Soil-rock mixture (SRM) in cold region is affected by frequent freeze-thaw cycles, resulting in the frequent discontinuously reorganized soil-rock skeleton and the strength deterioration. At present, studies on the SRMs mainly focus on the micro-pore changes and macro-mechanical properties under different rock contents, water content and freeze-thaw cycles. However, the analysis of strength degradation mechanism from a combined perspective (water migration, micro-damage evolution and macro-physical and mechanical properties) remains unknown. Therefore, this paper reviews the water migration, the micro-pore evolution, and the macro mechanical properties response of SRMs. Based on the theory of water migration, the evolution mechanism and law of water migration of SRM are described in detail considering the factors such as temperature gradients, water content and fine particle contents. The micro-pore test methods and the evolution law of micro-pore of SRM under freeze-thaw cycles, rock contents and water content were systematically evaluated. The test methods of macroscopic mechanical properties of SRM and the effects of freeze-thaw cycles, rock contents and water content on the shear strength and its indexes of SRM are compared and analyzed. The strength degradation mechanism of SRM is revealed by combining macro-meso evolution and multi-fields coupling. Based on the strength degradation mechanism, the future research work is prospected, providing a theoretical guidance for the construction of SRM projects and disaster prevention and control in cold regions.

Groundwater level fluctuation-induced collapse in deep loess threatens the long-term safety of deep-buried metro tunnels. A field sand-well immersion test is conducted along a Xi'an metro line, employing a water-level control system to regulate the leaching exploratory well water level precisely. This experimental setup simulates the wetting-induced deformation process under bottom-up infiltration with constant overburden stress, and a computational model for deep loess collapse deformation is established by considering the hydro-mechanical path. Results demonstrated an inverted-funnel-shaped moisture diffusion pattern in deep loess, with the saturation front diffusion angle measuring approximately 90 degrees within 2 m of the well, decreasing to 50 degrees at distances of 2-6 m, and increasing to 73 degrees beyond 6 m. During immersion, the deep loess exhibits three-stage deformation behavior: collapse governed by structural strength degradation, rebound dominated by unloading due to cavity formation with a positive correlation to water level height, and compression from residual structural strength failure with a negative correlation to water level height. Post-immersion consolidation settlement is also observed. Collapse and rebound develop from deep to shallow layers and from inner to outer zones, whereas consolidation settlement propagates from shallow to deep layers and from outer to inner areas. Based on the wetting-unloading hydro-mechanical path during bottom-up infiltration, a collapse deformation model is developed. Using a degree of wetting eta 1 = 0.8 combined with actual unloading ratios, the model achieves a relative error of only 8.85 %. This study provides valuable insights for evaluating collapsibility in deep loess foundations within groundwater fluctuation zones.

Rising groundwater levels and increasing depths of urban infrastructure lead to prolonged wetting of deep loess foundations, affecting long-term serviceability. However, research on the resulting collapsible deformation remains limited. This study reveals the staged deformation behavior of deep loess using sand-well immersion tests that simulate groundwater rise. Unsaturated triaxial tests further clarify the underlying mechanisms, and a calculation model incorporating the "collapse-unloading" stress path is developed. The results indicated that localized groundwater level rise induces vertical differential settlement, which is characterized by the collapse of deep loess and the partial or absence of collapse in shallow loess. This condition leads to an effective stress unloading state in deep loess, characterized by reduced total stress and increased pore water pressure, resulting in a staged deformation sequence consisting of collapse settlement, wetting-induced rebound, and recompression. The dominant mechanisms governing these three stages are identified as plastic yield triggered by the degradation of structural strength, elastic rebound driven by the accumulation of pore water pressure, and plastic yield caused by a gradual increase in the stress ratio, respectively. The proposed model, which accounts for unloading effects, effectively captures the staged deformation characteristics of deep loess. Under three working conditions, including pore pressure increase, total stress decrease, and their combined unloading, the model produces average relative errors of 4.5%, 5.0%, and 31.25%, respectively. The obtained regional correction factors (0.97-1.20) demonstrate strong consistency between calculated and measured values. These findings provide a valuable reference for evaluating the collapsibility of deep loess foundations under groundwater level fluctuations.

