Abstract:Eight sets of 50 new-old concrete interface specimens were subjected to double-sided direct shear tests using the interface processing method, lateral constraint form, concrete strength, and interface size as variables. The shear failure mode and shear strength slip curve of the interface were obtained, and the size effect law of the interface shear strength was analyzed. The conversion coefficient of the ultimate stress size effect of the new-old concrete double-sided direct shear specimens was fitted, and an expression for calculating the shear bearing capacity was established. The results show that in the direction of shear force, there is a significant size effect phenomenon in which the shear ultimate stress at the interface between new and old concrete decreases with the increase of interface height. The size effect of cracking stress, crack through stresses, and slip is not significant. Applying lateral constraints can increase the interface crack through stress and ultimate stress. Applying preloading stress can signifi-cantly increase the crack-through stress of the specimen and effectively limit the ultimate slip of the specimen. Under the condition of no lateral constraint, the chiseling form has a significant impact on the ultimate stress. Compared with the whole poured concrete specimen, the mechanical chiseling of new-old concrete with the same strength reduces the double-sided direct shear ultimate stress to below 0.22 of the whole poured specimens, while the reduction coefficient of the manual chiseling specimen is between 0.34 and 0.37. Under lateral constraint conditions, compared to the rough interface with chiseling, the regular tooth groove specimen has prominent advantages in cracking stress, crack through stress, and slip performance. The strength reduction coefficient under constraint can be increased to more than 2~2.5 times that of the unconstrained specimens under the same conditions, and the maximum strength can reach 0.97 times that of the cast-in-place specimens. The increase in the strength of new-old concrete can increase the crack through stress and ultimate stress of specimens, but the extent of improvement is limited.

Abstract:To enhance the shear strength of masonry structures while preserving their original appea-rance, steel strips or bars are bent to fit the shape of the masonry joints and used to reinforce the masonry specimens, and digital image correlation (DIC) method was used to conduct shear tests on the reinforced masonry specimens. Furthermore, a numerical simulation method was utilized to create a model of the masonry shear test specimen and analyze the impact of the steel strip width on the shear strength of the masonry. The findings indicate that the embedded reinforcement or steel strip can effectively limit the separation between layers, enhance the integrity of the masonry, and transform the failure mode from single shear failure to double shear failure, resulting in a significant increase in the bearing capacity. The ultimate load of the specimens strengthened with single-sided steel strip, double-sided steel strip, and double-sided reinforcement has increased by 23.63%, 61.18%, and 35.02% respectively. Additionally, the corresponding displacement at the ultimate load has increased by 16.38%, 23.41%, and 16.95%. The tensile restraint effect of steel strips or bars can increase the ductility of masonry structures and modify the characteristics of brittle failure of the masonry structure.

Abstract:The finite element method has the disadvantage of being time-consuming and is not suitable for evaluating the seismic performance of structures that require multiple response analyses. A genera-lized single degree of freedom model for linear seismic response analysis of cantilever structures was stu-died, and the polynomial shaped functions and single degree of freedom models based on the polynomial shaped functions were proposed. The effectiveness of the single degree of freedom model based on the polynomial shaped functions for structural response analysis under typical seismic wave excitation was investigated through comparative analysis with the finite element analysis results. The results show that the average error of the proposed generalized single degree of freedom model based on polynomial functions is 7.20%. To improve the modeling accuracy, it is recommended to use the method of applying horizontal concentrated loads for polynomial function parameter estimation.

Abstract:Based on the monitoring data of the temporary cofferdam project on the south bank of the Dalian Bay immersed tube tunnel, a numerical calculation model for the plastic concrete interlocking pile anti-seepage wall was established. The accuracy of the model was verified through measured data, and the deformation evolution law of the interlocking pile anti-seepage wall under different influencing factors was analyzed. The conclusion shows that the water pressure has a more significant impact on the deformation and internal force of the interlocking pile compared to soil pressure. The increase in the water pressure leads to the deformation and bending moment of the pile body, which disturbs the soil of the temporary cofferdam; The influence of the soil slope is relatively small, but the soil slope should gradua-lly decrease and not be less than 1∶1.5. The change in pile length has a significant impact on the deformation, with shorter piles that not embedded in the rock and longer piles experiencing maximum displacement at the top of the pile. As the pile diameter increases, the deformation of the pile top and the maximum bending moment gradually increase, and the distribution of bending moments is relatively consistent.

Abstract:In response to the non-uniformity of soil materials and the uncertainty of dynamic parameters, based on the orthogonal experimental method and taking a dam as an example, an equivalent li-near model was used to analyze the sensitivity of equivalent linear model parameters to the vertical seismic peak acceleration and vertical permanent deformation of the dam body. The results indicate that the parameters k₂, n, and λ_max have significant impacts on the vertical seismic peak acceleration of the dam body, with k₂ being the most sensitive, followed by n. The parameters k₂, k₁, and λ_max have significant impacts on the vertical permanent deformation of the dam body, with k₂ being the most sensitive, fo-llowed by k₁.

