The Foziling multi-arch dam, one of the few multi-arch dams in the world, was built on the bedrock with complicated geological conditions. It has undergone several reinforcements since it was put ...into service in the 1950s. In this study, the dam safety is evaluated by analyzing the measured displacements and simulating stresses in the concrete. Firstly, the multiple linear stepwise regression (MLSR) is used to train and test the relationships between the loads and displacement based on the hydrostatic-temperature-time (HTT) model. Subsequently, the contributions of water level, temperature, and time to displacements are determined, and the influence characteristics of water level and temperature on displacements are interpreted. Finally, the dam stress state is evaluated by establishing a dam finite element model and simulating the stress distribution in various operating conditions. The results indicate that (1) the dam is currently in an elastic state after the last reinforcement; (2) temperature contributes the most to the displacement, and the drastic fluctuation of temperature is the disadvantage factor for multi-arch dam safety; (3) the stresses generally can meet the requirements of code; and (4) the ideas and methods of the study can provide references for the safety evaluation of other concrete dams.
In order to study the physical and mechanical properties and internal damage mechanism of rock under freezing–thawing cycle, a total of 180 freezing–thawing cycle tests were carried out on gneiss ...under standard conditions, and conventional physical and mechanical tests and nuclear magnetic resonance tests were carried out after every 20 freezing–thawing cycles. The physical and mechanical test results show that as the number of freeze–thaw cycles increases, the mass, longitudinal wave velocity, uniaxial compressive strength, and elastic modulus of gneiss gradually decrease, and Poisson’s ratio gradually increases. And the porosity increased from 0.287 to 1.402%, an increase of 388.5%, a huge increase. According to the classification method of pore radius (
R
) measured by capillary pressure in the laboratory, gneiss pores are divided into three types: small pores (diameter 0.01 ~ 0.1 μm), medium pores (diameter 0.1 ~ 100 μm), and large pores (diameter 100 ~ 400 μm), combined with NMR test results. It is shown that during the entire freeze–thaw cycle, the proportion of small pores and large pores gradually increases due to the presence of frost heaving force, while the proportion of medium pores decreases, leading to the intensification of internal damage. Finally, on the basis of damage mechanics, the pore expansion coefficient
K
n
is introduced, and the constitutive relationship expression of rock freeze–thaw damage is derived. The research results have certain guiding significance for on-site construction in high-cold regions.
A series of uniaxial compression tests are carried out firstly to confirm the reasonable surrounding rock parameters. Then building up the finite element analysis models of the horseshoe tunnel ...subjected to the seismic loads. The tunnel buried in different geological conditions, like the different plane angles between tunnel and fault fracture zone (e.g. 0°, 30°, 60° and 90°), different width of the fault zone (e.g. 1 m, 0.5
D
, 1.0
D
, 1.5
D
, 2.0
D
) (
D
is the tunnel width). The paper mainly discusses the dynamic stress concentration factors and damage mode on the horseshoe tunnel. Based on the experimental and numerical results, analyzing the distribution of dynamic stress concentration and damage mode on the tunnel, it can be concluded that the tunnel crossing fault fracture zone with the plane angle of 60° and the width of 1.0
D
are more hazardous, whose vertical convergent deformation, equivalent plastic strain (tensile), tensile damage and the slipping displacement of the fault are in the high level, when compared with other geological conditions simulated in the numerical analysis.
Intermediate principal stress is a significant factor when calculate to determine the surrounding rock loose circles. Based on it, this paper is trying to modify the Hoek–Brown strength criterion, ...and put forwards a theoretical formula of the loose circle radius. The theoretical formula is applied to Shimen Tunnel, and a comparative analysis between theoretical calculations and field test results is conducted. Here are the results as follows: 1) With an increase of intermediate principal stress, the strength of the rock mass increases and the surrounding rock becomes more difficult to break. Consequently, loose circle thickness is gradually reduced and forms a significant negative linear relationship with the Lode parameter. 2) The results indicate that with a decrease of surrounding rock level in a three-lane hard rock tunnel, the radius of the loose circle increases continuously. 3) The results of the field acoustic wave test show that the theoretical calculation values are consistent with the field measurement results. According to above analysis, the deduced formula is feasible.
