A coal storage wharf located in Zhenjiang, Jiangsu province, China, has a planned annual capacity of 15 million tons. The thick Yangtze River floodplain is rich in muddy-silty clay with high compressibility, low bearing capacity, and poor stability, which needs to be improved to meet engineering requirements. In this paper, a case study on soft clay treatment with the vacuum preloading method (VPM) and combined vacuum and surcharge preloading method (CV-SPM) is introduced and discussed. Negative pore-water pressure was induced by vacuum pressure in the VPM, which led to the seepage of water and consolidation of soils. However, the vacuum pressure could never exceed 101,325 Pa (1 atm), so the additional filling surcharge was usually adopted to raise the preloading load in the CV-SPM when the bearing capacity requirement was higher. To perform ground improvement in the field, first in situ soil samples were taken from the construction site before the treatment, and the properties of soils were investigated through laboratory tests, which were used as the reference to analyze the effect of ground improvement. Second, during the construction process vacuum pressure, ground settlement, and pore-water pressure as well as lateral displacement of soils were monitored and analyzed. Finally, vane shear tests and shallow plate bearing tests were carried out to investigate and evaluate the effect of ground improvement. Test results show that the undrained shear strength increased remarkably, and the bearing capacity reached the design requirements after around 100 days of preloading, indicating that VPM and CV-SPM are appropriate and effective for ground improvement of the thick muddy-silty clay laying in the Yangtze River floodplain.

Field investigations and laboratory tests were performed to determine the cause of engineering distress due to the swelling of lime-stabilized and phosphogypsum-stabilized soil and subsequent cracks on a roadway in China. An exploratory pit was excavated to inspect the damage state. The thickness and water content of the subbase before and after failure were compared. Laboratory compaction and expansion tests were performed to investigate the swelling behavior and the expansion potential of both the mixture from the in-situ subbase and the newly made mixture in the laboratory. It was found that the main reason for heaving in the roadway was due to the overuse of phosphogypsum in mixture of the subbase. In addition, continuous heavy rainfalls were the triggering factor for a series of chemical reactions that occurred among the mixtures in the water-rich surroundings. These combined factors resulted in the failure of the roadway subbase. This work reveals that the dosage of phosphogypsum must be controlled in a reasonable range when it is used in roadway engineering.

Soft marine deposits are widely distributed in the coastal region of China. The marine soft clays have high water content and high sensitivity, which shows high compressibility and low strength. The installation of precast piles for wind turbines over soft marine clay will generate high excess pore water pressure (EPWP) with very low dissipation rate, resulting in low bearing capacity and large postconstruction settlement, which will affect long-term stability. This study investigated the generation and dissipation of the EPWP correlated with the change in soil structure during the installation of pile foundations in a project of 100 MW wind-power generation in Lianyungang, Jiangsu, China. The results show that the marine soft clay soils feature strong natural structures based on the intrinsic compression concept. The EPWP decreases with increasing distance from the pile, whose influence reaches a distance of 6 m (about 10 times the pile side length). The structural strength of natural sedimentary clay has a remarkable impact on the generated EPWP. The dissipation rate of the EPWP is very slow in mucky clay with more than half the residual value after 30 days, which is mainly attributed to the sharp decline of consolidation coefficient induced by the disturbance of natural clay soils from pile driving. Moreover, hydraulic fracturing can well explain the dissipation characteristics of the EPWP in clay. This phenomenon is actually an ongoing process especially in marine soft clay soils with a strong cementation effect.