PENGERTIAN TENTANG TANAH

Transkripsi

1 KLASIFIKASI TANAH

2 PENGERTIAN TENTANG TANAH UKURAN PARTIKEL BERUKURAN BESAR : quartz, feldspar BERUKURAN SANGAT LEMBUT : clay minerals RONGGA DIANTARA PARTIKEL DIISI UDARA/AIR

3 Aragonite-rich soil x 2000

4 Cemented calcareous sand

5 KLASIFIKASI YANG DIDASARKAN TEKSTUR / UKURAN DAN PERMUKAAN BUTIRAN UKURAN PARTIKEL BIASANYA DIKAITKAN DENGAN KANDUNGAN MINERALNYA, CONTOH Ukuran partikel kecil, biasanya mengandung CLAY

6 BEBERAPA STANDART KLASIFIKASI TANAH UNITED STATE DEPARTEMENT of AGRICULTURE (USDA) AMERICAN ASOSIATION of STATE HIGWAY and TRANSPORTATION OFFICIAL ( AASHTO ) UNIFIED SOIL CLASIFICATION SYSTEM (USCS)

7 PROSEDUR ANALISA UKURAN BUTIR Analisa dengan ayakan dipakai untuk ukuran partikel > 75 µm Analisa Hydrometer dipakai untuk butiran lembut Yakni analisa yang didasarkan Hukum Stoke s, dimana kecepatan mengendap butiran dianggap proporsional terhadap diameter butiran

8 KURVA UKURAN BUTIR % Finer P a rtic le size (mm) W U P C F Well graded Uniform Poorly graded Well graded with some clay Well graded with an excess of fines

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11 CONTOH 1 TANAH A TERDIRI DARI ; PASIR ; 30 % LANAU ; 30 % LEMPUNG ; 40 % ( BUTIRAN < 0,002 mm ) Plotkan dalam grafik ; Jenis tanah LEMPUNG TANAH LIAT CONTOH 2 TANAH A TSB MENGANDUNG KERIKIL 20 % DAN PASIR 10 % Pasir Lanau Lempung MAKA HARUS DIADAKAN KOREKSI 10 x100 ; x100 ; x100 ; = = = 12,5% 37,5% 50 %

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13 GRUP INDEX GI = (F-35)[0,2+0,005(LL-40)] + 0,01(F-15)(PI-10) F = persentase butir lolos ayakan no 200 LL = batas cair ( Liquid Limit ) PI = index plastisitas

14 USDA PASIR 2 S/D 0,05 mm LANAU 0,05 S/D 0,002 mm LEMPUNG < 0,002 mm

15 CONTOH USDA HANYA MENGKLASIFIKASI BUTIR LOLOS NO 10 JIKA ADA KANDUNGAN LEBIH BESAR, DIKOREKSI Tanah B dengan komposisi sbb : 20 % kerikil, 10 % pasir, 30 % lanau 40 % lempung Pasir = ( 10 x 100 ) / ( ) = 12,5 % Lanau = ( 30 x 100 ) / ( ) = 37,5 % Lempung = ( 40 x 100 ) / ( ) = 50,0 %

16 Atterberg Limits Analisa ukuran butir kurang cocok untuk partikel lembut

17 Atterberg Limits Volume SL PL LL Moisture Content (%) Hubungan antara Kadar Air vs Volume

18 Atterberg Limits Analisa saringan tidak bisa diterapkan pada tanah berbutir lembut Volume Kadar air >< volume saat proses pengeringan SL - Shrinkage Limit PL - Plastic Limit LL - Liquid limit SL PL LL Moisture Content (%)

19 Atterberg Limits SL - Shrinkage Limit PL - Plastic Limit LL - Liquid limit Moisture content = mass of water mass of solids Plasticity Index = LL - PL = PI or I p

20 BEBERAPA CONTOH KLASIFIKASI TANAH STANDART AAHSO 1. Well graded sand or gravel: may include fines 2. Sands and Gravels with excess fines 3. Fine sands 4. Low compressibility silts 5. High compressibility silts 6. Low to medium compressibility clays 7. High compressibility clays 8. Peat and organic soils

