eu limas liquefaction around marine structures workpackage 7, ntnu trondheim development of soil...
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EU LIMASLiquefaction around marine structures
Workpackage 7, NTNU Trondheim
Development of soil sampler for measurement of gas content in soils
Methods for gas measurements
By associate professors Rolf Sandven (NTNU) and Mike Long (UCD)
EU LIMASLiquefaction around marine structures
Soil - water gas systems (Hrydech et al (1987))
Sr = 5-9 % Sr = 9 - 70 %
Sr > 70 %
EU LIMASLiquefaction around marine structures
Effect of gas on soil characteristics
Sample disturbance due to gas exsolution and expansion
Influence on soil parameters
– shear modulus– bulk modulus
– strength and pore pressure parameters
– consolidation parameters Influence on geophysical
properties– wave velocity– magnetism
EU LIMASLiquefaction around marine structures
Detection of gas in soil samples
Computer tomography (CT) scan imaging
Scanning Electron Microscope (SEM) techniques
Uni- or multisensor scanning devices– sonic wave velocity– gamma-ray– magnetism
Volumetric measurement during water absorption
EU LIMASLiquefaction around marine structures
X-ray computed tomography set-up (Desrues et al)
sample
EU LIMASLiquefaction around marine structures
CT scan results
Abegg et alVolume of gas bubbles
Wong et alSand sample with variable air saturation
EU LIMASLiquefaction around marine structures
Research team
Scanner Resolution Comment
3S-IMG ND 8000 medical
0.7 mm x 0.7 mm Resolution set 4 mm slice
CALGARY 0.75 x 0.75 mm 3 mm slice
BOULDER 0.2 mm x 0.2 mm 10 mm slice NASA equipment
KIEL Elscint CT Twin
1.0 mm x 1.0 mm 1.00 mm -> 0.85 mm slice
Research work also available from other institutions, e.g. DTU, Denmark
Examples of CT soil research data
EU LIMASLiquefaction around marine structures
Scanning electron microscope (SEM)– Impregnation of specimen
sections using special resin– Imaging of thin sections
using SEM techniques– Computerised image
analysis is used to measure void sizes and distributions
– Obtainable resolution in the m - scale
Soil containing gas bubbles (Sills et al)
EU LIMASLiquefaction around marine structures
Multisensor core logger Combines a number of
parameters to derive a picture of the core– gamma ray– shear wave and/or
compression wave velocities
Software processing of image
Geoscan II image
EU LIMASLiquefaction around marine structures
Multi-sensor core logger with output results V M
sample
EU LIMASThe Geotek autoclave logger system
EU LIMASLiquefaction around marine structures
Use of backpressure techniques
Core sample is pressurised in pressure cell before backpressure is applied
Sample can absorb de-aired water
Precision measurement of water absorption for increasing pressures indicates gas volume
EU LIMASLiquefaction around marine structures
In situ gas detection– BAT probe for
sampling of water and gas
– CPTU based modules• seismic CPTU• resistivity CPTU
– Spectral analysis of surface waves (SASW)
EU LIMASLiquefaction around marine structures
Gas detection Preliminary
conclusions
Transportable and flexible pressure systems emphasised for common use– measurement of water volume
change during application of back-pressure
Selected samples or projects– use of X-ray, CT or MRI
imaging methods – indirect methods based on
influence on soil parameters• shear wave or compression
wave velocity• needs soil specific
calibrations
EU LIMASLiquefaction around marine structures
Use of backpressure saturation technique
Core sample is pressurised in pressure cell before back-pressure and a flow gradient is applied
Sample can absorb de-aired water
Precision measurement of water absorption for increasing pressures
indicates gas volume
Back- pressure
supply
Inlet valve for deaired water
Scaled precision burette
Sample with gas bubbles
Ball valve closure