To investigate the coupled time effects of root reinforcement and wet-dry deterioration in herbaceous plant-loess composites, as well as their microscopic mechanisms, this study focused on alfalfa root-loess composites at different growth stages cultivated under controlled conditions. The research included measuring root morphological parameters, conducting wet-dry cycling tests, and performing triaxial compression tests and microscopic analyses (CT scanning and nuclear magnetic resonance) on both bare loess and root-loess composites under various wet-dry cycling conditions. By obtaining shear strength parameters and microstructural indices, the study analyzed the temporal evolution of the shear strength and microstructural characteristics of root-loess composites under wet-dry cycling. The findings indicated that the alfalfa root-loess composite effective cohesion was significantly higher than that of the plain soil in the same growth stage. The alfalfa root-loess composite effective cohesion increased during the growth stage in the same dry-wet cycles. The alfalfa root-loess composite effective cohesion in the same growth stage was negatively correlated with the number of dry-wet cycles. The fatigue damage of the soil's microstructure (pore coarsening, cement hydrolysis, and crack development) increased continuously with the number of dry-wet cycles. However, due to the difference in mechanical properties between roots and the soil, the root-soil composite prevented the deterioration of the soil matrix strength by the dry-wet cycles. As the herbaceous plants grow, the time effect observed in the shear strength of the root-soil composite under the action of dry-wet cycles is the result of the interaction and dynamic coordination between the soil-stabilizing function of the herbaceous plant roots and the deterioration caused by drywet cycles.

Liquefaction behaviors of sand deposits with impervious stratum are quite different from that of homogeneous geological conditions. However, the micro- liquefaction behaviors of the interlayered deposits have been infrequently documented. This study introduces a novel experimental methodology aimed at examining the influence of silt interlayer on the liquefaction mechanisms of sand deposits from both macro and micro perspectives. In the experiments, the Excess Pore Water Pressure (EPWP) was analyzed in conjunction with recorded micro liquefaction images. The migration mechanism of fine sand particles beneath the silt interlayer was revealed. The existence of low permeability interlayer leads to prolonged retention of EPWP beneath the silt interlayer. Substantially, the water film on the base of the interlayer is demonstrated to be the mixture of pore water and silt particles flowing with high velocity under seismic motions, thereby resulting in significant strain localization. An agminated zone of loose fine sand particles is usually generated beneath the silt interlayer after the dissipation of EPWP.

Calcium carbide slag (CCS), phosphogypsum (PG), and red mud (RM), three types of industrial solid wastes, were employed to improve tunnel muck for assessing the feasibility of their reuse. A series of indoor tests were conducted to investigate the effects of their contents on the physical and mechanical properties of the improved tunnel muck. Microscopic tests were also conducted to reveal the improvement and interaction mechanisms involved. Results indicate that the incorporation of CCS, PG, and RM can significantly improve and enhance the physical and mechanical properties of tunnel muck. The improved tunnel muck containing 2% PG and 6% RM shows higher early strengths as CCS content exceeds 4%. However, after curing for more than 14 days, the unconfined compressive strength (UCS) of the tunnel muck with 4% PG and 4% RM is the maximum regardless of the CCS content. Microscopic analysis shows that reactive substances in industrial solid waste react chemically with soil components, exchanging ions and forming cementitious products such as calcium hydroxide, calcium silicate hydrate (C-S-H), calcium aluminosilicate hydrate (C-A-S-H), and ettringite (AFt). They bind, fill, and encapsulate soil particles, compacting the soil and significantly enhancing the physical and mechanical properties of tunnel muck. Moreover, there is a notable mutual synergy between PG and RM, primarily attributed to their acid-base neutralization and the complementary action of reactive ions. The improved tunnel muck containing 4% CCS, 4% PG, and 4% RM demonstrates the highest enhancement efficiency.

