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Significance of discontinuity surveying in motorway alignment selection, southern Turkey
ENGINEERENG GEOLOGY ELSEVIER
EngineeringGeology40 (1995) 41-48
Significance of discontinuity surveying in motorway alignment selection, southern Turkey I. Yilmazer Spectra Jeotek Co., Kumkapl Sokak 20/1, 06610 (ankaya, Ankara, Turkey Received 17 October 1994; accepted 22 March 1995
Abstract
A detailed discontinuity survey is an essential part of a route location study, because rock quality and subsurface geological conditions can be determined by examining discontinuity systems. It also helps to prepare a sound subsurface investigation programme in the later stages of an engineering project. Some of the more expensive structural elements of a motorway are tunnels, viaducts, reinforced retaining walls and contiguous piles. Each has special requirements depending on ground stability, cost and environmental aspects. A detailed discontinuity survey enables engineers to select the best route and to optimize the geotechnical design. A case study from the Tarsus-Adana-Gaziantep (TAG) motorway being constructed in southern Turkey displays well the role of a discontinuity survey in engineering geological and geotechnical work. The survey, which was carried out by visual inspection and practical field tests, indicated, on the basis of the consistency of the discontinuity systems in each rock exposure, that the suspected floating blocks were outcrops of in situ rock. Misinterpretation of the actual ground condition caused loss of both time and money.
1. Introduction
The Amanos mountain range trends N E - S W and forms a 150 km long topographical obstacle between two large basins, i.e. the t~ukurova (basin plain) and the H a t a y - K a r a s u Graben (Fig. 1). The northern part of the middle section of the range is called Nurmountain. Southern Turkey and the eastern part of Anatolia are connected by Nurmountain. The TAG motorway and a new railway are being designed and constructed (Yilmazer et al., 1992a, b) in the same narrow corridor across Nurmountain, where a railway tunnel, a highway, pipelines and local roads already exist. Many scientists have studied this area including Dean and Monad (1984) and references therein since 1843. 0013-7952/95/$09.50© 1995ElsevierScienceB.V. All rights reserved SSDI 0013-7952(95)00018-6
Nurmountain is described as a homoclinal structure dipping NW; metamorphic textures are quite distinct as stated by Yilmazer et al. (1992c). The terms "symmetrical anticline or anticlinorium and shale" have repeatedly been used to identify the geology of the area till 1990. However, Yilmazer (1990) and Yilmazer and Demirkol (1992) provided clear field evidences indicating the dominance of homoclinal structures and metamorphic rocks. The engineering properties of shale are given in Shamburger et al. (1975) and Hendron et al. (1970). Shales are in general extremely weak to weak rocks; they are comparatively weaker than metasediments. Pre-existing discontinuities become welded under increasing metamorphic conditions
42
L
Yilmazer/Engineering Geotog:v 40 (1995) 41-48
",~,":;"~i':~# ~i~:~iii~:~i::~y ~-~. . ;:~::i .~:!~.;:~:::::: ~
SIR DAM K.MARA~
I
Kozonc Kodidi 0 Asoo
~o ~ 2
0~.~o 50o
G~zi~ Azo
/
oKilis
~nd,
IO
0
.:: .
~
20
40
Kin.
S C/~LE
i
LEGEND MEDITERRANEAN SEA
Basle and Ultnabaslc=
I ~ HATAY
L\ g',. ,....,.r/'k'---''" "~"
(
~
Mesozoic
~
Paleozolc Elevation, m. 25
5O
J .c- ..J /'~,p
i,
(
SYRIA
%,,"
Fig. 1. Map showing the accessibility and general geology (M.T.A., 1989).
35
40
45
I. Yilmazer/Engineering Geology 40 (1995) 41-48
resulting in an appreciable improvement in rock quality. Active and large landslides (60 x 300 x 1000 m) have developed mainly along structural and tectonic contacts on the western side of the mountain belt where outslope and dipslope conditions prevail. The hydrogeology of an area is largely affected by altitude and major discontinuity systems. Mountain belts naturally receive higher precipitation (Yilmazer, 1992; Yilmazer and Congar, 1994). The western side of Nurmountain has numerous perennial springs and streams and artesian pressure, whereas the creeks and springs on the eastern side are seasonal or dry. Ground stability is adversely affected by prevailing wet conditions combined with the dominance of discontinuities dipping outslope (Yilmazer et al., 1994b).
