Improving the performance of loess significantly protects it against failure and degradation, and is important for rammed earth and infrastructure constructed with loess materials. The physical and mechanical properties of nano-SiO2-treated loess were tested with different contents and curing days-including unconfined compressive strength (UCS) and splitting tensile strength (STS)-and their corresponding water content, density, and void ratio. I paid close attention to the homogeneity during sample preparation-that is, sample quality-based on the UCS test. I then analyzed their relation to physical and mechanical properties to gain a better understanding. The results show that the UCS test is a valuable method for examining the quality of sample preparation. UCS, STS, and density increased, and the water content and void ratio decreased with increasing content and curing days due to nano-SiO2 addition. The improvement of mechanical strength is related to the ratio of water content to nano-SiO2 content and curing period rather than the physical properties and additive contents of treated loess. These findings reveal that nano-SiO2 can be an effective stabilizing agent for loess improvement, which has important implications for geohazard mitigation and engineering management in the Chinese loess area.

A large amount of waste clay is generated in shield tunnel engineering. Although the physical properties such as the unconfined compressive strength of the clay have been improved through lime modification, some still fail to meet the specifications for road embankment materials. In this study, a indoor carbonation device was used to carbonize lime-modified clay samples with different lime contents. The changes in water content (omega), plasticity index (IP), undrained compressive strength (qu), and softening coefficient (Kr) of the samples were analyzed. Microscopic mechanisms were investigated through tests such as Scanning electron microscope (SEM) and Diffraction of x-rays (XRD). The results showed that with increasing carbonation period, the omega and IP of soil samples with different lime contents gradually decreased and stabilized. After 2 hours of carbonation, the qu, elastic modulus (E50), and Kr of the soil samples significantly increased. After 1 hour of carbonation and 7 days of curing, the modified clay with lime content greater than 7% met the subgrade strength standards for secondary and lower-grade highways (IP = 500 kPa). The carbonation reaction resulted in the formation of CaCO3 crystals on the surface of soil particles and Ca(OH)2. With carbonation further developed, a CaCO3-Ca(OH)2-C-S-H hybrid material was generated, which filled the pore space in clay reinforcing the structure and improving the strength of lime-modified clay.

The Guanzhong Plain city group is located in the centre of inland China, which is an important fulcrum of the Asia-Europe Continental Bridge, and also the second largest urban agglomeration in the western region of China. However, the large thickness collapsible loess has always been a pain point in the process of urban development. In this paper, for the problem of collapsible loess in Guanzhong area, five typical geomorphological units in Xi'an, Xianyang, Tongchuan and Sanmenxia are targeted for sampling. Through a large number of indoor and outdoor experiments, the relevant data of physical properties, hydrophysical properties, mechanical properties, collapsible index of collapsible loess and the distribution pattern of each index in the study area are analysed.By analyzing the correlation among the indexes, four indexes which are closely related to the collapsibility of loess are obtained: natural density, void ratio, dry density and saturation, and the regression analysis of these four indexes and the collapsibility coefficient is carried out respectively.This finding provides a reference for a more in-depth study of the characteristics of collapsible loess in Guanzhong area, and can optimise the engineering investigation process in urban construction, which is very important for the urban construction in this area.