An Easy Method of Determining Hydraulic Conductivity of Soils using Pore Pressure Response of Piezocone Penetration Test

Chung R Song, Ph.D., University of MississippiSreekar Pulijala, Graduate Assistant, University of

Mississippi

Overview

Hydraulic Conductivity and Piezocone Hydraulic Conductivity by Piezocone

Penetration Test Previous work Current results Conclusions

Hydraulic Conductivity

Describes the rate at which water can move through a permeable medium.

Why do we need to know hydraulic conductivity of the soil ??

However, the determination of hydraulic conductivity is time consuming and not easy.

Piezocone

Used for Site exploration Assessment of ground improvement Evaluation of contaminant transport

Measures Frictional resistance Pore Pressure End bearing

Hydraulic Conductivity by Piezocone Penetration Test

(PCPT)

Advance Piezocone to the desired depth and hold it for dissipation test.

Reliable values of Hydraulic Conductivity, compared to other field tests.

This is still time consuming and expensive (half day).

Pore pressure response for soil element during PCPT

Chung R. Song and George Z. Voyiadjis (2003)

“New Method”

To overcome the drawbacks of conventional dissipation test and provide a more realistic theoretical background.

Key idea : Pore Pressure response of saturated soils is not

only a function of stress-strain parameters but also of hydraulic conductivity.

Song.C.R and Voyiadjis.G.Z (2003) Pore pressure observed by clayey soils and

sandy soils. Clay : High PWP Sand : Low or Zero PWP

Relations between the dimensionless excess PWP during Piezocone Penetration and dimensionless Hydraulic Conductivity

Chung R. Song and George Z. Voyiadjis (2003)

Previous work

Correlates the magnitude of pore water pressure to the Hydraulic Conductivity directly.

Potential for real time process.

An axi- symmetric FE program that is capable of simulating behavior of soils with the advancement of the Piezocone tip was developed and used.

Uses the coupled theory of mixtures

Finite Element Mesh

Chung R. Song and George Z. Voyiadjis (2003)

Coupled equations

Voyiadjis and Abu-Farsakh (1997)

δ W

Stiffness matrix; Coupling matrix,

Flow matrx that incorporates the hydraulic conductivity

Incremental nodal displacement

W=Incremental excess PWP

n n n

tn n n

n n

n

U

t

U

; Flow vector,

Equilibrium force

n

n

Objective

Use of Song and Voyiadjis (2003)’s method (i.e. New method)

To perform numerical analyses for various soil conditions and provide simple design charts (monogram type) that an engineer can use without great difficulties.

Current stage

Setting up penetration depth and number of increments

By changing some material properties like κ, λ Permeability, M

Corresponding values of PWP are obtained for each varying properties when others are kept constant.

1.00E-11 1.00E-09 1.00E-07 1.00E-05 1.00E-03

k (m/sec)

PWP

(KPa

)

600

200

300

400

500

100

Permeability (k) vs. PWP

0.1,005.0,13.0 M

2.1,02.0,17.0 M

0

100

200

300

400

500

600

0.5 0.6 0.7 0.8 0.9 1 1.1 1.2 1.3

M

PWP(

KPa

)

M vs. PWP

095.0,02.0,17.0 Ek

095.0,04.0,32.0 Ek

0

100

200

300

400

500

600

700

0 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08 0.09

kappa

PW

P (

KPa)

vs. PWPκ

κ

095.0,24.0,2.1 EkM

0

100

200

300

400

500

600

0.15 0.2 0.25 0.3 0.35 0.4 0.45

Lambda

PW

P (

KPa)

λ vs. PWP

075.0,02.0,0.1 EkM

095.0,04.0,2.1 EkM

λ

Conclusions

The trend of PWP observed by the change of different parameters is reasonable.

Easy to use design charts : a handy tool to geotechnical engineers for the determination of hydraulic conductivity

Reduction in the computation time

Can be used in seepage analysis, soil classification, detection of underground aquifers, etc…

THANK YOU