Research on Water Seepage Detection Technology of Tunnel Asphalt Pavement Based on Deep Learning and Digital Image Processing

In order to improve the traffic safety of the tunnel pavement and reduce the impact of water seepage on the pavement structure, a convolutional neural network (CNN) model is established based on image detection technology to realize the identification, classification and statistics of pavement seepage. First, compared with the MobileNet network model, the deep learning model EfficientNet network model was built, and the accuracy of the two models was analyzed for pavement seepage recognition. The F1 Score was introduced to evaluate the accuracy and comprehensive performance of the two models for different types of seepage characteristics. Then the three gray processing methods, six threshold segmentation methods, as well as three filtering methods were compared to extract water seepage characteristics of digital image. Finally, based on the processed image, a calculation method of water seepage area was proposed to identify the actual asphalt pavement water seepage. The result shows that the recognition accuracy of the EfficientNet network model in the training set and the validation set are 99.85% and 97.53%, respectively, and the prediction accuracy is 98.00%. The accuracy of pavement water seepage recognition and prediction is better than the MobileNet network model. Using the cvtColor function for gray processing, using THRESH_BINARY for threshold segmentation, and using a combination of median filtering and morphological opening operations for image noise reduction can effectively extract water seepage characteristics. The water seepage area calculated by the proposed method has a small difference with the actual water seepage area, and the effect is agreeable.

Fractal characteristics of the micropore throats in the shale oil reservoirs of the Chang 7 Member of the Yanchang Formation, Ordos Basin

With the development of the global shale oil and gas revolution, shale oil became an important replacement field to increase oil and gas reserves and production. The Chang 7 Member of the Yanchang Formation in the Ordos Basin was an important shale oil exploration series in China. To study the micropore-throat structure characteristics of the Chang 7 Member, we launched nuclear magnetic resonance (NMR) and high-pressure mercury injection (HPMI) experiments to analyze the pore-throat structure features of the Chang 7 reservoir, and we considered fractal theory to study the fractal characteristics. The NMR results indicated that the T2 spectral morphology of the Chang 7 reservoir could be characterized by three main patterns encompassing early and late peaks with different amplitudes: the type 1 reservoir contained mostly small pores and few large pores, and the porosities of the small and large pores range from 4.16% to 9.04% and 0.70% to 2.40%, respectively. The type 2 reservoir contained similar amounts of small and large pores, and the type 3 reservoir contained few small pores and mostly large pores, while the porosities of the small and large pores range from 1.81% to 2.74% and 3.32% to 5.64%, respectively. The pore-throat structure parameters were obviously affected by the pore size distribution, which in turn influenced the reservoir seepage characteristics of the reservoir. The micropore-throat structure of the reservoir exhibited obvious piecewise fractal characteristics and mainly included dichotomous and trilateral fractals. The type 1 reservoirs were dominated by dichotomous fractals, and these two fractal types were equally distributed in the type 2 and 3 reservoirs. The fractal dimension of the pore throats of different scales exhibited a negative correlation with the corresponding porosity, but no correlation was observed with the permeability, indicating that the size of the reservoir determined by pore throats imposed a strong controlling effect on their fractal characteristics.

Research on Boundary Layer Effect in Fractured Reservoirs Based on Pore-Scale Models

It is of great significance to study the seepage characteristics of heavy oil reservoirs, which are conducive to the efficient development of resources. Boundary layer effect (BLE) exists in the pore-scale flow process of macromolecular fluid media, which is different from the flow law of conventional fluid in the pore, yet the influence of BLE is ignored in the previous pore-scale simulation. Conventional porous media simulations have difficulty analyzing the mass transfer law of small-scale models under the influence of microfractures. Based on the CT scanning data and thin section data of the real core in the target area, the rock skeleton and flow space were extracted according to the maximum ball algorithm, and the pore network model representing the complex structure was constructed. The microscale effect of macromolecules in the flow process in the pores was characterized by modifying the effective flow. The effects of the BLE on the effective connectivity, displacement process, and oil distribution law were analyzed. The seepage characteristics of different wettability conditions and different water cut stages were compared. The results show that BLE reduces the effective flow space and leads to deviations in the relative permeability curve and capillary curve. For fractured porous media, the irregular shape of porous media was characterized by the morphological method, and the mass transfer process was analyzed by the equivalent flux method. The influence of the porous media shape on the macromass transfer process was compared. This study provides a solution to the problem of BLE in pore-scale simulation.

