TRAP-DOOR TESTS WITH SLOW DEFORMATION FOR BENTONITE MIXED SOILLINER
Kengo Kudo1, Hiroki Kato2, Sadahiko Usami3, Shigeyoshi Imaizumi4, Masataka Hanashima5, Toru Furuichi6
1 LSA, NPO (JDC Corp., Kanagawa pref., 243-0303, Japan)
2 LSA, NPO (Volclay Japan Co., Ltd., Minato-ku, Tokyo, 105-0004, Japan)
3 LSA, NPO (Yachiyo-Eng. Corp., Shinjuku-ku, Tokyo, 161-8575, Japan)
4 LSA, NPO (Utsunomiya Univ., Utsunomiya City, 321-8585, Japan)
5 LSA, NPO Chairperson (Minato-ku, Tokyo, 108-0074, Japan)
6 LSA, NPO Vicechairperson (Hokkaido Univ., Hokkaido, 060-8628, Japan)

ABSTRACTIn Japanese landfills, the bentonite mixed soil (BMS) has been often used for the material of their liners. The BMS
is made by adding about 10 % bentonite into a natural soil, and the compacted BMS liner has a low permeability. Itspermeability is required to be lower than 10 nm/s by the regulations of Japanese government.
In landfills, it is afraid that the foundation of the liner may experience subsidence with increasing the waste weightfilled in the landfill. And it is also afraid that the foundation above the groundwater collection pipes has a cavity withthe erosion by sucking out of soils around the pipes. The BMS liners on such foundations will be sure to be deformed.
If the deformation of the BMS liners becomes large, the liners have cracks in it. It can be also thought that thepermeability of the deformed liner will increase and the original performance won’t be able to accomplish. However
few papers concerning those deforming behaviors are reported until now. In the past papers, the authors reported
about the deformation behaviors of the BMS liner in the modeled tests that it was quickly deformed at a rate of 1mm/min. In this paper, they report about the deformation behaviors of the BMS liners in the cases that the trap-door
settles at a rate of 1 mm/day.
From these studies, it was found that the results of slow deformation didn’t differ from the case of fast deformation
tests too much. And it was also found that the deformation ability of BMS liners was not so high, and wasreconfirmed that the liner has a limit amount of vertical deformation against cracking.

Keywords: Bentonite mixed soil liner, subsidence, deformation rate, trap-doorINTRODUCTION

around the landfill. In Japan, the barrier system

In landfills, the barrier system is necessary to prevent

consisting of geomembrane and compacted clay liner

the leachate from infiltrating into the ground water

has been mainly used since 1998. And the quality of theused clay liner is required to have a permeability of lessClassification of Geomaterials for Engineering Purpose.

than 10 nm/s and a thickness of larger than 50 cm.

In the compaction test, the sand is compacted into aHowever , since it is difficult to get a natural clay withmold with a inside diameter of 10 cm and a volume ofsuch low permeability, the compacted clay soil liner

1,000 cm3 in three equal layers by dropping a hummerthat is made by mixing the bentonite with natural soils

with a mass of 2.5 kg. Blowing number is 25 for eachobtained in the area close to landfill site (BMS)1) has

layer. The maximum dry density(ρdmax) of 2.11 g/cm3

been used in Japan.

and the optimum water contents(wopt) of 9.6 % are

The foundation of landfill liners may experience aobtained.

compression or deformation due to increase of theoverlaid waste weight. When the underground water

Table 1 Particle size and density of the sandcollection pipes installed in the foundation wereGravel (%)

33.4

deformed by the overburden pressure of the waste orSand (%)

50.5

the soils around the pipes had the erosion by sucking,Silt (%)

7.1

Clay (%)

9.0

Max. Particle Size (mm)9.5

D60 (mm)

1.6

D30 (mm)0.3

D10 (mm)

0.008

In this study, the authors investigated the deformation

Uniformity Coefficient Uc

200.0

behaviors of the BMS liners in the tests that theCoefficient of Gradation Uc’

7.0the spaces between the foundation and the overlaid
bentonite mixed soil liners (BMS) are formed. Then thesoil liner would deform to fill the open spaces. If thedeformation was big, the soil liner would fail2),3) .

trap-door settled at a rate of 1 mm/day, and compared4), 5), 6)

the results

3

Particle density (g/cm )2.70

from the tests conducted at a rate of 1

mm/min reported former.

Bentonite mixed soil:

BMS was formed by adding

10 % in dry mass of bentonite into the sand. From theMATERIALS & METHODS

result of compaction tests, ρdmax of 1.88 g/cm3 andBentonite mixed soil liner

Wopt of 10.7 % were obtained.

Bentonite:

The bentonite used in this study is sodium

For the deformation tests, the BMS was compacted

one produced in U. S. A.. Its characteristics are shownstatically using oil jack to be a degree of compaction

as follows.

(Dc) of 95 %, and the BMS liner samples were trimmed
3Density = 2.86 g/cm , Free swelling = 38 ml/2g, pH =with the size of W800 mm*L200 mm*D100 mm. Their

9.8, Liquid Limit = 581 %, Plastic Limit = 38 %water contents were 10.7 – 15.0 %.

