TY - JOUR
T1 - Gas generation and accumulation by aquifer drawdown and recharge in the London basin
AU - Standing, J.
AU - Ghail, R. C.
AU - Coyne, D.
PY - 2013/7/30
Y1 - 2013/7/30
N2 - Air at high pressure has recently been encountered during ground investigation borehole drilling for the Thames Tideway project in London. The air was released from within the Upnor Formation (at the base of the Lambeth Group beds), which is at the top of the Lower Aquifer. Cavitation within the granular beds of the Lower Aquifer would have occurred as a consequence of drawdown from the extensive water extraction that began at the start of the nineteenth century, resulting in the water table dropping by almost 70 m. Estimated historical pore pressure profiles are postulated and the cavitation process that occurred, along with the subsequent pressurization of the air during recharge that has occurred in recent years, are discussed using behavioural concepts from unsaturated soil mechanics. The hypotheses are corroborated by a series of simple column experiments where the processes are modelled using analogous soils. Engineering implications of the presence of the pressurized air are discussed: besides the potential for borehole blow-out, another serious consideration is the depletion of oxygen from the trapped air by chemical reaction with the soil, increasing the risk of confined space hypoxia.
AB - Air at high pressure has recently been encountered during ground investigation borehole drilling for the Thames Tideway project in London. The air was released from within the Upnor Formation (at the base of the Lambeth Group beds), which is at the top of the Lower Aquifer. Cavitation within the granular beds of the Lower Aquifer would have occurred as a consequence of drawdown from the extensive water extraction that began at the start of the nineteenth century, resulting in the water table dropping by almost 70 m. Estimated historical pore pressure profiles are postulated and the cavitation process that occurred, along with the subsequent pressurization of the air during recharge that has occurred in recent years, are discussed using behavioural concepts from unsaturated soil mechanics. The hypotheses are corroborated by a series of simple column experiments where the processes are modelled using analogous soils. Engineering implications of the presence of the pressurized air are discussed: besides the potential for borehole blow-out, another serious consideration is the depletion of oxygen from the trapped air by chemical reaction with the soil, increasing the risk of confined space hypoxia.
UR - http://www.scopus.com/inward/record.url?scp=84884395086&partnerID=8YFLogxK
U2 - 10.1144/qjegh2013-030
DO - 10.1144/qjegh2013-030
M3 - Article
AN - SCOPUS:84884395086
SN - 1470-9236
VL - 46
SP - 293
EP - 302
JO - Quarterly Journal of Engineering Geology and Hydrogeology
JF - Quarterly Journal of Engineering Geology and Hydrogeology
IS - 3
ER -