Lecture 1 - Practices, Testing and Installations
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What installations would be made for gas and groundwater?
Gas - stand-pipe installed, gas valve at surface Groundwater - Ingress measured during sinking borehole, time for rise and fall is measured, may take multiple strikes, monitored by stand-pipe piezometer
What are the two modes of reinstatement with examples?
Sealed - top cap Back-filled - cement-bentonite grout or gravel
What are the four sampling techniques? How are they stored? What are they used for?
Undisturbed - taken for lab tests Disturbed - stored in plastic tubs, suitable for moisture content index tests Chemical jar samples - amber/clear glass jars, soil and groundwater studies Bulk disturbed - unsealed plastic bags, classification tests
What samples are taken from boreholes? How are they done?
Chemical jar - depends on budget U100 or Standard Penetration Test - 0.5m, 1m, every metre to 5, then every 1.5m Bulk disturbed - each soil type Small disturbed - topsoil and each change in soil type/consistency
What are two methods of borehole drilling?
Continuous flight/hollow stem auger Cable percussion drilling
How can continuous flight/hollow stem augers be identified? Give advantage and disadvantage
Casing with outer spiral Faster but more expensive
If access is restricted what kind of boreholes drills are used?
Terrier/competitor drills
How is a cable percussion drill operated? (four steps)
• Diesel engine powers winch drum which is raised using friction clutch. • Clutch release drops tool • Sunk repeatedly dropping drill tools • Hole established
Name 5 basic components of cable percussion drills
Collapsible 'A' frame with pulley at top Diesel engine Winch drum Winch lift tool Suspended cable
Name the three different drilling tools used in cable percussion drilling?
Clay-cutter Shell Chisel
What is a clay-cutter made of and how does it work?
Heavy steel tube, weight added by sinker bar After couple of blows, brought to surface, clay is then removed by press-out tool
What is a shell used for and how is it used?
Granular material she’ll is surged in water at bottom of hole, disturbs material which goes into suspension, this enters shell on downstroke, non-return valve closes on upstroke and soil is retained
What is a chisel used for? Give two disadvantages
Breaking through obstructions like cobbles and boulders Slow and expensive (many holes abandoned)
What kind of samples are given by cable percussion drilling and what are they used for?
Disturbed samples, used for some index tests
What can undisturbed sample be used for?
Record changes in stratum at regular intervals and can do geotechnical tests
Why are trial pits dug?
Provides visual log of strata from ground surface down
How are trial pits dug?
Back-hoe excavator
What is the maximum depth of trial pits?
4-5m
What is required when trial pits deeper than 1.2m
Cannot be entered without metal support frames
How are samples taken from trial pits? What kind of samples? How are they stored?
Bulk disturbed - every 1m Small disturbed - topsoil, each change in soil type and midway through bulk disturbed samples Stored in chemical jars
How are trial pits reinstated? (3 stages (2 end members))
Filled and compacted by excavator Topsoil and turf carefully replaced Remedial work (if left open, covered and fenced off)
Name three types of in-situ testing
Standard penetration test (SPT) Static core Penetrometer test Rotary drilling
How are static core Penetrometer tests carried out?
Pushing rod into ground
When are standard penetration tests used? Why are they being replaced?
Measure of consistency of soil Replaced because they are crude