scholarly journals Characteristics of Karst Cave Development in Urban Karst Area and Its Effect on the Stability of Subway Tunnel Construction

2021 ◽  
Vol 2021 ◽  
pp. 1-12
Author(s):  
Fei Xue ◽  
Minjun Cai ◽  
Tianzuo Wang ◽  
Tongyang Zhao
Keyword(s):  
Numerical Models ◽  
Karst Area ◽  
Risk Level ◽  
Tunnel Construction ◽  
Karst Cave ◽  
Subway Tunnel ◽  
Karst Caves ◽  
Metro Tunnel ◽  
The Stability

The existence of karst caves poses a large threat to safe tunnel construction in a karst area. This paper presents a synthetic method to evaluate the collapse risk before subway tunnel construction with Yang-Jian interval tunnel as a case study. The crosshole seismic Computed Tomography (CT) integrated with Geological Drilling (Geo-D) was first applied to accurately delineate the karst location and its scale. Then, 483 groups of seismic wave CT images were recorded, and 524 karst cave anomalies were found. The height of karst caves in the study area is 1–20 m and mainly concentrated at approximately 5 m. The vertical distance between the karst cave and the tunnel is mainly within 15 m. According to the detection results, a series of numerical models were built and calculated using FLAC3D to investigate the effect of different sizes and locations of karst caves on the displacement and stability of the surrounding rock in tunnels. Afterwards, based on the simulation results, the disturbance degree evaluation index was established to quantitatively evaluate the risk level of karst caves. The evaluation results indicate that the buried depth of the karst cave greatly affects the disturbance degree. No treatment is required for the deeply buried karst cave that is more than 7 m from the tunnel. When the distance between the cave and the tunnel is less than 7 m, there is a critical size of the cave. Karst caves that are larger than that critical value must be filled with a single slurry or binary slurry before tunnel construction to eliminate the risk of tunnel collapse. This study can be used to provide a more efficient and economical program for metro tunnel construction above a karst cave.

Study of the Effects of Karst Area Beneath the Tunnel on the Stability of Surrounding Rock

2014 ◽  
Vol 711 ◽  
pp. 402-405
Author(s):  
Li Wei Dong ◽  
Ping Cao ◽  
Jie Liu
Keyword(s):  
Large Scale ◽  
Surrounding Rock ◽  
Vertical Stress ◽  
Karst Area ◽  
Karst Cave ◽  
Karst Caves ◽  
Tunnel Floor ◽  
Stability Of Surrounding Rock ◽  
Karst Areas ◽  
The Stability

Geotechnical engineering in large scale is endangered by the karst areas which are close to the engineering. The stability of the tunnels is greatly affected by the sizes and locations of the karst caves. Based on a engineering example, a study of the effects of karst area beneath the tunnel on the stability of surrounding rock is conducted. It can be concluded that the displacement release of surrounding rocks and the distribution of the vertical stress in surrounding rocks are greatly affected by the sizes of the karst caves and the distance between the tunnel floor and the karst cave.

scholarly journals Compound Karst Cave Treatment and Waterproofing Strategy for EPB Shield Tunnelling in Karst Areas: A Case Study

2021 ◽  
Vol 9 ◽  
Author(s):  
Yongshui Kang ◽  
Zhi Geng ◽  
Linhai Lu ◽  
Lei Chen ◽  
Xuewei Liu ◽  
...  
Keyword(s):  
Water Inrush ◽  
Earth Pressure ◽  
Karst Area ◽  
Karst Cave ◽  
Karst Caves ◽  
Ground Collapse ◽  
Karst Areas ◽  
Shield Tunnelling ◽  
Epb Shield

There is high risk of water inrush and ground collapse accidents when tunnelling in karst areas. Based on the case study of an urban metro tunnel, this paper focuses on karst cave treatment and waterproofing strategies for earth pressure balancing (EPB) shield tunnelling in karst areas containing large amounts of karst caves and fissures. When the shield machine enters the karst area, water gush easily occurs, posing serious threats to tunnelling safety. The distribution characteristic of limestone fractures, karst caves, and fissures in the karst area were analyzed according to the geological survey results. Further, water inrush risk and engineering difficulties were analyzed. Subsequently, a compound karst cave treatment and waterproofing strategy for EPB shield tunnelling was proposed and implemented. Water inflow is successfully reduced and ground collapse accident is avoided using the compound karst cave treatment and waterproofing strategy.

