This paper presents an extensive comparative analysis of the experimental results of chemical stabilisation of clayey soil in laboratory conditions by comparing the effects of adding conventional stabilisers (lime, cement binder), stabilisers that can be considered as waste material (fly ash, rock flour), as well as alternative chloride-based materials (ferric chloride, calcium chloride, potassium chloride) on the geomechanical properties of the soil. With the aim of determining the stabiliser optimal content in the mixture with the soil, in the first part of the research, the effects of stabilisation of clayey soil of medium plasticity using the considered stabilisers with different percentage share on the change in uniaxial compressive strength (UCS) and pH value of the soil at different time intervals after the treatment were analysed. In the second part of the research, additional tests were conducted on soil samples with optimal content for each of the considered stabilisers by monitoring changes in the physical and mechanical properties of the soil. These include Atterberg's limits (liquid limit and plasticity limit), modulus of compressibility in the oedometer, California bearing ratio (CBR), and swelling potential at different time intervals after the chemical treatment to determine the durability of stabilisation effects. The results of the conducted research reveal that each of the conventional, waste, and alternative materials considered as chemical stabilisers contributes to the improvement of the geomechanical properties of the clayey soil, primarily in terms of increasing the bearing capacity and reducing the swelling of the treated soil.

To investigate the effect of fluid -solid coupling on the seismic performance of underground structures in watersaturated soil, a comparison study is conducted in this paper on three-dimensional (3D) nonlinear seismic behavior of a 3 -story 3 -bay subway station obtained using two different finite element methods (FEM), i.e., the generally used simplified method with equivalent single-phase soil model and a newly developed 3D numerical approach capable of considering the dynamic behavior of saturated two-phase media. A 3D user -defined element embedded in ABAQUS is first introduced to simulate saturated soil's dynamic fluid -solid coupling effect. Then, more essential demonstrations are presented for establishing and validating the two FEM. Based on the two methods with and without incorporating fluid -solid interaction, 3D nonlinear seismic response analysis is performed on the subway station considering three different input seismic waves. Discussions are conducted in terms of accelerations, lateral displacements, inter -story drift ratios, rotation of columns, damage characteristics, and internal forces, based on which the limitations of the simplified method are quantitatively interpreted. The results show that neglecting the fluid -solid coupling effect can bring about conservative evaluations of the seismic behavior of underground structures in saturated soil. The effect of fluid -solid coupling on the seismic performance of underground structures is quite sensitive to the peak ground acceleration. It is significant to consider the fluid -solid coupling effect during the performance -based seismic design of underground structures enclosed in saturated soil to gain realistic seismic responses, especially for those subjected to major earthquakes.