EU LIMAS Liquefaction around marine structures Workpackage 7, NTNU Trondheim Development of soil sampler for measurement of gas content in soils Sampling of gassy soils By associate professors Rolf Sandven (NTNU) and Mike Long (UCD)

EU LIMAS Liquefaction around marine structures n Sampling concept: –thin-walled piston sampler with inner liner and outer steel cylinder –possibility of sealing the sampler tip after sampling to prevent leakage of gas/air –possibility for bringing the cylinder under pressure (or vacuum) by means of a pump –screening of the cylinder at the surface after sampling

EU LIMAS Liquefaction around marine structures Methods for sealing and pressure control of the sample cylinder n Sealing mechanisms to obtain sufficient sealing of the sample chamber –inflation of a rubber membrane at the sample tip –other mechanical devices, e.g. using a diaphragm principle, ball valve or similar –injection of chemical injection compounds at the tip of the sample body n Pressure control: –vacuum/pressure pump with reservoirs to provide pressure, lead through a hose in the rod system Beeker sampler with inflatable membrane

EU LIMAS Liquefaction around marine structures High-quality sampling of gassy soils n Methods for sealing of sample cylinder n Ball valves n Spring-loaded and sealing core catchers n Inflatable end membranes –rubber, PVC n Chemical sealing techniques –two-component epoxy compounds

EU LIMAS Liquefaction around marine structures n Based on push sampling principle n Pressurised core-barrel containing thin-walled sampling tube n Working range m below deck level n Capable of obtaining multiple samples from each location n Testing of samples in manned hyperbaric chamber n Major test problem: ingress of soil in ball seal and pressure monitoring system Ball-valve operated sampler Texas University (1982)

EU LIMAS Liquefaction around marine structures Ball-valve operated sampler Texas University Core barrel with sample tube Pressurised transportation chamber Ball valve

EU LIMAS Liquefaction around marine structures Fugro BV ball-valve operated offshore sampler ball valve

EU LIMAS Liquefaction around marine structures n Core barrel with smooth entry for low disturbance n After coring, two full closure shells are activated by a heavy spring and cam mechanism n Inner tube of PVC, aluminium or fiberglass Baker-Hughes IHL corer with full-closure core catcher

EU LIMAS Recent development of samplers Hyace percussion corer

EU LIMAS Liquefaction around marine structures n Use of inflatable membranes n E.g. Beeker sampler –thin-walled piston sampler with various sample lengths –a rubber membrane mounted inside the cutting edge can be inflated to the right pressure to completely close the head –sampler body is pushed or hammered into the soil –use of hydro-pneumatic discharge and partitioning system

EU LIMAS Liquefaction around marine structures n Example: Beeker sampler for shallow sampling –substantial diameter, thin-walled piston sampler with various sample lengths –hardened cutting edge and a collar are mounted at the bottom end of the tube –a rubber membrane mounted inside the cutting edge can be inflated to the right pressure to completely close the head –sampler body is pushed or hammered into the soil, with or without a frame –the sampling and discharging processes can be controlled by a hydro-pneumatic discharge and partioning system

EU LIMAS Liquefaction around marine structures Chemical sealing n injection of two-component epoxy compound through sampler wall n allow time for hardening n may require mechanical support when retrieving the sample n much experience from petroleum industry, limited experience from sampling Injection tubes

EU LIMAS Liquefaction around marine structures n Sampling of gassy soils by freezing –freezing of soil volume by circulating coolant –sampling of frozen soil volume with special barrels or tubes –storage and transport in frozen conditions –main objective is to reduce sample disturbance when sampling in sands

EU LIMAS Liquefaction around marine structures Transportation and storage of frozen samples

EU LIMAS Liquefaction around marine structures Comparison between frozen and ordinary samples from Canada (Robertson et al)