Aeolian deposition is fundamental to the formation of the porous structure of present-day loess. However, the true initial packing structure of loess dust remains poorly understood. In this study, we reconstructed initial loess deposits by simulating the dust deposition process, using Malan loess, which is compositionally analogous to ancient dust, as the raw material. The microstructure of the simulated deposits was characterised using microcomputed tomography (mu-CT) scanning and compared with that of natural Malan loess. The results indicate that the initial loess deposits possessed an exceptionally loose particle packing, with void ratios ranging from 2.79 to 3.75. Loose clay or silt-clay aggregates formed extensively due to inter-particle forces (such as van der Waals force and electrostatic attraction) during deposition. These aggregates, along with isolated detrital particles, acted as the primary skeletal components. Surface clays on skeletal particles play a critical role in bonding adjacent particles, which is essential for establishing and stabilising the loose framework. Notably, the initial deposits with an intermediate clay content (23%) among the samples studied exhibited the loosest microstructure, featuring chain-like particle packing and abundant large overhead pores. The initially loose aggregates and open packings compact over geological time while retaining structural inheritance, resulting in the reduced but partially preserved pore space that shapes the microstructure of present-day loess. This study provides the first direct 3D visualisation and quantification of the initial particle-scale microstructure, offering a key reference for understanding subsequent post-depositional processes and associated geomechanical properties.

The durability evaluation of permafrost infrastructure heavily relies on interfacial strength characterization. However, existing constitutive models systematically underestimate the damage accumulation rate during freeze-thaw cycling while overestimating residual strength, leading to significantly increased structural safety risks and severely shortened engineering service life. This study investigates shear behavior at concrete-crushed rock soil interfaces under freeze-thaw cycles through laboratory direct shear tests. The shear stress-displacement relationship is analyzed as a function of cycle number, with nuclear magnetic resonance quantifying interfacial pore structure evolution. A four-parameter modified Duncan-Chang model is developed to establish a higher-order nonlinear constitutive framework that integrates freeze-thaw damage effects. Unlike traditional one- or two-parameter hyperbolic models, the proposed model captures complex deformation phases including plastic hardening and incipient strain softening, which are empirically observed in freeze-thaw-damaged interfaces. A two-stage energy decoupling mechanism was proposed to separately describe interfacial debonding energetics and particulate friction thermodynamics, establishing a direct correlation that correlates microstructural ice cementation rupture patterns with continuum-scale elastoplastic deformation characteristics under freeze-thaw cycles. Interfacial shear strength exhibits dual dependence on normal stress magnitude and freeze-thaw history, showing a 40.5% increase in strength at 300 versus 100 kPa normal stress after 15 cycles, followed by stabilized degradation rates attributed to self-organized ice recrystallization patterns. Porosity progressively expands by 0.9%-2.3% with cycling, driven by phase transition-induced microcrack bifurcation and bidirectional pore restructuring (micropore coalescence/macropore fragmentation), which inversely correlates with cohesion reduction. The four-stage constitutive model with cubic-hyperbolic cyclic damage corrections achieves R-2 > 0.95 via nonlinear least-squares validation. The model can explain the stress-displacement process of the interface and the strain softening phenomenon in detail, which can provide a basis for the numerical simulation and theoretical calculation of the structure in the frozen soil ground.

