REINFORCEMENT EFFECT EVALUATION FOR THE

GEOSYNTHETICE CLAY BANKING

NAGASAKI UNIVERSITY

K. TSUJIY.TANABASHI

Y.JIANG

Technology.

Background of study①Development of urban and underground space

•Security of the right spot is the difficult

•Increase of the cost

Low quality soft clay from construction

Society ＆ environment

Geosynetics reinforcement

The reuse of low quality soil is promoted.

Background of study ②

Drainage capability

Tension strength

Development of geocomposite.

The geocomposite is feasible and more economic.

The design of geocomposite is in a study phase.

+

Purpose of the study.

Kanto loam (The low quality soil)

The steep slope is assumed.

・ Change of the consolidation 　 of the every layer of the banking. ・ Reinforcement function of 　geoconposite.

The reinforcement effect of geocomposite is evaluated by finite difference analysis.

Behavior prediction

Suggestion for the design of geocomposite re

inforced embankment

Analysis method and outline. The difference between the construction period.

Friction angle of GC-soil.

Strength constant of the soil.

Mohr-Coulomb model

The membrane element is selected to simulate.

The behavior of the banking was evaluated.

Set at each layer.

1,1φc

5,5φc

3,3φc

4,4φc

6,6φc

2,2φc

11, vcU

22, vcU

33, vcU

44, vcU

55, vcU

66, vcU

cucuc ,cuscusc ,

Analysis case.

The difference between construction period and drainage distance by the laying interval.

Strength constant of the soil.

Friction angle of GC-soil

Height of the banking. (m)

8 12 16

Reinforcement laying space. (cm)

Non-reinforced. (N),45(GC45),90(GC90)

Slope gradient 1:0.6Construction period. 240,480,720 480,720 720,960

The physical property in analysis. Physical properti values of banking material 　 (Kanto lome)

Item Parameter Volumetric elastic coefficient bulk modulus K(kP

a)500

Cohesion c (kPa) 19.6Densityρ (g/cm3) 1.363

Angel of internal frictionφcu(deg) Expression (1)

Dilatancy angularψ(deg) 0Limit of tensile stressσ’ (kPa) 1.96

Physical properties value of geocompositeCohesion of interface (kPa) 4.41

Angel of internal friction of interfaceφcus(deg) Expression (2)

Rotation of elastic modulus (kPa) 280000

Calculated from direct shear test.

Result of direct shear test.

Choesion ： It is almost constant regardless of the progress of the consolidatio

n. Angle of internal friction ： After the primary consolidation end, it approaches in the constant value.

（1）（2）

Kanto lome

The friction angle of GC-soil interface

)9442.00895.3exp(

19665.21)(

c

ccust

t

)9413.00051.3exp(

11923.20)(

c

ccut

t

Choesion ： It is almost constant regardless of the progress of the consolidatio

n. Angle of internal friction ： After the primary consolidation end, it approaches in the constant value.

GC-soil interface

： kanto lome

： The friction angle of

Consolidation time (min)

ccus = 4.41 (kPa)

ccu =19.6 (kPa)

Banking consolidation period

Introduction of banking consolidation period.From layer ①, the subsequent

layers were heaped step by step, and actual consolidation period for every layer was calculated.

⑤④

②③

①

⑥

〔 Reference literature. 〕 Y.Tnahashi and H.Nagashima (2002): Geocomposite design method tentative plan.

In this study

Different consolidation coefficient and consolidation period were set at every 90cm/layer

Determination of the physical property.

Consideration of construction period.

The consolidation period for each layer is assumed to be the same, as illustrated

The construction process.

Erea

Construction period①

②③

④⑤

⑥

（m）

Time

Banking height

The analytical model

A footing loading is loaded at every 5-10 kPa step to the crown surface of the embankment

： The membrane element

Crown width B=2H

H(m)

Banking height

Loading –settlement curve (8m)

-2-1.8-1.6-1.4-1.2

-1-0.8-0.6-0.4-0.2

0

0 20 40 60 80 100 (kPa)荷重強度

(m

)沈

下量

GC90_30day

GC90_10day

Displaced linearly.