2. Engineering geology The most common rock types in the area are metasediments (including granoblastic schist, slate, hematite schist, metaquartzite and phyllite), recrystallized dolomitic limestone and silicified dolomitic limestone. Excluding the phyllite, the calcschist and the talc schist levels, moderately strong to very strong rocks constitute the majority of the unit. Schistosities are not persistent. Metamorphism caused amalgamation of bedding planes. Joints are rough, irregular and tight. In particular tensional joints are sealed, mainly with quartz and calcite. The weathering depth in these metamorphic units does not exceed 10 m except in thick shear zones, Surface inspection of shear zones is an essential part of the discontinuity survey. More than a hundred subsurface investigation boreholes have been drilled along a 4 km long section of the TAG motorway including the problematic zone across the mountain belt. Metasediments become watertight with increasing depth (> 20 m) and engineering properties improve noticeably. This condition naturally favours the stability of a tunnel excavation. The existing railway tunnel constructed in the same corridor is over 80 years old, about 6 km
43
long, and is mainly unlined. It is a self supporting tunnel and still works efficiently. Several earthquakes have occurred during the existence of the tunnel in the vicinity, but did not affect the stability of the tunnel. Several short (400 m) tunnels have been constructed through Miocene sedimentary units along the same railway. Although they were lined, they have suffered from groundwater and earthquakes. The interrelationship between ground motion, depth, elastic strain and basement rock is explained and well documented by Bolt (1970) and Housner (1970). Elastic strain in basement rocks increases with depth, whereas ground motion decreases. Wickam et al. (1974) have suggested that sedimentary rocks are not first class rocks from a tunnelling point of view. The engineering properties of both the sedimentary and metamorphic rocks along the motorway have been investigated using extensive geotechnical methods. Ultimate shear strength parameters, limiting pressure (PI) found by pressuremeter test and elastic modulus (E) values, as described by Hunt (1986) and references therein, are presented in Table 1 in order to give a general idea of the strength of the sedimentary and metamorphic rocks at the study area. The shear strength parameters, cohesion (C) and internal friction angle ( ~ ) are given in an interval rather than a certain value.
3. Discontinuity survey to predict subsurface conditions A motorway network, 3600 km long, is being designed and constructed throughout Turkey. A great number of landslides are closely connected with existing discontinuity systems (Yilmazer et al., 1994a). 60% of the motorway alignments take place on rugged and highly dissected areas where structural, tectonic, stratigraphic and lithological contacts and other discontinuity types are widespread. In addition to the discontinuity type, the spacing and aperture, water condition, infill properties, material property, weathering, slaking, number of discontinuity systems and other relevant data are
44
1. Yilmazer/Engineering Geology 40 (1995) 41 48
Table 1 Strength and deformation modulus values of the metamorphic and sedimentary rocks Rock type
C (kPa)
~ (')
Number of testsa
P/~ (kPa)
Standard deviation
E (MPa)
Standard deviation
Sandstone Siltstone Mudstone Claystone Phyllite Slate Hematite schist Calcschist Metaquartzite
70 150 40-100 25-70 25-70 40-250 70 300 95-500 35-200 95-500
30-45 25 35 20 30 15-25 30-40 30-45 35 55 20-35 40-55
36 30 68 15 94 23 30 Il 49
6363 3742 3010 2860 3680 16180 21369 5197 15240
522 295 127 118 110 651 435 352 758
197 117 114 55 251 504 662 145 469
21 20 8 2 23 21 13 13 24
aRandomly selected from a large number of tests. bLimit pressure. Note: Effects of weathering and depth are not taken into account.
gathered by visual inspection, practical field tests and laboratory work. Such engineering data could also be used in back analyses and be interpreted to predict internal friction angle ( ~ ) and cohesion (C). The reliability of a rock mass classification basically depends upon the accuracy of the results of the discontinuity survey (Bieniawiski, 1989; Steffen, 1976). Such a study is easy, inexpensive and quick to carry out and provides reliable data about ground stability in three dimensions. The ~ and C values obtained from sedimentary rocks by in situ and laboratory tests are generally too high to be directly used in cut slope stability analyses. For example, a few clay layers, 0.10 m thick, in a sedimentary sequence that dips outslope at a dip angle greater than ~ , can control slope stability. However, the same layer may not have any adverse effects if it dips inslope. Zika (1990) and Yilmazer et al. (1992a) have pointed out that kinematic analyses based on a discontinuity survey have practical and reliable applications, particularly for stratified and tilted units. Isolated bedrock outcrops in a suspected slide area were misinterpreted as floating blocks in a slide mass (Fig. 2). However, a one-day discontinuity survey revealed the actual field situation. As depicted in Fig. 2, the isolated rock exposures, under the remnants of the slide mass, were mapped as floating blocks in 1988 and the area was interpreted as a 65 m thick landslide. However, a more
~d t~
2
z
° I ,,-r!.
~
$ 7
....
