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Prediction of strength parameters of sand combined with three dimensional components using artificial neural networks
Conventional reinforcements used for soil strengthening are planar in nature. The concept of three dimensional reinforcements is gradually gaining popularity. Such reinforcements possess the inherent advantages of the conventional planar reinforcements. The additional protrusions on their surface adds to the passive resistance to shear deformation. In this study, a series of drained and undrained triaxial compression tests were performed on unreinforced and reinforced sands. The variables considered include the gradation of soil in terms of the effective grain size, volume ratio of reinforcement, reinforcement orientation, spacing and confining pressure. The results obtained were used to train two models, according to the testing conditions. The first model was used for predicting the peak shear stress in dry samples and the second predicted the peak shear in saturated samples. In each of these models, the output layer consisted of a single node i.e., peak shear. The results show that ensuring a proper training and a learning algorithm can help in developing an Artificial Neural Network (ANN) model that could serve as an effective tool in predicting shear strength improvement of sands reinforced with multi-directional inclusions. This would in turn help practising engineers to estimate the improvement in shear strength parameters before these 3D reinforcements are actually added to the soil.
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Effect of Suction History on the Small Strain Response of a Dynamically Compacted Soil
Small strain behaviour is a key indicator in the assessment of the performance of compacted fills. Compaction conditions i.e. initial moisture content and applied energy, govern compaction effectiveness and thus the structure and matric suction of compacted soil. During the service life of earth structures, they experience changes in hydraulic behaviour owing to climatic changes. While the results of previous research studies indicate that the effect of changes in suction on the dynamic response is significant, only limited research has been engaged in the assessment of the effect of post-compacted changes in suction induced by periods of intensive precipitation (i.e. wetting) and drought (i.e. drying). The seasonal fluctuations of moisture reflected in the soil’s suction history have an important impact on the geomechanical performance of compacted soil.
In this paper, the aspects related to the effect of suction history of a compacted silty sand soil subjected to cycles of wetting and drying are described. The results not only confirm the importance of the recent suction ratio (or CSR) in governing the mechanical response at small strain but also suggest that subsequent wetting-drying cycles further induce hysteretic changes, particularly when following the wetting paths.
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A partially drained model for soft soils under cyclic loading considering cyclic parameter degradation
Cyclic loading induced foundation instabilities including loss of bearing capacity and excessive plastic deformation of the subgrade are among the major concerns for the design and construction of transport infrastructure. There were limited studies on the modelling of cyclic loading of soft soils due to its complexities compared to static loading. In this study, a model for soft clays under partially drained condition subject to cyclic triaxial loading has been developed based on the Modified Cam-clay theory. The yield surface contraction for elastic unloading was governed by two additional cyclic degradation parameters to the modified Cam-clay model. This model was validated using the results of a series of undrained and partially drained cyclic triaxial loading tests on kaolin. A good agreement between the numerical prediction and the measured excess pore pressures was obtained. Furthermore, the factors which influence the cyclic performance of soft soils, e.g. the cyclic stress ratios, the anisotropic consolidation stress and the coefficient of consolidation were investigated. This model was then applied to the consolidation of soft soils under cyclic loading, which represents the application of partially penetrated vertical drains for road and rail infrastructure, at the soft soil sites for a rail project in Sandgate, NSW. The objective of the partially penetrated drains within this deep estuarine soil layer was to consolidate the shallow soft clays and stabilise the new built tracks.
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Numerical simulation of soft ground improved with cement
This paper examines, using a numerical model based on the finite element method, the undrained bearing capacity of shallow circular footings on soft ground improved with deep cement mixing. Guidelines are given to identify the importance of the degree of cementation on the bearing capacity of shallow footings. Using a bearing capacity improvement factor, the influence of the degree of cementation and the extent of the cemented region on bearing capacity has been investigated. Finally, the performance of deep cement-mixed columns has been investigated using the numerical model. The results indicate that there exists an optimum length to diameter ratio for the deep mixed cement columns and this optimum ratio depends on the degree of cementation of the soil.
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Numerical simulation of soft ground improved with cement
This paper examines, using a numerical model based on the finite element method, the undrained bearing capacity of shallow circular footings on soft ground improved with deep cement mixing. Guidelines are given to identify the importance of the degree of cementation on the bearing capacity of shallow footings. Using a bearing capacity improvement factor, the influence of the degree of cementation and the extent of the cemented region on bearing capacity has been investigated. Finally, the performance of deep cement-mixed columns has been investigated using the numerical model. The results indicate that there exists an optimum length to diameter ratio for the deep mixed cement columns and this optimum ratio depends on the degree of cementation of the soil.