Interpretation methods currently available in the literature were developed at a time when measurements were made in an analogous fashion and data was subsequently recorded by hand at rather large intervals of time. Current technology allows measuring and digital recording of data in real time, thus granting us an opportunity to update the interpretation procedures for Lugeon tests. This paper provides an interpretation method that expands the current procedures to benefit from the recent advances in data acquisition equipment. In contrast to other geotechnical parameters for which variations can usually be measured in percentage terms e. Selecting a representative value of hydraulic conductivity becomes of the outmost importance during design; especially, since under such a wide variation range, averaging the measured values will not suffice. Unlike soils, where seepage takes place through a series of small, closely spaced, interconnected pore spaces, seepage through rock masses occurs mostly along discrete planar discontinuities e.
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Interpretation methods currently available in the literature were developed at a time when measurements were made in an analogous fashion and data was subsequently recorded by hand at rather large intervals of time. Current technology allows measuring and digital recording of data in real time, thus granting us an opportunity to update the interpretation procedures for Lugeon tests. This paper provides an interpretation method that expands the current procedures to benefit from the recent advances in data acquisition equipment.
In contrast to other geotechnical parameters for which variations can usually be measured in percentage terms e. Selecting a representative value of hydraulic conductivity becomes of the outmost importance during design; especially, since under such a wide variation range, averaging the measured values will not suffice. Unlike soils, where seepage takes place through a series of small, closely spaced, interconnected pore spaces, seepage through rock masses occurs mostly along discrete planar discontinuities e.
Thereby, whereas in soils hydraulic conductivity is mostly controlled by the size, shape and arrangement of its voids Terzaghi et al. Discontinuity aperture plays a particularly important role in the hydraulic conductivity of a rock mass. Consequently changes in the stress condition of the rock mass can produce significant changes on its hydraulic conductivity. The existence of an interrelation between stress and hydraulic conductivity ultimately means that accurate estimates of the hydraulic conductivity of a rock mass can only be obtained using in-situ tests.
The Lugeon Test The most commonly in-situ test used to estimate hydraulic conductivity of rock masses is the Lugeon test — also called the packer test. Water at constant pressure is injected into the rock mass through a slotted pipe bounded by pneumatic packers Figure 1. A pneumatic packer is an inflatable rubber sleeve that expands radially to seal the annulus space between the drill rods and the boring walls. Figure 1. Lugeon test configuration Prior to the beginning of the test a maximum test pressure PMAX is defined.
As a rule of thumb, PMAX is usually established using Equation 1, where D is equal to the minimum ground coverage — depth in the case of a vertical boring in a flat site or minimum lateral coverage in the case of a test conducted in a hillside.
A single stage consists of keeping a constant water pressure at the test interval for 10 minutes by pumping as much water as required.
The first stage is held at a low water pressure, increasing the pressure in each subsequent stage until reaching PMAX. Table 1 shows the pressure magnitudes customarily used during the five test stages. Table 1. Subsequently, average values for P and q are then used to compute the hydraulic conductivity for each stage.
The term P0 corresponds to a reference pressure equal to 1MPa or psi. Under ideal conditions i. Table 2 describes the conditions typically associated with different Lugeon values, as well as the typical precision used to report these values. Table 2. On his work, geared towards establishing grouting requirements, Houlsby proposed that representative hydraulic conductivity values should be selected based on the behavior observed in the Lugeon values computed for the different pressure stages.
Houlsby classified the typical behaviors observed in practice into five different groups, as follows: - Laminar Flow: The hydraulic conductivity of the rock mass is independent of the water pressure employed.
This behavior is characteristic of rock masses observing low hydraulic conductivities, where seepage velocities are relatively small i. This behavior is characteristic of rock masses exhibiting partly open to moderately wide cracks.
This behavior — which is sometimes also observed at medium pressures — occurs when the water pressure applied is greater than the minimum principal stress of the rock mass, thus causing a temporary dilatancy hydro-jacking of the fissures within the rock mass.
Dilatancy causes an increase in the cross sectional area available for water to flow, and thereby increases the hydraulic conductivity.
Table 3 presents a graphic summary of the five behavior groups defined by Houlsby , as well as the representative Lugeon value that should be reported for each group. The minimum corresponding to the 4th Stage 4th Stage Lugeon value is observed highest water 5th Stage rd 5th Stage Water Pressure, P Lugeons at the stage with the pressure 3 stage 0.
The maximum corresponding either 4th Stage 4th Stage Lugeon value is observed to low or medium 5th Stage st 5th Stage Water Pressure, P Lugeons at the stage with the water pressures 1 , nd th th 0. However, the procedure was devised at a time when discrete readings were made using dial gages at rather large intervals of time. The procedure proposed below, aims to update the Lugeon interpretation process to incorporate the use of current technology. Furthermore, this procedure will not only contribute to streamline the Lugeon interpretation process, but will also facilitate interpretation in those occasions when the test does not proceed according to plan.