Sand: The sand used as parent material of BMS is theProcedure of deformation test

fine crushed rock. The characteristics of the sand are

Figure 2 shows the cross section of the deformation

shown in Table 1. It has a maximum particle size of 9.5

test equipment. The equipment is made by the steel

mm and well graded soil. The sand is classified as Sandcontainer, the inside size in that is W800 mm*L200

with Fine-soil(SF) according to the Method of Japanese

mm*D350 mm. The container has a trap-door (Ironplate, the width is 300-500 mm) at its bottom, and theheight of the door is controlled by a jack placed under
the door.
In the container, the compacted BMS liner (t=100mm) is placed on the bottom and is overlaid byprotective sand (t=200 mm). The airbag placed on thesand functions to apply uniformly distributed pressure
on the compacted BMS liner through the protective
sand. The amount of subsidence of BMS liner ismeasured through the displacement gauge tied to a thinsteel plate settled on the top and bottom center of theBMS liner.

Figure 2. Cross section of the deformation test
equipment

In the slow deformation tests, the trap-door waslowered by the jack with increasing the value of thedisplacement gauge in 1 mm per 24 hours. During thetests, the airbag had pressured the BMS liner with
107.8 kN/m2.

Table 2. Condition of the slow rate deformation tests
No.

Thickness ofBMS liner[mm]

Span[mm]

Water
content[%]

Degree ofcompaction
[%]

1100

300

16.3

95.7

2100

400

17.2

94.0

3100

500

16.5

95.5

RESULT
Figure 3 and 4 show the side view after deforming andthe displacements of the BMS liner with trap-door inFigure 1. Side view of the deformation test
equipmentcase of No.3 test, respectively. When the subsidence atthe top surface of the BMS liner reached to 12 mm, theshare crack (A, B) had taken place in the middle height

Case of the deformation testsof the BMS just above the edge of the trap-door. TheseIn the deformation tests, the thickness of the BMS

cracks had grown both upward and downward withliners was fixed to 100 mm. And three types of span

increasing the subsidence. When the center of the BMS(width of trap-door) were prepared such as 300 mm

liner subsided by 14.5 mm, Crack A had reached the top(No.1), 400 mm (No.2) and 500 mm(No.3). Since thesesurface of the BMS liner. And when the displacement

span had been used in the fast rate deformation tests4), 5),gauge showed 18.5 mm, Crack B had reached the6)bottom surface of the one.

previously, the results in these experiments could becompared with them.

On the other hand, when the center of the BMS liner

Table 2 shows the condition of these tests.

subsided by 18 mm, the bending crack (C, D) had taken

Crack from the inside of
the BMS linerCrack from the bottom
surface of the BMS liner

Crack B

Crack A

Crack D

Crack C

Amount of subsidence [mm]Figure 3. The appearance of cracks after finishing the deformation test (Case No.3)

Crack A
Reach to the
top surface

Displacement gauge on
the top surface

Crack B
Reach to the
top surface

Crack A
Reach to thebottom surface

Displacement gauge underthe bottom surface
Crack B
Reach to the
top surface
Crack A, B
incidence at theinside of BMS liner

Crack C, D
incidence at thebottom of BMS liner

Time [day]Figure 4. The relationship of the amount of the subsidence and the measurement time (Case No.3)
Table 3. Summary of the deformation test results and comparison with ones of fast rate deformation tests
Deformation
SpeedNo.

Thickness ofSpan
BMS liner
[mm]
[mm]

Density ofBMS liner[g/cm3]

Shear/Spanratio

Applied pressure*2[kPa]

Subsidence*2[mm]Type ofcrack

1100300

1.77

1.5

156.88no crack

2100400

1.74

2.0

107.8

11

Shear

3Slow(1 mm/day)

100500

1.77

2.5

107.8

12

Shear

*1100300

1.84

1.588.3

12

Shear

B7*1100400

1.88

2.0

58.8

23.7

Bending*1100500

1.84

2.5

29.4

12.8Bending

A2Fast(1 mm/min.)B9*1 These numbers are quoted from the paper4), 5),6) reported by us before.
*2 These values are at the moment that the BMS liner had experienced some cracks.

place around the bottom center of the BMS liner. Thenrate of 1 mm/min tests reported4), 5), 6) by the authors.

those cracks had been growing upward with increasing

From Table 3, it is found that the applied pressure of thethe deformation.

slow rate deformation tests had a greater value than thatFrom the above results, it was found that the failure ofof the fast rate tests at the moment that the BMS liner

the BMS liner in case of No.3 (That has a thickness of

had experienced some cracks. And the main type of

100 mm and a span of 500 mm) mainly caused in thecrack was different between the slow rate tests and theform of share crack.

fast rate tests. The reason is thought as follows. TheSimilarly, in the case of No.2, the shear cracks

shear strength and the bending strength are muchappeared when the displacement gauge on the top

affected by the strain rate and the trigger-strength issurface showed 11 mm (See Table 3) and the bending

different.

