The entrance of permafrost tunnels in cold regions is particularly vulnerable to frost damage caused by complex thermal-hydro-mechanical (THM) interactions in unsaturated frozen soils. The effects of temperaturedependent volumetric strain variations across different stratum materials on heat and moisture transport are often neglected in existing THM coupling models. In this study, a novel THM coupled model for unsaturated frozen soil integrating volumetric strain correction is proposed, which addresses bidirectional interactions between thermal-hydraulic processes and mechanical responses. The model was validated through laboratory experiments and subsequently applied to the analysis of the Yuximolegai Tunnel. The results indicate that distinct layered ice-water distribution patterns are formed in shallow permafrost under freeze-thaw cycles, driven by bidirectional freezing and water migration. Critical mechanical responses were observed, including a shift in maximum principal stress from the invert (1.40 MPa, frozen state) to the crown (5.76 MPa, thawed state), and periodic lining displacements (crown > invert > sidewalls). Frost damage risks are further quantified by the spatial-temporal zoning of ice-water content-sensitive regions. These findings advance unsaturated frozen soil modeling and provide theoretical guidance for frost-resistant tunnel design in cold regions.

Evaluating the stability of coral islands and reefs in dynamic marine environments, such as waves, tsunamis, storm surges, and earthquakes, is a critical scientific issue in the field of marine geotechnical engineering. Nansha coral sand was used as the study object, and stress-controlled drained and undrained cyclic-loading tests were conducted. The undrained excess pore-water pressure and the drained cumulative volumetric strain of saturated coral sand were determined at various non-plastic fine contents (FC), relative density (D-r), and cyclic stress ratio (CSR). The results indicated that cumulative volumetric strain (epsilon(vp)) developed in coral sand via two modes: cyclic stabilisation and cyclic creep. Analyses revealed that when the potential damage coefficient (DP) x CSR 0.05, epsilon(vp) transitioned into the cyclic creep mode. Utilising cumulative dissipation energy as a linking factor showed an arctangent function relationship between the excess pore water pressure ratio (R-u) and epsilon(vp) values of saturated coral sand with different FC, D-r, and CSR. This relationship was applicable to both stress- and strain-controlled cyclic-loading tests. Parameters m and n of the R-u-epsilon(vp) function model increased with an increasing CSR. Additionally, an increase in the D-r or FC resulted in a decrease in m and an increase in n. Multiple regression analysis further revealed that model parameters corrected for compactness and cyclic stress levels exhibited distinct trends as the void ratio (e) increased. Specifically, CSR alpha x m(D)(R) decreased, and CSR1-alpha x n(D)(R) increased. Both parameters displayed a single power function relationship with e. Based on these findings, a coupled incremental model for the cyclic pore pressure and volumetric strain of saturated coral sand, based on energy conversion, was developed.

Cyclic spherical stresses are prevalent in dynamic stress fields and significantly influence the dynamic behavior of loess, a material characterized by high compressibility and anisotropy. Previous research has primarily focused on shear stresses, often overlooking the impact of spherical stresses. This study investigated the deformation induced by cyclic spherical stress under different initial states. Irreversible and reversible components were identified from both volumetric and shear strains, and their variation patterns were analyzed. Shear strain is found to be generated by the material's anisotropy. The results indicate that the volume of the sample shrinks significantly under cyclic spherical stress, with irreversible volumetric strain increasing nonlinearly as the number of cycles increases. Irreversible shear strains can be categorized into two types based on their formation mechanisms. The first is when significant initial anisotropy leads to radial deformation greater than axial deformation under spherical stress, resulting in shear strain increasing in the negative direction. As consolidation stress increases, the initial anisotropy gradually diminishes. The second is when stress-induced anisotropy results in positive shear strain because consolidation deviatoric stress contributes to an increase in shear strain in the positive direction. As the stress ratio rises, the induced anisotropy is further enhanced. The axial reversible strain of the sample is minor, and the reversible components of volumetric and shear strains primarily arise from radial contraction and expansion. As the spherical stress increases, the sample volume shrinks (positive volumetric strain), whereas the initial anisotropy leads to negative shear strain, resulting in opposite signs. Finally, a method for predicting irreversible strain under cyclic spherical stress is established based on a memoryless geometric distribution.

Employing soil improvement techniques to mitigate and prevent the detrimental effects of liquefaction on foundations often leads to a significant increase in construction costs in engineering projects. Developing simple, cost-effective, and eco-friendly liquefaction mitigation methods has always been one of the main concerns of geotechnical engineers. Researchers introduced the induced partial saturation (IPS) method to increase the liquefaction resistance of the saturated foundations, which is based on decreasing the saturation degree of the saturated sand. In this study, hollow cylinder torsional shear tests were conducted on loose saturated and desaturated calcareous sand to assess the liquefaction behavior of desaturated sand. Soil compressibility is the primary parameter affecting the liquefaction behavior of desaturated sand. As saturation degree, back pressure, and effective confining pressure significantly influence soil compressibility, their effects on the liquefaction resistance of desaturated sand were investigated. The pore pressure development during cyclic loading reveal that, unlike saturated samples, desaturated samples do not exhibit an excess pore pressure ratio reaching one, even when the double amplitude shear strain surpasses 7.5 %. Finally, the test results demonstrated a notable correlation between liquefaction resistance ratio, maximum volumetric strain, and the maximum generated excess pore pressure ratio, and a pore pressure model was proposed.

Due to the widespread prevalence of respiratory diseases such as COVID-19 and H1N1, the use of disposable masks has increased significantly. Consequently, the environmental issues arising from their accumulation have become increasingly severe. This study, therefore, aims to investigate the potential of using masks as soil reinforcement materials. This study conducted triaxial and seepage tests on mask-calcareous sand mixtures with varying ratios to examine the effects of mask content on the strength, modulus, particle fragmentation, and permeability coefficient of calcareous sand, as well as the influence of different mask sizes on shear strength and shear dilation. The results demonstrate that with an increase in mask content, the peak stress ratio of the mask-calcareous sand mixture increases by 4% per level, and the internal friction angle rises by approximately 1.6% per level. Conversely, water permeability and shear swelling are reduced, and particle loss decreases by over 70%. The reinforcing effect of the mask is attributed to the high friction between the mask and the calcareous sand at the contact interface, which restricts the movement of soil particles during deformation, thereby enhancing the overall strength of the mixture. Among the three mask sizes, the smallest mask-calcareous sand mixture exhibited the greatest improvement in shear strength, and the shear shrinkage effect was more pronounced. This indicates that particle size also significantly influences the mechanical properties of the mixtures. The reinforcing effect of the mask on the soil results from the high friction at the interface between the mask and the calcareous sand. When the soil deforms, the mask enhances the overall strength of the mixture by restricting the movement of soil particles. Considering the impact of masks on the performance of calcareous sand, it can be concluded that the optimal mass content of masks is 0.3%. This study offers a new perspective on the reuse of discarded masks in civil engineering applications.

Seismic events and wave action can induce volumetric strain (ev) accumulation in saturated sandy soils, leading to damage to the ground surface and structures. A quantifiable relationship exists between the generation of ev in sandy soils under drained conditions and the development of pore water pressures under undrained conditions. In this study, the impact of relative density (Dr), cyclic stress path, and stress level on the characteristics of volumetric strain (ev) generation in saturated coral sands (SCS) was evaluated through drained tests employing various cyclic stress paths. The test findings demonstrate that the rate of ev accumulation in SCS is notably affected by the cyclic stress path. The rise in peak volumetric strain (evp) in SCS, as a function of the number of cycles, conforms to the arctangent function model. The unit cyclic stress ratio (USR) was employed as an indicator of complex cyclic loading levels. It was determined that coefficient (evp)u is positively correlated with USR at a specific Dr. At the same Dr, coefficient CN1 exhibits a positive correlation with USR, while coefficient CN2 displays a negative correlation with USR, following a power-law relationship. Irrespective of cyclic loading conditions, evp rises with an increase in generalized shear strain amplitude (yga). A power function model was established to represent the relationship between evp and yga. The coefficient 41 decreases as Dr increases. Comparisons were drawn between evp and yga for Ottawa sand and SCS. The results indicate that, as Dr of Ottawa sand increases from 30 % to 70 %, the coefficient 41 decreases from 1.54 to 0.73, representing a reduction of approximately 53 %. In contrast, under identical conditions, the coefficient 41 of SCS exhibits a less pronounced decrease, from 1.16 to 0.79, corresponding to a reduction of roughly 32 %. These observations suggest that variations in Dr have a more substantial impact on generating evp in Ottawa sand compared to SCS.

True triaxial tests of cyclic loading and unloading were carried out on remodeled loess, and the effects of the anisotropic consolidation ratio (K=sigma 1c/sigma 3c), intermediate principal stress coefficient (b=sigma 2-sigma 3/sigma 1-sigma 3), and cyclic loading on the deformation characteristics of the loess were analyzed. The results show that principal strain develops in two stages: a rapid initial increase followed by a slower increase until stabilization. Plastic volumetric strain is found to increase with increases in cyclic loading, anisotropic consolidation ratio, and intermediate principal stress coefficient. After normalization, the consolidation mode has a large effect on the plastic volumetric strain ratio, while the intermediate principal stress coefficient has a smaller effect. All types of plastic shear strain exhibit shear shrinkage, increasing with increases in cyclic loading and the intermediate principal stress coefficient, with no obvious relationship with the anisotropic consolidation ratio. After normalization, the consolidation mode and the intermediate principal stress coefficient have significant effects on the plastic shear strain ratio.

This paper aims to determine a non-liquefiable domain corresponding to the threshold of saturation degree where liquefaction does not occur under cyclic loading. To determine this threshold, sample volumetric strain at liquefaction state of unsaturated soil was modeled considering the suction. In low saturation degree zones, capillary suction is taken into account. In a high saturation degree zone, spherical suction caused by surface tension of air bubbles is considered by using its microscopic analysis and its equivalent size. Finally, three series of experimental tests have been made to give the data and verify the presented model.

Recycled aggregate base, usually utilized in permeable roadways, can be stabilized by geosynthetics to reduce rutting. However, the inclusion of geosynthetics would cause a magnified resilient behavior of the aggregate base under cyclic loading and the mechanism is still not well understood. In this study, cyclic triaxial tests were conducted to investigate the effect of the geosynthetic on the performance of the recycled aggregates. Results show that the resilient strains of aggregate samples stabilized by geosynthetics increased; correspondingly, the calculated loading/unloading moduli decreased and volumetric strains increased. However, a significant reduction of the cumulative plastic strains was observed. The main reason for such results is that the lateral confinement provided by geosynthetics was mobilized and caused the major principal stress to vary from the vertical direction to the lateral direction periodically along with the applied cyclic loading. This cyclic variation of the major principal stress would induce a cyclic shear action that causes the structural rearrangement of aggregates, leading to the dilation of samples. The major principal stress in the lateral direction during the unloading process results in a large vertical extension, which not only leads to a magnified resilient strain but also causes a reduced plastic strain.