Search Results (5)

This paper develops a model to calculate carbon emissions during the construction period of dredging projects. Carbon emission quotas for various types of dredgers and auxiliary vessels in different construction conditions and geotechnical soil types during the dredging project’s construction period are established, as well as the power consumption quota for management activities. Taking the construction of the main project of the cross-river channel from Shenzhen to Zhongshan (S09)’s foundation trench excavation and channel dredging, the Thilafushi Island reclamation project in Malé, and the second phase of the southern section of the Guangzhou Port Area channel maintenance project (2022–2023) as case studies, the validity of the quotas is verified. During the construction period, under the same dredging soil quality and the same working condition level, the carbon emissions of different types of dredgers are different. Conversely, under different dredging soil qualities and different working condition levels, the carbon emissions for the same dredger or auxiliary vessel are different. The carbon emissions of each dredger or auxiliary vessel increase with the increase in the ship’s specifications. The carbon emissions of dredging projects are huge, with direct carbon emissions accounting for 97%, and indirect carbon emissions from equipment deployment and management activities accounting for 3%, among which the carbon emissions from electricity consumption in management activities account for only 0.3%. Full article

During the construction of a large immersed tunnel crossing an ultra-wide inland river, the long drying time after the excavation of the foundation trench and changes in river flow velocity result in the river carrying a large amount of sediment into the foundation trench and the slope, increasing installation difficulties and threatening construction safety. This study investigates the back-silting characteristics and their impacts on foundation trench slope stability during an ultra-wide immersed tunnel excavation at LunGui Road in Foshan City, China. Numerical simulations reveal the spatiotemporal distribution patterns of deposited sediments at the trench bottom and side slopes, with distinct behaviors identified between the flood season and dry season. Siltation predominantly occurs at the trench bottom, with deposition thickness decreasing almost linearly from the bottom to the slope crest. Hydroperiod variations considerably influence the spatiotemporal distribution of back-silting. Then, the Morgenstern–Price method was employed to analyze slope stability under varying back-silting and dredging conditions, quantifying the relationship between safety factor and sediment thickness. Furthermore, the evolution of critical failure surfaces and the safety factor under different dredging strategies was systematically examined. The critical values of back-silting thickness corresponding to different dredging slope ratios are provided. The research findings provide valuable insights for formulating engineering strategies for trench excavation of extra-wide immersed tube tunnels in inland waterways. Full article

This study aims to evaluate the accuracy of different dynamic compaction (DC) load equivalent conversion methods in DC vibration calculations. It also investigates the effect of vibration isolation treatments on the vibration reduction performance of loess foundations, with the goal of optimizing vibration control during DC construction. Five classical methods were used to convert the DC loads into time-dependent surface loads, which were subsequently fed into Plaxis’s dynamic multiplier table for the numerical implementation of DC tests. By comparing the numerical simulation results with in situ monitoring data from a loess site, the accuracy of the five DC load equivalent conversion methods was evaluated. The momentum theorem method was identified as the most precise for both vibration velocity and settlement. Subsequently, the momentum theorem method was utilized to investigate the influence of depth and distance of vibration isolation trench, as well as the properties of vibration isolation materials on vibration reduction effect. It is indicated that the optimal depth for the vibration isolation trench of the loess site is 2 m, beyond which the improvement in vibration reduction effects is not notable. The excavation distance of the vibration isolation trench should be set as close as possible to the boundary of the construction site to achieve the best vibration reduction effect. As for the properties of vibration isolation materials, it is shown that the unit weight and damping ratio of the filling material have a significant effect on the vibration reduction effect, while the influence of the shear strength of the filling material is negligible. Besides the vibrating reduction influence of filling materials, utilizing spring dampers has a better vibration reduction effect. Increasing the stiffness of the spring dampers and reducing their spacing can significantly enhance the vibration reduction effect. In practical engineering applications, it is essential to consider both the effects and economic costs to select the optimal vibration reduction treatment and its parameters. This study provides a scientific basis for vibration control during DC construction, contributing to ensuring construction safety and efficiency while minimizing the impact on the surrounding environment. Full article

This paper aims to present the potential of observations of the Earth’s surface by means of remote sensing (survey), specifically via direct (active) visual prospection from low altitude to identify and map small components (such as postholes) of archaeological contexts, namely aboveground post-built structures dated to the Early Iron Age (appr. 800–380 B.C.). This work gives an example of archaeological data on buried settlement constructions identified by aerial reconnaissance (i.e., by a non-invasive method), the interpretation—and primarily dating—of which is based on information achieved by excavation practice (recently performed predominantly during rescue campaigns). This research points to the fact that nonetheless to the traditional idea on the limited potential of crop-marked archaeological heritage in terms of dating (the ability of cropmarks displayed over pits, ditches, graves, etc., to produce exact ground-plans of even small buried features, so that their original function and dating can be determined) the number of more or less precisely datable archaeological sites and features buried under the surface is growing, including wooden structures once constructed on the ground (i.e., not sunken under the ground) and leaving on cereal crops just tiny spots/dots regularly spaced into lines. These are features (constructions) with identical ground plans (postholes placed in 4 × 3 and/or 3 × 3 patterns) of which commonly just one in a group of them situated on one site is enclosed by a perimeter line—a foundation for a wall or a trench for a palisade. Consequently, a retrospective survey of air-photo analog archives and digital repositories now brings new evidence on the chronological setting of many crop-marked Early Iron Age sites that previously remained undated. Full article

The evaluation of the trench stability under the action of ocean waves is an important issue in the construction of an immersed tunnel. In this study, a two-dimensional coupling model of a wave-seabed-immersed tunnel is proposed for the dynamic responses of a trench under wave action in the immersing process of tunnel elements. The porous seabed is characterized by Biot consolidation equations. The $k-\epsilon$ model and RANS equation are adopted to achieve the flow field simulation, and the level set method (LSM) is used to capture the free surface between the water and air. The proposed numerical model is verified using the experimental data and analytical results. Then, the transient liquefaction and shear failure in the vicinity of the trench are discussed at two different conditions, namely, after the foundation groove is excavated and after the tunnel element is placed. The pore pressure amplitude on the weather side slope is demonstrated to be significantly smaller than that on the lee side slope. Also, the distribution of the surrounding flow field and pressure field change dramatically after the tunnel element is settled, leading to the significant changes of seabed stability. Full article