PAKSITYA PURNAMA PUTRA, S.T., M.T. Jurusan Teknik Sipil Universitas Jember MEKANIKA TANAH

MEKANIKA TANAH

PAKSITYA PURNAMA PUTRA, S.T., M.T.

KLASIFIKASI TANAH

BAGAN ALIR BAHASAN

PEM AM PATAN TANAH (9) PEM ADATAN (4) DISTRIBUSI TEGANGAN (8) TEGANGAN EFEKTIF (7) KLASIFIKASI TANAH (3)

REM BESAN AIR DALAM TANAH (5) GAYA ANGKAT DIBAW AH BANGUNAN AIR (6) KOM POSISI TANAH (2) TANAH (1) DAYA DUKUNG TANAH PERENCANAAN BANGUNAN TANAH STABILITAS DAN KEKUATAN TANAH PERENCANAAN PONDASI

1.

ANALISIS B UTIRAN

Gravel Sand Silt Clay

C M F C M F C M F C M F

Karakt erist ik t anah berdasar but iran

Kerikil dan pasir

Lanau

lempung

Ukuran butiran

-Berbutir kasar

(coarse grain)

-Dapat dilihat

secara kasat mata

-Berbutir halus

(fine)

-Tidak dapat dilihat

dengan mata

telanjang

-Berbutir halus

-Tidak dapat dilihat

dengan mata

telanjang

Karakteristik

Non plastis

Granular

Non plastis

Granular

plastis

Efek air terhadap

perilaku teknis

Tidak begitu

penting, keculai

untuk pasir lepas

dan beban dinamis

Penting

Sangat penting

Efek ukuran

butiran terhadap

perilaku teknis

Analisis

saringan =>

particle size > 7 µm

Analisis

saringan =>

particle size > 7 µm

▷

Bergradasi BAIK (well graded)

▷

_{Bergradasi SERAGAM (uniform graded)}

▷

Bergradasi jelek/ gap (gap graded)

▷

Bergradasi baik dengan mengandung but iran halus (fines)

▷

Bergradasi baik dengan jumlah but iran halus banyak

COARSE _{MEDIUM FINE}

S I L T

C L A Y

G R A V E L

UKURAN BUTIR, mm

F I N E S

S A N D

4. 76 2 0. 85 0. 425 0. 149 0. 075 0. 005 19. 05 # 20 # 40 _{# 100 # 200} # 4 _{# 10} 19. 05 0 10 20 30 40 50 60 70 80 90 100 0.001 0.01 0.1 1 10 100 PER SEN L OL OS (%)

A

- a poorly-graded medium SAND (probably estuarine or flood-plain

alluvium)

B - a well-graded GRAV EL-SAND (i.e. equal amounts of gravel and sand)

C - a gap-graded COBBLES-SAND

D - a sandy SILT (perhaps a deltaic or estuarine silt)

E - a typical silty CLAY (e.g. London clay, Oxford clay)

Ukuran

butiran

0.0001 0.001 0.01 0.1 1 10 100 0 20 40 60 80 100

Particle size (mm)

%

F

ine

r

Ukuran efektif D₁₀ = 0.06 mm _D 30= 0.25 mm D60= 0.7 mm 10 60

D

D

C

_u

=

( )

( )( )

₁₀

₆₀

2

30

D

D

D

C

_c

=

Koefisien keseragaman Koefisien kelengkungan

Grain size distribution

100

%

=

×

w

w

tertahan

i

∑

−

=

tertahan

halus

butiran

100

%

%

Distribusi

butiran

 Deskripsi butiran:

 D10 = 0.06 mm

Effect ive size

 D30= 0.25 mm

 D60= 0.7 mm

 Coef of Uniformity

 Coef of curvature

67

.

11

06

.

0

7

.

0

10 60

=

=

=

D

D

C

_u

)

sands

for

(

6

C

and

3

C

1

)

gravels

for

(

4

C

and

3

C

1

soil

graded

Well

u c u c

≥

<

<

≥

<

<

−

( )

( )( )

(

0

(

.

06

)( )

0

)

.

7

1

.

5

25

.