On December 18, 2023, the M S 6.2 Jishishan earthquake triggered a large-scale liquefaction disaster of loess sites in Jintian and Caotan villages, Zhongchuan town, Minhe County, Haidong City, Qinghai Province. To clarify the micro-mechanism of the liquefaction disaster, the Q3 Malan loess layer of the disaster site and its overlying red silty clay layer samples were selected and quantitatively analyzed for the differences in physical properties, structure, microstructural parameters, and mineral compositions. Based on the discrepancy results, the micro-mechanisms between loess microstructure and macro-mechanical properties of soil and liquefaction disaster were investigated. The research shows that compared with red silty clay, the dynamic index of loess corresponding to the physical indices of Zhongchuan loess obviously exceeds the critical threshold of liquefaction under actual seismic intensity. Additionally, its pore structure is dominated by point contact and weakly cemented overhead macropore structure, and its quantitative pore microstructure parameters and mineral composition show significant liquefaction potential. The comprehensive analysis of the liquefaction mechanism shows that the rapid deformation of the soil skeleton and the destruction of the cementation and contact system of the water-sensitive minerals under seismic loading and hydraulic force lead to the collapse of the overhead macropores, the damage of structural strength, the increase of the complex pore channels, the rapid accumulation of pore water pressure, and the reduction of the effective stress, which leads to the liquefaction of the loess.

Sulphoaluminate cement (SAC) is considered a low-carbon and energy-saving cementitious material, compared with ordinary Portland cement. However, the stabilization efficiency and improvement measures of SAC for dredged sediment (DS) are still unclear. This study used SAC as stabilizer for DS with high water content, and nanoparticles including nano-SiO2 (NS), nano-MgO (NM) and nanoAl2O3 (NA) were incorporated as nano-modifiers. Unconfined compressive strength (UCS) tests were carried out to evaluate the strength development of SAC-stabilized DS (SDS) and nano-modified SDS considering multiple influencing factors. Furthermore, the micro- mechanisms characterizing the strength development of SDS and nano-modified SDS were clarified and discussed based on X-ray diffraction (XRD) and scanning electron microscopy (SEM) tests. The results present that increasing SAC content or decreasing water content can obviously enhance the strength gaining of SDS, while the strength reduction also occurred. Incorporating suitable nanoparticles could significantly improve the strength gaining and simultaneously avoid the strength reduction of SDS. The optimum content of single NS, NM and NA was respectively 4 %, 6 % and 6 %. Composite nanoparticles containing two types of nanoparticles also exhibit positive effect on the strength gaining of SDS, and the optimum mass ratios of NS-NM, NS-NA and NM-NA were respectively 3:7, 1:9 and 5:5. By comparison, adding 6 % NA to SDS achieved the highest strength gaining. The hydration product ettringite was mainly responsible for the strength development of SDS and nano-modified SDS, and incorporating nanoparticles especially NA contributed to the formation of a tighter structure with stronger cementation inside nano-modified SDS. A conceptual model was proposed to characterize the micro-mechanism of strength development in nano-modified SDS. (c) 2024 Production and hosting by Elsevier B.V. on behalf of The Japanese Geotechnical Society. This is an open access article under the CC BY- NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).

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.

Geocell has a confinement effect, limiting the deformation of soil and enhancing the strength of reinforced soil, and has a wide range of application prospects in traffic transportation subgrade engineering. To investigate the confinement effect of geocell on the mechanical characteristics of reinforced sand subgrade, this paper analyzes the macro-mechanical properties of reinforced sand subgrade using triaxial tests, investigates the micro- reinforcement mechanism employing discrete element method (DEM)-based simulations. The potential macro- -micro linkages are studied. The experimental results revealed that the volumetric strain of the geocellreinforced samples increased with the material's elastic modulus, exhibiting a shear shrinkage phenomenon. The deformation pattern of the reinforced samples presented segmental deformation, which differed from that of the unreinforced sand samples. The geocell enhanced the cohesion intercept of the sand samples while having a minimal impact on friction angle. Through the analysis of numerical simulation results, it was found that the geocell constrained the displacement of the soil particles, altering the shear band development trend of the sample and resulting in segmental deformation. The geocell facilitated the concentration of force chains, enhancing their stability and resulting in improving the strength in the macro. Additionally, it was observed that the confinement effect of the geocell significantly reduced the fabric and force anisotropy of the granular soil, promoting consistent vertical alignment of force chains. This, in turn, enhanced the vertical force transmission capacity of the sample, explaining the micro-mechanism by which the confinement effect of the geocell increases the peak shear strength of the samples.

