Numerical investigation into the effect of various surcharge loadings on propped wall excavations and embankments

Several guidance and formulation have been developed in the literature to account for the analysis of external surcharges adjacent to a propped excavation but less attention has been paid to the presence of sloping ground or embankments. However, CIRIA C760 states that the actual ground profile should be modelled and analysed as a series of surcharge loading over the extent of the active side of the wall. In this research, two braced excavation models were analysed of which one was the actual ground profile and the second with a series of surcharge loading representing the embankment adjacent to the excavation. The accuracy, efficiency, and conservation of the proposed approaches were examined on a propped cantilever wall excavation using a finite element geotechnical analysis software PLAXIS 2D. The models were analysed and examined in terms of the bending moment and deflection of the diaphragm wall and the prop load, the model with the actual ground profile was also investigated for any thrust load on the support system should the embankment or sloping ground fail in shear. The results were presented, and comparisons were made. Merits and advantages of the proposed numerical approach were discussed

Effects of various surcharge loading conditions on the stability of soil slopes

The stability of soil slopes is a theme which has great significance within the field of civil engineering, this paper will focus on the analysis of soil slopes under varying surcharge loads. There are two main methods used in the analysis of soil slopes the first is the most commonly used method, the limit equilibrium method (LEM) and the second is a finite element method (FEM) which is becoming more commonly used due to three-dimensional analysis aspect. It is suggested by [1] that the factor of safety is greater for three-dimensional analysis compared to that of two-dimensional analysis. As the accuracy of software packages continues to improve (FEM) will be more commonly used by civil engineers. In this study both analysis methods are used to analyse the effects on various surcharge loading conditions on the stability of soil slopes. By using two different approaches to the analysis of different surcharge conditions, two sets of data are produced both of which can be compared to validate the work. As this topic is widely studied previous papers with a similar research question where used as reference to compare results [2, 3]. The purpose of this study is to highlight the importance of understanding the effects of surcharge loading, it can be seen from previous studies that the focus is generally based on other factors such as the cohesion of the soil, the slope angle, the friction angle and the soil parameters. Whilst they are all individually important, the surcharge loading conditions are often neglected never investing the effects different loads would have on the stability of the soil slope. This shows a gap in the current field of study which this paper will investigate

An evolutionary modelling approach to predicting stress-strain behaviour of saturated granular soils

Purpose: To develop a unified framework for modelling triaxial deviator stress - axial strain and volumetric strain – axial strain behaviour of granular soils with the ability to predict the entire stress paths, incrementally, point by point, in deviator stress versus axial strain and volumetric strain versus axial strain spaces using an evolutionary-based technique based on a comprehensive set of data directly measured from triaxial tests without pre-processing. 177 triaxial test results acquired from literature were used to develop and validate the models. Models aimed not only to be capable of capturing and generalising the complicated behaviour of soils but also to explicitly remain consistent with expert knowledge available for such behaviour. Methodology: Evolutionary polynomial regression was used to develop models to predict stress - axial strain and volumetric strain – axial strain behaviour of granular soils. EPR integrates numerical and symbolic regression to perform evolutionary polynomial regression. The strategy uses polynomial structures to take advantage of favourable mathematical properties. EPR is a two-stage technique for constructing symbolic models. It initially implements evolutionary search for exponents of polynomial expressions using a genetic algorithm (GA) engine to find the best form of function structure, secondly it performs a least squares regression to find adjustable parameters, for each combination of inputs (terms in the polynomial structure). Findings: EPR-based models were capable of generalizing the training to predict the behaviour of granular soils under conditions that have not been previously seen by EPR in the training stage. It was shown that the proposed EPR models outperformed ANN and provided closer predictions to the experimental data cases. The entire stress paths for the shearing behaviour of granular soils using developed model predictions were created with very good accuracy despite error accumulation. Parametric study results revealed the consistency of developed model predictions, considering roles of various contributing parameters, with physical and engineering understandings of the shearing behaviour of granular soils. Originality/Value: In this paper, an evolutionary-based data-mining method was implemented to develop a novel unified framework to model the complicated stress-strain behaviour of saturated granular soils. The proposed methodology overcomes the drawbacks of artificial neural network-based models with black box nature by developing accurate, explicit, structured and user-friendly polynomial models, and enabling the expert user to obtain a clear understanding of the system

A comparative analysis of the stability of homogeneous and non- homogeneous soil slopes subject to various surcharge loading conditions

