Geotechnical Testing Midterm Flashcards
(32 cards)
True or False, stress increases with depth
True
How do you calculate effective buoyant unit weight (𝛾buoy)
𝛾 buoy = 𝛾 sat - 𝛾 water (9.81 kN/m^3)
True or false, the deeper you go down into soil more load is felt
False the deeper you go into soil less load is felt
in the boussinesq equation
σz = (3P / (2πz³)) * ((r² + z²)^(5/2))
What does P stand for?
P =Point load applied at the surface
in the boussinesq equation
σz = (3P / (2πz³)) * ((r² + z²)^(5/2))
What does r stand for?
r = Horizontal distance from the point load application to the point where the stress is being calculated
in the boussinesq equation
σz = (3P / (2πz³)) * ((r² + z²)^(5/2))
What does z stand for?
z = Depth below the surface
True or false. Coarse grained soils have a largely elastic deformation
True
What is elastic deformation?
Strain recoverable upon unloading
What is plastic deformation?
Non recoverable strain
True or false. Fine-grained soils go through elastic deformation and are able to recover from the strain
False, fine-grained soils go through mostly plastic deformation, which can’t recover from strain.
True or false. Fine grained soils have low permeability
True
What are the three phases of settlement in fine-grained soils?
- Immediate settlement (volume distortion)
- Primary consolidation
- Secondary compression settlement (creep)
What causes primary consolidation settlement?
Primary consolidation results from drainage of water from the soil in response to loading
True or false. Primary consolidation settlement occurs quickly and rapidly.
False, primary consolidation occurs slowly over an extended period of time. Could be months or years.
Which form of settlement constitutes the majority of settlement for clays?
Primary consolidation settlement
What causes secondary compression settlement (creep)?
progressive breaking of clay particles and interparticle bonds
What three soil index properties are typically determined in conjunction with consolidation testing ?
- Specific Gravity
- Atterberg
- Particle Size Distribution
Define the term swelling pressure as it relates to the consolidation test
Pressure that is applied to a soil sample to prevent it from expanding in volume when it absorbs water
What three failure criteria are applicable for the unconfined compression test?
- The load dial has decreased for three consecutive readings
- The load dial remains consistent for 4 consecutive readings
- The axial strain is equal to 15% of the sample length
How do you calculate unit strain (ε)
ε = ΔH/Ho
How do you calculate Axial Strain
ε x 100
How do you calculate corrected area (Ac)
Ac = A0 / (1-ε)
How do you calculate Axial Load (P) ?
P = R * LRC
R= Load dial reading
LRC = Load ring calibration
How do you calculate compressive stress (qu)?
qu = (P/Ac) * 98.07
