Abstract
The Minxian tunnel is a key engineering of the Weiyuan-Wudu expressway that is excavated in layered jointed carbonaceous slate rock mass. During the construction process, the surrounding rocks of the tunnel encountered serious large deformations and failure, which brought about great difficulties to the safety and cost of the tunnel. In order to study the deformation and failure mechanism of the surrounding rocks, a physical model test was conducted, and integrated methods including strain gauges, a digital camera, and noncontact full-field digital imaging correlation technique were used to record the response information of the surrounding rocks. The evolution process of surrounding rocks failure was simulated successfully in the model test, and the deformation characteristics were basically consistent with the actual engineering. The modelling results show that concentrated stresses in the surrounding rocks were very uneven due to developed stratified and jointed rock mass structure. The maximum and minimum concentrated stresses appeared at the vault of the tunnel and left of inverted arc area, and concentration factors were 3.11 and 1.98, respectively. The main forms of surrounding rocks deformation and failure were large area spalling of surface, severe circumferential fractures, serious bending deformations of thin rock layers, and collapse of overlying strata. The maximum displacements occurred at left sidewall and right shoulder of the tunnel and the corresponding actual displacements were 460 mm to 500 mm. Caving and failure took place firstly at several key positions with maximum concentrated stresses or displacements and subsequently gave rise to massive collapse of surrounding rocks.
Highlights
With the development of western China, varieties of rock engineering including traffic facilities such as railway, metro, expressway connecting the western region and other developed areas, mining projects, slopes, and hydropower stations have increased rapidly in recent years
Physical modelling test is one of effective research methods to study the deformation process and failure mechanism in rock mechanics and rock engineering [12,13,14,15]. e carefully designed model tests based on the similarity theory firstly can simulate the engineering structure and surrounding rocks and the discontinuous planes such as bedding and fault [16]; secondly they can be able to record the whole process of deformation and failure of geotechnical engineering structures under a specific stress state and can reflect the mechanical characteristics of geotechnical engineering quantitatively or qualitatively [17]; thirdly they are more intuitive and easier to understand the failure mechanism of the underground openings, the variation trend, and stability conditions [18, 19]
Jeon et al [21] performed scaled model tests to investigate the effects of a fault and grouting on the stability of a tunnel. e experimental results showed that the displacements at sidewalls of the tunnel were relatively larger than other positions due to the shear failure along the weak planes. He et al [22,23,24] developed a new modelling method called physically finite elementary slab assemblage (PFESA), and a series of geomechanical model tests were carried out to systematically study deformation characteristics and mechanical responses of surrounding rocks around the underground roadways excavated in the stratified rock masses with dip angles of 0°, 45°, and 90°, respectively. e results showed that shear failure of bedding planes caused by the effect of excavation disturbance was the dominant failure mechanism of surrounding rocks
Summary
With the development of western China, varieties of rock engineering including traffic facilities such as railway, metro, expressway connecting the western region and other developed areas, mining projects, slopes, and hydropower stations have increased rapidly in recent years. E experimental results showed that the displacements at sidewalls of the tunnel were relatively larger than other positions due to the shear failure along the weak planes He et al [22,23,24] developed a new modelling method called physically finite elementary slab assemblage (PFESA), and a series of geomechanical model tests were carried out to systematically study deformation characteristics and mechanical responses of surrounding rocks around the underground roadways excavated in the stratified rock masses with dip angles of 0°, 45°, and 90°, respectively. A geomechanical model test was carried out using the modelling method, PFESA, to study the deformation process, characteristics, and failure mechanism of the Minxian tunnel excavated in layered jointed rock mass with a fault during different construction steps and provide a comprehensive and reasonable basis for the safety supporting of the tunnel. The deformation process and failure mechanism of surrounding rocks were investigated and analyzed
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