Rising groundwater levels alter the stress and moisture states of deep loess, inducing significant wetting-induced deformation that threatens the safety of deep-buried transportation infrastructure in western China. However, a systematic understanding of the deformation characteristics and mechanical mechanisms of deep loess under bottom-up wetting paths remains limited. This study investigates Q2 intact loess obtained from a depth of 26 m in Xi’an using unsaturated triaxial tests that simulate bottom-up wetting under a constant water head. It also examines the effects of venting conditions, pore water pressure, initial mean stress, and initial void ratio on deformation behavior. The results show that, during groundwater level rise, the specimens exhibit a three-stage deformation process consisting of collapse settlement, wetting-induced rebound, and re-compression. Although the gas-closed condition does not alter the staged deformation behavior, it suppresses wetting and prolongs the equilibrium time of each stage by 1.87% to 15.72%. In addition, it reduces collapse settlement and wetting-induced rebound by 2.78% to 8.26% and 3.91% to 10.10%, respectively, while increasing re-compression by 1.81% to 18.62%. Microscopic tests confirm that deformation progresses in the bottom-up wetting direction, and the gas-closed condition exacerbates vertical nonuniformity. Tests on remolded loess further reveal that higher pore water pressure increases both the duration and magnitude of rebound while significantly reducing the duration and magnitude of re-compression. Higher initial mean stress or a lower initial void ratio drives the soil toward a high-stress, high-density state in which rebound and re-compression gradually disappear. Mechanism analysis reveals that collapse settlement results from the weakening of cementation and pore collapse caused by water infiltration, wetting-induced rebound is driven by pore expansion resulting from accumulated pore pressure, and re-compression results from pore contraction induced by particle separation, water–air migration, and cementation degradation. These findings clarify the wetting-induced deformation mechanism of deep loess in groundwater fluctuation zones and provide a theoretical basis for developing a collapse deformation calculation method that considers coupled unloading-wetting effects.

The monolithic hydrophobic alkali-activated concrete (AAC) performs excellent long-term impermeability, while unavoidably accompanied with the lose of its mechanical strength. Microencapsulation can enhance hydrophobicity without significantly reducing compressive strength in cementitious materials; however, it still faces premature core material release issues, which inhibit the early alkali activation reaction of AAC. To overcome this limitation, a core-shell delayed release polysiloxane (DR-PS) was synthesized based on pH-time dual response coating. The effects of DR-PS incorporation on the mechanical performance and hydrophobicity of AAC were systematically evaluated, and the underlying mechanisms were elucidated through comprehensive microstructural characterization. The results revealed that, compared to the reference AAC, the 28-day compressive strength of DR-PS-AAC increased by 19.27 %, while the water contact angle (WCA) reached 90.5 degrees, demonstrating a synergistic improvement in both mechanical strength and surface hydrophobicity. Mechanistically, the delayed release of polysiloxane avoided interference with the critical early-stage depolymerization and polycondensation of reactive Si-Al species, thereby facilitating the formation of a continuous gel network. In the later hydration stages, the released polysiloxane imparted durable hydrophobicity, while the degradation of the DR-PS shell contributed to pore structure refinement, evidenced by a 24.08 % reduction in pores larger than 10 nm compared to PS-AAC. This work presents a mechanistically informed strategy to reconcile early-stage structural integrity with long-term durability in AAC, offering a viable pathway for the development of high-performance, hydrophobic, and low-carbon concrete materials for aggressive service environments.

The interface between concrete and soil-rock mixture (SRM-concrete interface) under freeze-thaw cycles is very prone to creep damage, threatening the long-term stability of the superstructure in cold regions. However, there is no study concerning the characteristics of the nonlinear accelerated creep stage using the existing creep model in SRM-concrete interface. Therefore, shear creep tests were conducted to study the creep displacement and failure modes at the SRM-concrete interface under varying rock contents (15%-65%) and freeze-thaw cycles (0-20 iterations). A modified Burgers viscoelastic-plastic constitutive model is proposed to illustrate the creep failure characteristics of SRM-concrete interface induced by freeze-thaw cycles, which contains a hardening and loosening component. Results reveal a notable decrease in creep deformation correlating with increased rock content at SRM-concrete interface. Notably, the resistance of SRM-concrete interface to shear creep behavior peaks after five freeze-thaw cycles. This modified creep model accurately describes the nonlinear hardening and loosening creep behavior at the SRM-concrete interface, offering a substantial theoretical foundation for studying the longterm deformation and service life of superstructures in cold regions.

