Evaluating permeability and groutability at the Karun 4 dam Iran using Lugeon values and grout Take Mohammad Hosseiny Sohi 1, Prof.Dr. Manfred Koch 1, Dr. Javad Ashjari 2 1 Department of Geohydraulics and Engineering Hydrology, Kassel University, Kassel, Germany 2 School of Geology, University of Tehran, Tehran, Iran
Contents Introduction Study area and dam specifications Methodology and data Results Conclusions References
Introduction Water leakage through the foundation and abutments of a dam which is built on limestone formations, is one of the most important challenges of the big dams construction and operation. The water- soluble carbonate structure of such limestone may lead to the development of fissures and fractures that may, eventually, expand to conduits and even caverns and caves; a process which is known as karstification (Milanović, 2004; Ford & Williams, 2007). In the present study, the permeability as the most important parameter determining water seepage of the Karun 4 dam, constructed on a limestone formation with karst potential will be presented.
Study area and dam specifications The Karun 4 Dam is located on the Karun River in the state of Chaharmahal and Bakhtiari, at a distance of 180 km from the State Capital of Shahrekord, in southwest Iran. It is the highest dam of Iran (230 m from foundation) and has been impounded since March 2010.
Karun 4 dam technical specifications
Location and details of the Karun 4 dam in Iran
Study area and dam specifications Grout Curtain To seal the dam foundation and abutments, a very large grout curtain was designed and constructed. The construction was done through the excavation of 5 series of galleries in both left and right abutments at different elevations. From inside these galleries the grouting boreholes are drilled and injected, to have an integrated virtually wall or barrier, called grout curtain against water leakage. Based on the obtained results from the exploratory boreholes, the grout curtain in two lines was designed and constructed, to sew/stitch the dam structure to the Pabdeh impermeable formation in the upstream.
Selected Exploratory-, line 1 and line 2 check holes in the grouting galleries
3D view of Karun 4 dam body and grouting galleries
Methodology Water pressure test (WPT) or Lugeon test Water pressure test, packer test or simply Lugeon test has been developed by Professor Maurice Lugeon (1933). A Lugeon unit is defined as one liter/minute of water absorption per meter of test length of drill hole when the water in the borehole remains at a pressure of 10 bars or 1 MPa over a period of 10 minutes (Lugeon, 1933; Houlsby, 1990; Singh and Goel, 1999).
Methodology Take The (grout) Take is defined as the rate of dry cement mass that is injected to the test section, divided to the length of section (kg/m) (Deere 1982).
Methodology Ewert Method Ewert (1985) proposed a qualitative method to interpret the relationship between permeability and groutability in the dam foundations. He classified the obtained results from different dam sites and tests in to following grouping:
Methodology Ewert Method Group A: large amount of Lugeon value and low grout Take indicates that water can pass through the numerous fine fissures of the rock, but the corresponding grout is not permitted. Group B: Approximately proportionality between water and Take justifies well the necessity of grouting. Group C: The small water pass versus large Take cause to the hydraulic fracture in the rock mass and shows that either the injection pressure is not proper or at all unnecessary. Group D: Low water and Take signs the sealing of area and no need no treatment.
Frequency % Frequency % Results Lugeon Permeability 60 55 Lugeon Values of Left Bank 60 56 Lugeon Values of Right Bank 50 50 48 40 30 20 34 27 20 21 43 33 20 18 18 Exploratory holes Line 1 check holes Line 2 check holes 40 30 20 34 41 34 38 24 16 Exploratory holes Line 1 check holes Line 2 check holes 10 0 2 7 0 1 0 0-3 3-10 10-30 30-60 > 60 Frequency distribution of Lugeon values in the different classes for exploratory, line 1 and line 2 check holes for the left and right banks. 10 0 9 0-3 3-10 10-30 30-60 > 60 10 1 5 7 0 0
Frequency % Frequency % Results Groutability 90 90 80 78 Take Values of Left Bank 80 81 Take Values of Right Bank 70 70 60 50 40 42 59 Exploratory holes Line 1 check holes Line 2 check holes 60 50 40 48 56 Exploratory holes Line 1 check holes Line 2 check holes 30 30 20 10 0 17 18 11 12 10 9 6 7 7 7 6 3 3 1 2 1 1 1 0-12.5 12.5-25 25-50 50-100 100-200 200-400 > 400 20 10 0 14 13 11 12 10 7 5 7 7 8 4 2 2 2 2 2 2 2 0-12.5 12.5-25 25-50 50-100 100-200 200-400 > 400 Frequency distribution of Take in the different classes for exploratory, line 1 and line 2 check holes for the left and right banks.
Results Correlation of Lu- permeability and Take- groutability based on Ewert s method Lugeon versus Take with the four Ewert s groupings for the exploratory holes
Results Correlation of Lu- permeability and Take- groutability based on Ewert s method Lugeon versus Take with the four Ewert s groupings for the line 1 check holes
Results Correlation of Lu- permeability and Take- groutability based on Ewert s method Lugeon versus Take with the four Ewert s groupings for the line 2 check holes
Results Correlation of Lu- permeability and Take- groutability based on Ewert s method Frequency distribution of Lu-Take pairs in the different groups for exploratory, and line 1 and line 2 check holes for the left and right banks.
Conclusions The grout curtain of Karun 4 dam is constructed on the dam foundation and abutments to prevent, or minimize the water leakage from the dam reservoir after impounding. The measurements include Lugeon- and grout- Take values of exploratory-, line 1 and line 2 check holes of the grout curtain. Totally, data from 64 selected boreholes are used to study the relation between Lugeon (Lu) permeability and groutability (Take) and, based on the values of these two variables, classified into four groups, following Ewert s methodology. The results indicate that the implemented grout curtains can seal leaking, as Take is lower than 50 kg/m in more than 90% of the boreholes the requirement for efficient grout Take -, although there are still areas with medium Lugeon values, i.e. data in Evert s class A.
Conclusions The Lu- values indicate that the permeabilities of the right bank are generally lower than those of the left bank. This can be explained by the geological characteristics underneath the dam of the Asmari formation (AS1) subunits. Nevertheless there is still some scattering of Lu-Take pairs into Evert s A- group, which means that water leakage exists at these locations. The technical solution would be to allow the extra water to seep through a drainage curtain.
Related and Ongoing studies The seepage analysis through the drainage curtain is the topic of the presented study of the authors as Poster in the Meeting: Monitoring of the seepage controlling system of the Karun 4 dam in Iran Furthermore, a numerical groundwater flow model is needed, to get a more comprehensive and quantitative picture of the water flow seepage through the dam foundation and abutments, which is the ongoing study of the authors
An example of the groundwater flow model results Code: CFP for Modflow 2005 GUI: Molde Muse USGS
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Contact S. Mohammad Hosseiny sohi Ph.D. Candidate in Civil Engineering mim.sohi@gmail.com Department of Geo-hydraulics and Hydrology Engineering Faculty of Civil- and Environmental Engineering University of Kassel Kurt-Wolters-Straße 3 34125 Kassel, Germany