Taking the medium-fine sand layer along Minjiang River as prototype, small-scale shaking table tests based on 3 factors and 3 levels orthogonal design were conducted to discuss the liquefaction characteristic qualitatively. Meanwhile, the dynamic numerical simulations for the typical excitation time-history were carried out upon the FLAC3D numerical platform by using Finn liquefaction constitutive model. The simulation results showed that the Finn constitutive model could well reflect the increase of pore pressure, the decrease of effective stress and the liquefaction characteristic of saturated sand under seismic excitation. On the other hand, the key parameters C1 and C2 in the Finn liquefaction constitutive model might influence the simulation results significantly. A large number of numerical simulations with different key parameters were carried out sequentially. The peak value and the stable value in the time-history of excess pore pressure ratio were focused and compared with experimental results. Therefore, the key parameters C1 and C2 for the Finn liquefaction constitutive model of Minjiang saturated sand were calibrated and suggested as 1.30 and 0.31, respectively. Meanwhile, the saturated sand also tended to dilate slightly during excitation time-history, which appeared synchronously with liquefaction.
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Open Access
Issue
The phenomenon of segment dislocation is prevalent in shield tunnel lining, thereby affecting the structural safety and service performance of tunnels in severe scenarios. Manual measurement of segment dislocation is subjective and time-consuming, while automated methods, such as 3D laser scanners, are not only expensive but also susceptible to environmental conditions. In recent years, advancements in camera technology and deep learning algorithms have significantly propelled the development of computer vision applications in civil engineering monitoring and inspection. Binocular vision technology has been utilized in crack detection and engineering quality evaluation due to its cost-effectiveness and reliable accuracy. This study introduces binocular vision technology to enable accurate measurement of segment dislocation.
The internal and external parameters of consumer-grade binocular cameras are initially obtained through a calibration experiment, followed by capturing binocular images of the segment joints. The accurate disparity information between the left and right images is further calculated using a deep-learning stereomatching algorithm. Finally, a camera attitude correction method is proposed to calculate the segment dislocation accurately. The primary challenge in camera attitude correction is determining key points on the segment surface without evident texture features. Therefore, a series of image processing techniques, such as graying, binarization, dilation, erosion, and target localization, are initially employed on the left photo to automatically identify the location of the segment joint. Then, the parallel thinning algorithm is applied to extract the skeleton of the segment joint (reduce the segment joint width from multi-pixel to single-pixel). The pixel coordinate data along the skeleton are extracted, and the least squares method is used to fit a straight line to the skeleton. Furthermore, the straight lines are shifted and flipped to form latitude and longitude lines, allowing the pixel and camera coordinates of the crossing point (key point) to be calculated in accordance with the triangulation principle. Finally, the segment coordinate system is established using these key points, and the actual segment dislocation is computed.
Field tests on the construction site of the shield tunnel were carried out to evaluate the efficiency of the proposed approach. Results were drawn as follows: (1) The calculation results from the vertical shooting of the binocular camera, after camera attitude correction, showed better consistency than the segment dislocation measurement via weld seam gauging. The specific performance demonstrated that the absolute error did not exceed 1.0 mm, and the overall processing time for the segmented image was approximately 10.00 s. (2) In multiple rounds of tests with left-leaning or right-leaning shooting scenarios, when the attitude angles of camera coordinate system relative to the segment coordinate system around its own Xc axis and Yc axis were in the ranges of(180.00±15.00)° and ±20.00°, respectively, the proposed method effectively corrected the calculation results with strong robustness.
By combining deep learning algorithms with traditional image processing techniques, binocular vision technology is used to achieve rapid and accurate measurement of segment dislocation. This approach provides a reference for tunnel engineering inspection.
Open Access
Issue
With the rapid development of traffic infrastructure construction in western mountain area, the lining-stratum interaction mechanism of mountain tunnel under seismic effects has attracted increasing attentions. Based on the prototype of a regular two-lane highway tunnel section with Ⅴ-grade surrounding rock, a static pushover model test for mountain tunnel was conducted. The variations of stratum displacement, stratum strain and ground pressure with pushover distance were carefully studied, and the lining-stratum interaction mechanism was thoroughly discussed. The test results show that: the lining-stratum interaction can be generally divided into compacting stage, overturning stage, and dragging stage. The stratum tends to circumferentially flow along the lining perimeter from the springing line in the overturning stage, and then drives the lining to shift together in the dragging stage. The stratum near the springing line experiences predominantly radial compression, forming a compression deformation zone, while the stratum near the lining shoulder mainly undergoes circumferential compression, forming a slip deformation zone. The response of the ground pressure on the left and right sides are exactly opposite. Specifically, the ground pressure in the compression deformation zone on the right side is greater than its counterpart on the left side, while the ground pressure in the slip deformation zone on the right side is less than its counterpart on the left side. These researches can provide some experimental basis and technical support for the anti-seismic calculation of mountain tunnels based on response displacement method.
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