Modelling of the Effect of Critical Seepage Force on the Aquifer Soil Medium of a Borehole (Published)
There have been records of failures and quicksand conditions in boreholes in recent times impeding the performance and operation of boreholes which may have resulted from various factors ranging from construction problems, drilling inaccuracies, fitting and installation problems, some chemical effects within the aquifer medium etc, but it has been ignored that the beneficial factor to the operation of water boreholes; seepage force could get to a considerable value that it becomes unsafe for the well operation thereby causing dislodgement of sand particles and sandstones from the wall of the borehole and the flow paths to the extent that sandstones experience boiling. The scouring of the particles collected at the wall of the transport pipe could damage the installations which is a huge financial loss to the owners of these facilities. Moreover, when soil particles flow, it makes the yield a poor one hence this research works to investigate the contribution of seepage force to the failure of boreholes. A mathematical/laboratory model was used and an expression for calculating the critical hydraulic head causing critical seepage deduced as =. Tables 2 and 3 and Figures 4, 5 and 6 have shown that there is strong agreement between the mathematical model and the laboratory check with closest agreement at the flow distance of 1.8m flow distance and a correlation analysis has shown a perfect correlation of 1.00975. It was also established that the well pump of 760watts power could be operated safely at 220volts beyond which the hydraulic head get more critical. Finally, irrespective of the fact that an increase in hydraulic head increases discharge, the system should be operated at a head safe for the performance of the well.
Keywords: Borehole, Failure, Groundwater, Modelling, Seepage Force
Equilibrium Effect Modelling Of Contact and Seepage Forces on the Failure of Water Borehole (Published)
Continuum and discontinuum problems were considered in the solid-liquid medium under study. The necessitated the use of combined finite-discrete element method to generate model expressions from contact force and seepage force considered to be the major forces contributing to the flow of fluid through soil mass and boiling or quicksand effect when seepage force becomes more in effect under critical hydraulic gradient and / or critical hydraulic head. The equilibrium model has deduced an expression for the safe hydraulic head during well pumping as = and this has been verified using a laboratory check; prototype well failure test. It has been established that there is strong agreement between model result and the laboratory check at 1.8m flow distance and the correlation analysis carried out has also shown a perfect correlation of 0.989879999701. Note, a perfect correlation lies between -1 (perfect negative) and 1 (perfect positive) (Agunwamba, 2007; Inyama and Iheagwam, 1995).For safe pumping and corresponding yield in the borehole system, inter-granular force between granular particles should equal the seepage force and this is achieved by ensuring that the deduced model expression is used to determine the safe hydraulic head. For the system under study, the safe hydraulic head must be maintained. Finally, as long as the model hydraulic head expression deduced is used under the above conditions, safe pumping can be achieved at any voltage between 150volts and 240volts.
Keywords: Borehole, Contact Force, Equilibrium, Modelling, Seepage Force