CIE3032 지반공학및실험 Lecture 02 subsurface exploration 1313
CPT (Cone Penetration Test)
A CPT device consists in a cylindrical probe with a cone-shaped tip with different sensors that allow a real time continuous measurement of soil strength and characteristics by pushing it into the ground at a speed of 2 cm/s. The typical CPT probe measures the stress on the tip, the sleeve friction and the pore water pressure. Some of them are equipped with a geophone in order to be able to perform shear wave velocity measurements.The data is normally read by a field computer that displays it real-time and stores it at regular depth intervals. Measurements can be taken at any intervals desired.
http://www.ce.gatech.edu/~geosys/Faculty/Mayne/Research/index.html
CIE3032 지반공학및실험 Lecture 02 subsurface exploration 14
Cone Penetration Testing (CPT)
Real-Time readings in computer screenPenetration at 2 cm/s
Sand
Clay
Buried Crust
Clay
http://www.ce.gatech.edu/~geosys/Faculty/Mayne/Research/index.html
CIE3032 지반공학및실험 Lecture 02 subsurface exploration 15
Cone Penetrometer Configuration
http://www.ce.gatech.edu/~geosys/Faculty/Mayne/Research/index.html
CIE3032 지반공학및실험 Lecture 02 subsurface exploration 16
CPTCone penetration test (CPT)
Originally known as the Dutch cone penetration test60 cone with a base area of 1000mm2 and diameter of 35.7mm attached to the lower end of a 15mm rod surrounded by a 20mm pipe. The cone is pushed 0.5 m into the ground at a rate of 1 - 2 cm/s. The pressure exerted on the rod is plotted against depth. Measures a) cone resistance (qc) and b) frictional resistance (fc)Modified CPT: Electronic cone and Mechanical cone
Correlation with N60 for sands
CIE3032 지반공학및실험 Lecture 02 subsurface exploration 17
Method of Exploration - CPTCorrelation with undrained shear strength
Nk = bearing capacity factor (Nk = 15 for an electric cone)(Nk = 10 - 20)vo = total vertical stress’vo = effective vertical stress
kv
vc
v
u
Nqs 1
'' 0
0
0
• Correlation with ’ of sands• Correlation with Dr• Correlation with ’p, OCR• Type of soil (Fig. 2.23) Fr = fc/qc
CIE3032 지반공학및실험 Lecture 02 subsurface exploration 18
DMT (Flat Dilatometer Test)
A Flat Dilatometer probe consists in a steel blade with a circular membrane in one of its sides. The membrane has electrical sensors which can detect its position (flexed to the inside or outside and parallel to the blade).This blade is pushed into the ground and at desired depths the membrane is inflated using any kind of compressed gas, normally nitrogen.When the probe is pushed into the ground the soil pressure makes the membrane flex to the inside of the dilatometer blade. At measurement depths the membrane is inflated and an "A" reading of pressure is obtained when the membrane reaches its initial position (parallel to the blade), and a "B" reading is obtained when the membrane displaces 1.1 mm to the outside.This parameters are used in several correlations to obtain properties of the soil, such as compressibility and soil behavior classification.
CIE3032 지반공학및실험 Lecture 02 subsurface exploration 19
DMT (flat Dilatometer Test)딜라토미터 시험
- 원형 멤브레인을 가스압력으로 수평방향으로 수축과 팽창시켜, 이 때 팽창과 수축 변위에서의 압력으로부터 지반의 특성을 추정하는 실험
1
2
3
1.05( ) 0.05( )p A A B Bp B Bp C A
Correlations: p 100
CIE3032 지반공학및실험 Lecture 02 subsurface exploration 20
DMT (flat Dilatometer Test)
1
2
3
1.05( ) 0.05( )p A A B Bp B Bp C A
D
2 12
D
1'
0
D
2 1
1
(dilatometer modulus, E )
34.7( )1
(lateral stress index, K )
(material or deposit index, I )
sD
Dv
D
EE p p
p uK
p pIp u
딜라토미터 계수
수평응력지수
지반지수
CIE3032 지반공학및실험 Lecture 02 subsurface exploration 21
PMT (Pressuremeter Test)
http://www.ce.gatech.edu/~geosys/Faculty/Mayne/Research/index.htmlCorrelations: p 98
CIE3032 지반공학및실험 Lecture 02 subsurface exploration 22
Field vane shear test, FVST
2
6
110 2 3
(
uTsK
D H DKH
비배수전단강도
여기서 D는베인의지름cm), H는베인의높이(cm)
현장 베인 시험
- 연약하고 포화된 점성토 지반의 비배수 전단강도를 추정하기 위해 실시하는 현장 시험
CIE3032 지반공학및실험 Lecture 02 subsurface exploration 23
Undrained shear strength (su) measurement Field Vane
su(mob) = su(FV)
Correction factor to account for:1. Direction of shearing2. Time to failure3. Disturbance4. Progressive failure
Can also be used to estimate OCR and ’p (p.89)
CIE3032 지반공학및실험 Lecture 02 subsurface exploration 25Lecture 3. Subsoil Exploration 25
Seismic Refraction Test
Vertical GeophonesSource(Plate)
Rock: Vp2
Soil: Vp1
oscilloscope
x1x2x3x4
t1t2t3t4
Note: Vp1 < Vp2
zR
Determine depthto rock layer, zR
http://www.ce.gatech.edu/~geosys/Faculty/Mayne/Research/index.html
CIE3032 지반공학및실험 Lecture 02 subsurface exploration 26Lecture 3. Subsoil Exploration 26
Crosshole TestingOscilloscope
PVC-cased Borehole
PVC-cased Borehole
DownholeHammer(Source) Velocity
Transducer(GeophoneReceiver)
t
x
Shear Wave Velocity:Vs = x/t
TestDepth
ASTM D 4428
Pump
packer
Note: Verticality of casingmust be established by
slope inclinometers to correctdistances x with depth.
SlopeInclinometer
SlopeInclinometer
CIE3032 지반공학및실험 Lecture 02 subsurface exploration 27Lecture 3. Subsoil Exploration 27
Downhole TestingOscilloscope
Cased Borehole
TestDepth
Interval
HorizontalVelocity
Transducers(GeophoneReceivers)
packer
PumpHorizontal Plank
with normal load
Shear Wave Velocity:Vs = R/t
z1z2
t
R12 = z12 + x2
R22 = z22 + x2
x
Hammer
http://www.ce.gatech.edu/~geosys/Faculty/Mayne/Research/index.html
http://www.ce.gatech.edu/~geosys/Faculty/Mayne/Research/index.html
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