Site Investigation

Question 1

What are benefits and use cases of the shell and augur method?

Answer 1

Cheap
Easily installed
Used in stiff clays
Installation of equipment

Question 2

How are undisturbed cores obtained?

Answer 2

Rotary core drilling

Question 3

Why are results obtained from coring often slightly inaccurate?

Answer 3

Drilling induces shear strains and external stresses, and the extraction affects water content

Question 4

When is driving (percussive blows) preferred to single push methods?

Answer 4

In fibrous material such as peat

Question 5

What is the preferred method for obtaining high quality samples of soft clay?

Answer 5

Piston sampling

Question 6

How are coarse grained soils characterised?

Answer 6

Particle size grading

Question 7

How are fine grained soils characterised?

Answer 7

Plasticity and liquidity

Question 8

How is the liquid limit of a soil determined?

Answer 8

By performing a falling come test. When the cone is able to fall 20mm in 5 seconds this is the limit

Question 9

How is the plastic limit of a soil determined?

Answer 9

Rolling a sample down to 3mm diameter and checking for the appearance of cracks

Question 10

How does a standard penetration test characterise soil strength?

Answer 10

By recording the number of blows required to drive the test unit a specific distance, usually 300mm

Question 11

What are the conditions of the SPT N value?

Answer 11

The number of blows by a 63.5kg hammer through 760mm required to drive the sampler 300mm deep

Question 12

What are the 3 values which can be obtained from a cone penetration test?

Answer 12

Cone tip pressure
Pore water pressure
Sleeve friction

Question 13

What are 3 advantages of a CPT?

Answer 13

Accurate and repeatable
Easy delineation of strata
Fast setup and operation

Question 14

What is a pressure meter test used for?

Answer 14

Measuring soil stiffness

Question 15

When is a ring shear test used?

Answer 15

To analyse very large displacements for residual strength testing

Question 16

What does a direct shear box test measure?

Answer 16

Total stress only

Question 17

How does a shear vane test measure shear strength?

Answer 17

The torque required to turn the blades to failure is related to shear strength

Question 18

Why does the friction sleeve on a CPT affect pore pressure measurements?

Answer 18

The sleeve position is flexible so the size of the pressure meter intake can change

Question 19

What are the typical properties of coarse grained soils?

Answer 19

High strength
High permeability
Poor compressibility

Question 20

How can soil under a CPT be assumed to fail?

Answer 20

Similarly to a shallow foundation

Question 21

What is the equation for relative density?

Answer 21

Max Void ratio - current vr
/
Max vr - min vr

Question 22

What a are the factors that relate torque of a shear vane to undrained strength?

Answer 22

Vane width and vane height

Question 23

What are the required assumptions for the shear vane test?

Answer 23

Minimal disturbance
No drainage
Homogeneity
The formation of a cylindrical surface
Uniform stress distribution
No progressive failure

Question 24

Where is the shear vane unsuitable?

Answer 24

In soil with strength over 100kPa

Question 25

What soil type can the self boring pressuremeter not be used in?

Answer 25

Gravels

Question 26

What is the initial stress state in a pressuremeter?

Answer 26

Radial stress = hoop stress = lateral stress

Question 27

How do radial and hoop stresses change as excess pressure is applied inside the pressuremeter?

Answer 27

Change in Radial = A+(B/r2)
Change in Hoop = A-(B/r2)
A and B are site specific contestants

Question 28

What must the change in pressure be if A=0?

Answer 28

B/R2

Question 29

How does hoop strain: 1/E (Δσθ - ν * Δσr) become: -Δp/2G?

Answer 29

Δσθ = -Δp
Δσr = Δp
(1 + ν)/E = 1/2G

Question 30

For small strain cavity expansion, what is the equation for pressure p?

Answer 30

p = σho + 2Gεc
Where εc = -εθ

Question 31

What is the equation for the state-dependent liquidity index IL?

Answer 31

w-wp
———
wL-wp

Question 32

What is the relationship between liquidity index and undrained strength?

Answer 32

Su = 2 * 100^(1-IL)

Question 33

In the equation qt = NktSu + σvo, what do each of the terms mean?

Answer 33

qt: cone tip resistance
Nkt: empirical cone factor
Su: undrained strength
σvo: initial vertical stress

Question 34

What factors are used to calculate torque of a shear vane test?

Answer 34

Moment of shear resistance on the side and moment of shear resistance at the ends

Question 35

What is the moment of shear resistance at the side of a shear vane?

Answer 35

Circumference * height * radius * undrained strength

Question 36

What is the moment of shear resistance at the ends of a shear vane?

Answer 36

2 * int(2 pi r2 su)dr
The integral is from 0 to r

Question 37

What is the plasticity index?

Answer 37

The water content at liquid limit - water content at plastic limit

Question 38

What numbers do you need to calculate water content?

Answer 38

Weight of soil (minus water and sample tin)
Weight of water

Question 39

What should you calculate to quantitatively classify soils from a CPT?

Answer 39

Normalised cone resistance
Normalised friction ratio
Pore pressure parameter

Question 40

What is the equation for normalised cone resistance?

Answer 40

Qt = (qt-σv)/σ’v

Question 41

What is the equation for normalised friction ratio?

Answer 41

Fr = (fs/(qt-σv))100%

Question 42

What is the equation for pore pressure parameter?

Answer 42

Bq = Δu/(qt-σv)

Question 43

After Qt, Fr and Bq are found, how are they used to classify soils?

Answer 43

Soil behaviour type graphs designate regions for specific soil types based on these values

Question 44

How do you reduce the disturbance of a thin walled sampler?

Answer 44

Decrease the ratio of width to thickness

Question 45

What are the pressuremeter boundary conditions?

Answer 45

A=0
B=delta p R^2