content (OMC) in soil compaction?

<p>To achieve the desired density of the soil with minimum compaction effort</p> Signup and view all the answers

What is the relation between the void ratio and the degree of saturation?

<p>The void ratio decreases with an increase in the degree of saturation</p> Signup and view all the answers

What is the purpose of the Standard Proctor Test?

<p>To determine the optimal water content for soil compaction</p> Signup and view all the answers

What happens to the dry density of the soil when the water content is above the optimum water content?

<p>It decreases</p> Signup and view all the answers

What is the unit of measurement for the compaction effort in the Standard Proctor Test?

<p>Foot-pounds per cubic foot</p> Signup and view all the answers

What is the difference between the Standard Proctor Test and the Modified Proctor Test?

<p>The Modified Proctor Test uses a higher compaction energy</p> Signup and view all the answers

What is the purpose of controlling soil water content during compaction?

<p>To achieve the desired density of the soil with minimum compaction effort</p> Signup and view all the answers

What is the term used to describe the energy applied to the soil to achieve the desired density?

<p>Compaction energy</p> Signup and view all the answers

What is the Zero-Air-Void (ZAV) curve used for?

<p>To represent the fully saturated condition of the soil</p> Signup and view all the answers

What is the degree of compaction that can be achieved when all air voids have been removed?

<p>S=1</p> Signup and view all the answers

What is the purpose of controlling the water content during compaction?

<p>To increase the dry density of the soil</p> Signup and view all the answers

What is the term used to describe the energy applied to the soil to achieve the desired density?

<p>Compaction energy</p> Signup and view all the answers

What is the purpose of the Standard Proctor equipment?

<p>To compact the soil to the desired density</p> Signup and view all the answers

How is the compactive effort calculated in the Standard Proctor test?

<p>By measuring the number of blows applied to the soil</p> Signup and view all the answers

What happens to the dry density of the soil when the water content is above the optimum water content?

<p>It decreases</p> Signup and view all the answers

What is the unit of measurement for the compactive effort in the Standard Proctor test?

<p>kJ/m^3</p> Signup and view all the answers

What is the ideal outcome of optimal soil compaction?

<p>Maximum dry density</p> Signup and view all the answers

What is the purpose of finding the Optimum Moisture Content (OMC) in soil compaction?

<p>To achieve the maximum dry density</p> Signup and view all the answers

What happens to the entrapped air in the soil as the water content increases?

<p>It increases</p> Signup and view all the answers

Study Notes

Shear Strength of Soil

  • Shear strength of soil determines its ability to support imposed loading or its own weight.

Definition of Shear Strength

  • Shear strength refers to the resistance along a plane that passes between or along long particle surfaces, but not through the particles.

Importance of Shear Strength

  • It is a crucial characteristic of soil that affects several aspects of foundation design and construction.
  • Shear strength is important in determining:
    • Bearing capacity of soil for foundation design
    • Ultimate bearing capacity of a soil for foundation design
    • Lateral pressure against retaining walls, sheeting, or bracing
    • Friction of slopes, hills, slides, cuts, embankments, and earth dams

Development of Shear Strength

  • Shear strength is developed due to compression or tension forces, commonly caused by compression.
  • When the applied stress exceeds the shear strength of soil, it leads to:
    • Sliding of soil particles upon each other
    • Change in volume
    • Part of the soil may move or be displaced with respect to the surrounding media
    • Shear failure of soil

Soil Compaction

  • The goal of soil compaction is to reduce air-void volume Va in soils as much as possible.
  • Compaction is done by dropping a hammer 25 times onto the confined soil, which is divided into three lifts, and each lift is compacted 25 times.

Standard Proctor Test

  • The test measures the maximum dry unit weight and optimum water content of a soil.
  • The test involves compacting the soil by dropping a hammer, and the process is repeated 4-6 times from dry to wet conditions.
  • The density is at its maximum at the optimum water content, and it does not increase any further.

Modified Proctor Test

  • The test was developed during World War II by the U.S.
  • The test is used to measure the maximum dry density and optimum water content of a soil.

Optimum Water Content (w/c)

  • The range of optimum w/c varies depending on the soil type: 6-10 for sand (sub-base material), 8-12 for silty sand (sandy silt), 12-16 for silt, and 15-22 for clay.

Compaction Curve

  • The curve shows the relationship between the water content and dry density of a soil.
  • The curve has three stages: below optimum water content, at optimum water content, and above optimum water content.

Zero-Air-Void (ZAV) Curve

  • The curve represents the fully saturated condition of a soil (S=100%).
  • The curve shows the maximum dry density that can be achieved for a given water content.

Importance of Soil Compaction

  • Compaction increases density, strength, and bearing capacity of a soil.
  • Compaction reduces permeability and compressibility of a soil.

