GeoE/EnvE 153: Earth Engineering - Soils II

Flashcards covering key vocabulary and concepts from the lecture on Soils II, including soil profiles, soil-forming factors, mass-weight-volume relationships, index properties, and Atterberg limits.

Soil Horizons

Classified by soil scientists (pedologists) based on layers that impact stockpiling for reclamation.

Unconsolidated vs. Consolidated

Geologists classify subsurface material as either unconsolidated or lithified (consolidated).

Unified Soil Classification System

A system used by engineers to characterize soils for engineering design purposes.

Transported soils

Deposits of rivers, glaciers, and other surficial processes.

Residual soils

Soils developed in place by weathering.

Soil-forming factors

Include climate, parent material, organisms, relief (topography), and time.

Water content ((\theta_w))

Ratio of the mass of water to the mass of solids in a soil sample: (\thetaw = \frac{Mw}{M_s}).

Water saturation ((S_w))

Ratio of the volume of water to the total volume of void space: (Sw = \frac{Vw}{V_v}), ranging from 0 to 1.

Air saturation ((S_a))

Ratio of the volume of air to the total volume of void space: (Sa = \frac{Va}{Vv}), ranging from 0 to 1, where (Sw + S_a = 1).

Void ratio (e)

Ratio of the volume of voids to the volume of solids: (e = \frac{Vv}{Vs}).

Porosity (n)

Ratio of the volume of voids to the total volume: (n = \frac{Vv}{VT}), with relationships (e = \frac{n}{1-n}) and (n = \frac{e}{1+e}).

Bulk density ((\rho_b))

The soil's mass divided by its volume: (\rhob = \frac{MT}{V_T}).

Bulk unit weight ((\gamma_b))

The soil's weight divided by its volume: (\gammab = \frac{MTg}{V_T}).

Specific gravity ((G_s))

Ratio of density of solids to density of water: (Gs = \frac{\rhos}{\rho_w})

Coarse-grained (cohesionless) Index Properties of Soils

Particle-size distribution, Shape of particles, In-place density, Relative density

Fine-grained (cohesive) Index Properties of Soils

Clay content, Consistency, Water content, Atterberg limits, Type and amount of clay, Sensitivity

Sensitivity (St)

Ratio of undisturbed to remoulded unconfined compressive strength: (St = \frac{(qu){\text{undisturbed}}}{(qu)_{\text{remoulded}}}).

Sieve Analysis

A method using sieves to determine the particle size distribution of a soil.

Hydrometer Analysis

A method to compute particle size at different times according to: (D[mm] = K \sqrt{\frac{L[cm]}{t[min]}}).

Coefficient of Uniformity (Cu)

Describes the particle size distribution: (Cu = \frac{D{60}}{D_{10}}) (>4-6 is well-graded, <4 is poorly graded).

Coefficient of Gradation/Curvature (Cc)

Describes the particle size distribution: (Cz = Cc = \frac{D{30}^2}{D{60} \times D_{10}}) (1-3 is well-graded).

Poorly graded soil

A soil that has most of the soil particles about the same size

Well graded soil

A soil that has a good representation of all particle sizes

Gap graded soil

A soil that is missing one or more sizes of particles

Colloids

Small particles in cohesive clay soils whose surface arrangement controls their behaviour.

Atterberg Limits

Water contents defining the boundaries between liquid, plastic, and solid states of cohesive soils.

Liquid Limit (LL)

Water content at which soil transitions from liquid to semi-solid plastic state, determined by Casagrande cup or fall cone test.

Plastic Limit (PL)

Moisture content at which soil crumbles when rolled to 1/8 inch diameter.

Plasticity Index (PI)

Difference between liquid limit and plastic limit (PI = LL - PL), indicating the range of water content for plastic behavior.

Activity (A)

Used to determine the dominant clay mineral present in the soil sample: (A = \frac{PI}{\% D < 2\mu m}).

Liquidity Index (LI)

Scales in-situ water content relative to LL and PL: (LI = \frac{\theta_w - PL}{LL - PL}).