Yunfei Guan

A composite bucket foundation (CBF) is a new foundation type of offshore wind turbine. The investigation of the bearing characteristic of CBF is a crucial part of the structural design and safety assessment of offshore wind turbines. This study investigates the bearing characteristic of CBF in sand and clay foundations using centrifuge model test and numerical simulation. Analysis revealed that as load increases, the rotation center of the CBF moves toward the central line and shallow area. The buried depth of the CBF rotation center in a clay foundation is shallower than in a sand foundation when the CBF is under ultimate loading. Due to the rotation and translation of CBF, the soil pressure–depth curves on the skirt wall in different directions will resemble parabolic, line, and triangle shapes, respectively. Under ultimate loading, the relationship between the depth and horizontal coordinate of the rotation center and embedment ratio is linear. The CBF's bearing capacity trend presents quadratic function characteristics as the embedment ratio increases. However, the bearing capacity ratio of the CBF in the clay foundation is faster than that in the sand foundation. The findings provide guidelines for offshore wind turbines.

Clayey sand is widely distributed and commonly encountered in geotechnical engineering practice. To understand its bearing capacity behavior under unsaturated conditions, plate load tests are performed on sand–kaolin mixture samples with varying water tables. The distributions of suction and volumetric water content with depth are measured by vibrating wire piezometers and soil moisture sensors, respectively. It is shown by the test results that the bearing capacity increases when the water table in the soil sample drops. The influence of suction on the bearing capacity is found to be dependent on the height of the water table and the hydraulic loading history of the soil sample. The plate load test results are interpreted using bearing capacity equations. Good agreement is obtained between measured and calculated bearing capacities. This study provides a simple method to estimate the bearing capacity of in situ unsaturated soil foundations.

At present, the sludge production has increased sharply, and sludge treatment remains a serious problem. Rapid sludge dewatering is the key problem of sludge treatment, and the main approach for reducing the cost of the sludge treatment is to reduce the cost of sludge dewatering. In this paper, two groups of sludge dewatering tests were carried out using homemade instruments and equipment. One group was conducted without rice straw, and the other group was conducted with rice straw. The relevant mechanism was analyzed, and the results indicate that sludge dewatering with a vacuum negative pressure load of the full section at the bottom is better than mechanical sludge dewatering. The sludge dewatering effect with rice straw is better than that without rice straw. Additionally, the vacuum degree inside the sludge decreased sharply. The pore water pressure slowly dissipates during the early and late stages and quickly during the middle stage. Sludge pore water seepage does not obey Darcy’s law, and sludge dewatering is intermittent.

The instability of the bank slope of the reservoir will cause great loss to the life and property of the people in the reservoir area. The landslide of the reservoir not only occurs in the period of water level plummeting, but also occurs in the period of water level rising. In this paper, the mechanism of slope landslide in the rising stage of water level was studied from the perspective of soil disintegration in water. A series of tests on the disintegration of prisms and cylinders with the same volume and different bottom side lengths (diameter) were carried out. The results show that the specific surface area of the same volume sample was different, and the disintegration behavior was different. The larger the specific surface area of the same shape sample was, the faster the disintegration speed was. The deeper the water depth was, the shorter the disintegration time was under the same initial conditions. It shows that when the water level of the reservoir rose, the deeper the water depth was, the greater the pore osmotic pressure was, and the more the soil mass of the slope collapsed. This led to the reduction of the pressure on the lower part of the slope, the decrease of the antisliding force of the soil, and the failure of the slope.

The dilatancy behavior of rockfills is relate to the stress level, the initial state and particle breakage. In this paper, based on the critical state theory, the state-dependent dilatancy theory of rockfills is established, and it is introduced into the state-dependent constitutive model of coarse materials, so the state-dependent constitutive model of rockfills is formulated. According to the large-scale triaxial testing results, using the Fortran program modelling the experimental results, then, comparing the test results and simulation results, only one set parameters of state-dependent constitutive model of rockfills can reflect the strain softening and dilatancy properties of rockfills under the condition of different density, gradation and confining pressure. Therefore, the rationality of the state-dependent constitutive model of rockfills is verified.