This paper aims to investigate the tunnelling stability of underwater slurry pressure balance (SPB) shields and the formation and evolution mechanisms of ground collapse following face instability. A laboratory SPB shield machine was employed to simulate the entire tunnelling process. Multi-faceted monitoring revealed the responses of soil pressure, pore water pressure, and surface subsidence during both stable and unstable phases. The morphological evolution characteristics of surface collapse pits were analyzed using three-dimensional scanning technology. The experimental results indicate that: (1) The key to stable tunnelling is balancing the pressure in the slurry chamber with the tunnelling speed, which ensures the formation of a filter cake in front of the cutterhead. (2) The torque of the cutterhead, soil pressure, and surface subsidence respond significantly and synchronously when the tunnel face becomes unstable, while the soil and water pressures are relatively less noticeable. (3) Excavation disturbance results in a gentler angle of repose and a wider range of collapse in the longitudinal direction of the collapsed pit. (4) A formula for predicting the duration of collapse is proposed, which effectively integrates the evolution patterns of the collapse pit and has been well-validated through comparison with the experimental results. This study provides a reference for the safe construction of tunnel engineering in saturated sand.

Gastrointestinal nematodes (GIN) are considered of major importance by livestock farmers, with burdens limiting production. Dung beetles have been reported to reduce GIN numbers by direct damage during ingestion, increasing aeration and desiccation in the dung pat, and moving dung deeper into the soil. This study investigates the impact of differing densities of the paracoprid dung beetle, Copris incertus, on GIN across different seasons in New Zealand. Treatments of different dung beetle abundances (Control, Low, Medium and High) were applied in field enclosures during four-week periods in spring, summer and autumn. A Natural treatment, with no enclosure to allow unrestricted colonisation of the dung, was included in summer and autumn. Dung pats containing nematode eggs were applied to all plots. In both spring and autumn there was increased dung removal at the highest dung beetle abundances. In spring the increased removal of dung from the soil surface was associated with more buried dung balls and an increase in the number of infective larvae stage 3 (L3) numbers in the herbage in the High dung beetle treatment. There was no evidence that Copris incertus reduced nematode larval numbers on pasture, regardless of beetle densities.

The excavation of the foundation pit impacts the safety, stability, and normal operational functionality of adjacent existing tunnels. With the increasing urban building density, it is becoming more common to conduct foundation pit excavation in close proximity to existing tunnels, which may result in deformation and damage to the tunnels. The impact of foundation pit excavation on adjacent existing tunnels was investigated using a transparent soil scale model and Particle Image Velocimetry technology. The horizontal and vertical distances between the foundation pit and tunnel, as well as the soil consolidation pressure, were individually examined to analyze their respective trends and magnitudes of impact on the maximum vertical deformation of adjacent existing tunnels. The findings suggest that as the excavation depth increases, the deformation of existing tunnels is increasingly impacted by the excavation of foundation pit. However, this impact decreases with greater horizontal or vertical distance between the foundation pit and tunnel. Furthermore, the impact of vertical distance between the tunnel and foundation pit on tunnel deformation is more significant. The pre-consolidation strength of the soil mass significantly impacts the deformation of the existing tunnel. In order to minimize tunnel deformation in practical engineering, constructive recommendations were proposed.

Land reclamation from the sea is increasingly common in coastal areas in China as its urban population continues to grow and the construction of subways in these areas becomes an effective way to alleviate transportation problems. Earth pressure balance shield (EPBS) tunneling in reclaimed lands often faces the problem of seawater erosion which can significantly affect the effectiveness of soil conditioning. To investigate the impacts, in this work, the stratum adaptability of EPBS foaming agents in seawater environments was evaluated based on a series of laboratory tests. The Atterberg limits and vane shear tests were carried out to understand the evolution characteristics of mechanical properties of clay-rich soils soaked in seawater and then conditioned with foams. The results revealed that, for the same foaming agents, the liquid limit and plastic limit of soils soaked in seawater were lower than those in deionized water due to the thinning of bound water films adsorbed on the surface of soil particles. Similarly, soils soaked in seawater had lower shear strength. In addition, the results indicated that the foam volume (FV) produced by foaming agents using seawater as the solvent was slightly higher than that when using the deionized water due to the higher hydration capacity of inorganic salt cations in seawater compared with organic substances. It was also shown that seawater had negative effects on the half-life time (T1/2) and the dynamic viscosity (eta) of foaming agents due to the neutralization reaction between anions in the foaming agents and Na+ present in seawater. The test results also confirmed that 0.5 % of the tackifier (CMC) can alleviate the issue of thin foam films caused by seawater intrusion and improve the dynamic viscosity of foaming agents more effectively, leading to superior resistance to seawater intrusion in EPBS tunnel constructions.

This paper investigates the application of an equivalent elastic beam model to predict the building displacements caused by mechanized tunnelling. A simplified Shear Slabs Portal Frame (SSPF) representation and 2D finite element analyses estimate the bending properties of buildings considering cross-sections transverse to the tunnel trajectory. The predictions are compared against measured building performance during tunneling through stiff London Clay, using an advanced soil model for non-linear ground stiffness. For twin Crossrail tunnels, reliable stuctural configurations and ground deformation data from Hyde Park enable accurate predictions of Avenfield House displacements. Similarly the study also examines the impacts of a single open-face shield tunnel (JLE project) on Westminster'sTreasury and ICE buildings. These cases involve greater uncertainties due to oblique tunnel angles and varying structural conditions, yet the analyses yield reasonable building settlement predictions. This research highlights the SSPF approach as an effective, simplified modeling tool.

