Techniques to safeguard the underground tunnels against surface blast load

Due to the growth of underground tunnels, the safety of structures under blast loading is a major threat. Therefore, this paper focused on various techniques such as tunnel burial depth, tunnel shape, tunnel lining materials and varying the location of the blast source to safeguard underground tunnels against blast load using numerical analysis. The behaviour of concrete, reinforcement steel and the soil were incorporated by using the different constitutive model available in ABAQUS v. 2020. The predicted results were compared with the experimental results available in literature and found in close agreement. It is concluded that the layering of soil filling and depth of the burial of the tunnel found to be most important in case of external blast, whereas the stress bearing capacity of the concrete found to be important in case of internal blast. It is also concluded that the circular shape tunnel is one of the best performing tunnels

The effects of dam-reservoir interaction on the nonlinear seismic response of earth dams

The objective of this study is to investigate the effects of dam–reservoir interaction (DRI) on the nonlinear seismic response of earth dams. Although DRI effects have for long been considered as insignificant for earth dams, that conclusion was mainly based on linear elastic investigations which focused only on the acceleration response of the crest without examining the seismic shear stresses and strains within the dam body. The present study explores further the impact of DRI focusing on the nonlinear behavior of earth dams. The effects of reservoir hydrodynamic pressures are investigated in terms of both seismic dam accelerations and nonlinear dynamic soil behavior (seismic shear stresses and strains). It is shown that although dam crest accelerations are indeed insensitive to DRI, the stress and strain development within the dam body can be significantly underestimated if DRI is ignored.</p

Load Transfer In Soil Anchors – Finite Element Analysis Of Pull-Out Tests

Soil anchors are widely used to stabilise soils and provide additional support to earth retaining structures. They are found in critical civil infrastructure such as transportation networks like highways and railways. Understanding their behaviour is important for the safety of these structures and the public. Therefore, careful design with appropriate soil parameters is required to ensure their efficiency.Finite element (FE) analysis is a powerful engineering tool that is able to predict the response of soil anchors. Various types of FE models are used, such as 2D axisymmetric or full 3D solid continuum and the more practical load-transfer FE analysis. Usually relevant field or laboratory tests are required in order to define the model parameters. Field pull-out tests are one of the most common and reliable type of such tests.This study presents field data from such field tests that were carried out on in-situ ground anchor systems, using strain gauges to evaluate the changes in the variations of axial load and skin friction along the nail during the tests. The results of these field tests provide details about the development of skin friction with induced displacements, thus offering the opportunity to perform load-transfer finite element analyses of the soil anchor.A FE model based on the load-transfer approach is developed to analyse this soil-structure interaction problem. A number of FE analyses using parameters derived from the field tests are run to validate the finite element load-transfer models which are compared with the field test results and exhibit an excellent agreement

The use of distributed fibre-optic strain data to develop finite element models for foundation piles

Distributed fibre-optic strain sensing using BOTDR or BOTDA is an instrumentation technique that offers a spatially-continuous data. This is superior to more conventional discrete point-based sensors which provided limited monitoring information at pre-specified location points. The availability of a distributed strain regime offers a number of advantages when it comes to studying soil-structure interaction problems such as foundation piles. Distributed strain profiles from foundation piles are useful in understanding the actual behaviour of these structures and can provide important information to develop relevant computational finite element models. Axial pile strains can be integrated to obtain absolute pile displacements or can be differentiated to get pile shaft friction values. This paper describes the use of BOTDR/A in monitoring axially-loaded foundation piles and presents recent case studies in London. It also proposes an approach to develop finite-element load-transfer models for future analysis and design of foundation piles