CELE Geotechnical Engineering — Stresses in Soil MassConcept Map

Concept

Effective Stress (σ')

Sub Concepts

• Terzaghi's Effective-Stress Equation
• Total Stress Component
• Pore Pressure Component
• Strength and Settlement Control

Relationship To Central

Foundation principle governing soil behavior

Concept

Total Stress (σ)

Sub Concepts

• Geostatic Stress
• Layer-by-Layer Summation
• Unit Weight Application
• Saturated vs. Unsaturated Conditions

Relationship To Central

First component of effective stress calculation

Concept

Pore Pressure (u)

Sub Concepts

• Hydrostatic Pore Pressure
• Seepage-Induced Pressure
• Water Table Position
• Quick Condition (u approaching σ)

Relationship To Central

Second component of effective stress; critical below water table

Concept

Stress Increase from Surface Loads (Δσ)

Sub Concepts

• Boussinesq Point Load Theory
• 2:1 Approximation Method
• Influence Factors
• Newmark's Chart

Relationship To Central

Application of effective-stress principle to foundation design

Concept

Boussinesq Point Load

Sub Concepts

• Vertical Stress Directly Below Load
• Stress at Horizontal Offset (r)
• Depth Dependency (z)
• Decay Function with Distance

Relationship To Central

Theoretical model for concentrated load stress distribution

Concept

2:1 Spread Method (Approximate)

Sub Concepts

• Footing Dimensions (B, L)
• Load Spreading at Depth
• Quick Field Calculations
• Depth and Area Relationships

Relationship To Central

Practical footing design method based on 2:1 slope assumption

Concept

Water Table Effects

Sub Concepts

• Submerged vs. Above Water Table
• Saturated Unit Weight (γsat)
• Buoyancy Effects
• Capillary Rise Complications

Relationship To Central

Controls pore pressure and effective stress profile

Concept

Seepage and Flow Conditions

Sub Concepts

• Upward Seepage Pressure
• Downward Seepage Pressure
• Hydraulic Gradient
• Critical Gradient (Quick Condition)

Relationship To Central

Alters pore pressure beyond hydrostatic; affects effective stress

Concept

Board-Exam Common Errors

Sub Concepts

• Forgetting Pore Pressure Below Water Table
• Using Wrong Unit Weight
• Misapplying 2:1 Spread Formula
• Ignoring Seepage Pressure

Relationship To Central

Practical knowledge for PRC licensure exam success

To

Total Stress

From

Effective Stress Principle

Strength

strong

Relationship

Effective stress is calculated as: σ' = σ - u; total stress is the first component

To

Pore Pressure

From

Effective Stress Principle

Strength

strong

Relationship

Pore pressure is subtracted from total stress in the effective-stress equation; both are equally critical

To

Unit Weight Selection

From

Total Stress

Strength

strong

Relationship

Total stress is computed by summing γ × z for each layer; correct unit weight is essential

To

Water Table Effects

From

Pore Pressure

Strength

strong

Relationship

Pore pressure develops only below the water table; water table position is the primary control

To

Seepage and Flow Conditions

From

Pore Pressure

Strength

strong

Relationship

Seepage pressure adds to or subtracts from hydrostatic pore pressure depending on flow direction

To

Strength and Settlement Control

From

Effective Stress Principle

Strength

strong

Relationship

Effective stress (not total stress) governs shear resistance, compressibility, and bearing capacity

To

Boussinesq Point Load

From

Stress Increase from Surface Loads

Strength

strong

Relationship

Boussinesq theory is one method to calculate stress increase beneath a point load

To

2:1 Approximation Method

From

Stress Increase from Surface Loads

Strength

strong

Relationship

2:1 method is an approximate alternative to rigorous solutions, suitable for quick footing estimates

To

Depth Dependency

From

Boussinesq Point Load

Strength

strong

Relationship

Boussinesq stress increase is inversely proportional to z²; deeper points experience lower stress

To

Foundation Design

From

2:1 Approximation Method

Strength

moderate

Relationship

2:1 method is widely used in foundation design for quick settlement and bearing-capacity estimates

To

Saturated Unit Weight

From

Water Table Effects

Strength

strong

Relationship

Below water table, γsat (not γ_moist) must be used for total stress calculation

To

Seepage and Flow Conditions

From

Quick Condition

Strength

strong

Relationship

Quick condition (u ≈ σ, σ' ≈ 0) occurs when critical hydraulic gradient ic is reached; upward seepage is the common cause

To

Pore Pressure Below Water Table

From

Board-Exam Common Errors

Strength

strong

Relationship

Most frequent exam error: forgetting that u is nonzero and reduces σ' below the water table

To

2:1 Formula Misapplication

From

Board-Exam Common Errors

Strength

strong

Relationship

Common error: using B×L instead of (B+z)(L+z) in the denominator

To

Foundation Bearing Capacity

From

Effective Stress Principle

Strength

moderate

Relationship

Bearing capacity equations (e.g., Terzaghi, Meyerhof) use effective stresses and effective stress parameters

To

Settlement Calculation

From

Stress Increase from Surface Loads

Strength

moderate

Relationship

Stress increase Δσ is input to settlement formulas; accurate Δσ is essential for reliable settlement estimates

To

Newmark Chart

From

Influence Factors

Strength

moderate

Relationship

Newmark's chart is a graphical tool based on influence factors for non-rectangular loaded areas

To

Hydraulic Gradient

From

Seepage Pressure

Strength

strong

Relationship

Seepage pressure is proportional to hydraulic gradient i; when i ≥ ic, quick condition is reached

To

Water Table Effects

From

Capillary Rise

Strength

moderate

Relationship

Capillary rise extends above the true water table; pore pressure in capillary zone is negative (tension)

To

Geostatic Stress

From

Total Stress

Strength

moderate

Relationship

Geostatic stress is the in-situ total stress before any external load is applied; foundation stress increases add to it