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In silt low subgrade, capillary effect is an important factor inducing site erosion and collapse, and it is necessary to control the rise of capillary water. In this paper, the effectiveness of eight kinds of capillary barriers formed by geotechnical materials on the vertical migration of water in silt was studied by an indoor model test. Further field tests were carried out to verify the indoor test results. Finally, the vertical deformation of silt roadbed under different schemes was investigated through numerical simulation, and a reasonable scheme was put forward. The results show that among the eight schemes, the four combinations formed by gravel, coarse sand, lime soil layer with 40 cm thickness (curing for 45 days) and lime soil layer with composite geomembrane had the better barrier effect on capillary water, in which the dual capillary barrier using lime soil layer and composite geomembrane had the best effectiveness. The effectiveness of capillary barrier using composite geomembrane and 3% cement soil was the second, and the barrier effect of 5% lime soil cured for 7 days was the worst. The effectiveness of capillary barrier formed by lime soil increased obviously with the increase in age and thickness of lime soil. The numerical simulation results demonstrate that the improved capillary barrier effect reduced the vertical roadbed displacement. The vertical displacement at the center of the embankment was in the following order: lime soil > composite geomembrane > cement soil > coarse sand > gravel. [ABSTRACT FROM AUTHOR]

Silt has the characteristics of capillary pore development and strong water sensitivity. The rise of capillary water in silt may cause the strength of the roadbed to decrease or instability. It is vital to identify the mechanical and engineering properties of silt roadbed under capillary water. In this paper, a typical silt in Nantong of Jiangsu Province was selected to investigate the variation rules of the cohesion c, the internal friction angle φ, and the compression modulus Es under different water content by quick direct shear test and compression test. Furthermore, based on the test results, the engineering characteristics of low embankment under capillary water were studied by numerical simulation. The results show that the saturation Sr had little effect on the φ but had an obvious effect on the c. The c of silt decreased with the increase of the Sr. With the increase of water content w, the Es of silt showed a strong nonlinearity. When the void ratio e was larger, the w was the main factor affecting Es. However, the experimental results have a certain applicability, that is, the form of water and gas in the silt was in the stage of "internal connectivity of gas phase." In the case of the same groundwater level, when the filling was low, the deformation of the subgrade was obviously affected by capillary water. According to the simulation results, it is preliminarily determined that the reasonable filling height of silt low embankment was between 1.2 and 1.5 m. [ABSTRACT FROM AUTHOR]

Because of its poor engineering properties, silt often needs to be treated to meet the design requirements. Solidification using binder is one of the most common methods to improve the engineering properties of silt. Lime or/and cement are often used to treat silt. However, the mechanical properties of soil are closely related to its microstructure. Although much research has been done on the mechanical properties and stabilization mechanism of lime or/and cement solidified silt, the multi-scale research between the microstructure and macroscopic mechanics properties of solidified silt has received no attention. Therefore, in this paper, unconfined compression, mercury intrusion, and scanning electron microscope (SEM) tests were conducted on lime, cement, and lime and cement mixtures (LC) solidified silt. The microstructure parameters of particle, pore, and contact zone were extracted from SEM images. Meanwhile, the effect of curing time and binder dosage on the microstructure parameters was analyzed. In addition, the relationship between micro-parameters and macro-mechanical strength was established. The results showed that the particle diameter, particle area, contact zone diameter, and contact zone area increased with increasing curing time and binder dosage, while the pore ratio, fractal dimension of particle size distribution (PSD), and fractal dimension of contact zone size distribution (CZSD) decreased with increasing binder dosage. The unconfined compressive strength (UCS) decreased with the increase of particle roundness, pore area, pore diameter, pore ratio, and fractal dimension of PSD, and increased with increasing fractal dimension of pore size distribution (PPSD). In addition, there were no obvious relationships between UCS and pore roundness, contact zone area, and fractal dimension of CZSD. [ABSTRACT FROM AUTHOR]