geologi rekayasa - Spada UNS

Prodi Teknik Sipil FT UNS

Lab. Mekanika Tanah FT UNS, Jl Ir Sutami 36 a Surakarta

GEOLOGI REKAYASA

TKS24082

….. dengan batuan ^?

Apa yang dimaksud ……

BATUAN adalah suatu bahan yang terdiri dari material padat ( solid ) baik berupa massa yang berukuran besar

maupun berupa fragmen-fragmen kecil.

- ASTM C 295-87, 1987 -

BATUAN adalah kumpulan atau

kesatuan mineral yang terdiri dari satu jenis mineral atau lebih.

- Glosarry of Geology, 1987 -

…..….. ROCKS ^.

Nature of ……

….. dalam kegiatan rekayasa, asumsi umum terhadap kondisi alamiah batuan meliputi :

 Homogen ( homogeneous )

 Kontinu ( continuous )

 Isotropik ( isotropic )

….. but …… NO!

….. batuan pada kenyataannya adalah

sangat kompleks dan bervariasi, sehingga yang umum dijumpai adalah :

 Heterogen ( heterogeneous )

 Diskontinu ( discontinuous ⁾

 Anisotropik ( anisotropic )

Homogeneous Continuous Isotropic

Heterogeneous Discontinuous Anisotropic

Sandstone Strength equal in

all directions

Shale

Sandstone

Fault

Joints

Strength varies with directions

Low High

Intact Rock

Rock Mass

versus

.….. the scale factor of rocks.

.….. the scale factor of rocks and the variation in strength of material depending on the size of the sample involved.

Minerals

Textures Rock Material Composition

Joint Properties Joints Jointing Pattern Density of Joints

Rock Mass

.….. the main features constituting a rock mass

…... batuan memiliki dua sifat utama yaitu sifat FISIK ^dan

sifat MEKANIK

….. yang dapat ditentukan berdasarkan

hasil pengujian laboratorium maupun

lapangan.

Physical Properties

Uji indeks ( index test ) dimaksudkan untuk memperoleh informasi dasar mengenai

sifat fisik batuan dalam kaitannya dengan usaha melakukan klasifikasi dan untuk

mendapatkan pengertian yang baik

karakter alami batuan.

• Densitas (density)

• Porositas (porosity)

• Permeabilitas (permeability)

• Kekerasan (hardness)

• Durabilitas (durability)

• Abrasifitas (abrasivity)

• Kekuatan (strength) dll.

….. examples of sampling requirements.

….. sampling for laboratory testing.

Sample preparation …..

….. to form perfect right-angled cylinders.

….. the sample preparation process usually involves drilling (drill press), cutting (diamond saw), and grinding (surface grinder).

Densitas …..

….. berat per satuan volume batuan.

w m

n

  

  ( 1  ) 

V

 W



• Densitas alami (bulk/natural)

• Densitas jenuh (saturated)

• Densitas kering (dry)

Dry density for various rock types

….. density changes with depth be low the sea floor in the Gulf of Mexico. The density in the figure is calculated from the core porosity data (Ostermeier et al. 2001).

25 .

741 0

.

1 _p

n 

v



Hubungan antara densitas dan kecepatan gelombang seismik untuk batuan

sedimen (Gardner et al., 1974) :

Porosity …..

….. is given as the volume of pore space divided by the total volume of sample.

….. porosity of some typical rocks showing effects of age and depth.

t v

V

 V



….. rock porosity decreases as the burial depth increases in the central deepwater Gulf of Mexico (plotted from the core test data presented by Ostermeier et al. 2001).

ae

^bZ

 

Persamaan umum hubungan antara porositas dan kedalaman :

Permeability …..

….. conveys information about the connectivity of pore space and fissures within a rock.

L h KA h

q 

¹

^

²

g k K

^f



 

Hardness …..

….. the Shore Scleroscope measures the rebound of a small rounded diamond hammer which falls from a fixed height and rebounds freely from the surface of rock specimen. Several reading are taken next to each other. The average rebound height, can than be correlated with the hardness and/or compressive strength.

Hardness …..

….. The Schmidt Hammer was originally developed for non-destructive testing of concrete. Four types of hammer are available with varying impact energy. The rebound of spring-loaded hammer mass after impact on the rock surface can be read directly from the instrument (Schmidt number) and correlate to

hardness.

Hardness …..

….. Relationship between Schmidt hardness and uniaxial compressive strength of rock.

Hardness …..

….. skala kererasan relatif batuan.

