Abstract:To effectively monitor the formation and development of cracks, a quantitative sensing method of static cracks using piezoelectric smart aggregates was proposed. The piezoelectric smart aggregate transducers were designed and the sensitivity of the sensing signals was tested and analyzed. The sensor shape, packaging material, input voltage and excitation frequency of smart aggregate were optimized. Quantitative sensing tests of crack location and depth were carried out, a relative energy index based on wavelet packet analysis was constructed, and the regular relationship among the energy indices and fracture location, depth was proved. Finally, a random aggregate FEM model was constructed to perform numerical simulation on the effect of cracks on the sensing signal. The results show that the numerical simulation results and the test results are well fitted, indicating that the use of piezoelectric intelligent aggregate can well monitor the crack damage of concrete structures. This method provides a new way for continuous, remote, and real-time monitoring of fracture occurrence and development.

Abstract:Current dam surface inspections in actual engineering applications mainly rely on manual on-site inspections or scaffolding observations to obtain the safety status of the dam surface structure. These methods have problems such as high safety risks, high costs, and low efficiency. In addition, false detection, missed detection, and subjective issues due to human eyes identification exist. The tethered UAV equipped with high-definition cameras is used to collect dam face images, which can reduce safety risks and improve efficiency. Convolutional neural networks are applied to achieve dam face image defect recognition and the accuracy of dam surface defect recognition is improved.The ResNet-152 is used as the backbone network to build a network model to extract the characteristics of cracks and defects, based on which a new decoding network layer to achieve crack pixel segmentation detection is designed. The testing results show that the crack defectsdetection precision P, recall rate R, comprehensive index F and average intersection ratio M of crack defects reach 74.61%, 78.71%, 74.99% and 73.34%, respectively. Comparative experiments were carried out with a variety of pixel-level segmentation methods, indicating that the proposed detection model can effectively identify crack defects on dam surface and provide auxiliary data support for the safety assessment of dam surface structure.

Abstract:The number of safety monitoring points of large-scale concrete dams is large and widely arranged. The analysis of the massive monitoring data makes it difficult to assess the safety state of dams timely and accurately, so the cloud model theory is introduced to analyze the difference and correlation of deformation monitoring data characterizing concrete dams. The monitoring data of each monitoring point of the dam is regarded as a cloud, and the monitoring values are regarded as cloud drops. The cloud parameters are then calculated to obtain the cloud numerical characteristics of the monitoring value sequence. Case analysis shows that the abnormal monitoring points in similar dam sections can be quickly discovered by the cloud similarity, and the clustering analysis of cloud similarity coefficients can be used to group the monitoring points. The grouping management of monitoring points can effectively improve the analysis efficiency of the monitoring data while realizing the correlation analysis of dam deformation properties.

Abstract:In order to better analyze the fluctuation characteristics for the measured data of dam deformation, and then to evaluate the overall deformation behavior, the measured data of a concrete gravity dam was taken as an example.The multifractal theory was applied to the analysis of dam deformation behavior, and the multifractal characteristics and asymmetry of deformation behavior were analyzed by using MF-DFA, MV-MFDFA and A-MFDFA. The result shows that the measured data has obvious multifractal characteristics for both multiple measuring points or a single point, and the multifractal feature has obvious asymmetric characteristics. The measured data shows good memory and long-range correlation characteristics from multiple measuring points to single point, from overall fluctuation to local trend. Under the influence of large fluctuation factors such as water level, the horizontal displacement of the dam crest develops well and the overall state of the dam is stable.

Abstract:Based on the discussion of the balance between supply and demand of water resources in Beijing in recent 12 years, water allocation and simulation (WAS) model was used to conduct a dynamic simulation study of water resources in Beijing from 1980 to 2018. The transformation model of regional natural-social water cycle was analyzed, and the transformation mechanism of social water cycle and natural water cycle was discussed. The results show that from 2007 to 2018, the average annual water demand of both real and imaginary parts of Beijing rises. The average of annual blue water supply is 3.685 billion m3 and green water supply is 1.69 billion m3. The water demand gap shows a significant increase trend with a perennial average of 16.52 billion m3. The verification results of the established WAS model show that the simulated and measured error rates of the annual average and characteristic frequencies of 25%, 50% and 75% runoff volume in Beijing from 1982 to 2010 are 7.0%, 4.8%, 1.2% and 0, indicating a high model accuracy. The flow rate of each calculation unit under the natural water cycle increases from northeast to southwest, while the actual flow rate decreases under the natural and social water cycle.

Abstract:Based on the comparison between physical model test and numerical simulation test, the hydrodynamic characteristics such as the transmission coefficient, reflection coefficient, wave pressure and wave climb of the permeable breakwater with forward inclined and backward vertical double baffle pile foundation were systematically studied by numerical simulation. The results show that, compared with the vertical wave baffle, the transmission coefficient and reflection coefficient of the structure can be significantly reduced by using the inclined front baffle, while the wave pressure and wave climb have little change, indicating the effect of the wave baffle. If the angle of the wave baffle reaches to 40°, the change of transmission coefficient tends to be stable. Considering all factors, the inclined baffle structure is better than the vertical baffle structure in general, and the angle of the front baffle can be designed less than 40° in engineering application.

Abstract:Aiming at the dynamic development process of piping in multi-stratum dike foundations, a finite element software was used to simulate the seepage field at different stages of piping. The hydraulic gradient in each area was compared to the critical hydraulic gradient for soil erosion in the corresponding area, so as to determine the erosion area at each stage of piping development. The results show that the occurrence of piping is marked by the breaking of the sandy interlayer in the case of the multi-stratum dike foundation with the burial depth of sandy interlayer of 1m. During the development of piping, the soil particles are eroded, and then the local soil permeability changes accordingly. The variation of permeability affects the distribution of seepage field, and then the loss of soil particles can be influenced. Therefore, the dynamic development of piping is a process in which soil erosion and permeability are influenced and coupled by each other. Multiple types of erosion occur in the development of piping, including the simultaneous effect of deep piping and shallow piping, resulting in a deep piping channel that can significantly in fluence dam safety.

Abstract:In order to explore the influence rule of fine particle content on the permeability of ocean ultra-fine sands and the meso-mechanism, the particle gradation of the ultra-fine sands from the coast of Mauritania was analyzed by a sieving method combined with laser particle size analyzer. According to the results of the particle gradation, the ultra-fine sands with different fine particle contents were configured indoor for variable head penetration test. Finally, combined with the SEM technology, the influence mechanism of permeability coefficient of fine particle content on ultra-fine sands was preliminarily explored. The results show that the content of fine particles changes the pore distribution structure of ultra-fine sands and the integrity of the sample in the microscopic view, thereby affecting the permeability coefficient. The content of silt fine sands (d=0.075~0.1mm) has minor effect on the saturated permeability coefficient k20of ultra-fine sands, and is linearly related. The content increases by 5%, k20 decreases by about 0.2×10-3cm/s. The content of fine particles (d ≤0.075 mm) has a relatively large influence on k20, showing a power function that first decreases and then stabilizes. The relationship between k20 and the fine sand gradation state parameters Cu and Cc is more accurately expressed by a power function.

Abstract:To accelerate the desalination improvement of coastal tidal flats in Jiangsu Province, a typical area was selected for field location tests. The variation rules of groundwater depth and mineralization under specific hydrological and environmental conditions were statistically analyzed. The results show that the rainfall on coastal tidal flat areas in Jiangsu is abundant, and the spatial and temporal distribution of rainfall is uneven. The rainfall from May to September accounts for 73% of the annual rainfall. The correlation coefficients between groundwater depth and rainfall, evaporation and the water level of the Liangduo River near the study area are 0.94, 0.78 and 0.51, respectively, showing extremely significant correlation. The groundwater mineralization is significantly correlated with rainfall and evaporation with the correlation coefficients of 0.79 and 0.66, respectively. It is also significantly correlated with groundwater depth with the correlation coefficient of 0.42.

Abstract:To understand the variation process of air temperature and pressure in an air cushion surge chamber and its influence on the stress and deformation characteristics of the surrounding rock, based on the water level fluctuation equation and the energy conservation equation, a thermodynamic model for the compressed air in the surge tank considering the effect of heat transfer between air and surrounding rock was proposed, and the rationality of the model was validated. With the thermo-mechanical coupling numerical method of fractured rock mass, the pressure and temperature of the air in the surge chamber were taken as the instantaneous change boundary conditions for numerical simulation, and the stress and deformation characteristics of the surrounding rock of the surge chamber were analyzed. The results show that under the operating conditions of the surge tank, the air pressure and temperature in the surge chamber can fluctuate considerably, resulting in the surrounding rock temperature change accordingly. The temperature distribution of the rock behaves significantly uneven characteristics. The temperature at the joints and fissures has relatively large variation, and larger tensile stress occurs.

