Anisotropy effect on strengths of metamorphic rocks

Ahmet ?zek,Murt Gül,Ergun Krcn,?vün? Alc

aDepartment of Geological Engineering, Kahramanmaras? Sutcu Imam University,Avsar Campus,Kahramanmaras?,Turkey

bDepartment of Geological Engineering,Mu?la S?tk? Ko?man University,Mu?la,Turkey

1.Introduction

Assessing the physico-mechanical properties,quality of intact rock masses,strength-deformation characteristics,and failure mechanism for economic and safe engineering applications is critically importantly(Behrestaghi et al.,1996;Nasseri et al.,1997;Bagde,2000).Rock anisotropy affects the stability of underground and surface excavations,rock cutting and other engineering applications in civil,mining,geological and petroleum engineering(Hoek,1964;Ulusay and G?k?eo?lu,1997;?zbek,2009;Cho et al.,2012;Kim et al.,2012;Khanlari et al.,2014;Heng et al.,2015;?zbek and Gül,2015).The anisotropy prevents easy and accurate determination of physico-mechanical properties(Behrestaghi et al.,1996).If rock anisotropy is not taken into consideration,significant errors can occur in applications(Cho et al.,2012;Kim et al.,2012).

The anisotropy of rock is caused by any directional or planar features such as mineral composition,grain size,crystal size,fabric,porosity,weathering,microstructure,joints,fractures and faults(Ramamurthy et al.,1993;Behrestaghi et al.,1996;Bagde,2000;Cho et al.,2012;Kim et al.,2012;Khanlari et al.,2014;Wong et al.,2015).The anisotropic rocks(due to foliation)have variable physico-mechanical properties in different directions(Nasseri et al.,2003;Cho et al.,2012;Khanlari et al.,2014;Heng et al.,2015).The anisotropy of metamorphic rocks(inherently anisotropic,or transversely isotropic)is generally higher than that of other rocks(Ramamurthy et al.,1993;Behrestaghi et al.,1996;Khanlari et al.,2014;Heng et al.,2015).High temperature and pressure lead to development of preferred orientation of minerals and parallel alignment of platy mica minerals in metamorphic rocks,namely foliation forms the phyllitic,schistose and gneissose texture,and so the anisotropy of metamorphic rocks(Ramamurthy et al.,1993;Behrestaghi et al.,1996;Nasseri et al.,2003;Heng et al.,2015).Elasticity modulus,P-wave velocity,thermal conductivity and other properties of gneiss,schist,phyllite and slate vary,depending on the direction of loading(Nasseri et al.,1997,2003;Kim et al.,2012).

Several types of metamorphic rocks crop out along the route of the Yata?an-?ine Highway(Fig.1).Those metamorphic rocks,namely southern(?ine)submassif of Menderes massif and its cover units,include orthogneiss,mica schist(metasandstone,psammitic schist),marble (calcschist),and phyllite.Moreover,several quartzite and feldspar quarries have been operated in those rocks.Various stability problems(e.g.rockfall and wedge type failure)were observed in this region,which have threatened public life.The aims of this study are to determine some engineering properties of the metamorphic rocks and discuss the effects of anisotropy,anisotropy ratio and metamorphism on rock strength even in a short distance.

2.Materials and method

Fig.1.(a)The study area located in Southwest Turkey.(b)Distribution of the central massif and southern(?ine)submassif of Menderes metamorphic massif(modified from Okay,2001;Whitney and Bozkurt,2002).Investigated metamorphic rocks crop out in southern part of the southern(?ine)submassif.

Fig.2.General geological map of the study area(modified from Bozkurt,2004).Four different locations were selected.

The study area covers 3 km2regions along the route of Yata?an(Mu?la)-?ine(Ayd?n)Highway(Figs.1 and 2).Hac?aliler, Seykel(north),Irmadan Districts(center)and Kafaca Village were settlements of the study area(Fig.2).Examined metamorphic rocks formed medium-height hill and showed good exposures on road cuts.The height of hills around the road varies from550 m to600 m(Fig.2).Predominant wind directions were SE,NE and SW in the study area(Haktan?r et al.,2010;?lgen and Gür,2012).The daily temperatures of Mu?la ranged from-12.6°C to 42.1°C,and the average annual temperature was 15°C(90 years’data;MGM,2013a).The average annual rainfall in and around Mu?la was 817.5 mm(29 years’data;MGM,2013b).The slope around the road contains pine trees.

