Distress mechanism and treatment measures in construction of large cross-section tunnel passing through Q2 soft-plastic loess layer

Hong, Qiuyang; Lai, Hongpeng; Liu, Yuyang; Chen, Rui

doi:10.1007/s10064-023-03197-1

Cited by 4 publications

(2 citation statements)

References 41 publications

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“…With the rapid development of tunnel engineering in China, it is inevitable to encounter complex and unfavorable geological strata during the construction process [1][2][3][4][5]. Among them, the loess strata, due to their obvious structure, high permeability, collapsibility, and vertical joint development [6][7][8][9][10], will face construction risks such as water leakage, large deformation, falling blocks, and collapse when constructing tunnels in this stratum [11][12][13][14]; especially, the collapsibility of loess often causes the sudden instability of the surrounding rock in a short period, leading to disasters [15][16][17]. In addition, the disaster characteristics of loess may also lead to the cracking of the lining structure, thereby affecting the safe operation of tunnel engineering in the later stage [18][19][20][21].…”

Section: Introductionmentioning

confidence: 99%

“…Hong [33] proposed a scheme for reinforcing soft loess through the use of a pipe roof, advanced small pipes, and grouting. Hong [11] proposed the use of segmented large pipe sheds with grouting to reinforce collapsed areas. The above reinforcement schemes are all directly applied in loess tunnels and have not taken into account the influence of water content thresholds; after the implementation of the disposal plan, not only did it not reflect the optimal effect of the reinforcement plan, but it also lacked environmental and economic benefits.…”

Section: Introductionmentioning

confidence: 99%

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Stability Assessment of Tunnels Excavated in Loess with the Presence of Groundwater—A Case Study

Deng,

Zhang,

et al. 2024

Water

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The high water content of the surrounding rock in loess tunnels will lead to the deterioration of rock strength, causing deformation and damage to the initial support structure and thereby affecting safety during construction and operation. This article first analyzes the strength characteristics of loess under different water contents through indoor physical and mechanical tests. Secondly, based on numerical simulation results, the ecological environment, and design requirements, the water content threshold is determined. Finally, a reinforcement scheme combining surface precipitation measures and curtain grouting measures is proposed, and the reinforcement effect is analyzed based on on-site monitoring data. The results show that as the water content of loess increases, the cohesion, internal friction angle, and elastic modulus of the surrounding rock all decrease, leading to an increase in the sensitivity of the surrounding rock to excavation disturbances and a deterioration in strength. During the construction process, it shows an increase in the vault settlement and sidewalls’ convergence. During the process of increasing the distance between the monitoring section and the palm face, the settlement and convergence of the tunnel show a rapid growth stage, slow growth stage, and stable stage. The water content threshold is determined to be 22%. The reinforcement scheme of combining surface precipitation measures with curtain grouting measures not only meets the requirements of the ecological environment but also makes the settlement and convergence values lower than the yellow warning deformation values required by the design.

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Stability Assessment of Tunnels Excavated in Loess with the Presence of Groundwater—A Case Study

Deng,

Zhang,

et al. 2024

Water

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Prediction model of loess immersion settlement based on improved K-G model

Zhang,

Hu,

et al. 2024

Bull Eng Geol Environ

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Loess is a problematic type of soil with a worldwide distribution due to its collapsibility. The temporal discontinuity and spatial nonuniformity of its collapsibility can bring severe damage to building foundations, roads and water pipelines. In this study, the relationship between the saturation and K-G model parameters is established based on indoor compression tests and collapsible tests; the deformation characteristics of loess immersed in water are studied via a large-scale trial immersion pit test. The test site is a circular pit with a diameter of 10 m. The loess is immersed for 46 days; the variation in its accumulated settlement over time is recorded for 60 days, and its deformation process is simulated using a self-designed programme. Results show that for the stress–strain relationship of unsaturated loess, the relationship between equivalent suction and saturation can be obtained through the principle of deformation equivalence and fitted using the exponential function. The maximum vertical displacements calculated in the simulation and on-site immersion pit experiment are 0.036 m and 0.032 m, respectively. Such relatively good consistency indicates that the proposed method can reasonably predict the collapse behaviour of loess due to immersion. This research provides a reliable method for the numerical simulation of loess immersion deformation, and the parameters in the model only need to be determined by conventional experiments.

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Mechanical and permeability characteristics of Q2 soft-plastic loess under coupled hydro-mechanical conditions

Hong,

Lai,

Liu

2024

Environ Earth Sci

Self Cite

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For the soft-plastic loess tunnel engineering, collapse and damage of the surrounding rock during excavation are often driven by the combined action of the seepage water and the unloading effect. Under water pressure and unloading, the soil suffers complex stress-seepage coupling action causing the inevitable change of permeability and mechanical properties. In this paper, seepage control devices were added to the GDS test device, and a new triaxial permeability measurement system was developed. Triaxial unloading-seepage tests were conducted on soft-plastic loess under the effect of hydraulic coupling. The variation of permeability characteristics of Q 2 soft-plastic loess under lateral unloading and the soil mechanical characteristics under different seepage pressure were analyzed. Meanwhile, microstructure characteristics of soft-plastic loess during the triaxial test were obtained by scanning electron microscope to clarify the deformation and seepage mechanism. The results show that the strength of soft-plastic loess decreases signi cantly with the increase of osmotic pressure. Under the condition of 50 kPa and 100 kPa osmotic pressure, the cohesive force of soft-plastic loess decreases by 15.5% and 39.0% and the friction angle decreases by 9.4% and 22.6%, respectively. The permeability coe cient of loess increases slowly at rst and then increases rapidly during the unloading process. The main reason for the signi cant increase of permeability coe cient is the penetration of soil ssures and the formation of shear bands after entering the plastic deformation stage.

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Distress mechanism and treatment measures in construction of large cross-section tunnel passing through Q2 soft-plastic loess layer

Cited by 4 publications

References 41 publications

Stability Assessment of Tunnels Excavated in Loess with the Presence of Groundwater—A Case Study

Stability Assessment of Tunnels Excavated in Loess with the Presence of Groundwater—A Case Study

Prediction model of loess immersion settlement based on improved K-G model

Mechanical and permeability characteristics of Q2 soft-plastic loess under coupled hydro-mechanical conditions

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