21 Unified Soil Classification SETIAP JENIS TANAH DIBERI TANDA DUA SETIAP JENIS TANAH DIBERI TANDA DUA HURUF, CONTOH SW ( PASIR GRADASI BAIK )

22 Unified Soil Classification Jenis tanah ditandai dengan dua huruf (contoh. SW). Prosedurnya sbb : Coarse grained (>50% lebih besar 75 µm) Huruf S jika > 50% butiran kasar adalah pasir Huruf G jika > 50% butiran kasar adalah Gravel Suffix tergantung prosentase kandungan butir halus Jika % butir halus < 5% suffix nya W atau P Jika % butir halus > 12% suffix nya M atau C Jika 5% < % butir halus < 12% Memakai Dua simbol

23 Unified Soil Classification Untuk menentukan jenis W atau P, hitung C u dan C c C C D D u = 6 0 c = D ( D D ) X % dari tanah berukuran lebih kecil dari Dx Contoh ; D10 adalah berapa ukuran terbesar butiran, dimana prosentase yang lolos saringan sebesar 10 % Cu = Koefisien keseragaman Cc = Koefisien gradasi

24 Unified Soil Classification % Finer P a r ti c l e s i z e ( m m ) D 90 = 3 mm

25 Unified Soil Classification C D D u = C c = D 2 30 ( D D ) If prefix is G then suffix is W if C u > 4 and C c is between 1 and 3 otherwise use P If prefix is S then suffix is W if C u > 6 and C c is between 1 and 3 otherwise use P

26 Unified Soil Classification Coarse grained soils To determine M or C use plasticity chart index Plasticity Comparing soils at equal liquid limit Toughness and dry strength increase with increasing plasticity index CH OH "A" line CL or CL OL MH ML or ML Liquid limit Plasticity chart Below A-line use for laboratory suffix classification M - Silt of fine grained soils Above A-line use suffix C - Clay

27 Unified Soil Classification Tanah berbutir halus (> 50% lebih kecil 75 µm) Kedua huruf ditentukan dari plasticity chart Plasticity in ndex Comparing soils at equal liquid limit Toughness and dry strength increase with increasing plasticity index CH OH "A" line CL or CL OL MH ML or ML Liquid limit Plasticity chart for laboratory classification of fine grained soils