Four different rock types were taken into consideration during field studies,including phyllite,schist,gneiss and marble(calcschist).The dip and dip direction of foliation,and discontinuities were recorded for each rock type(Table 1).Roughness,filling,water condition,and spacing of discontinuities were determined based on Ulusay and Hudson(2007).Small hand samples were collected for petrography studies,in terms of specific unit weight and porosity.The results are presented in Table 2.“Proceeq Silver-Schmidt PC Type L Concrete Test Hammer”was applied in the directions perpendicular and parallel to the foliation of rock in order to determine the in situ strength of rocks(Table 3).Four blocks were collected for laboratory experiments.The size of each block is listed in Table 4.“Proceeq Silver Schmidt PC Types L and N Concrete Test Hammers”were applied to four rock samples in three dimensions based on the foliation in laboratory(Table 5).All the testswere performed in the Natural Stone Research Laboratory and Rock Mechanic Laboratory,Mining-Geological Engineering Department of Mu?la S?tk? Ko?man University.Discontinuity analyses were performed using DIPS program(Diederichs and Hoek,1989)to determine the dominant joint sets.Petrographical analyses were performed using the thin section of each rock samples.Mineralogical contents of the rocks and textural features of schistositygneissic banding were examined under the binocular microscope.

Table 1Discontinuity sets and foliation measurements of examined metamorphic rocks.

Table 4Sizes of rock blocks.

3.Regional geology

The Menderes massif is one of the largest metamorphic core complex of Anatolia,evolving from the Alpine Orogeny,and contains southern(?ine)submassif,central massif and northern submassif(Fig.1;S?eng?r et al.,1984;Bozkurt et al.,1995;Bozkurt and Oberhansli,2001;Whitney and Bozkurt,2002).This massif covers large areas of west Turkey.Upper Proterozoic metasediments,mica schist,orthogneiss,metagabro,and metanorite form the core of the southern(?ine)submassif(Candan and Dora,1998;Dora et al.,2001).They are overlaid by the cover units including Paleozoic-Lower Tertiary platform carbonates,marl,clayey limestone and marble(Okay,2001;?zer et al.,2001).

Table 2Dry and saturated densities and unit weights and porosities of the metamorphic rocks.

Table 3Rebound values of metamorphic rocks obtained after the application of the L-type Schmidt hammer in the field.

Table 5Rebound values of metamorphic rocks obtained after the application of the N-and L-type Schmidt hammers to blocks in laboratory.

During general geology evaluations,three studies were taken into consideration:geological map prepared by Mineral Research&Exploration General Directorate(MTA),Bozkurt(2004)and Koralay et al.(2012).Precambrian migmatite,gneiss,augen gneiss and metagranitoid,Paleozoic augen gneiss and Paleozoic phyllite,schist,marble and quartzite(to the south)were delineated in 1/25,000-scaled MTA geological map.K-feldspar,plagioclase,quartz, muscovite,biotite,tourmaline,zircon,rutile,monazite and opaque minerals bearing leucogranites were identified in and around Hac?aliler District(Fig.2)by Bozkurt(2004).The northern part of this unit is covered by orthogneiss,while the southern part contains cover units.Bozkurt et al.(2015)reported that the leucogranites(Late Middle Eocene)intruded into the orthogneisses and structurally overlaid the cover sediments.Blastomylonitic orthogneisses contain muscovite,biotite,quartz band and flattened feldspar-augen(Bozkurt,2004).The cover units contain semipelitic schist(finegrained biotite+quartz+muscovite schist with sporadic occurrence of garnet),psammitic schist(quartz+muscovite+ biotite schist),pelitic schist(mica+quartz+garnet+chloritoid schists)with marble lenses,and marble with mica-schist intercalations(Bozkurt,2004).Koralay et al.(2012)classified leuco-tourmaline orthogneiss and biotite orthogneiss to the north.Those units intruded into the garnet-mica schist and biotite-albite schist in the southern part(Koralay et al.,2012).

