Abstract:With the simulated runoff data at the 5.km×5.km grid cells from 1981 to 2020 based on the VIC model and the confluence model, a long-term and grid SRDI (standardized runoff drought index) was constructed. Then, the spatiotemporal evolution characteristics of drought in the Pearl River Basin were analyzed. The results show that: the grid SRDI based on simulated runoff can better simulate the spatiotemporal variation of drought in the Pearl River Basin; the temporal evolution characteristics of drought are obvious, hydrological drought mainly occurs in summer, and a large-scale drought may probably occur in autumn; on the seasonal scale, it is possible that extreme drought occurs all the year around; spatially speaking, the hydrological droughts in the Pearl River Basin present a transitional distribution from the east with high-frequency, to the west with long-duration and high-intensity.

Abstract:Taking the annual and monthly maximum one-hour precipitation intensity and its occurrence time as indexes, the temporal and spatial variation characteristics of the maximum one-hour precipitation in the Three Gorges Reservoir (TGRR) from 1998 to 2020 were explored by using the trend test, period analysis, empirical orthogonal function and comprehensive intensity assessment of precipitation process. The results show that the occurrence time of the maximum one-hour precipitation in the reservoir area moves to the pre-flood period every 10 years, and the maximum one-hour precipitation intensity in the main flood season in July has an 8-year cycle. Compared with that before 2010, the heavy precipitation area in the reservoir area shows a trend of migration from the upstream to the dam site after 2010. The maximum precipitation intensity of one hour is close, but the precipitation process with long duration and wide coverage has higher comprehensive intensity and has more impact on flood control safety.

Abstract:Aiming at the inconsistency between the results of precipitation water resources assessment and annual scale water resources assessment, a new evaluation method of precipitation water resource is proposed in this paper by splitting the runoff components such as antecedent precipitation recession and annual scale base flow, in order to realize the refined evaluation of precipitation water resources. The analysis results in the typical basin of Chaobai River show that the method has good adaptability, significantly improve the pertinence and accuracy of the assessment results of precipitation water resources, and fulfills the needs of water resources assessment with multiple temporal and spatial scale coordination.

Abstract:In order to effectively improve the utilization efficiency of the Yangtze River shoreline resources, this article explores and practices the system of paid use of the Yangtze River shoreline resources in the Jiangsu section based on the concept of sustainable development of the Yangtze River. Through the comprehensive consideration of the natural conditions and socio-economic conditions of shoreline waters and land areas, the pricing method for the paid use of Yangtze River shoreline in the Jiangsu section is proposed with the benchmark price of water depth, the shoreline grade coefficient, the actual utilization grade matching coefficient of shoreline, and the shoreline utilization efficiency coefficient as indicators. Based on this method, the practice application in the Yangzhou section of Yangtze River shoreline shows that most of the original enterprises on the Yangzhou sections have high utilization efficiency of the shoreline, but there are also a few companies occupying excellent shoreline and the utilization efficiency is low. It is recommended to adopt the system of paid use of shoreline to promote the exit or transformation and upgrading of enterprises, and to improve the rational and efficient use of shoreline resources.

Abstract:Throughthe analysis of factors affecting the hydrochemical characteristics of various water bodies in the reservoir area of Taishan Pumped Storage Power Station in Shandong Province from 2009 to 2020, this study discussed the tracing function of hydrochemical characteristics variation in detecting the water leakage. The results showed that the reservoir water and groundwater of Taishan Pumped Storage Power Station are weakly alkaline, the hydrochemical types are mainly HCO3-Ca, and some are HCO3-SO4-Ca, HCO3-SO4-Ca-Mg and SO4-Ca-Mg, while the chemical types of surface water in Bashangou are SO4-Ca and SO4-Ca-Mg. The ion ratio analysis shows that the weathering of silicate rock is the main source of chemical ions in the reservoir water, the groundwater and the surface water of Bashangou. The surface water of Bashangou is controlled by the rock weathering and atmospheric precipitation at the same time, and the atmospheric precipitation without sufficient water-rock reaction is mixed in. The hydrochemical cluster analysis shows that the water samples of the drainage gallery on the right bank and the measuring weir behind the dam come from the leakage supply of the reservoir water, and the water sources of the measuring weir in the gallery at the bottom of the reservoir, the B2 high-pressure branch gallery, the NO.6 and No.1 construction adits are from the regional groundwater. The results of hydrochemical analysis are consistent with the results of hydrogen and oxygen isotope analysis of water body.

