Diskripsi Singkat (GBPP)

Mata kuliah ini membahas tentang:

1. Pengenalan umum (permasalahan dan aplikasi mekanika

tanah),

2. Tanah dan proses pembentukannya,

3. Sifat indeks (kadar air, berat jenis, berat satuan, angka pori,

derajat kejenuhan, analisis ukuran butir, batas Atterberg)

4. Klasifikasi tanah (BS, ASTM, AASHTO),

5. Pemadatan (laboratorium & lapangan, kontrol kepadatan),

6. Tegangan dalam tanah,

7. Rembesan (permeabilitas, uji permeabilitas laboratorium &

lapangan; tanah berlapis/anisotropis, flownet, tekanan

rembesan, rembesan pada bendungan tanah, filter),

8. Pengenalan kuat geser tanah.

Contoh soal

1. Butiran tanah tinggal dalam saringan no. 4 = 91% atau lolos

saringan no. 4 = 9% dan hanya 4% lolos saringan no. 200.

Koefisien keseragaman Cu = 8, koefisien gradasi Cc = 4 dan

indeks plastisitas PI = 3 %

- Tanah yang tinggal dalam saringan no. 4 = 91 %, maka tanahkerikil (G).

- Karena lolos saringan no. 200 = 4%, maka harus diperiksa

gradasinya. Diketahui Cu = 8 > 4 dan Cc = 4 > 3, maka tanah

bergradasi buruk (P)

- Tanah termasuk klasifikasi GP

Contoh soal

2. Butiran lolos saringan no. 200 (0,075 mm) = 65%; batas cair LL

= 40%, dan batas plastis = 22%.

- Tanah lolos saringan no. 200 = 65% > 50%, maka termasuk

berbutir halus.

- LL = 40% < 50%, maka harus diperiksa PI-nya

- PI = LL PL = 40% - 22% = 18% > 7%,

- Menurut grafik plastisitas tanah adalah CL.

Contoh soal

3. Butir tanah lolos saringan no. 200 = 51%, batas cair LL = 53%,

batas plastis PL = 40%, tanah anorganik

Contoh soal

4. Hasil uji lab : LL = 41% dan PL = 14%. Hasil analisis saringan:

Klasifikasikan tanah menurut: USCS

No. Saringan % butiran lolos

4 100

10 92,9

40 79,4

200 59,1

Example :

Soil A : Cu = 34, Cc = 1.6, fines 0 % , gravel : sand = 76 : 24

Soil B : Cu = 800, Cc = 0.25, fines 34 % , gravel : sand = 41 : 25,

LL = 26 %, PI = 9 %

Soil C : fines 95 % , LL = 42 %, PL = 24 %, PI = 18 %

Soil D : Cu = 1.8, Cc = 0.95, fines 8 % , gravel : sand = 4 : 96

LL = 25 %, PL = 19 %,

Soil E : fines 75 % , LL = 40 %, PL = 20 %, gravel : sand = 35 : 65

Find classification of these soils (USCS)

Cu = D60/D10

Cc = D302/(D10*D60)

Soil Classification (Bristish Standard)

Klasifikasi : pengelompokan tanah berdasar karakteristik material

(gradasi butir dan plastisitas), tidak tergantung kondisi lapangan

Kelompok tanah group symbols :Huruf pokok

Huruf diskripsi/kualifikasi

Huruf pokok :

G = gravel, S = sand,

M = silt, C = clay atau F = fine-soil (fines)

Pt = peat (humus/gambut)

Huruf diskripsi/kualifikasiW = well graded

P = poorly graded :

Pu = uniform graded

Pg = gap graded

L = low plasticity

I = intermediate plasticity

H = high plasticity

V = very high plasticity

E = extremely high

plasticity range

O = organic

Soil A : Cu = 34, CZ = 1.6, fines 0 % , gravel : sand = 76 : 24

Coarse fraction = 100 % GRAVEL / SAND

Gravel : sand = 76 : 24 GRAVEL (G)

Cu = 34 > (4 - 6) well graded (W)

CZ = 1.6 (1 - 3)

Soil A : GW = well graded sandy GRAVEL

Soil B : Cu = 1.8, CZ = 0.95, fines 3 % , gravel : sand = 4 : 96

Fines = 3 % coarse grained soil

Gravel : Sand = 4 : 96 SAND (S)

Cu = 1.8 < (4 - 6)

CZ = 0.95 ( 1 - 3)

Soil B : SPu uniform slightly silty SAND

poorly graded

Cu = 1.8 uniform

Soil C : Cu = 800, CZ = 0.25, fines 34 % , gravel : sand = 41 : 25,

LL = 26 %, PI = 9 %

Fines = 34 % coarse grained soil

Gravel : Sand = 41 : 25 GRAVEL (G)

Fines = 34 % (15 - 35 %) very silty/clayey use plasticity chart :