28 Unified soil classification (including identification and description) Coarse grained soils More than half of material is larger than.075mm sieve size Fine grained soils More than half of material is smaller than.075mm sieve size smallest particle visible to the naked eye The.075mm sieve size is about the Field identification procedures (Excluding particles larger than 75mm and basing fractions on estimated weights) Gravels More than half of coarse fraction is larger than 2.36mm Sands More than half of coarse fraction is smaller than 2.36mm Clean gravels (little or no fines) Gravels with fines (apreciable amount of fines) Clean sands (little or no fines) Sands with S Silts and clays liquid limit less than 50 Silts and clays liquid limit greater than 50 Highly organic soils fines appreciable ount of fines) (a amo Wide range of grain size and substantial amounts of all intermediate particle sizes Predominantly one size or a range of sizes with some intermediate sizes missing Non-plastic fines (for identification procedures see ML below) Plastic fines (for identification procedures see CL below) Wide range in grain sizes and substantial amounts of all intermediate particle sizes Predominantely one size or a range of sizes with some intermediate sizes missing Non-plastic fines (for identification procedures, see ML below) Plastic fines (for identification pro- cedures, see CL below) Identification procedure on fraction smaller than.425mm sieve size Dry strength crushing characteristics None to slight Medium to high Slight to medium Slight to medium High to very high Medium to high Dilatency (reaction to shaking) Quick to slow None to very slow Slow Slow to none None None to very high Toughness (consistency near plastic limit) None Medium Slight Slight to medium High Slight to medium Readily identified by colour, odour spongy feel and frequently by fibrous texture Group symbols 1 GW GP GM GC SW SP SM SC ML CL,CI OL MH CH OH Pt Typical names Well graded gravels, gravelsand mixtures, little or no fines Poorly graded gravels, gravelsand mixtures, little or no fines Silty gravels, poorly graded gravel-sand-silt mixtures Clayey gravels, poorly graded gravel-sand-clay mixtures Well graded sands, gravelly sands, little or no fines Poorly graded sands, gravelly sands, little or no fines Silty sands, poorly graded sand-silt mixtures Clayey sands, poorly graded sand-clay mixtures Inorganic silts and very fine sands, rock flour, silty or clayey fine sands with slight plasticity Inorganic clays of low to medium plasticity, gravelly clays, sandy clays, silty clays, lean clays Organic silts and organic siltclays of low plasticity inorganic silts, micaceous or dictomaceous fine sandy or silty soils, elastic silts Inorganic clays of high plasticity, fat clays Organic clays of medium to high plasticity Peat and other highly organic soils Information required for describing soils Give typical names: indicate approximate percentages of sand and gravel: maximum size: angularity, surface condition, and hardness of the coarse grains: local or geological name and other pertinent descriptive information and symbol in parentheses. For undisturbed soils add information on stratification, degree of compactness, cementation, moisture conditions and drainage characteristics. Example: Silty sand, gravelly; about 20% hard angular gravel particles 12.5mm maximum size; rounded and subangular sand grains coarse to fine, about 15% nonplastic lines with low dry strength; well compacted and moist in places; alluvial sand; (SM) Give typical name; indicate degree and character of plasticity, amount and maximum size of coarse grains: colour in wet condition, odour if any, local or geological name, and other pertinent descriptive information, and symbol in parentheses For undisturbed soils add information on structure, stratification, consistency and undisturbed and remoulded states, moisture and drainage conditions Example Clayey silt, brown: slightly plastic: small percentage of fine sand: numerous vertical root holes: firm and dry in places; loess; (ML) the fractions as given under field identification Use grain size curve in identifying t De etermine percentages of gravel and sand from grain size curve De epending on percentages of fines (fraction smaller than.075mm sie eve size) coarse grained soils are classified as follows Le ss than 5% GW, GP, SW, SP Mo ore than 12% GM, GC, SM, SC 5% to 12% Bordeline case requiring use of dual symbols Plasticity index Laboratory classification criteria C = D U Greater than 4 D10 2 (D ) C = c Between 1 and 3 D10 x D60 Not meeting all gradation requirements for GW Atterberg limits below "A" line or PI less than 4 Atterberg limits above "A" line with PI greater than 7 Above "A" line with PI between 4 and 7 are borderline cases requiring use of dual symbols C = D U Greater than 6 D10 2 (D ) C = c Between 1 and 3 D10 x D60 Not meeting all gradation requirements for SW Atterberg limits below Above "A" line with "A" line or PI less than 4 PI between 4 and 7 are borderline cases Atterberg limits above "A" requiring use of dual line with PI greater than 7 symbols Comparing soils at equal liquid limit Toughness and dry strength increase with increasing plasticity index CL CL-ML CI OL ML or CH OH Liquid limit or MH "A" line Plasticity chart for laboratory classification of fine grained soils

29 CONTOH % Finer Particle size (mm)

30 CONTOH % Finer Particle size (mm) %fines (% finer than 75 µm) = 11% - Dual symbols required

31 CONTOH % Finer Particle size (mm) %fines (% finer than 75 µm) = 11% - Dual symbols required D 10 = 0.06 mm, D 30 = 0.25 mm, D 60 = 0.75 mm

32 CONTOH % Finer Particle size (mm) Particle size fractions: Gravel 17% Sand 73% Silt and Clay 10%

33 CONTOH Plas sticity index Comparing soils at equal liquid limit Toughness and dry strength increase with increasing plasticity index CL CL OL ML or CH OH "A" line ML Liquid limit or MH Plasticity chart for laboratory classification of fine grained soils

34 Fraksi kasar 80% berupa pasir, pakai huruf S C u = 12.5, C c = 1.38 Suffix 1 = W Dari Atterberg Tests LL = 32, PL = 26 I p = = 6 Dari Plasticity Chart titik terletak dibawah garis A Suffix 2 = M Dipakai simbol ganda SW-SM Untuk melengkapi, simbol harus diberi diskripsi