Abstract:The effects of ZnO nano particles (ZnO NPs) on the composition and diversity of microbial communities in the periodic and long-term submerged areas of coastal wetlands were studied with coastal wetland simulation systems, and the microbes with significant changes were identified by 16S rRNA amplicon sequencing. The results showed the relative abundances and diversities of microbial communities were varyingly affected under the ZnO NPs exposure. ZnO NPs concentration was an important factor that motivated the changes of relative abundances and β diversities of microbial communities in coastal wetland environment. With the increase of the concentration of ZnO NPs, the increased particle size of NPs after agglomeration weakened the impact on microbial community. β diversity was the lowest when the mass concentration of ZnO NPs was 80 mg/L. The influence on microbial community in the periodic submerged area was smaller than that in the long-term submerged area and submerging conditions lead to significantly different bacteria with different classification levels. Different environmental conditions (e.g. dissolved oxygen and organic matter) in periodic submerging area and long-term submerging area led to different effects of ZnO NPs on microbial abundance and community diversity.

Abstract:To explore the flow structure and head loss at surcharged nodes in the surcharging process, this paper simulated 87 cases with different boundary conditions using three-dimensional structural model based on the experimental pipeline node model. Comparison validation between the indoor experiment and the numerical simulation was completed. Qualitative and quantitative analysis, data correlation fitting and π theory were used to study the effect of diameter ratio (the ratio of node diameter Φ m to pipe diameter Φ p), pipe slope and confined pressure head on the flow structure and local head loss. The results show that the water flow interaction at the node-outlet is the main cause of head loss. The local head loss coefficient K is positively correlated with the diameter ratio, but negatively correlated with surcharging depth and confined pressure head. It is feasible to propose K=f(Re) relation formula by π theory. In addition, the value of K with two diameter ratios has different responses to the pipeline slope change, therefore, the effect of diameter ratio should be considered in the design of pipeline slope. The research results supplement the flow structure in the storm flood model, and can provide empirical values and law reference for the calculation of head loss of one-dimensional pipe network at the nodes.

Abstract:The three-dimensional mathematical model was used in the numerical simulation of the flow pattern in the fishway with trapezoidal cross-section. The results showed that the trapezoidal fishway has obvious three-dimensional characteristics of the water flow. It will weaken the three-dimensional characteristics of the flow within trapezoidal fishway when the water area ratio in the vertical slot increases. When the water area ratio is less than 0.375, the three-dimensional characteristics is more obvious. The aspect ratio of the pool room has little effect on the three-dimensional flow characteristics in the fishway.

Abstract:Large-diameter monopile is taken as the research object to analyze the deformation behavior of pile, soil and rock, and the stiffness of pile foundation under seismic loads. A nonlinear viscoelastic constitutive model of soil and a damage model of rock mass are introduced to describe the stiffness degradation characteristics of soil and rock media around piles in the finite element-infinite element coupled numerical simulation. The numerical simulation results show that the dynamic responses of large-diameter rock-socketed pile, such as displacement and acceleration, the nonlinear hysteresis characteristics of soil and the damage degree of rock are mainly affected by the depth of rock-socketed pile, the degree of rock weathering and seismic intensity, and should be deeply analyzed in the design.

Abstract:To better understand the water absorption (WA) characteristics and changes in mechanical properties caused by water absorption of tuff, carboniferous sandstone and argillaceous sandstone, this paper conducted the X-ray diffraction, Scanning Electron Microscope (SEM) and Mercury Intrusion Porosimetry(MIP) tests to obtain their mineralogical composition, micro-structure feature and pore size distribution features. A soft-rock hydrophilic experiment system was used to study the WA characteristics of rock samples, and the strengths of rock samples before and after absorbing water were tested. The results show that the WA process of three rocks includes the non-linear stage and linear stage, and the functions of the WA characteristic curves are all negative exponential function. The WA value has positive correlation with the clay mineral content and the amount of the effective holes. The reduced strength of the rocks shows negative correlation with WA value and clay mineral content, moreover the little WA value can contribute bigger effect on the mechanical properties of rocks.