LL = 26 % above-A line C

PI = 9 % LL < 35 % L

Soil C : GCL = very clayey GRAVEL (clay of low plasticity)

Soil D : fines 95 % , LL = 42 %, PL = 24 %, PI = 18

Fines 95 % SILT/CLAY

Use Plasticity chart

LL = 42 % & PI = 18 % above-A line C

LL = 42 % (35 - 50 %) I

Soil D CI : CLAY of intermediate plasticity

Note :

1. If detail is not required liquid limit in plasticity chart 2 parts L or U (I, H,V, E) U = The upper plasticity range

2. First letter dominant soil fraction name of soilExample :

SW = well graded SAND

SCL= very clayey SAND of low plasticity

CIS = intermediate plasticity sandy CLAY

MHSO = sandy organic SILT of high plasticity

3. Classification (symbol) suggested sub-group symbol ifpossible

4. Symbol F could be used when clay (C) or silt (M) is not animportant consideration.

5. The presence of COBBLES (Cb) & BOULDERS (B) presentedusing +GW + Cb : well graded GRAVEL with COBBLES

B + CL : BOULDERS with low plasticity CLAY

SOIL DESCRIPTION

detail materials & characteristics of soil mass

Example of soil description at field :

Dense, reddish-brown, subangular, well graded, gravelly SAND

Dense, brown, heterogeneous, well graded, very silty SAND andGRAVEL with some COBBLES.

Stiff, brown, closely fissured CLAY of high plasticity London clay.

Spongy, dark brown, fibrous PEAT

AASHTO Designation : M - 145 (1982)

Coarse grained soil > 0.075 mm

Fine grained soil < 0.075 mm.

Granular soils : fine fraction < 35 %

Silt - Clay materials : fine fraction > 35 %

Soil classified into groups and sub-groups

Granular materials :

A 1 A - 1 - aA - 1 - b

A - 3

A - 2 A - 2 - 4, A - 2 - 5, A - 2 - 6, A - 2 7

Silt - Clay material :

A - 4, A - 5, A - 6

A - 7 A - 7 - 5, A - 7 - 6Highly organic soil (peat) visual identificationA - 8 not suitable for embankment/subgrade

The AASHTO Soil Classification System was developed by the American Association of State Highway and

Transportation Officials,

It is used as a guide for the classification of soils and soil-aggregate mixtures for highway construction purposes.

The classification system was first developed in 1929, but has been revised several times

AASHTO Soil Classification System

summation

GROUP INDEX

Group-index = (F - 35) 0.2 + 0.005 (LL-40)+0.01(F-15)(PI-10)

F = % fine fraction (percentage of material < 0.075 mm)

LL = liquid limit

PI = plasticity index

For negative group index reported as nil

Dinyatakan dalam angka bulat terendah

using group index chart :

Fine fraction LL PGIPI PGI

For group index from A - 2 - 6 & A - 2 - 7 use PI only.

Example

Group-index = (F - 35) 0.2 + 0.005 (LL-40)+0.01(F-15)(PI-10)

F = % fine fraction (percentage of material < 0.075 mm)

LL = liquid limit

PI = plasticity index

a) Soil A - 6 , F = 55 % , LL 40 % , PI = 25 %

Group index = (55 - 35) [0.2 + 0.005(40 - 40)] + 0.01

(55 - 15) (25 - 10) = 4.0 + 6.0 = 10

b) Soil A - 2 - 7, F = 30 %, LL = 50, PI = 30

Group index = 0.01 (30 - 15) (30 - 10 ) = 3

Application of group index :

1. For evaluation in groups clayey granular material & silt-clay material

a) Group A - 1 - a, A - 1 - b, A - 2 - 4, A - 2 - 5 & A - 3 satisfied for subgrade

when good drainage and good compaction.

b) A - 2 - 6 & A - 2 - 7 (clayey granular) and silt clay (A - 4, A - 5, A - 6, & A -

7) require subbase layer or increasing base course thickness.

c) Dianggap % F minimum kritis 35 %, dengan mengabaikan plastisitas

15 % affected by PI > 10

d) LL 40 % critical

e) PI 10 % critical

f) non-plastic soils group index 0

2. No upper limit of group index, evaluation : F, LL & PI

3. With good drainage and good compaction supporting value for a subgradematerial dianggap berbanding terbalik terhadap group index. group index = 0 good subgrade material group index = 2 bad

Contoh soal

5. Hasil uji lab : LL = 41% dan PL = 14%. Hasil analisis saringan:

Klasifikasikan tanah menurut: AASHTO

- Dari Tabel, karena butiran lolos saringan no. 200 = 59,1% > 35%,

maka tanah termasuk lanau atau lempung

- LL = 41% A-5 atau A-7.- PI = 27% dan PL = 14% A-7-6- GI = 12,44

- Jadi tanah termasuk klasifikasi A-7-6(12)

No. Saringan % butiran lolos

4 100

10 92,9

40 79,4

200 59,1