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The clay soil is composed of solid skeleton and porous and can be studied in the framework of porous media. During the drying process, the initial saturated clay soil deforms mainly due to the changes of water content and capillary pressure. With the further increase in capillary pressure, the soil cracks. In fact, the deformation and the stress in clay soil are tightly related with the water content and capillary pressure. Therefore, it is of great interest to understand the changes in capillary pressure and water content within the clay soil during the drying process. However, it is difficult to obtain these field variables by experiments alone. Therefore, the numerical simulation could be good choice for deeper understanding of the dry process in clay soil. In current research, the combined numerical simulation and laboratory experiments research are conducted; the numerical results are compared with the laboratory observation. This research is the basis for the further study of the cracking process of clay soil due to drying.

The objective of this study is to examine the performance of the shallow reinforced concrete foundation of a large-scale wind turbine under the influence of environmental loads. A 2 MW horizontal-axis onshore wind turbine supported by a shallow concrete foundation was considered. The foundation stresses, foundation settlements, and static and dynamic contact pressures at various positions of the shallow foundation were monitored from the construction phase to the operation phase in the field. Numerical simulations were also performed to further analyze the behavior of the wind turbine foundation in different cases. The results demonstrate that the responses of the reinforced concrete foundation, i.e., foundation stresses, contact pressures, and foundation settlements, were variables closely related to the wind direction and wind speed. The distribution of foundation stresses suggested that a reasonable design of steel reinforcement cages around the foundation steel ring is important. The dynamic contact pressure of the foundation could reach 5 kPa, so the influence of dynamic wind loads on the foundation response could not be always neglected, particularly for the foundations seated on weak soils. The foundation settlement during the operation phase could be characterized by the logistic model, but its distribution was uneven due to the presence of eccentric upper weight and wind load. The findings would provide guidance for the foundation design of onshore wind turbines in hilly areas.

This study aimed to investigate the influence of loosely bound water (LBW) on the compressibility of compacted fine-grained soils and accurately determine the soil’s compression index. Four fine-grained soils (i.e., heavy clay, heavy silt, lean clay, and lean silt) and a coarse-grained soil were examined. The volumetric flask method was used to measure the LBW contents of the five soils. X-ray diffraction (XRD) analysis was then performed to test the mineral compositions and help explain the reason why the LBW content varied between different soils. A concept of modified void ratio was proposed by assuming that LBW is a part of the solid phase in soil. Subsequently, consolidation tests and permeability tests were conducted on saturated compacted specimens. The results show that the compression indexes or permeability coefficients tend to be the same for the soils with identical initial modified void ratios. Consolidation tests were also carried out on the unsaturated compacted heavy silt of four different dry densities prepared at a water content higher than the optimum. They show that the compression of unsaturated soil occurs if pore air is discharged when the water content is less than the LBW content. This confirms the previous assumption that LBW can be regarded as a part of the soil solid phase. A modified compression index was deduced and implemented to predict the settlement of a road embankment. The result suggests that the modified compression index is capable of calculating the compression of fine-grained soils, whose water contents are higher than their LBW contents.

Because of low resilient modulus, high plasticity soil is often not allowed to fill road subgrades and is discarded as construction and demolition waste (CDW). To make use of the CDW, this study explored the possibility of improving high plasticity soil with gravel and examined the effect of gravel gradation on the resilient modulus of the soil-gravel mixture. A series of dynamic triaxial tests, tests of voids in coarse aggregate, and X-ray CT scans were carried out on high plasticity soil-gravel mixtures of different gravel contents and gravel gradation types. The test results show that there is a critical gravel content, that is, 44.1%. When the gravel content is less than 44.1%, the mixture shows a dense suspended structure and its modulus increases slowly with increasing gravel content. When the gravel content is greater than 44.1%, the mixture exhibits a dense skeleton structure and the modulus increases rapidly as the gravel content rises. Moreover, as the gravel gradation tends to the lower type, coarse aggregates increase in quantity and contact each other to form a dense skeleton; thus, the modulus increases accordingly. As the gravel gradation approaches the upper type, coarse aggregates decrease in quantity and tend to suspend in the soil, so the modulus decreases. With the increase in contact number, the skeleton structure is continuously improved, and thus the modulus is enhanced progressively. The results indicate that the gravel mixing method with a gravel content of 40%–45% can effectively improve high plasticity soil and shows great environmental and economic benefits.

This study aims to examine the deformation behavior and internal mechanism of coarse-grained soil as an embankment filler under cyclic loading. Numerical dynamic triaxial tests were performed on coarse-grained soil using the discrete element software PFC3D. The numerical model was verified by comparing the numerical results with the experimental data. Afterward, the changes in the porosity, force chain, and particle movement of coarse-grained soil samples were analyzed, and the mesoscopic deformation behavior of coarse-grained soil under cyclic loading was investigated. The research results show that with the increase of the deviatoric stress amplitude, moisture content, and loading frequency, the deformation of the soil increases and the ability to resist deformation decreases at the same loading cycles. Due to the inhomogeneous distribution of particles with different sizes, the velocity and displacement of the sample vary in different directions, exhibiting mesoscopic anisotropy. The contact force is relatively even in the downward direction while dispersed near the edge of the sample. This means that the particles at the bottom are less affected by loads and the internal evolution of soil samples conforms to its macroscopic deformation behavior during cyclic loading.

Completely disintegrated carbonaceous mudstone, a common embankment material, has significant swelling-shrinkage behavior under cyclic wetting and drying, which often causes the instability of embankments. In this paper, the evolution of the cracks in the completely disintegrated carbonaceous mudstone subjected to cyclic wetting and drying was studied by laboratory tests. The vacuum saturation method and the drying method based on heat lamps and a fan were employed to simulate the wetting and drying processes, respectively. The image processing technique was used to treat the images of the sample surface. Afterward, various geometric parameters of the cracks appeared on the sample surface were measured, and the evolution characteristics of the cracks were analyzed. The results show that with the increase in the number of wetting and drying cycles, the number of cracks on the sample surface gradually increases. After four wetting and drying cycles, the existing cracks produce a large number of small branches, which are connected to form irregular polygonal grids. The development of the cracks in the completely disintegrated carbonaceous mudstone sample can be divided into three stages, i.e., slow development, rapid development, and stable development. Both the surface density of crack and the crack rate first increase and then tend to be stable with the increasing number of wetting and drying cycles. New cracks are mainly generated on the basis of the existing cracks, and some cracks appear to heal under cyclic wetting and drying. The early cracks are mainly developed in the directions of 0°–90° and 300°–360°, and the development rate of the cracks in the directions of 30°, 90°, 140°–150°, and 180°–270° is significantly higher than that of the cracks in other directions.