Better understanding the failure modes of tunnels excavated in the boulder-cobble mixed strata by distinct element method

Self Cite

Techniques including pre-grouting, long pipe roof, and parameter optimization were employed to ensure the safety of loess metro tunnelling under an existing glass building. Their effects were proved through monitoring the settlement of building and surface during tunnelling. Besides, division of settlement monitoring according to processes, a new method, was conducted to control settlement in time. The highest surface settlement after construction was 16 mm only, meeting the requirement. The result indicates that it is practicable to control the tunnelling settlement strictly in extremely difficult geological areas. The settlement regularities were also studied through numerical simulation; their deformation is larger compared with in situ results while their change trends coincide during most processes. Soil excavations cause settlement primarily, accounting for more than 60%. It is suggested that dual slurry pre-grouting and process-based measurement should be employed before each excavation in water-rich loess areas.

Section: Distribution Of Surface Settlementmentioning

confidence: 92%

Tunnelling‐Induced Settlement and Treatment Techniques for a Loess Metro in Xi’an

Lai

et al. 2020

Self Cite

“…Keeping in mind that the transportation infrastructure of China has been rapidly developed during the past 20 years, the construction processes of railways, highways, and subways are no longer similar to what they were before: only consider its own construction conditions and not close to other projects [1][2][3][4][5][6]. In particular, in urban underground space engineering practices, new tunnels would inevitably underpass the existing buildings and important traffic lines.…”

Section: Introductionmentioning

confidence: 99%

“…During the construction of the underpass of a new tunnel, the excavation unloading effect disturbs surrounding rock masses and promotes surrounding rock deformation [4,5,8], inevitably changing stress and displacement in the existing tunnel. Such engineering problems has continuously attracted the attention of a great number of engineers and researchers around the world [20,21].…”

Section: Introductionmentioning

confidence: 99%

Stability Analysis of TBM Tunnel Undercrossing Existing High‐Speed Railway Tunnel: A Case Study from Yangtaishan Tunnel of Shenzhen Metro Line 6

Zhao

Cheng

Song

et al. 2021

During the construction of the underpass of a new tunnel, the excavation unloading effect disturbs surrounding rock masses and promotes surrounding rock deformation, inevitably changing stress and displacement in the existing tunnel. Taking Yangtaishan tunnel excavation of Shenzhen Metro Line 6 as an engineering example, effects of excavation programs of left and right lines on the deformation characteristics of newly excavated and existing tunnels were evaluated based on Midas numerical model and priority excavation advantages of the left line were determined. The settlement and horizontal deformation characteristics of the existing tunnel were analyzed using the construction monitoring method. Results showed that maximum settlement and horizontal deformation of the existing tunnel were 1.35 and 0.23 mm, respectively. Settlement of invert and inverted top along axis direction was from growth to decline, and then a V-shaped settlement trough was formed with maximum settlement values of 1.36 and 0.97 mm, respectively. Maximum settlement and uplift of the newly built tunnel appeared on the upper and bottom parts of invert, respectively. In the newly built tunnel segments, the top settlement was dominated and deformation was mainly distributed in both side areas. At the top of the existing tunnel segment, convergence settlement was 3.09 mm and settlement rate was slow first which was accelerated, then stabilized, and finally slowed down again which was opposite to the uplift development trend of the bottom of tunnel segment. The top of the existing tunnel segment showed four settlement stages, slow, rapid, stable, and slow settlement stages. Compared with the right line, preferential excavation of the left line had obvious advantages in terms of tunnel stability. The unloading effect of TBM excavation created vault settlement in the existing tunnels where actual settlement values were 1.12 and 1.13 times, which theoretically calculated settlement. The horizontal deformation of the existing tunnel was varied first linearly and then nonlinearly with maximum deformation in the convergence stage of 1.47 mm.

“…Considering the temperature variations according to coordinates, Qin et al [24,25] and Prashantk [26,27] employed the superposition principle and the variable separation approach to obtain analytical solutions for a transient temperature field in a multilayer cylinder under the convective boundary condition. Based on the extensive testing of inner and outer tunnel temperature fields, Chen and Zan [28,29] determined the temperature change regularity and the change characteristics of the maximum frozen soil depth.…”

Section: Introductionmentioning

confidence: 99%

Experimental Investigation of Ground and Air Temperature Fields of a Cold‐Region Road Tunnel in NW China

Zhong

et al. 2020

Self Cite

To fully understand the temperature distribution of cold regions and the variation law of temperature fields in cold-region tunnels, this paper presents a case-history study on a tunnel located on the eastern Qinghai-Tibet Plateau, China. The conclusion is as follows: the temperature outside the tunnel and the ambient temperature are affected by wind speed and light. The law of the temperature field in the tunnel is greatly affected by wind speed and wind direction. According to the field test, the wind speed in the tunnel is about 2.8 m/s in winter, and the daily average temperature at the exit of the tunnel is basically lower than that at the entrance. From the central to the entrance, the temperature in the tunnel decreases by 0.11°C every 10 meters along the longitudinal direction; from the central to the exit, the temperature in the tunnel increases by 0.07°C every 10 meters. In this regard, for the problems of lining frost damage and central drainage pipe freezing, it is suggested to adopt the way of heating and drainage, but heating the freezing area outside the drainage pipe should be avoided. The test results can provide references for the design, construction, and research of the temperature field of the tunnel antifreezing system in the cold region. It is hoped that the test results can be useful in the design and construction of frost damage prevention systems and the investigation of temperature fields in cold-region tunnels.