Abstract
Tayi tunnel is one of the component tunnels in the Jian‐Ge‐Yuan Highway Project located in Yunnan Province, southeast of China. It mainly passes through talus‐like formations comprised of rock blocks of diverse sizes and weak interlayers with clayey soils with different fractions. Such a special composition leads to the loose and fractured structure of talus‐like formations, which is highly sensitive to the excavation perturbation. Therefore, Tayi tunnel has become the controlled pot of the whole highway project as the construction speed has to be slowed down to reduce the deformation of surrounding talus‐like rock mass. To better understand the tunnel‐induced ground response and the interaction between the surrounding rock mass and tunnel lining, a comprehensive in situ monitoring program was set up. The in situ monitoring contents included the surrounding rock pressure on the primary lining, the primary lining deformation, and the stress of steel arches. Based on the monitoring data, the temporal and the long‐term spatial characteristics of mechanical behavior of surrounding rock mass and lining structure due to the excavation process were analyzed and discussed. It is found that the excavation of lower benches released the surrounding rock pressure around upper benches, resulting in the decrease of the surrounding rock pressure on the primary lining and the stress of steel arches. In addition, the monitoring data revealed that the primary lining sustained bias pressure from the surrounding rock mass, which thereby caused unsymmetrical deformation of the primary lining, in accordance with the monitored displacement data. A dynamically adaptive support system was implemented to strengthen the bearing capacity of the lining system especially in the region of an extremely weak rock mass. After such treatment, the deformation of the primary lining has been well controlled and the construction speed has been considerably enhanced.
Highlights
Southwestern China has a complex terrain and complicated geological conditions with crisscrossed mountains and rivers, inducing complex geotechnical formations such as round gravel and mudstone mixture [1], layered phyllite strata [2], and rock-soil mixtures [3]. e talus-like rock masses, widely distributed in Yunnan Province in western China, are a special kind of geotechnical mixture, which is distinguishingly different from the common rocks, soils, or rock-soil mixture. e talus-like rock masses are mainly distributed in the elurium, colluvium, and diluvial layers of Quaternary System. e main components of the talus-like rock masses are rock blocks with diverse sizes with interlayers filled with weak rock or clayey soils with different fractions, which can be regarded as special weak rock masses
Tayi tunnel was shut down from the noon of September 19th in 2020 to the morning of September 24th in 2020 due to scheduled maintenance of large-scale mechanical equipment. erefore, it is reasonable to regard the duration from September 20th to 23rd as downtime, when the chainage of the excavation face was Z5K64 + 576.6. e monitoring data from September 11th to 28th were selected to show the deformation of the primary lining before, during, and after the downtime
Taking Z5K64 + 600 as an example, Figure 8 illustrates the displacements of five monitoring points. e diurnal displacement of the primary lining during the downtime was smaller than the data before and after the downtime, especially from September 21st to 23rd
Summary
Southwestern China has a complex terrain and complicated geological conditions with crisscrossed mountains and rivers, inducing complex geotechnical formations such as round gravel and mudstone mixture [1], layered phyllite strata [2], and rock-soil mixtures [3]. e talus-like rock masses, widely distributed in Yunnan Province in western China, are a special kind of geotechnical mixture, which is distinguishingly different from the common rocks, soils, or rock-soil mixture. e talus-like rock masses are mainly distributed in the elurium, colluvium, and diluvial layers of Quaternary System. e main components of the talus-like rock masses are rock blocks with diverse sizes with interlayers filled with weak rock or clayey soils with different fractions, which can be regarded as special weak rock masses. Different from the traditional rock-soil mixture, the talus-like formations are a special kind of geotechnical mixture and have very complicated compositions with a wide range of grain diameters. Xu et al [13] obtained the rock proportion and the granular distribution of soil-rock mixture using a combined method with large-scale direct shear test and digital image analysis, which was implemented to investigate the mixture’s shear strength characteristics and failure mechanism. Kalender et al [14] developed a preliminary empirical strength criterion for determining the strength parameters of an unwelded rock-soil mixture by considering the mechanical behavior of the boundaries between matrix and blocks based on in situ and lab tests data. Afterwards, the influence of construction activities on the taluslike ground and the stability characteristics of the tunnel in talus-like rock masses are analyzed based on in situ monitoring. A dynamically adaptive support system is presented based on the mechanical characteristics of taluslike formations
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