Effectively describing the heat transfer process of ground heat exchangers is crucial for fully utilizing geothermal energy. The current progress in heat transfer analysis models is to divide the soil into several non-isothermal soil layers based on the assumption of uniform borehole wall temperature and heat flux in traditional models, but the temperature and heat flux inside the layers are uniform. Rarely consider the non-uniformity of heat flux within the layer and the boundary problem of vertical heat flux at the ground level. This article adopts a composite medium method to modify the segmented model, considering the heat transfer problem between soil layers. The assumption of uniform temperature of the borehole wall was removed to improve the fluid analysis model. Afterwards, analyze the impact of the heat transfer process inside and outside the borehole on the heat flux of the borehole wall. Using the segmented trial-and-error technique to couple the fluid and soil heat transfer models, a new comprehensive model of the U-shaped grounded heat exchanger was established. Conducted initial underground soil temperature distribution and thermal response tests in different geomorphic units in Guanzhong, Shaanxi, and verified the model's reliability based on experimental data. Analyze three influencing factors, namely fluid mass flow rate, initial underground soil temperature considering variable temperature layer, and temperature difference between average initial underground soil temperature and inlet fluid temperature, to evaluate system performance. The results indicate that the recommended range of fluid mass flow rate in the Guanzhong region is 0.32-0.42 kg/s. It was found that the heat transfer capacity of the heat exchanger will be underestimated if it ignores the influence of the variable temperature layer. Furthermore, the determination of the heat extraction result is not due to the high inlet fluid temperature but rather to the high difference between the inlet fluid temperature and the initial underground soil temperature. This study can promote better system design and achieve higher system performance.

Dynamic compaction vibrations (DCV) cause significant environmental impacts. Quantifying key influencing factors is essential for mitigation. This study examines how tamper radius, tamping energy, tamping times, and tamping settlement affect DCV velocity (4000-25000 kN·m energy range) in a miscellaneous fill site. A BP neural network model was developed with these four parameters as inputs and vibration velocity as output, and the influence of each factor on vibration velocity was evaluated in combination with Sobol sensitivity analysis. The results show that Vibration velocity and tamper radius follow a negative exponential power function relationship. 97% of total vibration attenuation occurs within a 60 m radius. Vibration velocity growth rate decelerates with increasing tamping energy. 98% of velocities are below 30 mm/s, demonstrating strong data clustering. With the increase of tamping times or tamping settlement, the vibration velocity first rises to the "peak point", and the peak point corresponds to 4-6 tamping times and tamping settlement at 0.68-0.82 m and 3.08-4.30 m, and then declines or stabilizes. The tamper radius is the main factor affecting the vibration velocity. Optimizing or controlling the tamper radius can significantly reduce the vibration of DCV. The influence of tamping settlement is second, and the tamping energy and tamping times have a smaller impact.

Several global or regional databases for various types of soils have been developed due to their importance in engineering design and analysis. However, a database is not yet available for collapsible loess in which severe geohazards often occur. In this study, a comprehensive loess database with twelve soil parameters is compiled by collecting results of field and laboratory tests on collapsible loess from the city of Xi’an, China. Basic statistics, marginal probability distribution functions (PDFs), and a correlation matrix for loess parameters are estimated from the database. To the best of the authors’ knowledge, this is the first collapsible loess database at a municipal level. In addition, existing databases often lack sufficiently complete multivariate measurement data for a proper estimation of statistical correlations among multiple soil properties. In this study, this incomplete multivariate measurement data problem is tackled by Bayesian methods (i.e., Bayesian Gaussian mixture model and Bayesian compressive sampling (BCS) with Karhunen–Loève (KL) expansion, BCS-KL), which are illustrated and validated using the incomplete and complete subsets of the loess database, respectively. Both the Bayesian Gaussian mixture model and BCS-KL are non-parametric, and they offer a flexible way of modeling marginal PDFs and a correlation matrix from incomplete measurements in a realistic manner.