Abstract:To alleviate the contradiction between the efficiency and accuracy of the composite material in the fluid-structure interaction (FSI) simulation, an equivalent method of the composite material is proposed based on the constitutive homogenization theory, and the iterative algorithm of FSI is explained. The open-source tool preCICE is used to verify the accuracy and efficiency of this method in terms of FSI analysis under both constant and time-varying fluid boundary conditions. The results show that the error of the equivalent method is within a reasonable range compared with the direct layered simulation, and even if the benefits of reducing the number of solid elements brought by the equivalent method are ignored, the calculation efficiency is still significantly improved; the relative error of simulation results under constant fluid boundary conditions is less than 5%, and the coupling iteration efficiency is increased by 20%; the relative error of the coupling scenario under time-varying fluid boundary is less than 10%, and the coupling iteration efficiency is increased by 40%.

Abstract:In order to further investigate the static and dynamic characteristics of single soilbag filled with different materials, a series of simple shear tests and cyclic shear tests were performed through a large indoor shear apparatus. The test results show that the shear behavior of single soilbag follows the Mohr-Coulomb failure criterion basically, and its shear-resistant properties is mainly provided by the surface tension of the soilbag and the friction between soil particles in the soilbag. Different filling materials have a certain influence on the shear characteristics of single soilbag. By comparing the static and dynamic characteristics of single soilbag filled with river sand, loam and gravel respectively, it can be found that the single soilbag filled with river sand has the best shear performance, vibration and energy reduction effect, and deformation resistance ability. Therefore, it’s a good choice to use river sand as a common building material for loading in practical earthquake isolation engineering, from the perspective of shear resistance, vibration reduction and energy dissipation characteristics of single soilbag.

Abstract:Aiming at the common problems of poor durability and dry shrinkage performance of traditional inorganic-binder solidified soil, super absorbent polymer (SAP) material was added on the basis of mucky clay reinforced by the inorganic binder. Through the unconfined compressive strength test, compaction test, dry wet cycle test, dry shrinkage deformation test and XRD test, the influence and action mechanism of SAP material on the engineering properties of inorganic-binder solidified soil were analyzed and discussed. The test results show that the addition of SAP material can not only improve the unconfined compressive strength of inorganic-binder solidified soil, but also significantly improve the compactness, durability and dry shrinkage performance. Mechanism analysis shows that SAP material mainly depends on the filling effect to improve the engineering properties of inorganic-binder solidified soil.

Abstract:In order to ensure the engineering properties of sandy pebble soil during EPB shield tunneling through the sandy pebble stratum, foam agents of different stability were added to the sandy pebble stratum with 20%, 40% and 60% pebble content under the background of Mingjiu section No.2 air shaft to Jiujiangbei section of Chengdu rail line 17. Indoor slump test, seepage test and spewing test were carried out to study the changing laws of fluidity, permeability and time-dependent nature, which reflects the adaptability between the stability of foam agent sand and sandy pebble soil. The results show that: 1)The foam agent with good stability can adapt to sandy pebble soil with less than 60% pebble content, that is, foam stability is beneficial to enlarge the application scope of sand cobble soil; 2)The foam with good stability can keep the good fluidity and impermeability in the whole process of excavating and discharging the conditioned sandy pebble soil; 3)Excessive foam mixed into the improved sandy pebble soil is easy to disintegrate, which means that the improved soil is difficult to achieve good workability; 4)The gusher pressure of improved sandy pebble soil is an important index to test the improvement effect.

Abstract:Based on the Reynolds averaged N-S equation closed by the Spalart-Allmaras turbulence model(S-A model), the third-order Runge-Kutta method along the uniform streamline and Galerkin method are used for the temporal and spatial discretization respectively, and the finite element discretization scheme of the turbulence equation is obtained. Based on the self-compiled MATLAB program, the flow past an iced conductor under different wind attack angles is numerically simulated. The transient and time averaged flow fields, the time history curves of aerodynamic coefficient and the average aerodynamic coefficients variation with wind attack angle are obtained. The comparison with the experimental results shows the effectiveness of the proposed finite element algorithm. Based on the analysis of flow field evolution and average pressure distribution, it can be found that the transfer of boundary layer separation point caused by the change of wind attack angle is the main reason for the sharp jump of lift coefficient.

Abstract:Aiming at the problem that the effective texture features in the space-time image become blurred in complex noisy scenes such as flare, turbulence and rainfall, which limits the accuracy of the existing main direction detection algorithms of texture, a space-time image velocimetry method based on residual network regression model is proposed by combining the idea of deep learning, and the powerful nonlinear learning ability of the model is used to construct a regression prediction function. The residual network regression model is tested by constructing synthetic datasets and natural river datasets containing space-time images of complex scenes. The experimental results show that the detection accuracy of the proposed model under the synthetic datasets can reach 0.1°. For the natural river datasets, the detection accuracy of the ResNet regression model with residual structure is better than that of VGG16; in terms of the number of model layers, ResNet50-STIV can better balance the detection accuracy and execution efficiency. The detection accuracy in normal scenarios can reach 0.7°, while in flare, turbulence, and rainfall scenarios, it can be controlled within 1.3°, and ResNet50-STIV is better than the existing STIV method. Meanwhile, the maximum relative error is less than that of the instrument method in the surface velocity ratio measurement of multiple scenarios by 12%.