0

2

60

10

2

30

=

=

=

D

D

D

C

_c

Criteria:

 Ukuran

butiran < 7 µm



Analysis berdasarkan hukum Stoke’s



K ecepatan kecepatan sebandingkan dengan

diameter

 50 gram butiran halus kering dan dicampur air menjadi

adonan



Letakkan adonan pada gelas ukur 1 liter dan tambahkan

air distilasi sampai 1 liter, beri tanda dan

guncang

gelasnya



Letakkan hidrometer dan hitung waktunya



D = diameter; t

_d

= time ;

µ = viscosity of water (10.09

milipoises at 20

o

_C

Analisis hidrometer

(

G

_s

)

_w

t

_d

z

D

γ

µ

1

18

−

=

Tanah

berbutir halus

Terbagi at as 4 kondisi:



Solid (padat)



Semisolid



Plastis



Cair

Tanah

berbutir halus

Misalkan kadar airnya sangat besar



tanah bersifat

cair (liquid

) (bisa

mengalir)

Air berkurang

kadar air turun

Tanah

berbutir halus

Jika air berkurang

 menjadi lebih liat dan

tidak bisa mengalir lagi batas cair LL

Tanah bisa dibentuk tanpa ada retakan yang

terlihat kondisi

plast is

Air berkurang

kadar air turun

Tanah

berbutir halus

Jika air berkurangretakan mulai terlihat,

tetapi tanah masih bisa dibentuk bersifat

semisolid

 batas plastis PL

Range ketika tanah bersifat plastis:

indeks

plast isit as

PI

Tanah

berbutir halus

Jika air semakin berkurang



tanah

menjadi keras, volume tidak bisa

berubah lagibersifat

solid

 batas

susut SL

Berguna untuk mengetahui kembang

susut tanah

Tanah

berbutir halus

Perubahan kondisi t anah berbut ir halus hanya

karena perubahan

kadar air

kekuatan dan deformasi tanah bisa

diasosiasikan dengan set iap kondisi.

Tanah

berbutir halus

CAIR

▷

_{Kondisi t erlemah}

▷

_{Deformasi t erbesar}

Padat (solid)

▷

_Terkuat

▷

_{Deformasi kecil}

Indeks likuiditas

LI = (w – PL)/PI

Tanah

berbutir halus

Indeks

plastisitas

PI

=

LL

−

PL

PI

PL

w

LI

=

−

Indeks likuiditas

%

lempung

fraksi

PI

A

=

Aktifitas

Batas

cair LL (Fall cone)

2.

SISTEM KLASIFIKASI

TANAH

Kenapa

?

Tanah berbeda dengan mat erial, dimana

manusia t idak bisa mengont rol sifat -sifat

dari t anah

Kenapa

?

Klasifikasi akan memberikan pedoman umum bagi

prakt isi geot eknik mengenai sifat -sifat t anah

Indeks

sederhana

GSD, LL, PI

Sistem

klasifikasi

(Bahasa)

Estimasi sifat

teknis

Memperoleh

tujuan teknis

Berdasarkan

pengalaman

Communicate

between

engineers

Sistem

klasifikasi

 Geologic Soil Classification System

 Agronomic Soil Classification System

 Textural Soil Classification System (USDA)



American Associat ion of St at e Highway

Transport at ion Officials Syst em (AASHTO)



Unified Soil Classificat ion Syst em (USCS)



American Society for Testing and Materials

System (ASTM)

Sistem

klasifikasi

 Sistem klasifikasi biasanya berdasarkan

ukuran but iran

 Sifat teknis tanah dapat ditentukan

berdasarkan ukuran but iran

Kerikil Pasir Lanau Lempung

C M F C M F C M F C M F

60 20 6 2 0.6 0.2 0.06 0.02 .006 .002 .0006 .0002 mm

Ukuran

butiran

Boulders Cobbles

Gravel

Sand

Silt and

Clay

Coarse Fine Coarse Medium Fine

300 mm 75 mm 19 mm No.4 4.75 mm No.10 2.0 mm No.40 0.425 mm No.200 0.075 mm (75 µm)

Symbols



Soil symbols:



G: Gravel



S: Sand



M: Silt



C: Clay



O: Organic



Pt: Peat



Liquid limit

symbols:



H: High LL (LL>50)



L: Low LL (LL<50)



Gradation symbols:



W: Well-graded



P: Poorly-graded

Example: SW, Well-graded sand

SC, Clayey sand

SM, Silty sand,

MH, Elastic silt

₍

_for

_sands

₎

6

C

and

3

C

1

)

gravels

for

(

4

C

and

3

C

1

soil

graded

Well

u c u c

≥

<

<

≥

<

<

−

Tanah berbutir kasar:

Kerikil Pasir

Tanah berbutir halus:

Lanau Lempung

NO.200

0.075 mm

•Distribusi butiran

•C

_u

•C

_c

•PL, LL

•Plasticity chart

50 %

NO. 4

4.75 mm

Uji yg dibutuhkan:

Analisis saringan

Atterberg limit

LL>50

LL <50

50%

Unified Soil Classification System

(USCS)

Tanah diberi 2 huruf klasifikasi (e.g. SW). Dengan

prosedur sbb:.

