Site Investigations Flashcards
What must the design of geotechnical structure do?
Prevent failure and ensure serviceability
What is an example of failure
Collapse of a retaining wall
Landslide on slope
Large penetration of footing or pile foundation
What’s an example of serviceability failure
Excessive settlement disrupting access and drainage
Define parent material
The rocks from which a soil is made from
Define residual soils
The parent material of a soil is directly below
Define transported soil
Wind, water or glaciers have transported the soil far from the parent material
What is top soil
Organic material
What is superficial soil
Less organic material
What is the fragmented rock layer made of
More rock is found in the soil
What is the grain size of gravel and how do you identify it
63-2mm and by eye
What is the grain size of sand and how do you identify it
2-0.063mm and by eye
What’s the grain size of silt and how do you identify it
0.063-0.002mm and by optical microscope/magnifying glass
What is the grain size of clay and how do we identify it
<0.002mm and electron microscope
What are the three behaviours of coarse soil
Cohesion less
Permeable
Less compression
What are the three behaviours of fine soil
Cohesive
Impermeable
Compressible
What are the three circles of the geotechnical triangle
Ground profile
Soil behaviour
Modelling
What’s included in the ground profile section of the GT?
Genesis
Geology
Site investigation
Ground description
What’s included in the soil behaviour section of the GT?
Lab testing
Field testing
Observation
Measurement
What’s included in the modelling section of the GT?
Idealisation
Then evaluation
Conception/numerical/physical modelling
What does the geotechnical triangle achieve?
Empiricism
Precedent
Experience
Risk management
Why is site investigation needed?
To enable a geotechnical and geo-enviromental assesment of the ground conditions followed by an analysis of these
Name three conditions of the subsurface that we research during site investigations
Soil and rock profile
Geological features
Contamination
Why do we carry out site investigations?
To determine the type of foundation needed
To make recommendations of safe bearing capacity and pile load capacity
To enable adequate and economical design
What are the three sections of site investigation?
Planning
Execution
Report
Why do we plan site investigations?
Minimise cost of explorations
Give reliable info
Decide on quality and quantity of investigations depending on the project type
What kind of tests are conducted as part of a site investigation?
Collection of Disturbed and undisturbed samples
Conducting Insitu tests if subsurface material
Student of ground water conditions
Geophysical exploration
Lab testing on samples
Name 3 site exploration methods
Test pits
Boreholes
Probes
What are the two types of soil sample?
Disturbed and undisturbed
Define a disturbed sample
Natural structure of the soil gets modified or destroyed during the sampling process
Define an undisturbed sample
Natural structure of the soils and material properties are preserved during the sampling process
Pros of test pits
permits visuals of subsurface in a natural state
useful for gravelly soils where boreholes are unusable
Cons of test pits
max depth of 5-6m
Sampling and testing is done on an exposed surface
Pros of auger borings
Simplest method
Can be powered or hand driven
Suitable in all types of soil above GWT
Hollow system augers can be used for the SPF and sampling
Cons of auger borings
Maximum depth of 10m
In soil below GWT can only be used in cohesive soil
Only produces highly disturbed samples
Casing may need to be installed in some soils
What does SPT stand for
Standard penetration test
