Field and laboratory experience with the use of strip drains in organic soils

The results of field and laboratory investigations performed on two test sites located on organic soils in northwestern Poland are presented. Comprehensive investigations comprising observations at four test embankments and a laboratory investigation were carried out to study the influence of vertical drains on the consolidation process in organic subsoil and the behaviour of Geodrains-type strip drains in organic soils. It was shown that vertical strip drains may effectively improve the bearing capacity of amorphous peat and gyttja for stage-constructed embankments. However, it has been observed that there is a significant decrease in discharge capacity of Geodrains during embankment construction, depending on the type of drain filters (paper or polyester). Nevertheless, the vertical drain effectiveness was found to be quite satisfactory because the observed decrease of discharge capacity has practically no influence on consolidation rate. It was also detected that the buckling effect, probably owing to large horizontal displacements, does not significantly affect the discharge capacity of drains. Moreover, it is shown that there is a significant difference in pore-pressure distribution under embankments with and without vertical drains. As a result of the vertical drain installation under part of the slopes, a significant decrease in the horizontal displacements took place. Key words : consolidation, soil improvement, organic soils, vertical drains, field and laboratory tests.