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.

Caves affected the load transfer mechanism of bridge pile foundation, and then the safety of the bridge was threatened. This study was to investigate the effect of karst cave under bridge pile foundations on the vertical bearing characteristics of bridge pile foundations by static load test, finite element analysis and mechanical model. The settlement of the pile was measured by displacement meter, and the axial force were measured by stress gauges in the test. The load-settlement, the axial force, the unit skin friction and the ratios of side and tip resistances were compared with the result of the simulation. Then sixteen conditions were selected in finite element analysis, one of them was a conventional pile not on cave. The others were about five kinds of height, five kinds of span and six kinds roof’s thickness of the cave. The simply supported and fixed wide beam were established to calculate the allowance roof thickness. The results reveal that when the cave span is greater than 9 m × 9 m or the roof thickness is less than 2 D (pile diameter), the stress and deformation of piles are significantly affected.

This study investigated the corrosion damage and bearing characteristics of bridge pile foundations under a dry‐wet‐freeze‐thaw cycle of composite salt in an alpine salt marsh area using an in situ test, laboratory test, and numerical simulations. The in situ test showed that the dry‐wet‐freeze‐thaw cycle has little effect on the quality of the concrete specimens and rebar. The area of the rebar at a depth of 0.25 m had the highest corrosion rate of 91%. The application of epoxy resin on the surface improved erosion resistance. After one year of outdoor dry‐wet‐freeze‐thaw cycle test, due to the interaction of compound salts, the quality of specimens is reduced under the denudation of chloride ions, while the mass of specimens is increased by the corrosion products formed under the joint action of carbonate and sulfate, resulting in less obvious change of specimen quality, the antierosion coefficient of the specimens decreased, the maximum loss rate of compressive strength was 38.2%, and the pile foundation began to deteriorate. The laboratory test showed that expansive substances, such as Friedel salt, appeared in the concrete specimens of pile foundation during 225 cycles of dry‐wet‐freeze‐thaw cycles, the relative dynamic elastic modulus was reduced by 60.9%, the antierosion coefficient was reduced to 0.51, and the compressive strength loss rate was 65.9%. As such, the pile foundation was seriously damaged. The numerical simulation shows that, with an increase of the peeling thickness and the corrosion depth, the bearing capacity of the pile foundation will gradually decrease after 8 years. Without maintenance, the bearing capacity of a pile foundation will decrease by 34.45% in the 20^th year.

This study investigates the water pressure distribution and deformation patterns in tunnel linings within water-rich tunnels traversing fault zones, focusing on the Gudou Mountain Tunnel. The study utilized field tests and numerical simulations to assess the water pressure distribution around test sections. Following the confirmation of consistent water pressure distribution patterns from field tests and simulations, we analyzed the deformation patterns of tunnel linings at various water levels. The results showed that water pressure is highest at the tunnel’s inverted arch and arch foot, moderately high at the vault and spandrel, and lowest at the arch waist. The sections RK51 + 590 and LK51 + 640, located on opposite sides of a fault crush zone, experience high fragmentation of surrounding rock. This allows rainfall and reservoir water to seep through fractures, causing increased water pressure and significant deformation at the inverted arch of these sections. With rising groundwater levels, deformation intensifies at the inverted arch, arch foot, and vault. The appearance of macro-cracks in these critical areas leads to groundwater seepage through the cracks, severely impacting tunnel operations. Consequently, reinforcing the inverted arch, arch foot, and vault is crucial to reduce the risk of water leakage in the tunnel.

There are many methods to predict the bearing capacity of bridge pile foundation in karst area, and the accuracy of each method is different. In order to find out that the bearing capacity of pile foundation in karst area is affected by the change of cave size and predict the bearing capacity of pile foundation in karst area better, this paper is based on the engineering characteristics of pile foundation in karst area and the gray system theory and the finite element numerical simulation. The numerical simulation models of different cave sizes were used to analyze the changing rules of the bearing capacity of piles when the cave size was changed. At the same time, a metabolic GM (1,1) model was established, and the time response of pile foundation bearing capacity was deduced. Compared with the original GM (1,1) model, the P-S curve obtained from the FEM simulation was predicted. Finally, the engineering formula is used to validate the predicting formula of the pile bearing capacity in karst area. The results show that the bearing capacity of pile foundation in karst area is significantly affected by the size of caverns, of which the influence by cave caverns is the most obvious, and the bearing capacity of pile foundations decreases with the increase of cave spans. When the hole span increases from 6m to 9m, The bearing capacity decreased by 33.44%. Compared with the bearing capacity obtained by numerical simulation of the finite element method, the prediction error of the pile foundation by the metabolic GM (1,1) model can reach 1% and the precision is high. The obtained bearing capacity and precision of the obtained pile prediction formula can be used to predict the bearing capacity of pile foundation in karst area, which has some theoretical and engineering practical value.

This study investigated the antiliquefaction property of the pile group. It is shown in the pore pressure ratio, pile acceleration, and bending moment response of saturated silt fine sand. The response law of pile acceleration and bending moment during liquefaction development is proved. The results show that liquefaction occurs in single piles, four piles, and six piles under the action of 0.35 g seismic wave. But the time of liquefaction is different. There is an obvious difference in the response of pile acceleration and bending moment during liquefaction. Liquefaction in the saturated silt fine sand develops from shallow to deep. The complete liquefaction of six piles takes the longest time, while the single pile takes the shortest time, and the average delay was 8.82 s. With the increase of the number of piles, there are some differences in pile acceleration, magnification factor, and pile bending moment, which are mainly reflected in time. The peak acceleration appearance of six piles was 3.08 s later than that of the single pile on average. The maximum bending moment appearance of six piles was 1.96 s later than that of the single pile on average. The acceleration and bending moment of the pile begins to attenuate when the pore pressure ratio increases. It shows that the saturated silt fine sand has softening and damping effect before liquefaction. In summary, the antiliquefaction performance of the pile group is better than that of a single pile. In the seismic design of pile foundation in liquefied soil, the antiliquefaction performance of the pile group is better.