Lime stabilization is a traditional method for improving foundation soils, and it also has potential applications for embankments and earth structures. In this study, several experimental techniques, including scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), and nuclear magnetic resonance (NMR), were used to provide a clear picture of the microstructural evolution of a lime-stabilized loess (LSL) from China. SEM micrographs were used not only to qualitatively highlight the dual porosity nature of the material, but also to provide quantitative information using Image-Pro Plus (IPP) 6.0 software. As the lime content increases, the pore area ratio decreases, the shape of the macropores and mesopores flattens, and the pore angle distribution becomes more uniform. The FTIR results show that the functional group strength of the LSL samples first increases and then decreases with increase in lime content, while the pore volume continues to decrease. A non-monotonic evolution of the strength with the lime content is then expected, as also confirmed by unconfined compression tests performed at different lime contents and curing times: at low lime contents, the reduction of the pore volume and the increase in the functional group strength imply an increase in the strength; at high lime contents, the competing effects of the reduction of the pore volume and the increase in the functional group strength lead to an overall decrease in the strength with the lime content. Then, as an intermediate step toward further quantitative predictions of the hydromechanical behavior of LSL, a pore size distribution model inspired by the proposal of Della Vecchia et al. (Int J Numer Anal Meth Geomech 39:702-723, 2015) was developed and used to reproduce NMR experimental data. The pore size distribution model proved to be able to reproduce the cumulative porosity curves for the whole range of lime content and curing time studied, with only four parameters kept constant for all the simulations. The predictive capabilities of the model were also confirmed by simulating experimental data from recent literature.

Loess has poor engineering performance and needs to be improved for engineering applications by adding a large amount of lime or cement, which is not consistent with the goal of carbon peaking and carbon neutrality. In this study, nano-SiO2 (NS) and nano-MgO (NM) were applied to improve the engineering performance of lowdosage lime/cement- stabilized loess. The improvement mechanisms of each binder on loess were analyzed by X-ray diffraction (XRD) and scanning electron microscopy-energy dispersive spectrometer (SEM-EDS) tests. The impact of binder dosage and curing time (T) on unconfined compressive strength (UCS), resilient moduli (MR), California bearing ratio (CBR), internal friction angle (phi), cohesion (c), and compression coefficient (a1-2) of each stabilized loess were also explored by conducting a range of laboratory experiments. The results show that the addition of NS did not result in the formation of new substances. However, the formation of MH was noted with the addition of NM. The combination of lime and NS can significantly enhance the UCS, CBR, MR, and c of the stabilized loess, followed by the combination of cement and NS. With the increasing NM content, the above mechanical indices first increased and then decreased for the stabilized loess. Both the binder content and type caused a lesser impact on the phi and a1-2 than on other mechanical indices. Moreover, the mix ratio and feasibility of each stabilized loess applied in various engineering fields were analyzed based on relevant standards and the construction requirements of lime and cement. Finally, estimation models were established for the above mechanical indices of lime-NS stabilized loess, which can provide a reference for engineering design and quality control.

Determining a rational mix ratio for lime -fly ash -stabilized loess (LFSL) can achieve multiple benefits of economy, environmental protection, and engineering quality improvement. This research was designed to optimize the mix ratios of LFSL applied in the pavement structure, subgrade, slopes, and foundations by conducting the unconfined compressive strength ( UCS ) test, California bearing ratio ( CBR ) test, resilient moduli ( M R ) test, triaxial test and uniaxial consolidation test on LFSL and lime -stabilized loess (LSL). Combined with the initial consumption of lime (ICL) test result and relevant specifications, the optimized mix ratios are as follows: 2% lime + 11.82% fly ash and 2% lime + 3.95% fly ash can reach the strength requirement of road base and subbase, respectively; 2% lime + 3.84% fly ash in building foundations and subgrade and 2% lime + 3.55% fly ash in slopes can reach the equal improvement effect of the LSL with 8% lime content. Three -factor comprehensive models were established and fitted in well with the experimental results of the LFSL with 2% lime content. Moreover, the development of correlations between UCS and other mechanical indices offers a shortcut for engineering property estimation. Finally, based on the abundant literature on LSL, another approach to estimating engineering quality was proposed for the LFSL with 2% lime content, which enhances the universality and practicability of the estimation models further.

The cement composite calcium lignosulfonate is used to enhance the mechanical properties and the freeze-thaw resistance of loess. Based on an unconfined compressive test under different freeze-thaw cycles, the influence of cement dosage, curing age, and freeze-thaw cycles on compressive strength are discussed. The results indicate that the strength of loess can increase by up to 13 times, and the loss of strength is reduced from 72% to 28% under the reinforcement of cement dosage and curing age. The loss of strength is mainly concentrated in the initial 5 freeze-thaw cycles, and the structure gradually stabilizes after 10 freeze-thaw cycles. In addition, according to the X-ray diffraction test, it is found that the stabilized loess exhibits a comparatively more stable mineral composition. The scanning electron microscope results reveal that hydration products enveloped the soil particles, forming a mesh structure that strengthens the connection between the soil particles. The freeze-thaw damage makes the small and medium pores turn into large pores in loess, while the stabilized loess changes micro and small pores into small and medium pores, with no large pores found. It is feasible to improve loess with the cement composite calcium lignosulfonate, which can provide references for the reinforcement treatment of loess.