Learning by Identification of Mistakes in Workings in Engineering Modules

10.1080/14703297.2016.1180256Innovations in Education and Teaching International55134-4

Report on industrial attachment with Future Builder Pte Ltd

This report records the key tribute of the author?s industrial training and reflections. The content is segregated into 3 core areas of duties and responsibilities; mainly Sales and Marketing, On-Site Training and Inspection, and Project Management

Robustness of remediation measures against liquefaction induced manhole uplift under mainshock-aftershock sequence

Earthquakes generally consist of one mainshock and subsequent aftershocks. Although effects of aftershocks following the mainshock on surface structures has been studied extensively, similar studies on underground structures are rarely reported in the literature. With the fast advances in underground space development, robustness of remediation measures against underground structures uplift induced by soil liquefaction shall be examined to ensure their functioning subject to not only the mainshock but also the subsequent aftershocks. This paper studies the uplift behaviour of a conventional manhole subjected to the mainshock-aftershock sequence. It was found that, in the ground that becomes liquefied during the mainshock, manholes become more vulnerable when faced with aftershocks. Due to this reason, some of the previously proposed remediation measures, such as increasing the manholes’ self-weight, roughening the sidewalls, were examined using centrifuge modeling in this study. It was found that such measures had little effect in the aftershocks despite their effectiveness in the precedent mainshock. In contrast, the methods that mitigates manhole uplift by enhancing the manhole’s base permeability, demonstrated better performance in the aftershock than in the mainshock, indicating its promising application potential in future mitigation design

Pseudo-static/dynamic solutions of required reinforcement force for steep slopes using discretization-based kinematic analysis

This paper presents a procedure for assessing the reinforcement force of geosynthetics required for maintaining dynamic stability of a steep soil slope. Such a procedure is achieved with the use of the discretization technique and kinematic analysis of plasticity theory, i.e. discretization-based kinematic analysis. The discretization technique allows discretization of the analyzed slope into various components and generation of a kinematically admissible failure mechanism based on an associated flow rule. Accordingly, variations in soil properties including soil cohesion, internal friction angle and unit weight are accounted for with ease, while the conventional kinematic analysis fails to consider the changes in soil properties. The spatial–temporal effects of dynamic accelerations represented by primary and shear seismic waves are considered using the pseudo-dynamic approach. In the presence of geosynthetic reinforcement, tensile failure is discussed providing that the geosynthetics are installed with sufficient length. Equating the total rates of work done by external forces to the internal rates of work yields the upper bound solution of required reinforcement force, below which slopes fail. The reinforcement force is sought by optimizing the objective function with regard to independent variables, and presented in a normalized form. Pseudo-static analysis is a special case and hence readily transformed from pseudo-dynamic analysis. Comparisons of the pseudo-static/dynamic solutions calculated in this study are highlighted. Although the pseudo-static approach yields a conservative solution, its ability to give a reasonable result is substantiated for steep slopes. In order to provide a more meaningful solution to a stability analysis, the pseudo-dynamic approach is recommended due to considerations of spatial–temporal effect of earthquake input. Keywords: Geosynthetics, Pseudo-static/dynamic approach, Discretization technique, Discretization-based kinematic analysis, Reinforced soil, Seismic stabilit

Reply to the discussion on “effect of soil spatial variability on failure mechanisms and undrained capacities of strip foundations under uniaxial loading” by Zhe Luo

The authors recently published work on failure mechanisms and undrained capacities of strip foundations on spatial variable soils (Shen et al., 2021, called the original paper hereafter). In order to improve the computational efficiency of random finite element analysis (RFEA), a non-uniform mesh was employed in the original paper. Luo (2021) stated that such non-uniform mesh resulted in a different degree of variance reduction over the random field (RF) and thus disobeyed the stationarity of the RF based on viewpoints of spatial averaging (SA) discretization method. However, as introduced in Section 3.2 in the original paper, the midpoint (MP) discretization method was used to discretize the RF, rather than the SA discretization method. Note that MP and SA are two very different methods for the discretization of RF in the RFEA. The material value for an element is represented by the RF value calculated at its centroid for the MP discretization method, whereas the material value for an element is represented by the spatial average of RF over the element for the SA discretization method. There is spatial averaging for SA, which results in significant variance reduction for a very coarse mesh. In contrast, there is no spatial averaging for MP, and thus no variance reduction (Tabarroki and Ching, 2019). Therefore, the discusser’s judgement based on viewpoints of the SA discretization method to a RF discretized by the MP method is not relevant

Modelling smear effect of vertical drains using a diameter reduction method

Vertical drains are used to accelerate consolidation of clays in ground improvement projects. Smear zones exist around these drains, where permeability is reduced due to soil disturbance caused by the installation process. Hansbo solution is widely used in practice to consider the effects of drain discharge capacity and smear on the consolidation process. In this study, a computationally efficient diameter reduction method (DRM) obtained from the Hansbo solution is proposed to consider the smear effect without the need to model the smear zone physically. Validated by analytical and numerical results, a diameter reduction factor is analytically derived to reduce the diameter of the drain, while achieving similar solutions of pore pressure dissipation profile as the classical full model of the smear zone and drain. With the DRM, the excess pore pressure u obtained from the reduced drain in the original undisturbed soil zone is accurate enough for practical applications in numerical models. Such performance of DRM is independent of soil material property. Results also show equally accurate performance of DRM under conditions of multi-layered soils and coupled radial-vertical groundwater flow

Soil deformation during monotonic and seismic pipe uplift in liquefiable soil

Journal of Pipeline Engineering14133-4