Abstract:The determination of the vertical ultimate failure mechanism and the bearing influence depth of the bucket foundation under varying geological conditions holds immense importance in accurately calculating the ultimate bearing capacity. The current study employs the numerical simulation analysis app-roach to examine the vertical ultimate failure mechanism in laminated clay through the layer-down me-thod. It investigates the variation in bearing capacity of the bucket foundations in laminated clay and determines the influence depth for the foundations in this type of soil. The investigation is conducted separately on the basis of whether the bucket foundation is penetrated at the interface between the upper and lower layers of laminated clay. Empirical equations for the influence depth are developed to account for varying conditions. The investigation of the vertical bearing depth of the bucket foundation unveils the influence of the strength ratio between the upper and lower soil layers, as well as the positioning of the soil layer interface, when combined with the outcomes of the numerical analysis.

Abstract:Foreign various commercial serial softwares possess some disadvantages, such as the limited applicability, small-scale computing capacity and low efficiency. To overcome these disadvantages, we developed StrataKing (a GPU parallel computing system of strata motion) based on the hybrid Lagrangian-discrete element method in the past more than ten years. In this paper, the flow chart, basic principle and main features were introduced. Each computing modules were executed on GPU. The validation of StrataKing was conducted by modeling the cracking process of the three-point bending beam. Under the hydrostatic pressure, for finer meshes, cracks in the vicinity of the tunnel are more curved and gentle, extending toward the depth. The phenomenon is different from of the ring plastic zone in which failure occurs everywhere in plastic mechanics. During excavation, the peaks of the abutment and horizontal pressures were presented. The latter is related to the cohesion between strata, which is different from the radical stress of the thick-wall tube based on the continuous assumption. Thus, the large-scale computing capacity, wide applicability and apparent mining characteristics of StrataKing were further demonstrated.

Abstract:The muddy soft soil under the miscellaneous fill foundation can easily be squeezed into the pores between the miscellaneous fill particles under the action of the overlying load, causing mutual settlement. This part of the settlement is not considered in traditional foundation settlement calculation methods. Using a self-developed soil intercalation experimental instrument, one-time loading, conventional graded loading, and composite multi-stage loading tests were conducted on soft soil and miscellaneous fill in the Qinhuai River area of Nanjing, revealing the development law of intercalation settlement under different loading methods. The results show that under different loading methods, the total settlement and embedded settlement show a stepwise growth trend, with a sudden increase in settlement at the moment of loading, then gradually slowing down and stabilizing. The difference in the total settlement and embedded settlement mainly comes from the settlement changes at the moment of load application. In the case of multi-level loading, the embedded settlement is negatively correlated with the loading order and positively correlated with the load proportion. Through curve fitting, it was found that the embedded settlement is logarithmically correlated with the loading order and exponentially correlated with the load proportion. The proportion of embedded settlement is negatively correlated with the loading order and positively correlated with the proportion of load. Moreover, when the particle size is large, the sensitivity of the embedded settlement proportion to the loading method decreases.

Abstract:Reinforced concrete structures located in coastal atmospheric areas are susceptible to harmful ions such as chloride ions and sulfate ions, resulting in a shortened service life of the structure. The pore size distribution of steam-cured and standard-cured concrete was studied through low-field nuclear magnetic resonance experiments, revealing the corrosion evolution law of chloride ions and sulfate ions on steam-cured concrete. The results indicate that compared to standard cured concrete, the harmless pore content of steam-cured concrete decreases, while the harmful and multi-harmful pore content increases, resulting in a higher degree of hydration. The compressive strength of steam-cured concrete is lower than that of standard-cured concrete. Adding a certain amount of mineral powder can significantly improve the resistance of steam-cured concrete to chloride ion corrosion. The greater the chloride ion binding ability, the smaller the chloride ion diffusion coefficient, and the lower the surface chloride ion concentration. When the content of mineral powder is 25%, the chloride ion diffusion coefficient of steam-cured concrete is low, indicating that the optimal pore size effect of the secondary hydration of mineral powder is achieved; As the amount of mineral powder increases, the reaction coefficient of sulfate ions gradually decreases. When the amount of mineral powder is 50%, the reaction coefficient of sulfate ions is the lowest due to the lowest content of calcium phase substances in concrete.

Abstract:In order to study the law of salt transport in loessial soil with diffferent particle sizes and contents of spherical microplastics under different rainfall conditions, a vertical infiltration experiment was carried out by using the indoor one-dimensional soil column model, and the scatter diagram of the infiltration conductivity of soil columns with different contents and particle sizes of microplastics under different rainfall conditions was obtained. The results showed that a low content of microplastics in loessial soil significantly promoted the infiltration of NaCl solution, while a high content of microplastics blocked the infiltration of NaCl solution, and the rainfall conditions changed the critical content of microplastics. In loessial soil, a slightly smaller particle size of microplastics significantly promoted the infiltration of NaCl solution, and a slightly larger particle size of microplastics blocked the infiltration of NaCl solution. The microplastics with lower content and smaller particle size are more sensitive to the rainfall response.

