Ponding-infiltration processes on wide platforms can readily induce local instability of high-fill slopes during heavy rainfall events. This study aims to clarify the slope hydrological processes under intense y rainfall and to reveal their influences on the local instabilities of the high-fill slopes, thereby providing a scientific basis for engineering design and disaster prevention of this kind of slope. The numerical models for coupling surface water and groundwater processes and simulating the stress-strain state of soil were built through COMSOL Multiphysics. A variety of numerical simulations were carried out to analyze the relationship between the ponding-infiltration processes on the wide platform and the local instability of high-fill slope. Rainfall infiltration forms transient saturated zones in the shallow filling body. When the transient saturated zone expands to the vicinity of the filling interface, the flow direction of groundwater changes, causing groundwater to migrate along the filling interface. It can be observed that the groundwater level rises with time, and that groundwater discharges to surface water near the retaining wall. The increase of slope water content diminishes the soil shear strength, associated with an interface effect, which is especially obvious in the saturated area near the retaining wall (with the maximum reduction of 70.3%). Ponding on the wide platform raises the local groundwater level and increases slope deformation, thereby reducing slope stability. It is found that of the value and duration of the instability of the slope are larger and longer compared with no ponding considered. The installation of anti-seepage geotextiles under the wide platforms can improve the stability of the slope by reducing groundwater seepage. Specifically, the spatial continuity of the transient saturated zones is decreased, reducing the hydraulic connectivity of groundwater seepage channels and the groundwater level at the foot of the slope. Ponding-infiltration processes on wide platforms of high-fill slope can rise the groundwater level, strengthen the interaction of surface water and groundwater, increase the pore water pressure of the shallow soil, and aggravate local deformation, which decrease the stability of the slope. The use of anti-seepage geotextiles under the wide platforms can reduce rainfall infiltration and improve the stability of the slope.
Nonuniform soil profiles can induce seismic ground-motion amplification and deformation incompatibility, thereby intensifying the seismic response and altering the deformation patterns of shield tunnels. To address this critical issue, this study takes a cross-river tunnel project in the lower reaches of the Yangtze River as a case study. Considering the dynamic nonlinearity of riverbed soil and the refined assembly of segments, a 3D refined finite element model with a longitudinal length of 500 m was established. The effects of seismic wave characteristics and the shear wave velocity ratio of adjacent soil layers on the failure mechanism and deformation mode of tunnels crossing longitudinally heterogeneous ground were systematically investigated. The results indicate that under seismic loading, the tunnel exhibits significant longitudinal non-uniform deformation, with the peaks of longitudinal joint opening and staggering concentrated on the soft soil side near the strata interface. The tunnel manifests a distinct “S-shaped” bending deformation at the interface, and the zone significantly affected by the abrupt change in strata extends to a range of 5 times the tunnel diameter into the soft soil side. Furthermore, concrete damage in tunnel segments presents asymmetric evolution. In soft-soil sections, damage is mainly concentrated along conjugate directions of the tunnel cross-section, whereas in hard-soil sections, damage is primarily localized near the springline region. The findings provide useful guidance for the anti-seismic design of cross-river tunnels in heterogeneous ground conditions.
Groundwater inorganic nitrogen contamination is one of the most widespread water environmental issues in the Jianghan Plain.Agricultural activities constitute an important source of inorganic nitrogen in groundwater.However,in agricultural regions characterized by dense river networks,the sources,migration pathways,and transformation mechanisms of inorganic nitrogen in shallow groundwater recharged by precipitation and surface water remain insufficiently understood.Taking the agricultural area of the eastern Jianghan Plain as a case study,the chemical characteristics,the source of inorganic nitrogen,and its migration and transformation mechanism of surface water and groundwater were analyzed by hydrochemistry combined with hydrogen-oxygen and strontium isotopes.The results show that the cations of surface water and groundwater samples in the study area were dominated by Ca2+and Na+,and the anions were dominated by HCO-3.The water chemical type was dominated by HCO3-Ca •Na and HCO3-Ca.The inorganic nitrogen in surface water and groundwater was mainly nitrate,and the concentration of inorganic nitrogen in groundwater was significantly higher than that in surface water.The groundwater with high nitrate concentration was mainly distributed around the northern and southern towns,and the distribution of ammonia nitrogen with high concentration was scattered.Precipitation was the primary source of surface water and groundwater recharge in the region.The chemical characteristics of surface water and groundwater were mainly controlled by silicate and evaporite weathering,and were obviously affected by human activities.The surface water with extreme low concentration of inorganic nitrogen was mainly from atmospheric precipitation,while the groundwater with relatively high concentration of inorganic nitrogen was mainly from domestic sewage and feces in agricultural areas.The mutual transformation of inorganic nitrogen components was affected by the redox conditions.The inorganic nitrogen of the pollution source in the surface layer was mainly ammonia nitrogen,and the concentration of ammonia nitrogen in groundwater is high.Nitrate was gradually enriched by nitrification,accompanied by the downward migration of atmospheric precipitation.This study is of great significance for understanding the causes and migration and transformation mechanism of inorganic nitrogen enrichment in groundwater in agricultural areas with dense water networks,and for the prevention and control of groundwater pollution in Jianghan Plain.
