mektan-i-4 soil classification - exercise
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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 tanah
kerikil (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 soil
Example :
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 if
possible
4. Symbol “F” could be used when clay (C) or silt (M) is not an
important consideration.
5. The presence of COBBLES (Cb) & BOULDERS (B) presented
using “+”
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 and
GRAVEL 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 - a
A - 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 - 6
Highly organic soil (peat) visual identification
A - 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 PGI
PI 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 subgrade
material 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
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