An Empirical Relationship between In

An Empirical Relationship between
In-situ Permeability and RQD of
Discontinuous Sedimentary Rocks
Mohsin Usman Qureshi
Assistant Professor, Sohar University, PO Box. 44, PC. 311, Sohar, Oman
Email: [email protected]
Kamran Muzaffar Khan
Associate Professor, University of Engineering and Technology Taxila,
Taxila, Pakistan
Nabil Bessaih
Assistant Professor, Sohar University, PO Box. 44, PC. 311, Sohar, Oman
Khalid Al-Mawali
Student, Sohar University, PO Box. 44, PC. 311, Sohar, Oman
Khaloud Al-Sadrani
Student, Sohar University, PO Box. 44, PC. 311, Sohar, Oman
ABSTRACT
In-situ permeability of rock mass is governed by its discontinuities and is important to correlate it
with a widely accepted parameter, “rock quality designation (RQD)”. In this regard, site
investigations conducted during the construction of hydraulic structures in complex lithological
units of Oman were reviewed with aim to summarize the data obtained by drilling of boreholes
with recovered cores (RQD) and Lugeon’s tests (in-situ permeability) in discontinuous
sedimentary rocks. The plot of RQD and in-situ permeability suggested a consistent relationship,
with respect to the each lithological unit and the extent of investigation as well. An empirical
relationship is derived between permeability and RQD for the onsite delineation of apparent
permeability of discontinuous sedimentary rocks by recovering the RQD values only. The
development this relationship for a specific project will assist the site supervisor in the planning of
detailed investigations for the determination of permeability with cost effectiveness. However, the
effects of aperture, extent and orientation of discontinuity are limiting in the empirical
relationship.
KEYWORDS:
In-situ permeability; discontinuous sedimentary rocks; RQD
INTRODUCTION
The in-situ permeability of discontinuous rocks is of major concern in tunneling, dam
engineering and reservoir water tightness issues. The overall success of such projects
profoundly depends on the robust elucidation of in-situ permeability with reliability and cost
effectiveness. In most of cases the hydraulic properties are sampled by time consuming and
expensive investigations such as hydraulic testing (Long and Witherspoon 1985). The
delineation of in-situ permeability in rock mass is carried out by widely accepted Lugeon’s
water pressure test (Lugeon 1933; Houlsby 1976) The flow through the intact rock matrix is
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usually so low that significant fluid movement can only take place through the fractures
(Witherspoon and Gale 1983). Therefore, to characterize the hydraulic conductivity of
discontinuous rock mass the fracture characteristics should be taken in to account. According
to Zhang (2013) the degree of anisotropy in permeability for the jointed rock masses depends
on the distribution of discontinuities and is much higher than that of intact rock, therefore
should be carefully evaluated.
In past many researchers (Angulo et al. 2011; Magnusson and Duran 1984; Hamm et al.,
2007; Nappi et al. 2005) attempted to correlate the in-situ permeability of rock mass with
other related parameters, such as in the borehole investigation by Angulo et al. 2011, the
relationship of hydraulic conductivity was statically more significant with electrical
resistivity as compared to the fracture frequency. They logged the electrical resistivity records
and fracture data along with the delineation of hydraulic conductivity by performing 25 lowpressure permeability tests (LPT) at different sections of two boreholes drilled to a depth of
100 and 120m in karst massif formation (limestone and calcite).
In contrast, Magnusson and Duran (1984) compared the hydraulic and resistivity
measurements in a core log and concluded that the fractures and micro-fractures in crystalline
rock constituents are the main transport path for electric current and the ground water. They
concluded that “the hydraulic conductivity is governed by a few discrete fractures and the
variation between two methods is due to the effect of restricted water flow on few channels
with small apertures, while electric surface conduction was possible through fractures with
very small apertures”. Hamm et al. (2007) studied the relation of hydraulic conductivity to
fracture frequency, squared fracture aperture, and the squared aperture of major fracture
orientation for granite which was obtained by acoustic televiewer and core log data. They
concluded that the fracture aperture had stronger relationship to hydraulic conductivity than
fracture frequency. In another study by Nappi et al. (2005) hydraulic characteristics of
sandstone were elucidated by outcrop measurements and Lugeon’s tests. The convergent
results from two methods were indicative of the complementary nature of two approaches.
