1. Chapter 1Chapter 1
Introduction to Soil MechanicsIntroduction to Soil Mechanics

2. What is Soil?What is Soil?
 SoilSoil –– uncementeduncemented aggregate of mineralaggregate of mineral
grains with liquid and gas (water and air)grains with liquid and gas (water and air)
in the spaces between (pore spaces)in the spaces between (pore spaces)
 Created from the breakdown ofCreated from the breakdown of RockRock
 As cementation increases, soil becomesAs cementation increases, soil becomes
RockRock
 Must understand various properties sinceMust understand various properties since
soils are used as a construction materialsoils are used as a construction material
and to support structuresand to support structures

3. FundamentalFundamental
PropertiesProperties
 Grain size distributionGrain size distribution
 PermeabilityPermeability
 CompressibilityCompressibility
 Shear strengthShear strength
 Bearing capacityBearing capacity

4. Role of WaterRole of Water
 Water is typically the fluid contained inWater is typically the fluid contained in
the pore spacesthe pore spaces
 Because it is incompressible and dipolar,Because it is incompressible and dipolar,
water greatly affects the behavior of soilswater greatly affects the behavior of soils

6. Recognize this mess?

7. Brief History of SoilBrief History of Soil
MechanicsMechanics
 Began ~ 18Began ~ 18thth
centurycentury
 Since then, the science of Soil MechanicsSince then, the science of Soil Mechanics
has evolved through 4 phaseshas evolved through 4 phases
 Pre-classical (1700 A.D. to 1776 A.D.)Pre-classical (1700 A.D. to 1776 A.D.)
 Classical – Phase I (1776 A.D. to 1856 A.D.)Classical – Phase I (1776 A.D. to 1856 A.D.)
 Classical – Phase II (1856 A.D. to 1910 A.D.)Classical – Phase II (1856 A.D. to 1910 A.D.)
 Modern (1910 A.D. to Present)Modern (1910 A.D. to Present)

8. Pre-classical PeriodPre-classical Period
 Angle of repose of clean, dry sand andAngle of repose of clean, dry sand and
natural earthnatural earth
 Unit weight of clean, dry sand andUnit weight of clean, dry sand and
natural earthnatural earth
 Early laboratory work on retaining wallEarly laboratory work on retaining wall
behavior and lateral earth pressurebehavior and lateral earth pressure
 Rock and clay were not studiedRock and clay were not studied

9. Discussion QuestionDiscussion Question
 What is the difference betweenWhat is the difference between PressurePressure
andand StressStress??

10. AnswerAnswer
 Pressure is omni-directional – the samePressure is omni-directional – the same
magnitude in all directionsmagnitude in all directions
 Stress is unidirectional – acts along aStress is unidirectional – acts along a
given axis onlygiven axis only
 Note: in soil mechanics, we often use theNote: in soil mechanics, we often use the
termsterms PressurePressure andand StressStress
interchangeablyinterchangeably

11. Classical – Phase IClassical – Phase I
 Advances in lateral earth pressure andAdvances in lateral earth pressure and
retaining wall theoryretaining wall theory
 Coulomb used principles of calculus toCoulomb used principles of calculus to
determine slip planes in soils behind retainingdetermine slip planes in soils behind retaining
wallswalls
 Sloped backfill and surcharge loadings wereSloped backfill and surcharge loadings were
also studiedalso studied
 Rankine published his first theory on earthRankine published his first theory on earth
pressurespressures

12. Classical – Phase IIClassical – Phase II
 Darcy – coefficient of permeability (a.k.a.Darcy – coefficient of permeability (a.k.a.
Hydraulic Conductivity)Hydraulic Conductivity)
 Boussinesq – stress distribution underBoussinesq – stress distribution under
load bearing areasload bearing areas
 Reynolds – dilatency of sandsReynolds – dilatency of sands

13. Modern Soil MechanicsModern Soil Mechanics
 Dr. Karl Terzaghi – “Father of ModernDr. Karl Terzaghi – “Father of Modern
Soil Mechanics”Soil Mechanics”
 Consolidation theories for clay soilsConsolidation theories for clay soils
 Bearing capacity, settlement, piping underBearing capacity, settlement, piping under
damsdams
 Atterberg – Soil plasticityAtterberg – Soil plasticity
 Fellenius – Slope stability of claysFellenius – Slope stability of clays

14. Dr. Karl TerzaghiDr. Karl Terzaghi
(1883 – 1963)(1883 – 1963)

15. Q & AQ & A

16. ProfessionalProfessional
Development ActivityDevelopment Activity
#1#1
 Begin working on your first PD activityBegin working on your first PD activity
 Reports are due no later than 9:45 A.M.Reports are due no later than 9:45 A.M.
on Tuesday, September 27on Tuesday, September 27thth
 Meet with me or email me to discussMeet with me or email me to discuss
your activity and have it approvedyour activity and have it approved