1} The Unified Soil Classification System (USCS):
⇒4 major group: coarse,fine,organic & peat(Pt)
⇒general engg purpose
⇒coarse grain : based on size(sand,gravel)
⇒fine grain : based on plasticity chart.(fine sand, silt, clay)
2} American Association of state Highway & Transportation Official (AASHTO):
⇒into 8 groups
⇒GI = 0.2a + 0.005ac + 0.01bd (range 0 - 20) if -ve it is reported as 0.
GI=0 ←good subgrade material, GI = 20 ←very poor subgrade material.
3} Indian standard soil classification system.
⇒coarse grain : based on size,fineness,Cc & Cu.
⇒fine grain : basis of PI,LL & compressibility.
★BIS classified soil in 18 groups.
⇒Highway research → 7 types of soil (based on particle size & plasticity)
★clay : aquiclude
Boulder > 300mm
Cobble : 300 - 80mm
Gravel : 80 - 4.75mm
Sand : 4.75 - 0.075mm(75μ)
Silt : 0.075mm - 0.002mm(2μ)
Clay < 0.002mm(2μ)
★partical size ↓ : surface area ↑ : permeability↓ : compressibility↑.
⇒sand particle are madeup of Quartz (rock mineral)
FINE GRAIND SOIL CLASSIFICATION:
⇒A-line : Ip = 0.73(LL- 20) –(i)
⇒Ip = LL - PL –(ii)
⇒(ii)>(i) : clay (C) & (ii)<(i) : silt(M) or organic soil
⇒ Ip or PI = 4 - 7 ←CL-ML soil.
⇒LL<35 : low plastic (L) , 35<LL<50: intermediate plastic (I) , LL>50: Highly plastic (H)
★CH→highly plastic clay.
CLAY MINERALS:
i) montmorillonite:
⇒Vanderwall force ( weakest force)
⇒Black cotton soil & Bentonite
⇒activity 1 - 7
ii) illite :
⇒activity 0.5 - 1
⇒K+ve Bond (ionic bond)
⇒stiff clay & soft clay
iii)kaolinite:
⇒Activity 0.4-0.1
⇒china clay
Hydrogen bond (most stable bond)
★M>i>K>silica →Dry strength , PI , plasticity, swelling & shrinkage , Activity
Grain size : K>i>M
SOIL STRUCTURE:
i} Single Grained str : (>0.02mm)
⇒C-less soil , Gravel & Sand
ii} Honey combed str : (0.02mm - 0.002mm)
⇒gravity & surface electric force
⇒sand & silt
iii} flocculated str: (<0.002mm)
⇒edge of face orientation
⇒clay partical settle on sea bad
⇒low compressibility, High permeability & shear strength
iv} Dispersed str : (w of soil >omc)
⇒face to face configuration, ∥ to each other.
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