Stability Analysis of Dam Foundation with Karst Cave

2011 ◽  
Vol 90-93 ◽  
pp. 2640-2643
Author(s):  
Wei Ma ◽  
Chong Shi ◽  
Wei Jing Pan
Keyword(s):  
Stability Analysis ◽  
Work Conditions ◽  
Karst Cave ◽  
Dam Foundation ◽  
Safety Coefficient ◽  
Karst Caves ◽  
Load Analysis ◽  
Dip Angle ◽  
The Stability ◽  
Structure Plane

Stability of dam foundation with Karst caves is analyzed in the presented work.Conceptual model is established according to load analysis such as dam gravity and water press. The curve of point safety coefficient on the structure plane is draw out by using stress checking method.With the comparison of curves under different work conditions, it shows that the most dangerous position of Karst cave is at the dam toe area,with the increasing of dip angle of the structure plane,the safety coefficient declines.Then the possible damage zones,mechanism and failure mode of the dam foundation with Karst caves are analyzed. The result can be used in evaluating the stability of dam foundation with Karst cave.

scholarly journals Subway Tunnel Construction Settlement Analysis Based on the Combination of Numerical Simulation and Neural Network

2021 ◽  
Vol 2021 ◽  
pp. 1-9
Author(s):  
Qiangqiang Ma ◽  
Wentao Li ◽  
Yongjun Zhang
Keyword(s):  
Neural Network ◽  
Numerical Simulation ◽  
Risk Assessment ◽  
Traffic Congestion ◽  
Urban Traffic ◽  
City Size ◽  
Tunnel Construction ◽  
Subway Tunnel ◽  
Settlement Analysis

Under the background of rapid economic development and the continuous expansion of city size, people’s travel is deeply troubled by the problem of urban traffic congestion. Subway is an effective way to relieve traffic pressure and plays an important role in its use. In the process of building the city subway, the excavation of the underground tunnel is the most critical. However, the excavation of the tunnel will inevitably disturb the nearby soil, change the stratum stress conditions, and make the stress distribution uneven. If the surface settlement is too large, it will not only affect the normal construction of the tunnel but also cause damage to the surrounding buildings (structures), roads, underground pipelines, and so on, resulting in very serious malignant consequences. In this study, Cuobuling Station is taken as a case study. First, the construction status of the subway tunnel in the station is analyzed, and then the monitoring results are analyzed. According to the cross-section settlement law, the numerical simulation and neural network are used to build a model, calculate the numerical simulation results, and carry out a risk assessment of regression model. Finally, combined with the tunnel construction situation of the station, according to the risk assessment results, the concrete measures are put forward to deal with the subway tunnel construction settlement problem.

scholarly journals Safe-economical route and its assessment model of a ship to avoid tropical cyclones using dynamic forecast environment

2013 ◽  
Vol 1 (3) ◽  
pp. 1857-1893
Author(s):  
L. C. Wu ◽  
Y. Q. Wen ◽  
D. Y. Wu
Keyword(s):  
Tropical Cyclones ◽  
Numerical Models ◽  
Economic Cost ◽  
Assessment Model ◽  
Risk Level ◽  
Proposed Model ◽  
Study Results ◽  
Capsizing Probability ◽  
Forecasting Errors