The Menderes massif was affected by two main metamorphisms,which were regional HT/MP Barrovian-type in Eocene and subsequent green schist retrograde metamorphism(Bozkurt and Sat?r,2000;Bozkurt and Oberhansli, 2001;Bozkurt,2004).The southward transport of Lycian Nappes(including ophiolites,accretionary prisms,volcanosedimentary units,carboniferous Permian-Upper Cretaceous sedimentary rocks)over the Menderes massif was responsible for this regional metamorphism (S?enel,1997;Robertson, 2000;Bozkurt,2004).Bozkurt et al.(2015)reported the exhumation age of the massif as the earliest Miocene based on the unconformable cover sediments.After the emplacement of Lycian Nappes in the southern part of ?ine Town,this region has been under the effects of compressional and extensional forces.Those forces caused initially east western Kale-Tavas Graben during Oligocene,NNW-SSE directed Milas-?ren and Yata?an grabens during Early-Middle Mioecene,and finally active EW G?kova Graben evolution(G?rür et al.,1995;Gürer and Y?lmaz,2002).

4.Sampling and experimental program

4.1.Lithological and mineralogical characterization

Phyllite-slate,schist and gneiss are classified as foliated metamorphic rocks,while marble is classified as a non-foliated metamorphic rock.Foliation is observed in the appearance of the marble,thus it may be classified as calcschist;however,the fresh fracture surface is typical of marble.Foliated metamorphic rocks are classified as anisotropic rocks,and there are some difficulties in determination of strength characteristics(Hoek and Brown,1997).

The phyllite is one of the cover units of Menderes massif(Bozkurt,2004).It crops out at 500 m south of Irmadan District(Fig.2).Macroscopically fractured phyllite is dark green,black colored,fine-grained and laminated.Foliation texture thickness of the phyllite is always less than 1 mm.This rock has weak appearance.It can be easily crumbled by fingers.Water leakage was observed inside and at the upper and lower boundaries with older and younger rocks,respectively(Fig.3a).

The psammitic schist and quartz-muscovite-biotite schist are another cover units of the Menderes massif(Bozkurt,2004).The schist is yellow-gray colored,thin to medium foliated,lineated rock in outcrops in Irmadan District.Upper foliated part of schist can be easily disintegrated.The cracks parallel to upper and lower surfaces and diagonal fractures cause easily fragmentation of rocks(Fig.3b).They include primarily quartz,muscovite, biotite,and plagioclase and K-feldspar minerals with foliated schistosity,nematoblastic texture,and mosaic texture among quartz with 1.5-2 m thick,folded quartz bands(Fig.3c).

Fig.3.(a)General field view of the phyllite(man for scale of 185 cm).The phyllite shows fractured and weak appearance.(b)General field view of the schist(man for scale of 185 cm).5-50 cm thick foliated structures were observed.1-3 cm thin to very thin schistosity planes were described at the top of the layers.(c)Microview of the schist.Quartz(Q)and biotite(Bi)minerals were found in thin sections.(d)Microview of the gneisses.Quartz(Q)porphyroclasts and biotite(Bi)minerals were found in thin sections.(e)Close view of the gneiss.(f)General field view of the gneiss(man for scale of 185 cm).The gneiss was affected by spheoridal weathering.

The gneiss-orthogneisses widelycrop out in the northernpart of the study area.They form domed baldhills(Fig.2).These rocks show minor geomorphological features such as tafoni,honey comb weathering,exfoliation,boulders,corestone,spheroidal weathering,flared slopes,local grus development and weathering zone(Gül and Uslular,2014,2015,2016).Macroscopically,the gneiss massively appears and is white and foliated-gneissic banded including large elongated-flattened feldspar porphyroclast and quartz.It contains abundant K-feldspar,quartz, muscovite, biotite,microcline,plagioclase,and garnet minerals,with foliated-gneissic banding(gneissosity),mosaic texture(among quartz),and poikoblastic texture(Fig.3d-f).

Marble lenses were separated in schist(Bozkurt,2004).For instance,the marble situated 1 km SW of Irmadan District(Fig.2)contained very hard,gray-dark gray colored marble lenses.White colored calcite filled cracks,quartz bands,and some lamination bedded traces were also found during the macroscopic examination,thus this marble could also be classified as calcschist.It(calcschist)included dominant calcite and lesser quartz minerals(Fig.4).

