scholarly journals Deterioration and Cavity of Surrounding Rocks at the Bottom of Tunnel Under the Combined Action of Heavy-Haul Load and Groundwater: An Experimental Study

2021 ◽  
Vol 9 ◽  
Author(s):  
Zheng Li ◽  
Kunping Chen ◽  
Ziqiang Li ◽  
Weiwei Huang ◽  
Xinsheng Wang
Keyword(s):  
Hydrodynamic Pressure ◽  
Cohesive Soil ◽  
Surrounding Rock ◽  
Structural Defects ◽  
Soil Pressure ◽  
Railway Tunnel ◽  
Heavy Haul ◽  
Combined Action ◽  
Cavity Characteristics ◽  
Heavy Haul Railway

In China, the first tunnel was built in accordance with the 30-ton heavy-haul railway standard. Based on the change in water and soil pressure obtained from long-term on-site monitoring, the cavity mechanism of the surrounding rock at the bottom of a heavy-haul railway tunnel under rich water conditions was explored in this study. The cavity characteristics and degradation depth of the three types of surrounding rock under different axial loads and hydrodynamic pressures were analyzed through laboratory tests. The structural defects at the bottom of the tunnel and local cracks in the surrounding rock were determined to provide a flow channel for groundwater. The dynamic load of heavy-haul trains causes groundwater to exert high hydrodynamic pressure on the fine cracks. The continuous erosion of the bottom surrounding rock leads to a gradual loss of surrounding rock particles, which would further exacerbate with time. The cohesive soil surrounding rock is noticeably affected by the combined action of heavy-haul load and groundwater in the three types of surrounding rock, and the surrounding rock cavity is characterized by overall hanging. In the simulation experiment, the particle loss of the surrounding rock reached 1,445 g, which is 24.2% higher than that of the pebble soil surrounding rock and 40.8% higher than that of sandy soil surrounding rock. The findings of this study could be helpful for developing methods for defect prediction and treatment of heavy-haul railway tunnels.

scholarly journals Research on Dynamic Response Characteristics for Basement Structure of Heavy Haul Railway Tunnel with Defects

Mathematics ◽  
2021 ◽  
Vol 9 (22) ◽  
pp. 2893
Author(s):  
Jinfei Chai
Keyword(s):  
Constitutive Model ◽  
Dynamic Response ◽  
Principal Stress ◽  
Surrounding Rock ◽  
Railway Tunnel ◽  
Basement Structure ◽  
Measuring Point ◽  
Heavy Haul ◽  
Damage Constitutive Model ◽  
Heavy Haul Railway

Based on the basic principle of thermodynamics, an elastoplastic damage constitutive model of concrete is constructed in this paper. The model is realized and verified in FLAC3D, which provides a solid foundation for the study of dynamic response and fatigue damage to the base structure of a heavy haul railway tunnel. The dynamic response and damage distribution of the base structure of a heavy-duty railway tunnel with defects were numerically simulated by the concrete elastic-plastic damage constitutive model. Then, by analyzing the response characteristics of the tunnel basement structure under different surrounding rock softening degrees, different foundation suspension range and different foundation structure damage degree are determined. The results show the following: (1) The elastoplastic damage constitutive model of concrete can well describe the stress–strain relationship of materials, especially with the simulation results of post peak softening being in good agreement with the test results, and the simulation effect of the unloading–reloading process of the cyclic loading and unloading test also meet the requirements. (2) The initial stress field and dynamic response of the tunnel basement structure under the action of train vibration load are very different from the ideal state of the structure design when the surrounding rock of the base is softened, the base is suspended, or the basement structure is damaged. With the surrounding rock softening, basement hanging, or basement structure damage developing to a certain extent, the basement structure will be damaged. (3) The horizontal dynamic stress amplitude increases with the increase in the softening degree of the basement surrounding rock. The horizontal dynamic stress of the measuring point increases with the increase in the width of the hanging out area when the hanging out area is located directly below the loading line. When the degree of damage to the basement structure is aggravated, the horizontal dynamic tensile stress of each measuring point gradually decreases. (4) The maximum principal stress increment increases with the increase in the fracture degree of the basement structure, while the minimum principal stress increment decreases with the increase in the fracture degree of the basement structure, but the variation range of the large and minimum principal stress increments is small. The research results have important theoretical and practical significance for further analysis of the damage mechanism and control technology of the foundation structure of a heavy haul railway tunnel with defects.

