Liyun Tang

Earthen materials are attractive sustainable building solutions due to their low embodied energy and ecological benefits. However, their inherent weaknesses, such as low strength and poor durability, severely restrict modern engineering applications. Traditional physical or chemical modification methods struggle to balance significant improvement in mechanical performance with the preservation of their core sustainable attributes. To overcome this long-standing challenge, this study proposes a paradigm-shifting solution: a prefabricated monolithic lattice–earth composite wall structure. This system abandons the single-material-centered modification approach. Instead, through macroscopic system-level composite design, reinforced concrete lattices and earthen blocks are prefabricated into integral wall panels in a factory. These panels then work collaboratively with the peripheral frame through reliable integral connections. Via quasi-static tests and theoretical analysis on four scaled wall specimens with different design parameters, this study systematically reveals the working mechanism and performance regulation principles of this composite system. The core findings indicate: (1) The system achieves multiple seismic defense lines and a controllable energy dissipation path through a sequential damage mechanism: “earthen material cracking and friction → lattice yielding and energy dissipation → final defense by the frame.” (2) The ratio of the equivalent lateral stiffness of the prefabricated wall panel to the stiffness of the outer frame is a key dimensionless design parameter controlling the failure mode (ductile shear or brittle bending), and the lattice configuration is an effective means to adjust this parameter. (3) Based on tests and an equivalent stiffness model, quantitative design guidelines are proposed, focusing on optimizing lattice density (recommended: 3–4 lattice columns), limiting the aspect ratio (preferably ≤1.5), and ensuring “strong connections.” This study demonstrates that the system, without sacrificing the intrinsic sustainable advantages of earthen materials, successfully endows them with high performance, meeting modern seismic code requirements and potential for prefabricated construction through system integration innovation. It provides a new path with theoretical foundation and practical feasibility to resolve the core contradiction in the modernization of traditional earthen buildings—the incompatibility between ecological attributes and engineering performance. This lays an important foundation for developing next-generation high-performance green building structural systems.

This study systematically investigates the efficacy of nano-silica (NS) and nano-alumina (NA) in mitigating the detrimental effects of low-temperature curing (5 °C) on concrete performance through a multi-scale experimental approach. Macroscopic tests revealed that an incorporation of 2 % NS or 1 % NA not only optimized compressive strength under standard curing but also effectively counteracted the strength reduction induced by low-temperature curing. Microstructural analysis using Scanning Electron Microscopy (SEM), X-ray Diffraction (XRD), and Mercury Intrusion Porosimetry (MIP) revealed that both nanomaterials improve performance by densifying the pore system, speeding up the hydration process, and encouraging the generation of more calcium silicate hydrate (C-S-H) at the expense of calcium hydroxide (CH). Notably, 1 % NA yielded superior microstructural improvement compared to 2 % NS, achieving comparable mechanical enhancement at a 50 % lower dosage. The findings indicate that nano-alumina, owing to its higher efficiency and cost-effectiveness, presents an ideal admixture for producing durable concrete in cold-region applications.

Conventional slurry wall protection exhibits reduced film performance upon exposure to water in saturated sand layers with high permeability, frequently resulting in hole wall instability. Optimizing the slurry ratio to enhance film performance is thus critical for borehole stability. A multiple regression model was developed to determine the optimal slurry ratio for saturated sand. Slurry permeability tests assessed filtration loss, film formation time, and film morphology changes. Scanning electron microscopy (SEM) further elucidated the film formation mechanism. Bentonite, clay, Na₂CO₃, and sodium carboxymethyl cellulose (CMC) significantly affected the slurry’s properties: specific gravity and sand content increased with bentonite/clay; viscosity increased with CMC; and pH increased with Na₂CO₃. The optimized slurry (water–bentonite–Na₂CO₃–clay–CMC = 1000:220:32:110:1; specific gravity, 1.20 g/cm³; viscosity, 29 s) demonstrated low filtration loss and stable film morphology. SEM revealed that simultaneous CMC and clay addition (ratio of 1:110) improved film surface flatness, reduced porosity and pore size, enhanced formation surface filling, and produced a denser film. The optimized slurry ratio significantly enhanced film performance in saturated sand layers. The findings provide a theoretical and engineering framework for bored pile wall protection slurry design and film formation mechanisms.

