Exploration Methods Flashcards
Factors affecting choice of exploration methods
In choosing methods, four main sets of factors to be considered:
(a) Geological nature of site (Soil, Rock etc)
(b) Topographical nature of site (Ease of access, over water, congested site , mud flats, etc)
(c) Type of info req’d (soil/water samples, in situ properties, presence of voids)
(d) Cost and time
Types of sub-surface exploration methods
Trial pits
(b) Large bored shafts
(c) Boring and drilling
(d) Probing
(e) In situ examination
Positives of trial pits?
Easily dug with excavator (fast and cheap)
Can be extended into trenches
High quality blocks can be taken w/ tube and hand penetration test samples
Disadvantages of trial pits
Can only investigate near surface (2-5m)
They are potentially dangerous (require support and possibly pumping, without batter and support maximum depth 1.2m)
Types of drilling and boring methods
(a) Hand auger
(b) Light percussion drilling
(c) Power auger methods
(d) Rotary core drilling
(e) Wash boring
benefit of shell and augur (light cable drilling)
Soils without cobbles boulders can provide good progress.
Relatively fast.
What does a shell and augur consist of?
Clay cutter
The shell (used for grnaular materials)
Winch to raise above hole and drop cuttting tool
How to carry out SPT (Stnadard peneration test)
Split spoon driven 450mm
first 150mm considered “seating blow”, count recorded but not used for N value
Max number of blows 25
Blow count for 450mm recorded in 75mm increments
N value calcuated from number of blows recorded for 300mm of penetration after the seating blow
max number of blows 50 for 300mm
If maximum number of blows reached then record penetration
Density in relationship to N values, Blows
Very loose 0-4 loose - 4 - 10 medium dense 10- 30 dense - 30 - 50 very dense 50 >
why use Rotary core drilling and how is it carried out
Hard soil with rock
consists of small diamater hollow tube, fitted at the end with a coring bit
core barrel rotates at 600-1200 rpm. Water flushing fluid circulates
fragments are removed and raised up spiral design out to surfaace
drill run of 1-3m made before raising barrel and removing core
s
types of power augur drilling
flight augurs - short stemmed or continous.
Bucket augur
why is flight augurs better in some areas than stemmed
better for shallow depth; vice versa
how does bucket augur work
soil passing into bucket, which is raised at intervals
wash boring, why is it bad?
disturbs soil, high pressure jet etc
probing, types:
makintosh probe: rods connected together for length
hammer at top, driving point of bottem
N of blows per 150mm
other types:dynamic, swedish weight penetrometer