Use of Automated Data Acquisition Systems Automated data acquisition systems capable of measuring, displaying and recording Lugeon test and grouting data in real time have become available over the last years. This equipment measures flow rate and pressure at regular intervals of time and displays the information on an LCD display Figure 2. Lugeon Test Interpretation Figure 2. Data acquisition equipment for real time monitoring of Lugeon tests and grouting Photo by Atlas Copco Since this equipment is able to measure both pressure and flow rate in real time it is possible to monitor the behavior of the Lugeon value as the test proceeds.
In order to take advantage of this possibility, it is proposed to analyze the Lugeon test results using the flow loss vs. Lugeon interpretation using the flow loss vs. According to this interpretation, if the results of the Collaborative Management of Integrated Watersheds Lugeon test are plotted in a flow loss vs.
Furthermore, this line — which will start at the origin — will have a slope equal to the Lugeon value. The shape of this loop describes the behavior of the Lugeon value as the test proceeds, and thereby can be used for interpretation purposes. For example, if all the points lie atop of a line crossing through the origin it is known that the Lugeon value remained constant throughout the test, implying that a laminar behavior was observed.
The same type of analysis can be performed for each of the behavior categories proposed by Houlsby, as summarized in Table 4. The proposed Lugeon interpretation procedure conserves the same behavior categories proposed by Houlsby , while using an approach that renders it compatible with the use of automated data acquisition systems. It is expected that the use of this interpretation procedure will allow real time monitoring and interpretation of test data.
The choice of the representative Lugeon value for each behavior category remains essentially unchanged. However, in those cases where turbulent or dilation behaviors are observed, it is recommended that the Lugeon value selected corresponds to those values observed at the range of pressures expected during operation e. Lugeon Test Interpretation Table 4. Proposed Lugeon interpretation procedure using the flow loss vs. If the water pressures increase. Although, it would be advisable to ignore these data points, there are occasions where the amount of information at hand is so limited that disregarding data is not an option.
The procedure above allows using the limited information available to gain a better understanding of the rock mass permeability. However, by reporting lower and higher bound values —rather than representative values —, it assigns a lower level of reliability to these results. It has been estimated that the effect of the Lugeon tests — with a test interval length of 10 feet - is restricted to an approximate radius of 30 feet around the bore hole Bliss and Rushton, This suggests that the hydraulic conductivity value estimated from this test is only representative for a cylinder of rock delimited by the length of the test interval and the radius given above.
Although the use of well-pumping tests with observation wells can overcome this limitation Cedergren, , such tests are seldom conducted since they involve drilling several holes which increases the exploration cost considerably. Due to the spatial limitation of the Lugeon test it is not recommended to estimate the hydraulic conductivity using closed-form analytical solutions that rely on the assumption that a large portion of the rock mass is engaged during the test.
Furthermore, such analytical solutions usually require an adequate knowledge of the location of the ground water table elevation. However, it is usually observed that ground water elevation measurements while drilling can be artificially high due to the large amounts of water pumped into the hole to circulate the cuttings. As observed by Hoek and Bray many of the mathematical theories available in the literature have gone beyond the bounds of practical application.
In most practical cases, the assumptions used by the analytical methods do not correspond to the actual conditions of the rock mass to be studied i. Due to these limitations it is recommended to avoid over reliance on such analytical methods and limit their use to perform sensitivity analysis that can be used to assess the validity of the results obtained from Equation 2. Under this updated procedure data corresponding to different stages of the test are plotted in the flow loss vs.
Equations that can be used to automate this procedure are provided to facilitate its use with automated data acquisition systems. It is expected that the use of this method can contribute to focus the interpretation of hydraulic conductivity exclusively on data collected in the field.
This will avoid the use of elaborate closed-form analytical solutions that rely on assumptions that seldom correspond to the conditions observed in practice. The reliability of packer tests for estimating the hydraulic conductivity of aquifers.
Cedergren, H. Seepage, Drainage, and Flow Nets. Third Edition. New York, N. Fell, R. Geotechnical Engineering of Dams. Goodman, R. Introduction to Rock Mechanics. First Edition. Hoek, E. Rock Slope Engineering. Institute of Mining and Metallurgy, London. Houlsby, A. Routine Interpretation of the Lugeon Water-Test. Lugeon, M. Paris Terzaghi, K. Soil Mechanics in Engineering Practice.
Lugeon test, complete online calculator
It is indeed In situ test of formation permeability performed by measuring the volume of water taken in a section of test hole when the interval is pressurized at given pressure 10 bars psi. It is used primarily in variably permeable formations under evaluation of fracturating. The test is named after Maurice Lugeon , a Swiss geologist who first formulated the test. The water is injected into the isolated portion of the borehole using a slotted pipe which it self is bounded by the inflated packers.
There are several variations and interpretations of the Lugeon test. Readers are encouraged to consult the supporting materials in the References section. A more thorough description of the field procedure can be found in ISO Geotechnical investigation and testing -- Geohydraulic testing -- Part 3: Water Pressure Tests in Rock Based on the drill core, an assessment of the expected injection rates and pressure can be made.