Nowadays, biopolymer stabilization as a promising eco-friendly approach in soft ground improvement has attracted wide attentions. However, the feasibility of using biopolymer as a green additive of cementstabilized dredged sediment (CDS) with high water content is still unknown. In this study, guar gum (GG) and xanthan gum (XG) were adopted as typical biopolymers, and a series of unconfined compressive strength (UCS), splitting tensile strength (STS) and scanning electron microscopy (SEM) tests were performed to evaluate the mechanical and microstructural properties of XG- and GG-modified CDSs considering several factors including biopolymer modification, binder-soil ratio and water-solid ratio. Furthermore, the micro-mechanisms revealing the evolutions of mechanical properties of biopolymermodified CDS were analyzed. The results indicate that the addition of XG can effectively improve the strength of CDS, while the GG has a side effect. The XG content of 9% was recommended, which can improve the 7 d- and 28 d-UCSs by 196% and 51.8%, together with the 7 d- and 28 d-STSs by 118.3% and 42.2%, respectively. Increasing the binder-soil ratio or decreasing the water-solid ratio significantly improved the strength gaining but aggravated the brittleness characteristics of CDS. Adding XG to CDS contributed to the formation of microstructure with more compactness and higher cementation degrees of ordinary Portland cement (OPC)-XG-stabilized DS (CXDS). The micro-mechanism models revealing the interactions of multiple media including OPC cementation, biopolymer film bonding and bridging effects inside CXDS were proposed. The key findings confirm the feasibility of XG modification as a green and high-efficiency mean for improving the mechanical properties of CDS. (c) 2024 Institute of Rock and Soil Mechanics, Chinese Academy of Sciences. Production and hosting by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/ licenses/by-nc-nd/4.0/).

This study aims to assess the effectiveness of an industrial residue-based soil stabilizer (GDP) and recycled fine aggregate (RFA) in enhancing the properties of soft clay. The GDP is composed of ground granulated blast furnace slag (GGBS), desulfurized gypsum (DG), and Portland cement (PC). The optimal formula for GDP and the appropriate amount of RFA needed to reinforce the soft clay were determined through unconfined compressive strength (UCS) testing. The microscopic characteristics and reinforcement mechanism of the GDP-RFA-reinforced soft clay were then analyzed using X-ray diffraction (XRD), Fourier transform infrared (FTIR), thermogravimetry (TG), and scanning electron microscopy (SEM) techniques. The effectiveness of utilizing GDP and RFA as reinforcement additives in soft clay ground was also validated through field testing. The experiments showed that using GDP instead of cement significantly increased the strength of soft clay, with the optimal mass ratio of GGBS, DG, and PC in GDP being 6:1:3. The strength of the GDP-reinforced sample initially increased and then decreased as the RFA content increased, reaching its peak at a RFA content of 30 %. The formation of C-S-H and C-A-H gels, along with AFt crystals, in the GDP-RFA-reinforced sample greatly enhanced its mechanical properties. RFA helped to form more hydrated products and provide effective mechanical support, but excessive RFA could lead to large pores in the matrix. The use of GDP and RFA in reinforcing soft clay ground significantly improved its specific penetration resistance, bearing capacity, and compressive modulus. A significant linear correlation was found between the compressive modulus of reinforced clay and its specific penetration resistance or UCS. As a result, an empirical model has been developed to predict the compressive modulus of reinforced clay based on this correlation.

MgO carbonization is a green and low-carbon soil improvement technology. The use of MgO carbonization to solidify dredged sediment and transform it into road-building materials has significant environmental sustainability advantages. A series of microscopic characterization tests, including X-ray Diffraction (XRD), Scanning Electron Microscope-Energy Dispersive Spectrometer (SEM-EDS), and Mercury-in-Pressure (MIP) tests, were conducted to elucidate the evolution characteristics of mineral composition, microscopic morphology, and pore structure of sediment under carbonation. Based on the results, the mechanism of MgO carbonation-solidification of dredged sediment was explored. In order to verify the improvement of carbonation on the road performance of sediment, comparative tests were carried out on sediment, non-carbonated sediment, and carbonated sediment. The results indicate a significant improvement in the solidification of MgO-treated sediment through carbonation, with enhanced macroscopic strength and densified microscopic structure. This can be attributed to the encapsulation, cementation, and pore-filling effects of the hydration products and carbonation products of MgO on soil particles. The rebound modulus and splitting strength of carbonated sediment were 3.53 times and 2.16 times that of non-carbonated sediment, respectively. Additionally, the carbonated sediment showed improved saturated stability, resistance to salt solution wet-dry cycles, and resistance to freeze-thaw cycles.