The long-term settlement of subsea pipelines on a clayey seabed is crucial for the on-bottom stability of the pipelines, especially in deep waters. In this study, a poro-elasto-viscoplastic finite element analysis is performed for predicting long-term settlement of subsea pipelines by incorporating a rheological constitutive model. A method for identifying the creep-settlement (Sc) from the total-embedment (Sk) is proposed on the basis of the obtained linear relationship between the secondary consolidation coefficient (C alpha e) of the clayey soil and the total-embedment (Sk) of the pipe. The identifying method is validated with the existing theoretical solutions and experimental data. Parametric study is then performed to investigate the key influential parameters for long-term settlement of subsea pipeline. A non-dimensional parameter Gc is introduced to quantitatively characterize the soil rheology effect on pipeline settlement. The relationship between the proportion of creep-settlement in the total-embedment (Sc/Sk) and Gc is eventually established for identifying whether the proportion of creep-settlement in the total-embedment is remarkable.

This paper presents an efficient two-and-a-half dimensional (2.5D) numerical approach for analysing the long-term settlement of a tunnel-soft soil system under cyclic train loading. Soil deformations from train loads are divided into shear deformation under undrained conditions and volumetric deformation from excess pore water pressure (EPWP) dissipation. A 2.5D numerical model was employed to provide the dynamic stress state owing to the moving train load and the soil static stress state by the gravity effect for the determination of their accumulations. Then, an incremental computation approach combined with the initial strain approach in the framework of the 2.5D model was developed to compute the long-term deformation of the tunnel-soft soil system, considering the influence of the soil hardening due to EPWP dissipation. This approach helps to determine the distribution of the progressive settlement, transverse and longitudinal deformations in the tunnel-soil system, overcoming traditional limitations. A comparison of settlements computed using this approach with measured settlements of a shield tunnel in soft soil shows good agreement, indicating the effectiveness of the proposed approach in analysing train-induced progressive deformation of the tunnel-soil system.

This study investigates the long-term settlement behaviour induced by shield tunnelling in soft ground, employing a case study and numerical modelling to achieve a comprehensive understanding. Soil consolidation plays a critical role in long-term surface settlement, necessitating precise calibration of essential tunnelling parameters such as face pressure and grouting pressure. The findings indicate that soil settlement progressively increases with increasing face pressure P f and grouting pressure P g during the excavation of a shield tunnel. Furthermore, for long-term consolidation settlement, it has been established that setting P f at 90% of the lateral earth pressure 6 xx consistently minimizes settlement across all cover depths. This phenomenon is attributed to the soil arching mechanism, which also reduces the height of the loosened zone at this specific P f level. Similarly, the optimal P g is identified to be within the range of 130% to 150% of the vertical earth pressure 6 zz . For cover depths within the loosened zone, the smallest consolidation settlement and loosened zone height are observed at P g of 150% of 6 zz . Conversely, for shallower cover depths, beyond the loosened zone but within the arching zone, the smallest consolidation settlement and loosened zone height occur at P g of 130% of 6 zz . This study reveals that adjusting the cover depth significantly influences the reduction in vertical stress and the resulting settlement, demonstrating the importance of tailored grouting pressure calibration for varying depths to limit consolidation settlement.

The paper is dedicated to developing a comprehensive analysis method of the criteria for defining the compressible thickness critical for estimating long-term settlements in buildings and structures situated on soft soils, focusing on their creep behavior. This study introduces an engineering method grounded on the criterion of soil's undrained condition within the mass, considering both elastic and residual deformations through equivalent creep deformations. Unlike previous methodologies, the proposed method facilitates the assessment of long-term settlements by incorporating creep effects over time, employing undrained shear strength for both normally consolidated and overconsolidated soils. The method enables settlement calculations based on static-sounding data, enhancing predictions' accuracy and reliability. This research endeavors to broaden the application of numerical and analytical calculations in real-world practices, employing elastoviscoplastic soil models to design structures on weak foundations.