In view of the complexity of the pile foundation underpinning structure system and the stringent requirements of the construction process, this paper briefly describes the necessity of introducing epoxy resin reinforcing adhesive of planting rebar in the design of pile foundation underpinning beam structure to improve the mechanical properties of the reinforced beam new and old concrete joint surfaces and proposes a new type of pile foundation replacement beam system construction method by “chiseling + prestressed reinforcement + epoxy resin reinforcing adhesive”. This paper uses an actual pile foundation underpinning project of an urban overpass as a prototype, designs and creates a model structure with a similarity ratio of 1/6, and performs repeated progressive static loading tests to study the load carrying capacity, displacement change, and other properties of the strengthened replacement structure, as well as analyses and distorts the overall working performance and failure mode of them. On this basis, the prototype structure’s finite element analysis model was built, and the finite element analysis results were compared with the test results to obtain the mechanical properties and deformation characters of the actual pile foundation underpinning structure system corresponding to the actual underpinning beam load. This paper’s study can lay the theoretical and experimental foundation for the smooth development of similar projects.

Compared with the traditional frame structures, the novel composite frame with replaceable steel links can realize the rapid recovery of building occupancy after seismic actions to provide the capacity of reducing structural damage and ensure the reuse of a structure. In this system, plastic deformation and damage mainly concentrated in the steel links serving as the structural fuses and other structural members still remained elastic or minor plastic, and then the damaged steel links can be easy for replace. In order to study the seismic performance of the replaceable steel links, a total of four test specimens with different short length ratios were designed. A low-cycle reversed loading test was carried out in terms of failure characteristic, hysteretic response and shear strength. The results indicated that all tested specimens presented a stable and full hysteretic response while the steel links especially exhibited a large inelastic deformation capacity and fully developed shear strength as the structural fuses. Besides, failure modes of steel links included two types of shear failure and bending-shear failure, followed by two types of damage features, including web-to-stiffener weld tear, web buckling, flange-to-end plate weld tear and flange buckling, respectively. Finally, nonlinear finite element models (FEMs) of test specimens were implemented by the Abaqus software. The numerical results were in good agreement with the experimental results in terms of load-deformation curves, initial stiffness, the development of Von Mises stress and cumulative plastic equivalent strain (PEEQ) indexes to facilitate design practice.

Pile raft foundation (PRF) is a common foundation type for buildings and bridge piers which has been commonly subjected to eccentric vertical load in engineering applications. Dissimilar PRF is often adopted to reduce the excessive settlement and differential settlement of superstructures. The behavior of dissimilar PRF under eccentric vertical load is a significant issue and investigated with the boundary element method in this paper. In this method, the dissimilar pile–soil system is decomposed into extended soil elements and fictitious pile elements. The second kind of Fredholm integral governing equation of the axial force of fictitious piles is established based on the compatibility condition of axial strain between the extended soil and fictitious piles. An iterative procedure is adopted to analyze the average settlement w and rotation slope θ of raft stemming from the settlement compatibility condition of the top of each element and the equilibrium condition of the raft. Furthermore, the axial force and settlement of each element along its depth can be predicted. The corresponding results agree well with a reported case and the finite element method. The characteristics of 3 × 1 and 3 × 3 dissimilar PRFs under eccentric vertical load, including non-dimensional vertical stiffness N₀/wE_sd, differential settlement w_d and the load sharing ratio of typical elements N_i/N₀, are systematically investigated by considering different eccentricity e, length/diameter ratios of pile l/d and pile–soil stiffness ratio E_p/E_s conditions. The N₀/wE_sd increases with l/d, while the load sharing ratios of the raft N_raft/N₀ and w_d decreases with l/d. The eccentricity e has a significant effect on w_d and N_i/N₀ and a neglect effect on N₀/wE_sd and N_raft/N₀. The N₀/wE_sd, w_d and N_i/N₀ are significantly increased with E_p/E_s. This research is expected to provide insights to the practitioners into the dissimilar PRF design under eccentric vertical load.

In view of the complexity of the pile foundation underpinning structure system and the stringent requirements of the construction process, this paper briefly describes the necessity of introducing epoxy resin reinforcing adhesive of planting rebar in the design of pile foundation underpinning beam structure to im-prove the mechanical properties of the underpinning beam new and old concrete joint surfaces and proposes a new type of pile foundation underpinning beam system construction method by “chiseling + prestressed reinforcement + epoxy resin reinforcing adhesive”. This paper uses an actual pile foundation underpinning project of an urban overpass as a prototype, designs and creates a model structure with a similarity ratio of 1/6, and performs repeated pro-gressive static loading tests to study the load carrying capacity, displacement change, and other properties of the underpinning structure, as well as analyses and distorts the overall working performance and failure mode of them. On this basis, the prototype structure's finite element analysis model was built, and the finite element analysis results were compared with the test results to get the mechanical properties and deformation characters of the actual pile foundation under-pinning structure system corresponding to the actual underpinning beam load. This paper's study can lay the theoretical and experimental foundation for the smooth development of similar projects.

The Three Gorges Reservoir area of the Yangtze River has formed vast riverine fallout zones as a result of its periodic water storage and flood discharge operations, and the main constituents of this area are quaternary loose clays. It is important to study the microscopic characteristics of clay minerals in these fallout zones and their adsorption properties of Hg²⁺ to guide the environmental safety of the fallout zones in the Three Gorges Reservoir area. In this context, the authors of this paper used X-ray diffraction (XRD) experiments to reveal the main clay mineral compositions in the fallout zones and then constructed the molecular model structures of the clay minerals based on molecular dynamics theory and studied the adsorption characteristics of these clay minerals with Hg²⁺ in depth. The results show that the main clay minerals in the Three Gorges Reservoir area fallout zone include illite, illite-mixed layer and green-mixed layer, in which the content of illite ranges from 21% to 54%. Taking illite as the study object, the heat of adsorption of Hg²⁺ in illite ranged from 14.83 kJ·mol⁻¹ to 31.92 kJ·mol⁻¹, which is a physical adsorption. The heat of adsorption was mainly affected by the water content and had little relationship with temperature. With the gradual increase in water content, the heat of adsorption gradually decreases. The adsorption amount of Hg²⁺, on the other hand, is jointly affected by water content and temperature and decreases with the increase in water content and temperature; under natural environmental conditions (P = 0.1 Mpa), the adsorption characteristics of Hg²⁺ in illite change with the change in water content. When the water content was between 0% and 6.95%, the increase in water content led to an increase in the interlayer spacing of illite, and the adsorption of Hg²⁺ in illite was in a monolayer state, with the adsorption peaks located from 4.5~5.5 Å. When the water content increased to 6.95% to 13.90%, the layer spacing of illite reached the maximum, and the adsorption of Hg²⁺ in illite transitioned from a monolayer to a bilayer, with the adsorption peaks located between 5 Å and 9~10 Å, respectively. When the water content was further increased to 13.90% to 20.85%, the increase in water content instead led to a slight decrease in the layer spacing of illite, showing a tendency of transitioning from a bilayer to a monolayer adsorption layer, which at the same time changed the number of adsorption layers of Hg²⁺; the study also revealed that the interaction between illite and Hg²⁺ was regulated by van der Waals and Coulomb forces, whereas the increase in temperature promoted the Hg²⁺ +diffusion, and an increase in water content inhibits the diffusion of Hg²⁺. In summary, these findings provide valuable theoretical support for solving the problem of Hg²⁺ pollution in the Three Gorges Reservoir Decline Zone.