Experimental Investigation of Sand Seam Effects on Consolidation Behavior of Vertical Drain-Installed Soft Soils

Abstract

Thin-layered sand seam in soft deposits can be formed artificially or naturally. It affects significantly the consolidation behavior of subsoil. To investigate the consolidation settlement of soft deposits with thin-layered sand seam, a series of consolidation tests of the layered soft soil-sand systems improved by prefabricated vertical drain (PVDs) is performed. To estimate the effects of thin sand layers, three cases of consolidation tests are carried out as follows: in Case 1, the PVD-soil column is tested without thin sand layer; one and two thin sand layers were placed between the soft soil layers in Case 2 and Case 3, respectively. The experimental results indicate that the rate of consolidation settlement of PVD-installed soft deposit with the thin sand layers is faster than that of the case without sand seam, because the thin sand layers can provide a shorter drainage path for consolidation of the soft soil. As expected, this result is obviously appeared in Case 3. However, the final settlement of PVD-installed soft soil with thin sand layers is smaller than that of the case without sand seam. It can be seen that the existence of thin sand layers interbedded with soft soil layer can improve the strength of soft soil.