Abstract This case study presents a full-scale field test on the impact of superlarge diameter slurry shield tunneling on adjacent pile foundations during the construction of the Zhanjiang Bay subsea tunnel. Through systematic in situ monitoring of four full-scale test piles at the tunnel exit portal, this study elucidates the disturbance mechanisms that arise from superlarge diameter slurry shield tunneling in ultrashallow overburden strata. For this purpose, an innovative monitoring framework combining a self-anchored loading system with high-resolution densely distributed optical fiber sensor array is developed, enabling both load application and continuous internal force measurement during shield advancement. Key findings indicate that shield tunneling induces significant axial stress redistribution in adjacent piles, particularly during the critical advancement stage with shield cutterhead at the position of 0.0 D ± 0.5 D (where D is the excavation diameter of shield tunnel), with disturbance zones extending up to + 2.0 D in unreinforced strata. Furthermore, prereinforcement strategies were found to substantially alter the responses of the piles: reinforced zones exhibited higher axial forces but lower bending moments compared to their unreinforced counterparts. The vertical spatial relationship between pile tips and adjacent tunnels plays a crucial role in governing disturbance patterns, with peak axial forces generally shifting downward as pile length increases, whereas bending moments escalate in proportion to relative excavation ranges. Safety assessments confirm that control measures effectively limit surface settlements to less than 12 mm, pile head displacements to less than 8 mm, and anchor force loss to lower than 6%, thereby ensuring compliance with safety thresholds.
Abstract Mechanically stabilized earth (MSE) construction presents a viable approach for the effective utilization of space, particularly in the design and stabilization of slopes and embankments. This research examines the behavior of a steel pipe that incorporates embossed and debossed surface patterns around its circumference. To study the influence of surface feature characteristics such as orientation, length, and spacing on the pullout performance of reinforcement with alternating embossed and debossed features, the investigation combined a physical model test using a two-dimensional carbon rod geometry and a three-dimensional sand box setup, together with numerical simulations. Both experimental and numerical findings show that maintaining proper spacing between surface features is essential to ensuring sufficient reinforcement. The study demonstrated that incorporating embossed and debossed surface features significantly improved pullout resistance. Compared with smooth-surface steel pipes, pullout resistance of embossed/debossed steel pipes increased by 62.9%–140.2% in physical tests and 86.5%–238.4% in simulations, depending on feature length and spacing. These results demonstrate the effectiveness of optimized surface features in enhancing soil reinforcement and highlight the potential of high-strength metal reinforcements to overcome the tensile limits of conventional geogrids, advancing the design of MSE structures.
Abstract The ultimate vertical pullout capacity of single-helix anchors in sand was explored using the coupled Eulerian–Lagrangian (CEL) technique to account for large deformation processes. A semifluidized bounding surface plasticity model was incorporated in a novel manner to improve the continuum representation of highly disturbed sand around the anchor, particularly under very low confinement. The model was shown to be necessary for reproducing the soil backflow beneath the helix and the experimentally measured load-displacement response. A series of CEL analyses was conducted to investigate the effects of helix pitch size, embedment depth, sand relative density, and helix-to-shaft ratio on the pullout behavior of single-helix anchors in sand. The pitch size was found to have little influence on the ultimate pullout capacity, consistent with available centrifuge observations. Increasing sand relative density contributes to greater capacity but changes the relative contributions of the shaft and helix. The helix resistance becomes more dominant in dense sand, whereas the shaft and helix provide nearly equal contributions in loose sand. The numerical results were used to extend an analytical solution for estimating the ultimate pullout capacity. The proposed solution provides excellent predictions across different sand densities and anchor geometries, suggesting its potential use in practical design.
Abstract Microbially induced calcite precipitation (MICP) has gained increasing attention as a potential sustainable ground improvement technique. This study investigates the influence of soil particle size, shape, and mineralogy on the MICP process and on the evolution of shear-wave velocity (Vs) in biocemented soil columns. MICP experimental soil column tests were conducted using three silica sands (Ottawa 20/30, F-75, and F-110), a naturally carbonate-rich silty sand (Blessington soil), and artificially graded carbonate–silica sand mixtures (75% silica sand and 25% Iceland spar). Vs and chemical measurements were performed during MICP experiments, and biocemented samples were preserved for scanning electron microscopy (SEM) analyses. Results showed that the amount of precipitated calcite in carbonate-rich Blessington soil columns was up to twice that observed in the silica sand columns, highlighting the strong influence of soil mineralogy on the MICP process. The Vs profiles showed an overall trend of decreasing Vs with an increase in median particle size tested, which indicated the dominant effect of the number of particle contacts on the evolution of Vs with cementation. Furthermore, carbonate–sand mixtures exhibited increased calcite precipitation, but reduced Vs compared to their pure silica sand counterpart columns, demonstrating the combined effects of soil mineralogy and particle shape on both calcite precipitation and stiffness development. SEM observations revealed a distinct change in the morphology of precipitated calcite on the surfaces of carbonate soil particles (Blessington and Iceland spar) forming closely packed, uniform calcite crystals resembling the growth of a preexisting carbonate phase, which suggested that carbonate soil particles offered a lower energy barrier that facilitated a more extensive calcite precipitation compared to silica sands. Furthermore, the nature of cementation bonds evolved from contact cementation to cementation matrix and ultimately to pore filling as the median particle size of the tested soils decreased, implying that the formation, morphology, and extent of cementation bonds are governed by the specific surface area of soil. Based on these insights, a new model is proposed that relates Vs to normalized calcite content, which effectively captures the variation of Vs with cementation across different soil types tested in the present study, as well as within a broader dataset compiled from the literature.
Abstract This study investigates the long-term cyclic response of sand containing controlled amounts of nonplastic silt, with the objective of quantifying how fines content influences strain accumulation, stiffness degradation, and pore-pressure generation. The loading conditions considered represent repeated actions in granular foundations, such as traffic, wind, wave, and machine-induced vibrations, under both drained and undrained conditions. While most previous studies have focused on clean sands or plastic fines under low-cycle or liquefaction conditions, the influence of nonplastic fines in the long term, low-amplitude cyclic loading remains insufficiently understood. To address this gap, a comprehensive experimental program was conducted, including monotonic and high-cycle triaxial tests (3,000 cycles) on mixtures with 0%, 15%, and 30% fines. Both sand and silt were derived from the same parent rock to ensure consistent mineralogy. Tests were performed under varying mean effective stresses (126.6–253.3 kPa), cyclic stress amplitudes (30–100 kPa), loading frequencies (0.2–0.6 Hz), and consolidation anisotropy values of η ave = 0 – 0.63 . The results demonstrate that fines content fundamentally governs cyclic response. Below a threshold fines content, the soil maintains a sand-dominated structure with limited strain accumulation, whereas beyond this threshold, the response transitions to a fines-influenced behavior with significantly increased deformation and stiffness degradation. For example, doubling mean effective stress increased accumulated strain by ∼ 23 % in clean sand but up to ∼90% at 30% fines, while increasing cyclic stress amplitude from 40 to 60 kPa produced progressively larger strain increases (14.5%, 35%, and 175% for 0%, 15%, and 30% fines, respectively). The cyclic response is strongly controlled by loading amplitude and stress-path proximity to the critical state line (CSL), while frequency effects remain negligible within the quasi-static range investigated. Under undrained conditions, fine-rich mixtures exhibited rapid pore-pressure buildup and reached ∼5% axial strain within approximately 800 cycles, in contrast to the stable response of clean sand. A comparative discussion situates these findings within prior work and highlights their relevance for long-term performance assessments of granular foundations subjected to repeated loading.
