Synthetic polymer fluids are increasingly being applied to support excavations in deep foundations. As these fluids are molecularly engineered, their underlying microstructure interaction with in situ soils significantly affect excavation stability and soil dispersion. However, little molecular‐scale research has been done on the rheological behavior of partially hydrolyzed polyacrylamides (PHPA) polymer fluids on the clay surface. Molecular models of the clay–polymer systems are constructed using PHPA on montmorillonite (MMT) clay surface. Initial rheological properties and soil‐binding ability at different shear rates, temperatures, and polymer concentrations are first studied using molecular dynamics (MD) simulations. It is found that the functional groups of PHPA can interact with the MMT surface and form a viscous film under the atomic interaction of hydrogen bonds, water bridges, and electrostatic attraction. The shear stress, σ increases with the shear rate and follows the power‐law model. And the viscosity, η decreases as the shear rate increases, which is consistent with the experimental trend. However, the σ and η decrease with the increase of temperature. And the action mode of PHPA concentration has been identified from the MD perspective. This work provides insight into the molecular mechanism for PHPA's rheology on the clay surface and their interaction.
The three-dimensional ground-penetrating radar system is an effective method to detect road void disease. Ground penetrating radar image interpretation has the characteristics of multi-solution, long interpretation period, and high professional requirements of processors. In recent years, researchers have put forward solutions for automatic interpretation of ground-penetrating radar images, including automatic detection algorithm for subgrade diseases based on support vector machines, etc., but there are still some shortcomings such as training models with a large amount of data or setting parameters. In this article, a three-dimensional ground-penetrating radar void signal recognition algorithm based on the digital image is proposed, and the algorithm uses digital images to characterize radar signals. With the help of digital image processing methods, the images are processed by binarization, corrosion, expansion, connected area inspection, fine length index inspection, and three-dimensional matching inspection, so as to identify and determine the void signals and extract the void area volume index. The algorithm has been verified by laboratory tests and engineering projects, and the results show that the void identification algorithm can accurately identify the void area position; the error level between the measured values and the measured values of length, width, buried depth, and area is between 2.2 and 17.3%, and the error is generally within the engineering acceptance range. The volume index calculated by the algorithm has a certain engineering application value; compared with the support vector machine, the regressive convolution neural network, and other recognition methods, it has the advantage of not needing a large amount of data to train or modify parameters.
The swelling behavior of clay minerals is widely known for its importance in soil and environmental sciences and its detrimental effects in engineering fields. Although more than 70 percent of all clays are of mixed-layer types, the vast majority of the previous experiments and simulations are focused on pure clays, which cause the swelling mechanism of the widespread mixed-layer clay (MLC) and its role in soils are little understood, especially the most common illite-montmorillonite (I-M) mixed-layer clay (MLC). This paper reports on a molecular dynamics (MD) study of the differences in swelling behavior between I-M MLCs containing K+ and Na+ and Na-montmorillonite (MMT). It captures the evolution of quantitative properties such as basal spacing d, interaction energy, and many hydrogen bonds in the clay interlayer, increasing hydration for the first time through the scripts. It is found that MLCs have smaller swellings than Na-MMT due to the asymmetric interlayer charges and mixed counterions in the I-M interlayer. However, in terms of the interaction energy for the in-depth reason of swelling, it is found that the clay-clay interaction energy and the clay-ion interaction energy drop, while the clay-water interaction energy increases with increasing hydration. In addition, the attractive interaction of clay-bound water seriously promotes swelling, and it is mainly composed of Coulomb interaction and Van der Waals interaction. The higher the K+ concentration, the more noticeable these phenomena are. Besides, it is also reported that the number and distribution mechanism of hydrogen bonds in MLCs are very different from that of pure clay. This work provides insight into the molecular mechanism for initial swelling and clay-bound water interaction in widespread MLCs. This will help to decipher its specific role in soils and minimize clay swelling.
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