Soft clay soil improvement using stone columns and dynamic compaction techniques

الملخص EN

Soft clays are widely spread in Iraq particularly in its southern Mesopotamian plain.

As many sites within these regions may be used for vital projects ; an adequate solution has been found out to improve such clays using stone column and dynamic compaction methods.

For this purpose, the present paper has presented the laboratory measurements of the properties of such clays and their settlements at different applied stresses.

Thirteen soil model tests have been made, at 27 % water content and 9 kPa undrained shear strength, to examine their behaviors under loading .

The tested models include : (1) model for untreated soil ; (3) models for soil treated with stone columns (1,2 and 3 columns) with 30mm in diameter and 180mm length ; (9) models for soil treated with dynamic compaction using drop weights 2, 3 and 5kg at three different drop heights ( 500, 750, and 1000mm ).

For dynamic compaction, the behavior of soil stress- settlement reflects two stages for 2 and 3 kg drop weights with slow and rapid settlements respectively.

Whereas, three stages were identified using 5kg drop weight with slow, medium and quick settlements.

No considerable effect of drop height and no noticeable improvements have been indicated with soil model treated by dynamic compaction except for weight drop of 5kg but with less improvement ratio compared with stone columns model test.

Whereas, the behavior of stresssettlement using stone columns reflects three stages with slow, rapid and slow (again) settlements.

In comparison with untreated soil, the maximum cumulative settlement improvement ratios were 69 % and 178 % at applied stress of 30 kN / m2 for soil models treated with dynamic compaction ( 5kg drop weight ) and 3 stone columns respectively.