scholarly journals Experimental Investigation of Load-Bearing Mechanism of Underwater Mined-Tunnel Lining

2021 ◽  
Vol 9 (6) ◽  
pp. 627
Author(s):  
Zhiqiang Zhang ◽  
Binke Chen ◽  
Qingnan Lan
Keyword(s):  
High Speed ◽  
Large Scale ◽  
Water Pressure ◽  
Tunnel Lining ◽  
Scale Model ◽  
Soil Pressure ◽  
Railway Tunnel ◽  
Load Bearing ◽  
Water Head ◽  
Design Speed

A series of model tests were performed to investigate the load-bearing mechanism of a mined railway tunnel lining under water pressure. To investigate the load-bearing characteristics of different types of linings, a fully closed water pressure exerting device for a noncircular section tunnel was invented. A large-scale model test (1:30) under combined water and soil pressures was conducted to investigate the mechanical characteristics, deformation, stress distribution, crack development process, and failure mode of the underwater mined-tunnel lining. The test results indicated that for the high-speed railway tunnel of Class IV surrounding rock with a design speed of 350 km/h, both the drainage lining and the waterproof lining were controlled by a small eccentric compression under the two test conditions. One had only water pressure, and the other had a variable water pressure and constant soil pressure. The key sections for controlling instability were the bottom of the wall and the inverted arch. The ultimate water head of the drainage lining was 49 m, and the ultimate water head of the waterproof lining was 78 m. In comparison with the drainage lining, the waterproof lining could significantly improve the water-pressure resistance. Thus, design loads of 30 and 60 m are recommended for the drainage and waterproof lining structures, respectively.

scholarly journals An Experimental Study of Horizontal Bearing Capacity of Vertical Steel Floral Tube Micropiles with Double Grouting

2018 ◽  
Vol 2018 ◽  
pp. 1-11
Author(s):  
Kaiyang Wang ◽  
Yanjun Shang
Keyword(s):  
Bearing Capacity ◽  
Large Scale ◽  
Slip Surface ◽  
Bending Moment ◽  
Shear Capacity ◽  
Soil Reinforcement ◽  
Scale Model ◽  
Soil Pressure ◽  
Floral Tube ◽  
Grouting Pressure

This paper examines the performance of a novel technology, vertical steel floral tube micropiles with double grouting. It is the combination of micropile technology and double grouting technology. A large-scale model tank was applied to impart horizontal bearing capacity, and the slope soil pressure and flexural performance of the micropile were investigated under four experimental conditions. The peak grouting pressure during the double grouting process was defined as the fracturing pressure of the double grouting, and it was positively correlated to the interval time between first grouting and secondary grouting. Compared with traditional grouting, double grouting increased the horizontal bearing capacity of the single micropile with the vertical steel floral tube by 24.42%. The horizontal bearing capacity was also 20.25% higher for the structure with three micropiles, compared with a 3-fold value of horizontal sliding resistance. In the test, the maximum bending moment acting on the pile above the sliding surface was located 2.0–2.5 m away from the pile top, and the largest negative bending moment acting on the pile below the slip surface was located 4.0 m away from the pile top. The ultimate bending moment of the single pile increased by 12.8 kN·m with double grouting, and the bending resistance increased by 96.2%. The experimental results showed that the double grouting technology significantly improved the horizontal bearing capacity of the micropile with the steel floral tube, and the soil reinforcement performance between piles was more pronounced. Also, the shear capacity and the flexural capacity were significantly improved compared with the original technology.

scholarly journals Stability Improvement Method for Embankment Dam with Respect to Conduit Cracks

2022 ◽  
Vol 12 (2) ◽  
pp. 567
Author(s):  
Young-Hak Lee ◽  
Jung-Hyun Ryu ◽  
Joon Heo ◽  
Jae-Woong Shim ◽  
Dal-Won Lee
Keyword(s):  
Large Scale ◽  
Pore Water Pressure ◽  
Water Pressure ◽  
Three Dimensional ◽  
Internal Erosion ◽  
Scale Model ◽  
Seepage Analysis ◽  
Large Scale Model ◽  
Proposed Model ◽  
Improvement Method

In recent years, as the number of reservoir embankments constructed has increased, embankment failures due to cracks in aging conduits have also increased. In this study, a crack in a conduit was modeled based on the current conduit design model, and the risk of internal erosion was analyzed using a large-scale model test and three-dimensional deformation–seepage analysis. The results show that when cracks existed in the conduit, soil erosion and cavitation occurred near the crack area, which made the conduit extremely vulnerable to internal erosion. Herein, a model is proposed that can reduce internal erosion by applying a layer of sand and geotextiles on the upper part of the conduit located close to the downstream slope. In the proposed model, only partial erosion occurred inside the conduit, and no cavitation appeared near the crack in the conduit. The results suggest that internal erosion can be suppressed when the water pressure acting intensively on the crack in the conduit is dispersed by the drainage layer. To validate these results, the pore water pressure, seepage line, and hydraulic gradient were investigated to confirm the erosion phenomenon and reinforcement effect.