4.2.Discontinuity survey

Any planar structures of rock are responsible for the anisotropy of the rock mass(Ramamurthy et al.,1993;Singh et al.,2002;Saeidi et al.,2013). Discontinuities are one of the important planar structures of rock mass,and their relation with other intact rock orientation can affect the failure mode and strength characteristic of rock(Ramamurthy et al.,1993;Singh et al.,2002;Saeidi et al.,2013).The studied metamorphic rocks have also suffered from tectonic activities.

Discontinuity positions were determined by the measurements of discontinuity dip/dip direction in line survey scanning.This study was performed for the phyllite,schist,gneiss(north and south),and marble(calcschist).Contour diagrams of discontinuity sets were drawn using DIPS program(Diederichs and Hoek,1989).Dominant discontinuity sets were marked on these figures.Three dominant discontinuity sets and random discontinuities were determined for schist,phyllite,marble(calcschist)and gneiss(east).However,the gneiss(north)had two dominant discontinuity sets and random discontinuities in northern part(Table 1,Fig.5).

Bozkurt(2004)reported the N-NNE bulk shearing based on a variety of kinematic indicators,and showed that foliation suggests the N-NNE shearing during its metamorphism.The schist,marble(calcschist)and phyllite had foliation in direction of 40°-46°/SSW(dip/dipdirection)(Bozkurt,2004;Koralayetal.,2012).However,the gneiss foliation dipped to NW(Bozkurt,2004;Koralay et al.,2012).

Fig.4.(a)General field view of the marble(calcschist)(man for scale of 185 cm).(b)Close view of the marble(calcschist).Dark gray and white colored bands were observed in macroview.However,they were not differentiated in thin section.(c)Microview of the marble.Only calcite(Ca)minerals were found in thin sections.

The phyllite has SW,NW and NE directed fractures and NE directed foliation(Table 1,Fig.5).The fractures in the phyllite have very low(＜1 m)to medium(3-10 m)persistence,one-end visible termination,tight aperture width(0.1-0.25 mm),close(60-200 mm)to wide(600-2000 mm)spacing,and polished and planar fracture surfaces,and are filled with clay materials.The fractures show seepage but no continuous flow.

The schist has NW-N directed fractures and S directed foliation(Table 1,Fig.5).The fractures in the schist have very low(＜1 m,especially in the direction perpendicular to the foliation)to high(10-20 m)and very high(＞20 m)persistence,one-end visible termination,open aperture width(0.5-2.5 mm),wide spacing(600-2000 mm),and rough and planar fracture surfaces,and are filled with clay materials.The fractures show a few seepages but no continuous flow.

The gneiss has NE-SE directed fractures,NW directed foliation in north,and SW-NW-W directed fractures and NW directed foliation in east(Table 1,Fig.5).The fractures in the gneiss have very low(＜1 m,especially in the direction perpendicular to the foliation),high(10-20 m)to very high(＞20 m)persistence,one end visible termination,extremely wide(10-100cm)and cavernous aperture width(＞1 m),wide spacing(600-2000 mm),and clean,rough and planar fracture surface.The fractures show a few seepages but no continuous flow.

The marble(calcschist)has NE-SE directed fractures and SW directed foliation(Table 1,Fig.5).The fractures in the marble(calcschist)have very low(＜1 m,especially in the direction perpendicular to the foliation)to low(1-3 m)persistence,one-end and both-end visible termination,very wide(1-10 cm)to wide(600-2000 mm)spacing,and smooth and planar fracture surfaces.The fractures are clay-quartz-calcite filled and damp without free water.

4.3.Physical and mechanical characterizations

Statistical evaluations of dry and saturated densities and unit weights,and porosities of each metamorphic rock are listed in Table 2.The phyllite has the lowest average dry and saturated densities and unit weights,while the marble(calcschist)has the highest values.The phyllite has the highest average porosity,while the marble(calcschist)has the lowest value(Table 2).

Based on Moos-Quervain classification(Moos and De Quervain,1948),the phyllite and schist were classified as “high porosity”rocks,the gneiss was a“medium porosity”rock,and the marble was a “very compact”rock.According to Anon(1979)classification,the phyllite and schist were classified as “medium porosity”rocks,the gneiss was a “l(fā)ow porosity”rock,and the marble(calcschist)was a“very low porosity”rock.Also based on Anon(1979),the phyllite is classified as a “l(fā)ow density”rock;while the schist,gneiss and marble(calcschist)are classified as “medium density”rocks.

4.4.Application of Schmidt hammer to blocks in laboratory and in the field

The “Schmidt hammer rebound index”test was designed for concrete testing,which was also used to determine the strength of rock(Lassnig et al.,2012;Karaman et al.,2015).Different Schmidt hammers have been developed based on their levels of impact energy;however,only two Schmidt hammers,the L-and N-type,have been widely used in engineering applications(Lassnig et al.,2012).Lassnig et al.(2012)reported that the N-type hammer is more efficient for assessing the geotechnical parameters according to previous studies,and the L-type hammer delivers smaller values.

This test was used to determine the strength of all four different rock types of the study area.During the field study,the L-type hammer was applied in three different directions:perpendicular to the foliation,parallel to the foliation,and with an angle of approximately 45°to the foliation.The phyllite rebound values are lower than the “weak rocks”rebound values based on De Beer(1967)classification.According to the rebound values,two of the schist samples were classified as“strong”rocks,and the other two were classified as“weak”rocks.The gneiss and marble(calcschist)rebound values represent the “very strong”and “strong”rocks,repectively(Table 3,Figs.6 and 7).

Fig.5.Stereonet diagrams of the joints in phyllite,schist,gneiss(location 1 in Fig.2 is for gneiss(north),and gneiss(east)measurements were taken in southwest of Memis?ler Village)and marble-calcschist.

Based on the Schmidt hammer application in laboratory to rock blocks,the phyllite was classified as a “strong”rock(De Beer,1967),The schist was classified as a “strong”and “soft”rock.The gneiss and marble(calcschist)are “very strong”and “strong”rocks,respectively(Table 5,Fig.7).The N-and L-type hammers gave similar results for the finest crystalline rock-phyllite(Fig.7).By examining the coarse crystalline,non-foliated(marble)or thickly foliated(schist,gneiss)rocks,it can be found that the N-type hammer rebound values are significantly higher than the L-type hammer values.

Fig.8 shows the changes of porosity,dry density and the Schmidt hammer rebound values.High dry density with low porosity of studied rocks led to high rebound values;to the contrary,low dry density with high porosity led to low rebound values.

Fig.6.Rebound values of selected metamorphic rocks obtained after in situ application of the L-type Schmidt hammer in the directions parallel and perpendicular to the foliation surfaces.Standard deviation values were obtained from Table 3(P:Phyllite,S:Schist,G:Gneiss,M:Marble(calcschist)).

Fig.7.Rebound values of selected metamorphic rocks obtained in laboratory after application of the N-and L-type Schmidt hammers in the directions perpendicular and parallel to the short and long edges of the foliation surfaces.Standard deviation values were obtained from Table 5.Arrows show application directions of Schmidt hammer to the surface.

4.5.Anisotropy ratio

The anisotropy ratio is used to indicate the anisotropy scale,which varies depending on rock type,fabric and mineral alignment(Ramamurthy et al.,1993;Khanlari et al.,2014).This ratio is defined asa ratio of any properties in the direction parallel to the foliation at the anisotropy angle of 90°to the minimum value at other anisotropy angles(Singh et al.,1989;Ramamurthy et al.,1993;Nasseri et al.,2003;Cho et al.,2012;Kim et al.,2012).The anisotropy ratio is changeable,depending on the used properties(Kim et al.,2012).

During the calculation of representative anisotropy ratio of the southern(?ine)submassif,only the Schmidt hammer results at anisotropy angles of 0°(perpendicular to the foliation)and 90°(parallel to the foliation)were take into consideration during the field application.The gneiss and marble(calcschist)anisotropy ratios were less than 1,and the rebound values in the direction perpendicular to the foliation(gneiss)and in the horizontal surface(marble-calcschist)were larger than the values in the direction parallel to the foliation(gneiss)and in the vertical surface(marblecalcschist).The phyllite anisotropy ratio was roughlyequal to 1.The schist ratio was greater than 1.The rebound values in the direction parallel to the foliation of schist were larger than the values in the direction perpendicular to the foliation.

Fig.8.Dry density and porosity of phyllite,schist,gneiss and marble(calcschist)versus the L-and N-type Schmidt hammer rebound values obtained in the field and in laboratory.

By examining the Schmidt hammer applications to blocks in laboratory,it can be found that theoretical mineral lineation and foliation led to the development of three different surfaces in three dimensions(perpendicular to foliation or horizontal surface(Per);perpendicular to long axis of foliation,with large mineral coverage(ParL);and perpendicular to the short axis of foliation,with small mineral coverage(ParS);Fig.7).Thus the anisotropy in these three surfaces was evaluated separately(Table 5).The results show that thinly foliated finer-crystalline phyllite sample has the lowest anisotropy ratios less than 1,and the ratios of thickly foliated coarse crystalline schist and gneiss are higher than 1.The marble(calcschist) anisotropy ratios are around 1.The foliated marble(calcschist)has roughly similar rebound values in all directions,which represents similar mineral distribution in interior part.While the schist and gneiss rebound values in the direction perpendicular to the long mineral axis that presents more regular mineral coverage(ParL)are higher than those in the direction perpendicular to the short mineral axis(ParS).

5.Results and discussion

The planar structures are responsible for the anisotropy of the rock mass(Ramamurthy et al.,1993;Singh et al.,2002;Saeidi et al.,2013). Metamorphism and joints are main reasons accounting for the anisotropy of studied rocks in this paper.Metamorphic history of the study are a led to the development of foliation,schistosity and gneissosity.The phyllite has the thinnest foliation structure,while the schistosity and gneissoity are thicker.Strength variations of schist and gneiss are also explained with mineral strength differences on rock surface,i.e.mica layers are weak,while the quartz is harder(Lassnig et al.,2012).Another reason for anisotropy of studied rocks is the discontinitues.Singhet al.(2002)proposed that if the rock mass is not highly fractured or has joint sytems(five or less),then it behaves anisotropically.Geological history of the studied rocks led to the development of 2-3 joint sets(Table 1,Fig.5).

Considering the average values of the physico-mechanical properties of the studied rocks,it is shown that the phyllite has the lowest dry and saturated densities and unit weights,while the marble(calcschist)has the highest values(Table 2).Consistent with these results,the marble(calcschist)has the lowest porosity values,while the phyllite has the highest ones.The values of gneiss and schist are located between these two bound values,and the gneiss values are more close to the marble(calcschist)ones(Table 2).

The phyllite reported in Iran and Spain had higher density and lower porosity values(Ramamurthy et al.,1993;Garzón et al.,2010)than the studied phyllite of the southern(?ine)submassif.The schists reported in India had lower porosity and higher density(Behrestaghi et al.,1996;Nasseri et al.,2003)than the studied schist of the southern(?ine)submassif,while the schist in Iran(Khanlari et al.,2014)had higher porosity and lower density.Permian-Permo Carboniferous-Triassic-Upper Cretaceous-Paleocene marbles in Mu?la(Kus??u,1992;Yavuz,2001;Yavuz et al.,2002,2005a,b;Ba?c?,2006;Gül,2015)have similar porosity and dry density values with the marble(calcschist)of ?ine submassif of Menderes metamorphic massif.

By examining the Schmidt hammer testing results in the field,the rebound values of the studied rocks are obtained and listed in Table 3.It can be seen that the marble has the maximum rebound values,followed by the gneiss and schist,and the phyllite has the minimum rebound values.Similar results were expected during the laboratory application of Schmidt hammer(Table 5).The marble(calcschist)and gneiss show the highest rebound values,while the values of schist and phyllite are much lower and closer.The N-type Schmidt hammer rebound values are roughly 20%-25%higher than that of the L-type hammer in the coarser crystalline rocks like schist,gneiss and marble-calcshist(Table 5,Fig.7).