Kekerasan Simbol Deskripsi

Sangat Lunak RH-0 Sama dengan OH-4 dan OH-5 dan hanya dapat diambil dengan pemboran kering. Contohnya beberapa jenis tuf dan batulempung.

Lunak RH-1 Dapat digores dengan kuku dan diambil dengan palu geolog serta cepat dibor dengan mata bor widya, misalnya beberapa jenis batupasir, batulanau dan serpih.

Agak Lunak RH-2 Dapat digores dengan pisau dan cukup baik dibor degnan mata bor widya, contohnya batupasir yang tersemen baik dan batugamping.

Agak Keras RH-3

Sukar digores dengan pisau, sukar diambil dengan palu geologi tetapi ujung contoh batu masih mudah dipecahkan dengan palu.

Batu masih dapat dibor dengan mata bor widya tetapi kadang- kadang memerlukan matabor intan, contohnya basalt.

Keras RH-4 Ujung contoh batu sukar dipecah dengan palu, tak dapat digores dengan pisau dan pemboran memerlukan mata bor intan, contohnya kuarsit.

Sangat Keras RH-5 Kemajuan pemboran dengan mata bor intan sangat lambat, contohnya rijang, batuan terslifikasi.

Durability …..

….. Durability measure the changes in rock properties due to processes of chemical and mechanical breakdown (e.g.

exfoliation, hydration, solution, oxidation, abrasion, etc.).

Water Trough Testing Drum Counter Plate

Rubber Belt Motor Drive

Auto counter with Speed Adjustment

Rock Lumps

Swelling …..

….. The swelling strain index is a measure of the axial swelling strain developed when radially confined undisturbed rock specimen is immersed in water.

Strength …..

….. an index test for rock strength is provided by the point load test. The rock is hydraulically loaded by spherically truncated, hardened, conical steel platens and fails by the development of tensile cracks parallel to the axis of loading, often

normal but sometimes to the longer axis of the specimen.

Rock Sample Rigid Frame Pressure Gauge with Max. Indicator

Hand Pump Release Valve

Hydraulic Piston Platen

Steel Rule

…..

batuan

^?

Sifat mekanik……

Banyak metode uji laboratorium yang digunakan untuk mengetahui sifat-sifat mekanik batuan. Sifat mekanik umumnya digunakan sebagai parameter desain utama dalam pekerjaan rekayasa.

• Kuat tekan (compressive strength)

• Kuat geser (shear strength)

• Kuat tarik (tensile strength)

• Perilaku rayapan (creep behaviour) dll.

Kekuatan Batuan

…... Hoek and Brown (1997)

Kuat Tekan (Compressive Strength)

• Bisa merupakan kuat tekan uniaksial (UCS), biaksial ataupun triaksial.

• Uji tekan uniaksial merupakan uji yang paling tua, sederhana dan praktis untuk mengetahui kuat tekan.

• Selain nilai UCS, uji tekan uniaksial juga dilakukan untuk mendapatkan nilai modulus elastisitas dan nisbah

Poisson.

A UCS  P

^max

) 50 (

) 50 ( a

E

c



 

) 50 (

) 50 ( a r



   

As the rock is gradually loaded, it passes through several stages:

Stage I

Existing cracks preferentially aligned to the applied stress will close (_cc)

Stage II

Near linear elastic stress- strain behaviour occurs Stage III

Initiating cracks propagate in the stable fashion (_ci)

Stage IV

Cracks begin to coalesce and propagate in an unstable

fashion (_cd)

Modulus Elastisitas

• Untuk kebanyakan batuan, kurva tegangan-regangan uniaksial sebelum mengalami keruntuhan umumnya mendekati bentuk linear (=E).

• E dikenal sebagai modulus elastisitas (modulus Young) yang mencerminkan kapasitas deformasi batuan atau kekakuannya (stiffness).

) 50 (

) 50 ( a

E

c



 

Nisbah Poisson

merupakan rasio antara regangan lateral (radial/tranversal) dan vertikal (aksial).

a r



   

) 50 (

) 50 ( a r



   

The uniaxial compressive test for mudstone, shandy shale and fine-grained sandstone in Eastern China’s coal

Measures (Peng and Wang 2001).

Uniaxial compressive test results in Eastern China’s coal measures (Peng and Wang, 2001).

Influence of specimen size on the strength of intact rocks (after Hoek and Brown 1980).

