The convergence-confinement method (CCM) is a simplified widely utilised tool for assessing the interplay between the rock mass behaviour and the support effect, so it is quite helpful for tunnel support design purposes. However, the direct application of this technique has shown some limitations, many of which are directly related to the three-dimensionality issue. Indeed, the CCM tries to solve the three-dimensional (3D) problem of tunnel advance deformation and support response, by means of a series of two-dimensional (2D) plane strain analyses. So, regardless purely elastic cases, certain deviation is observed when comparing CCM and 3D numerical modelling results. The reasons behind this deviation have been studied from different points of views, but they seem to be still not well understood. With the aim of advancing towards a better knowledge of this issue, this paper discusses the limitation of CCM to correctly reflect the 3D tunnelling effect by comparing CCM and 3D numerical deformation, support pressure and liner load results in a typical tunnel case for various geological conditions. The reasons for CCM results in different rock deformation and support pressure in comparing to the 3D numerical modelling are explained. Some guidelines are eventually given recommending when the use of CCM can be acceptable according to the rock mass strength and tunnel depth, and when a more rigorous 3D approach is convenient.

Long-term water seepage in shield tunnels has a serious impact on water and soil loading on the outer surfaces of a shield segment near water areas. A theoretical analysis was used to obtain a formula to express the average vertical seepage gradient at the top of the tunnel. A formula for calculating the coefficient of lateral earth pressure for the principal stress arch effect was utilized. A model that takes into consideration the effects of long-term water seepage on the shield tunnel’s water and soil load was designed. Based on this calculation model, the variation law of the water and soil loading on top of shield tunnel near water area with the internal friction angle in the soil body, the density of the soil, the tunnel depth-to-diameter ratio, the water head of the external section, and the amount of water seepage per unit length is studied. Based on the geological conditions and field survey results of water and soil loading of two typical segments of the Maliuzhou Waterway section of the Hengqin Tunnel, a comparative analysis of the theoretical results and field survey measurements was performed for different calculated conditions. The research shows that the proposed model is able to perform a reasonably effective evaluation of the water and soil pressure at the top of the shield tunnel for the marine and land segments of the shield tunnel; and, when compared with Dimitrios Kolymbas’ effective stress method and Terzaghi’s Principle, the method shown in this paper has fewer errors. The results of the associated research are sufficient to reasonably design and propose a theoretical basis for underwater shield tunnels.

An experimental study aimed at providing insights into the cyclic deformation behavior of saturated marine silt under principal rotation, as induced by wave loading, is presented. Using the GDS hollow cylinder apparatus, a series of undrained tests are performed and the specimens at identical initial states are subjected to combined axial–torsional cyclic loading that imposes different levels of stress rotation. The cumulative generalized shear strain γg is used to describe the deformation of the silt under complex stress paths. The test results show that the cumulative generalized shear strain is significantly dependent on the cyclic stress ratio (CSR) and cyclic loading amplitude ratio δ. The cumulative generalized shear strain increases with the increase in CSR and decreases with the increase in δ. The development trend of γg can be well predicted through the correct Monismith model in the non-liquefaction silt, with a low error that is generally less than 10%.