Abstract:In order to study the degree of influence of the maximum size of recycled coarse aggregate on the bending and tensile strength, compressive strength and folding ratio of recycled concrete, four groups of recycled concrete prismatic specimens (100 mm×100 mm×400 mm) and four groups of cubic specimens (100 mm×100 mm×100 mm) were prepared by using different volume combinations of the recycled coarse aggregate with maximum sizes of 10, 15, 25, and 31 mm under the same mixing ratios and the bending and tensile strengths and compressive strengths of the recycled concrete specimens of the various groups were obtained through tests. The results show that under the same water-binder ratio, the flexural strength and flexural-compression ratio of recycled concrete decrease with the increase of the maximum particle size of recycled coarse aggregate, while the compressive strength increases first and then decreases with the increase of the maximum particle size of recycled coarse aggregate.

Abstract:To fully utilize the engineering waste soil, it is thoroughly mixed with a curing agent and water to prepare a new type of filling material that does not require compaction after backfilling and has good engineering properties. In this paper, depending on a foundation pit fertilizer trench backfill project in Nanjing, direct shear tests were carried out on different proportions of premixed fluid soil to study the shear characteristics of premixed fluid soil. Based on the neural network model, the prediction of the shear stress versus shear displacement curve of premixed fluid soil was carried out. The results indicate that the type of shear stress versus shear displacement curve of premixed fluid soil is influenced by the cement mix ratio, curing age, and vertical pressure. The shear strength and cohesion of premixed fluid soil are influenced by the water cement ratio, vertical pressure, curing age, and cement mix ratio. The neural network prediction model for shear stress versus shear displacement curve of premixed fluid soil has a high accuracy in predicting the shear strength.

Abstract:In order to study the physical and mechanical properties of Beishan granite, conventional triaxial, creep, and relaxation tests were conducted. The main research process and conclusions are as follows:(1) Conventional triaxial compression tests were conducted on Beishan granite under different confining pressure conditions and mechanical characteristics, such as the deformation and failure modes of the samples, were compared and analyzed. It was found that the irreversible deformation of Beishan granite rock during failure was relatively small and there is no brittle ductile transition phenomenon with the increase of confining pressure; (2) Single stage creep tests on Beishan granite and multi-level creep tests were conducted under different confining pressure conditions and the deformation of different deviatoric stress pairs and the creep rate of single stage creep were analyzed, which showed that the creep form of Beishan granite was unstable creep, and its strain curve showed typical third-order creep characteristics; and (3) Single stage stress relaxation and cyclic relaxation tests were conducted on Beishan granite and the variation law of deviatoric stress was analyzed, which found that the deviatoric stress of Beishan granite decreased rapidly during the initial relaxation stage of stress relaxation process and reached a stable state in a relatively short period of time.

Abstract:Due to the large shrinkage deformation and high cost of high ductility fiber reinforced cementitious composites (HDCC), domestic materials such as PVA fibers and fly ash have been used to prepare HDCC with low shrinkage and low-cost. In this study, the micro and macro experiments on HDCC were conducted and analyzed. It is shown that the hydration reaction of HDCC is delayed with the increase of fly ash content, resulting in a decrease in the mechanical properties and a variation in the interface micro mechanical parameters of the fiber matrix. This promotes the extraction of fibers from the matrix, significantly improves the ductility and toughness, and reduces the shrinkage deformation.

Abstract:In order to study the improvement effect of polyacrylamide (PAM) on the flow state solidification soil, the effects of PAM dosage, liquid-solid ratio, and ash soil ratio on the widely distributed soft soil in the middle and lower reaches of the Yangtze River were studied. The results showed that PAM can quickly reduce the flowability of cement-based flow state solidification soil, improve viscosity, and slow down the early solidification speed of cement-based soil. The improvement effect of PAM on the flowability of fluidized solidification can be quantitatively described by net flow rate. It can be concluded that the net fluidity of fluid cement soil with different initial liquid-solid ratios decreases at the same level after adding a certain proportion of PAM. For soft soil with a liquid-solid ratio of 70% to 80%, it is recommended to control the PAM content at 0.02% to 0.03% to ensure that the flowability meets the backfill requirements and the on-site construction effect is better. At the same time, PAM effectively improves the freedom of the construction process. On this basis, the relationship between the dynamic shear force and fluidity of the soil was obtained, which can better fit the measured data.