scholarly journals Dynamic Response of the Entrance Structure of an Elliptical Mountain Tunnel under the Action of SH Waves

2021 ◽  
Vol 2021 ◽  
pp. 1-10
Author(s):  
Zhenyu Wang ◽  
Junsheng Yang ◽  
Xinghua Wang
Keyword(s):  
Analytical Solution ◽  
Mirror Symmetry ◽  
High Speed ◽  
Large Scale ◽  
Strain Curve ◽  
Shaking Table ◽  
Railway Tunnel ◽  
Tangential Strain ◽  
Entrance Section ◽  
Mountain Tunnel

Generally, the surrounding rock at the entrance of a mountain tunnel is loose, and the entrance has more slopes due to topography, which causes the tunnel entrance section to be easily destroyed under an earthquake. Based on the established slope model with a single free surface, this paper adopted the elastic wave theory to derive the analytical solution of the strain at the entrance of the mountain tunnel when the SH wave is incident perpendicularly to the bottom of the tunnel; besides, the factors affecting strain were also analyzed. The tangential strain curve at each point of the entrance section takes the centre of the elliptical tunnel as the centre of symmetry, forming symmetry between the left and right sides and mirror symmetry between the top and bottom sides. Then, large-scale shaking table model experiments were conducted to model the actual working conditions, and the correctness of the analytical solution was verified. The research can provide a theoretical reference for the seismic design of the entrance section of the high-speed railway tunnel and greatly improve the understanding of its seismic response.

Three-Dimensional Dynamic Response Analysis of Shield Tunnel under Train Loads

2011 ◽  
Vol 90-93 ◽  
pp. 2062-2067 ◽  
Author(s):  
Zhan Rui Wu ◽  
Tai Yue Qi ◽  
Lin Zhong
Keyword(s):  
Dynamic Response ◽  
High Speed ◽  
Pore Water Pressure ◽  
Water Pressure ◽  
Three Dimensional ◽  
Shield Tunnel ◽  
Response Analysis ◽  
High Speed Train ◽  
Lining Structure ◽  
Design Speed

The vibration loads will be produced between wheel and rail on the running of the high-speed Train. The vibration energy will be transferred to the ground formation through the rail, guiding bed and tunnel lining structure, thereby causing vibration between the formation and surface and environmental interference effect problems. Thus the research of related issues caused by the high-speed train vibration has the vital great significance. The train design speed of the Shiziyang shield tunnel for Guangzhou-Shenzhen-Hong Kong passenger dedicated line is up to 350km/h. In this paper the research object is located in the segment of the homogeneous formation of the Shiziyang shield tunnel. The analysis of this paper includes the dynamic response rules of the shield tunnel and formation under the single high-speed train loads and the law of the pore water pressure accumulation and dispersion under train cyclic loading.

scholarly journals Analysis on Vibration Characteristics and Suppression Strategy of Vehicle Mounted GPR Detection Device for Tunnel Lining

Machines ◽  
2021 ◽  
Vol 9 (12) ◽  
pp. 309
Author(s):  
Yang Lei ◽  
Yong Zou ◽  
Tian Tian ◽  
Falin Qi ◽  
Bo Jiang
Keyword(s):  
High Speed ◽  
Control Program ◽  
Vibration Characteristics ◽  
Tunnel Lining ◽  
Railway Tunnel ◽  
Tunnel Detection ◽  
Adaptive Adjustment ◽  
And Control ◽  
Suppression Strategy

The GPR antenna is installed on the high-speed railway tunnel detection vehicle through the detection device to carry out non-contact nondestructive and rapid detection of the lining condition. Through simulation calculation and field vibration test data analysis, the vibration characteristics of the detection device are obtained. Vibration excitation is applied to GPR antennas to explore the amplitude-frequency sensitivity of echo signal affected by vibration when GPR detects tunnel lining, thus as to provide a basis for mechanism design and vibration control strategy. Through the optimization of the material properties, structural design, and control program of the detection device, the vibration frequency and amplitude of the detection device are optimized, the adaptive adjustment stability of the control system is improved, and the quality of GPR detection data is enhanced.

