Uncertainty of lugeon unit value related to the influence of drill diameters and aquifer layers

Suny Sunyoto

Thursday 2 july 2015

16:45 - 17:00h at Oceania Foyer (level 0)

Themes: (T) Hydro-environment, (ST) Renewable energy resources

Parallel session: 13L. Water resources - Flow interactions

The Lugeon test (1930), extensively used in Europe, is a special case of double packers bore hole inflow test that was made at constant hydraulic head to measures transmissivity in rocks, which is determined by pressurized injection of water through a bore hole driven through the rock. The standard is that ‘One Lugeon Unit (1LU) is equal to one liter of water per minute injected into one meter length of borehole at constant hydraulic head by an injection pressure of ten bars’. The test is carried out for 5 minutes each and the value of 1LU is approximately equivalent to 1x10-5 cm/s or 1x10-7 m/s. This test did not take into consideration the holes diameter, nor hole layer position of aquifer. This paper tried to develop of computation of conductivity formula based on Sunjoto’s formula (1988) in steady state flow condition which is basically to compute discharging or recharging of flow on the well, depends on shape factors, hydraulic conductivity and hydraulic head. The value of shape factors depend on the diameter of holes and other holes condition. Computation result from the proposed formulas shows that the value of Lugeon Unit is appropriate only for certain drill diameter and certain layer of aquifer and for the available drill size, the result deviation is about 40% greater and 37% smaller compared to the standard conductivity which equal to 1 LU. By these formulas, the hydraulic conductivity of rock can be determined by just any data of inflow discharge, hydraulic head, and length of bore hole between two packers. Using proposed formula of computation with pressure is 10 bars, the length of hole is 1 m and discharge is 1 liter/minute, the conductivity K = 10-7 m/s can be achieved for the hole of layer condition (a), (b) and (c) when the diameter of hole are 187.10 mm, 89.40 mm and 43.72 mm respectively. Keywords: Lugeon Unit, conductivity, discharge, hydraulic head, shape factor