18 . 0 50

50



 ^c d

cd 



• Uji tekan triaksial merupakan merupakan uji yang paling penting untuk mengetahui sifat mekanik batuan.

• Tegangan utama terbesar ( 

₁

) diberikan

sepanjang aksis sampel batuan silinder dan tegangan utama terkecil ( 

₃

) diberikan oleh tekanan fluida pembatas pada permukaan sampel.

• Baik UCS dan selubung keruntuhan (failure envelope) dapat diketahui dari pengujian ini.

Kuat Tekan Triaksial

Servo-controlled triaxial compressive test apparatus of MTS Systems.

Estimate of Geological Strength Index (GSI) based on geological descriptions (after Hoek, 2007).

Kuat Tarik (Tensile Strength)

• the capacity of the rock to resist tensile stress.

• Terdapat metode pengujian langsung maupun tidak langsung untuk mengukur kuat tarik

batuan.

Uji Beban Titik (Point Load Test)

2

) 50 ( 0

22 7 . 1

 





 



 



s a

I L P

P T S

S_a : shape factor

• for diametral test S_a = 0.79

• for other test S_a = 0.79 D/L

Brazilian Test

Dt T F ^c



2

0



F_c : yield load

D : diameter sampel t : tebal sampel

Seringkali overestimate untuk batuan yang

terkonsolidasi buruk.

The comparison of the compressive and tensile strength and elastic modulus for different lithologic samples under the uniaxial compressive tests (Meng et al., 2006).

8 T

0

UCS 

Griffith (1921)

sin 0

1

) sin 1

(

4

T

UCS 





 

(McClintock and Walsh 1962)

12 T

0

UCS 

Murrell (1963)

Tipe Keruntuhan Batuan

…… dalam uji laboratorium mekanika batuan, hal yang biasanya menarik perhatian kita untuk diketahui adalah :

 Bagaimana tipe keruntuhan batuan atau karakteristik deformasi yang terbentuk

 Seberapa besar tegangan yang dapat diberikan hingga sesaat sebelum keruntuhan terjadi

Tipe Keruntuhan batuan.

Splitting Shear Failure

Multiple Shear Fractures

Tensile Failure

Tensile Failure Induced by Point

Load

The most useful description of the MECHANICAL BEHAVIOUR of intact rock is the complete stress- strain curve in compression. From this curve,

several features of interest are derived:

Deformation moduli (E, )

Brittle fracture parameters

Peak strength criteria

The post-peak behaviour

high stiffness high strength

very brittle

medium stiffness medium strength medium brittleness

low stiffness low strength

brittle

low stiffness low strength

ductile

Rock Mass QUALITY

Intact Rock

Rock Mass

.….. the scale factor of rocks and the variation in strength of material depending on the size of the sample involved.

DISCONTINUITY

Kondisi diskontinu alamiah massa batuan.

Intact Rock +

Discontinuities

=

Rock Mass

Diskontinuitas Batuan

Fault

Joints

Continuous Discontinuous

• Diartikan sebagai segala sesuatu yang membatasi sikuen kontinuitas batuan.

• Secara mekanik, diskontinuitas umumnya memiliki kuat tarik kecil atau bahkan nol (zero tensile strength)

0.01 0.1 1 10 100 1000 10,000 Length (m)

seams/shears bedding planes

fissures cracks

partings

joints

faults

Rock Defects Joints ^Weakness

Zone

.….. the main discontinuities of rock according to size.

Schematic of the primary geometrical properties of discontinuities in rock (from Hudson, 1989).

Karakterisasi Diskontinuitas Batuan

Frekuensi diskontinuitas,  = N/L m

^-1

Spasi rata-rata,  = L/N m

L = Panjang garis observasi

N = Jumlah diskontinuitas sepanjang garis observasi

Metode Scanline

Scan line sampling pada salah satu lereng batuan dan hasil pengukuran kedudukan bidang-bidang diskontinuitas utama.

• Ada berapa jenis bidang diskontinuitas?

• Bagaimana kedudukan dan penyebarannya?

• Bagaimana karakteristik fisik dan keteknikannya?

• Adakah hal-hal lain yang khas pada bidang

diskontinuitas tersebut?

Strength of rock

masses depends on intact rock material

and rock mass

discontinuities .

Kualitas Massa Batuan

• Rock Quality Designation atau RQD (Deere et al., 1967) merupakan estimasi kuantitatif kualitas massa batuan dari log inti peboran (umumnya untuk NX-size core)

• RQD dapat dikatakan sebagai modifikasi dari perolehan inti bor (core recovery)

• RQD pada dasarnya mengukur derajat

(densitas) diskontinuitas massa batuan.

