Although lignin improves the strength and modulus of soil, it is less active when unmodified, and it exhibits more limited effects on soils in combination with traditional Ca-based curing agents. Lignin-solidified soil also exhibits deficiencies, such as poor durability under dry–wet cycling conditions, and thus, the amelioration effect is limited. This study investigated the enhancement of cement-solidified soil using hydroxylated lignin with sodium silicate and quicklime used as activators to improve the engineering performance and durability of the treated soil. Using respective cement, sodium silicate, quicklime, and lignin contents of 7%, 0.4%, 0.2%, and 0.2% with respect to the dry mass of the slag soil, the strength and cohesion of the composite-solidified soil were 1.5 times those of cement-solidified soil, whereas the internal friction angle increased by 5.1°. At a solidifying age of 14 d, the penetration resistance almost doubled, indicating a significant improvement in the bearing capacity of the soil. The results suggest that modified lignin-based admixtures may significantly enhance the performance of cement-solidified soil. The cement curing admixture used in this study provides theoretical and technological support for curing agent preparation and the utilization of slag.

Exogenous nitrogen input triggers sediment bacterial reassembly driving self-purification of water.

In this study, MgO as an environmentally friendly silt-solidifying material was first mixed with silt and then carbonized by injection with CO₂. The strength and contaminant leaching characteristics of the MgO-solidified silt were studied using unconfined compressive strength and toxicity leaching tests, and the results were compared with those of cement-solidified silt. The unconfined compressive strength of the silt reached 111 kPa with 9% MgO content and a 14 d curing time. The CO₂ injection further increased the unconfined compressive strength of the MgO-solidified silt by approximately 25%: the values for MgO-solidified silts without and with a CO₂ injection were approximately 60% and 80%, respectively, of those of the cement-solidified silts with the same additive additions. The leaching concentrations of nutrient salts and heavy metal pollutants in the silt decreased with increased MgO content. Compared with the dredged silt, MgO solidification with carbonization reduced the leaching of total nitrogen and total phosphorus by more than 10% and 50%, respectively: these values were approximately 5% points higher than those of cement-solidified silt. Of the heavy metals, the leaching concentration of Ni was reduced the most. This study provides a theoretical basis and technical support for low-carbon treatment and green resource utilization of dredging silt.

This paper presents an analytical model for one-dimensional consolidation analysis of multi-layered unsaturated soils under depth-dependent initial conditions. The general solutions are derived explicitly using the Laplace transform. By combining these general solutions with interfacial continuity conditions between layers and the boundary conditions, the reduced-order system is solved via the Euler method to obtain analytical solutions in the Laplace domain. Numerical inversion of the Laplace transform is then performed using Crump’s method to yield the final analytical solutions in the time domain. The model incorporates initial conditions that account for both uniform and linear distributions of initial excess pore pressure within the soil stratum. The proposed solution is verified by reducing it to degenerated cases (e.g., uniform initial pressure) and comparing it with existing analytical solutions, showing excellent agreement. This confirms the model’s correctness and demonstrates its generalization to multi-layered systems with depth-dependent initial conditions. Focusing on a double-layered unsaturated soil system, the one-dimensional consolidation characteristics under depth-dependent initial conditions are investigated by varying the physical parameters of individual layers. The proposed solution can serve as a theoretical reference for the consolidation analysis of multi-layered unsaturated soils with depth-dependent initial conditions.