Effectiveness of sand compaction piles in improving soil bed formed of alluvial deposites of Bangladesh

Abstract

The study was mainly concerned with the effectiveness of Sand Compaction Pile (SCP) in improving the density of alluvial soil deposits of Bangladesh. Miniature sand compaction pile device, miniature dynamic cone penetrometer (DCP), soil tank and sand shower bowl were designed and fabricated for the purpose of the study. Alluvial sandy soil samples were collected from two selected locations of Bangladesh. Soil beds were formed in the soil tank by pouring sand shower from different heights using the specially prepared sand shower bowl so as to achieve sand beds of various densities. The density of soil bed, thus prepared, was measured using density pots and dynamic cone penetration readings were taken to calibrate the soil bed density against cone penetration. For the purpose of investigating the effectiveness of sand compaction piles in improving the density of loose soil deposits, a sand bed of loose density were formed by sand raining from pre-calibrated height. Initial density of the soil bed was measured using the miniature dynamic cone penetrometer. Sand compaction piles were installed in the soil bed using the miniature sand compaction pile device where a hole was formed in the soil bed by displacing the soil in the lateral direction, and pouring sand in the holes and densified. Square and triangular arrangements of sand compaction piles were used with various spacing. The density of the sand bed with installed sand compaction pile was measured at locations in between the sand piles using the miniature DCP apparatus following the principles outlined in ASTM D6951-09. A term penetration index for the DCP test value was introduced to indicate the density of soil bed. The data of DCP value and field density thus measured at various depths were analyzed to obtain correlation parameters between dynamic cone resistance (Penetration Index) and relative density of sand. This correlation was used to determine the relative density of improved soil bed due to sand compaction piles of various spacing and arrangements. Results indicated that a triangular arrangement of SCP with a spacing of 2.5 times the diameter of the pile would the most efficient arrangement for improvement of soil bed formed of alluvial soil of Bangladesh. The study yielded useful correlation equations to estimate density from DCP values, and also between SCP spacing and density. This is perhaps one of the noble studies that attempt to replace the field study of huge SCP construction replaced by physical models in the laboratory.