Search Results (13)

To investigate the impact of subsurface karst cavities on the stability of pipe jacking construction, this study utilizes the Yunnan Central Water Diversion Project as a real-world case. Employing ABAQUS finite element software to establish a numerical model, it systematically analyzes construction stability under the specific condition of “karst cavities present ahead of the excavation direction” in karst formations. The research focuses on examining the effects of four key scenarios on the displacement and stress response of surrounding rock and pipe segments. These conditions specifically include the following: tunnel burial depth (10 m, 15 m, 20 m, 25 m), cavity diameter beneath the tunnel (1–4 m), cavity filling status, and distance between the cavity and the tunnel (1–4 m). The study reveals that in composite stratum tunnel construction, when cavities exist in the strata ahead, multi-area displacements increase progressively with cavity size. Displacement changes accelerate and magnify when the cutting face of the jacking machine approaches within approximately 2.5 m of the cavity. However, no significant difference is observed between soft plastic clay reinforcement and slurry reinforcement effects. When composite stratum tunnels traverse beneath karst caves, the maximum upward bulge at tunnel bases occurs at 1-meter diameter caves, reaching approximately 2.5 mm. When the diameter of the cave increases to 4 m, the arching settles to a maximum. As tunnel burial depth increases, the arch base rises while the crown sinks, with settlement magnitude exceeding bulge amount. The displacement and stress fields from the initial excavation phase become disturbed, intensify, and then stabilize. When the jacking machine reaches directly above the cavern, stress at the crown base increases while stress at the crown top decreases. The pipe bottom exhibits uplift, and the pipe top shows reduced settlement directly above the cavern. Cavern filling has a minor effect on pipe-segment displacement, with segments deforming into an approximate elliptical shape. At the completion stage of excavation, the maximum Mises stress occurs at the top of the launch-end pipe segment. While cavern-related factors have a limited influence on the pipe-segment Mises stress, this stress gradually increases as excavation progresses. Full article

The Central Yunnan Water Diversion Project (CYWDP) is currently under construction and represents China’s most extensive and geologically challenging water transfer infrastructure, facing significant geohazard risks induced by intensive engineering activities, posing severe threats to its entire lifecycle safety. Therefore, monitoring and spatiotemporal evolution analysis of surface deformation along the CYWDP is critically important. This study presents the first integrated analysis of geometric distortions and multi-dimensional spatiotemporal deformation characteristics along the CYWDP, utilizing both ascending and descending orbit data from Sentinel-1. First, by integrating the Layover-Shadow Mask (LSM) model and R-Index method, we identified geometric distortion types in SAR imagery and evaluated their suitability for deformation monitoring. Subsequently, SBAS-InSAR technology was employed to derive line-of-sight (LOS) deformation information from 124 images (ascending) and 90 images (descending) acquisitions (2022–2024), enabling the identification of significant deformation zones and analyzing their spatial distribution characteristics. Finally, two-dimensional (2D) deformation fields were obtained through the joint inversion of ascending and descending orbit data in typical deformation zones. The results reveal that geometric distortions in Sentinel-1 imagery along the CYWDP are dominated by foreshortening effects, accounting for 35.3% of the study area in the ascending-orbit data and 37.9% in the descending-orbit data. A total of 10 significant deformation-prone areas were detected, and the most pronounced subsidence, amounting to −164 mm/y, was observed in the northern Jinning District (Luoci-Qujiang section), showing expansion trends toward water conveyance infrastructure. This study reveals surface deformation’s multi-dimensional spatiotemporal evolution patterns along the CYWDP. The findings support geohazard mitigation and provide a methodological reference for safety monitoring of major water conservancy projects in complex geological environments. Full article

