To address the technical challenges in widening existing embankment due to terrain constraints, a new composite supporting structure termed as adjacent composite pile-sheet wall (ACPSW) is proposed, i.e., the new pile-sheet walls are installed side-by-side in the middle of the old pile-sheet walls. Based on the Lanzhou Hub project of Zhongwei to Lanzhou Railway, this paper investigates the pile horizontal deformation, pile bending moment, soil pressure behind the pile and sheet, as well as load-sharing ratio between the old and new pile of ACPSW at different construction stages through field tests and numerical simulations. The results obtained from the field tests were compared with that obtained from the numerical simulation to validate the reliability of the numerical model. Moreover, a serviceability assessment on old pile of ACPSW is also conducted. The results indicate that the new pile-sheet wall and the old pile-sheet wall can deform synergistically and bear the external loads together under new widening embankment loads and train loads, and the load-sharing ratio between old and new pile is 0.62:1.0. The research results can provide a reference for the design and construction of existing line reconstruction and new projects adjacent to existing lines.

Concrete-filled FRP (Fiber Reinforced Polymer) tube composite piles offer superior corrosion resistance, making them a promising alternative to traditional piles in marine environments. However, their performance under cyclic lateral loads, such as those induced by waves and currents, requires further investigation. This study conducted model tests on 11 FRP composite piles embedded in sand to evaluate their behavior under cyclic lateral loading. Key parameters, including loading frequency, cycle count, loading mode, and embedment depth, were systematically analyzed. The results revealed that cyclic loading induces cumulative plastic deformation in the surrounding soil, leading to a progressive reduction in the lateral stiffness of the pile-soil system and redistribution of lateral loads among piles. Higher loading frequencies enhanced soil densification and temporarily improved bearing capacity, while increased cycle counts caused soil degradation and reduced ultimate capacity-evidenced by an 8.4% decrease (from 1.19 kN to 1.09 kN) after 700 cycles under a 13 s period, with degradation rates spanning 8.4-11.2% across frequencies. Deeper embedment depths significantly decreased the maximum bending moment (by similar to 50%) and lateral displacement, highlighting their critical role in optimizing performance. These findings directly inform the design of marine structures by optimizing embedment depth and load frequency to mitigate cyclic degradation, ensuring the long-term serviceability of FRP composite piles in corrosive, high-cycle marine environments.

Carbonation technology using MgO and CO2 has been considered a rapid, effective, and environmentally friendly method for improving weak soils, mainly applied in shallow foundation treatments. This study introduced a novel MgO-carbonated composite pile (MCP) technique developed by injecting CO2 through a gas-permeable pipe pile into a MgO-mixing column for carbonation and solidification and its applications in weak subgrade treatments. Several field tests were carried out to study the characteristics of MCP as well as the performance of the MCP-reinforced foundations, including carbonation reaction temperature monitoring, pore-water pressure monitoring, standard penetration tests (SPTs), unconfined compressive strength (UCS) tests, static load tests, and subgrade deformation monitoring. Results showed vigorous and uniform carbonation within the MgO-mixing column, confirming the feasibility of constructing large-diameter MgO-mixing columns. The distribution, evolution, and affected zone of excess pore-water pressure induced by MCP installation were determined. The MCP exhibited good pile quality, with average SPT blow count and UCS value of 39 and 1021 kPa, respectively. MCP's bearing capacity was superior to prestressed high-strength concrete pipe piles, with ultimate vertical and lateral bearing capacities of 1920 and 119 kN, respectively. The MCP-reinforced foundation exhibited a small settlement of 54.5 mm under embankment loads. Life cycle assessment indicated significant carbon reduction benefits for MCP, with 44.7% lower carbon emissions compared to traditional composite piles.

Stiffened composite pile (SCP) composed of cement-soil mixing piles and precast pipe piles have been widely used in the construction industry to effectively handle soft soil in foundation treatments. In this study, the mechanical properties of a SCP were analyzed through field tests and numerical simulations and the optimal arrangement of the SCP group was obtained. The greenhouse gas (GHG) emissions during the construction process of the SCP group were calculated by considering three aspects: material consumption, mechanical requirements, and labor consumption. The results were then evaluated and compared with those of the traditional bored cast-in-place pile (BCP) group. It was found that the optimal arrangement of ground treatment with the SCP group was determined with a pile having an inner core diameter of 500 mm, an outer diameter of 700 mm and pile spacing of 2.8 m, which is four times the pile outer diameter. Compared to the BCP group, the SCP group has advantages of 6.16 % reductions GHG emissions of building materials, 42.76 % that of mechanical usage, and 53.11 % that of labor consumption. The final settlement of pile groups exhibits a clear negative correlation with their GHG emissions. The variation in GHG emissions is primarily dependent on changes in pile spacing, while the effect of the inner core pile diameter is relatively minor. The scientific significance of this study is rooted in the quantitative evaluation and comparison of GHG emissions during the construction phase of two different types of pile foundations. It also elucidates the interplay between the load-bearing capacity of SCP group and their GHG emissions. This study can serve as a crucial reference for the design and construction of foundation engineering, ensuring that pile foundation construction aligns with both the requisite load-bearing performance and low-carbon construction standards.

The implementation of composite piles has emerged as an appealing technology for reinforcing soft ground through fulfilling the requisite bearing capacity and facilitating consolidation. Nonetheless, previous investigations into the consolidation behavior of composite pile-improved ground have neglected the nonlinearity of soil compression and permeability. In this context, the logarithm models of e-lgcr and e-lgk are introduced to establish an analytical model for the nonlinear consolidation of composite ground with composite piles. Based on equal strain assumption and annular equivalent method, detailed solutions under four special loading schemes are then obtained. Additionally, a comprehensive analysis is conducted to assess the influence of various parameters on the nonlinear consolidation behavior of composite ground, and the feasibility of current model is verified by degenerations. The results show that ignoring the nonlinearity will lead to an overestimation of consolidation rate when the soil's compression indices exceed the permeability indices. Moreover, the consolidation rate of composite ground is inversely proportional to cru/cr ' s0 and Cc/Ckh(v), while demonstrating a direct proportionality to Ksp, Ksg, and kg/kv0. However, cru/cr ' s0 mainly influences excess pore water pressure at the upper layer, and the influence of Cc/Ckv on the consolidation rate is limited and can even be ignored in comparison to Cc/Ckh. Finally, the proposed model is successfully applied to an engineering project in situ, where the obtained results exhibit a noteworthy agreement with the measured data.