15 research outputs found

    Translational upper bound limit analysis of shallow landslides accounting for pore pressure effects

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    Many rainfall-induced landslides are reported to be shallow. Therefore, when regional slope stability analysis, or landslide hazard mapping is carried out, simple approaches, such as the infinite slope model, are often used. However, the infinite slope model is known to underestimate the factor of safety due to the absence of boundary effects. More sophisticated methods that account for the boundary effects at the toe and head of the landslide are much more computationally expensive. In this paper upper bound limit analysis (UBLA) is presented with a novel failure mechanism which consists of a translational parallelogram in the middle slope and two log-spiral components at the slope crest and slope toe to capture the boundary effect. The new approach is derived for a full range of pore water pressure conditions and validated by finite element limit analyses. For shallow landslides the translational UBLA is found to outperform the conventional log-spiral UBLA. The results of a large parametric study using the translational UBLA are then used to develop a novel analytical shallow landslide model which retains the simplicity of the traditional infinite slope model, but yet improves accuracy considerably, making this an attractive alternative for routine analysis such as landslide hazard mapping

    Flood Suspended Sediment Transport: Combined Modelling from Dilute to Hyper-concentrated Flow

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    YesDuring flooding, the suspended sediment transport usually experiences a wide-range of dilute to hyper-concentrated suspended sediment transport depending on the local flow and ground con-ditions. This paper assesses the distribution of sediment for a variety of hyper-concentrated and dilute flows. Due to the differences between hyper-concentrated and dilute flows, a linear-power coupled model is proposed to integrate these considerations. A parameterised method combining the sediment size, Rouse number, mean concentration, and flow depth parameters has been used for modelling the sediment profile. The accuracy of the proposed model has been verified against the reported laboratory measurements and comparison with other published analytical methods. The proposed method has been shown to effectively compute the concentration profile for a wide range of suspended sediment conditions from hyper-concentrated to dilute flows. Detailed com-parisons reveal that the proposed model calculates the dilute profile with good correspondence to the measured data and other modelling results from literature. For the hyper-concentrated profile, a clear division of lower (bed-load) to upper layer (suspended-load) transport can be observed in the measured data. Using the proposed model, the transitional point from this lower to upper layer transport can be calculated precisely

    Numerical Modelling of Pipe Loading Using a Linear Interpolation Method

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    The movement of pipe in sand and clay are presented, formulated and analyzed using a linear interpolation method within the framework of elastic perfectly plastic Mohr Coulomb criteria and a new two-mechanism non-associative piecewise linear Drucker Prager formulation. The two mechanisms are found when the variation of shear strength due to mean effective stress is separated from that due to plastic deviatoric strain. The modelling framework is intended to show thedeformation and displacement of soil surrounding pipe. Furthermore it also describes the relationship between displacement and the force. Horizontal and vertical displacement are applied into pipe and they are modelled using finite element program, CRISP version 4. Slip element (interface) is attached in the vicinity of pipe to compare the deformation produced in this case with those without interface.Different material properties of cohesive and granular soil taken from laboratory tests are set in the model. All main parameters are recorded from lateral and horizontal loading test, as a part of the Collaborative Project on Soil/Pipe Interaction Mechanisms and Modelling. Application of the approach are presented and discussed with emphasis on identifying and optimizing some of the important factors that control the displacement of soil because of the movement of pipe. Several conclusions are drawn regarding the difficulties encountered in the numerical implementation. Illustrative numerical results 'for common geotechnical experiments on clay and sand using finiteelement software demonstrate the stable derivation of the two linear non associative Drucker Prager model

    Soil–water characteristic curves of gap-graded soils

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    Soil–water characteristic curves (SWCCs) of compacted mixtures of residual soil and gravel with different particle sizes were determined from laboratory tests. The study involved compacted mixtures of 50% residual soil by dry mass and 50% gravel of different particle sizes. The compacted mixtures were gap-graded in grain–size distribution with bimodal characteristics, but their SWCCs did not exhibit a bimodal characteristic. The gap-graded nature of the grain–size distribution of the mixtures did not affect the conventional sigmoidal shapes of the SWCCs. The pore-size distribution of the mixtures indicated that large pores within the compacted mixtures were filled with fine-grained soils. The air-entry value of the compacted mixtures was found to be high due to the high dry density of the specimens. The different particle sizes of the gravel used in the mixtures resulted in a variation of air-entry value of the mixtures. The dry density and coefficient of uniformity of the grain–size distributions were found to affect the air-entry values of the mixtures and the SWCC fitting parameters n and m, respectively. The variation of SWCC fitting parameters n and m showed significant correlations between grain–size distribution and pore-size distribution of the mixtures, whereas the SWCC fitting parameter a was not the air-entry value of soil