$20 780
Fig. 2. Suspected slip surfaces (SS) and floating blocks (FB).
recent discontinuity survey found that the discontinuity system of each exposure was identical. In other words, the attitudes of joints (compressional,
45
I. Yilmazer/Engineering Geology 40 (1995) 41-48
conjugate and tensional), bedding and schistosity were consistent (Fig. 3). Interpreting this slope as a 65 m thick active slide, it could not be crossed using any available engineering method at reasonable cost. Without any further consideration of the discontinuity results the alignment was shifted to the north of the adjacent creek where large scale ground instability problems are distinct. Three years have been spent on further geotechnical investigations along this new alignment. The discontinuity survey carded out before the investigation programs started, indicated that the new location had potential groundwater problems. However, 40 m deep contiguous piles together with 100 m long cable anchors were suggested to stabilize an active landslide with average dimensions of 35 x 800 x 1000 m. Ultimately, cost analyses based on a three year investigation, were reported toward the end of 1992. The calculated comparatively high costs was found unacceptable and then, two deep boreholes (70 m) were drilled at the first alternative area (the suspected slide) to check the discontinuity test
a Bo
N
\~,
results of 3 years ago. The thickness of the slide, first estimated as greater than 60 m, was found less than 15 m (Fig. 2). The same result was achieved originally by the discontinuity survey. Finally, the alignment was shifted back to this former location. Groundwater movement is mainly governed by major discontinuities such as faults and bedding planes in a stratified and tilted unit, which is explained in detailed by Yilmazer (1991 ). The conventional recharge area boundary follows the topographic divide which is not convenient in a region comprising tilted stratification. One of the best examples is the study area where the mountain range is characterized by homoclinal structures (Fig. 4). High angle thrusts, reverse faults, bedding planes, compressional joints and schistosities all dip northwestward. Numerous perennial springs and creeks are observed along the western flank, whereas almost all creeks along the eastern side are seasonal or dry. The groundwater condition could also be predicted practically by recognizing major discontinuity systems and their subsurface conditions.
N
(bl N
(c} N LOCATION
POLE
B: BEDDING
I
F: FAULT d i JOINT SI SCHISTOSITY
o -KMI+IO0-1+300 b - KMO-I-800-O÷900 e -KM.O'I-600 -0-1-600 d - KM.O-t-500---O+600
e- KM.O+O00-O+IO0
[d)
(e)
Fig. 3. Stereographicprojectionof discontinuitiesfrom suspectedfloatingblocks(a-c) and adjacentbedrock outcrops (d-e).
L Yilmazer/Engineering Geology 40 (1995) 41-48
46
AKCADAfiHILL
t179sl
J
KAPAPINAR I ~ / I
.,I-----
, , Z CREEK
,
~-...-u. ~. One: "'
j "-
/.
(950) ASLANLIB[L
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,
~~
EXPLANATION
'-
",'"'
@c : [ O L U M ~
,SWW
Kd : OOLE111TE Ks :SERPENIINITE Kp : P i n . m E Ol : D(1DI~ITIC LKSTONE
NEF.~W L ~
t /
.~,'w.,x,k~.~-N
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E
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~
~
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,
SCALE'
~"
# ~
/,'~i-#',,,",,d]
/
e
'
~
: LAHOSLIDES
Fig. 4. Geology and linear engineering structures across Nurmountain.
4. Discussion and conclusions
The 150 km long Amanos mountain chain forms an impassable highland between southern and southeastern Turkey. Highway, railways, motorway and other linear structures have all been located in a narrow corridor which attains a height of 900 m between the two plains with an elevation of 500 m. The detailed discontinuity survey carried out in 1990 (during the preliminary design phase), modified the conclusions of previous studies about the general geology and engineering geology of the corridor. The mountain range has been identified as consisting of sedimentary rocks forming a symmetrical anticline. However, schistosity is well
developed and most of the bedding planes are amalgamated (welded) by regional metamorphism. The mountain range also comprises homoclinal structures dipping northwest, rather than a symmetrical anticline or anticlinorium. Tensional joints are more or less oriented parallel to the compressional stresses that were active during Upper Cretaceous Lower Tertiary thrusting. The joints have been sealed mainly with quartz. The engineering properties of such metasediments are appreciably better than the shaly sequence which was identified as the main lithology in the literature completed before 1990. A very improper motorway alignment was selected because of this misinterpretation. Seven viaducts, four tunnels, two special viaducts, numerous high embankments and cuts,
I. Yilmazer/Engineering Geology 40 (1995) 41-48
and several other m a j o r structures were designed to cross the mountain. The m o t o r w a y grade is 4% which is m u c h higher than the m a x i m u m allowable grade (2%) for tunnels and special viaducts. The old (80 years) railway tunnel across the m o u n t a i n range lies in the same corridor where the new highway is planned. It is basically unlined (open sided and self supporting) providing thus fresh outcrops to carry out discontinuity surveys at depths up to 600 m. A l m o s t all discontinuities become impersistent, watertight, irregular and very widely spaced with depth. Such subsurface geological conditions naturally favour the stability o f u n d e r g r o u n d excavation. Therefore, a 7.0 k m long straight tunnel with a gradient < 1% was suggested following the execution o f the detailed discontinuity survey in 1990. The proposal was submitted before the c o m m e n c e m e n t o f the detailed geotechnical investigation and design. However, it was n o t accepted because o f the fast track character o f this international project. I f the d o m i n a n t geologic unit, as distinguished during the preliminary phase, were a shaly sequence, such a long tunnel could not be constructed at a reasonable price or schedule. The unit price o f a tunnel t h r o u g h a shaly rock (class 6 - 7 ) is 3 to 10 times greater than that o f a tunnel t h r o u g h the existing metasediments (class 2 - 3 ) . If a detailed discontinuity survey should have been performed and local knowledge instead o f the available literature should have been used during the route location phase, a less expensive and more stable alignment would have been selected.