Conducting ecological restoration has emerged as a critical governance strategy for enhancing ecosystem diversity, stability, and sustainability. The scientific identification of priority restoration areas is a prerequisite for effective ecological restoration projects. Current research on identifying priority restoration zones predominantly relies on administrative-scale frameworks, and the reliability and scientificity of the identified results are somewhat insufficient. To address this gap, this study selected Dali Prefecture in Yunnan Province, a region characterized by dense river networks, as the research area to identify the priority areas of ecological restoration. In view of the application of the InVest model in watershed-scale restoration, biodiversity assessment, and other fields, we utilize sub-watershed units and the InVEST model, and five key ecosystem services—water conservation, water purification (N/P), habitat quality, climate regulation, and soil retention—were quantified. Temporal changes in these services from 2015 to 2020 were analyzed alongside ecological risk assessments and restoration zoning. Priority areas were further identified through Ordered Weighted Averaging (OWA) operators under varying decision-making preferences. The optimal threshold for watershed delineation was determined as 11.04 km², resulting in 1513 refined sub-watershed units after correction, with 71.59% concentrated in the 10–50 km² range. A spatial analysis revealed an east-to-west gradient in ecosystem service distribution, where eastern regions consistently exhibited lower values compared to central and western areas. From 2015 to 2020, soil retention per unit area increased by 5.09%, while water purification for N and P showed marginal improvements of 0.97% and 0.39%, respectively. Conversely, water conservation declined significantly by 10.00%, with carbon sequestration and biodiversity protection experiencing slight reductions of 1.74% and 1.92%, all within a 2% variation margin. Ecological risk zoning identified low-risk areas (grades 1–3) predominantly in western and northeastern Dali, encompassing 1094 sub-watersheds (77.36% by count and 73.92% by area), while high-risk zones (grades 4–5) covered 386 units (26.08% by area). Integrating ecological quality and risk levels, the study area was classified into four functional zones: Zone I (high quality, high risk), Zone II (low quality, high risk), Zone III (low quality, low risk), and Zone IV (high quality, low risk). With increasing risk tolerance, the priority restoration areas expanded from eastward to central regions. Based on the scenario simulations under ecological priority, status quo, and development-oriented policies, the critical restoration areas include the Sangyuan River Basin, mid-reach of the Juli River, and upper Miyu River. This methodology provides a theoretical and technical foundation for ecosystem service enhancement and degraded ecosystem rehabilitation in Dali Prefecture and similar regions. Full article

In order to control the stability of tunnel surrounding rock, reduce the construction cost, and improve the construction schedule, the deformation behavior and instability mechanisms of tunnel surrounding rock are studied by numerical simulation and field monitoring methods according to the engineering characteristics of the fractured slate zone under construction of Longshu Tunnel in the central Yunnan water diversion project. The results show that step excavation technology can effectively control the deformation of the tunnel surrounding rock. The deformation range of the top and bottom of the tunnel is 32 mm~35 mm, the deformation range of the left shoulder is 25 mm~28 mm, and the deformation range of the right shoulder is 26 mm~29 mm. The stability range of the tunnel surrounding rock is about 25 m away from the palm surface, and the concentrated stress on both sides of the tunnel is at a low level. Full article

High external water pressure poses significant challenges to the construction of long-distance water diversion tunnels under complex geological conditions. This study developed a large-scale geomechanics model to explore the effects of tunnel depth, water head, and drained conditions on external water pressure, focusing on the Songlin Tunnel in the Central Yunnan Water Diversion Project. The results show that external water pressure is most affected by water head and tunnel depth, particularly under undrained conditions. At water heads over 160 m, the external water pressure significantly decreases with an increasing tunnel depth. The suggested coefficients are 0.65–0.80 for shallowly buried tunnels with high water heads and 0.50–0.65 for deeply buried tunnels with low water heads. For drained conditions, the recommended reduction coefficients are 0.30–0.55 for the arch vault and spandrels. For the haunch, arch springing, and arch bottom, the suggested coefficients are 0.50 to 0.60 under the low water head and 0.40 to 0.60 under the high water head. These findings offer practical guidance for the design and safety of hydraulic tunnels under high external water pressure. Full article