Berbut ir kasar(>50% lebih besar dari 75 µm)

Prefix S if > 50% of coarse is Sand

Prefix G if > 50% of coarse is Gravel

Suffix depends on %fines

if %fines < 5% suffix is either W or P

if %fines > 12% suffix is either M or C

Bagan

Alir Unified Soil Classification

System (USCS)

Run sieve analysis

< 50% pass #200

passing #4 = A% Gravel fraction = 100 – A = B%

B > D ► Gravel

passing # 200 = C % Sand fraction = A - C = D%

B < D ► Sand

> 50% pass #200

Use plasticity chart

(Fig. 3.8)

USCS

Untuk Gravel

G

> 12 %

pass #200

GC

GM

GC-GM

Use gradation

curve and plasticity

chart to designate

(Gb.3.8)

<5% pass

#200

G W

G P

Use gradation

curve to

designate

5-12% pass

#200

GW-GC

GW-GM

GP-GC

GP-GM

Use gradation

curve to

designate

USCS

Untuk Gravel

Cu> 4 and 1 < Cc < 3 GW Well graded gravel

C_u< 4 and 1 >C_c > 3 GP Poorly graded gravel Cu> 4 and 1 < Cc < 3 and fines

classify as CL or CH GW - GC

Well graded gravel with clay

Cu> 4 and 1 < Cc < 3 and fines

classify as ML or MH GW - GM

Well graded gravel with silt

C_u< 4 and 1 >C_c > 3 and fines

classify as CL or CH GP - GC

Poorly graded gravel with clay

Cu< 4 and 1 >Cc > 3 and fines

classify as ML or MH GP - GM

Poorly graded gravel with silt

Fines classify as CL or CH ( LL

and PL above A-line) GC Clayey gravel Fines classify as ML or MH ( LL

and PL below A-line) GM Silty gravel Fines classify as CL - ML ( LL

and PL in shaded area) GC - GM Silty, clayey gravel Run sieve analyasis and if less than 50% passed the #200 sieve, then the soil is coarse. If more than 50% of the coarse material is retained on the #4 sieve, then the soil is gravel.

% passing

#200 sieve Unified Soil Classification Criteria Group Symbol Group Name Less than 5% Between 5 % & 12% More than 12%

USCS

Untuk Sand

> 12 %

pass #200

SC

SM

SC-SM

Use gradation

curve and

plasticity chart

to designate

<5% pass

#200

SW

SP

Use

gradation

curve to

designate

5-12%

pass #200

SW-SC

SW-SM

SP-SC

SP-SM

Use

gradation

curve to

designate

S

USCS

Untuk Sand

Cu> 6 and 1 < Cc < 3 SW Well graded sand

Cu< 6 and 1 >Cc > 3 SP Poorly graded sand

Cu> 6 and 1 < Cc < 3 and fines

classify as CL or CH SW - SC

Well graded sand with clay

Cu> 6 and 1 < Cc < 3 and fines

classify as ML or MH SW - SM

Well graded sand with silt

Cu< 6 and 1 >Cc > 3 and fines

classify as CL or CH SP - SC

Poorly graded sand with clay

Cu< 6 and 1 >Cc > 3 and fines

classify as ML or MH SP - SM

Poorly graded sand with silt

Fines classify as CL or CH ( LL

and PL above A-line) SC Clayey sand Fines classify as ML or MH ( LL

and PL below A-line) SM Silty sand Fines classify as CL - ML ( LL

and PL in shaded area) SC - SM Silty, clayey sand Group Symbol Group Name Less than 5% Between 5 % & 12% More than 12%

Run sieve analyasis and if less than 50% passed the #200 sieve, then the soil is

coarse. If less than 50% of the coarse material is retained on the #4 sieve, then the soil is sand

% passing

USCS

Untuk Lanau, Lempung, Organik

Silt,

organic, or

clay

LL < 50% LLR>0.75 LL and PI plot below A-line LL and PI plot in shaded area LL and PI plot above A-line ML CL-ML CL LLR<0.75 OL LL > 50% LLR<0.75 OH LLR>0.75 LL and PI plot below A-line LL and PI plot above A-line MH CH

USCS

Untuk Lanau, Lempung, Organik

SILT OR CLAY

LLR < 0.75 OL Organic silt or clay LLR > 0.75 and PI < 4 or plots

below A-line in Fig. ML Inorganic silt LLR > 0.75 and PI > 7 or plots

above A-line in Fig. CL Lean clay LLR > 0.75 and PI > 7 and LL and

PI in shaded area of Fig. CL-ML Silty clay

LLR < 0.75 OH Organic silt or clay LLR > 0.75 and PI plots below

A-line in Fig. MH Elastic silt LLR > 0.75 and PI plots on or

above A-line in Fig. CH Fat clay More than

50%

Run sieve analyasis and if less than 50% passed the #200 sieve, then the soil is fine.Run liquid limit and plastic limit tests on materials passing #40 sieve. Note that ASTM requires that the liquid limit be determined using oven dried and undried samples . The ratio of the dried to the undried value is called the liquid limit ratio LLR.

