Buried pipes are subjected to static and dynamic loads depending on their areas of use. To mitigate the risk of damage caused by these effects, various materials and reinforcement methods are utilized. In this study, five buried uPVC pipes designed in accordance with ASTM D2321 standards were reinforced with three different ground improvement materials: Geocell, Geonet, and Geocomposite, and experimentally subjected to dynamic impact loading. Acceleration, velocity, and displacement values were obtained from the experiments. Subsequently, finite element analysis (FEA) was performed using the ABAQUS software to determine stress values and volumetric displacements in the pipes, and the model was validated with a 5-7% error margin. In the final stage of the study, a parametric analysis was conducted by modifying the soil cover height above the pipe and the Geocell thickness in the validated finite element model. The parametric study revealed that the displacement value in the pipe decreased by 78% with an increase in soil cover height, while a 16% reduction was observed with an increase in Geocell thickness. The results demonstrate that the soil improvement techniques examined in this study provide an effective solution for enhancing the impact resistance of buried pipeline systems.

During the global coronavirus (COVID-19) pandemic, a huge amount of personal precautionary equipment, such as disposable face masks, was used, but further usage of these face mask leads to adverse environmental effects. Here, we evaluated the feasibility of using mask chips to reinforce clayey soil, testing this with static and impact loading, including uniaxial compression, diametral point load, and drop-weight impact loading tests. The concurrent influences of shape, size, and percentage of waste material were considered. Generally, the contribution of shredded face mask (SFM) was majorly attributable to its tensile reinforcement. As a consequence, the strength of the mixture, measured by the static tests, was increased. This property was enhanced by the addition of rectangular mask chips. We determined the optimum percentage of SFM, beyond which the uniaxial compression strength and the point load strength index decreased. An increase in the percentage of SFM in the soil produced a higher damping coefficient and lower stiffness coefficient, causing greater flexibility. This trend increased beyond 1.2% of SFM (by volume of clay soil). Generally, based on our results, 1-1.5% of SFM was the optimum content.

In this study, impact compression tests on low-temperature concrete were conducted using a split Hopkinson pressure bar. The impacts of low temperatures on the strength, fractal, and energy characteristics of concrete were analyzed. The damage evolution mechanism of the microcrack density was discussed based on microscopic damage theory and microscopic tests. The results demonstrated that the impact fractal dimension and energy dissipation density of low-temperature concrete were positively correlated with the strain rate. The strain rate sensitivity of the impact fractal dimension was significantly affected by low temperature at low strain rates; however, low temperature had little effect at high strain rates. The pore water transformed into ice at negative temperatures, the fracture energy of the concrete increased, and the energy dissipation density increased. More than 50 % of the capillary and free water inside the concrete was frozen at -10 degrees C; approximately 30 % of the capillary and free water and 65 % of bound water did not freeze when the temperature was -30 degrees C. The macropores did not collapse under the action of ice filling at high strain rates; however, microcracks were generated around them. With a decreasing temperature, the threshold stress for microcrack propagation increased, crack propagation required more energy, and the microcrack density decreased.

The complex multiphase composition of frozen soil induces significant coupling interactions between the thermal, hydrological, mechanical, and damage fields during deformation, particularly under dynamic loading conditions. This study presents a hybrid decomposition phase-field model to investigate the multi-field coupling behavior and damage mechanisms of frozen soil. Unlike the spectral decomposition model, the proposed framework integrates isotropic degradation and the spectral decomposition methods, thereby enabling the simulation of damage evolution under compressive-dominated loading conditions. The model incorporates the viscous effects and strain rate sensitivity to accurately capture the dynamic response of frozen soil and establishes governing equations for coupled displacement, temperature, and fluid pressure fields. The applicability of the model was validated through confined compression experiments on frozen soil, demonstrating its capability to predict distinctive damage features, such as compaction bands oriented perpendicular to the loading direction, which represent the competitive interaction between the softening mechanism of pore collapse and the hardening mechanism of microstructural densification. This study provides significant advancements in the theoretical understanding and numerical simulation of the dynamic mechanical behavior of frozen soil.

Determining the burial depth for offshore pipelines to resist impact load is challenging owing to the spatial variability of soil strengths, which proves to significantly affect failure behaviours of soils and pipelines. To facilitate the design, accurate and fast evaluation on pipeline damage is required. Here, an integrated surrogate model was developed to forecast impact damage of pipelines buried in spatially varied soils. Through coupling the random field and numerical simulation, a stochastic finite element analysis framework was derived and verified to yield the datasets; Based on the scheme of feature extraction - integration from convolution neural network, the surrogate model was established, which mapped the three-dimensional soil spatial field to the structural response. Prediction mechanism of the developed model was explored, where correlations among soil spatial distribution patterns, failure mechanisms and feature recognitions were discussed. The models enabled to capture the key features representing the failure mechanisms under random soil conditions, including the local failure mode of soil and pipe-soil interactions, which theoretically explained its feasibility in damage estimation. Further, model performance was comprehensively evaluated with regard to prediction accuracy, uncertainty quantification, and transfer learning, and the corresponding causes were investigated. Satisfactory performance and high computation efficiency were demonstrated.