Climatic warming accelerates permafrost ice thawing, resulting in ground subsidence and subsequent loss of load‐bearing capacity. Compensating the loss of ice content by using ice nucleation active (INA) bacteria in permafrost can be efficient to solve this problem. However, the performance and work mechanism of INA bacteria catalyzing ice formation in permafrost under climatic warming remain unclear. Therefore, the effect of INA bacterium Pseudomonas syringae on the ice formation and shear strength of frozen soil is investigated by conducting nuclear magnet resonance (NMR) and direct shear tests. The unfrozen water content and the shear strength of specimens with P. syringae concentrations of 0–20 g/L under temperatures ranging from −5°C to −0.1°C are measured and compared. The classic nucleation theory is used to illustrate the work mechanism of P. syringae in permafrost. Results indicate that P. syringae can significantly increase the shear strength of frozen soil by 13%–64% during soil thawing. The enhanced shear strength is attributed to the ice‐bonding cohesion at temperatures from −5°C to −1°C, and the internal friction angle from −0.5°C to −0.1°C. Adding P. syringae with a concentration of 1 g/L can slow down the permafrost warming rate and maintain the unfrozen water content at a constant value. P. syringae exhibits higher ice‐triggering ability near 0°C resulting from the decreased nucleation barrier during soil thawing. Using INA bacteria provides a sustainable solution to deal with permafrost warming and thawing, and the resulting landform changes and structural instability.

The China–Russia crude oil pipeline (CRCOP) operates at a temperature that continuously thaws the surrounding permafrost, leading to secondary periglacial phenomena along the route. However, the evolution and formation mechanisms of these phenomena are still largely unknown. We used multi-temporal airborne light detection and ranging (LiDAR), geophysical, and field observation data to quantify the scale of ponding and icing, capture their dynamic development process, and reveal their development mechanisms. The results show that the average depth of ponding within 5 m on both sides of the pipeline was about 31 cm. The volumes of three icings (A–C) above the pipeline were 133 m³, 440 m³, and 186 m³, respectively. Icing development can be divided into six stages: pipe trench settlement, water accumulation in the pipe trench, ponding pressure caused by water surface freezing, the formation of ice cracks, water overflow, and icing. This study revealed the advantages of airborne LiDAR in monitoring the evolution of periglacial phenomena and provided a new insight on the development mechanisms of the phenomena by combining LiDAR with geophysics and field observation. The results of our study are of great significance for developing disaster countermeasures and ensuring the safe operation of buried pipelines.

Understanding the capillary imbibition laws of brackish water in rocks is necessary to reveal the mechanism of fluid, salt, and ion transport. In this study, we investigated the capillary imbibition laws of a Na₂SO₄ solution of different concentrations in sandstone by measuring the parameters of water absorption mass, water migration front height, nuclear magnetic resonance (NMR) T₂ spectra, and stratified moisture distribution. The results indicate the following: (1) With an increase in the salt solution concentration, the water absorption rate of samples increases, specifically manifested in an increase in the rate of absorption mass and a rising rate of the absorption front. (2) With an increase in the salt solution concentration, the total NMR signals in samples measured at the end of water absorption decreases; that is, the total amount of water absorption decreases. (3) When the solution concentration exceeds 0.50 g/L, variations in the NMR signal of samples and the absorbed water mass over time are not synchronic and are even opposite at some stages. Based on the capillary dynamic theories of liquid, the influence of salts on solution properties and the modification of the pore structure by crystallization are considered when discussing the underlying mechanism of capillary imbibition in sandstone. By calculating the physical properties such as the density, viscosity, surface tension, and contact angle of solutions with different concentrations, the imbibition process does not exhibit any significant variation with the difference in the properties of the liquid. The equivalent capillary radii of the samples at varying salt concentrations are obtained by fitting the capillary dynamics curves with the theoretically calculated values. The equivalent capillary radii of samples in higher salt concentrations are larger, i.e., the difference in capillary imbibition laws introduced by the salt concentration should be attributed to modifications to the pore structure caused by salt crystallization.

The mechanical properties of frozen fissured rock masses are crucial considerations for engineering in frozen earth. However, there has been little research on the mechanical properties of frozen fissured sandstone, including its strength, deformation, and geometric parameters. In this study, sandstone samples with three open en echelon fissures were observed using high-speed photography and acoustic emissions during uniaxial compression tests. The aim was to investigate sandstone’s strength, deformability, and failure process in order to elucidate the effects of freezing on its mechanical properties. In the frozen-saturated and dried states, the uniaxial compression strength (UCS) initially decreases and then increases with an increase in fissure inclination angle. Conversely, the UCS of samples in the saturated state continuously increases. The UCS follows a decreasing trend, as follows: frozen-saturated state > dried state > saturated state. The initial crack angle decreases as the fissure inclination increases in all states, irrespective of temperature and moisture conditions. However, the initial crack stress and time show an increasing trend. The uniaxial compression strength (UCS) of frozen fissured sandstone is influenced by four mechanisms: (1) ice provides support to the rock under compression, (2) ice fills microcracks, (3) unfrozen water films act as a cementing agent under tension or shearing loads, and (4) frost damage leads to softening of the rock.