With the development of large-scale projects such as high-rise buildings, deep-sea platforms, bridges, etc., these construction facilities are affected by many factors such as environment and geological conditions, which put forward higher requirements for pile-bearing capacity. Compared with the straight-hole grouted piles, the CEP (concrete expanded-plate) piles have an increased bearing plate, which has stronger resistance to pullout under the action of axial tension. The location of the bearing plate is the main factor affecting the bearing capacity of a CEP pile. This study simulates and analyzes CEP double piles on ANSYS software (Ansys R19.0 versions) under ideal conditions, designs five types of model piles with different bearing plate positions, and divides them into six groups for simulation. Finally, a complete model of the two-pile system is established. It is obtained that when the bearing plate is in the same position, the longer the pile length above the bearing plate, the greater the ultimate bearing capacity of the CEP double piles; when the bearing plates of a double pile are at different positions, the antipull-force-bearing capacity of the double pile mainly depends on the pile with a smaller pile length above the bearing plate, and determines the calculation mode of a CEP double-pile antipull-force-bearing capacity at different bearing plate positions, so as to provide a theoretical basis for the design and application of CEP pile foundations in large building structures in the future.

In order to study the seismic wave attenuation characteristics of complex plate tectonics in and around the Kanto Basin, based on the focal mechanism and Slab1.0 model, the research area is divided into four regions. The one-step non-parametric generalized inversion technique was used to analyze the seismic wave attenuation characteristics of each region separately. The results show that the seismic path attenuation of earthquakes occurring in the shallow crust (Reg.1) is weak, and the seismic wave refraction at the crust–mantle boundary leads to almost no attenuation over a long hypocentral distance (>60 km), the frequency–dependent inelastic attenuation is also weak with the 0.5–20 Hz quality factor Q = 92.33f^1.87. The seismic path attenuation of the upper mantle earthquakes occurring in the Kanto Basin (Reg.2) is strong, and the attenuation curve decreases with the increase of hypocentral distance, which is approximately parallel to the geometric diffusion R^−2.0, the frequency–dependent inelastic attenuation is stronger with the quality factor Q = 27.75f^1.08. The seismic path attenuation of subduction zone earthquakes (Reg.3 and Reg.4) is more obvious in the high–frequency band and has a frequency correlation, indicating that the attenuation of subduction zone earthquakes includes more inelastic attenuation. The frequency–dependent inelastic attenuation Q of Reg.3 and Reg.4 are 52.58f^0.95 and 58.07f^0.89, respectively.

Concrete expanded-plate piles (CEP piles) are novel variable-section piles that offer broader applicability, greater bearing capacity, and superior economic benefits compared to conventional straight-shaft piles. Their increasing use in construction projects underscores these advantages. While previous studies have demonstrated the favourable bearing performance of CEP monopiles, the influence of pile spacing on the performance of CEP double piles remains unexplored. This study combines laboratory-scale unitary soil tests with ANSYS Workbench 2022R1 finite element simulations to investigate the effects of pile spacing on the bearing behaviour and soil failure mechanisms of CEP double piles. An optimal pile spacing range is proposed, and the compressive bearing capacity formula is modified accordingly. These findings establish a theoretical foundation for the development of CEP double-pile and pile group foundations, thereby supporting their wider use and promotion in geotechnical engineering.

Anchorage force comprises bond force and bearing pressure when headed bars are used. Pull-out tests were conducted on 120 concrete specimens to derive a method for calculating the bond force for reinforcement in straight anchor sections at the yield moment. The parameters include the diameter d, embedded length l_ae, and yield strength f_y of the reinforcement, as well as the strength grade of the concrete f_cg. The experimental results indicated that the specimens underwent three failure modes depending primarily on the embedded length l_ae. The nominal average bond stress τ^u concept was proposed and the difference between τ^u and the actual average bond stress τ caused by the headed bars was observed. To reduce the difference between the τ^u and τ values, the correction coefficient γ was proposed. Analysis indicated that γ increased with an increase in the l_ae/d (on average, 146% higher than the initial value) and decreased with an increase in the f_y/f_t (on average, 33% less than the initial value). A formula was developed to calculate γ, and the bond force in the straight anchor sections at the yield moment for the reinforcement was determined. Thus, a distributive relationship was established for the anchorage force, the bond force, and the bearing pressure.

In an effort to investigate the attenuation characteristics and site effects in eastern Guangdong, 659 strong-motion recordings received by 27 stations were selected for spectral analysis to separate path attenuation, site effects and source spectra. The path attenuation curves are generally close to the simplest form of distance decay described by R^−0.5, and decays the slowest at a frequency of 4 Hz. We decomposed the path attenuation into a combination of geometric spreading and inelastic attenuation. The geometric spreading R^−0.15 exhibits a slower distance decay at local distances, indicating that the seismic energy close to the epicenter is not easily dissipated. The quality factors were regressed as Q_s(f) = 114.81f^.922 in the frequency range .9–20 Hz, lower than those reported for the whole Guangdong region, indicating stronger anelastic attenuation in eastern Guangdong. The site responses in eastern Guangdong show a strong correlation with geological and geotechnical characterization. The stations located in the central mountains have higher predominant frequencies (>10 Hz) accompanied by smaller site amplifications. Larger site amplification is in the southeast coastal area (i.e., Shantou area), where the surface is covered with a thicker layer of soft soil and the predominant frequency of site is relatively low (∼2 Hz). The far-field earthquake will cause greater vibration and damage to this area.

In order to obtain the calculation model for the local bearing capacity of concrete F_l under two headed bars, six pull-out concrete specimens were prepared. The effect of the net distance between two headed bars c on F_l was mainly investigated. The test results show that the local bearing capacity of concrete would first decrease and then increase with the increase in c, and the boundary point of the two stages was c = 40 mm. It is determined that the stress transformation from the local compression state to the axial compression state in the stress distribution model is characterized by the variation rate of the vertical stress under individual headed bars, which would infinitely approach a constant value. The constant value under individual headed bars is used as the limit value. The height of the vertical stress under two headed bars is modified, and then the height of the tensile region of the specimen with different c values is determined. Combined with the experimental phenomena and the results, two stages of calculation models are established, respectively: the integral calculation model and the individual calculation model. The integral calculation model focuses on the interaction of the compression region under two headed bars. The individual calculation model mainly focuses on the interaction of the tensile region under two headed bars. The calculation equations considering the influence of the height of the tensile region are established. Two groups of similar test data regarding the local bearing capacity were collected and verified as the integral calculation model and the individual calculation model. The average value of the ratio between the test value and the calculated value is 1.057 and 1.061, the standard deviation is 0.153 and 0.091, and the coefficient of variation is 0.055 and 0.086. It is proved that the calculation model proposed in this paper has a certain accuracy. It can provide a reference for calculating the local bearing capacity of concrete under multiple headed bars.