Scaling Laws for Ultra-Short Hydrostatic Gas Journal Bearings

2003 ◽  
Author(s):  
Z. S. Spakovszky ◽  
L. X. Liu
Keyword(s):  
High Speed ◽  
Large Scale ◽  
Scaling Laws ◽  
Damping Ratio ◽  
Journal Bearings ◽  
Gas Bearings ◽  
Outer Periphery ◽  
Order Of Magnitude ◽  
Design Speed ◽  
Annular Seals

The journal bearings of the MIT micro-devices are located at the outer periphery of the rotor and are designed to operate at rotational speeds of order 2 million rpm in order to enable high-power densities with turbomachinery tip speeds near 500 m/s. These journal bearings are very short compared to their relatively large bearing diameters such that the bearing L/D is typically less than 0.1, that is at least one order of magnitude smaller than in conventional gas bearings. Thus, the ultra-short micro gas journal bearings essentially act as short annular seals and operate at Reynolds numbers of order 300, two orders of magnitude lower than conventional annular seals. The concepts that hold for turbulent flow, large scale annular seals do not apply to micro bearings and the laminar flow regime sets new challenges in the design, implementation and operation of ultra-short, high-speed gas bearings. In order to reach the goal of operating the MIT micro devices at full design speed, the micro-bearing design must be improved and engineering solutions need to be found to overcome the challenges of high-speed bearing operation. This paper is the first to derive the scaling laws for the dynamics of ultrashort hydrostatic gas journal bearings. The theory is established from first principles and enables a physics based characterization of the dynamic behavior of ultra-short hydrostatic gas bearings. The derived scaling laws for natural frequency and damping ratio show good agreement with experimental data. A simple criterion for whirl instability is found that only depends on bearing geometry. The scaling laws together with this criterion are used to delineate engineering solutions critical for stable high-speed bearing operation. Design charts are developed which provide the link between fabrication tolerances, bearing performance, and the tolerable level of rotor unbalance for a minimum required whirl ratio.

Numerical Simulation on Mesoscopic Damage Evolution Mechanism of High-Speed Railway Tunnel Lining Concrete

2011 ◽  
Vol 90-93 ◽  
pp. 2248-2253
Author(s):  
Yun Dong Ma ◽  
Bo Li ◽  
Bin Fan
Keyword(s):  
High Speed ◽  
Damage Mechanism ◽  
Tunnel Lining ◽  
Concrete Lining ◽  
Railway Tunnel ◽  
High Speed Railway ◽  
Main Research ◽  
Elastic Module ◽  
Fatigue Loads ◽  
Research Stage

For the high-speed railway tunnel concrete lining, there have been some such initial damages as initial pores or cracks, therefore the initial damages will be expanded gradually under aerodynamic fatigue loads resulting from the high-speed train passing by tunnel, elastic module attenuation laws of concrete was adopted to reflect the effects of fatigue loads on the tunnel lining mesoscopic concrete, taking the second stage of the elastic module attenuation as the main research stage, the mesoscopic damage mechanism and fatigue damage cracks developing-and-changing laws of high-speed railway lining concrete were simulated under the repetitive aerodynamic loads. Study indicates: for the concrete lining with initial damages, under the repeated aerodynamic fatigue loads, the mechanical properties of the tunnel lining concrete will gradually deteriorate to the whole damage of the concrete structure, which will cause serious inference on the durability of the tunnel especially during the middle and later periods of the high-speed railway tunnel serving.

Scaling Laws for Ultra-Short Hydrostatic Gas Journal Bearings

2005 ◽  
Vol 127 (3) ◽  
pp. 254-261 ◽  
Author(s):  
Z. S. Spakovszky ◽  
L. X. Liu
Keyword(s):  
High Speed ◽  
Large Scale ◽  
Scaling Laws ◽  
Damping Ratio ◽  
Journal Bearings ◽  
Gas Bearings ◽  
Outer Periphery ◽  
Order Of Magnitude ◽  
Design Speed ◽  
Annular Seals

The journal bearings of the MIT micro-devices are located at the outer periphery of the rotor and are designed to operate at rotational speeds of order two million rpm in order to enable high-power densities with turbomachinery tip speeds near 500m/s. These journal bearings are very short compared to their relatively large bearing diameters such that the bearing L/D is typically less than 0.1, that is at least one order of magnitude smaller than in conventional gas bearings. Thus, the ultra-short micro gas journal bearings essentially act as short annular seals and operate at Reynolds numbers of order 300, two orders of magnitude lower than conventional annular seals. The concepts that hold for turbulent flow, large scale annular seals do not apply to micro bearings and the laminar flow regime sets new challenges in the design, implementation and operation of ultra-short, high-speed gas bearings. In order to reach the goal of operating the MIT micro devices at full design speed, the micro-bearing design must be improved and engineering solutions need to be found to overcome the challenges of high-speed bearing operation. This paper is the first to derive the scaling laws for the dynamics of ultra-short hydrostatic gas journal bearings. The theory is established from first principles and enables a physics based characterization of the dynamic behavior of ultra-short hydrostatic gas bearings. The derived scaling laws for natural frequency and damping ratio show good agreement with experimental data. A simple criterion for whirl instability is found that only depends on bearing geometry. The scaling laws together with this criterion are used to delineate engineering solutions critical for stable high-speed bearing operation. Design charts are developed which provide the link between fabrication tolerances, bearing performance, and the tolerable level of rotor unbalance for a minimum required whirl ratio.

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