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C

The height to which water will rise above the water table due to capillarity.

Soil particles less than 0.002mm in size.

Soils with less than 35% by mass of grains less than 0.06mm in size.
Coarse soil: grain size is predominantly 0.06-60mm
Very coarse soil: grain size is predominantly greater than 60mm

The ratio of the minimum horizontal effective stress to the vertical effective stress at a point in a soil mass retained by a surface as the surface moves away from the soil.

A measure of the rate of change of volume during primary consolidation; referred to either vertical drainage (c_v) or horizontal drainage (c_h). Units: m²/s

(Also curvature coefficient) A measure of the shape of a grading curve:
C_z = d₃₀² / (d₆₀ x d₁₀).
See particle size characteristics

The ratio of horizontal effective stress to vertical effective stress at a point in a soil mass loaded in conditions of zero horizontal strain.

The ratio between the tangential force (T) required to cause a body to slide along a plane and the normal force (N) between the body and the plane:
T = mN.

Along a wall or foundation surface:
m = tan d
where d = angle of wall friction

The ratio of the maximum horizontal effective stress to the vertical effective stress at a point in a soil mass retained by a surface as the surface moves toward from the soil.

The constant average discharge velocity (v) of water passing through soil when the hydraulic gradient (i) is 1.0; defined by Darcy’s law:
v = k.i

The change in volumetric strain per log₁₀ cycle of time after primary consolidation is complete.

(Also uniformity coefficient) A measure of the slope of a grading curve and therefore the uniformity of the soil in particle size analyses:
C_u = d₆₀ / d₁₀
See particle size characteristics

The change in volumetric strain per unit volume per unit change in effective stress in one-dimensional compression. (Units m²/MN)
Compressibility is the reciprocal of stiffness.

Apparent cohesion (c´) is the intercept on the shear stress axis of a straight-line Mohr-Coulomb envelope. For critical states and residual states, c'_c = c'_r = 0 in most cases. For peak states, a curved strength envelope also passes through the origin, but a straight-line fitted to a small number of results is often extrapolated to give an intercept c'_p > 0. (In physics, cohesion is described as ‘the force that holds together molecules or like particles within a substance’.)
See also adhesion and true cohesion.

Volume change in soil in which air is expelled, but with the water content remaining constant. Compaction may occur due to vibration in loose sands and gravels, and in fill due to self-weight. In soil constructions, compaction is achieved by rolling, tamping or vibrating.

The relationship between the strains in a deforming body so that no holes appear and no material is destroyed.

The ratio of the change in volumetric strain to the change in isotropic stress.
For a saturated soil, C_v = ¥

The slope of the normal compression line (NCL) and critical state line (CSL).

The resistance force divided by the end area of the cone tip, measured during the cone penetration test.

A penetration test in which a sleeved cone (diameter 35.7mm, end area 1000mm², apex angle 60º) is pushed into the ground at a rate of 20 mm/min and the force required measured. The magnitude of this force divided by the end area is called the cone penetration resistance (q_c). The cone and the sleeve can be advanced separately and so the frictional resistance along the sleeve (1000mm² area) or local side friction (f_s) can also be measured.

A confined aquifer is contained between two strata of low permeability; in flow analyses, a confined aquifer is often assumed to be saturated throughout its depth.

A measure of the relationship between the current water content and the consistency limits, similar in form to the density index, but expressed in terms of water content.
I_c = (w_L - w)/I_P
At liquid limit, I_c = 0
At plastic limit, I_c = 1.0

(Also called Atterberg limits) Measures of water content corresponding to changes in physical state of a soil:
liquid limit (w_L) = w/c at the change from liquid to plastic
plastic limit (w_P) = w/c at the change from plastic to semi-solid
shrinkage limit (w_s) = w/c below which no further shrinkage upon drying occurs

Volume change due to dissipation of excess pore pressure, usually with constant total stress.

The settlement of a foundation due to consolidation.

(After Charles Augustin Coulomb, 1736-1806) An equation relating the shear strength of soil to the normal effective stress on a failure plane.

t_f = c' + s' tanf'
= c' + (s - u) tanf'

Deformation or volume change which occurs in soil at constant effective stress progressing with time.

In slope stability analyses the slip circle corresponding to the lowest factor of safety.

The ground slope angle that corresponds to a slope-stability factor of safety of 1.0.

The height of a slope (e.g. embankment, cutting, trench) for which the factor of safety against collapse is 1.0.

The hydraulic gradient at which effective stresses becomes zero; with upward seepage, sand may become quicksand.

The shear stress developed along a slip surface during shearing at constant volume; also known as ultimate shear strength.

The state of a soil in which it strains; critical states occur on the critical state line.
Note: The critical state is not the same as the residual state; at the critical state, soil particles continue to rotate and the flow is turbulent; at the residual state, in clay soils, flat particles become aligned to the slip plane and the flow is laminar.

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The unique relationship at failure between deviator stress, average normal stress and volume (or shear stress, normal stress and void ratio) is defined by the critical state line.

q´ = Mp´
v = G - l lnp´

t´ = s´_n tanf´
e = e_G - C_c logs´_n

The void ratio of a soil at which its volume remains constant during shearing. Note: critical void ratio depends on the mean stress.

The current state of a soil is described by its voids ratio (e) or specific volume (v), the current stress (s' or p') and the overconsolidation ratio or yield stress ratio (R_y).