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 degrees C to -0.1 degrees 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 degrees C to -1 degrees C, and the internal friction angle from -0.5 degrees C to -0.1 degrees 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 degrees 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.

Understanding the percolation process of water in unsaturated soils during rainfall is crucial. A mathematical model representing the movement of water in unsaturated soils was established on the basis of the one-dimensional Richards’ equation and the fractional-derivative Darcy model. By assuming that the soil-water characteristic curve can be described by the Gardner model, a semi-analytical solution was derived. The solution was verified through the finite element software COMSOL Multiphysics (COMSOL). The effects of fractional order α on percolation process and the efficiency of the fractional model were investigated.

A fully automated modified borehole shear test (MBST) device in which, the shear failure mechanism is revealed using computed tomography scanning technology is presented. The equipment was evaluated as an accurate method for determining normal stress, consolidation time, and shear strength characteristic values. A comparative analysis of the MBST and Handy borehole shear test (HBST) results for investigating a slope was performed. This showed that failure occurs when the soil sheared along a weak surface, and the normal stress-displacement curve for a typical test in loess could be divided into initial, quasi-elastic, and plastic stages. The shear plate and soil could form a stable relationship when the normal stress is in the quasi-elastic stage. The initial σ1 and maximum σn normal stresses were approximately equal to the σ0 and plastic σf normal stresses. Based on the increment of normal displacement S0, the initial normal displacement S0 and the plastic normal displacement Sf satisfied the relationship: 0.16≤ ∆S ≤ (Sr-S0)/4 or 0.16 ≤ ∆S ≤ (Sr-S0)/3. The remaining normal stress was determined by linear interpolation. Moreover, the consolidation time under the initial normal stress in a typical loess site was 13 min, while that under the remaining normal stresses was 10 min. The proportional limit, peak, and residual strengths were easily determined from the shear stress-displacement curve. The cohesion c value measured by the MBST device did not have a negative value as can occur with the HBST, which could more accurately reflect the shear strength parameters of the soil.

The high hydrophilicity and permeability of concrete caused by many pores and hydroxyl groups produced by cement hydration are the main factors leading to dry shrinkage, cracking, and poor corrosion resistance of concrete. Giving concrete internal curing and hydrophobicity is an effective measure to solve the above problems. In this paper, a new idea and preparation method for an organic combination of hydrophilic and hydrophobic materials are proposed to improve the service life of concrete structures. Furthermore, the combined effects of hydrophilic and hydrophobic amphoteric materials (HAM) on the mechanical properties, internal curing properties, and hydrophobic properties of concrete were comprehensively investigated. In addition, the physical and chemical action mechanisms were analyzed in conjunction with microscopic tests. The results indicated that HAM rapidly released water within 3-7 days before concrete curing, and then slowly released water accompanied by the release of hydrophobic materials, gradually from hydrophilic to hydrophobic properties; The addition of HAM did not reduce the mechanical properties of concrete, which solved the problem of low compressive strength of integral hydrophobic concrete; The addition of HAM reduced the drying shrinkage of concrete by 154.12 %, increased the contact angle to 96 degrees, and decreased the water absorption rate by 36 %, allowing the concrete to achieve better internal curing and a hydrophobic effect. The preparation of this material can open up a new way to solve the hydrophilic and hydrophobic properties required by concrete at the same time, and fill the gap that concrete can not balance hydrophilic and hydrophobic properties.

