The structural design of offshore wind turbines must account for numerous design load cases to capture various scenarios, including power production, parked conditions, and emergency or fault conditions under different environmental conditions. Given the stochastic nature of these external actions, deterministic analyses using characteristic values and safety factors, or Monte Carlo Simulations, are necessary. This process involves a large number of simulations, ranging from ten to a hundred thousand, to achieve a reliable and optimal structural design. To reduce computational complexity, practitioners can employ low-fidelity models where the soil-foundation system is either neglected or simplified using linear elastic models. However, medium to large cyclic soil-pile lateral displacements can induce soil hysteretic behaviour, potentially mitigating structural and foundation vibrations. A practical solution at the preliminary design stage entails using stiffness-proportional viscous damping to capture the damping generated by the soil-pile hysteresis. This paper investigates the efficacy of this simplified approach for the IEA 15 MW reference wind turbine on a large-diameter monopile foundation subjected to several operational and extreme wind speeds. The soil-pile interaction system is modelled through lateral and rotational springs in which a constant stiffness-proportional damping model is applied. The results indicate that the foundation damping generated by the nonlinear soil-pile interaction is significant and cannot be neglected. When fast analyses are required, the stiffness-proportional viscous damping model can be reasonably used to approximate the structural response of the wind turbine. This approach enhanced the accuracy of the computed responses, including the maximum bending moment at the mudline for ultimate limit design and damage equivalent loads for fatigue analysis, in comparison to methods that disregard foundation damping.

Laboratory experiments have shown that the proportional shearing of granular materials along arbitrary strain path directions will lead to stress states that converge asymptotically to proportional stress paths with constant stress ratios. The macro- and microscopic characteristics of this asymptotic behaviour, as well as the existence of asymptotic states exhibiting a constant stress ratio and a steady strain-rate direction, have been studied using the discrete element method (DEM). Proportional shearing along a wide range of strain-rate directions and from various initial stress/density states has been conducted. The simulation results suggest that general contractive asymptotic states (except for isotropic states) do exist but may be practically unattainable. Dilative strain path simulations, on the other hand, result in continuously changing stress ratios until static liquefaction occurs, indicating the absence of dilative asymptotic states. Despite this difference, a unique relationship between the stress increments and the current stress ratio gradually emerges from all strain path simulations, regardless of strain path direction and initial stress/density conditions. At the particle scale, the granular assembly sheared along proportional strain paths exhibits a constant partition ratio between strong and weak contacts. Although general proportional strain paths are associated with changing geometric and mechanical anisotropies, the rates of change in these anisotropies for contractive strain paths are synchronised to maintain a constant ratio of their contributions to the mobilised shear strength of the material, with a higher proportion being contributed by geometric anisotropy for more dilative strain paths.

During tunnel excavation in a soft soil stratum, a transparent model test can present the whole failure process, and a similar transparent material with stable physical and mechanical properties is essential for obtaining valid experimental results. Therefore, a new type of similar transparent material was developed in which fused quartz sand served as the coarse aggregate, nanoscale hydrophobic fumed silica powder acted as the binder, and a mixture of n-dodecane and 15# white oil was used as the pore fluid. The key parameters of the developed similar transparent material, including unit weight, internal friction angle, cohesion, and compression modulus, were evaluated. Furthermore, the consistency between the similar transparent material and natural soft soil was verified in three aspects, namely, physical properties, compressive strength characteristics, and shear properties. Finally, appropriate adjustment measures were proposed based on the results of the analysis of variance (ANOVA) and the analysis of range (ANOR) to meet the similarity requirements of parameters under different engineering conditions.

The proportional strain loading test is a prevalent method for investigation diffuse instability. The majority of current research concentrates on narrowly graded materials, with relatively less focus on binary mixtures under proportional strain loading. Therefore, a series of numerical tests have been conducted using the discrete element method to study the influence of fine content and strain increment ratio on the binary mixtures. The test results show that the fine content of binary mixtures is intimately connected to the critical strain increment ratio which precipitate a transition from stability to instability. Binary mixtures characterized by a low stress ratio at the onset of instability also demonstrate a heightened sensitivity to shifts in strain increment ratio. The macroscopic responses, such as the stress ratio at the onset of instability, shear strength, and pore water pressure, exhibit different trends of variation with the fine content compared to microscopic responses, including coordination number, friction mobilization index, and the proportion of sliding contacts. Furthermore, the anisotropy coefficient is introduced to dissect the sources of anisotropy at onset of instability, revealing that strong contact fabric anisotropy can mirror the evolution of the stress ratio. The stress ratio at onset of instability is predominantly influenced by anisotropy in contact normal and normal contact force.

