A combined ground-improvement method has recently been adopted for embankments on soft soil that involves the use of both deep mixed (DM) columns and prefabricated vertical drains (PVDs) to increase the bearing capacity and accelerate the consolidation of the soft soil. A well-instrumented embankment was constructed in a field using this ground-improvement method to verify its performance. Three- (3D) and two-dimensional (2D) finite-element analyses were conducted to evaluate the performance of an embankment constructed over soft soil improved by the DM columns and PVDs. In the 2D analysis, a plane-strain conversion method was used to simulate the 3D condition. The finite-element software ABAQUS was used for these analyses. The computed settlements, excess pore-water pressure, load transfer from the surrounding soil to the columns, and lateral displacements in both analyses are compared with the field data, and good agreement was found between the computed and measured data. The field and numerical results show that the DM columns enhanced the stability of the embankment over soft soil, whereas the PVDs accelerated consolidation of the soft soil.

Construction technology has a considerable impact on the bearing behavior of bridge pile foundations. Considering practical bridge engineering, this study examined the mechanical characteristics of rock-socketed bored piles under different pile-forming methods using a self-balanced load test and explored the postgrouting effect on the load capacity of the piles. The results indicated that the dry rotary drilling pile method was conducive to ensuring the bearing strength of rock-socketed bored piles in bridge foundations, whereas the mud rotary drilling pile method significantly reduced the shaft resistance of rock-socketed bored piles as well as the pile-end resistance. The mud rotary drilling pile method also increased the settlement from the negative impact of sediment and the softening of carbonaceous shale. The postgrouting technique can effectively enhance the unit-shaft and end resistance of the rock-socketed bored pile and reduce its settlement by approximately 42 and 100% bearing capacity increment compared with dry and mud rotary drilling piles, respectively. Under their respective ultimate loads, the settlements also decreased by 37.5 and 54.4%. The postgrouting technique had a tremendous impact on the proportion of the end resistance to the shaft resistance, markedly increasing the end resistance for mud rotary drilling piles. These results provide an important reference for the design and construction of rock-socketed bored piles with a large diameter and length in bridge foundations.