Fatigue damage of a heavy-haul railway tunnel invert under a 33-tonne axle cyclic load

2019 ◽  
Vol 234 (5) ◽  
pp. 498-510
Author(s):  
Mingnian Wang ◽  
Yinting Zhao ◽  
Ziqiang Li ◽  
Dagang Liu ◽  
Li Yu
Keyword(s):  
Fatigue Damage ◽  
Cyclic Load ◽  
Large Scale ◽  
Surrounding Rock ◽  
Monitoring Methods ◽  
In Situ Tests ◽  
Railway Tunnel ◽  
Severe Fatigue ◽  
Heavy Haul ◽  
Heavy Haul Railway

The average cyclic load of heavy-haul railway trains is generally larger than that of a conventional mixed passenger and freight railway. This load leads to more severe fatigue damage to structures, including the concrete in a tunnel invert. This study focuses on the fatigue damage of a tunnel invert under a cyclic load of 33 tonnes. The damage classifications for the tunnel inverts are given based on field investigations. With large-scale in-situ tests on the Zhang-Tang Heavy-Haul Railway Tunnel, the pressure–time distributions for the additional dynamic stresses on the surface of the track-bed for various classes of the surrounding rock are proposed. They were subsequently validated against numerical simulation using the ANSYS Workbench module. Fatigue damage of the tunnel invert is demonstrated using both numerical and monitoring methods. It has been observed that the damage to the tunnel invert becomes severe and extensive if the quality of the surrounding rock degrades. Damage zones develop first at the top of the invert and then expand to a deeper position, depending on the rock grade.

scholarly journals Fatigue Performance of Tunnel Invert in Newly Designed Heavy Haul Railway Tunnel

2019 ◽  
Vol 9 (24) ◽  
pp. 5514 ◽  
Author(s):  
Cong Liu ◽  
Limin Peng ◽  
Mingfeng Lei ◽  
Chenghua Shi ◽  
Ning Liu
Keyword(s):  
Numerical Simulation ◽  
Rock Pressure ◽  
Coupling Effect ◽  
Surrounding Rock ◽  
Fatigue Performance ◽  
Railway Tunnel ◽  
Heavy Haul ◽  
Surrounding Rock Pressure ◽  
Bottom Structures ◽  
Heavy Haul Railway

The Haoji railway in China is the longest heavy haul railway in the world, including 235 tunnels located along the 1837 km railway. With the increasing axle load of the new line and the basal deterioration of the existing heavy haul railway in China, studying the fatigue performance of the newly designed tunnel structure is essential. To study the coupling effect of the surrounding rock pressure and 30 t axle load train, in this study, we combined three-dimensional numerical simulation and three-point bending fatigue tests to investigate the fatigue performance of the basal structures. The results of numerical simulation indicate that the center of the inverted arch secondary lining is the position vulnerable to fatigue in the lower tunnel structures; the surrounding rock pressure performance exerts a stronger influence on the stress state of the vulnerable position than the dynamic train loads. The S–N formula obtained from the experiment showed that the fatigue life of tunnel bottom structures decreases with increasing surrounding rock pressure and dynamic load. In typical grade V surrounding rock and 30 t axle loads, fatigue failure will not occur in the newly designed tunnel bottom structures within 100 years if bedrock defects are lacking and pressure of surrounding rock is not excessive.

scholarly journals Study on Structural Service Performance of Heavy-Haul Railway Tunnel with Voided Base

2018 ◽  
Vol 2018 ◽  
pp. 1-12 ◽  
Author(s):  
Zhiqiang Zhang ◽  
Bowen Zeng ◽  
Chaolong Dai ◽  
Wanping He
Keyword(s):  
Fatigue Life ◽  
Time History ◽  
Vertical Displacement ◽  
Surrounding Rock ◽  
Dynamic Loads ◽  
Vehicle Body ◽  
Monitoring Point ◽  
Heavy Haul ◽  
Heavy Haul Railway

The structural design of heavy-haul railway tunnels still follows the design method of ordinary railway tunnels. Most of them do not take into account the influence of large axle load of 30 t or more, let alone such problems as void of surrounding rock under long-term dynamic loads. In order to analyze the dynamic response of heavy-haul railway tunnels under long-term reciprocating cyclic dynamic loads, considering the factors such as axle load of vehicle body, unsprung mass, and track irregularity, the vibration load time-history curve of heavy-haul railway trains is determined, the three-dimensional dynamics coupling model of dynamic load-tunnel-surrounding rock is established, and the fatigue life of the structure under different void conditions is analyzed based on the S-N curve of concrete. According to the study, the loading, unloading, and vibration caused by train passing will lead to fluctuations in the vertical displacement response of the monitoring point. The peaks and valleys of the response time-history curve correspond to the effect of the train wheels rolling through. When the void is 6 m wide and 10 cm thick, the vertical displacement of the inverted arch is increased by about 9 times, the peak velocity of the inverted arch is increased by about 3.8 times, and the maximum principal stress is increased by about 47.3%, compared with the condition without void. With the same void thickness, the vertical displacement and velocity curves of the inverted arch vary significantly with the increase of the void width. The width of the base void has a significant effect on the fatigue life of the structure of heavy-haul railway tunnels. Based on the operation requirement of 100-year service life, the ultimate void width is 2 m.

