Small-scale micropiles to control heave on expansive clays

The main purpose of this study was to examine the effectiveness of using micropiles as a technique to control upward movement of lightweight structures over expansive soils. For this purpose, smooth and roughened steel laboratory small-scale micropiles surrounded by dense sand were inserted in predrilled holes of larger diameter made in highly expansive clay. The expansive clay was compacted in a steel box (50 cm × 50 cm × 35 cm) to a final height of 20 cm. Steel plates (25 cm × 25 cm × 1 cm) were used to model footings. The heads of the model micropiles were fastened to the steel plate. Footings with zero, one, two or four micropiles were prepared then the compacted clay in the laboratory box was flooded with water then upward movement of the model footings due to compacted clay swelling was monitored with time. The results showed that the percentage reduction in heave due to micropile reinforcement was larger for roughened micropiles and increased with increasing number and diameter of micropiles. The maximum measured percentage reduction in heave was 87·2% obtained when four 18 mm diameter roughened micropiles were used. A comparison between measured and predicted percentage reduction in heave using the proposed method of Nusier and Alawneh (Geotechnical and Geological Engineering Journal, 2004, 22, No. 1, 89–104) was made, and the results of the comparison showed acceptable agreement.