Puqian Bridge is located in a quake‐prone area in an 8‐degree seismic fortification intensity zone, and the design of the peak ground motion is the highest grade worldwide. Nevertheless, the seismic design of the pile foundation has not been evaluated with regard to earthquake damage and the seismic issues of the pile foundation are particularly noticeable. We conducted a large‐scale shaking table test (STT) to determine the dynamic characteristic of the bridge pile foundation. An artificial mass model was used to determine the mechanism of the bridge pile‐soil interaction, and the peak ground acceleration range of 0.15 g–0.60 g (g is gravity acceleration) was selected as the input seismic intensity. The results indicated that the peak acceleration decreased from the top to the bottom of the bridge pile and the acceleration amplification factor decreased with the increase in seismic intensity. When the seismic intensity is greater than 0.50 g, the acceleration amplification factor at the top of the pile stabilizes at 1.32. The bedrock surface had a relatively small influence on the amplification of the seismic wave, whereas the overburden had a marked influence on the amplification of the seismic wave and filtering effect. Damage to the pile foundation was observed at 0.50 g seismic intensity. When the seismic intensity was greater than 0.50 g, the fundamental frequency of the pile foundation decreased slowly and tended to stabilize at 0.87 Hz. The bending moment was larger at the junction of the pile and cap, the soft‐hard soil interface, and the bedrock surface, where cracks easily occurred. These positions should be focused on during the design of pile foundations in meizoseismal areas.

This study aims at investigating the effect of steel casing on vertical bearing characteristics of steel tube-reinforced concrete piles in loess area by centrifugal model test. Five piles were selected, one of them was a conventional reinforced concrete pile which was 35 cm in length and 2.5 cm in diameter as a contrast pile, and the length of steel casing for the remaining four steel tube-reinforced concrete piles was 8 cm, 12 cm, 16 cm, and 20 cm respectively. The results show that the axial force, unit skin friction, tip resistance, and shaft resistance of steel tube-reinforced concrete piles with different steel casing lengths were different from conventional reinforced concrete pile. Additionally, the ultimate bearing capacity of steel tube-reinforced concrete piles was compared with a conventional reinforced concrete pile. Moreover, advantages of steel casing in pile foundation engineering were summarized. The results of this study can provide reference for vertical bearing characteristics of steel tube-reinforced concrete piles in loess area.

The objective of this study was to investigate the effect of different moisture contents of clay (13%, 15%, 17%, 19%, and 21%) and different coatings on the ability to reduce negative skin friction during a large‐scale shear test. Four coating treatments of the concrete surface were investigated, i.e., no treatment, coating with a paraffin‐oil mixture, coating with a polymer nanomaterial, and coating with paint. The results showed that when the moisture content of the clay was slightly larger than that of the plastic limit, the ability to reduce negative skin friction was the best, and the performance was similar for the paraffin‐oil mixture, the polymer nanomaterial, and the paint. When the moisture content of the clay was lower than that of the plastic limit, the paraffin‐oil mixture provided the best performance. The position of the neutral point can be determined by different methods, and the negative skin friction of piles should be reduced by applying coatings that are most suitable to different conditions.

Steel casings (SCs) are extensively and increasingly used to stabilize the borehole wall in the construction of bridge pile foundations. Steel casings (SCs), together with reinforced concrete piles (RCPs), form composite concrete‐filled steel tube piles (CCFSTPs), which differ significantly from ordinary RCPs in horizontal bearing capacity. In this study, based on the characteristics of CCFSTPs, the horizontal bearing capacity of a CCFSTP was examined through a centrifugal model test with the length of the steel casing (L_SC) and the modulus of the soil mass in the steel casing soil compaction zone (E_{SCSC_zone}) as variables. Pile‐side soil resistance, load‐displacement curves, and pile moment curves were obtained for the CCFSTP. The results show that increasing L_SC within a range of 12 cm significantly increases the ultimate horizontal bearing capacity of the CCFSTP, and further increasing L_SC beyond 12 cm produces a continuous increase in the ultimate horizontal bearing capacity of the CCFSTP but only to an insignificant extent. In addition, increasing E_{SCSC_zone} increases the ultimate horizontal bearing capacity of the CCFSTP, but to a relatively small extent. The results of this study provide a theoretical basis and technical support for the design and construction of CCFSTPs.

The soil stabilizer of the Consolid system (content: 0%–2.46%) was used for the modification of collapsible loess. The consolidation test, compression test, collapsibility test, and strength test of modified loess were conducted. In addition, X-ray diffraction (XRD), scanning electron microscopy (SEM), and mercury injection tests were carried out to study the loess before and after modification. The results indicated that with an increase in the content of the stabilizers, the optimal water content of the modified loess increased, whereas the dry density decreased. Furthermore, as the content of the stabilizers increased, the compressibility and collapsibility of the modified loess decreased. When the stabilizer content was 0.86%, the modified loess exhibited almost no collapsibility. The unconfined compressive strength of the modified loess demonstrated an exponential relationship with the content of the stabilizers. The shear strength increased with the increase in the content of the stabilizers. When the stabilizer content reached 1.66%, the friction angle started to decrease. The microstructure analysis indicated that the cumulative pore volume of the modified loess decreased with the increase in the content of the stabilizers, which could facilitate the formation of a more stable soil structure and improve the impermeability and strength.

In order to investigate the dynamic response variations between isolated pile and pile-group systems in high-seismicity regions, we performed extensive shaking table experiments. These tests examined the acceleration characteristics, displacement patterns, and bending moment distributions across single-pile, four-pile, and six-pile configurations when exposed to four different seismic waveforms at a design-level intensity of 0.35g. Additionally, the structural integrity and damage conditions of the pile foundations were systematically assessed. The experimental data revealed that the greatest displacement at the pile head and the highest bending moment values were specifically caused by Kobe wave excitation. Conversely, the El-Centro wave produced the highest acceleration amplifications. The six-pile foundation exhibited optimal resistance to displacement and bending moment, particularly under the 5010 wave, and the single-pile foundation consistently showed the least acceleration amplification. Post-test inspections, including white-noise scanning and visual checks, showed no evidence of significant macroscopic damage across all foundation types, indicating an essentially elastic response at this intensity level. Engineering suggestions for the seismic design of bridge pile foundations in strong earthquake areas are proposed.