Slope stability is a topic of great importance within the scope of civil engineering, this study investigates the differences between homogeneous and non-homogenous soil slopes when various surcharge loading conditions are applied. To analyze slope stability the finite element method is used, this method uses the shear strength reduction method. This method gradually reduces the cohesion and friction angle of the soil until failure occurs in the model. Typically, the limit equilibrium method is used by civil engineers, which splits the model into slices to identify the failure mechanisms and the factor of safety. However, as the software improves, and the accuracy of analysis increases, finite element analysis will become the more commonly used method [1, 2]. In this study 6 different models are used in the analysis, three homogenous soil slopes and three nonhomogeneous soil slopes to aid in the analysis, the soil properties were obtained from [3]. Each model was subject to surcharge loading, which was incrementally increased until failure occurred, recording the factor of safety at each point. The results gathered suggest that point loads caused failure in models to occur much quicker than surcharge loading from a uniformly distributed load, however, the failure area is much smaller. The comparison of homogenous and non-homogenous soil slopes shows that stability is dependent on three key properties including cohesion, unit weight, and friction angle, with the properties of the soil slope influencing the maximum surcharge loading that can be applied to a model. The results indicate that homogenous soils can withstand higher surcharge loading conditions compared to that of nonhomogeneous soil slopes, except for homogenous models consisting of silty sand

The effect of cut-off wall angle on seepage and uplift pressure under dams

Seepage under dams can result in high uplift pressure experienced usually under the downstream of the dam which may lead to instability and potentially the failure of the dam. Cut-off walls are the primary solution to minimize the effects caused by the flow of water, as they extend the flow path which results in decreasing seepage, as well as uplift pressure and exit gradient. (Rice & Duncan, 2010) This study aims to research how designing a cut-off wall at an angle under a concrete dam increases its efficiency. The angles will vary from 0° to 180°, progressively increasing at an interval of 30°. Following that, two walls will be designed originating from the same point at the nose of the dam, as well as another design where the walls are under both ends of the structure. The modal analysis will be completed using the finite element geotechnical software – PLAXIS 2D, as it has proved to be extremely precise in discharge analysis specifically (Galavi, 2010). A typical impervious concrete dam will be designed in the program in a uniform soil profile with the only variable being the angle of the cut-off wall and its originating point. This is done to put the attention simply on the discharge value that is obtained from the software. The feasibility of the construction will always be taken into account, as this study intends to complete research by taking a realistic and economic approach. The results show that seepage is smallest when the cut-off wall is positioned at a 60° angle, as in this position water has to travel the furthest distance compared to the other configurations. In terms of uplift pressure, the dam experienced the least pressure when the wall is at 120°. As seepage and uplift pressure are the two main factors playing significant roles in the stability of dams – two combined configurations were introduced into the model in order to minimize both values; one being the addition of the 60° and 120° angle walls originating at both ends of the dam, and the other where the two formerly mentioned walls originated from the same point (the heel of the dam). The configuration where the two walls are constructed under the heel and the toe show a significant decrease in seepage, as well as uplift pressure at the toe. When the two walls are both constructed originating from the same point (heel) – seepage is determined to be lower compared to when only one wall is considered, however a significant reduction in uplift pressure is not present. When taking all data into account, the most feasible, economical and practical solution to decreasing seepage and uplift pressure considerably appears to be the arrangement where a 60° cut-off wall is constructed at the heel of the dam and 120 ° wall at the toe of the dam

Relationship between shallow foundation shape and contact area, and the settlement in granular soils

The aim of this investigation is to discover the effects of foundation shape and contact area on foundation settlement. There is little research at the current time which relates the increase in size or scale effects to the settlement, with current research in the subject area being much more focused on bearing capacity, [1], [2]. This is carried out using Oasys [3], a geotechnical software that predicts the settlement of foundations when a pressure load is applied to a foundation. The results showed a clear relationship between area of foundation and maximum settlement. As expected, as area increases so does the settlement, however, it is seen that there are clear differences between the effects from different shapes of foundations in terms of settlement values. It was discovered that the data shows similar patterns between different shapes, however the values for each shape do vary

Lateral load bearing capacity modelling of piles in cohesive soils in undrained conditions; an intelligent evolutionary approach

The complex behaviour of fine-grained materials in relation with structural elements has received noticeable attention from geotechnical engineers and designers in recent decades. In this research work an evolutionary approach is presented to create a structured polynomial model for predicting the undrained lateral load bearing capacity of piles. The proposed evolutionary polynomial regression (EPR) technique is an evolutionary data mining methodology that generates a transparent and structured representation of the behaviour of a system directly from raw data. It can operate on large quantities of data in order to capture nonlinear and complex relationships between contributing variables. The developed model allows the user to gain a clear insight into the behaviour of the system. Field measurement data from literature was used to develop the proposed EPR model. Comparison of the proposed model predictions with the results from two empirical models currently being implemented in design works, a neural network-based model from literature and also the field data shows that the EPR model is capable of capturing, predicting and generalising predictions to unseen data cases, for lateral load bearing capacity of piles with very high accuracy. A sensitivity analysis was conducted to evaluate the effect of individual contributing parameters and their contribution to the predictions made by the proposed model. The merits and advantages of the proposed methodology are also discussed