Kuat Geser Tanah

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Kuat Geser Tanah
Direct Shear Test (Uji Geser Langsung)

• Reza P. Munirwan, ST, M.Sc

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Determination of shear strength parameters of
soils (c, f or c, f)
Percobaan laboratorium lainnya, Direct simple
shear test, torsional ring shear test, plane
strain triaxial test, laboratory vane shear test,
laboratory fall cone test
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Percobaan Laboratorium
Kondisi Lapangan
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Percobaan Laboratorium
Simulasi kondisi lapangan di laboratorium
Step 2 Berikan tegangan seperti yang akan
diberikan dilapangan
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Direct shear test
Skema alat percobaan direct shear
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Direct shear test
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
Persiapan sampel pasir
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Direct shear test
Persiapan sampel pasir
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Direct shear test
Prosedur Percobaan
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Direct shear test
Step 2 Lower box is subjected to a horizontal
displacement at a constant rate
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Direct shear test
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Direct shear test
Analisis hasil percobaan
Note Cross-sectional area of the sample changes
with the horizontal displacement
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Direct shear tests pada pasir
Stress-strain relationship
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Direct shear tests pada pasir
Cara menentukan parameter kuat geser c dan f
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Direct shear tests pada pasir
Percobaan Direct shear adalah drained dan tekanan
air pori terdissipasi, maka u 0
Pasir tanah non-kohesi, maka c 0
Kesimpulan, f f dan c c 0
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Direct shear tests pada lempung
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)
Failure envelopes for clay from drained direct
shear tests
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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)
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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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Lets do some examples
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Contoh Soal
Hasil-hasil pengujian yang diperoleh dari
pengujian geser langsung (direct shear) dengan
ukuran sampel 60mm x 60mm pada tanah lempung
berpasir sebagai berikut
Percobaan Beban Normal (kN) Beban Geser pada Keruntuhan (kN)
1 0.20 0.205
2 0.40 0.26
3 0.80 0.355
Gambar garis selubung kegagalannya. Tentukan
nilai dari parameter kuat gesernya.
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Penyelesaian
Percobaan Tegangan Normal (kN/m2) Tegangan Geser(kN/m2)
1 56 57
2 111 72
3 223 99
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Penyelesaian
Shear stress at failure, tf (kN/m2)
Normal stress, s (kN/m2)
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In-situ shear tests

• Vane shear test

• Torvane

• Pocket Penetrometer

• Pressuremeter

• Static Cone Penetrometer test (Push Cone
  Penetrometer Test, PCPT)

• Standard Penetration Test, SPT

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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

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Vane shear test
This is one of the most versatile and widely used
devices used for investigating undrained shear
strength (Cu) and sensitivity of soft clays
Rate of rotation 60 120 per minute Test can
be conducted at 0.5 m vertical intervals
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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

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Torvane
Torvane is a modification to the vane
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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

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Pocket Penetrometer
Pushed directly into the soil. The unconfined
compression strength (qu) is measured by a
calibrated spring.
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Swedish Fall Cone (suitable for very soft to soft
clays)
Cu 8 Mass of the cone 8 1/(penetration)2
Soil sample
The test must be calibrated
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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

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Pressuremeter
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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

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Static Cone Penetrometer test
Cone penetrometers with pore water pressure
measurement capability are known as piezocones
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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)

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Standard Penetration Test, SPT
SPT is the most widely used test procedure to
determine the properties of in-situ soils
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
Various correlations have been developed to
determine soil strength parameters (c, f, ect)
from N
The test can be conducted at every 1m vertical
intervals
Standard penetration resistance (SPT N) N2 N3
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Standard Penetration Test, SPT
SPT (Manual operation)
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THE END