Acknowledgment I a m grateful to m y colleagues w h o worked hard to select proper m o t o r w a y routes by never forgetting to love N a t u r e by remembering never to challenge it.
References Bieniawiski, Z.T., 1989. Engineering Rock Mass Classifications: A complete Manual for Engineers and Geologists in Mining, Civil and Petroleum Engineering. Wiley, New York, N.Y.
47
Bolt, A.B., 1970. Causes of earthquakes. In: R.L. Wiegel (Editor), Earthquake Engineering. Prentice Hall, Englewood Cliffs, N.J., pp. 75-92. Dean, W.T. and Monad, O., 1984. An interpretation of Ordoviclan stratigraphy in the Bahce area, northern Amanos Mountains, South Central Turkey. Geol. Mag., 122(1): 15-25. Hendron, H.J., Mesri, G., Gamble, J.C. and Way, G., 1970. Compressibility characteristics of shales measured by laboratory and in situ tests: Determination of the in situ modulus of deformation of rock. STP 477, ASTM, Philadelphia, Pa., pp. 137-153. Housner, G.W., 1970. Strong ground motion. In: R.L. Wiegel (Editor), Earthquake Engineering. Prentice Hall, Engiewood Cliffs, N.J., pp. 75-92. Hunt, R.E., 1986. Geotechnical Engineering Analysis and Evaluation. McGrraw-Hill, New York, N.Y., 730 pp. M.T.A., 1989. Geological map of Turkey, scale 1/500,000, Hatay Sheet. Maden Tetkik Arama Enstitusu, Ankara. Shamburger, C.H., Patrick, D.M. and Lutter, R.J., 1975. Survey of problem areas and current practices. Ntl. Tech. Inf. Serv., U.S. Dep. Commerce, Springfield, Va. 22161. Steffen, O.K.H., 1976. Research and development needs in data collection for rock engineering. Proc. Symp. Exploration for Rock Engineering, 2. Balkema, Rotterdam, pp. 95-104. Wickam, G.E., Tiedman, H.R. and Skinner, E.H., 1974. Support determinations based on geologic predictions. Proc. 2nd North American Rapid Excavation and Tunneling Conf., 1. AIME, Chicago, II1., pp. 691-707. Yilmazer, I., 1990. Engineering geology of the section III of the TAG motorway. Unpublished reports, Highway Division-KGM, Ankara, Turkey. Yilmazer, I., 1991. An approach to construct groundwater recharge area boundary over a stratified and tilted geological unit. Proc. Symp. Precipitation, Flood and Landslide. Ankara, Turkey, pp. 205-218 (in Turkish). Yilmazer, I., 1992. Altitude and discontinuity factors in hydrogeology. Proc. 3rd Natl. Eng. Geol. Symp. Cukurova University, Turkey, pp. 111-128 (in Turkish). Yilmazer, I. and Congar, B., 1994. Significanceof discontinuity survey and physiographical study in engineering works. Proc. 7th Congr. Int. Assoc. Eng. Geol. Organising Committee, 5-9 Sept., 1994, Lisbon, Portugal, pp. 1105-1111. Yilmazer, I. and Demirkol, C., 1992. About the geology of the Nurmountain Range (NMR). Proc. 1st Int. Symp. East Mediterranean Geology. Cukurova University, Turkey, p. 313. Yilmazer, I., Ertunc, A. and Erhan, F., 1992a. Engineering geology of the Duzici-Komurler region. Proc. 1st Int. Symp. East Mediterranean Geology. Cukurova University, Turkey, pp. 77-89. Yilmazer, I., Ertunc, A. and Kaya, S., 1992b. Cut slope design and kinematic analysis (in Turkish). 3rd Natl. Eng. Geol. Symp. Cukurova University, Turkey. Yilmazer, I., Isler, F. and Duman., T., 1992c. Metamorphism in Nurmountain Range and its effect on engineering geology of the region. Proc. 1st Int. Symp. East Mediterranean Geology. Cukurova University, Turkey, pp. 67-76.
