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Kuat Geser Tanah
Reza P. Munirwan, ST, M.Sc
Direct Shear Test(Uji Geser Langsung)
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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, forc, f)
Percobaan Laboratoriummenggunakan 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. Pressuremeter6. Static cone penetrometer
7. Standard penetration test
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Percobaan Laboratorium
Simulasi kondisi lapangan
di laboratorium
Step 1
Atur alat tes dan
sampel sedemikian
rupa untuk kondisi
tegangan awal
svc
svc
shcshc
Model sampeltanah dari
lapangan
0
00
0
Step 2
Berikan tegangan
seperti yang akan
diberikan dilapangan
svc + Ds
shcshc
svc + Ds
svc
svc
t
t
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Direct shear test
Skema alat percobaan direct shear
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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
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Direct shear test
Leveling the top surface
of specimen
Persiapan sampel pasir
Specimen preparation
completed
Pressure plate
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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
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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
PProsedur Percobaan
Pressure plate
Steel ball
Proving ring
to measure
shear force
S
Porous
plates
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Direct shear test
Analisis hasil percobaan
sampletheofsectioncrossofArea
(P)forceNormalstressNormal s
sampletheofsectioncrossofArea
(S)surfaceslidingat thedevelopedresistanceShearstressShear t
Note: Cross-sectional area of the sample changes with the horizontaldisplacement
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Direct shear tests pada pasir
Shearstres
s,t
Shear displacement
Dense sand/OC claytf
Loose sand/
NC clayf
Dense sand/OC Clay
Loose sand/NC ClayChangeinheight
ofthesample Ex
pansion
Com
pression Shear displacement
Stress-strain relationship
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tf1
Normal stress = s1
Direct shear tests pada pasir
Cara menentukan parameter kuat geser c danf
Shearstress,
t
Shear displacement
tf2
Normal stress = s2
t
f3
Normal stress = s3
S
hearstressat
failure,t
f
Normal stress, s
f
Garis keruntuhan MohrCoulomb
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Direct shear tests pada pasir
Hal penting menggenai parameter kuat geser c andf
pada pasir
Pasir = tanah non-kohesi,
maka c = 0
Percobaan Direct shearadalah drained dan
tekanan air pori
terdissipasi, maka u = 0
Kesimpulan,
f
=f
dan c= c =0
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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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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
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 56 572 111 72
3 223 99
sampletheofsectioncrossofArea
(P)forceNormalstressNormal s
sampletheofsectioncrossofArea
(S)surfaceslidingat thedevelopedresistanceShearstressShear t
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Penyelesaian
Sh
earstressatfa
ilure,t
f
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 (PushCone 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 (PushCone Penetrometer Test, PCPT)
Standard Penetration Test, SPT
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PLAN VIEW
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
Bore hole
(diameter = DB)
h > 3DB)
Vane
D
H
AppliedTorque, T
Vane T
Rupture
surfaceDisturbed
soil
Rate of rotation : 60120 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 (PushCone Penetrometer Test, PCPT)
Standard Penetration Test, SPT
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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 (PushCone 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)
The test must be calibrated
Soil sample
CuMass of the cone1/(penetration)2
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In-situ shear tests
Vane shear test
Torvane
Pocket Penetrometer
Pressuremeter (suitable for all soil types)
Static Cone Penetrometer test (PushCone Penetrometer Test, PCPT)
Standard Penetration Test, SPT
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Pressuremeter
Prebored or
selfbored hole
Guard cell
Measuring cell
Guard cell
Coaxial tube
Water
Air
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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
40
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Static Cone
Penetrometer
test
Cone penetrometers
with pore water
pressure measurement
capability are known as
piezocones
40 mm
40 mm
40 mm
40 mm
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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
63.5 kg
0.76 m
Drill rod0.15 m
0.15 m
0.15 m
Number of blows = N1
Number of blows = N2Number of blows = N3
Standard penetration resistance (SPT N) = N2+ N3
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, f, ect) from N
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