However, those studies were mostly applicable to the shallow surface of rock mass which
necessitates the development of a quick, reliable and cost effective method for the estimation
of permeability of discontinuous rocks in the case of deep extent.
The reviewed literature revealed the governance of various characteristics of
discontinuities on in-situ permeability of rock mass. The most simplest and standardized
method to quantitatively describe them is “rock quality designation (RQD)” (ISRM 1978).
The present research aims to develop a relationship between the in-situ permeability and
RQD of discontinuous rock mass by utilizing the data of numerous boreholes drilled with
recovered cores and Lugeon’s water pressure tests performed during the detailed design and
construction of hydraulic structures in Oman. RQD is easy to obtain, either from borehole or
from field mapping of fractures on the surface of outcrop.
METHODOLOGY
Goodman (1980) suggested that the hydraulic conductivity in the rock mass depends on
the aperture, spacing and infilling of its discontinuities. So, this interrelation suggests that the
accurate estimate of hydraulic conductivity of a rock mass can only be obtained by using the
in-situ tests.
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Figure 1: Schematic diagram of Lugeon’s test and elucidation of RQD
(Lugeon 1933; Deere 1963)
The RQD was obtained by the visual observation of recovered cores and the in-situ
permeability was delineated by conducting Lugeon’s water pressure tests during the progress
of drilling. The schematic diagram of the testing methodology is shown in Figure 1. A brief
procedure for the performance of Lugeon’s water pressure test is described below.The
Lugeon’s test (Lugeon 1933) is a constant head type test which is conducted in an isolated
section of borehole. Water at constant pressure is injected in to the rock mass through a
slotted pipe bound by pneumatic packers (Figure 1) and this discharge is measured. The
maximum test pressure, Pmax which should not exceed the geostatic stress acting at the center
of respective section and is calculated as 1psi per unit depth of borehole measured in feet.
The tests were performed by injecting water at five incremental pressures (Houlsby 1976;
Houlsby 1990) as shown in Figure 2.
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Figure 2: Time history of injected water pressure during the Lugeon’s test
(Houlsby 1976; Houlsby 1990)
To calculate the Lugeon’s value (LU) following equation is employed.
LU = α
qPo
LP
(1)
where, α is a dimensionless parameter whose value is 1 in SI units and 12.42 for the English
system of units, q is discharge, Po is reference pressure equivalent to 1MPa or 145Psi, L is
length of section (Figure 1) and P is the applied pressure at any stage (Figure 2). According to
Fell et al. (2005) the value of Lugeon (LU) is equivalent to 1.3 x 10-5 cm/s. The results of
permeability presented in this paper are in the units of velocity.
The rock quality designation (RQD) which is a widely accepted index to characterize the
rock quantitatively was first introduced by Deere (1963). This concept of quantitative
description of rock is defined as “the percentage ratio of the sum of rock cores greater than
10cm in the core run of 100cm length” which is elucidated during the drilling of boreholes
with recovered cores.
Table 1: Lithological description of the rock formations (Qureshi and Khan 2007)
Rock Type
Claystone
Age
Tertiary
Limestone
Tertiary
Conglomerate
Sandstone
Quaternary
Tertiary
Generalized Lithology
Light yellowish pink, weak to moderately strong with some gypsum
of primary origin
Grayish to brownish yellow- bioclastic, nodular and micritic
limestone, yellowish brown-argillaceous limestone, Grayish brownarenaceous and ferrogenous limestone
Invariably cemented conglomerate layers
Whitish grey, poorly cemented, fine grained, massive and friable,
with intercalated thin beds/layers of claystone and siltstone.