48
L Yilmazer/Engineering Geology 40 (1995) 41 48
Yilmazer, I., Kale, S. and Doyuran, V., 1994a. Significantly large and typical landslides. Proc. 7th Congr. Int. Assoc. Eng. Geol. Organising Committee. 5 9 Sept., 1994, Lisbon, Portugal, pp. 1377 3919. Yilmazer, I., Selcuk, S. and Tumer, H., 1994. Cut slope recommendation. Proc. 7th Congr. Int. Assoc. Eng. Geol. Organis-
ing Committee. 5-9 Sept., 1994, Lisbon, Portugal, pp. 3909-3919. Zika, P., 1990. Engineering Geological Evaluation of the Rock Cuts Stability along the D1 Highway. IAEG Congr., Balkema, Rotterdam.
EngineeringGeology40 (1995) 41-48
Significance of discontinuity surveying in motorway alignment selection, southern Turkey I. Yilmazer Spectra Jeotek Co., Kumkapl Sokak 20/1, 06610 (ankaya, Ankara, Turkey Received 17 October 1994; accepted 22 March 1995
Abstract
A detailed discontinuity survey is an essential part of a route location study, because rock quality and subsurface geological conditions can be determined by examining discontinuity systems. It also helps to prepare a sound subsurface investigation programme in the later stages of an engineering project. Some of the more expensive structural elements of a motorway are tunnels, viaducts, reinforced retaining walls and contiguous piles. Each has special requirements depending on ground stability, cost and environmental aspects. A detailed discontinuity survey enables engineers to select the best route and to optimize the geotechnical design. A case study from the Tarsus-Adana-Gaziantep (TAG) motorway being constructed in southern Turkey displays well the role of a discontinuity survey in engineering geological and geotechnical work. The survey, which was carried out by visual inspection and practical field tests, indicated, on the basis of the consistency of the discontinuity systems in each rock exposure, that the suspected floating blocks were outcrops of in situ rock. Misinterpretation of the actual ground condition caused loss of both time and money.
1. Introduction
The Amanos mountain range trends N E - S W and forms a 150 km long topographical obstacle between two large basins, i.e. the t~ukurova (basin plain) and the H a t a y - K a r a s u Graben (Fig. 1). The northern part of the middle section of the range is called Nurmountain. Southern Turkey and the eastern part of Anatolia are connected by Nurmountain. The TAG motorway and a new railway are being designed and constructed (Yilmazer et al., 1992a, b) in the same narrow corridor across Nurmountain, where a railway tunnel, a highway, pipelines and local roads already exist. Many scientists have studied this area including Dean and Monad (1984) and references therein since 1843. 0013-7952/95/$09.50© 1995ElsevierScienceB.V. All rights reserved SSDI 0013-7952(95)00018-6
Nurmountain is described as a homoclinal structure dipping NW; metamorphic textures are quite distinct as stated by Yilmazer et al. (1992c). The terms "symmetrical anticline or anticlinorium and shale" have repeatedly been used to identify the geology of the area till 1990. However, Yilmazer (1990) and Yilmazer and Demirkol (1992) provided clear field evidences indicating the dominance of homoclinal structures and metamorphic rocks. The engineering properties of shale are given in Shamburger et al. (1975) and Hendron et al. (1970). Shales are in general extremely weak to weak rocks; they are comparatively weaker than metasediments. Pre-existing discontinuities become welded under increasing metamorphic conditions
42
L
Yilmazer/Engineering Geotog:v 40 (1995) 41-48
",~,":;"~i':~# ~i~:~iii~:~i::~y ~-~. . ;:~::i .~:!~.;:~:::::: ~
SIR DAM K.MARA~
I
Kozonc Kodidi 0 Asoo
~o ~ 2
0~.~o 50o
G~zi~ Azo
/
oKilis
~nd,
IO
0
.:: .
~
20
40
Kin.
S C/~LE
i
LEGEND MEDITERRANEAN SEA
Basle and Ultnabaslc=
I ~ HATAY
L\ g',. ,....,.r/'k'---''" "~"
(
~
Mesozoic
~
Paleozolc Elevation, m. 25
5O
J .c- ..J /'~,p
i,
(
SYRIA
%,,"
Fig. 1. Map showing the accessibility and general geology (M.T.A., 1989).
35
40
45
I. Yilmazer/Engineering Geology 40 (1995) 41-48
resulting in an appreciable improvement in rock quality. Active and large landslides (60 x 300 x 1000 m) have developed mainly along structural and tectonic contacts on the western side of the mountain belt where outslope and dipslope conditions prevail. The hydrogeology of an area is largely affected by altitude and major discontinuity systems. Mountain belts naturally receive higher precipitation (Yilmazer, 1992; Yilmazer and Congar, 1994). The western side of Nurmountain has numerous perennial springs and streams and artesian pressure, whereas the creeks and springs on the eastern side are seasonal or dry. Ground stability is adversely affected by prevailing wet conditions combined with the dominance of discontinuities dipping outslope (Yilmazer et al., 1994b).
