Part A Learning Outcomes Flashcards
List the phases if a standard site investigation
Planning stage: desk study, site walkover, fieldwork specification
Main stage: fieldwork, lab testing, factual reporting
Review stage: monitoring
List the application of drilling and sampling methods
Categorisation by particle size
Identification of fractions
Identifying soil origin
Retrieving samples for lab testing
Performing in situ tests
Groundwater observations
Describe the triaxial test
A cylindrical sample is sealed in a membrane within a chamber of pressurised water. A loading cap is placed on top and used to alter axial stress while water pressure alters radial stress.
Describe the direct shear test
A specimen is confined in a metal box which is split horizontally at mid height. A vertical force is applied to consolidate the sample before it is sheared
Describe the oedometer test
The sample is placed inside a steel ring between two porous stones. Constant vertical stress is applied by a loading cap and excess water pressure is allowed to dissipate
Describe the standard penetration test
A sample tube is placed at the bottom of a borehole and a hammer drives it 150mm into the soil through successive blows. The test then measures the number of blows to drive the sampler a further 300mm
Describe the cone penetration test
A 60 degree cone is jacked into the ground at 20mm/s from a rig on the surface. Continuous measurements are taken of axial stress, frictional stress and pore pressure
Describe the vane shear test
A cruciform blade is driven into the soil at the base of a borehole. It is then rotated at 0.1 degrees/s until the soil undergoes shear failure
Describe the pressuremeter test
A cylindrical rubber membrane is installed in the soil and inflated laterally against the soil. Variation of pressure and radius is used to find shear modulus and undrained shear strength
Why might the wood method for approximating undrained strength from liquidity index not agree with in situ results?
The wood method is empirical
Soil can lose strength when remoulded
Nkt could be incorrect due to sample disturbance
What should be remembered about the relationship between Po and σho for a pressuremeter?
There are the same
What is the equation for expansion of a pressuremeter?
PL - Po = Su(1 + ln(G/Su))
Aside from geological records, what else constitutes part of the desk study?
Maps of underground services
Local records of buildings and geological events
What are the three primary purposes of lab testing?
Classify materials
Investigate soil behaviour
Obtain relevant parameters
Why can a standard penetration test be unreliable?
The results are dependent on the equipment used and often need a lot of correction
