Uplift resistance of horizontal strip anchors in sand: a cavity expansion approach

This letter presents an analytical cavity expansion theory-based method for predicting peak uplift resistance of shallow horizontal strip anchors buried in sand. Based on an analytical two-dimensional stress solution for loading analysis around a cylindrical cavity, the method was developed by assuming that the peak anchor uplift resistance can be approximated by the cavity breakout pressure. In the new cavity expansion model, the ultimate failure is reached once the plastic zone develops to the ground surface, and the biaxial state of in-situ ground stresses is taken into account. A database consisting of 75 model tests on shallow strip anchors in sands was compiled to valid the new method. The predicted results and measured data are in reasonable agreement, with a mean over-prediction of the peak uplift resistance by 1.6%. The reliability of the new solution was also checked by comparing with other commonly used analytical solutions. It is shown that the present solution can provide a simple analytical tool for predictions of the peak uplift resistance of strip anchors in sand while a sliding-block failure mechanism dominates

The performance of stochastic designs in wellbore drilling operations

© 2018, The Author(s). Wellbore drilling operations frequently entail the combination of a wide range of variables. This is underpinned by the numerous factors that must be considered in order to ensure safety and productivity. The heterogeneity and sometimes unpredictable behaviour of underground systems increases the sensitivity of drilling activities. Quite often the operating parameters are set to certify effective and efficient working processes. However, failings in the management of drilling and operating conditions sometimes result in catastrophes such as well collapse or fluid loss. This study investigates the hypothesis that optimising drilling parameters, for instance mud pressure, is crucial if the margin of safe operating conditions is to be properly defined. This was conducted via two main stages: first a deterministic analysis—where the operating conditions are predicted by conventional modelling procedures—and then a probabilistic analysis via stochastic simulations—where a window of optimised operation conditions can be obtained. The outcome of additional stochastic analyses can be used to improve results derived from deterministic models. The incorporation of stochastic techniques in the evaluation of wellbore instability indicates that margins of the safe mud weight window are adjustable and can be extended considerably beyond the limits of deterministic predictions. The safe mud window is influenced and hence can also be amended based on the degree of uncertainty and the permissible level of confidence. The refinement of results from deterministic analyses by additional stochastic simulations is vital if a more accurate and reliable representation of safe in situ and operating conditions is to be obtained during wellbore operations.Published versio

Oxidations with permanganate in a strong alkaline medium: Calculation of deprotonation constant

417-422The process 2MnO + substrate -> + 2MnO + product, has been studied employing the substrates methanol, ethanol, n-butanol and formaldehyde in aqueous solutions of [alkali] in the region of 0.1-2.0 mol dm-3. The reactive species is the alkoxy anion and the deprotonation constant (KB) of these substrates can be calculated from the kinetic data, which are in good agreement with literature data obtained by other methods. The procedure seems to be applicable for the determination of the deprotonation constant of other organic substrates containing a hydroxyl group. A mechanism based on electron abstraction from the alkoxy anion and simultaneous nucleophilic attack by OH- has been proposed

Analysis of the Oedometer Test Results using a New Method

The oedometer test, which represents the in situ stress conditions (typically called k0 conditions), is one of the most important geotechnical engineering laboratory tests. For any geotechnical engineering application, k0 is often used to calculate the lateral stress of the at-rest stress state. Most of the existing analytical expressions for k0 suffer one or more of the following limitations: (1) they have unrealistic assumptions; (2) k0 was derived as a constant value for the very high stress state, but implicitly applied to the whole stress range; (3) k0 equation is often implicit and complicated. In this paper, a new method is used for the data analysis and prediction of k0 value, which overcomes all of these limitations and was derived upon the definition of k0 condition without any additional assumption. In addition, the expression can be adopted for any critical state constitutive model for saturated soils. The modified Cam clay model was used to demonstrate the application of the proposed expression. Using this new method, the lateral stresses can be calculated for the oedometer test, and therefore, the stress paths are predicted and compared with the available methods. For verification purposes, the lateral strain increments are predicted and compared to zero. Finally, to check the accuracy of the new method, the predicted void ratio using the new method are compared to the experimental results in the v-logσv′ plane. A good agreement is reached between the measured and predicted specific volumes. Calculations indicated that a coefficient of determination greater than 99% is reached between the measured and predicted void ratios