Abstract:Aiming at the durability problem of waterproof gasket for segment joints of shield tunnel, the hydrothermal accelerated aging test of rubber gasket was carried out. The tensile mechanical performance test of the aging sample, the scanning electron microscope test of the contact surface and the long-term waterproof performance test were carried out. Thereafter, the waterproof failure mechanism of the rubber gasket surface was analyzed at the microscopic scale. The ultimate waterproof pressure of the gasket was used as the durability evaluation index. Combined with the ” P-T-t “ ternary model based on the Arrhenius equation, the reduction formula of the aging waterproof performance of the gasket was deduced. The results showed that: the deterioration of the contact condition of the sealing pad surface and the hardening of the rubber material accelerate the formation of the leakage channel between the contact surface of the sealing pad; the waterproof performance of the gasket decreases with the increase of aging time, but the decline rate decreases gradually; taking the rubber gasket used in the shield tunnel of Rongjiang-Guanbu Diversion Project in Guangdong as an example, the durability prediction results using the proposed prediction formula of waterproof performance are 12.36% smaller than those only considering the mechanical properties of rubber materials, and the aging coefficient is 0.390 after 100 years of service, which provides reasonable explanation and more accurate life prediction for the frequent leakage phenomenon in the service life of original design .

Abstract:This paper sorted out the current situation of the variation of shield tunnel distance and introduced four typical long-distance shield-tunneling engineering examples. Combined with the typical engineering, five problems in the long-distance excavation, such as the cutter wear, shield tail sealing failure, pipeline wear, opening chamber in complex stratum and underground junction of shield, were systematically analyzed. The principle, technical process, application scope, advantages and disadvantages of main technologies in the long-distance excavation were summarized. The development of intelligent and rapid construction technology has also been prospected. It can provide some references for the formation of a systematic and standardized long-distance shield construction technology in the future.

Abstract:In order to realize the effective judgment of surrounding rock classification under the condition of imbalanced surrounding rock classification and improve the simulation accuracy of tunnel construction, a study on the tunnel construction simulation is carried out based on the advanced classification of imbalanced surrounding rock with improved eXtreme Gradient Boosting (XGBoost). The Automatic Neighborhood size Determination-SMOTE (AND-SMOTE) method is used to optimize the class imbalance of surrounding rock, and the improved XGBoost model is used for advanced classification of surrounding rock, and then the simulation parameters are optimized, which improved the accuracy of tunnel construction simulation. In order to improve the accuracy of surrounding rock classification, the Harris Hawks Optimization (HHO) algorithm is used to automatically optimize the hyperparameters of XGBoost ensemble classifier. The engineering application shows that the improved XGBoost model has higher classification accuracy than the unimproved XGBoost, KNN, SVC and other 6 models. The classification accuracy of the improved XGBoost model is improved by 8.6% after considering the class imbalance of surrounding rock. In addition, the relative deviation between the results of tunnel construction simulation based on the advanced classification of surrounding rock and the actual progress is reduced by 11.3% compared with the traditional simulation, which is more in line with the engineering reality.

Abstract:Based on the Mohr-Coulomb strength criterion and uncorrelated flow rule, Abaqus is used to simulate the passive failure of the excavation surface of underwater shield tunnel in sandy soil layer, and influences of the buried depth ratio C/D, height of overlying water level H and friction angle φ in sandy soil on the surface displacement are analyzed. The failure mode of the soil in front of the excavation face is also discussed. The results show that the support pressure of standard excavation face is related to C/D, sand φ , and there is a positive correlation between them; the surface displacement is greatly affected by the change of C/D, and when C/D increases from 0.8 to 1.5, the maximum longitudinal and transverse displacement decrease by 80% and 86% respectively; hydrostatic pressure will only limit the development of lateral surface displacement and has little effect on longitudinal surface displacement; when C/D is small, the passive failure mode presents an inverted pyramid shape extending to the surface, which belongs to overall failure; when C/D increases to 4.3, the soil arch cannot reach the ground surface, which belongs to local damage.