Abstract:In order to analyze the problems of lining deformation, cracking, and even tunnel collapse caused by the presence of weak interlayers in the surrounding rock of highway tunnels in mountainous areas under the orthogonal system, based on the theory of tensile shear strength reduction method and FLAC3D finite difference software, this paper takes the planned expansion of a certain tunnel slope as the engineering background, and studies the changes in the stability and safety coefficient of the tunnel slope surrounding rock with different slope slopes and tunnel burial depths. The results indicate that as the slope gradient continues to increase, the maximum shear strain value and distribution range of the surrounding rock gradually increase, the plastic zone range continues to increase, and the safety factor of the surrounding rock stability continues to decrease. As the depth of the tunnel increases, the maximum shear strain value of the surrounding rock first increases, then decreases, and finally increases. However, the ranges of the shear strain and plastic zone continues to increase, and the safety factor of the surrounding rock stability shows a first decrease and then increase. When there is no weak interlayer, the maximum safety factor is calculated. When there is a weak interlayer, the safety factor calculated using the asynchronous reduction method is higher than that using the synchronous reduction method.

Abstract:In order to solve the problems of low energy utilization efficiency and many shortcomings in environmental and economic aspects of traditional single heating forms, it is considered to organically combine the green sustainability of renewable energy with the stability of conventional energy. Taking a deep geothermal energy+multi energy complementary heating project in a university campus in southern Hebei as an example, the project overview, energy supply plan, and energy station construction were introduced, and the system operation and testing data were organized and analyzed. The results show that the system operates well, saving 20 860 tons of standard coal annually, reducing 54 650 tons of carbon dioxide annually, reducing 175 tons of sulfides, 154 tons of nitrogen oxides, and approximately 210 tons of waste residue. The economic and environmental benefits are significant.

Abstract:The efficient use of low rank coal distillation residue is one of the important ways to achieve clean and efficient use of low rank coal. The extracted pitch was obtained by extracting the residue of rapid destructive distillation of low-rank coal using washing oil as solvents. The pyrolysis kinetics of the extracted pitch was investigated using a thermogravimetric analyzer. The activation energy of the pyrolysis reaction of the extracted pitch was calculated using Flynn-Wall-Ozawa and Kissinger-Akahi-ra-Sunose, and the kinetic parameters of the pyrolysis reaction were solved using the Satava-Sestak analysis method. The experimental results showed that G(α)=[-ln(1-α)]⁴ was the optimal mechanism function (n=4), with a reaction activation energy of 91.43 kJ/mol and a pre-exponential factor of A=4.07×10¹³. The extracted pitch was subjected to thermal conversion treatment to obtain pitch coke. The properties of the extracted pitch coke were studied using methods, e.g., polarizing microscopy, microstrength testing, Raman spectroscopy, and the corresponding peak fitting. The results showed that the extracted pitch coke was a mosaic structure mainly composed of medium particle mosaic structure (Mm) and fine particle mosaic structure (Mf). The microstrength of the pitch coke was 85.05%, the graphitic carbon microcrystal content (I_G/I_All) was 15.13%, and the amorphous carbon content (I_D3/I_All) was 12.07%. This study explores the utilization pathways of low rank coal carbonization residue from the perspective of asphalt recovery and utilization, providing a theoretical and experimental basis for achieving clean and high-value utilization of low rank coal.

Abstract:The seismic inversion and single seismic attribute reservoir prediction of Xishanyao Formation in Hu218 of Santanghu Oilfield have poor results, and the understanding of sand body distribution patterns is unclear, which restricts the development effect of the oilfield. In response to the current situation of reservoir prediction in the research area, a three-step strategy was adopted to achieve effective prediction of delta reservoirs. Firstly, the relationship between seismic attributes and sand to ground ratio was analyzed, and seismic attributes with high correlation were selected. The sand to ground ratio distribution map was obtained through multi-attribute fitting, clarifying the macroscopic boundary characteristics of sedimentary facies; Secondly, analyze the relationship between sedimentary microfacies and seismic waveforms in each well, and establish six typical seismic facies identification charts; Finally, a distribution map of sedimentary microfacies in the study area is drawn by combining macroscopic boundary characteristics with seismic identification diagrams of sedimentary microfacies. The results indicate that the combination of seismic multi-attribute fitting and seismic analysis can reflect the distribution characteristics of sedimentary microfacies from both macro and micro levels.

Abstract:To reveal the strength characteristics of sandy loess under freeze-thaw cycles, taking sandy loess in Zizhou, Yulin, as a research object, the freeze-thaw cycle experiments on the sandy loess with different initial conditions was carried out, and the triaxial shear strength of the soil was determined after freezing and thawing. The results showed that:the surface of sandy loess after freezing and thawing showed a obvious structural damage phenomenon; the cohesion of soil body decreased with the increase of the number of freeze-thaw cycles firstly and then rebounded; the cohesive force of soil body after freezing and thawing decreased with the increase of the initial water content, and the freezing temperature had different influences on the cohesive force of soil body of different water content. It was also found that the friction angle of soil body decreased under freeze-thaw cycles, but the overall decrease was not significant and the decrease of soil body strength was mainly affected by the deterioration of cohesive forces. Both extreme low-temperature freezing at higher water contents and higher-temperature freezing at lower water contents accelerate the destruction of soil strength under freeze-thaw cycles.