The Qilu Lake is an eutrophic shallow lake located in Yunnan Province, China. An ecological fishery project was initiated in the lake from 2011 to 2021 to introduce filter-feeding fish species that feed on algae, with the aim of improving water quality. In January 2022, when the ecological fishery project expired, all fisheries-related activities (including fish stocking and fishing activities) ceased in the lake. To comprehensively evaluate the initial alterations in fish community structure and diversity resulting from the fishing cessation in the Qilu Lake, the present study conducted field surveys within the one year before the fishing cessation (referred to as BFC) and the one year after the fishing cessation (referred to as AFC). A total of twenty-one fish species were collected, including four native species. Four species were recorded in the lake for the first time, including Pelteobagrus fulvidraco, Pelteobagrus vachelli, Paramisgurnus dabryanus, and Hyporhamphus intermedius. The number of fish species decreased from 21 to 13 following the fishing cessation. The fishes collected in both BFC and AFC are mainly omnivorous-feeding and of bottom-dwelling habits. The mean size of the fishes in the AFC sample shows a significant decrease compared to those in BFC. After the fishing cessation, the Shannon–Wiener diversity index and Margalef richness index of the fish slightly declined. The fish community structure of the Qilu Lake exhibits a high degree of similarity to adjacent lakes in central Yunnan. Our study demonstrates a significant shift in the fish community of the Qilu Lake following the fishing cessation, one which may adversely impact the stability of the lake ecosystem. To enhance fish species diversity in the Qilu Lake, it is recommended that policies be implemented to promote the ecological fishery project and improve habitat restoration for native fish species, while also regulating fish community structure. Full article

The water diversion project in Central Yunnan Province (WDP-YN) is the largest water diversion project under construction in China. However, the ecological effects of this water diversion project are still unclear. This study utilized Sentinel-2 remote sensing data to estimate fractional vegetation cover (FVC), maps spatiotemporal variations of FVC in construction areas from 2017 to 2022, and evaluates the impact of the WDP-YN on regional vegetation coverage using buffer analysis and vegetation type transition matrix methods. The study led to the following findings: (1) From 2017 to 2022, FVC within 10 km of the tunnel construction route showed a slightly downward trend or remained relatively stable with no significant changes in the spatial pattern of FVC. (2) Before and after the construction of WDP-YN, over 60% of the area within 10 km of the tunnel construction route showed no change in FVC. On Construction Route Section I (CRS-I), vegetation improved and/or degraded within 12.90% (14.10%) of the area and the regions with degraded FVC concentrated in the northern CRS-I. For Construction Route Section II (CRS-II), 11.96% and 27.51% of the regions were dominated by improved and/or degraded FVC. Vegetation changes near Groundwater Monitoring Point a (GMPa) were relatively stable. (3) The WDP-YN degraded vegetation within 2 km of both sides of CRS-I, slowing down the increase in FVC, while the WDP-YN improved vegetation within 2–6 km of both sides of CRS-II, the closer the distance to CRS-II, the faster the increase in FVC and the decrease in FVC slowed down within 0–2 km of both sides of CRS-II. This study sheds light on the impacts of water diversion infrastructure on vegetation coverage and provides practical guidance and reference for eco-environment protection and ecological restoration given water conservancy projects in China and other regions of the world. Full article

Calcareous mudstone, a type of red-bed soft rock, is prevalent in the surrounding rock of the Central Yunnan Water Diversion Project (CYWDP) in Yunnan Province, China, significantly impacting both construction and operation. The mechanical properties of calcareous mudstone vary with depth. This study investigates its mechanical properties, permeability characteristics, energy evolution, and macro- and micro-failure characteristics during deformation using triaxial compression tests under different confining pressures. Results reveal distinct stage characteristics in the stress–strain behavior, permeability, and energy evolution of calcareous mudstone. Crack propagation, permeability evolution, and energy dissipation are closely linked, elucidating the deformation and failure process, with fluid pressure playing a crucial role. The confining pressure σ₃ increased from 2 MPa to 4 MPa and 6 MPa, while the peak stress σ_c (P_w = 1 MPa) of the calcareous mudstone increased by 84.49% and 24.89%, respectively. Conversely, the permeability at σ_c decreased from 11.25 × 10⁻¹⁷ m² to 8.99 × 10⁻¹⁷ m² and 5.72 × 10⁻¹⁷ m², while the dissipative energy at σ_c increased from 12.39 kJ/m³ to 21.14 kJ/m³ and 42.51 kJ/m³. In comparison to those without fluid pressure (P_w = 0), the value of σ_c at P_w = 1 MPa was reduced by 36.61%, 23.23%, and 20.67% when σ₃ was 2, 4, and 6 MPa, respectively. Increasing confining pressure augments characteristic stresses, deformation and failure energy, and ductility, while reducing permeability, crack propagation, and width. These findings enhance our understanding of calcareous mudstone properties at varying depths in tunnel construction scenarios. Full article