Less than 50%

Classification Procedure

Coarse-grained

material

Grain size

distribution

Fine-grained

material

LL, PI

(Santamarina et al., 2001) Highly

Example

Passing No.200 sieve 30 %

Passing No.4 sieve 70 %

LL= 33

PI= 12

PI= 0.73(LL-20), A-line

PI=0.73(33-20)=9.49

SC

(≥15% gravel)

Clayey sand with

gravel

(Santamarina et al., 2001)

Passing No.200 sieve 30 %

Passing No.4 sieve 70 %

LL= 33

PI= 12

Example

• %fines (% finer than 75 µm) = 11% - Dual symbols required

• D

₁₀

= 0.06 mm, D

₃₀

= 0.25 mm, D

₆₀

= 0.75 mm

0.0001 0.001 0.01 0.1 1 10 100 0 20 40 60 80 100

Particle size (mm)

%

F

ine

r

Example

0.0001 0.001 0.01 0.1 1 10 100 0 20 40 60 80 100

Particle size (mm)

%

F

ine

r

Particle size fractions: Gravel

17%

Sand

73%

Silt and Clay 10%

Example

▷Of the coarse fraction about 80% is sand, hence

Prefix is S

▷

Cu = 12.5, Cc = 1.38

▷

Suffix1 = W

▷From Atterberg Tests

▷

LL = 32, PL = 26

▷

Ip = 32 - 26 = 6

▷

From Plast icit y Chart point lies below A-line

▷

Suffix2 = M

▷Dual Symbols are SW-SM

▷To complete the classification the Symbols should be

accompanied by a descript ion

American Association of State Highway

and Transportation Officials system

American Association of State Highway

and Transportation Officials system

(AASHTO)

<50% Pass #40 >51% Pass #40 <10% pass #200 A-3 <15% pass #200 <30% pass # 40 <50% pass #10 PI is less than 6 <25% pass #200 <50% pass # 40 PI is less than 6 A-1-a A-1-b <25% #200 Run LL and PL on material passing # 40 Run LL and PL on material passing # 40 ≤ 35% pass #200 PI<10 PI>11 A-2-4 LL<40 LL>41 A-2-5 LL<40 A-2-6 LL>41 A-2-7 Run sieve analysis ≤ 35% pass #200 implies granular > 36% pass #200 implies silt-clay PI>11 PI<10 LL<40 A-4 LL>41 A-5 LL<40 A-6 LL>41 PI ≤ LL-30 or PL ≥ 30 A-7-5 PI > LL-30 or PL < 30 A-7-6 Run LL and PL on material passing # 40

Pedoman

Umum

8 grup ut ama: A1~ A7 (dg beberapa sub-grup) dan

t anah organik

A8

Pengujian yang dibutuhkan: analisis saringan dan batas Atterberg.

DiThe group index, an empirical formula, is used to further

evaluate soils within a group (subgroups).

The original purpose of this classification system is used for road

construction (subgrade rating).

A4 ~ A7

A1 ~ A3

Granular Materials

≤ 35% pass No. 200 sieve

Silt-clay Materials

≥ 36% pass No. 200 sieve

Using LL and PI separates silty materials

from clayey materials

Using LL and PI separates silty materials

from clayey materials (only for A2 group)

Group Index

[

]

)

10

PI

)(

15

F

(

01

.

0

)

40

LL

(

005

.

0

2

.

0

)

35

F

(

GI

200 200

−

−

+

−

+

−

=

)

10

PI

)(

15

F

(

01

.

0

GI

=

₂₀₀

−

−

For Group A-2-6 and A-2-7

The first term is determined by the LL

The second term is determined by the PI

Mutu subgrade berbanding terbalik dengan nilai, GI.

use the second term only

F200: percentage passing through the No.200 sieve

Klasifikasi

Example

Passing No.200 86%

LL=70, PI=32

LL-30=40 > PI=32

[

]

33

47

.

33

)

10

PI

)(

15

F

(

01

.

0

)

40

LL

(

005

.

0

2

.

0

)

35

F

(

GI

200 200

≅

=

−

−

+

−

+

−

=

Round off

A-7-5(33)

Passing No.200 86%

LL=70, PI=32

▷Langkah

1:

Tentukan prosentase lolos saringan no 200

Tanah A: 59 + 29 = 88%  berbutir halus

Tanah B: 20%  berbutir kasar

▷Langkah

2:

Buat tabel di atas

Hitung GI tanah A

Tanah B: non plastis, GI = 0

Cont oh

200 200

(

35)[0.2 0.005(

40)] 0.1(

15)(

10)

5.4

▷Langkah 3:

▷Langkah

3: