Current Issue : July-September Volume : 2022 Issue Number : 3 Articles : 5 Articles
The safe thickness of concrete retaining walls for curtain grouting on tunnel faces is an essential factor related to tunnel safety and grouting effects. In this research, the concrete retaining wall was simplified into a standard rectangular slab structure. The Rankine active earth pressure theory and the plastic hinge theory were used to analyze the lateral force of the concrete retaining wall. By deriving the safety‐thickness equation of the concrete retaining wall, a quantitative criterion that can display the mechanism of the concrete retaining wall was obtained. The traditional empirical formula and Kalmykov formula had a particular connection with the method in this paper in determining the safe thickness of the concrete retaining wall. This was negatively related to the compressive (tensile) strength of the concrete and the groundwater level and positively associated with the buried depth of the tunnel. The conversion relationship between the traditional empirical formula and the theoretical formula was established, and the exact solution formula for the value of safety coefficient K0 was given. Finally, the rationality of the theoretical formula was verified by a field test, in novel work that provides a reference for similar projects....
In this study, ultrasonic pulse velocity (UPV) and ultrasonic shear-wave tomography are combined to measure the residual compressive strength (RCS) of small-scale lining concrete blocks and to detect inner defects in the lining structure. The characteristics of and variations in the RCS of test blocks after being exposed to elevated temperatures (200–800 ◦C) and constant heating times (2 h, 3 h, and 4 h) were studied. At 800 ◦C, the RCS values reduced by 64.4%, 69.2%, and 74.6% at heating times of 2 h, 3 h, and 4 h. Scanning electron microscopy (SEM) was used for the micro-phase analysis of the samples that had been exposed to high temperatures. The heating time and RCS as well as the SEM micro-structure relationship were compared. Finally, a tunnel lining slab sample was designed to simulate the post-fire damage inside the blocks. Additionally, shear-wave tomography with 32 probes was able to detect the φ10 mm void defects at a depth of 200 mm....
In this paper, we survey sandstone tunnels using sensor testing technology and conduct an in-depth analysis and research on the model of sandstone tunnel cracking based on the theory of fracture mechanics. This paper systematically investigates the static mechanical properties, energy evolution and distribution law, acoustic emission monitoring, and digital image correlation methods of intact and jointed rock chamber enclosures (including parallel jointed rock chamber enclosures and cross jointed rock chamber enclosures) under static loads, based on physical simulation test methods and combined with other technical means such as acoustic emission monitoring and digital image correlation methods. In this paper, the effects of parallel and cross-joint angles on the static mechanical properties, energy evolution and distribution, acoustic emission variability, progressive destabilization, and their mechanisms are compared and analyzed. This paper takes fiber Bragg grating (FBG) sensing theory and technology research as a breakthrough, relies on major underground engineering geohazard model tests, and proposes a grating spectral reconstruction theory based on the wavelength position constraint of the spectral center and its improvement based on an in-depth analysis of the influence of fiber grating intrinsic parameters and strain distribution on the reflection spectral properties. Based on an in-depth analysis of the influence of spectral center wavelength location and strain distribution on the reflectance spectral properties, we propose the grating spectral reconstruction theory based on the spectral center wavelength location constraint and its improved genetic algorithm optimization method; realize the fast and accurate identification and rejection of the melancholy effect of fiber grating; propose the sensor numerical simulation optimization design method; develop the high sensitivity seepage pressure sensor, new strain sensor, target flow sensor, microdisplacement sensor, and multipoint displacement sensor; and build a large capacity, multi-parameter fiber grating real-time monitoring network....
The existence of loose landslides not only poses a huge safety hazard to the construction of tunnel entrances, but also significantly increases the difficulty of site construction. In this paper, we investigate the comprehensive slope reinforcement management technology for tunnel entrances in thick landslide strata, using the finite element analysis software ABAQUS to study the slope safety coefficients, displacements and plastic zone changes under different management conditions, propose a design structure for slope stability enhancement in thick landslide strata, and analyse the effect of the application of slope stability enhancement measures for thick landslide strata. The results show that the enhanced design structure is used to enhance slope stability. The results show that after the landslide treatment with the enhanced design structure, the slope safety factor was increased from 0.961 to 1.512, the maximum horizontal tangential displacement was reduced from 330.2 mm to 32.74 mm, and the area of plastic zone was significantly reduced, and the landslide support effect was remarkable....
The skid resistance of asphalt pavement is of great importance to the driving safety, but deterioration of pavement skid resistance is inevitable owing to the coupling effect of traffic loading and climate conditions. The existing prediction models of skid resistance were mainly established based on the laboratory accelerated polishing tests (for instance Polished Stone Value, PSV), and these models can only consider the influence of a single factor; they fail to reflect the coupling effect of different factors under the real service condition. For the purpose of investigating the influences of seasonal variation, and aggregate type on the skid resistance of asphalt pavement, the skid resistance of three test tracks were continuously measured for 48 months through five different test methods. The results show that different test methods exhibit significant inconsistency. The aggregate type is the internal factor that determines the long-term skid resistance performance of pavement. The skid resistances of the selected test tracks were ranked as greywacke pavement > diabase pavement > rhyolite pavement. This is in well agreement with the ranking of aggregate polishing resistance obtained from the laboratory Wehner/Schulze (W/S) test. This indicates that the W/S test is effective in distinguishing the aggregates that used in pavement construction. It is also found that the skid resistance of asphalt pavement shows significant fluctuation with respect to seasonal variation. The skid resistance is generally high in autumn and low in summer. Therefore, it is suggested to use the low measurement value of skid resistance in summer as the lower limit for the evaluation and prediction of the skid resistance performance of asphalt pavement....
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