Search Results (9)

Metals in the Pearl River Estuary are of great importance due to the dense population and rapid industrialization, but they have not been systematically studied. This study investigates the spatial distribution and environmental impacts on dissolved and particulate metals (Cr, Mn, Fe, Co, Ni, Cu, Zn, Mo, Cd, Tl, Pb) in the Pearl River Estuary by integrating statistical methods and spatial analysis techniques. The areas with high concentrations of particulate metals are mainly located north of the Humen Bridge. Some metals also show higher concentrations near the Hong Kong–Zhuhai–Macao Bridge or around Macau. Overall, the spatial distribution patterns of metals such as Mn, Co, Ni, Cu, Mo, Cd, Tl, and Zn show clustering features. Oxygen content, salinity, and temperature significantly influence most particulate metals. The areas with high concentrations of dissolved metals are mainly located north of the Humen Bridge or in waters closer to the sea. Cr, Cd, Cu, Fe, Ni, Mo, and Tl show a clustered distribution. Dissolved Fe, Ni, and Mo are significantly influenced by environmental factors, except for water depth. This study fills the research gap on dissolved and particulate metals in the Pearl River Estuary, providing essential data to support metal pollution management in the region. Full article

The freeze-sealing pipe roof (FSPR) method was applied as an innovative construction technology to the Gongbei Tunnel of the Hong Kong–Zhuhai–Macau Bridge. A freezing scheme involving master freezing tubes, enhancing freezing tubes, and limiting freezing tubes is the key component of the freezing effect of the FSPR method during the construction process under various working conditions. This is related to whether the thickness and temperature of the frozen soil meet the design requirements under various complex working conditions, and it is also related to frost heave control and energy saving. Based on the unsteady-state conjugate heat transfer model, different freezing schemes of enhancing freezing tubes—that is, the shape, layout, operating duration, and heat preservation—were simulated to analyze the freezing effect, which can be measured by the thickness of frozen soil around the steel pipes and the average temperature of the frozen soil curtain. The results show that the greater the contact area between the enhancing tube and the inner wall of the steel pipe, the better the freezing effect, and that the semicircle enhancing freezing tube scheme is superior to the other three shapes of freezing tubes. The arrangement of enhancing freezing tubes far away from the excavation surface, without heat preservation measures, has a better freezing effect due to the function of the hollow pipe as a freezing pipe. Moreover, the enhancing freezing tube can be operated intermittently to control frost heave. Our research simulated the temperature fields of different media—such as steel pipes, frozen soil, and air—providing a design basis for similar projects, such as the combination of the pipe-roofing method and artificial freezing method. Full article

The risky behaviours of bus drivers are of great concern to public health and environmental sustainability, especially for the buses operated between cities. With this in mind, the present study examined the distribution of risky behaviours among bus drivers, and the contributing factors to risky performance. To achieve this, 1648 records of GPS trajectory data and 8281 records of advance warning message data from Hong Kong–Zhuhai–Macau Bridge shuttle buses were obtained. The temporal and spatial distribution of risky behaviours was analysed. A random parameters negative binomial model was developed to further investigate the relationship between speed-related factors and risky behaviours. The results indicated that the warning of safety distance, lane departure, forward collision, and distraction were more likely to occur on weekdays. The period between 14 and 16 o’clock obtained the highest frequency of safety distance and lane departure warnings. Regarding the model estimation results, indicators reflecting average speed, acceleration, and number of trips per day showed a statistically significant impact on safety distance and lane departure warnings. Also, the acceleration of bus drivers showed a mixed impact on lane departure warnings. Corresponding implications were discussed according to the findings to reduce the frequency of risky behaviours in shuttle bus operations. Full article

The durability design of reinforced concrete (RC) structures that are exposed to aggressive environmental attacks (e.g., corrosion due to chloride ingress in marine environment) plays a vital role in ensuring the structural serviceability within a reference period of interest. Existing approaches for the durability design and assessment of RC structures have, for the most part, not considered the spatial distribution of corrosion-related structural properties. In this paper, a closed-form approach is developed for durability assessment of RC structures, where the structural dimension, spatial variability, and correlation of structural properties such as the concrete cover thickness and the chloride diffusion coefficient are taken into account. The corrosion and crack initiations of an emerged tube tunnel segment that was used in the Hong Kong-Zhuhai-Macau bridge project were assessed to demonstrate the applicability of the proposed approach. The accuracy of the method was verified through a comparison with Monte Carlo simulation results based on two-dimensional random field modeling. The proposed method can be used to efficiently assess the durability performance of RC structures in the marine environment and has the potential to become an efficient tool to guide the durability design of RC structures subjected to corrosion. Full article