Accurate assessment and prediction of water shortage risk are essential prerequisites for the rational allocation and risk management of water resources. However, previous water shortage risk assessment models based on copulas have strict requirements for data distribution, making them unsuitable for extreme conditions such as insufficient data volume and indeterminate distribution shapes. These limitations restrict the applicability of the models and result in lower evaluation accuracy. To address these issues, this paper proposes a water shortage risk assessment model based on kernel density estimation (KDE) and copula functions. This approach not only enhances the robustness and stability of the model but also improves its prediction accuracy. The methodology involves initially utilizing kernel density estimation to quantify the random uncertainties in water supply and demand based on historical statistical data, thereby calculating their respective marginal probability distributions. Subsequently, copula functions are employed to quantify the coupled interdependence between water supply and demand based on these marginal probability distributions, thereby computing the joint probability distribution. Ultimately, the water shortage risk is evaluated based on potential loss rates and occurrence probabilities. This proposed model is applied to assess the water shortage risk of the Yuxi water receiving area in the Central Yunnan Water Diversion Project, and compared with existing models through experimental contrasts. The experimental results demonstrate that the model exhibits evident advantages in terms of robustness, stability, and evaluation accuracy, with a rejection rate of 0 for the null hypothesis of edge probability fitting and a smaller deviation in joint probability fitting compared to the most outstanding model in the field. These findings indicate that the model presented in this paper is capable of adapting to non-ideal scenarios and extreme climatic conditions for water shortage risk assessment, providing reliable prediction outcomes even under extreme circumstances. Therefore, it can serve as a valuable reference and source of inspiration for related engineering applications and technical research. Full article

The soft and fractured strata can cause significant deformation of surrounding rock during tunnel excavation. This study analyzes field monitoring test results and compares numerical simulations from the third bid project of the Dali I section construction within the water diversion project in central Yunnan to address the issue of significant deformation following tunnel excavation in soft and fractured strata. It proposes an optimized support scheme consisting of a densified steel arch and enhanced initial support strength and stiffness. In addition, the research investigates support effectiveness considering varying support strengths and steel arch ring spacing. The study findings indicated the following: (1) The tunnel traverses soft and fractured strata, causing unevenly distributed vertical convergence deformation around the cavern. The maximum settlement occurs at the crown, showing pronounced nonlinearity. (2) The maximum stress in the steel arch is concentrated at the arch crown, measuring −19.02 MPa. The arch remains compressed, with stress decreasing from the crown to the waist. (3) The axial force in the anchor bolt reduces from the crown to the arch’s waist on both sides. As the depth of the rock mass increases, the axial force in each anchor bolt decreases and the tension state is maintained. The maximum axial force reaches 46.57 kN. (4) The maximum displacement decreases from 4.21 to 0.15 cm after the optimized support structure is implemented, demonstrating the optimization scheme’s effectiveness. Future constructions can refer to this scheme and make necessary adjustments based on various terrain conditions to ensure safety. Full article

