Dynamic consolidation is widely applied in the consolidation of soft soil foundation, though there is no in-depth subdivision research on the mechanism of dynamic consolidation of coastal soft soil foundation, and there is no independent, complete, theoretical system to support engineering practice. The effects of dynamic consolidation replacement rates on the shear strength of coastal soft soil were studied by the dynamic consolidation replacement undrained shear (CU) tests. CU tests were conducted for each set of samples under four confining pressures of 50 kPa, 100 kPa, 200 kPa, and 300 kPa, stress-strain curves and effective stress paths were obtained, and then shear strength parameters at different displacement rates were determined: effective cohesion and effective internal friction angle. The effective cohesion decreases, while the effective internal friction angle increases, with the increment of displacement rate. The shear strength of coastal composite soil is improved with the rising displacement rate, and the effects of multi-pile displacement on the shear strength of coastal soft soil are more significant at the same displacement rate. There is a quantitative power function relationship between the pile-soil interaction coefficient and displacement rate of coastal composite soil. Based on the test results, a modified formula for the shear strength parameters of dynamic tamper-replaced coastal soft soil is proposed.

Bottom ash (BA) is a byproduct produced during coal combustion and can be utilized in mortar as a column material to conserve natural resources and promote sustainable ground stabilization. In this paper, the load-carrying capacity performance of the embankment resting on cement bottom ash columns (CBAC) improved ground was examined. Physical model tests and numerical analysis were conducted for the soft soil improved with three columns spacing to diameter ratios (s/d) of 1.8, 2.4, and 3.6 and two columns length to diameter ratios (L/d) of 6 and 8. Three earth pressure transducers, load cell, and pore water pressure transducer were employed to measure the applied vertical stress on the bottom and top of the column and surrounding clay, embankment surface, and excess pore water pressure (u '), respectively. The findings obtained from both physical and numerical models demonstrated that ultimate bearing capacity (qult) increased by reducing the s/d and increasing the L/d values. The qult increased by almost 1.15, 1.39, 1.70 times and 1.18, 1.44, and 1.77 times as compared to the unimproved soil for the s/d of 3.6, 2.4, and 1.8 with L/d values of 6 and 8, respectively. The maximum improvement was achieved for the model with CBAC having L/d of 8 and s/d of 1.8. In addition, a mathematical equation with R2 of 0.999 was established for the determination of the predicted qult. The results of this paper can lead to the usage of BA as a green material in the column for ground stabilization.