Laboratory Work

  • Laboratory tests are used to obtain the maximum dry density and optimum water content of a soil.
  • The results are used to guide field compaction.

Field Compaction

  • Field compaction is done by contractors using rollers and compactors.
  • The compaction execution is checked in the field using several methods.

Soil Compaction

  • There are two types of soil compaction tests: Standard Proctor and Modified Proctor.

Soil Types and Properties

  • Fine material: Standard Proctor test uses a 4 * 4.6 hammer with 12 drops per layer, and Modified Proctor test uses a 4 * 4.6 hammer with 18 drops per layer.
  • Coarse material: Standard Proctor test uses a 6 * 4.6 hammer with 12 drops per layer, and Modified Proctor test uses a 6 * 4.6 hammer with 18 drops per layer.
  • Sand (sub-base material): range of optimum water content is 6-10%.
  • Silty sand (sandy silt): range of optimum water content is 8-12%.
  • Silt: range of optimum water content is 12-16%.
  • Clay: range of optimum water content is 15-22%.

Proctor Test Results

  • The test results in a curve that shows the relationship between water content and dry density.
  • The maximum dry unit weight is achieved at the optimum water content.
  • The unconfined compressive strength of the soil can also be measured.

Compaction Curve

  • The curve shows the effect of water content on dry density.
  • Below the optimum water content, the density increases as the water content increases.
  • At the optimum water content, the density is at a maximum and does not increase further.
  • Above the optimum water content, water starts to replace soil particles in the mold, and the density decreases.

Zero-Air-Void Curve (ZAV)

  • The curve represents the fully saturated condition (S=100%).
  • It shows the relationship between the degree of saturation and the void ratio.

Goal of Compaction

  • The goal is to find the appropriate amount of water (optimum water content) and the maximum dry density for a soil to be used in the field.
  • The test helps to determine the compactive effort required to achieve the maximum dry density.

Soil Compaction

  • There are two types of soil compaction tests: Standard Proctor and Modified Proctor.

Soil Types and Properties

  • Fine material: Standard Proctor test uses a 4 * 4.6 hammer with 12 drops per layer, and Modified Proctor test uses a 4 * 4.6 hammer with 18 drops per layer.
  • Coarse material: Standard Proctor test uses a 6 * 4.6 hammer with 12 drops per layer, and Modified Proctor test uses a 6 * 4.6 hammer with 18 drops per layer.
  • Sand (sub-base material): range of optimum water content is 6-10%.
  • Silty sand (sandy silt): range of optimum water content is 8-12%.
  • Silt: range of optimum water content is 12-16%.
  • Clay: range of optimum water content is 15-22%.

Proctor Test Results

  • The test results in a curve that shows the relationship between water content and dry density.
  • The maximum dry unit weight is achieved at the optimum water content.
  • The unconfined compressive strength of the soil can also be measured.

Compaction Curve

  • The curve shows the effect of water content on dry density.
  • Below the optimum water content, the density increases as the water content increases.
  • At the optimum water content, the density is at a maximum and does not increase further.
  • Above the optimum water content, water starts to replace soil particles in the mold, and the density decreases.

Zero-Air-Void Curve (ZAV)

  • The curve represents the fully saturated condition (S=100%).
  • It shows the relationship between the degree of saturation and the void ratio.

Goal of Compaction

  • The goal is to find the appropriate amount of water (optimum water content) and the maximum dry density for a soil to be used in the field.
  • The test helps to determine the compactive effort required to achieve the maximum dry density.

Soil Compaction

  • Objective: increase density, strength, bearing capacity, and reduce permeability and compressibility
  • Laboratory work: obtain maximum dry density and optimum water content
  • Field compaction: executed by contractors using rollers and compactors

Compaction Process

  • Definition: increasing soil unit weight by reducing the soil void ratio using mechanical devices
  • Modified Proctor Test: compacting soil in five layers with a 10 Lbs hammer, 18 inches drop height, and 25 blows/layer
  • Modified Proctor Energy: 56,250 ft-lb/ft³, calculated by (25 blows/layer) * (5 layers) * (10 lbs) * (1.5 ft) / (1/30) ft³

Comparison of Standard and Modified Proctor Tests

  • Mold size: 1/30 ft³ for both tests
  • Standard Proctor Test: 12" height of drop, 5.5 lb hammer, 3 layers, 25 blows/layer, and energy 12,375 ft-lb/ft³
  • Modified Proctor Test: 18" height of drop, 10 lb hammer, 5 layers, 25 blows/layer, and energy 56,250 ft-lb/ft³

Compaction Procedure in Lab

  • Method: removing air voids to achieve a degree of compaction (S=1)
  • Water content: wW / vt vw

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Soil Compaction PDF

Description

Learn about the shear strength of cohesive and cohesionless soils, and its significance in supporting imposed loading and self-support. Understand laboratory and field tests for measuring shear strength.

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