Transcript Kuat Geser Tanah – Direct Shear

Kuat Geser Tanah
Direct Shear Test
(Uji Geser Langsung)
Reza P. Munirwan, ST, M.Sc
Determination of shear strength parameters of
soils (c, f or c’, f’)
Percobaan Laboratorium
menggunakan sampel
tanah tidak terganggu
(undisturbed sample)
Percobaan lab yang umum,
1.Direct shear test
2.Triaxial shear test
Percobaan laboratorium lainnya,
Direct simple shear test, torsional
ring shear test, plane strain triaxial
test, laboratory vane shear test,
laboratory fall cone test
Percobaan Lapangan
1.
2.
3.
4.
5.
6.
7.
Vane shear test
Torvane
Pocket penetrometer
Fall cone
Pressuremeter
Static cone penetrometer
Standard penetration test
Percobaan Laboratorium
Kondisi Lapangan
Model sampel
tanah
z
svc
shc
shc
svc
Sebelum konstruksi
svc + Ds
shc
z
shc
svc + Ds
Selama dan
sesudah konstruksi
svc + Ds
Percobaan Laboratorium
Simulasi kondisi lapangan
di laboratorium
svc
0
0
0
shc
0
Model sampel
tanah
dari
lapangan
shc
shc
svc + Ds
svc
shc
svc
t
t
svc
Step 1
Atur alat tes dan
sampel sedemikian
rupa untuk kondisi
tegangan awal
Step 2
Berikan tegangan
seperti yang akan
diberikan dilapangan
Direct shear test
Skema alat percobaan direct shear
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
Porous
plates
Komponen dari shear box
Persiapan sampel pasir
Direct shear test
Persiapan sampel pasir
Leveling the top surface
of specimen
Pressure plate
Specimen preparation
completed
Direct shear test
Prosedur Percobaan
P
Steel ball
Pressure plate
Porous
plates
S
Proving ring
to measure
shear force
Step 1: Apply a vertical load to the specimen and wait for consolidation
Direct shear test
Prosedur Percobaan
P
Steel ball
Pressure plate
Porous
plates
S
Proving ring
to measure
shear force
Step 1: Apply a vertical load to the specimen and wait for consolidation
Step 2: Lower box is subjected to a horizontal displacement at a constant rate
Direct shear test
Shear box
Dial gauge to
measure vertical
displacement
Proving ring
to measure
shear force
Loading frame to
apply vertical load
Dial
gauge
to
measure horizontal
displacement
Direct shear test
Analisis hasil percobaan
Normalforce(P)
s  Normalstress 
Area of crosssectionof thesample
Shear resistancedevelopedat thesliding surface (S)
t  Shear stress 
Area of crosssectionof thesample
Note: Cross-sectional area of the sample changes with the horizontal
displacement
Direct shear tests pada pasir
Shear stress, t
Stress-strain relationship
Dense sand/
OC clay
tf
tf
Loose sand/
NC clay
Expansion
Compression
Change in height
of the sample
Shear displacement
Dense sand/OC Clay
Shear displacement
Loose sand/NC Clay
Direct shear tests pada pasir
Shear stress, t
Cara menentukan parameter kuat geser c dan f
Normal stress = s3
Normal stress = s2
tf3
tf2
tf1
Normal stress = s1
Shear stress at failure, tf
Shear displacement
Garis keruntuhan Mohr – Coulomb
f
Normal stress, s
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,
f’ = f dan c’ = c = 0
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)
Shear stress at failure, tf
Failure envelopes for clay from drained direct shear tests
Overconsolidated clay (c’ ≠ 0)
Normally consolidated clay (c’ = 0)
f’
Normal force, s
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)
P
Soil
S
Foundation material
t f  ca  s ' tan
Where,
ca = adhesion,
 = angle of internal friction
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.
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
parameter kuat gesernya.
kegagalannya.
Tentukan
nilai
dari
Penyelesaian
Normalforce(P)
s  Normalstress 
Area of crosssectionof thesample
Shear resistancedevelopedat thesliding surface (S)
t  Shear stress 
Area of crosssectionof thesample
Percobaan
Tegangan
Normal (kN/m2)
Tegangan
Geser(kN/m2)
1
56
57
2
111
72
3
223
99
Shear stress at failure, tf (kN/m2)
Penyelesaian
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)
 Standard Penetration Test, SPT
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
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
Applied
Torque, T
Bore hole
(diameter = DB)
Disturbed
soil
Rupture
surface
h > 3DB)
T
Vane
Vane
H
PLAN VIEW
Rate of rotation : 60 – 120 per minute
D
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)
 Standard Penetration Test, SPT
Torvane
Torvane is a modification to the vane
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
Pocket Penetrometer
Pushed directly into the soil. The unconfined compression
strength (qu) is measured by a calibrated spring.
Swedish Fall Cone (suitable for very soft to soft clays)
Cu ∞ Mass of the cone
∞ 1/(penetration)2
Soil sample
The test must be calibrated
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
Pressuremeter
Air
Coaxial tube
Water
Pre – bored or
self – bored hole
Guard cell
Measuring cell
Guard cell
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
Static
Cone
Penetrometer
test
40 mm
40 mm
40 mm
40 mm
Cone
penetrometers
with
pore
water
pressure measurement
capability are known as
piezocones
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)
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
63.5 kg
Various correlations have been
developed
to determine
soil
The test
can be conducted
at every
1m
0.76 (c,
m f, ect)
vertical
intervals
strength parameters
from
N
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
Standard Penetration Test, SPT
SPT (Manual operation)