Formation Mechanism of Preferential Flow Paths and Seepage Characteristics of a Novel Growable Pile for Heap Leaching of Rare Earth

In the traditional heap leaching of rare earth minerals, the top of the rare earth pile is covered with leaching liquid. This creates trouble for vegetation restoration carried out timely on the top of the pile. In order to solve this trouble, a novel pile structure into which leaching liquid is laterally injected is proposed for heap leaching of rare earth. In this study, a laboratory test is carried out to study the formation and distribution of preferential flow paths for the rare earth pile under a horizontal liquid injection condition. Furthermore, numerical simulations based on a dual-permeability model are conducted to investigate the influence of the preferential flow paths on the seepage characteristics in the rare earth pile. The results show that, under the horizontal liquid injection condition, the fine particles of the rare earth move away from the liquid injection end and also toward the lower part of the pile. The migration of the fine particles results in the formation and connection of macropore, thereby generating preferential flow paths in the rare earth pile. The preferential flow paths are mainly distributed in the lower part of the pile near the liquid injection end. This causes the fluid in the lower part of the pile to seep faster significantly than that in the upper part. Within the region where the preferential flow paths develop, the seepage in the early stage of the horizontal liquid injection is dominated by preferential flow. The preferential flow is more significant at the locations farther away from the liquid injection end.

Experimental Investigation of the Effects of the Gangue Particle Size on the Evolution Rules of Key Seepage Parameters

In order to deal with solid wastes and protect the fragile ecological environment on the ground, using gangues as the filling materials in the underground goaf can not only achieve favorable waste disposal but also alleviate surface subsidence and protect surface buildings and the ecological environment, with great practical significance and application prospects. During the water seepage process, the evolution rules of inner seepage channels in the bulk filling materials are the theoretical foundation for the realization of water-preserved mining. In order to gain clear knowledge of the seepage characteristics of the bulk filling gangues with different sizes, the evolution rules of some seepage parameters mainly including the displacement, the porosity, and the permeability of gangues and hydraulic pressure were analyzed via COMSOL numerical simulation. The evolution rules of the seepage characteristics of the bulk filling materials with different sizes were revealed by combining the present experimental and numerical results. Moreover, the present seepage experiment was proved to be reliable by comparing with numerical simulation results. This work can provide theoretical foundation for investigating the evolution characteristics of inner seepage paths in the bulk filling materials and selecting appropriate bulk filling materials under different stress and seepage environments.

Experimental Study of the Water-Sediment Two-Phase Seepage Characteristics in Rock Fractures and the Influencing Factors

The water-sediment two-phase seepage in coarse fractures is one of the major factors to trigger mine water inrush disasters. Based on seepage mechanics theory, a mechanical model of the water-sediment two-phase seepage in coarse fractures was established. An experimental system was also developed to study the seepage characteristics under various conditions. The relationships between the absolute value of the pressure gradient and the seepage velocity were analyzed during the test process. The nonlinear characteristics of the seepage test were revealed. In addition, variation laws of the absolute value of the pressure gradient with the sand volume fraction and the sand particle size were illustrated, which were related to the loss of pressure during the particle movement. The impacts of the sand volume fraction and the sand particle size on the equivalent fluidity and β -factor of non-Darcy flow were discussed and analyzed. It was determined that the local turbulence was the main reason for the change of nonlinear variation characteristics of seepage parameters.

Numerical Analysis of Concrete Gravity Dam Seepage Characteristics Evolution considering the Calcium Leaching Effect

During the long-term service life of hydraulic structures, the calcium compounds in cement-based materials decompose in the aqueous environment, leading to the continuous change of seepage characteristics. To study the influence of calcium leaching on the concrete dam seepage characteristics, we proposed a new mathematic model of the cement-based material calcium leaching model under advection-diffusion-driven leaching. A solid-liquid nonequilibrium model is adopted to model the decomposition of calcium hydroxide (CH) and calcium silicate hydrate gel (C-S-H). To calculate the porosity more accurately, the proposed model takes the effect of different calcium compound decomposition on the porosity increase in consideration, respectively. Shimantan dam is selected for the three-dimensional (3D) calcium leaching analyses. The 3D finite element model of this dam is analyzed using COMSOL Multiphysics software that is based on the finite element method. Based on the proposed model, seepage characteristics evolutions of the Shimantan dam are studied. Good agreement between the numerical results and the monitored data indicates the accuracy of this simulation. The result shows that after 100 a leaching duration, the uplift pressure increases by 40.8%, and the leakage quantities of the dam body and foundation increase by 48 and 17 times. The rise of uplift pressure and leakage changes caused by curtain deterioration are the main influences of calcium leaching on the dam seepage. The parameter sensitivity results show that it is necessary to reduce CH content in cement-based materials to obtain better calcium leaching durability. This model and simulation results can guide the operation of concrete dams under advection-diffusion-driven leaching.