Plant roots improve the stability of collapsing walls and prevent their collapse; they are thus important for controlling the degree of Benggang erosion in southern China. The vegetation species on the collapsing walls are diverse, and the interaction of the root systems with soil affects the stability of the collapsing walls. Most recent studies have only examined the effects of single plants. In order to investigate the effects of the roots of different vegetation types on the shear strength of soil in collapsing walls and their interaction mechanisms of action, this study was conducted using the roots of the herb Dicranopteris dichotoma and the shrub Melastoma candidum. A direct shear test of indoor remodeled soil was carried out by varying water content (15%, 25%) and herb to shrub root ratio (100:0, 75:25, 50:50, 25:75, and 0:100). The results showed that the shear strength (96.09 kPa) and cohesion (49.26 kPa) of root-containing soil were significantly higher than plain soil (91.77 kPa, 42.17 kPa), and the highest values were obtained when herb to shrub root ratio was 100:0 (113.27 kPa, 62.85 kPa). Here, tensile tests and scanning electron microscopy revealed that the tensile force and tensile strength of the roots of Dicranopteris dichotoma were weaker but effective for maintaining soil stability because of their abundance roots, which could achieve a stronger bond to soil. Simultaneously, herbaceous roots have a small diameter, the Root Area Ratio (RAR) of the roots is larger under the same mass condition, which can better contact with soil and the mechanical properties of roots are fully utilized. Therefore, the soil shear strength is higher and can better resist external damage when herbaceous roots accounts for a larger proportion. The results of this research have implications for the selection and allocation of ecological measures for prevention and control of Benggang.

The distribution range of soil-rock mixtures (S-RM) in fault zones is wide, with significant differences in mechanical properties, making them the main sites for rock instability and support structure failure in mines. This paper takes the Sanshan Island fault zone as the engineering background, and uses a self-designed small-scale test device to conduct triaxial compression tests to study the strength and deformation failure laws of S-RMs with different rock block proportions (20%, 40%, 60%, and 80%). Combined with numerical simulation test results, the spatial transport laws and microscopic deformation failure characteristics of particles with different particle sizes in the S-RM are revealed. The main conclusions drawn are as follows: (1) For S-RMs with rock block proportions (RBP) of 20%, 40%, and 60%, there is a linear positive correlation between confining pressure and peak strength. When the RBP increases to 80%, there is a non-linear positive correlation between the confining pressure and peak strength of the S-RM sample. Under the same increase in confining pressure, the increase in peak strength of the sample decreases. The influence of confining pressure on the strength and deformation characteristics of S-RMs with high RBP is reduced. (2) During the process of increasing the RBP from 20 to 60%, there is a linear positive correlation between the RBP and peak strength of the S-RM sample. When the RBP increases to 80%, the peak strength of the sample experiences a sudden increase, with an increase of nearly 80 kPa in peak strength. When the RBP is high, the S-RM sample exhibits the mechanical properties of block rocks. (3) The cohesion and internal friction angle of the S-RM sample are positively correlated with the RBP. During the process of increasing the RBP from 20 to 80%, the cohesion increases from 83.12 kPa to 119.38 kPa, and the friction angle increases from 6 degrees to 11 degrees. (4) When the RBP is low (20% and 40%), as the experiment progresses, a significant conjugate shear deformation zone will form within the S-RM sample, and block rock particles will migrate towards this area and undergo shear slip failure between particles. When the RBP is high (60% and 80%), splitting failure mainly occurs at the bonding surface between block rock particles and soil particles inside the sample, and the contact force between particles is relatively large. The relevant research results have important social and economic value for revealing the fracture failure laws of rock masses in fault zones and ensuring the safe development of human engineering activities.

Investigating the mechanical properties of sandy cobble strata is essential for optimizing the design and construction of urban tunnels, thereby controlling ground deformation and ensuring tunnel stability. This paper aims to comprehensively investigate the mechanical properties and energy characteristics of heterogeneous sandy cobble strata. Numerical simulations are employed to examine the stress-strain behavior and energy evolution mechanism in scenarios with and without interfaces between the soil matrix and blocks. Subsequent analysis focuses on elucidating the effects of the internal stochastic structures, which characterize heterogeneity, on the overall strength and energy characteristics. The results indicate that the presence of interfaces significantly compromises the overall strength, while exacerbating the occurrence of a tortuous plastic zone around blocks. The volumetric block proportion (VBP), which represents the volumetric content of cobbles, has a significant impact on the overall mechanical behaviour. In the context of high VBP, block sizes, counts and orientations play substantial roles. Finally, the discussion reveals that when blocks are modelled using the elastic model, the overall strength is significantly overestimated compared to the strain-softening and Mohr-Counlomb models, especially in scenarios with high VBP and in-situ stress. It provides an unsafe evaluation (i.e., overestimation) of tunnel stability.

