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EARTH PRESSURE DUE TO VIBRATORY

COMPACTION IN RETAINING WALL

EFFECTS ON HORIZONTAL EARTH PRESSURE ANDVERTICLE OVERBURDEN PRESSURE

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Introduction

This study’s objective is to determine the effect of horizontal and vertical earth pressure due to soil vibratory compaction against a nonyielding retaining wall

Compaction is one of the oldest methods for improving existing soil. Hand tampers and vibratory equipment are used to compact soil.

By applying backfill soil filling and vibratory compaction in five layers, a relative density of soil increased by 75%.

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For a compacted backfill, the vertical overburden pressure can also be properly estimated with the traditional equation σv = γ * z

Lateral earth pressure at the top of the wall is almost same as passive Rankine pressure.

The objective of the compaction of soil is to improve the engineering properties of the soil such as bearing capacity, density of backfill soil

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MODEL RETAINING WALL 1.5 m long 1.5 m wide 1.6 m high 45 mm thick

•Model wall is actually the front side of the reinforced steel box•24, 20 mm thick steel columns were welded to reduce lateral displacement during loading

Backfill Characteristics:- Air Dry Ottawa Sand Gs=2.65 , D60=0.39 mm; D10=0.26 emax=0.76, emin=0.50

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Soil Bin:- fabricated by steel plate The bottom of the soil bin was covered with

a layer of antislip frictional material to reduce the friction between soil and wall

15 transducer were arranged at centre of model wall along the wall height to measure horizontal earth pressure (σh) and 15 transducer were buried behind the model wall to measure vertical stress in the backfill.

Data Acquisition system:- For collecting considerable amount of data

collection, dynamic strain amplifier was used for transfer data to the computer.

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Test Result

Due to the compaction of the soil in 5 layers, the settlement of soil lift occurs after compaction.

From the experiment settlement of the soil lift was approximately 22 mm per 300 mm thickness of soil lift which was about 6.8% of the original lift thickness (range 3-8% generally)

To minimize the shear stress between backfill and sidewall by creating a lubrication layer between the side wall and the soil.

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Stresses in loose sand

It can be seen that the vertical earth pressure (σv) increases linearly with increasing depth (z) from the top of the backfill.

From traditional equation σv=γ z = 15.5 *1.5 σv =23.25 KN/m^2

Horizontal earth pressure at rest = σv(1-sin φ)

= 23.25(1-sin 30.7) =11.38 KN/m^2

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Stresses in compacted sand

Due to compaction of soil overburden pressure( σv )in compacted sand is slightly greater because it has higher unit weight (γ) of soil.

σv=γ z = 16.6 *1.5=24.25 KN/m^2

It is concluded that there is no much impact on vertical earth pressure due to soil compaction

The lateral earth pressure measured near the top of the backfill was almost same to the passive earth pressure estimated with Rankine theory

Pp=1/2 γKpH^2 where Kp=tan^2(45+φ/2) Kp=tan^2(45+40.8/2) Kp=4.77

Pp=0.5*16.6*4.77*1.5^2Pp=89.07 KN/m

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Soil behavior in compacted backfill

When compaction is applied on the surface of the first layer(0.3 m thick), passive zone is compressed laterally and after compacting three layer, passive zone goes to a higher level so the compaction influenced zone rises with rising compaction surface.

There is no horizontal stress in soil element (zone III) next to the wall because of the relatively rigid model wall so horizontal stress below the passive Rankine zone is almost same to the horizontal earth pressure at rest by Jaky’s equation.

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Conclusion In loose backfill vertical overburden pressure can be

estimated by traditional equation (σv=γ z) and horizontal earth pressure can be estimated by Jaky’s equation

For compacted dense backfill, vertical pressure obtain with equation σv=γ and lateral earth pressure measured near the top of wall was almost same to the passive earth pressure estimated by Rankine theory

The compaction influenced zone rise with the rising compaction surface and below the compaction influenced zone, measured horizontal stress is almost same to the earth pressure at rest condition

Compaction induced dynamic earth pressure can be reduced by installing cushion material such as rubber tire strips.

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References T-J Chen and Yung-Shaw Fang (2008) ,”Earth

pressure due to vibratory compaction “,Journal of Geotechnical and Geoenvironmental Engineering,Vol. 134,No. 4,April 1,.@ASCE,ISSN 1090-0241/2008/4-437-444

Massarsch K.Rainer and Fellenius,Benqt.H(2002) ,“ Vibratory Compaction of coarse grained soils “ ,Canadian Geotech Journal 39(3)-695-709,page 695

H.S. Roh and H.S. Lee(2006), Korea Highway Corporation, SeongNam, Korea

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Questions??