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Kuat Geser Tanah Reza P. Munirwan, ST, M.Sc Direct Shear Test (Uji Geser Langsung)

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Presentasi berjudul: "Kuat Geser Tanah Reza P. Munirwan, ST, M.Sc Direct Shear Test (Uji Geser Langsung)"— Transcript presentasi:

1 Kuat Geser Tanah Reza P. Munirwan, ST, M.Sc Direct Shear Test (Uji Geser Langsung)

2 Percobaan laboratorium lainnya, Direct simple shear test, torsional ring shear test, plane strain triaxial test, laboratory vane shear test, laboratory fall cone test Determination of shear strength parameters of soils (c,  or  c’  ’  Percobaan Laboratorium menggunakan sampel tanah tidak terganggu (undisturbed sample) Percobaan Lapangan Percobaan lab yang umum, 1.Direct shear test 2.Triaxial shear test 1.Vane shear test 2.Torvane 3.Pocket penetrometer 4.Fall cone 5.Pressuremeter 6.Static cone penetrometer 7.Standard penetration test

3 Percobaan Laboratorium Kondisi Lapangan z  vc  hc Sebelum konstruksi Model sampel tanah z  vc +   hc Selama dan sesudah konstruksi  vc + 

4 Percobaan Laboratorium Simulasi kondisi lapangan di laboratorium Step 1 Atur alat tes dan sampel sedemikian rupa untuk kondisi tegangan awal  vc  hc Model sampel tanah dari lapangan Step 2 Berikan tegangan seperti yang akan diberikan dilapangan  vc +   hc  vc +  Traxial test  vc   Direct shear test

5 Skema alat percobaan direct shear

6 Direct shear test Persiapan sampel pasir Komponen dari shear box Persiapan sampel pasir Porous plates Direct shear test adalah percobaan yang paling sesuai untuk kondisi percobaan consolidated drained khususnya pada tanah granular (contoh: pasir/sand) atau lempung keras/stiff clays

7 Direct shear test Leveling the top surface of specimen Persiapan sampel pasir Specimen preparation completed Pressure plate

8 Direct shear test Prosedur Percobaan Porous plates Pressure plate Steel ball Step 1: Apply a vertical load to the specimen and wait for consolidation P Proving ring to measure shear force S

9 Direct shear test Step 2: Lower box is subjected to a horizontal displacement at a constant rate Step 1: Apply a vertical load to the specimen and wait for consolidation P Prosedur Percobaan Pressure plate Steel ball Proving ring to measure shear force S Porous plates

10 Direct shear test Shear box Loading frame to apply vertical load Dial gauge to measure vertical displacement Dial gauge to measure horizontal displacement Proving ring to measure shear force

11 Direct shear test Analisis hasil percobaan Note: Cross-sectional area of the sample changes with the horizontal displacement

12 Direct shear tests pada pasir Shear stress,  Shear displacement Dense sand/ OC clay ff Loose sand/ NC clay ff Dense sand/OC Clay Loose sand/NC Clay Change in height of the sample Expansion Compression Shear displacement Stress-strain relationship

13  f1 Normal stress =  1 Direct shear tests pada pasir Cara menentukan parameter kuat geser c dan  Shear stress,  Shear displacement  f2 Normal stress =  2  f3 Normal stress =  3 Shear stress at failure,  f Normal stress,   Garis keruntuhan Mohr – Coulomb

14 Direct shear tests pada pasir Hal penting menggenai parameter kuat geser c and  pada pasir Pasir = tanah non-kohesi, maka c = 0 Percobaan Direct shear adalah drained dan tekanan air pori terdissipasi, maka u = 0 Kesimpulan,  ’ =  dan c’ = c = 0

15 Direct shear tests pada lempung Failure envelopes for clay from drained direct shear tests Shear stress at failure,  f Normal force,  ’’ Normally consolidated clay (c’ = 0) In case of clay, horizontal displacement should be applied at a very slow rate to allow dissipation of pore water pressure (therefore, one test would take several days to finish) Overconsolidated clay (c’ ≠ 0)

16 Interface tests on direct shear apparatus In many foundation design problems and retaining wall problems, it is required to determine the angle of internal friction between soil and the structural material (concrete, steel or wood) Where, c a = adhesion,  = angle of internal friction

17 Kelebihan percobaan direct shear  Drainase yang cepat dapat diperoleh, karena ketebalan sampel percobaan yang kecil.  Dapat digunakan untuk menggetahui parameter kuat geser pada pertemuan tanah. Kekurangan percobaan direct shear  Arah bidang keruntuhan sudah diketahui.  Luas permukaan sliding berubah seiring dengan berjalannya proses percobaan.  Ketidak seragaman distribusi kuat geser sepanjang bidang runtuh.