The control of settlement.

GC45_10day

GC45_30day

Strength of load (kPa)

Set

tlem

ent

(m)

Increases with the consolidation degree

N_10day

N_30day

A limit in the strengthning

-2-1.8-1.6-1.4-1.2

-1-0.8-0.6-0.4-0.2

0

0 10 20 30 40 50 60

(kPa)荷重強度

(m

)沈

下量

Loading –settlement curve (12m)

The rapid settlement.

12m seem to be the limit

N_20 日N_30 日

Displaced linearly

The control of settlement.

GC90_20day

GC90_30 日 day

GC45_20day

GC45_30day

The effect of consolidation period is not remarkable

Set

tlem

ent

(m)

Strength of load (kPa)

Fs= - 0.8132Ln(H) + 3.172

R2 = 0.99570

0.20.40.60.8

11.21.41.61.8

2

0 5 10 15 20

H (m)盛土高

Fs

安全

率Limit of embankment height

Banking height (m)

Evaluation of limit of banking height.

Saf

ety

fact

or

A height of　11.3m

The limit of embankment height is 14.4 ｍ

-3

-2.5

-2

-1.5

-1

-0.5

0

0 20 40 60 80 100 (kPa)荷重強度

(m

)沈

下量

The crown settlements of different height cases with

GC45cm

H=16m_GC45_40 day

H=12m_GC45_30 day

H=8m_GC45_30 day

Strength of load (kPa)

Set

tlem

ent

(m)

The difference between the settlement.

The settlement of the higher

embankment is large

Load strength-deformation slope (8m)

100 ｃｍ

初期法面

N 10kPa

N 50kPa

GC90cm 10kPa

GC90cm 50kPa

GC45cm 10kPa

GC45cm 50kPa

The embankment

collapses

A large deformation occurred under a surface load of 50kPa

N_50kPa

The embankment is stable.

GC90_50kPa

No large deformation

GC45_50kPa

Initial slope

初期法面

N_10kPa

GC90cm_10kPa

GC90cm_50kPa

GC45cm_10kPa

GC45cm_50kPa

Load strength-deformation slope (12m)

100 ｃｍ

Deformation is restrained

Deformation strength is small

GC90_50kPa

GC45_50kPa

Initial slope

Shear failure region (N)

Load strength

Destruction：

10kPa20kPa30kPa40kPa50kPa55kPa

The embankment collapses

The destruction area develops.

8mCase N

10kPaLoad strength

Displacement vector(N)

20kPa30kPa40kPa

10kPa

50kPa55kPa

The displacement is large.

The destruction area

Case N

8m

Displacement vector ( GC45cm)

10kPa20kPa40kPa60kPaLoad strength

Displacement control.

Case GC45

The embankment is stable.

8m

Shear failure region ( GC45cm)

Load strength 10kPa20kPa40kPa60kPa80kPa

8m

No progress of breakdown region to

banking upper part.

：

ケース GC45

The embankment is stable.

Destruction

05

10152025

3035404550

0 5 10 15 (m)法面からの距離

(kP

a)補

強材

に働

く引張

応力

90cm 270cm360cm 540cm

720cm

Tensile stress the reinforcement material

The effect of the stress concentration on the toe slope.

Distance from slope (m)

Geo

com

posi

te te

nsile

str

ess

(kP

a)

The stress is also concentrating each GC near 4～ 6m from the slope

The displacement control by the reinforcement maternal.

05

10152025

3035404550

0 5 10 15 (m)法面からの距離

(kP

a)補

強材

に働

く引張

応力

90cm 270cm360cm 540cm

720cm

Tensile stress of the reinforcement material

The dispersion of the stress.

Geo

com

posi

te te

nsile

str

ess

(kP

a)

Distance from slope (m)

The embankment is stable.

Conclusion

Loading –settlement curve,Deformation of slope & Displacement vector.

The strengthening by consolidation.

The effect of restraining the displacement of the slope.

Considering the construction period.

Tensile stress of the reinforcement material

Design of geocomposite reinforced embankment.