2. Engineering geology The most common rock types in the area are metasediments (including granoblastic schist, slate, hematite schist, metaquartzite and phyllite), recrystallized dolomitic limestone and silicified dolomitic limestone. Excluding the phyllite, the calcschist and the talc schist levels, moderately strong to very strong rocks constitute the majority of the unit. Schistosities are not persistent. Metamorphism caused amalgamation of bedding planes. Joints are rough, irregular and tight. In particular tensional joints are sealed, mainly with quartz and calcite. The weathering depth in these metamorphic units does not exceed 10 m except in thick shear zones, Surface inspection of shear zones is an essential part of the discontinuity survey. More than a hundred subsurface investigation boreholes have been drilled along a 4 km long section of the TAG motorway including the problematic zone across the mountain belt. Metasediments become watertight with increasing depth (> 20 m) and engineering properties improve noticeably. This condition naturally favours the stability of a tunnel excavation. The existing railway tunnel constructed in the same corridor is over 80 years old, about 6 km
43
long, and is mainly unlined. It is a self supporting tunnel and still works efficiently. Several earthquakes have occurred during the existence of the tunnel in the vicinity, but did not affect the stability of the tunnel. Several short (400 m) tunnels have been constructed through Miocene sedimentary units along the same railway. Although they were lined, they have suffered from groundwater and earthquakes. The interrelationship between ground motion, depth, elastic strain and basement rock is explained and well documented by Bolt (1970) and Housner (1970). Elastic strain in basement rocks increases with depth, whereas ground motion decreases. Wickam et al. (1974) have suggested that sedimentary rocks are not first class rocks from a tunnelling point of view. The engineering properties of both the sedimentary and metamorphic rocks along the motorway have been investigated using extensive geotechnical methods. Ultimate shear strength parameters, limiting pressure (PI) found by pressuremeter test and elastic modulus (E) values, as described by Hunt (1986) and references therein, are presented in Table 1 in order to give a general idea of the strength of the sedimentary and metamorphic rocks at the study area. The shear strength parameters, cohesion (C) and internal friction angle ( ~ ) are given in an interval rather than a certain value.
3. Discontinuity survey to predict subsurface conditions A motorway network, 3600 km long, is being designed and constructed throughout Turkey. A great number of landslides are closely connected with existing discontinuity systems (Yilmazer et al., 1994a). 60% of the motorway alignments take place on rugged and highly dissected areas where structural, tectonic, stratigraphic and lithological contacts and other discontinuity types are widespread. In addition to the discontinuity type, the spacing and aperture, water condition, infill properties, material property, weathering, slaking, number of discontinuity systems and other relevant data are
44
1. Yilmazer/Engineering Geology 40 (1995) 41 48
Table 1 Strength and deformation modulus values of the metamorphic and sedimentary rocks Rock type
C (kPa)
~ (')
Number of testsa
P/~ (kPa)
Standard deviation
E (MPa)
Standard deviation
Sandstone Siltstone Mudstone Claystone Phyllite Slate Hematite schist Calcschist Metaquartzite
70 150 40-100 25-70 25-70 40-250 70 300 95-500 35-200 95-500
30-45 25 35 20 30 15-25 30-40 30-45 35 55 20-35 40-55
36 30 68 15 94 23 30 Il 49
6363 3742 3010 2860 3680 16180 21369 5197 15240
522 295 127 118 110 651 435 352 758
197 117 114 55 251 504 662 145 469
21 20 8 2 23 21 13 13 24
aRandomly selected from a large number of tests. bLimit pressure. Note: Effects of weathering and depth are not taken into account.
gathered by visual inspection, practical field tests and laboratory work. Such engineering data could also be used in back analyses and be interpreted to predict internal friction angle ( ~ ) and cohesion (C). The reliability of a rock mass classification basically depends upon the accuracy of the results of the discontinuity survey (Bieniawiski, 1989; Steffen, 1976). Such a study is easy, inexpensive and quick to carry out and provides reliable data about ground stability in three dimensions. The ~ and C values obtained from sedimentary rocks by in situ and laboratory tests are generally too high to be directly used in cut slope stability analyses. For example, a few clay layers, 0.10 m thick, in a sedimentary sequence that dips outslope at a dip angle greater than ~ , can control slope stability. However, the same layer may not have any adverse effects if it dips inslope. Zika (1990) and Yilmazer et al. (1992a) have pointed out that kinematic analyses based on a discontinuity survey have practical and reliable applications, particularly for stratified and tilted units. Isolated bedrock outcrops in a suspected slide area were misinterpreted as floating blocks in a slide mass (Fig. 2). However, a one-day discontinuity survey revealed the actual field situation. As depicted in Fig. 2, the isolated rock exposures, under the remnants of the slide mass, were mapped as floating blocks in 1988 and the area was interpreted as a 65 m thick landslide. However, a more
~d t~
2
z
° I ,,-r!.
~
$ 7
....
