GROUND IMPROVEMENT BY DRY CONCRETE COLUMNS-Paper

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The paper describes the first use in Belarus of dry concrete columns to improve saturated, soft ground where conventional pile foundations are costly or difficult to construct. The method is intended to compact and drain the surrounding soil while accelerating consolidation.<br /><br />Columns are formed by pressing a closed-ended casing into the ground with a vibratory hammer. Dry concrete mix is placed in the casing, which is then withdrawn under vibration, compacting the mix. Columns are installed in two stages, with a sand cushion placed above them to distribute structural loads and help prevent soil loosening.<br /><br />Because established design methods were not available, the work’s effectiveness was assessed through static penetration and load tests at two sites. At Site A, columns improved soft loess soils beneath a proposed raft foundation. Soil toe resistance increased by an average of 3.5 times between columns and 1.7 times in underlying soils. Young’s modulus rose from 10.3 MPa to about 40 MPa. The improved raft foundation was estimated to cost 32% less than a driven-pile alternative.<br /><br />At Site B, where soft clay, organic soils, peat, and other weak layers extended to great depth, columns were used beneath a foundation slab. Penetration tests showed an average 2.5-fold increase in toe resistance; load tests indicated that Young’s modulus increased from about 8 MPa to 55.8 MPa. The foundation was estimated to cost 75% less than a bored-pile alternative.<br /><br />Overall, the results indicate that dry concrete columns can strengthen both the treated soils and underlying layers, with effects extending roughly three to seven column diameters from the column toes. The authors conclude that the technique can provide substantial cost savings, though further research is needed to develop design and concrete-mix selection methods.

Keywords

dry concrete columns

soil improvement

saturated soft ground

Belarus

vibratory hammer

ground consolidation

static penetration test

load test

raft foundation

cost savings