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

Kuat Geser Tanah

Reza P. Munirwan, ST, M.Sc

Direct Shear Test

(Uji Geser Langsung)

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,

f

or

c’

, f

’)

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

Percobaan Laboratorium

Kondisi Lapangan

z

s

_vc

s

_vc

s

_hc

s

_hc

Sebelum konstruksi

Model sampel tanah

z

s

_vc

+

Ds

s

_hc

s

_hc

Selama dan

sesudah konstruksi

s

_vc

+

Ds

Percobaan Laboratorium

Simulasi kondisi lapangan

di laboratorium

Step 1

Atur alat tes dan

sampel sedemikian

rupa untuk kondisi

tegangan awal

s

_vc

s

_vc

s

_hc

s

_hc

Model

sampel

tanah

dari

lapangan

0

0

0

0

Step 2

Berikan tegangan

seperti yang akan

diberikan dilapangan

s

_vc

+

Ds

s

_hc

s

_hc

s

_vc

+

Ds

s

_vc

s

_vc

t

t

Direct shear test

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

Direct shear test

Leveling the top surface of specimen

Persiapan sampel pasir

Specimen preparation completed

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

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

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

Direct shear test

Analisis hasil percobaan

sample

t he

of

sect ion

cross

of

Area

(P )

force

Normal

st ress

Normal





s

sample

t he

of

sect ion

cross

of

Area

(S)

surface

sliding

at t he

developed

resist ance

Shear

st ress

Shear





t

Note: Cross-sectional area of the sample changes with the horizontal displacement

Direct shear tests pada pasir

Shear st ress, t Shear displacement Dense sand/ OC clay

t

_f

Loose sand/ NC clay

t

_f

Dense sand/OC Clay

Loose sand/NC Clay

Change i n heigh t of the sa mple Expansion Com pression Shear displacement Stress-strain relationship

t

_f1 Normal stress = s1

Direct shear tests pada pasir

Cara menentukan parameter kuat geser c dan f

Shear stress, t Shear displacement

t

_f2 Normal stress = s₂

t

_f3 Normal stress = s₃ Shea r s tre ss at failu re , t f Normal stress, s

f

Direct shear tests pada pasir

Hal penting menggenai parameter kuat geser c and f pada pasir

Pasir = tanah non-kohesi,

maka c = 0

Percobaan Direct shear adalah drained dan tekanan air pori terdissipasi, maka u = 0

Kesimpulan,

Direct shear tests pada lempung

Failure envelopes for clay from drained direct shear tests

Shea r s tre ss at failu re , t f Normal force, s

f

’

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)

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)



s

t

_f



c

_a



'

tan

Where, _c

a = adhesion,

 = angle of internal friction

Foundation material Soil P S Foundation material Soil P S

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

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

Penyelesaian

Percobaan Tegangan Normal (kN/m2) Tegangan Geser(kN/m2) 1 56 57 2 111 72 3 223 99

sample

t he

of

sect ion

cross

of

Area

(P )

force

Normal

st ress

Normal





s

sample

t he

of

sect ion

cross

of

Area

(S)

surface

sliding

at t he

developed

resist ance

Shear

st ress

Shear





t

Penyelesaian

Shea r s tre ss at failu re , t f ( k N/ m 2) Normal stress, s (kN/m2)

In-situ shear tests

 Vane shear test

 Torvane

 Pocket Penetrometer

 Pressuremeter

 Static Cone Penetrometer test (Push

Cone Penetrometer Test,

PCPT

)

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)

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 : 60– 120_{per minute}

Test can be conducted at 0.5 m vertical intervals

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)

Torvane

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)

Pocket Penetrometer

Pushed directly into the soil. The unconfined compression

strength (q

_u

) is measured by a calibrated spring.

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

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)

Pressuremeter

Pre – bored or self – bored hole

Guard cell Measuring cell Guard cell Coaxial tube Water Air

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)

Static

Cone

Penetrometer

test

Cone penetrometers with pore water pressure measurement capability are known as piezocones

40 mm

40 mm

40 mm

In-situ shear tests

 Vane shear test

 Torvane

 Pocket Penetrometer

 Pressuremeter

 Static Cone Penetrometer test (Push

Cone Penetrometer Test, PCPT)

 Standard Penetration Test, SPT

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 0.15 m 0.15 m Number of blows = N₁ Number of blows = N₂ Number 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

Standard Penetration Test,

SPT