Quantitative Properties Soil PhasesVolumeWeight –Solids V S W S –Liquid (water) V W W W –Gas (Air) V A W A –Voids V V = V W + V A W V = V W + V A –Total (Mass)V M =V T =V S + V V W T =W S + W V Parameters –Volume –Weight (force) –Density (  ) –Ratios Porosity (n) = Vv/V T Unit weight (  W ) = weight/volume Moisture (water) content (w) = W W /W T Degree of saturation (e.g., Sw) = Vw/Vv

Functional Relationships F = ma (wt = mass*gravitational acceleration) Mass = density*volume –Solid: m S =  S * V S (e.g., 2.5 g/cm 3 * cm 3 ) Wt (force; lbs, N) = mass * g 9.8 m/sec 2 e.g. =  S * V S *g For given values of known parameters, can solve for unknowns, e.g.,: –Water content –Degree of saturation –Etc.

Role of Fluid Pressure Effective pressure (p eff ) = pressure acting on grain-to- grain contact Neutral (water) pressure (  w ) = h *  W h = height of water column  W = Unit weight of water = 1x10 4 N/m 2 Total pressure (p T ) = p eff +  w p T = p usat + p sat –  w where p i = h i *  i p eff at a given depth = p T –  w

Shear Strength of Soil S = C + p eff tan  = C + (p T –  w ) tan  From example, increased saturation decreases effective pressure AND shear strength Effects of decreased shear strength –Landslides, downslope movement