$20 780
Fig. 2. Suspected slip surfaces (SS) and floating blocks (FB).
recent discontinuity survey found that the discontinuity system of each exposure was identical. In other words, the attitudes of joints (compressional,
45
I. Yilmazer/Engineering Geology 40 (1995) 41-48
conjugate and tensional), bedding and schistosity were consistent (Fig. 3). Interpreting this slope as a 65 m thick active slide, it could not be crossed using any available engineering method at reasonable cost. Without any further consideration of the discontinuity results the alignment was shifted to the north of the adjacent creek where large scale ground instability problems are distinct. Three years have been spent on further geotechnical investigations along this new alignment. The discontinuity survey carded out before the investigation programs started, indicated that the new location had potential groundwater problems. However, 40 m deep contiguous piles together with 100 m long cable anchors were suggested to stabilize an active landslide with average dimensions of 35 x 800 x 1000 m. Ultimately, cost analyses based on a three year investigation, were reported toward the end of 1992. The calculated comparatively high costs was found unacceptable and then, two deep boreholes (70 m) were drilled at the first alternative area (the suspected slide) to check the discontinuity test
a Bo
N
\~,
results of 3 years ago. The thickness of the slide, first estimated as greater than 60 m, was found less than 15 m (Fig. 2). The same result was achieved originally by the discontinuity survey. Finally, the alignment was shifted back to this former location. Groundwater movement is mainly governed by major discontinuities such as faults and bedding planes in a stratified and tilted unit, which is explained in detailed by Yilmazer (1991 ). The conventional recharge area boundary follows the topographic divide which is not convenient in a region comprising tilted stratification. One of the best examples is the study area where the mountain range is characterized by homoclinal structures (Fig. 4). High angle thrusts, reverse faults, bedding planes, compressional joints and schistosities all dip northwestward. Numerous perennial springs and creeks are observed along the western flank, whereas almost all creeks along the eastern side are seasonal or dry. The groundwater condition could also be predicted practically by recognizing major discontinuity systems and their subsurface conditions.
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(e)
Fig. 3. Stereographicprojectionof discontinuitiesfrom suspectedfloatingblocks(a-c) and adjacentbedrock outcrops (d-e).
L Yilmazer/Engineering Geology 40 (1995) 41-48
46
AKCADAfiHILL
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Fig. 4. Geology and linear engineering structures across Nurmountain.
4. Discussion and conclusions
The 150 km long Amanos mountain chain forms an impassable highland between southern and southeastern Turkey. Highway, railways, motorway and other linear structures have all been located in a narrow corridor which attains a height of 900 m between the two plains with an elevation of 500 m. The detailed discontinuity survey carried out in 1990 (during the preliminary design phase), modified the conclusions of previous studies about the general geology and engineering geology of the corridor. The mountain range has been identified as consisting of sedimentary rocks forming a symmetrical anticline. However, schistosity is well
developed and most of the bedding planes are amalgamated (welded) by regional metamorphism. The mountain range also comprises homoclinal structures dipping northwest, rather than a symmetrical anticline or anticlinorium. Tensional joints are more or less oriented parallel to the compressional stresses that were active during Upper Cretaceous Lower Tertiary thrusting. The joints have been sealed mainly with quartz. The engineering properties of such metasediments are appreciably better than the shaly sequence which was identified as the main lithology in the literature completed before 1990. A very improper motorway alignment was selected because of this misinterpretation. Seven viaducts, four tunnels, two special viaducts, numerous high embankments and cuts,
I. Yilmazer/Engineering Geology 40 (1995) 41-48
and several other m a j o r structures were designed to cross the mountain. The m o t o r w a y grade is 4% which is m u c h higher than the m a x i m u m allowable grade (2%) for tunnels and special viaducts. The old (80 years) railway tunnel across the m o u n t a i n range lies in the same corridor where the new highway is planned. It is basically unlined (open sided and self supporting) providing thus fresh outcrops to carry out discontinuity surveys at depths up to 600 m. A l m o s t all discontinuities become impersistent, watertight, irregular and very widely spaced with depth. Such subsurface geological conditions naturally favour the stability o f u n d e r g r o u n d excavation. Therefore, a 7.0 k m long straight tunnel with a gradient < 1% was suggested following the execution o f the detailed discontinuity survey in 1990. The proposal was submitted before the c o m m e n c e m e n t o f the detailed geotechnical investigation and design. However, it was n o t accepted because o f the fast track character o f this international project. I f the d o m i n a n t geologic unit, as distinguished during the preliminary phase, were a shaly sequence, such a long tunnel could not be constructed at a reasonable price or schedule. The unit price o f a tunnel t h r o u g h a shaly rock (class 6 - 7 ) is 3 to 10 times greater than that o f a tunnel t h r o u g h the existing metasediments (class 2 - 3 ) . If a detailed discontinuity survey should have been performed and local knowledge instead o f the available literature should have been used during the route location phase, a less expensive and more stable alignment would have been selected.