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(a)
4785
(b)
Figure 3: Typical test results – depth profile of RQD and permeability measured by
Lugeon’s water pressure tests, (a) In limestone formation, (b) In sandstone formation
Later, Deere and Deere (1988) signified its versatility in the practice of tunneling and
foundation of hydraulic structures. The most important classification systems for the
quantitative description discontinuous rocks which is standardized by the International
Society of Rock Mechanics (ISRM 1978) also employs RQD which also justifies correlating
it with the in-situ permeability of discontinuous sedimentary rock mass.
RESULTS AND DISCUSSIONS
The borehole logs obtained from the site investigations performed during the construction
of hydraulic structures in Oman included the results of Lugeon’s water pressure tests and the
RQD values for the respective sections of the boreholes drilled in sedimentary rock
formations. In total, 367 Lugeon’s water pressure tests performed in 33 boreholes with a
maximum depth of 120m, in the discontinuous sedimentary formations were reviewed. Those
sedimentary rocks included sandstone, conglomerate, claystone and limestone whose
lithological descriptions (Qureshi and Khan 2007) are presented in Table 1. Among the total
number of Lugeon’s tests in the reviewed data, 23 were in claystone, 296 in limestone, 5 in
conglomerate and 43 in sandstone formation (Qureshi et al. 2013). The typical data of a
borehole drilled in limestone formation having a depth of 100m and in sandstone formation
with a depth of 50m are shown in Figure 3. It is quite evident form Figure 3 that the
delineated values of RQD and permeability are consistent. i.e., the sections of borehole with
low value of RQD exhibited a high permeability and vice versa.
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K a = 0.01382 − 0.003 ln RQD
Permeability, K (cm/s)
0.01
4786
K a = 0.01382 − 0.003 ln RQD
(R2=0.71)
1E-3
1E-4
Lithology
Sandstone
Conglomerate
Claystone
Limestone
1E-5
1E-6
0
20
40
60
80
100
RQD (%)
Figure 4: Lithologically plotted permeability against the RQD
The data of in-situ permeability and rock quality designation, RQD obtained from the
field tests was summarized with respect to each lithological unit in the plot of permeability
and RQD as shown in Figure 4. The data for each lithological unit has a wide range but no
firm relationship can be drawn with respect to the rock-type. In contrast, the depth-wise plot
of in-situ permeability and RQD pronounce an interesting fact in Figure 5. A few tests
performed in a depth range of 0-20m showed a high permeability and low RQD. On contrary,
the good quality rock having high RQD value with very low permeability was revealed at
greater depth. This shows that the rock formed on surface is highly discontinuous with low
RQD and high in-situ permeability. So, the shallow investigation for the delineation of in-situ
permeability should be conducted precisely, depending upon the site situation. In Figures 4
and 5, the trend of data reveals a decreasing function.
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K a = 0.01382 − 0.003 ln RQD
K a = 0.01382 − 0.003 ln RQD
(R2=0.71)
Permeability, K (cm/s)
0.01
1E-3
1E-4
1E-5
1E-6
Depth Range
0~20m
20~40m
40~60m
60~80m
80~100m
100~120m
20
40
60
80
100
RQD (%)
Figure 5: Depth-wise plot of permeability against the RQD
The present study aims to correlate the permeability with the RQD in the discontinuous
sedimentary rocks. Therefore regression analysis has been performed to derive a relationship
between the apparent permeability and RQD as shown in Figure 4 and 5. The following
empirical relationship was derived from the borehole data which have been best fitted to the
natural logarithm regression.
K a = 0.01382 − 0.003 ln RQD (R2=0.71)
(2)
where Ka is apparent permeability is in cm/s and RQD in percentage.
The empirical relationship shown in Eq. (2) is statically significant as the one developed
by El Naqa (2000) for the measured permeability and RQD of Cambrian sandstone mass in
central Jordan as shown in Eq. (3).
