In recent decades, early warning systems to predict the occurrence of landslides using tilt sensors have been developed and employed in slope monitoring due to their low cost and simple installation. Although many studies have been carried out to validate the efficiency of these early warning systems, few studies have been carried out to investigate the tilting direction of tilt sensors at the slope surface, which have revealed controversial results in field monitoring. In this paper, the tilting direction and the pre-failure tilting behavior of slopes were studied by performing a series of model tests as well as two field tests. These tests were conducted under various testing conditions. Tilt sensors with different rod lengths were employed to investigate the mechanism of surface tilting. The test results show that the surface tilting measured by the tilt sensors with no rods and those with short rods located above the slip surface are consistent, while the tilting monitored by the tilt sensors with long rods implies an opposite rotational direction. These results are important references to understand the controversial surface tilting behavior in in situ landslide monitoring cases and imply the correlation between the depth of the slip surface of the slope and the surface tilting in in situ landslide monitoring cases, which can be used as the standard for tilt sensor installation in field monitoring.

During the construction stage of the small radius TBM (tunnel boring machine) interval, the improper control of the boring parameters and the boring posture can cause the horizontal axis deviation of the shield tunnel. In order to address this issue, the TBM segments lining structure of the small radius interval is simplified as the continuous circular curved beam based on the longitudinal equivalent continuous model and Winkler elastic foundation beam theory. The theoretical model is solved through the transfer matrix method, and its applicability is verified by comparing it with the field monitoring data. It is found that the horizontal axis deviation of the completed tunnel increases with the total jack thrust, and the lateral displacement tends to be stable when the distance between the ring and the tail is far. The horizontal axis deviation has a negative relationship with the thrust difference or path difference when the jack thrust in the outside of the shield curve is larger than that of inside the shield curve. The horizontal axis deviation has a positive relationship with the thrust difference or path difference when the jack thrust in the outside of the shield curve is smaller than that of inside the shield curve.

Collapse is one of the most dangerous geological disasters in tunnel construction, and it is an urgent engineering problem which needs to be solved. Taking the collapse of the top of an actual tunnel face as an example, through field investigation and theoretical calculation methods, the mechanism of tunnel collapse was studied, and the treatment and evaluation of the collapse area were proposed based on field monitoring data. The results show that the extrusion and bulging deformation on the palm surface and the tensile fracture in the top inclined stratum led to the shear slip of the block along the structural surface and the local collapse of the surrounding rock. Based on the block theory, the potential unstable block at the top of the tunnel was successfully identified, and the treatment method of ‘protecting before filling and then digging’ was proposed. The comprehensive treatment measures of advance bolts, steel arch support, collapse backfill, and step excavation were adopted, with on-site monitoring followed up step by step. Based on the analysis of surrounding rock deformation and stress characteristics, in this paper we demonstrate that the treatment effects of the collapse area are good, and ensure the safety and smooth progress of construction. The proposed treatment method achieved the expected goal and was shown to be able to provide successful treatment for similar collapse cases of tunnel engineering.