Epoxy asphalt concrete, mortar asphalt concrete and Gussasphalt concrete are commonly used types of deck pavement materials in bridge deck pavement engineering. However, achieving the high-temperature stability and anti-fatigue performance of the deck pavement materials is still challenging. In order to reduce the rutting and cracking risks of the asphalt mixture, this paper proposed pre-coated aggregates grouting asphalt concrete (PGAC) for bridge deck pavement. Laboratory tests were conducted to determine the optimum grouting materials and to evaluate the mechanical performances of the PGAC material. Test results showed that the mechanical properties for PGAC with grouting material of high-viscosity-modified asphalt binder blending with mineral filler were superior to that of GMA-10 used for the Hong Kong-Zhuhai-Macau Bridge deck pavement. Microstructural analysis showed that the PGAC had a more stable skeleton structure compared to other typical aggregate mixtures. This study highlights the performances of the proposed PGAC and sheds light on the deck pavement material improvement of both high-temperature stability and anti-fatigue performance that could be achieved. Full article

The Hong Kong-Zhuhai-Macau Bridge crosses the Pearl River Estuary and is the largest bridge and tunnel project in the world. During the construction period of this project, the excessive suspended sediment was found in the construction region. The suspended sediment generated by sand excavation in the upstream was assumed to have a significant impact on the suspended sediment in the tunnel region. In this study, we assessed the impact of upstream sand excavation on the suspended sediment in the Hong Kong-Zhuhai-Macau Bridge construction area using Landsat OLI, ETM+, and TM data. Regional suspended sediment algorithms were developed for Landsat using a symbolic regression method based on data from in situ measurements in the study area from 2003 to 2014. A band shift was conducted on the remote sensing reflectance data from Landsat ETM+ and OLI to produce a time series of the suspended sediment concentrations that was internally consistent with that of the Landsat TM data. The suspended sediment distribution was extracted and used to compare under two different conditions, with and without sand excavation. The correlations of the time series of the suspended sediment concentrations in different regions in the surrounding waters, including the correlations between the construction regions and the sand excavation regions, were calculated. Our results indicated that the sand excavation north of the Pearl River Estuary had a limited impact on the surface suspended sediment concentrations in the Hong Kong-Zhuhai-Macau Bridge tunnel area. Full article

Conventional wavelet transform (WT) filters have less effect on de-noising and correction of a north-seeking gyroscope sensor exposed to vibration, since the optimal wavelet decomposed level for de-noising is difficult to determine. To solve this problem, this paper proposes an optimized WT filter which is suited to the magnetic levitation gyroscope (GAT). The proposed method was tested on an equivalent mock-up network of the tunnels associated with the Hong Kong‒Zhuhai‒Macau Bridge. The gyro-observed signals exposed to vibration were collected in our experiment, and the empirical values of the optimal wavelet decomposed levels (from 6 to 10) for observed signals were constrained and validated by the high-precision Global Navigation Satellite System (GNSS) network. The result shows that the lateral breakthrough error of the tunnel was reduced from 12.1 to 3.8 mm with a ratio of 68.7%, which suggests that the method is able to correct the abnormal signal of a north-seeking gyroscope sensor exposed to vibration. Full article

A new pre-supporting technology named the freeze-sealing pipe roof (FSPR) method was adopted in the construction of Gongbei tunnel (Zhuhai, China), a critical part of the Hong Kong–Zhuhai–Macau bridge (HZMB) project. The method combined pipe-roofing with artificial ground freezing (AGF). The pipe roof which included a number of large-diameter steel pipes was designed to play a primary role in load bearing, while the frozen wall between pipes was designed for water sealing. The refrigeration proceeded in two stages called the active freezing period and excavation period. This paper mainly focuses on the freezing characteristics of FSPR to explore how the frozen soil wall developed and changed over time during both periods based on field temperature data. The results show that the development of the frozen wall met the design requirements in fewer than 80 days of refrigeration considering the most unfavorable situation. The distribution of frozen soil along the entire tunnel was non-uniform. Frost heave and thaw weakening problems should be taken into account, since some of the bottom section of the frozen wall was more than 3 m. The frozen soil at the excavation side was visibly influenced by the replenishment of heat due to excavation, while the frozen soil outside the excavation face was much less influenced. The thermal effects of Hurricane Nicole on the frozen soil wall was also observed. The conclusions provide experience, reference, and guidance for the development of similar projects in the future. Full article

In order to solve the water sealing problem of soil between pipes of long distance curved pipe-jacked technology, Freeze-Sealing Pipe Roof (FSPR) as an innovative pre-supporting method in tunnel engineering is being applied to the Gongbei Tunnel in the Hong Kong-Zhuhai-Macau Bridge. The definition of FSPR is that large diameter steel pipes are laid out in a circle around the cross section of tunnel in advance, then the artificial ground freezing method is adopted to freeze soil between steel pipes to form water-sealing curtain. An effective freeze control system, which contains master freezing tubes, enhancing freezing tubes and limiting freezing tubes, is established for building up the frozen soil curtain, maintaining its stability during excavation and controlling the volume of frozen soil to limit frost heave dynamically. An in-situ test was carried out to explore the optimal freezing scheme and control mode. The results of the test show that the principal freezing scheme of the solid pipe with hollow pipe as a complement is the most optimal scheme in active freezing phase of the real construction. Meanwhile, cold control mode is suggested to control frost heave in maintained freezing phase. The conclusions have important guiding significance for this kind of engineering construction. Full article