Acknowledgment I a m grateful to m y colleagues w h o worked hard to select proper m o t o r w a y routes by never forgetting to love N a t u r e by remembering never to challenge it.
References Bieniawiski, Z.T., 1989. Engineering Rock Mass Classifications: A complete Manual for Engineers and Geologists in Mining, Civil and Petroleum Engineering. Wiley, New York, N.Y.
47
Bolt, A.B., 1970. Causes of earthquakes. In: R.L. Wiegel (Editor), Earthquake Engineering. Prentice Hall, Englewood Cliffs, N.J., pp. 75-92. Dean, W.T. and Monad, O., 1984. An interpretation of Ordoviclan stratigraphy in the Bahce area, northern Amanos Mountains, South Central Turkey. Geol. Mag., 122(1): 15-25. Hendron, H.J., Mesri, G., Gamble, J.C. and Way, G., 1970. Compressibility characteristics of shales measured by laboratory and in situ tests: Determination of the in situ modulus of deformation of rock. STP 477, ASTM, Philadelphia, Pa., pp. 137-153. Housner, G.W., 1970. Strong ground motion. In: R.L. Wiegel (Editor), Earthquake Engineering. Prentice Hall, Engiewood Cliffs, N.J., pp. 75-92. Hunt, R.E., 1986. Geotechnical Engineering Analysis and Evaluation. McGrraw-Hill, New York, N.Y., 730 pp. M.T.A., 1989. Geological map of Turkey, scale 1/500,000, Hatay Sheet. Maden Tetkik Arama Enstitusu, Ankara. Shamburger, C.H., Patrick, D.M. and Lutter, R.J., 1975. Survey of problem areas and current practices. Ntl. Tech. Inf. Serv., U.S. Dep. Commerce, Springfield, Va. 22161. Steffen, O.K.H., 1976. Research and development needs in data collection for rock engineering. Proc. Symp. Exploration for Rock Engineering, 2. Balkema, Rotterdam, pp. 95-104. Wickam, G.E., Tiedman, H.R. and Skinner, E.H., 1974. Support determinations based on geologic predictions. Proc. 2nd North American Rapid Excavation and Tunneling Conf., 1. AIME, Chicago, II1., pp. 691-707. Yilmazer, I., 1990. Engineering geology of the section III of the TAG motorway. Unpublished reports, Highway Division-KGM, Ankara, Turkey. Yilmazer, I., 1991. An approach to construct groundwater recharge area boundary over a stratified and tilted geological unit. Proc. Symp. Precipitation, Flood and Landslide. Ankara, Turkey, pp. 205-218 (in Turkish). Yilmazer, I., 1992. Altitude and discontinuity factors in hydrogeology. Proc. 3rd Natl. Eng. Geol. Symp. Cukurova University, Turkey, pp. 111-128 (in Turkish). Yilmazer, I. and Congar, B., 1994. Significanceof discontinuity survey and physiographical study in engineering works. Proc. 7th Congr. Int. Assoc. Eng. Geol. Organising Committee, 5-9 Sept., 1994, Lisbon, Portugal, pp. 1105-1111. Yilmazer, I. and Demirkol, C., 1992. About the geology of the Nurmountain Range (NMR). Proc. 1st Int. Symp. East Mediterranean Geology. Cukurova University, Turkey, p. 313. Yilmazer, I., Ertunc, A. and Erhan, F., 1992a. Engineering geology of the Duzici-Komurler region. Proc. 1st Int. Symp. East Mediterranean Geology. Cukurova University, Turkey, pp. 77-89. Yilmazer, I., Ertunc, A. and Kaya, S., 1992b. Cut slope design and kinematic analysis (in Turkish). 3rd Natl. Eng. Geol. Symp. Cukurova University, Turkey. Yilmazer, I., Isler, F. and Duman., T., 1992c. Metamorphism in Nurmountain Range and its effect on engineering geology of the region. Proc. 1st Int. Symp. East Mediterranean Geology. Cukurova University, Turkey, pp. 67-76.
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L Yilmazer/Engineering Geology 40 (1995) 41 48
Yilmazer, I., Kale, S. and Doyuran, V., 1994a. Significantly large and typical landslides. Proc. 7th Congr. Int. Assoc. Eng. Geol. Organising Committee. 5 9 Sept., 1994, Lisbon, Portugal, pp. 1377 3919. Yilmazer, I., Selcuk, S. and Tumer, H., 1994. Cut slope recommendation. Proc. 7th Congr. Int. Assoc. Eng. Geol. Organis-
ing Committee. 5-9 Sept., 1994, Lisbon, Portugal, pp. 3909-3919. Zika, P., 1990. Engineering Geological Evaluation of the Rock Cuts Stability along the D1 Highway. IAEG Congr., Balkema, Rotterdam.