Damage to a masonry building induced by tunneling greatly depends on the settlement of its foundation. Compared with pile foundations, group cemented soil column (GCSC) foundations have lower bearing capacity and stiffness. Tunneling through a GCSC foundation may have a significant influence on the settlement of the above masonry building. Field tests and numerical simulations were performed to investigate the settlement behavior of a single cemented soil column (CSC) and GCSC foundation during tunneling. Moreover, the stiffness of the GCSC foundation was investigated by using the concept of area replacement ratio. The reinforcement effect of the GCSC foundation was much greater than that of a single cemented soil column (CSC). From the test result, the settlement of a single CSC was four times that of GCSC. The GCSC foundation could be considered a large reinforcement area that could reduce settlement. The volume loss decreased from 0.2 to 0.02% as the tunnel passed through the reinforcement area, and the relationship describing the transition between the reinforcement area and the green field was linear. Compared with the in situ test results, the building stiffness yielded reasonable results, particularly for the interaction between the building and GCSC foundation at the final stage of tunneling. The results of this study could be used to evaluate the settlement of a building with a GCSC foundation during tunnel construction.

The exponential growth of tunnelling projects worldwide necessitates efficient management of excavated soil, particularly from Earth Pressure Balance Tunnel Boring Machines (EPB-TBMs). This study investigates the temporal evolution of mechanical properties in EPB-excavated soil, focusing on the conditioning process's impact. Through a comprehensive literature review, gaps in understanding the soil's transition from a liquid-like state back to its solid form are identified. Existing studies touch on mechanical property changes over time but lack detailed temporal analyses. Our research addresses this gap by examining the recovery of soil compactability over time, crucial for its reuse. By conducting modified Proctor tests at different time intervals post-conditioning, we elucidate the relationship between soil properties and conditioning parameters. Our findings reveal a direct correlation between recovery time and total water content, influenced by added water and foam injection ratio. We demonstrate that different conditioning parameter combinations yield similar immediate properties but divergent recovery times, which are crucial for logistical planning and environmental suitability. This study offers valuable insights into optimizing EPB-TBM excavation logistics, enhancing soil reuse efficiency, and advancing sustainability in civil engineering projects.

This paper investigates the role of masonry elastoplastic constitutive models on tunnelling-induced damage in buildings. A two-stage analysis method (TSAM) is adopted, incorporating input greenfield displacements, 3D masonry walls, and an elastic model for the soil. The paper focuses on four masonry constitutive models that can be readily adopted for routine analysis in industry. Comparison of in-plane yield surfaces with experimental data indicates that, among the considered masonry models, the Concrete Damaged Plasticity model under biaxial calibration gives the best overall performance. The TSAM is then used to study selected tunnel-masonry wall scenarios, confirming a significant effect of the constitutive model and its parameters on masonry wall response to tunnelling, particularly after volume losses where moderate damage is triggered. Also, as masonry stress paths are shown to concentrate in the tensile-compressive areas, with damage prediction being sensitive to the yield surface within this quadrant, numerical damage predictions must rely on the accurate calibration of the constitutive model in the tensile-compressive quadrants. This appraisal indicates that, in the context of routine structure modelling for tunnelling assessments, the selection of elastoplastic masonry models and their biaxial calibration have a non-negligible impact on the damage category estimate.

The stress state of soil may affect the building settlements induced by tunnelling, which, however, has not been well understood. In this study, three dimensional numerical analyses combined with in situ measurements were performed to investigate the geostress-associated settlements of a raft-foundation building due to tunnelling in soft ground. Basically, two types of geostress fields were investigated: the first type considered the effect of additional stress generated in the foundation soil (FAS) due to building weight, while in the second type, a sequential twin tunnelling was presumed, and the effect of additional soil stress induced by the first tunnel (TAS) on the building response to the second tunnel was considered. The results indicated that FAS may aggravate the stress release of the foundation soil, and thus gave rise to a larger building settlement or inclination. In the sequential tunnelling process, the effect of TAS can be more complex: when the first tunnel lowered the stress of foundation soil, TAS effect of the first tunnel may help reduce the building settlements induced by the second tunnel; otherwise, it may aggravate building settlements. In addition to TAS effect, the sheltering effect was also found to play an important part in twin tunnelling.

This study investigates the long-term settlement behaviour induced by shield tunnelling in soft ground, employing a case study and numerical modelling to achieve a comprehensive understanding. Soil consolidation plays a critical role in long-term surface settlement, necessitating precise calibration of essential tunnelling parameters such as face pressure and grouting pressure. The findings indicate that soil settlement progressively increases with increasing face pressure P f and grouting pressure P g during the excavation of a shield tunnel. Furthermore, for long-term consolidation settlement, it has been established that setting P f at 90% of the lateral earth pressure 6 xx consistently minimizes settlement across all cover depths. This phenomenon is attributed to the soil arching mechanism, which also reduces the height of the loosened zone at this specific P f level. Similarly, the optimal P g is identified to be within the range of 130% to 150% of the vertical earth pressure 6 zz . For cover depths within the loosened zone, the smallest consolidation settlement and loosened zone height are observed at P g of 150% of 6 zz . Conversely, for shallower cover depths, beyond the loosened zone but within the arching zone, the smallest consolidation settlement and loosened zone height occur at P g of 130% of 6 zz . This study reveals that adjusting the cover depth significantly influences the reduction in vertical stress and the resulting settlement, demonstrating the importance of tailored grouting pressure calibration for varying depths to limit consolidation settlement.