crack appeared after that. The shear crack proceeded

In Table 3, the amounts of subsidence on the top

toward top and bottom inside the BMS liner withsurface of the BMS liner under an overburden pressure

increasing the deformation. And it reached to the topof 107.8 kPa are 11 mm and 12mm for 400 mm in spansurface when a displacement gauge showed 15mm and(No. 2) and 500 mm in span (No.3), respectively. Thisto the bottom surface when that showed 18 mm.

suggests that the lager the span become, the lager theIn the case of No.1, under a applied pressure of 107.8

amount of subsidence before cracking become. In thekPa, the amount of subsidence of the BMS liner did not

beam theory, if the strength of the beam wasn’t

proceed over 4 mm and the BMS liner experienced noconsidered, the deflection at the center of the beam

cracks. Therefore the pressure was raised up to 156.8

becomes larger with increasing the length of span.

kPa. As the result, the value of the subsidence became 8

Therefore the beam theory will be applicable to themm. However the subsidence did not increase any more.

analysis of the trap-door tests.

The reason why the BMS liner did not experience aFigure 5 shows the relationship between the span andcrack is thought such that the bending stress and thethe applied pressure at the moment that the BMS liner

shear stress were smaller than the bending strength andjust has failed, however the results with the span of 300

shear strength of the compacted BMS. Their bending

mm under slow rate had no crack.

and shear stress are induced by the applied pressures

From Figure 5, in the deformation test with a fast rate

against the modeled BMS liner with a thickness of 100of 1 mm/min (This test had been conducted by mean ofmm and a span of 300 mm, that Shear/Span ratio isstress-controlled), it can be regarded that the applied

1.5(Deep beam).

pressure when the BMS liner just have experienced
some cracks becomes smaller as the span becomes

DISCUSSION

wider. In comparison with the applied pressure to theThe trap-door tests in this paper were carried outBMS liner with equal span length, it is found that theunder the condition of a slow rate of 1 mm/day tovalue for the slow rate tests are larger than that for theinvestigate the ability of BMS liner following thefast rate tests when the BMS liner just have

deformation of the foundation at that time. Table 3

experienced some cracks. This is thought that theshows these results, and also shows the results of a faststrengthoftheBMS

liner

becamelargebyrearrangement of the soil particles in the slow

This study was a part of the research results supporteddeformation.

by LSA, NPO in 2007. The authors would like toexpress my appreciation to all members (write below)
of Research Committee for Construction of the Landfill

Applied pressure at failure[kPa]

200

Foundation and Liners.

Fast rate test

Mr. H. Kano, Mr. T. Harada, Mr. Y. Yuge, Mr. K.

Slow rate test

Shibata, Mr. S. Matsuyama, Mr. H. Morizono, Mr. T.

150

Kouketsu, Mr. I. Norimatsu
They are also deeply thankful to Mr. Y. Shinozaki

100and Mr. T. Yoshinao at Utsunomiya University for theirconducting the trap-door tests.

50

REFERENCE
0200

300

400500Span [mm]600Figure 5. Relationship between the span and theoverburden pressure at failure

1) D. E. Daniel and R. M. Koerner (1995): Waste
Containment Facilities – Guidance for Construction,
Quality Assurance and Quality Control of Liner andCover System, ASCE Press, pp.61-62
2) S.C.Cheng, J.L.Larralde and J.P.Martin (1994),

SUMMARY

Hydraulic conductivity of compacted clayey soils

The main results obtained from this study are as

under distortion or elongation conditions, Hydraulicfollows.

Conductivity and Waste Contaminant Transport in(1) In the slow rate deformation tests, the BMS linerSoil, pp.266-283

has been mainly failed by the shear cracks.

3) B. V. S. Viswanadham and S. Senguputa (2005):(2) When the BMS liner was deformed under theDeformation Behaviour of Compacted Clay Liners

constant overburden pressure, the amount ofof Landfills in a Geocentrifuge, Proc. of the 10th

vertical subsidence at the center of the liner until

International Waste Management and Landfill

some cracks experience becomes larger withSymposium, CD-ROM No.367

increasing the span length.
(3) For the equal span length, the overburden pressures

4) S. Usami, K. Kudo, S. Imaizumi, H. Kato and K.
Shibata(2006):

Deformationperformanceofwhen the BMS liner just has failed in slow rate tests

bentonite mixed soil liner used to landfill andare larger than those of the fast rate tests.

proposal for landfill design, Proceedings of the 17th(4) Therefore it is thought that the landfill would be
able to design safety according to using the result
based on the fast rate deformation test.

Annual Meeting of the Japan Society of Waste
Management Experts, pp.935-937 (in Japanese)
5) H. Kato, S. Usami, S. Imaizumi, K. Kudo and S.
Matsuyama (2007): Experimental study and analysisACKNOWLEDGMENT

on deformation of bentonite mixed soil liner,Proceedings of the 11th International Landfill
Symposium, Sardinia, CD-ROM6) Y. Shinozaki, S. Imaizumi, T. Yoshinao and K. Kudo
(2007): Deformation tests of bentonite mixed soilliner with applied pressure, Proceedings of the 4th
Annual Meeting of Kanto Chapter of the Japanese
Geotechnical Society, pp.343-345