Abstract:To set up the lay out monitoring points scientifically and reasonably for comprehensive management of watershed, the Fuhe River basin was taken as an object. Cluster analysis method was adopted to optimize the monitoring layout. The rationality analysis of layout optimization was carried out by combining relative deviation analysis with variance analysis, and the optimization scheme of monitoring layout was constructed in the Fuhe River basin. According to the optimization scheme of monitoring layout, two monitoring points were set up in the upstream, middle and downstream of the river trunk respectively. One monitoring point was set up in the upstream and downstream for the larger tributaries, and for smaller rivers only one monitoring point was set up at the river confluence. The results show that after optimization, monitoring points were reduced from 40 to 16, accounting for 40% of the initial monitoring points. The optimized points still cover the upper, middle and lower reaches, trunk and tributaries and important nodes of the Fuhe River basin. After optimization, the relative deviation of each category and index is small, and there is no significant difference between the indicators of each category before and after optimization.

Abstract:Different understandings and definitions of water supply capacity exist in practice from concepts to calculation methods due to many factors involved. The relevant concepts of water supply capacity were discussed and the key factors affecting water supply capacity were analyzed. Differences and linkages between a single project, a water supply system and the reginal overall water supply capacity were discussed. The meanings of water supply capacity in different situations were suggested. The relationships between water supply capacity and available water supply, water supply guaranteed rate and other related concepts were compared. Chengdu city was taken as an example, of which the regional water supply capacity was accurately accounted. Some suggestions were put forward for the calculation and application of related concepts in water supply capacity.

Abstract:A model based on support vector machine (SVM) was developed for predicting the local scour depth around circular piers. The model was trained by 440 experimental local scour data of circular pier foundation under the condition of steady flow. The sensitivity of the factors affecting the scour depth was also evaluated. The results show a good agreement between the predicted scour depth and the measured value, indicting the applicability and effectiveness of the developed model. The developed model is sensitive to the geometric standard deviation of sediment and flow intensity.

Abstract:Based on the model test, the aeration concentration of the water flow in a stilling pool with drop sill and sudden expansion was measured, and the influence of incoming flow conditions, sudden expansion ratio, and flow state on the aeration characteristics was studied. The results show that the typical flow pattern of the aerated water flow in a sudden-expansion slumping stilling pool is a hydraulic jump superimposed on the jet of which the head is split into two parts. The bubble zone is within the extension of the chute and the length is reduced compared with the stilling pool without sudden expansion. The length of the drip zone is increased, but its length near the bottom is reduced. A pure water recirculation zone containing bubbles occurs at the sudden expansion. The aeration concentration of the bottom plate of the stilling pool without sudden expansion shows a peak-decreasing curve distribution, and the aeration concentration of each longitudinal section is evenly distributed. The aeration concentration of the bottom plate of the stilling pool with sudden expansion shows a peak-rising curve distribution, with the highest aeration concentration at the 1/4 midline of the floor, the second highest concentration at the 1/2 midline of the floor, and the lowest concentration near the side walls. Under the same hydraulic conditions, the aeration concentration at the bottom of the sudden expansion stilling pool is significantly lower than that without sudden expansion, and the aeration concentration does not decrease with the increase of the sudden expansion ratio.

Abstract:Aiming at the problem that the separation relationship between design parameters and linear elastic operators should be known in advance for the reduced basis method, a method based on inversion reduced basis method is proposed to solve linear elastic operators independent of design parameters. In the off-line stage, a low dimensional solution space is constructed without knowing the relationship between design parameters and linear elastic operators. Different design parameters are selected, and the linear elastic operators can be extracted from ANSYS software. The linear elastic matrix independent of design parameters is then solved by inversion reduced basis method. In the on-line stage, the calculation results can be obtained quickly when the new design parameters are selected. A planar frame structure was taken as an example, in which the results from the improved reduced basis method and the finite element method were compared, showing that the improved reduced basis method has high accuracy and the traditional application scope of reduced basis method is expanded.

Abstract:Since more and more high and steep rockfill slopes appear in engineering, the stability, failure process and influence range are critical to the engineering operation safety. The discrete element method was used to simulate the failure process of a high and steep rockfill slope. Taking a pumped storage power station project as an example, a discrete element model was established, and the failure process under the limit condition was simulated. The movement, retaining wall stress and change of the slope were analysed in detail. According to the variation of the average unbalanced force ratio, the failure process of the rockfill slope can be divided into five stages. The change of slope shape, displacement and velocity in each phase were mainly analysed. Besides, the instability mechanism of the rockfill slope was further clarified by monitoring the energy change and the stress change of the concrete retaining wall. Comparing with the displacement of accumulation body and the number of rock blocks crossing the specific position, the protection effect of the retaining wall was demonstrated. Furthermore, through quantitative analysis of the number of rock blocks reaching the riverbed and the force changes on the retaining wall, the concrete retaining wall at the bottom of the rockfill slope should be strengthened urgently. Through the discrete element numerical simulation, the failure process and influence range of the high and steep rockfill slope are defined and the suggested height of the concrete retaining wall is proposed.