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19 Hasil-hasil pengujian yang diperoleh dari pengujian geser langsung (direct shear) dengan ukuran sampel 60mm x 60mm pada tanah lempung berpasir sebagai berikut: Contoh Soal PercobaanBeban Normal (kN) Beban Geser pada Keruntuhan (kN) Gambar garis selubung kegagalannya. Tentukan nilai dari parameter kuat gesernya.

20 Penyelesaian PercobaanTegangan Normal (kN/m2) Tegangan Geser(kN/m2)

21 Penyelesaian Shear stress at failure,  f  k  m  Normal stress,  k  m 

22 In-situ shear tests  Vane shear test  Torvane  Pocket Penetrometer  Pressuremeter  Static Cone Penetrometer test (Push Cone Penetrometer Test, PCPT)  Standard Penetration Test, SPT

23 In-situ shear tests  Vane shear test (suitable for soft to stiff clays)  Torvane  Pocket Penetrometer  Pressuremeter  Static Cone Penetrometer test (Push Cone Penetrometer Test, PCPT)  Standard Penetration Test, SPT

24 PLAN VIEW Vane shear test This is one of the most versatile and widely used devices used for investigating undrained shear strength (C u ) and sensitivity of soft clays Bore hole (diameter = D B ) h > 3D B ) Vane D H Applied Torque, T Vane T Rupture surface Disturbed soil Rate of rotation : 6 0 – 12 0 per minute Test can be conducted at 0.5 m vertical intervals

25 In-situ shear tests  Vane shear test  Torvane (suitable for very soft to stiff clays)  Pocket Penetrometer  Pressuremeter  Static Cone Penetrometer test (Push Cone Penetrometer Test, PCPT)  Standard Penetration Test, SPT

26 Torvane Torvane is a modification to the vane

27 In-situ shear tests  Vane shear test  Torvane  Pocket Penetrometer (suitable for very soft to stiff clays)  Pressuremeter  Static Cone Penetrometer test (Push Cone Penetrometer Test, PCPT)  Standard Penetration Test, SPT

28 Pocket Penetrometer Pushed directly into the soil. The unconfined compression strength (q u ) is measured by a calibrated spring.

29 Swedish Fall Cone (suitable for very soft to soft clays) The test must be calibrated Soil sample C u ∞ Mass of the cone ∞ 1/(penetration) 2

30 In-situ shear tests  Vane shear test  Torvane  Pocket Penetrometer  Pressuremeter (suitable for all soil types)  Static Cone Penetrometer test (Push Cone Penetrometer Test, PCPT)  Standard Penetration Test, SPT

31 Pressuremeter Pre – bored or self – bored hole Guard cell Measuring cell Guard cell Coaxial tube Water Air

32 In-situ shear tests  Vane shear test  Torvane  Pocket Penetrometer  Pressuremeter  Static Cone Penetrometer test (Push Cone Penetrometer Test, PCPT) (suitable for all soil types except very course granular materials)  Standard Penetration Test, SPT

33 Static Cone Penetrometer test Cone penetrometers with pore water pressure measurement capability are known as piezocones 40 mm

34 In-situ shear tests  Vane shear test  Torvane  Pocket Penetrometer  Pressuremeter  Static Cone Penetrometer test (Push Cone Penetrometer Test, PCPT)  Standard Penetration Test, SPT (suitable for granular materials)

35 Standard Penetration Test, SPT SPT is the most widely used test procedure to determine the properties of in-situ soils 63.5 kg 0.76 m Drill rod 0.15 m Number of blows = N 1 Number of blows = N 2 Number of blows = N 3 Standard penetration resistance (SPT N) = N 2 + N 3 Number of blows for the first 150 mm penetration is disregarded due to the disturbance likely to exist at the bottom of the drill hole The test can be conducted at every 1m vertical intervals Various correlations have been developed to determine soil strength parameters (c,  ect) from N

36 Standard Penetration Test, SPT SPT (Manual operation)

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