A sequences of unconfined compressive strength tests and flexural tests were conducted in this study to evaluate the curing performance of a new type of polyurethane sand fast-curing polymer material. The mechanical properties of the material were investigated under different curing temperatures (-10 degrees C to 60 degrees C), particle sizes (10-15 mesh, 60-80 mesh, 100-120 mesh, and 325 mesh), and material proportions (20% to 60%). Additionally, SEM analysis was employed to further reveal the reinforcement mechanism. The results demonstrated that the developed polyurethane polymer material exhibited superior curing properties and applicability across a wide temperature range of -10 degrees C to 60 degrees C. Both the compressive strength and flexural strength of the solidified sand increased with the increase in solidification temperature, resulting in improved curing effects. This material exhibited the best curing properties when using sand within the 100-120 mesh range. As the particle size decreased under the remaining specifications, there was a reduction in specimen strain and an increase in strength, while still maintaining favorable ductility. The optimal proportion for polyurethane material was 40%. Moreover, the nonlinear mathematical relationships between the strength and multiple influencing factors were established through multivariate regression analysis. The sand consolidation specimens exhibited X-shaped conjugate shear failure, which tended to occur at the weak interface between the sand and material. Lastly, Pearson's correlation analysis revealed a strong positive correlation between temperature and material content with strength.

Soil-rock mixtures in fault fracture zones are composed of rock blocks with high strength and fault mud with low strength. In this paper, in order to study the mechanical properties of the soil-rock mixture with non-cohesive matrix, a large-scale laboratory triaxial compression test with a specimen size of 500 mmx1000 mm is conducted, combined with numerical simulation analyses based on the two-dimensional particle flow software PFC2D. The macroscopic mechanical response and mesoscopic fracture mechanism of soil-rock mixtures with varying rock block proportions, block orientation angles and matrix strengths are studied. The results indicate the following: (1) When the proportion is less than 30%, the shear characteristics of the mixture are similar to those of its non-cohesive matrix. When the proportion is in the range of 30-70%, the internal friction angle and cohesion increase rapidly, and the softening characteristics of the mixture become more apparent. When the proportion exceeds 70%, the aforementioned effect slows. (2) The strength of the mixture is positively correlated with its matrix strength, and the influence of the matrix strength on the loading curve of the mixture is related to the block proportion. (3) When the block orientation angle is 0 degrees, the cohesion and internal friction angle are slightly greater than those at an angle of 90 degrees. Based on the above, for the soil-rock mixture with non-cohesive matrix, a strength prediction model based on the block proportion is given when the block orientation angle and matrix strength are consistent.

Civil excavation projects frequently produce significant amounts of excess spoil. Repurposing this spoil into usable backfill material instead of disposing of it offers economic and environmental benefits. This study explores the prospect of converting red-bed mudstone construction waste, a type of soil frequently found at shallow depths, into a ready-mixed soil material (RMSM). It assesses the fresh mixture's workability characteristics (initial flowability, bleeding rate, and density) and the hardened material's mechanical properties (compressive strength and stress-strain relationship) by adjusting the water-to-solid ratio (W/S) and cement-to-soil ratio (C/S). The study investigates the impact of W/S, C/S and time on RMSM's flowability loss and proposes an empirical formula to provide a scientific reference for RMSM's flowability design in engineering applications. Findings highlight the significant influence of W/S on flowability, bleeding rate, and compressive strength, while showing C/S has a limited effect on flowability and bleeding. A negative exponential relationship is observed between flowability and time for all mixes, with the flowability loss ratio increasing over time, ranging from 22.9% to 35.6% after 1 h and stabilizing after 3 h. These insights are crucial to optimize RMSM's performance and suggest the need to further improve the flowability retention of RMSM. Furthermore, in comparison to soil cement and concrete, RMSM reduces backfill costs by 30.8% and 80.0%, respectively, while also achieving a reduction in CO2 emissions by 25.9% and 69.2%. Therefore, RMSM presents as an economically and environmentally friendly alternative for backfill applications.