Abstract:As the moisture content of the expansive soil slope increases, a certain amount of lateral expansion deformation occurs, and a certain amount of lateral pressure is generated which is composed of the lateral expansion force generated by the constraint deformation of the surrounding soil and the lateral soil pressure caused by the self-weight of the soil and the overlying load. The lateral pressure, especia-lly the generation of lateral expansion force, is one of the main reasons for the shallow failure of the expansive soil slope. A lateral pressure test was conducted using a self-made instrument to control the late-ral strain, and the variation law of the lateral pressure under the influence of factors such as the lateral strain, overlying pressure, and wet-dry cycles was studied. The experimental results show that the late-ral pressure increases linearly with the overlying pressure, and the increase trend does not change with the influence of other conditions. The progress of wet-dry cycles will lead to a certain degree of reduction in the lateral pressure, but it will gradually stabilize after a certain number of cycles. The lateral pressure decreases significantly with the increase of lateral strain, but the decrease extent gradually decreases. Within the existing range of changes, the lateral strain has the most significant effect on lateral pressure, followed by the overlying pressure, and the impact of wet-dry cycles is relatively small.

Abstract:The external steel shell concrete special-shaped cable tower structure of cable-stayed bridges is subjected to complex forces, and there are problems such as deformation and excessive stress during the construction stage. To ensure the construction safety and linear standards of this type of cable tower, three support schemes were designed to reduce the stress and deformation of the cable tower, and the technical performance of different support schemes was analyzed using the finite element method. The analysis results show that the arch axis of the irregular cable tower has a significant impact on the stress and deformation of the tower column, and the stress and deformation of the cable tower calculated by different modeling methods vary greatly. The support of all three schemes can significantly reduce the deformation of the cable tower and the tensile stress of the concrete inside the cavity, while the four channel double pipe scheme is the most effective in reducing construction difficulty and errors. The deformation of tower columns and the tensile stress of concrete are sensitive to wind pressure, and the design of wind resistance measures for tower columns should be strengthened during construction.

Abstract:In order to study the effect of horizontal rotary jet grouting pile plus advanced small pipe combination pre-reinforcement in the rich water sand layer tunnel, based on a section of the Qingdao Metro tunnel, the finite element numerical simulation method was used to compare and analyze the reinforcement effect of three working conditions: non-pre-reinforcement, using horizontal rotary jet grouting pile alone, and rotary jet grouting pile combined with advanced small pipe combination pre reinforcement. The results show that compared with the non-pre-reinforcement scheme, the use of horizontal rotary jet grouting pile pre -reinforcement alone can reduce surface settlement, arch settlement, and longitudinal displacement of the palm face by about 61%, 59%, and 38%, respectively. The combination of horizontal rotary jet grouting pile and advanced small conduit pre reinforcement scheme can reduce surface settlement, arch crown settlement, and longitudinal displacement of the palm face by about 66%, 77.6%, and 38.9%, respectively. The groundwater seepage flow at typical excavation sections and arch feet can be reduced by 93.4% and 96.7%, respectively. The pre-reinforcement effect and water stop effect are significant.

Abstract:Based on the collapse accident of a shallow buried loess tunnel in Ningxia, this paper first discusses and analyzes the collapse failure mechanism and mode of the shallow buried loess tunnel. Then, based on the on-site collapse situation, the causes of the tunnel collapse are analyzed and the disposal plans are proposed. Finally, the disposal effect is evaluated through numerical simulations and on-site monitoring. The results show that the vulnerability of loess itself, adverse terrain, disturbance du-ring shallow tunnel construction, and heavy rainfall infiltration jointly lead to the formation of a certain range of loess soft and collapsible zones in the surrounding rock above the tunnel. The original tunnel support structure cannot resist the degraded surrounding rock, and the deformation and structural stress of the surrounding rock increase significantly. Among them, the settlement of the arch crown increases by 91.8%, and the initial positive bending moment at the arch shoulder increases by 60.7%; The instability and failure of the excavation face in loess strata can be divided into two modes: the instability and failure of the palm face reaching the weak and collapsible zone, and the instability and failure of crossing the entire weak and collapsible zone. Combining the finite element simulation and on-site monitoring verification, the comprehensive anti-collapse treatment technology of "temporary support system plus arch replacement plus advanced pipe shed grouting reinforcement" has shown significant application effects.

Abstract:In order to understand the influence mechanism of grouting pressure fluctuations on pipe joints in large cross-section rectangular pipe jacking, this paper relies on a large cross-section rectangular pipe jacking project in Nanjing, and uses research metho-ds such as theoretical analysis, engineering analogy, and numerical simulation to investigate the influence mechanism of grouting pressure fluctuations on the stress state of large cross-section rectangular pipe joint structures under local pressure suppression condit. The external loads of large cross-section rectangular pipe joints was calculated, and the concrete damage plasticity model built-in ABAQUS software was used for numerical modeling to study the damage evolution mechanism of reinforced concrete pipe joints under different grouting pressures. The results show that: (1) grouting load, as a variable load, has a significant impact on the stress distribution of the pipe joint, such that the grouting pressure should be included in the design of the pipe joint; (2) For this project, the theoretical grouting pressure is 0.311 MPa. In view of the need to suppress the carrying-soil effect, the grouting pressure should be appropriately increased, but it must be controlled within a reasonable range; and (3) From the perspective of damage evolution, when the grouting load reaches 0.6 MPa, the tensile damage to the top plate of the pipe joint has reached a high level. Therefore, 0.6 MPa is used as the grouting pressure warning indicator for this project, while 0.9 MPa should be used as a control indicator for grouting pressure.

Abstract:To study the settlement characteristics of subway shield tunneling passing through settlement sensitive areas in cities, a three-dimensional finite element model is established based on the example of subway shield tunneling passing through gas stations. The settlement distribution curves of the ground and oil tanks during the process of shield tunneling approaching gas stations are obtained. Furthermore, by changing the position of oil tanks, the influence of tunnel excavation on oil tanks under different a-rrangement modes is compared and analyzed. The results show that under the double-layer arrangement of oil tanks, surface settlement increases with the excavation of the tunnel, and the maximum settlement reaches 11.48 mm after construction is completed, close to the left side of the tunnel. Under the disturbance of tunnel construction, the maximum settlement of the oil tank reached 2.85 mm. Compared to the double-layer arrangement, the final settlement of oil tanks is reduced to 2.68 mm in the single-layer arrangement. The maximum settlement difference between the upper and lower sides of the oil tank has been reduced by 38%, and the settlement change rate of the surface measurement points of the oil tank has been reduced by 41%, significantly improving safety.

Abstract:In order to conduct in-depth research on the stress redistribution state of the lining GFRP protective composite pipe wall at the corrosion defect pit in its original pipeline and its repair effect. A mathematical model of corrosion defects in pipelines was established using the equilibrium differential equation within elastic-plastic mechanics. A pipeline model containing a single corrosion defect was established using the finite element method, and the stress state at the corrosion defect pit before and after repair was compared and analyzed by changing the depth ratio of the corrosion defect pit. The analysis results indicate that the depth ratio of corrosion defect pits has a significant impact on the stress distribution of pipelines, so attention should be paid to the influence of corrosion pit depth when conducting pipeline safety assessments. During the process of increasing the depth ratio of corrosion defect pits from 0.1 to 0.8 in stages, the circumferential stress, radial stress, and Mises stress at the corrosion defect site on the pipe wall show an increasing trend. The circumferential stress at the corrosion defect pit before repair is similar to the Mises stress, while the radial stress is smaller than the previous two and the circumferential stress is the largest among the three. Before and after repair, the control stress at the corrosion defect of the pipeline is generally the circumferential stress, and the failure of the pipeline can be judged based on the circumferential stress. After repair, the inner lining of the GFRP protective composite pipe wall experienced stress redistributions at the original corrosion defect pit, and both the circumferential stress and Mises stress decreased, indicating a significant repair effect.

Abstract:In order to grasp the thermal environment characteristics of the waterfront space in the ancient town, the South Canal coastal block of Yangliuqing Ancient Town was taken as the research object. Through on-site measurement of environmental parameters, the impact and laws of factors such as solar radiation, underlying surface type, spatial enclosure form, water body layout, and vegetation combination on the thermal environment were analyzed. The results show that the waterfront space of Yangliu-qing Ancient Town exhibits a high temperature and low humidity thermal environment in summer. In summer, there is a significant difference in the environmental temperature with and without shading conditions, and the significant increase in the average radiation temperature at noon is the main reason for the decrease in the comfort of waterfront spaces. The combination of greenery and architectural shadows has the best cooling effect among landscape elements. Based on the above conclusions, the measures are proposed to improve the thermal environment of the waterfront space in Yangliuqing Ancient Town.

Abstract:In this study, first principles calculations based on density functional theory (DFT) were used to accurately quantify the equilibrium Cd isotope fractionations produced during the formation of organic surface complexes (OSCs) and metal-organic frameworks (MOFs). The results showed that the equilibrium Cd isotope fractionations between OSCs and the aqueous solution at 25 ℃ were small and insensitive, i.e., Δ^114/110Cd_OSCs-aq=-0.34‰ to 0.02‰. In contrast, the formation of MOFs produced significant Cd isotope fractionations, i.e., Δ^114/110Cd_MOFs-aq=-1.92‰ to-0.29‰. Additionally, the more N and S atoms appear in the first coordination layer of Cd, the greater the equilibrium fractionation of Cd isotopes between MOFs and aqueous solutions. Our calculation results cover the experimental determination of Cd isotope fractionation in surface soil, indicating that the different occurrence states of Cd in soil organic matter control its isotopic composition. Finally, these fractionation data enrich the Cd isotope database, making it easier for scholars to quantitatively use Cd isotope methods to limit the migration and transformation process of Cd.