K = 177.45e −0.0361RQD (r=0.64)
(3)
where K is the permeability measured in LU (1LU=1.3 x 10-7m/s). In comparison, the
empirical relationship developed in Eq. (2) as a result of present study is not only applicable
to a wide range of sedimentary rocks but also elucidated with a huge confidence of field data.
It is important to mention here that various characteristics of discontinuities which may
affect the in-situ permeability have not been taken in to account in the present study.
Therefore the permeability estimated from RQD by using Eq. (2) is termed as apparent
permeability. In past many researchers (Hamm et al. 2007; Goodman 1980; Snow 1968;
Louis 1974; Barton et al. 1985) studied the effect of discontinuity characteristics on the
permeability. By assuming the parallel flow within smooth fractures, Snow (1968) developed
a relationship which showed that the permeability is directly proportional to the cube of
Vol. 19 [2014], Bund. R
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aperture of discontinuity. Later Louis et al. (1974) developed a formula to calculate the
permeability of discontinuity with infilling. The roughness of discontinuity aperture
distinguishes the equivalent hydraulic aperture from the hydraulic aperture which is studied
in detail by Bartonet al (1985). To some extent those parameters are reflected in the
permeability interpretation from Lugeon’s tests performed in the discontinuous sedimentary
formations. And that in-situ measured permeability is correlated with the respective RQD
which is a standardized (ISRM 1978), simple and quick technique to characterize the
discontinuous rock. So the relationship statically derived in Eq (2) and is based on the field
measurements is proposed to estimate the apparent permeability from the RQD determined
from the recovered cores during borehole advancement.
Geostatic stress has a great effect on the permeability of both intact rock and
discontinuous rock mass (Zhang 2013) which is also revealed in Figure 5. During the
laboratory study by Ghabezlo et al. (2009), they proposed an empirical power relationship
between permeability and effective pressure based on the constant head permeability tests on
limestone in a triaxial cell with different conditions of confining pressure and pore pressure.
Another simplified negative exponential relationship between the permeability of intact rock
and the effective pressure is presented by Louis et al. (1977). The consideration of this
important factor to be included in the relationship of apparent permeability and RQD will be
of future interest. However, the authors believe that the measured value of in-situ
permeability already includes the effects of geostatic stress.
CONCLUSIONS
The outcomes of the present study are stated below;
Based on the in-situ data of permeability, the shallow discontinuous sedimentary rocks
are more conductive as compared to the low or negligible permeability at deeper extent.
These results confirm the effects of stress conditions on the permeability of discontinuous
rocks.
A decreasing natural logarithm relationship is derived between the in-situ permeability
delineated by Lugeon’s tests and RQD in discontinuous sedimentary rocks by regression
analysis.
This statistically significant relationship is proposed to estimate the apparent in-situ
permeability from the RQD of discontinuous sedimentary rock obtained during the borehole
drilling, which will assist in the planning of detailed field investigations during the design and
construction of hydraulic structures. This approach will improve the overall scope of issues
related to time saving and cost effectiveness in the detailed site investigations for a specific
site. The apparent permeability values obtained by using this methodology can be considered
valid for the area having similar nature of geo-structural characteristics.
ACKNOWLEDGEMENTS
The present study is conducted with the support of Research and Industry Collaboration
division of Sohar University, Oman. The authors are also indebted to the Ministry of
Regional Municipalities and Water Resources, Oman for providing access to review and
analyze the presented data.