The thermal conductivity of soil is an essential parameter for designing geothermal energy foundations and borehole heat exchange systems. To effectively improve the development efficiency of geothermal resources in the loess region of China, the plane heat source method was used to measure the thermal conductivity of loess samples with different water contents and temperatures, and scanning electron microscopy tests were conducted. Analyze the effects of water content, temperature, and soil microstructure on thermal conductivity. A weighted geometric mean model considering the soil temperature effect is proposed and compared with the traditional model. The experimental results reveal that soil thermal conductivity increases in stages as the temperature rises. After the temperature exceeds 30℃, the contribution of steam latent heat transfer to soil thermal conductivity gradually becomes significant. Within the temperature range of 1–60℃, the thermal conductivity increases with increasing saturation and tends to stabilize after saturation exceeds 60

The complicated heterogeneity and discontinuity of soil-rock mixture (SRM) usually cause high variability in SRM's creep characteristics, which can easily cause geological disasters (e.g., landslides) under harsh environment such as freeze-thaw (F-T) cycles. However, the nonlinear creep behaviors of SRM material, under varying internal structures induced by F-T cycles, skeleton changes and stress states, have not been reported and it is still challenging to describe these complicated creep behaviors using current existing creep models. Therefore, direct shear creep tests were carried out to study the creep evolutions of SRM under various F-T cycles (0 to 15 cycles) and rock contents (15% to 55%). A new element combination creep model was then proposed to describe SRM's nonlinear creep behaviors involving the instantaneous elastoplastic and viscoelastic-plastic deformations. Results showed that the creep deformation tended to decrease as the rock content increased. The initial 3 to 5 F-T cycles significantly affected the creep behaviour of SRM. The proposed new creep model could well describe the nonlinear creep behaviors of SRM material under different stress states.

The creep properties of soil-rock mixture (SRM) usually exhibit high variations after suffering harsh field conditions in cold regions such as freeze-thaw cycles, which can easily trigger landslides and threat the long-term stability of SRM slopes. However, the creep properties of SRM induced by freeze-thaw cycles have not been studied, especially in terms of the evolution of creep deformation and failure types under multiphase transitions within SRM material. Therefore, the shear and creep properties of SRM specimens under different freeze-thaw cycles (0 to 15 cycles) and rock contents (15% to 55%) were investigated to reveal the creep failure mechanisms of SRM using large-scale direct shear and direct shear creep tests. The shear stress-displacement curves, shear strengths, the creep curves and long-term strengths of SRM specimens were analyzed. Results showed that increasing freeze-thaw cycles tended to decrease the shear strength of the SRM specimen. The final creep deformation of SRM generally decreased with increasing rock content, and the first 3 to 5 freeze-thaw cycles resulted in significant creep displacement and the decrease of long-term strength.

Vibrations generated during dynamic compaction impose adverse consequences, significantly compromising the structural integrity and stability. Quantifying the relative significance of each factor influencing vibration in dynamic compaction proves to be a challenging task. The impact of the tamper radius, tamping energy, tamping times, and tamping settlement on intense compaction vibrations at a tamping energy ranging from 4000 to 25000kN·m was investigated in miscellaneous fill site. These factors were incorporated into the Bp neural network and subjected to modeling. The Sobol sensitivity analysis approach was employed to assess sensitivity, and an examination of how terrain affects vibration speed was conducted. The findings indicate a notable "inflection point" in both safety distance and the growth rate of vibration speed with increasing tamping energy. Beyond this critical point, both safety distance and growth rate exhibit a decline. As the tamping times escalate，the vibration speed reaches a critical "peak point." Specifically, when the tamper radius is denoted as (10m, 90m], the vibration speed typically remains below 30mm/s, encompassing 98% of the dataset and revealing a conspicuous aggregation phenomenon. The responsiveness of vibration speed to tamper radius and tamping quantity is more pronounced compared to tamping times and tamping energy. Enhancing both the tamping energy and the tamping times proves effective in mitigating the influence of intense tamping vibration. The slope shoulder demonstrates an "energy concentration" effect that intensifies with an escalating tamping times. Under the same tamper radius, the measured vibration speed on the slope typically surpasses that on flat ground, and the vibration velocity shows an increase at the slope surface.