TERMINOLOGI SOIL PROPERTIES

� BONGKAHAN TANAH BIASANYA TERDIRI DARI BAGIAN BUTIRAN PADAT, AIR DAN UDARA

PADAT AIR UDARA

Vs

Vw

Va

MATERIAL VOLUME MASSA BERAT

UDARA Va 0 0

AIR Vw Mw Ww

BUTIR Vs Ms Ws

Unit

� PANJANG (L) meter

� MASSA (M) ton(1 ton= 103 kg)

� DENSITY (ρ) t/m3

� BERAT (W) kilonewtons (kN)

� TEGANGAN (σ) kilopascals (kPa) 1 kPa= 1 kN/m2� TEGANGAN (σ) kilopascals (kPa) 1 kPa= 1 kN/m2

� Unit weight (γ) kN/m3

� Accuracy Density of water, ρw = 1 t/m3

Stress/Strength to 0.1 kPa

BERAT DAN BERAT VOLUME

� W = M g

� Berat Volume γ =W

V

γ =M g

V

γ = ρ gV

σvz σv = ρ g z

σv = γ z

Specific Gravity

w....

ρρ==

AirDensity

MaterialDensityG

w....

....

γγ==

AirWeightUnit

MaterialWeightUnitG

G ( Specific Gravity) adalah :

� Gs ≅ Umumnya berkisar 2.65

ws

s

s

s

ws

s

s

ss G

WW

G

MMV

γγρρ====

Voids ratio

� Voids Ratio

� Porosity

Jika digabungkan : Vs = V - Vv = (1 - n) V

eV

Vv

s

=

nV

Vv=

Jika digabungkan : Vs = V - Vv = (1 - n) V

Jadie

V

V

V

n V

n

nv

s

v= =−

=−( )1 1

DERAJAD KEJENUHAN (Degree of Saturation)

Untuk perhitungan, disubstitusikan nilai e, S and Vs

� Vw = e S Vs Va = Vv - Vw = e Vs (1 - S)

Dengan mengambil Vs = 1 m3, nilai parameter tanah yang lain dapat dilihat pada tabel berikut ;

SV Vw w= =S

V V Va w v

=+

=

Volume Masa Berat

Udara e (1 - S) 0 0

Air e S e S ρw e S γw

Butir 1 Gs ρw Gs γw

Unit Weights

� Bulk unit weight

� Saturated unit weight (S = 1)

γγ γ γ

bulkw s s w s

s s

w sW

V

G V eSV

V eV

G eS

e= =

++

=+

+( )

1

γγ

satw sG e

e=

++

( )

1

� Dry unit weight (S = 0)

� Submerged unit weight

γγ

d r yw sG

e=

+1

γ γ γ' = −sat w

Moisture Content

� The moisture content, m, is defined as

In terms of e, S, Gs and γw

mWeight of Water

Weight of Solids

W

Ww

s

= =

Ww = γw Vw = γw e S Vs

Ws = γs Vs = γw Gs Vs

hencem

e S

G s

=

CONTOH 1

Komponen Trimmings Mass

(g)

Sample Mass, M

(g)

Sample Weight, Mg

(kN)

Total 55 290 2845 × 10-6

Butiran 45 237.3 2327.9 × 10-6

Air 10 52.7 517 × 10-6

• Berat dan Massa contoh tanah

• Distribution by volume (assume Gs = 2.65)

Total Volume V = π r2 l

Water Volume

Solids Volume

Air Volume Va = V - Vs - Vw

VW

ww

w

=γ

VW

Gss

w s

=γ

Moisture content

Voids ratio

Degree of Saturation

Bulk unit weight

mW

Ww

s

= = = =10

450 222 22 2. . %

eV

V

V V

Vv

s

a w

s

= = + = 0 755.

SV

V

V

V Vw

v

w

a w

= =+

= =0 780 78 0. . %

γ bulk

W

VkN m= = 181 3. /

γ W= =Dry unit weight

Saturated unit weight

Note that γdry < γbulk < γsat

γ drysW

VkN m= = 148 3. /

γ sat

W

VkN m= + × × =

−( . . ). /

14 9 10 98119 04

63

Example 2Volume and weight distributions

Phase Volume

(m3)

Dry Weight

(kN)

Saturated Weight

(kN)

Voids 0.7 0 0.7 × 9.81 = 6.87

Solids 1.0 2.65 × 9.81 = 26.0 26.0

Dry unit weight,

Saturated unit weight

Moisture content (if saturated)

γ dry

kN

mkN m= =

260

17153

3

3.

.. /

γ sat

kN

mkN m= + =( . . )

.. /

260 687

17193

33

m = = =687

26 00264 26 4%

.

.. .

�SOAL�Berat tanah asli + cawan = 5300 gram�Volume tanah = 1,2 cm3�Setelah dikeringkan , berat tanah + cawan =

5010 gram�Berat cawan = 3000 gram

SG = 2,65�SG = 2,65�HITUNGLAH

�Berat volume tanah γ�Kadar air, angka pori, porositas, derajad

kejenuhan, dan kandungan udara

� PENYELESAIAN

� Massa tanah = 5300 – 3000 = 2300 gram

� Kerapatan ρ = M/V = 2300/1,2 = 1.917 gram/cm²

� Berat isi γ = ρ x g = 1.917 x 9,8 = 18.787 N/cm³

� Massa tanah kering = 5010 - 3000 = 2010 gram

� Massa air = 2300 – 2010 = 290 gram

� Kadar air = 290/2010 = 0,144 ~ 14,4 %

� Angka pori = e = SG ( 1 + w ) ρw/ρ – 1

� = 2,65 ( 1 + 0,144 ) x 1000/1.917 – 1

� = 0,58

� Porositas ; n = e/(1+e) = 0,58/(1+0,58 ) = 0,367

� Derajad kejenuhan ; Sr = w.SG/e = 0,144 x 2,65 / 0,58 = 0,658

� Kandungan udara = A = n ( 1-Sr ) = 0,367(1-0,658) = 12,6 %

�SOAL LATIHAN�Berat tanah asli + cawan = 6400 gram�Volume tanah = 1,75 cm3�Setelah dikeringkan , berat tanah + cawan =

6010 gram�Berat cawan = 3050 gram

SG = 2,60�SG = 2,60�HITUNGLAH

�Berat volume tanah γ�Kadar air, angka pori, porositas, derajad

kejenuhan, dan kandungan udara

� PENYELESAIAN

� Massa tanah = 6400-3050 = 3350 gram

� Kerapatan ρ = M/V = 3350/1,75 = 1.914 gram/cm²

� Berat isi γ = ρ x g = 1.914 x 9,8 = 18.757 N/cm³

� Massa tanah kering = 6010 - 3050 = 2960 gram

� Massa air = 3350-2960= 390 gram

� Kadar air = 390/2960 = 0,13 ~ 13 %

� Angka pori = e = SG ( 1 + w ) ρw/ρ – 1

� = 2,60 ( 1 + 0,13 ) x 1000/1.914– 1

� = 0,535

� Porositas ; n = e/(1+e) = 0,535/(1+0,535 ) = 0,349

� Derajad kejenuhan ; Sr = w.SG/e = 0,13 x 2,60 / 0,535 = 0,631

� Kandungan udara = A = n ( 1-Sr ) = 0,349(1-0,631) = 12,9 %