The coarse crystalline(marble-calcschist,gneiss),thickly foliated(gneiss)rocks have higher density,lower porosity,higher strength,and higher rebound values than the fine crystalline-thinly foliated metamorphic rocks(such as phyllite and schist)(Tables 2,3 and 5;Figs.6-8).Permian-Permo Carboniferous-Triassic-Upper Cretaceous-Paleocene marbles in Mu?la have similar rebound vaues(56-65)with the marble(calcschist)in the study area(Kus??u,1992;Yavuz et al.,2002,2005a,b;Ba?c?,2006;Gül,2015).The rebound values of phyllite are significantly different.The reason is that the Schmidt hammer applied to the phyllite sample was rather humid in the field,while the phyllite block in the laboratory was dry and tight.Moreover,the heterogeneities due to microcracks,calcite or quartz veins may form weakness zone and decrease the rock strength in the field(Wong et al.,2015).

Fig.9.Anisotropy ratio of selected metamorphic rocks obtained from the ratio of values in the direction parallel to the foliation to those in the direction perpendicular to the foliation after the application of the L-type Schmidt hammer in laboratory.Arrows show application direction of Schmidt hammer to the surface.

Fig.10.Anisotropy ratio of selected metamorphic rocks obtained from the ratio of values in the direction parallel to the foliation to those in the direction perpendicular to the foliation after the application of the N-type Schmidt hammer in laboratory.Arrows show application direction of Schmidt hammer to the surface.

The anisotropy ratios of the studied rock samples based on the Schmidt hammer rebound values are quite variable(Tables 3 and 4;Figs.9 and 10).They significantly indicate that the rebound value variations depend on planar structures in all rocks.However,only the schist shows similar anisotropy ratios both in the field and in laboratory application,while the other rocks have not consistent results(Tables 3 and 4;Figs.9 and 10).The reason may come from the difference in characteristics of rock mass in the field and blocks in laboratory.

Foliation,type and thickness of metamorphic textures,microcracks,discontinuity planes,exfoliation cracks,mineralogical content,mineral alignment-lineation,mineral strength differences on rock surface(mica layer is weak,and the quartz layer is hard,as was found in the schist and gneiss in the study area),crystal size,quartz and calcite veins affect the physical and engineering properties of metamorphic rocks(Ramamurthy et al.,1993;Behrestaghi et al.,1996;Nasseri et al.,2003;Song et al.,2004;Luque et al.,2010;Khandelwal and Singh,2011;Cho et al.,2012;Kim et al.,2012;Khanlari et al.,2014;Heng et al.,2015;Wong et al.,2015).The complex tectonic and metamorphic histories of the region like southern(?ine)submassif of Menderes metamorphic massif increase negative effects of foliation,metamorphic textures,and mineral alignments on the rock strength.Thus,any of the data mentioned above must be taken into consideration for safe mining engineering application in quartz-feldspar-marble quarries and drift excavation.

6.Conclusions

The southern(?ine)submassif contains a variety of metamorphic rocks.The complex tectonic and metamorphic histories of this area were responsible for mineral alignments,foliation in different thickness(＜1 mm in phyllite,＞1 m in schist and gneiss),2-3 joint sets development,exfoliation cracks,and calcite-quartz veins of these rocks.The main conclusions drawn in this paper are as follows:

(1)The finest crystalline phyllite in the study are a has the lowest density and strength and the highest porosity.The coarser crystalline gneiss and marble (calcschist)have lower porosity and higher strength values.

(2)The L-type Schmidt hammer rebound values obtained in the field are significantly lower than the results obtained in laboratory.The damp condition in the field,irregular distribution of discontinuities,different weathering degrees,and very thin metamorphic structures may be responsible for those lower strength values in the field.

(3)The N-type Schmidt hammer rebound values are 20%-25%higher than the L-type Schmidt hammer values.However,this significant difference was not fixed in finer crystalline phyllite rocks.

(4)Safe mining activities,drift construction and other engineering applications require detailed investigations of mineral content,mineral alignment-lineation,strength determination,anisotropy angle,discontinuity and weathering.

Conflict of interest

The authors wish to confirm that there are no known conflicts of interest associated with this publication and there has been no significant financial support for this work that could have influenced its outcome.

The authors want to thank two annonymous reviewers and editors for their valuable contributions during the revising of manuscript.

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