Abstract
Packer test is one of the commonly applied methods in determination of hydraulic conductivity particularly in low permeability fractured rock mass. Originally, hydraulic conductivity is defined in Lugeon units which correspond to 1 litre per minute per meter of intake section less than 10 atmospheres of pressure. Since the test is applied under different pressures, which gives the opportunity to observe the hydraulic behaviour of the rock under different stresses. Calculations of hydraulic conductivity for each step of pressure usually give different value of hydraulic conductivity. Selection of a representative hydraulic conductivity value therefore becomes an issue. The arithmetic mean is the commonly accepted value, without justifying its representativeness. In this paper, about 75 packer tests conducted at 17 core wells at different depth with 3.5 m long test sections using double packer were evaluated. The tests are conducted at five pressures that run in three increasing and two decreasing pressures according to the recommendation of Houlsby. Hydraulic conductivity was calculated for every pressure step and evaluated to find a representative value using different methods. The representative values found by different methods is then compared. Results indicate that the arithmetic mean has good correlation with all the methods in particular it is nicely correlated with the modified Lugeon analysis for hydrogeological investigations with a correlation value of R 2 =0.91. Therefore, it is concluded that the uncertainty associated with the use of the simple arithmetic mean is within an acceptable range of error. Keywords: Hydrogeology; Lugeon Value; Packer test; Permeability.
Highlights
Packer tests are one of the hydraulic test methods conducted in the field to obtain the hydraulic property of a rock mass
Hydraulic conductivity is defined in Lugeon units which correspond to 1 litre per minute per meter of intake section less than 10 atmospheres of pressure
Hydraulic conductivity was calculated for every pressure step and evaluated to find a representative value using different methods
Summary
Packer tests are one of the hydraulic test methods conducted in the field to obtain the hydraulic property of a rock mass. The tests are performed by measuring the flow rate of water injected into the isolated test section of the borehole at a given pressured head. The hydraulic conductivity is given in terms of Lugeon value, which is empirically defined as the hydraulic conductivity required to achieve a flow rate of 1liter per minute per meter of test interval under a reference water pressure equal to 10bar (Quiñones-Roza, 2010). Water is injected under pressure at a constant hydraulic head in an isolated portion of the boreholes measuring the flow rate at a steady state condition. Houlsby (1976), in his work, has indicated how to select the representative Lugeon value from the range of pressure tests conducted in a given section based on Lugeon patterns for his geotechnical purposes. The objective of this work is to see if the different mean value method of selecting representative Lugeon value can be correlated with specified method of Houlsby (1976); and Houlsby (1990); and Roeper et al (1992) within the acceptable range of error
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