To realize the practical value of historical earthquake data in the seismic resilience assessment of urban rail transit network (URTN), it is essential to establish links between resilience metrics and real-world network characteristics, including network topology, service coverage capacity, passenger flow patterns, the spatial distribution of earthquakes, and the vulnerability of civil infrastructure, thereby improving the fidelity of resilience assessment. In this study, taking Shanghai as a case study, a ground-motion estimation model based on historical earthquake data and a civil infrastructure vulnerability model were first developed. These models were then embedded into the URTN topology model, and their coupling was achieved by controlling the failure states of nodes and links in the topology model under earthquake scenarios. For resilience calculation and assessment, fractal dimension was computed using information dimension theory and taken as the functional indicator of network resilience, while the resilience triangle was used to characterize the variation of network resilience over time. Subsequently, this method was applied to obtain the resilience assessment results of Shanghai URTN. Before the earthquake, the fractal dimension was approximately 1.2; under MS 3.0 and MS 4.0 earthquakes, the fractal dimension showed no obvious change; under MS 5.0 and MS 6.0 earthquakes, however, the fractal dimension exhibited significant attenuation, and the corresponding recovery times were 3 400 h and 5 000 h, respectively, both indicating severe resilience losses. After preventive reinforcement measures were implemented, the Shanghai URTN was able to maintain an essentially normal operational state under MS 5.0 earthquakes. Under MS 6.0 earthquakes, the post-earthquake recovery time was shortened by approximately 30%, and the resilience loss was reduced by about 34%. The results show that using fractal dimension for seismic resilience assessment can incorporate more real-world elements and comprehensively and quantitatively evaluate the performance and resilience characteristics of URTN before and after earthquake disasters. Preventive reinforcement measures can also significantly improve the seismic resilience of URTN.
Under complex geological and geostress conditions, the design of mountain-adjacent tunnels in hard rock areas faces numerous challenges, particularly in determining the tunnel’s buried depth. This study proposed a method for determining the buried depth of mountain-adjacent tunnels, comprehensively integrating high-level tectonic stress, the superimposed effects of valley stress fields, and the potential for rockbursts triggered by depth. The specific methods include: (1) Determining the influence range of the superimposed tectonic stress field and valley stress field. This involves initially estimating the influence depths of the tectonic stress and valley stress fields based on measured geostress data from boreholes in the slope zones of canyon areas, and then uses numerical simulation technology to optimize the preliminary estimation results to ensure the accuracy and reliability of the initial obtained range. (2) Determining the limit of severe rockbursts caused by burial depth. Firstly, it calculates the statistical mean value of saturated uniaxial compressive strength (Rc) by rock physical and mechanical tests in the tunnel site area, and then selects the typical geological section of the tunnel site to simulate the stress field. It uses the strength stress ratio method, introducing the σmax=Rc/2 as the basis to judge whether the buried depth may cause severe rockbursts. (3) It should be emphasized that on the basis of the above two steps, the relatively safe buried depth range of the tunnel is determined, while the deep buried depth section (≥1200 m) should be minimized as far as possible in the design process to achieve the final optimization of the tunnel buried depth. This study provides a scientific basis and practical method for the buried depth design of hard rock mountain-adjacent tunnels, and has a wide application prospect and popularization value in the future design of mountain-adjacent tunnels.