In order to overcome the difficulty in rapid detection for expressway tunnels, the coherence calculation of dual-frequency radar signal in the time domain is proposed to suppress the interference. A ...dual-frequency (400 MHz and 900 MHz) GPR and a manipulator are developed. In the horizontal direction, it has a −90°~90° range, a vertical rotation range from 0 to 90°, a length range from 5~9.5 m, and an antenna rotation between −40°~40°. The mobile scanning has been realized in the expressway tunnel, taking the vehicle as the mobile carrier. The research shows that: This equipment realizes the rapid detection of the tunnel without affecting the expressway’s opening. The imaging algorithm recognizes the structural thickness, reinforcement distribution characteristics, and structural diseases. According to the detection carried out in Zhejiang, China, the spacing between reinforcement in the second lining is 4 cm, and the thickness of the structure is about 0.55 m. However, the reinforcement has deformed badly, and the defects are also discerned in the structure. Compared with the traditional handheld radar detection, the equipment dramatically reduces the labor demand, time, and cost and can meet engineering needs. With the proposed method, the detection time is reduced to 12 min/km from 0.5 d/km, and the cost is reduced by more than two times. Furthermore, during the detection, the traffic can be maintained normally.
Jointed rock masses contain complexly distributed fractures that have significant impacts on the mechanical behavior of the surrounding rock, especially during the tunneling process. In this paper, a ...field test was carried out to record the vertical displacement and deformation of the constructing tunnel passing through jointed rock masses. To further investigate the deformation characteristics of tunnels excavated in jointed rock masses, numerical simulations utilizing discrete element methods (DEM) were conducted. Numerical models simulated different sizes and shapes of blocks in jointed rock masses. The results show that during the process of tunnel excavation, the vertical displacement of surrounding rock undergoes the rapid growth phase and the gradual stabilization phase, and the time interval of these two stages is different due to the different depths of the tunnel. In the same monitoring section, the closer to the vault of the tunnel, the larger the vertical displacement of the monitoring point. The displacement value of the section closer to the tunnel face is larger than that far away from the tunnel face, while the tunnel section in shallower buried depth performs relatively larger liner deformation. For the same size of blocks, jointed rock masses formed by tetrahedral blocks perform relatively larger vertical displacement of surrounding rock, deformation of the tunnel, and positive and negative moments of liner structures than those formed by cubic or polyhedral blocks.
Under the dual effects of the rapid growth of tunnel mileage and operating years, the application and research of tunnel crack identification based on machine vision are increasing with the vigorous ...development of machine vision. However, due to the complex environment in tunnels, it is difficult to quickly obtain tunnel lining cracks via computer visions in the tunnel. Therefore, this paper presents the design of a fast acquisition system with the geometric feature analysis for tunnel lining cracks, which has been integrated into a tunnel fast inspection vehicle with a machine vision module. Through the research on the image acquisition system of the tunnel lining, the parameter selection of the crack shooting hardware system is determined, and the fast calculation method of shooting parameters is proposed. The geometric characteristic analysis of the tunnel lining crack image is employed to calculate crack width and determine the optimal gray value of crack extraction. Field tests have been conducted in the highway tunnels in Zhejiang and Yunnan provinces in China and the result indicates that the proposed approach yields much better performance in the detection efficiency, whose time of detection is only 1%, and the number of personnel required is only 40% of the traditional pure manual method. Compared with similar systems, it also has significant advantages in crack resolution and detection speed. This research provides a means of rapid acquisition of tunnel cracks and laying a foundation for the evaluation of the service performance of the tunnel.