scholarly journals Analysis of the Mechanical Characteristics of Different Track Bed Types in Heavy-Haul Railway Tunnels

2021 ◽  
Vol 2021 ◽  
pp. 1-11
Author(s):  
Ziqiang Li ◽  
Weiwei Huang ◽  
Zhifan Xu ◽  
Xiao Tang ◽  
Mingnian Wang ◽  
...  
Keyword(s):  
Measurement Data ◽  
Added Value ◽  
Design Parameters ◽  
Railway Tunnel ◽  
Analysis And Design ◽  
Slab Track ◽  
Long Term Effect ◽  
Heavy Haul ◽  
Heavy Loads ◽  
Heavy Haul Railway

Based on field measurement data from the Fuyingzi Tunnel and Hongshila Tunnel on the Zhangtang Railway, a comparative analysis was conducted on the characteristics of a ballast bed and ballastless slab track, which are commonly used in the track structures of heavy-haul railway tunnels. According to the relevant domestic standards and the theory of the stress diffusion angle, a wheel-rail sharing ratio and theoretical calculation method for the added value of the trainload on the surface and bottom of different track bed types was proposed. In accordance with the measured data, the dynamic load thresholds and distributions on the surface and bottom of different track bed types were analysed and compared with the theoretical results. The results show that the theoretical equation has high accuracy and good applicability. The ballast bed can better cushion the heavy loads, while the ballastless slab track is better able to accomplish train load attenuation. In addition, the distribution on the bottom of the ballastless slab track is “triangular”, while the distribution at the surface or bottom of the ballastless track and ballast bed is “saddle-shaped.” The ballast bed is subjected to a greater load from the vehicle, and the long-term effect is more pronounced. These results can provide a theoretical basis for the stress analysis and design parameters of heavy-haul railway tunnel track beds.

scholarly journals Research on Design Parameters and Fatigue Life of Tunnel Bottom Structure of Single-Track Ballasted Heavy-Haul Railway Tunnel with 40-Ton Axle Load

2020 ◽  
Vol 2020 ◽  
pp. 1-9
Author(s):  
W. B. Ma ◽  
J. F. Chai ◽  
Z. L. Han ◽  
Z. G. Ma ◽  
X. X. Guo ◽  
...  
Keyword(s):  
Fatigue Life ◽  
Concrete Strength ◽  
Side Wall ◽  
Damage Mechanism ◽  
Calculation Model ◽  
Surrounding Rock ◽  
Design Parameters ◽  
Single Track ◽  
Railway Tunnel ◽  
Heavy Haul

The coupling calculation model of tunnel and surrounding rock is established by the finite difference method, and the main design parameters of lining structure of single-track ballasted tunnel under 40-ton axle load, heavy train load, are studied in combination with cumulative damage mechanism of surrounding rock at tunnel bottom and the fatigue life characteristics of concrete structure at tunnel bottom. The results show that (1) inverted arch shall be set in sections of III-grade and above. Whether an invert is set in sections of II-grade and below shall be determined according to lithology and groundwater conditions. When the surrounding rock condition is good and the tunnel bottom structure (without invert structure) is adopted, the thickness is recommended to be more than 20 cm, and the concrete strength grade should not be lower than C35. (2) Connection mode: the inverted arch and side wall of the tunnel should be connected in sequence to reduce the stress concentration and improve the stress state of the connection part between the inverted arch and the side wall. (3) It is suggested that the rise-span ratio of invert of single-track tunnel should be 1/6 ∼ 1/8; the larger value should be taken when the surrounding rock condition is poor and the small value should be taken when the surrounding rock condition is good. (4) The thickness of inverted arch is recommended to be no less than 20 cm under the condition of V-grade surrounding rock, to be no less than 15 cm under IV-grade surrounding rock, and to be no less than 10 cm under the condition of III-grade surrounding rock and II-grade surrounding rock sections requiring inverted arch. (5) The recommended value of bedding thickness meeting the design service life is 20 cm under the condition of II-grade surrounding rock.

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