The frozen moraine soil is geographically distributed across the Qinghai-Tibet Plateau and its surrounding areas, serving as a fundamental substrate for engineering projects such as the Sichuan-Tibet Railway and the ChinaPakistan Highway. As an economical and efficient construction technique, blasting is a commonly employed in these projects. Understanding the dynamic mechanical response, damage, and failure characteristics of moraine soil is crucial for accurately predicting the impact of blasting. Therefore, this study utilizes the Split Hopkinson Pressure Bar (SHPB) equipment to conduct impact tests on moraine soil under different temperatures and strain rates. Additionally, a model for predicting the dynamic mechanical response of frozen moraine soil has been proposed based on peridynamic theory, decohesion damage theory, and the ZWT model, in which the debonding damage and the adiabatic temperature rise are considered. This model focuses on considering the bonds between different substances within frozen moraine soil. By defining the mechanical response of these bonds, the impact deformation mechanism of frozen moraine soil is unveiled. Within this, the modeling of icecemented bonds contributes to a deeper understanding of the crack propagation characteristics in frozen moraine soil. The model prediction results demonstrate its capability to predict various aspects of the dynamic response of frozen moraine under impact loading, including the macroscopic stress-strain behavior, the mesoscopic crack initiation and propagation, and the influence of adiabatic temperature rise on the damage mechanism, as well as evaluate the damage state of frozen moraine soil under impact loading.

Burial is an effective approach to offshore pipeline protection for impact loads. However, few studies address the influences of inherent soil spatial variabilities on failure behaviour of soil covers and pipelines, causing deviations. Therefore, a random field-large deformation finite element analysis framework is developed to explore the failure mechanisms of buried pipelines in spatially varying soils. The failure mode of soil cover is conformed to a local mode, where the failure path is insensitive to soil variability. The failure mechanism of pipelines depends on the competition mechanism between soil strengths and pipe-soil interactions, based on which two typical failure modes are summarized. Soil variability not only aggravates the impact damage but also stimulates the diversity of structural responses. Correlations between probabilistic damage degrees and multiple influential factors are discussed. Further, inspired by the principle of energy dissipation, an integrated quantitative risk assessment model is derived to reveal the failure risk evolution, where uncertainties from soil variabilities and structure-related factors are considered. The latter shows a significant influence, which may pose an additional failure probability of over 50 %. Different safety design approaches are compared, and spatial failure probability surfaces are configured for burial depth determination.

This study evaluates the vertical stress transmission through a sand-tire mixture layer under impact, focusing on this innovative blended material that can impact underground structures such as tunnels or pipelines. By conducting consolidated undrained triaxial tests, the friction angle (phi) of the sand-tire mixture was determined, ranging from 29 degrees for pure tire to 41 degrees for pure sand. The vertical stress factor (alpha), representing the ratio of response load to applied load, was found to decrease significantly with increased tire content, with a reduction of up to 50% for mixtures containing 20% tire. Additionally, the vertical stress response decreased from 35 kPa for pure sand to as low as 15 kPa for mixtures with a high tire content under a consistent applied load of 65 kPa. This study not only presents a methodological advancement in analyzing sand-tire mixtures under dynamic loads but also suggests a sustainable approach to utilizing waste tire material in civil engineering projects, thereby contributing to environmental conservation and improved material performance in geotechnical applications.

Submerged floating tunnels (SFTs) represent a promising innovative transportation infrastructure, offering advantages for crossing long, large, and deep bodies of water in the future. However, critical issues regarding their responses mechanism and technique remain unclear, leading to the absence of constructed SFT prototypes globally. A pier-type SFT (PSFT) is a typical SFT configuration with relatively high stability and safety. This study reviews the progress in PSFT research and discusses critical issues and solutions, including structural design, dynamic response characteristics, and feasibility analysis. Suggestions are provided for future research and applications. PSFTs can be considered as immersed tunnels supported by underwater bridge piers. Although adequate research has been conducted on piers, piles, and tunnel tubes, limited investigations have focused on PSFTs. Existing studies are primarily based on conceptual designs of PSFT, lacking theoretical and experimental investigations. The dynamic response characteristics and progressive collapse mechanism of PSFTs under the influence of waves, currents, and earthquakes are complicated. Scouring and liquefaction can significantly reduce the bearing capacity and alter the dynamic responses of PSFTs. Refined numerical simulations and underwater shaking table tests for PSFTs remain limited. In addition, the performance degradation mechanism and damage evolution process caused by accidental loads, such as impact and explosion, should be emphasized. PSFTs are recommended for broad waters with depths ranging from 30 m to 150 m and lengths larger than 1000 m. Although construction technologies for PSFT components are sufficient and mature, guidelines specifically for PSFTs remain imperative. This highlights the necessity for extensive investigations on PSFTs, considering their mechanism and characteristics under extreme environmental loads.

Due to its distinct characteristics of instantaneity and abruptness, the stress variation characteristics of unsaturated soil under impact loads significantly differ from those under static and conventional dynamic loads. To investigate the spatial stress state under impact loads, in-situ testing was conducted on an unsaturated soil roadbed using three-dimensional stress testing technology. The three-dimensional soil pressure cells were set at depths of 0.3 m and 0.6 m below the ground surface. Continuous vertical impact loads were applied at the ground projection of the buried points. Stress testing data was collected in real time, and stress transformation methods were applied to obtain the corresponding three-dimensional stress, principal stresses, and the evolution of principal directions. Based on this, a comparison was made with existing one-dimensional stress testing methods and results, further illustrating the rationality and scientific validity of three-dimensional stress testing. The testing data revealed that under impact loads, the stress component in the impact direction (i.e., the z-axis direction) shows a notable instantaneous increase with a positive increment, whereas the increment of positive stress in the y-direction is negative. The principal stress direction angles alpha, beta, and gamma undergo considerable deviations during the impact. Specifically, alpha varies within a 90 degrees range, while beta and gamma rapidly decrease from their initial values to their supplements. Moreover, all three directional angles experience multiple reciprocating changes within a single impact duration. This research has theoretical significance in deepening the understanding of stress response and evolution processes in unsaturated soils under impact loads, providing valuable references for constitutive models, engineering design, and construction research related to seismic or other impact loadings.