Shape optimisation of the support section of a tunnel at great depths

The shape optimisation of a cavity is typically performed without considering the previous support, which may significantly reduce the practical significance of such analyses. Even when an excavation section is optimised, failure of the surrounding rock in a tunnel cannot be prevented in the presence of excessive in situ stress. Thus, a support should be established to protect the stability of a tunnel from the failure of the surrounding rock. This study examines the optimal shape of the support that satisfies the optimisation criterion, which minimises the largest tangential stress along the inner edge of the support, for a specific net tunnel size and support strength. The optimisation process is to solve a series of forward problems using the conformal mapping method for a plane elasticity complex function. The tangential stress along the inner edge of the support is selected as the objective function, and the coefficients of the mapping function are considered as the design variables. The minimum value of the objective function is calculated based on the mixed penalty function method and the optimal support shape that satisfies the given constraints can be obtained. The stress state of an optimally shaped tunnel support is significantly improved compared to non-optimal configurations, and the stress concentration along the inner edge of the support is minimised.     

Applying bi-directional evolutionary structural optimisation method for tunnel reinforcement design considering nonlinear material behaviour

In the empirical methods for reinforcement design of underground excavations, an even distribution of rock bolts is generally recommended. This work proves that this design is not necessarily optimal and shows how the state-of-the-art reinforcement design could be improved through topology optimisation techniques. The Bidirectional Evolutionary Structural Optimisation (BESO) method has been extended to consider nonlinear material behaviour. An elastic perfectly-plastic Mohr–Coulomb model is utilised for both original rock and reinforced rock. External work along the tunnel wall is considered as the objective function. Various in situ stress conditions with different horizontal stress ratios and different geostatic stress magnitudes are investigated through several examples. The outcomes show that the proposed approach is capable of improving tunnel reinforcement design. Also, significant difference in optimal reinforcement distribution for the cases of linear and nonlinear analysis results proves the importance of the influence of realistic nonlinear material properties on the final outcome.     

Nature Conservation versus Scenic Quality：A GIS Approach towards Optimized Tourist Tracks in a Protected Area of Northwest Yunnan,China

Development of appropriate tourism infrastructure is important for protected areas that allow public access for tourism use.This is meant to avoid or minimize unfavourable impacts on natural resources through guiding tourists for proper use.In this paper,a GIS-based method,the least-cost path（LCP） modelling,is explored for planning tourist tracks in a World Heritage site in Northwest Yunnan（China）,where tourism is increasing rapidly while appropriate infrastructure is almost absent.The modelling process contains three steps：1） selection of evaluation criteria（physical,biological and landscape scenic） that are relevant to track decision; 2） translation of evluation criteria into spatially explicit cost surfaces with GIS,and 3） use of Dijkstra＇s algorithm to determine the least-cost tracks.Four tracks that link main entrances and scenic spots of the study area are proposed after optimizing all evaluation criteria.These tracks feature lowenvironmental impacts and high landscape qualities,which represent a reasonable solution to balance tourist use and nature conservation in the study area.In addtion,the study proves that the LCP modelling can not only offer a structured framwork for track planning but also allow for different stakeholders to participate in the planning process.It therefore enhances the effectivenss of tourism planning and managemnt in protected areas.     

Vertical dynamic response of an inhomogeneous viscoelastic pile

The vertical dynamic response of an inhomogeneous viscoelastic pile embedded in layered soil subjected to axial loading has been investigated. The interaction between pile and soil is simulated by a general Voigt model, one that has been demonstrated by earlier investigators to be capable of representing the plane strain case of soil adequately. The analytical solutions of pile responses in the frequency domain are obtained by using the (two-sided) Laplace transform. The corresponding semi-analytical solutions in the time domain for the case of a pile subjected to an instantaneous half-sine exciting force applied at the pile top are obtained via Fourier transform inversion. Using these solutions, a parametric study of the influence of the pile and soil properties on the vertical dynamic responses has been undertaken. It is shown that an abrupt variation of the soil properties with depth cannot yield evident reflection signal that may lead geotechnical engineers to assess the pile integrity wrongly from the velocity curve of the pile top, and the influence of viscosity of the pile material on the response is different from that of the damping of the soil surrounding the pile. The theoretical model developed in the present paper has also been validated in field studies, where it is shown by means of three examples that the solution developed in this study has been adequately verified by comparison of the theoretical pile model and field measurements of the dynamic responses.     

上海软土地区静力压桩若干问题的探讨

我国目前桩基设计规范对压桩施工过程中的桩身结构强度验算,尚未做出明确的规定,本文围绕这一问题讨论了以下问题:(1)进入持力层不同深度对压桩阻力的影响;(2)用静力触探比贯入阻力预估压桩阻力;(3)压桩施工过程中桩身结构强度的验算。     

Viscous fluid characteristics of liquefied soils and behavior of piles subjected to flow of liquefied soils

Lateral movement of sloping ground due to flow liquefaction has caused many pile foundations to fail, especially those in ports and harbor structures. Several researchers have found and verified that the behavior of liquefied soils can be simulated appropriately by modeling the liquefied soils as viscous fluid. In this study, the influence of the lateral movement of liquefied sloping ground on the behavior of piles was analyzed on the assumption that the flow of liquefied soils can be treated as viscous fluid flow. Sinking ball tests and pulling bar tests were performed to measure the viscosity of liquefied Jumoonjin sand. Then, the behavior of a single pile installed in liquefiable infinite slopes consisting of sand was investigated by numerical analyses. The liquefied sand behaved as non-Newtonian fluid, whose viscosity decreased with increasing shear strain rate. Furthermore, the flow of liquefied soils had a crucial effect on the stability of piles installed in the sloping ground.