RQD* = -3.68  + 110.4.

Rock Mass Classifications

• Geomechanics System - Rock Mass

Rating (RMR) by Bieniawski (1984, 1989)

• Q-System - Norwegian Geotechnical Institute (Barton et al., 1974)

• Rmi – Rock mass index (Arild Palmstrom, 1995)

• Geological Strength Index, GSI (Hoek et

al., 1995), dll.

• Bahasa komunikasi antar ahli

• Membandingkan (kondisi) massa batuan

• Klasifikasi perilaku massa batuan

• Kajian kualitas massa batuan

• Kajian kebutuhan perkuatan (ground support)

• Mendapatkan parameter desain awal

Tujuan Klasifikasi Massa Batuan

Rock Mass Rating (RMR)

• RMR based on five parameters:

– Uniaxial strength, qu

– Rock Quality Designation, RQD – Spacing of Discontinuities

– Condition of the Discontinuities – Groundwater Conditions

• RMR = R1+R2+R3+R4+R5

• Adjustment for Joint Orientation relative to construction

Rock Mass Rating (RMR)

Geomechanics Systems (CSIR) [after Bieniawski, 1984, 1989]

0 2 4 6 8 10 12 14 16

0 50 100 150 200 250 300

Unconfined Compressive Strength, qu (MPa)

RMR Rating R1

0 5 10 15 20 25

0 10 20 30 40 50 60 70 80 90 100

Rock Quality Designation, RQD

RMR Rating R2

0 5 10 15 20 25

0.01 0.1 1 10

Joint Spacing (meters)

RMR Rating R3

0 5 10 15 20 25 30 35

0 1 2 3 4 5 6

Joint Separation or Gouge Thickness (mm)

RMR Rating R4 Slightly

Rough Weathered

Slickensided Surface or Gouge-Filled

Soft Gouge-Filled

0 2 4 6 8 10 12 14 16

0 0.1 0.2 0.3 0.4 0.5 0.6

Joint Water Pressure Ratio, u/₁

RMR Rating R5

u = joint water pressure

1 = major principal stress

Al t er nat e 2 Def i ni t i ons f or P ar amet er R₅

0 2 4 6 8 10 12 14 16

1 10 100 1000

Inflow per 10-m Tunnel Length (Liters/min)

RMR Rating R5

Al t er nat e 1 Def i ni t i ons f or P ar amet er R₅ Dry

Damp

W et

Dripping

Flowing Rough/Unweathered

0 5 10 15 20 25

0.01 0.1 1 10

Joint Spacing (meters)

RMR Rating R3

0 5 10 15 20 25 30 35

0 1 2 3 4 5 6

Joint Separation or Gouge Thickness (mm)

RMR Rating R4 _Slightly

Rough Weathered

Slickensided Surface or Gouge-Filled

Soft Gouge-Filled

0 2 4 6 8 10 12 14 16

0 0.1 0.2 0.3 0.4 0.5 0.6

Joint Water Pressure Ratio, u/₁

RMR Rating R5

u = joint water pressure

1 = major principal stress

Al t er nat e 2 Def i ni t i ons f or P ar amet er R₅

0 2 4 6 8 10 12 14 16

1 10 100 1000

Inflow per 10-m Tunnel Length (Liters/min)

RMR Rating R5

Al t er nat e 1 Def i ni t i ons f or P ar amet er R₅ Dry

Damp

W et

Dripping

Flowing

ROCK MASS RATING (RMR) also CSIR System 5

Geomechanics System - ( Bieniawski, 1984, 1989) RMR =  R_i

Geomechanics Classification for Rock Masses i = 1

CLASS DESCRIPTION RANGE of RMR

I Very Good Rock 81 to 100 NOTE: Rock Mass Rating is obtained by summing the five index II Good Rock 61 to 80 parameters to obtain an overal rating RMR. Adjustments for dip III Fair Rock 41 to 60 and orientation of discontinuities being favorable or unfavorable IV Poor Rock 21 to 40 for specific cases of tunnels, slopes, & foundations can also be

V Very Poor Rock 0 to 20 considered.

