CVEN 365 Final

What is the equation for effective stress? Define the parameters

σ´= σ - α*u_w

Where:

σ´= effective stress

σ = normal stress

α = water area ratio

u_w = water stress/ pore pressure

What is the equation for shear strength? Define the parameters

s = c' + (σ - αu_w) tan(φ')

Where:

s = shear strength on the failure plane

c' = effective stress cohesion

σ = total normal stress on failure plane

α = water area ratio

u_w = water stress

φ' = effective stress friction angle

What is Mohr's circle?

A graphical representation that shows the relationship between normal and shear stress at a point. It is used to determine the stress state on any plane and assess soil strength and failure conditions.

What is the undrained shear strength?

The maximum shear strength a saturated soil can resist without any drainage occurring -- the pore water pressure does not dissipate during loading.

When would you use undrained shear strength?

This would need to be used when analyzing short-term stability of saturated soils, particularly in conditions where loading occurs rapidly, like during construction or in clayey soils.

What are the 6 equations of elasticity in the x, y, z, coordinates?

1) ε_x​x = (1/E)*(σ_xx ​− ν(σ_yy​ + σ_zz​))

2) ε_yy = (1/E)*(σ_yy ​− ν(σ_xx​ + σ_zz​))

3) ε_zz = (1/E)*(σ_zz ​− ν(σ_xx​ + σ_yy​))

4) γ_xy ​ = (τ_xy​)/G

5) γ_yz ​ = (τ_yz)/G

6) γ_zx ​ = (τ_zx)/G

Give 3 factors influencing the modulus of a soil.

State Factors: density, water content, overconsolidation ratio (OCR)

Loading Factors: strain level, confinement, # of loadings

Explain the Consolidation process.

The process by which a saturated soil gradually decreases in volume over time due to the expulsion of pore water under sustained loading. This leads to an increase in effective stress and settlement of the soil, especially in clayey soils.

What is the preconsolidation pressure?

The maximum effective vertical stress that a soil sample has experienced in the past -- determined during consolidation testing. It acts as the yield stress separating elastic and plastic compression. It is critical for identifying whether the soil is normally consolidated or overconsolidated.

If it takes 3 years for the consolidation settlement of a 2m high embankment to take place, how long does it take for a 6m high embankment?

3 years, because time of settlement does not depend on initial height

What is the shrink swell modulus?

Ess = (Δw)/(Δv/v) = (Δw)/((1/f)(ΔH/H)

Ess is important for foundation construction on shrink-swell soils

What is the coefficient of consolidation?

Cv - a measure of how quickly a saturated soil undergoes consolidation due to dissipation of excess pore water pressure under loading

What is the compression index?

Cc = (Δe) / Δlog(σ'))

a soil parameter that represents the slope of the compression curve for normally consolidated clays.

What is the pole? (On Mohr's circle)

The pole is a point on the mohr circle such that a line going through the pole and the stress point will be parallel to the plane on which the stresses are acting

Why do we need 2 triaxial tests to get failure envelope?

We need at least two triaxial tests to draw a failure envelope because each test gives one Mohr's circle at failure, and two circles are required to determine the line's slope (friction angle) and intercept (cohesion).

UU

unconsolidated undrained

CU

consolidated undrained

CD

consolidated drained

What is consolidation settlement affected by?

magnitude and time rate

What does over consolidated mean?

The soil is experiencing a consolidation or load less than past conditions.

What does normally consolidated mean?

The soil is experiencing a consolidation or load equal to preconsolidation pressure

What is the typical range for the soil modulus?

1-100 MPa

List the types of foundations.

- Stiffened slab on grade

- Elevated structural slab on piles

- Slab on grade and on piles

- Post-tensioned slab on grade