Poyang Lake is the largest wintering habitat for migratory birds in Asia. In the last decade, the lake has experienced an early-occurring and prolonged dry season that has deteriorated the lake’s ...ecological status. To tackle this issue, the Chinese government has proposed the construction of the Poyang Lake Hydraulic Project (PLHP) to regulate water flow to the lake. However, its impact on migratory bird habitats is unknown. In this study, we simulated the habitat suitability for migratory birds in Poyang Lake during wet and dry years, with and without the presence/operation of the hydraulic project. A two-dimensional hydrodynamic model was used to simulate the water conditions for each case. Matter-element theory, 3S technology and ecological knowledge were combined to develop a matter-element-based habitat suitability model in a geographic information system (GIS)-based platform. We assessed and compared the habitat suitability in four scenarios: (1) Wet year without the hydraulic project, (2) wet year with the hydraulic project, (3) dry year without the hydraulic project, and (4) dry year with the hydraulic project. The results showed that the operation of the hydraulic project can effectively alleviate the water shortage issue in the wetland and increase the area of habitats suitable for migratory birds in typical dry years. However, it can reduce the area of suitable habitats in the northern provincial nature reserve of the lake. In addition, a reasonable management of the lake’s fishing activities can also increase habitat suitability and promote balanced patterns between human activities and migratory bird habitats.
Columnar jointed basalts (CJB) are featured by the joint network of discontinuities, which is hard for geotechnical design and construction. Therefore, investigating the mechanical behaviors of CJB ...is significant for the long-term use of the engineering structures. In this paper, field research studies, such as the rigid bearing plate tests and acoustic tests, were employed, to obtain the deformation modulus and the acoustic velocity of columnar jointed basalts, and the formula expressed by deformation modulus and acoustic velocity was then established, which would be a useful guidance for the site operation. Based on the monitoring and testing data of CJB, several numerical simulation models with different joint angles and weak thickness were built to further discuss the mechanical behaviors of CJB. The numerical simulation results show that the joint angle of 30° ∼ 60° presents weak antipressure abilities, for the shearing slipping force and interformational sliding are remarkable in them. Besides, the small material property difference is helpful for the compressive strength of rock masses. After adopting the most unfavorable joint angle and width to model the tunneling process in CJB, it suggests that it is easily damaged along the directions of rock joints in CJB when constructing in tunnels.
•A dam deformation spatiotemporal hybrid model considering chaotic effect in residual series is proposed.•The model has good ability to predict the overall deformation simultaneously.•Effective ...components contained in residual series are extracted by PSO-SVM model.
Single-measuring point deformation monitoring model is the most popular method in dam health monitoring. Considering that single-point monitoring model cannot comprehensively reflect the overall deformation properties of dams, a spatiotemporal hybrid model of multi-point deformation monitoring for concrete arch dams is proposed. Meanwhile, considering the chaotic effect of residual series, the support vector machine optimized by particle swarm optimization algorithm (PSO-SVM) is adopted to analyze and forecast the residual series. Hence, a spatiotemporal hybrid model for concrete arch dam deformation monitoring considering the chaotic effect of residual series is proposed in the study. Based on the theory of single-measuring point deformation monitoring, a spatiotemporal hybrid model is established by introducing space coordinate and calculating hydraulic component with finite element method. Then, with the good nonlinear processing ability of PSO-SVM, the chaotic effect of residual series is analyzed and predicted by PSO-SVM. Subsequently, a spatiotemporal hybrid model for concrete arch dam deformation monitoring considering chaotic effect of residual series is established by superimposing the residual prediction term with the predicted value of the spatiotemporal hybrid model. Engineering example show that the proposed model has better fitting and predicting precisions compared with the conventional single-point monitoring models, and it can analyze and predict the deformations of multi-point simultaneously. In addition, the proposed model reduces the workload of modelling point by point in single-point monitoring model, which considerably improves the practicality and computational efficiency of deformation-based health monitoring of concrete arch dams.
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