0 2 4 6 8 10 12 14 16

0 50 100 150 200 250 300

Unconfined Compressive Strength, qu (MPa)

RMR Rating R1

0 5 10 15 20 25

0 10 20 30 40 50 60 70 80 90 100

Rock Quality Designation, RQD

RMR Rating R2

NGI- Q Rating of Rock Masses

• Q-Rating based on 6 parameters:

– Rock Quality Designation, RQD (100 – 10) – Number of Joint Sets, J

_n

(1 – 20)

– Roughness of Discontinuities, J

_r

(4 – 1) – Discontinuity Condition/Filling, J

_a

(1 – 20) – Groundwater Conditions, J

_w

(1 – 0.1)

– Stress Reduction Factor, SRF (1 – 20)

• Rating of Rock Formation :

– (RQD/J_n) = crude measure of block size – (J_r/J_a) = roughness/friction of surfaces

– (J_w/SRF) = ratio of two stress parameters (active stress)

 

 



 



 



 



 



 

SRF J

J J J

Q RQD ^w

a

r

n

NGI Q-System Rating for Rock Masses

( Bar ton, Lien, & Lunde, 1974)

Nor wegian Classif ication f or Rock Masses Q - Value Quality of Rock Mass

< 0.01 Exceptionally Poor 4. Discontinuity Condition & Infilling = Ja

0.01 to 0.1 Extremely Poor 4.1 Unfilled Cases

0.1 to 1 Very Poor Healed 0.75

1 to 4 Poor Stained, no alter ation 1

4 to 10 Fair Silty or Sandy Coating 3

10 to 40 Good Clay coating 4

40 to 100 Very Good 4.2 Filled Discontinuities

100 to 400 Extremely Good Sand or cr ushed r ock inf ill 4

< 400 Exceptionally Good Stif f clay inf illing < 5 mm 6

Sof t clay inf ill < 5 mm thick 8

PARAMETERS FOR THE Q-Rating of Rock Masses Swelling clay < 5 mm 12

Stif f clay inf ill > 5 mm thick 10 1. RQD = Rock Quality Designation = sum of cored pieces Sof t clay inf ill > 5 mm thick 15 > 100 mm long, divided by total core run length Swelling clay > 5 mm 20 2. Number of Sets of Discontinuities (joint sets) = J_n 5. Water Conditions

Massive 0.5 Dr y 1

One set 2 Medium W ater Inf low 0.66

T wo sets 4 Lar ge inf low in unf illed j oints 0.5

T hr ee sets 9 Lar ge inf low with f illed j oints

Four or mor e sets 15 that wash out 0.33

Cr ushed r ock 20 High tr ansient f low 0.2 to 0.1

High continuous f low 0.1 to 0.05 3. Roughness of Discontinuities* = J_r

Noncontinuous j oints 4 6. Stress Reduction Factor** = SRF

Rough, wavy 3 Loose r ock with clay inf ill 10

Smooth, wavy 2 Loose r ock with open j oints 5

Rough, planar 1.5 Shallow r ock with clay inf ill 2.5

Smooth, planar 1 Rock with unf illed j oints 1

Slick and planar 0.5

Filled discontinuities 1 **Note: Additional SRF values given

*Note: add +1 if mean joint spacing > 3 m for rocks prone to bursting, squeezing and swelling by Barton et al. (1974)



 







 







 



 

SRF J J

J J

Q RQD ^w

a r n

Joint Sets

10cm 5

0

1 2 4

6 8 9

10 ₁₈～20

16～18 14～16 10～12 6～8 2～4 0～2

JRC

7 ^12～14

5 ₈～10

3 ^4～6

Surface of joint

• Estimasi nilai Q berdasarkan log bor

• Desain awal perkuatan berdasarkan estimasi nilai Q

• Nilai aktual Q berdasarkan pengamatan visual (selama konstruksi)

• Revisi desain perkuatan berdasarkan nilai aktual Q

Desain Perkuatan dari Nilai Q

Geological Strength Index (GSI)

• Developed by Hoek, Kaiser, & Bawden (1995), Hoek & Brown (1997).

• GSI from Geomechanics system where RMR

> 25:

• GSI from Q-system:

• Chart approach based on structure and surface quality

44 log

9  



 



 



 







 



 

a r

n J

J J

GSI RQD

  





 ⁴

1

10

i Ri

GSI

GSI

Evaluation from Chart

(Hoek, 2000)

Illustrative cases for defining rock shear strength for cut slope.

itas Diskontinu

Jumlah Batuan 1

Lereng

Stabilitas 

Potensi keruntuhan lereng batuan sangat

dipengaruhi oleh keberadaan diskontinuitas :

Tim KBK Geoteknik Prodi Teknik Sipil UNS

92