Shear strength of the loess joint has significant influence on the stability of loess engineering with joints. “Joint” is the weak structural plane of loess, and its shear strength determines the stability of loess. In this study, a series of loess joint samples was collected from Binxian County, Liquan County, and Zichang County in Shaanxi Province. The shear strength of the loess joint was determined by means of the direct shear test. The influence of the water content on the shear strength parameters of the loess joint was investigated by means of tests. The results showed that initially the internal friction angle varied slightly with the water content but decreased very quickly as the water content surpassed the threshold value of 14 %. The relationship between shear strength and water content can be expressed as an exponential function. This study devised a new empirical formula that determines the peak internal friction angle by observing the effects of dry density, water content, shear strength, and joint surface morphology.

With the continuous development of loess tunnel construction in western China, there are more and more complex situations, which have received extensive attention and research. However, there is a lack of research on the interaction between tunnel excavation and land subsidence when mountain tunnel passes through the settlement area of village residents. During the excavation of Anxing tunnel through residential area, the average deformation value is as high as 202 mm, while the average deformation value of non-residential section is lower than the actual control value, and the average deformation value is 78 mm. In order to expand the survey samples, through literature statistics, it is found that among the 67 cases of large deformation of loess tunnel, 16 cases occurred considerable deformation in the residential area, accounting for 23.9%. The influence of the strength and frequency of human activities on the regional geology of residents can not be ignored and should be regarded as an independent factor. On this basis, combined with other main factors affecting the large deformation of the tunnel, a risk assessment model is established, and the influence degree of human activities and other factors on the tunnel deformation is quantitatively analyzed and verified by fuzzy analytic hierarchy process (AHP). The results show that the risk assessment grade of Anxing tunnel is graded III, and the risk assessment model of large deformation in residential area under the tunnel is in good agreement with the engineering practice. It can provide reference for the risk assessment of similar projects.

In this paper, the bacterial solution was mixed with cementing solution and the generation time of calcium carbonate precipitation was delayed during microbial curing. The optimal pH value and the concentration of cementing solution were determined. The reinforcement effect of pH-adjusted mixed grouting method on sandy soil was analyzed by the unconfined compressive strength, the generation amount and distribution of calcium carbonate precipitation. The results show that the strength of the specimen by low pH mixed grouting method is 235% higher and more calcium carbonate precipitates is generated than other. The utilization rate of cementing fluid and the distribution of calcium carbonate are better.