Experimental Evaluation of Consolidation Behavior of Double-Layer Soft Soil Ground

Double-layer grounds are characterized by one layer of soft soil on the top of another, which are frequently encountered in land reclamation projects in China. Consolidation behavior of the double-layer grounds is complicated compared with that of single-layer soil because of the complex drainage conditions that exist between two soil layers and the different consolidation properties of the two soils. The consolidation behavior of the double-layer ground becomes more complicated when it is subjected to a surcharge preloading. Therefore, it is necessary to understand the consolidation behavior of individual soils that make up the double-layer ground as well as the double-layer ground as a whole. In this article, double-layer specimens were prepared to simulate double-layer grounds, which include an upper layer clay with high plasticity and a lower layer clay with low plasticity. Consolidation tests were performed on both single-layer specimens and double-layer specimens using a modified consolidation test device. The influences of surcharge ratio and surcharge preloading duration on the consolidation behavior of double-layer ground, such as consolidation settlement and consolidation rates, were studied in addition to the influence of the thickness ratio (i.e., the ratio of the thickness of the upper layer of soil to the lower layer of soil). The experimental results show that a longer surcharge preloading duration could reduce the time needed to complete the rebound of the double-layer ground. The secondary consolidation settlement of double-layer ground can be reduced by increasing either the surcharge ratio or surcharge preloading duration. In addition, an increase in the thickness ratio could result in an increase in the primary consolidation settlement and a decrease in the consolidation rate. However, the effect of the thickness ratio on the consolidation settlement and the consolidation rate gradually decreased with the increase in the thickness ratio.