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To investigate the settlement behaviour under alternate vacuum preloading, a series of laboratory tests considering different influencing factors, such as vacuum pressure and alternating criterion, were conducted. Based on experimental data, a new settlement prediction model, which can synthetically reflect the effects of vacuum pressure, alternating criterion, and improvement time, was proposed. The prediction model took into account the influence of improvement depth and variations in vacuum pressure. The model was validated using several case studies and laboratory tests. Comparisons between the proposed model and layer-wise summation method results indicate that the calculated results of the proposed model are closer to the actual settlement with errors consistently less than 10%. The proposed model can conveniently and accurately predict the ultimate settlement of high water content dredger fill improved by vacuum preloading method. [ABSTRACT FROM AUTHOR]

An extensive geotechnical assessment of a hospital building under-crossed by twin tunnels is presented in this paper. The case study considered in the study is Phase III of Delhi Metro Gray line, which has been built recently using Tunnel Boring Machine. Finite element analysis was carried out to simulate the construction of two tunnels underneath the building, and the soil is simulated using an advanced constitutive model. The numerical model was validated against the field monitoring data, and the effect of tunnelling on the building deformation is also studied. Also, the comparison of building settlements with greenfield conditions is carried out. The study showed that the building influences the pattern of the settlement trough. Quantitative study of the settlement showed that there was no undue distress to the building due to the construction of twin tunnels, suggesting the safe crossing of twin tunnel below hospital building. [ABSTRACT FROM AUTHOR]

In this article, the ability of the artificial neural network-genetic algorithm (ANN-GA) to perform back analysis and predict maximum surface settlement in mechanised tunnelling is investigated. The required data of the ANN meta-model was generated using 150 three-dimensional finite-difference simulations. The global sensitivity analysis was performed on 19 parameters, including 17 geotechnical parameters of soil layers and 2 operational parameters of face pressure and grouting pressure. The predicted results using ANN were in good agreement with the numerical simulations so that R = 99% and rRMSE = 1.5% are obtained. Then, back analysis was performed using the ANN-GA hybrid algorithm and the geotechnical data of the monitoring point were updated using the maximum surface settlement monitored at this point. Also, for the geotechnical parameters considered in the design phase, using the same algorithm, the number of operational parameters required for optimal settlement was predicted. [ABSTRACT FROM AUTHOR]

Increasing tunnel excavations in dense urban areas faces the issue of accurately predicting tunnelling-induced surface settlement. The quality of those predictions closely depends on the choice of soil constitutive model. In this context, some widely used soil models in engineering practice not only fail to reproduce some characteristics of soil behaviour on the constitutive level but also lead to shallower settlement. This article studies the influence of the choice of the soil model on tunnelling-induced displacements through a case study. Three different soil models are used to simulate soil behaviour, namely the hardening soil model, the modified cam clay model and a proposed enhanced critical state model incorporating deviatoric and volumetric hardening. The proposed model is first validated on different triaxial tests and its features are especially highlighted for overconsolidated soils. This model is then compared to the other two models on tunnelling simulations. The results show great predicted settlement sensitivity to the choice of soil model. The proposed model engenders deeper settlement and, consequently, enables a more conservative design. Furthermore, parametric studies demonstrate significant disparities in the predicted displacements by the different soil models depending on the initial conditions and the stress relaxation ratio. [ABSTRACT FROM AUTHOR]

Based on a self-designed preloading consolidation model test system with vertical drains, saturated marine soft clay drainage consolidation and thermal drainage consolidation model tests were carried out at room temperature and high temperature, respectively. The variations in the soil temperature, excessive pore water pressure and surface subsidence over time were recorded in the tests. The results showed that thermal drainage consolidation can accelerate the consolidation rate of marine soft clay. Furthermore, the thermal drained consolidation method can increase the final settlement of the surface and enhance the treatment effect of marine soft clay ground. [ABSTRACT FROM AUTHOR]

Surface settlements developed in subway tunnels are one of the most important aspects in urban areas. Tunnelling through urban areas is principally related to soil movement around the tunnel and the surface settlement. The factors which affects this settlement may include soil conditions and tunnel parameters. This study investigates the effect of soil conditions and tunnel parameters on surface settlement in subway tunnels. A finite element numerical model has been developed for the analysis of surface settlement. In the model, geotechnical conditions and tunnel parameters were varied to calculate surface settlement. Geotechnical and tunnel parameters have been obtained from different case studies of Subway Tunnels across the world that were excavated in different types of soils below the groundwater level using different mechanism. This paper presents the regression analysis, which focuses on the soil properties and tunnel parameters. The influence of various soil properties has been determined for different condition using the finite element numerical model. The results demonstrate that geotechnical conditions and tunnel parameters significantly affect the surface settlement. Among these parameters, tunnel diameter is more sensitive to surface settlement. And the regression analysis enables an easy approach for predicting settlements in tunnel, and this prediction technique is very simple and reasonably accurate. [ABSTRACT FROM AUTHOR]

After studying the development law of surface settlement induced by excavation of foundation pit and the characteristics of the settlement curve, the paper introduces the idea of combination forecasting based on S-shaped growth curves and establishes the weight combination prediction model, which is applied to the actual project to verify the rationality of the model. Results show that the model cannot only reflect the settlement development process along with time, but also predict the surface settlement accurately. In addition, the combination prediction model is more superior to other single ones, and provides an effective and practical method for surface settlement forecasting. [ABSTRACT FROM AUTHOR]

In this paper, the nature of wall deformation and surface settlement for deep excavation in soft soil was studied. Excavation was carried out in eastern metro city of India in the bank of Hooghly River. This excavation was the part of underground metro station construction. Numerical analysis was performed to predict the soil behaviour during excavation. Accordingly, the most suitable excavation method was finalised. Vertical and horizontal deformations were measured during construction on adjacent area to ensure the safety of nearby existing structures. Predicted deformation was relatively high when compared with measured one. Back calculation from measured deformation shows the conservative estimation of stiffness during investigation and anisotropic soil behaviour. This study indicates that the numerical analyses can be very effective tools to predict the behaviour of soil during excavation with installation of support systems. Thus, it helps for necessary planning to ensure the safety of nearby structures. However, accuracy of such analysis depends on the judicial estimation of soil parameters. [ABSTRACT FROM PUBLISHER]