July_1971 — Page 43

Vibratory compaction

on the Pedu Dam project

COMPACTION by vibration is now commonly accepted as an effective and economical compaction method which can be applied for compacting almost all kinds of soil, stabilized materials and asphalt and concrete mixes.

In the early stages of their develop ment vibratory compaction machines such as vibrating rollers and plate com- pactors had a rather low dead weight, and their compaction forces were much lower than those generated by the equipment in use today. Never theless, the use of these light-weight compactors resulted in a considerable increase of the depth of compaction, in particular when compacting non- cohesive soils; and it was also found that the required densities were reach- ed with considerably fewer passes than hitherto possible with conventional static compactors.

by Ing. R. Prang and K. H. Zeidler, Hameln, West Germany

is largely dependent on the centrifugal force it must be as large as possible for compacting cohesive materials and re- latively small for the compaction of non-cohesive soils. The only exception to this rule is the compaction of coarse rockfill which can only be effectively compacted with very high dynamic forces and large amplitudes.

Large amplitudes can, however, only be achieved if the vibrator pro- duces a very high centrifugal force. The kind of vibration that is required for the thorough compaction of both coarse rockfill and cohesive soils can best be described as 'tamping vibra- tion' or 'impact vibration'

Comprehensive tests

On the Pedu Dam, Muda River Ir- rigation project in Malaysia, the con-

No.

Attempts to use these light-weight Pad No. Embankment compactors for compacting cohesive soils inevitably failed because the installed dynamic forces and the ap- plied load were insufficient. This may well account for the fact that some highway engineers are still reluctant to employ vibration compaction equip- ment on cohesive soils. However, the much heavier and more powerful vibratory compactors available today can effectively compact both cohesive soils and rockfill placed in thick lifts.

The compaction characteristics of vibratory compactors are mainly deter- mined by the dynamic force generated by the installed vibration system, the applied load, the vibration frequency and amplitude. Experience has shown that non-cohesive soils can best be compacted with vibration frequencies between 1800 and 3000 cycles/min. or even higher whereas cohesive soils can only be adequately compacted with considerably lower frequencies 1200 to 1800 cycles/min.

Rock Grade

tractor made no proposals concerning the placing and compaction of the rockfill.

It was therefore decided to do fairly comprehensive tests on different grades of rock with the intention of discovering the effect of the thickness of lift, amount and method of applica- tion of sluicing water, the number of passes of the roller and method of placing the rockfill.

The majority of the work was carri- ed out between April 6 and June 2, 1967. Three 80 ft. x 30 ft. foundation pads of 2 ft. nominal thickness were formed by compacting zone 1 rockfill in 9 in. to 12 in. layers with the ABG Model SAW 180 vibrating roller pulled by a Komatsu D 80 bulldozer. On top of each foundation pad, test embank- ments were formed as below:

Embankment Compacted dry Levels taken layer Depth or after Variation sluicing

A

1

B (Zone 2) 2' to 6'

Dry (May 12, 14, 15, 16).

B

after these number of roller passes

10, 12, 14, 16,

18, 20 (passes

0-8 taken

with faulty level)

0, 2, 4, 6, 8,

10, 12, 14, 16, 18

2

B (Zone 2) 2.67' to

6.26'

After Sluicing (May 28 & 29).

1

A (Zone 3) 1.52' to

6.29'

Dry

(May 14, 15, 16, 17).

0, 2, 4, 6.8,

10, 12, 14,

16, 18, 20,

22

2

A (Zone 3) 3.14' to

7.07'

After Sluicing

0, 2, 4, 6, 8, 10

C

1

of

B (Zone 2). 1.66' to

6.72'

Dry (May 19 & 20)

0, 2, 4, 6, 8, 10, 12, and

14.

With regard to the amplitude which

Far East BUILDER, July 1971

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