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 24

Seismic Reflection Test

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

CIE3032 지반공학및실험 Lecture 02 subsurface exploration 28

Boring Log