REFERENCES
1. Long, J. C., Witherspoon, P. A. (1985) The relationship of the degree of
interconnection to hydraulic conductivity of fractured networks, Journal of
Geophysical Research 90(B4):3087-3098
Vol. 19 [2014], Bund. R
4789
2. Lugeon, M. (1933) Barrage et Geologie. Dunod. Paris
3. Houlsby, A. (1976) Routine Interpretation of the Lugeon Water-Test. Quarterly
Journal of Engineering Geology 9:303-313
4. Witherspoon, P. A., Gale, J. E. ( 1983) Hydrogeological testing to characterize a
fractured granite, Bulletin of IAEG 26-27:515-526
5. Zhang, L. (2013) Aspects of rock permeability, Frontiers of Structural and Civil
Engineering 7(2):102-116
6. Angulo, B., Morales, T., Uriarte, J., Antiguedad, I. (2011) Hydraulic conductivity
characterization of a karst recharge area using water injection tests and electrical
resistivity logging. Engineering Geology 117(1-2):90-96
7. Magnusson, K. A., Duran, O. (1984) Comparison between core log and hydraulic and
geophysical measurements in boreholes. Geoexploration 22(3-4):169-186
8. Hamm, S., Kimb, M., Cheonga, J., Sona, M., Kim, T. (2007) Relationship between
hydraulic conductivity and fracture properties estimated from packer tests and
borehole data in a fractured granite. Engineering Geology 92(1-2):73-87
9. Nappi, M., Esposito, L., Piscopo, V., Rega, G. (2005) Hydraulic characterization of
some arenaceous rocks of Molise (Southern Italy) through outcropping measurements
and Lugeon tests. Engineering Geology 81:54-64
10. ISRM (1978) Rock characterization testing and monitoring: suggested methods for
quantitative description of fractures in rock mass, International Journal of Rock
Mechanics and Mining Sciences, Geomechanical Abstracts 15:319-368
11. Goodman, R. (1980) Introduction to Rock Mechanics. First Edition. J. Wiley, New
York, 32-34
12. Houlsby, A. (1990) Construction and design of cement grouting. J. Wiley, New
York.
13. Fell, R., MacGregor, P., Stapledon, D., Bell, G. (2005) Geotechnical Engineering of
Dams. Taylor & Francis. London. UK
14. Deere, D. U. (1963)Technical description of rock cores for engineering purposes.
Rock Mechanics and Engineering Geology 1(1):16-22
15. Deere, D. U., Deere, D. W. (1988) The rock quality designation (RQD) index in
practice. Rock Classification Systems for Engineering Purposes, ASTM STP 984,
Louis Kirkaldie Ed., American Society of Testing Materials, Philadelphia, 91-101
16. Qureshi, M. U., Khan, K. M. (2007) Engineering geological assessment of Wadi
Dayqah Dams and reservoir area, Proceeding of JSCE 9th International Summer
Symposium, Yokohama, Japan, 175-180.
17. Qureshi, M. U., Al-Mawali, K., Khan, K. M. (2013) Using RQD to estimate the insitu permeability of discontinuous sedimentary rocks, Advances in Soil Mechanics
and Geotechnical Engineering 2:447-450
18. El-Naqa, A. (2000) The hydraulic conductivity of the fractures intersecting Cambrian
sandstone rock masses, central Jordan, Environmental Geology 40:973-982
19. Snow, D. T. (1968) Rock Fracture spacings, openings and porosities, Journal of Soil
Mechanics and Foundation Division 94:73-91
20. Louis, C. A. (1974) Rock Hydraulics, In: Muller L, ed. Rock Mechanics. Vienna:
Springer Verlag, 299-382
Vol. 19 [2014], Bund. R
4790
21. Barton, N., Bandis, S., Bakhtar, K. (1985) Strength , deformation and conductivity
coupling of rock joints, International Journal of Rock Mechanics and mining
Sciences & Geomechanics Abstracts 22(3):121-140
22. Ghabezloo, S., Sulem, J., Guedon, S., Maritineau, F. (2009) Effective stress law of
the permeability of limestone, International Journal of Rock Mechanics and Mining
Sciences 46(2):297-306.
23. Louis, C. A., Dessenne, J. L., Feuga, B. (1977) Interaction between water flow
phenomenon and the mechanical behavior of soil or rock masses, In: Gudehus G.,
eds. Finite Elements in Geomechanics, New York: Wiley, 479-511
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