Abstract. In heavy sea conditions related to tropical cyclones (TCs), losses to shipping caused by capsizing are greater than other kinds of accidents. Therefore, it is important to consider capsizing risk in the algorithms used to generate safe-economic routes that avoid tropical cyclones (RATC). A safe-economic routing and assessment model for RATC, based on a dynamic forecasting environment, is presented in this paper. In the proposed model, a ship's risk is quantified using its capsizing probability caused by heavy wave conditions. Forecasting errors in the numerical models are considered according to their distribution characteristics. A case study shows that: the economic cost of RATCs is associated not only to the ship's speed and the acceptable risk level, but also to the ship's wind and wave resistance. Case study results demonstrate that the optimal routes obtained from the model proposed in this paper are significantly superior to those produced by traditional methods.

scholarly journals Numerical prediction of the optimal shield tunneling strategy for tunnel construction in karst regions

PLoS ONE ◽  
2021 ◽  
Vol 16 (6) ◽  
pp. e0252733
Author(s):  
Zhen Liu ◽  
Weihua Ming ◽  
Jieming Li ◽  
Cuiying Zhou ◽  
Lihai Zhang
Keyword(s):  
Iteration Process ◽  
Karst Region ◽  
Tunnel Construction ◽  
Karst Cave ◽  
Shield Tunneling ◽  
Shield Tunneling Machine ◽  
Karst Areas ◽  
Tunneling Machine ◽  
The Stability ◽  
Shield Machine

Shield tunneling in karst areas poses significant challenges, as vibration caused by the shield machine can disturb the stability of the karst caves, ultimately resulting in the collapse of a tunnel. In the present study, a numerical model involving an iteration process was developed based on the Mindlin solution scheme to identify the optimal shield tunneling speed for minimizing the disturbance to karst cave stability. The developed model was then implemented to investigate an underground tunnel constructed in a karst region with different shield tunneling strategies. By using the variation in the energy density of a karst cave as a performance index, the model predicts that when approaching the affected zone of a karst carve (e.g., approximately 5 m from the carve), the shield tunneling machine should be controlled within a certain speed (i.e., < 30 mm/min). Once the shield tunneling machine moves into the affected zone of the cave, the speed of the machine needs to be decelerated to 11 mm/min, and the speed of 30 mm/min can be restored when the shield machine moves out of the affected zone. This finding demonstrates that the developed model could potentially be used to identify the optimal shield tunneling speed to minimize the disturbance to karst cave stability and ensure the safety of tunnel construction in karst regions.

Observations of Diurnal Variability under the Cirrus Canopy of Typhoon Kong-rey (2018)

2021 ◽  
Author(s):  
Benjamin C. Trabing ◽  
Michael M. Bell
Keyword(s):  
Numerical Models ◽  
Vertical Wind Shear ◽  
Rapid Intensification ◽  
Broad Distribution ◽  
Diurnal Variability ◽  
Brightness Temperatures ◽  
Upper Level ◽  
The Stability ◽  
Differential Reflectivity

AbstractA growing body of work has documented the existence of diurnal oscillations in the tropical cyclone outflow layer. These diurnal pulses have been examined primarily using satellites or numerical models, and detailed full tropospheric observations or case study analyses of diurnal pulses are lacking. Questions remain on the vertical extent of diurnal pulses and whether diurnal pulses are coupled to convective bands or constrained to the outflow layer. During the Propagation of Intraseasonal Tropical Oscillations (PISTON) field campaign, diurnal oscillations in the upper-level clouds were observed during Typhoon Kong-rey’s (2018) rapid intensification. Over a 3.5 day period where a broad distribution of cold upper-level clouds was overhead, detailed observations of Typhoon Kong-rey’s rainbands show that convection had reduced echo tops but enhanced reflectivity and differential reflectivity aloft compared to other observations during PISTON. Shortwave heating in the upper-levels increased the stability profile in an overall favorable thermodynamic environment for convection during the day, which could help to explain the diurnal differences in convective structure. Under the cirrus canopy, nocturnal convection was deeper and daytime convection shallower in contrast to the rest of the PISTON dataset. Diurnal oscillations in the brightness temperatures were found to be coupled to radially outward propagating convective rainbands that were preceded ~6 hours by outflow jets. The cooling pulses occurred earlier than found in previous studies. The pulses were asymmetric spatially which is likely due to a combination of the vertical wind shear and storm intensity.

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