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Abstract This paper develops a numerical procedure for investigating settlement induced by circular tunnels in soft soils. The numerical procedure aims to simulate the movement and relaxation of the soil around the shield and lining annulus that occurs due to the overcutting and grouting of the tunnel void by a tunnel boring machine. A stress relaxation technique that progressively reduces the tunnel support pressure from a specific amount until a point of failure is detected. For three separate stages before this point of failure, the surface settlement data is exported for analysis. Using a regression of the commonly used Gaussian equation on the settlement data, i x values can be determined for each case. This is done for a number of geometry and soil stiffness and strength ratios which will cover the most practical range for soft cohesive soils. The results of this study are quite positive, settlement results compare well with previous experimental and observational results. Design charts using dimensionless ratios have therefore been presented. [ABSTRACT FROM AUTHOR]

• A state of art approach to study 3D sinkhole stability due to underground cavities. • Advanced 3D finite element limit analysis for circular and square openings. • Rigorous 3D upper bound and lower bound solutions of active and passive trapdoors. • Comprehensive design charts, tables and equations presented. • Stability numbers and factors of safety for a wide range of design parameters. There has been an increasing interest in the study of sinkhole occurrences due to frequent underground activities. Most of the research direction are related to the detection of the underground cavity using geophysics techniques. Very little is done in the area of soil stability. This paper investigates the three-dimensional stability of circular and square trapdoors. The combined effect of surcharge pressure, soil weight and supporting pressure is considered in Broms and Bennermarks' original stability number for a cohesive soil. The study uses the finite element limit analysis to compute upper bound and lower bound minimum supporting pressures for both collapse and blowout scenarios. The obtained critical stability numbers and factor of safety are compared with other published results in both two- and three- dimensions. Design charts, tables and equations are presented to cover a wide range of design parameters and a practical example is introduced to illustrate how to use the them. [ABSTRACT FROM AUTHOR]

This paper investigates the use of stability factors to estimate tunnel heading pressures. The primary method adopted is a conventional equation based on the soil property and stability factors, analogous to the bearing capacity factors (N c , N s and N γ) of strip footings. The finite element limit analysis (FELA) is employed to determine rigorous upper bound (UB) and lower bound (LB) solutions of stability factors (F c , F s and F γ), which are functions of the depth ratio (C/D) and soil internal friction angle (Ø). The obtained results are compared and validated by using the finite difference analysis as well as other available published results in the literature. A number of examples are illustrated on how to use the factors to estimate tunnel heading pressures. [ABSTRACT FROM AUTHOR]

• Novel coupled approach for undrained stability of rectangular tunnels. • Isogeometric analysis and deep learning ensure accuracy and efficiency. • High accuracy with mean squared error of 10−6 in predicting tunnel stability. The problem considered in this paper is for the stability evaluation of a rectangular tunnel in undrained clay during lining process. The approach adopted involved the use of isogeometric analysis (IGA) and the upper bound limit analysis formulation for the stability analysis. For the geometrical representation, B-spline basis functions are used to generate a set of B-spline surfaces that define the boundary of the soil domain, allowing for the exact representation of the tunnel geometry. The upper bound limit analysis is then formulated as a second-order cone program (SOCP), which can be solved by using a numerical optimization algorithm. The accuracy and reliability of the proposed method are validated by comparing the results with those published in previous studies. Furthermore, a large dataset is generated by randomly varying the input parameters, and a deep learning model is trained to learn the dataset. The deep learning model is trained using the mean squared error (MSE) metric, which yields an MSE as small as 10−6, indicating the high accuracy and precision of the proposed approach. Feature analysis and Partial Dependence Plots (PDPs) were used to gain insights into physical behavior by identifying important variables and understanding their individual and collective effects. In conclusion, the coupling of IGA and upper bound limit analysis provides a comprehensive and reliable solution to the stability of rectangular tunnels. The results obtained from this approach are accurate and can be achieved with reduced computational cost, making it an attractive approach for practical engineering applications. This approach can be used as a basis for future research on tunnel and tunnel stability analysis and may be extended to other types of soil structures under complex geometries. [ABSTRACT FROM AUTHOR]