1. EU LIMAS Liquefaction 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)

2. EU LIMAS Liquefaction around marine structures Soil - water gas systems (Hrydech et al (1987)) S r = 5-9 %S r = 9 - 70 % S r > 70 %

3. EU LIMAS Liquefaction around marine structures n Effect of gas on soil characteristics n Sample disturbance due to gas exsolution and expansion n Influence on soil parameters –shear modulus –bulk modulus –strength and pore pressure parameters –consolidation parameters n Influence on geophysical properties –wave velocity –magnetism

4. EU LIMAS Liquefaction around marine structures n Detection of gas in soil samples n Computer tomography (CT) scan imaging n Scanning Electron Microscope (SEM) techniques n Uni- or multisensor scanning devices –sonic wave velocity –gamma-ray –magnetism n Volumetric measurement during water absorption

5. EU LIMAS Liquefaction around marine structures X-ray computed tomography set-up (Desrues et al) sample

6. EU LIMAS Liquefaction around marine structures CT scan results Abegg et al Volume of gas bubbles Wong et al Sand sample with variable air saturation

7. EU LIMAS Liquefaction around marine structures Examples of CT soil research data

8. EU LIMAS Liquefaction around marine structures n 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)

9. EU LIMAS Liquefaction around marine structures n Multisensor core logger n Combines a number of parameters to derive a picture of the core –gamma ray –shear wave and/or compression wave velocities n Software processing of image Geoscan II image

10. EU LIMAS Liquefaction around marine structures Multi-sensor core logger with output results V  M sample

11. EU LIMAS The Geotek autoclave logger system

12. EU LIMAS Liquefaction around marine structures n Use of backpressure techniques n Core sample is pressurised in pressure cell before backpressure is applied n Sample can absorb de- aired water n Precision measurement of water absorption for increasing pressures indicates gas volume

13. EU LIMAS Liquefaction around marine structures n 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)

14. EU LIMAS Liquefaction around marine structures Gas detection n Preliminary conclusions n Transportable and flexible pressure systems emphasised for common use –measurement of water volume change during application of back-pressure n 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

15. EU LIMAS Liquefaction around marine structures n Use of backpressure saturation technique n Core sample is pressurised in pressure cell before back- pressure and a flow gradient is applied n Sample can absorb de-aired water n Precision measurement of water absorption for increasing pressures indicates gas volume