The No. 2 conduit of the Xiaopu Tunnel in the Yuxi section of central Yunnan’s water diversion project is taken as the research object, starting from the geological conditions along with the characteristics, formation mechanism and evolutionary model of dolomite sanding. This paper discusses the engineering problems of the project’s tunnels with dolomite sanding in the water-rich section, and its corresponding engineering reinforcement plan. It was found that in the tunnel section with normal level of dolomite sanding, there was no water seepage, where measures such as advanced small conduit, mechanical excavation, short grubbing and strong support could all be adopted for safe passage. Even in the water seepage section of the weak dolomite sanding tunnel, the surrounding rock was found in close interlock with strong self-stability. The excavation and support were implemented according to the category of normal surrounding rock. In the water-rich sections with strong and intense dolomite sanding, gushing of water and sand were quite frequent, with developed fissures, broken rock masses and rich waters. During the engineering operation, phosphoric acid and sodium silicate slurry in addition to urea formaldehyde resin and oxalic acid slurry plus Malisan and liquid catalyst slurry were first prepared for water plugging. Then, pure water slurry was used for surrounding rock reinforcement, which exerted an excellent effect. This method can provide reference for reinforcing tunnels of sandy dolomite in other areas of projects. Full article

Grouting can effectively seal and reinforce broken rock masses in deep geotechnical engineering, which have an important impact on groundwater-related disaster prevention and control. Based on multi-field coupling mechanics and rotational viscosity experiments, an advance grouting migration model of cement slurry in tunnels with high-stress broken surrounding rock is built against the background of the Xianglushan Tunnel for water diversion in central Yunnan Province. The influence characteristics of water–cement ratio, grouting pressure, and initial permeability on the process of grouting material migration are analyzed by combining classical column theory and spherical theory. The results show the following: Overall, the growth rate of grouting radius is fast during the earlier 5 min and slows down later. At the fifth minute, the normal grouting ranges are 22 cm, 51 cm, and 58 cm, at water–cement ratios 0.6, 0.8, and 1.0, respectively, while the normal grouting ranges are 58 cm, 51 cm, and 36 cm at grouting pressures 2 MPa, 1 MPa, and 0.5 MPa, respectively; the normal grouting ranges are 58 cm, 24 cm, and 11 cm at initial permeabilities 5D, 0.5D, and 0.05D, respectively. At the 60th minute, the normal grouting ranges are 47 cm, 133 cm, and 155 cm at water–cement ratios 0.6, 0.8, and 1.0, respectively; the normal grouting ranges are 155 cm, 131 cm, and 96 cm at grouting pressures 2 MPa, 1 MPa, and 0.5 MPa, respectively; meanwhile, the normal grouting ranges are 155 cm, 63 cm, and 29 cm at initial permeabilities 5D, 0.5D, and 0.05D, respectively. This study can provide theoretical guidance for on-site grouting design in unfavorable geological treatment projects. Full article

Fault-crossing tunnels are often severely damaged under seismic dynamics. Study of the dynamic response characteristics of tunnels crossing faults is thus of great engineering significance. Here, the Xianglushan Tunnel of the Central Yunnan Water Diversion Project was studied. A shaking table experimental device was used, and four sets of dynamic model tests of deep-buried tunnels with different fault inclination angles were conducted. Test schemes of model similarity ratio, similar material selection, model box design, and sine wave loading were introduced. The acceleration and strain data of the tunnel lining were monitored. Analysis of the acceleration data showed that when the input PGA was 0.6 g, compared with the ordinary tunnel, the acceleration increases by 117% when the inclination angle was 75°, 127% when the inclination angle was 45°, and 144% when the inclination angle was 30°. This indicates that the dynamic response of the cross-fault tunnel structure was stronger than that of the ordinary tunnel, and the effect was more obvious as the fault dip angle decreased. Analysis of the strain data showed that the strain response of the fault-crossing tunnels was more sensitive to the fault dip. The peak strain and increase in fault-crossing tunnels were much larger than those of ordinary tunnels, and smaller fault dips led to larger increases in the strain peak; consequently, the tunnel would reach the ultimate strain and break down when the input PGA was smaller. Generally, the influence of fault inclination on the dynamic response of the tunnel lining should receive increased consideration in the seismic design of tunnels. Full article