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Application of vertically installed columnar materials made of natural gravels or crushed aggregate is one of the commonly implemented practices to improve the performance of soft clay grounds under footing load. Alternative materials like cinder gravel also plays a reinforcing role when blended with soft clay. However, information on the precise extent to which a vertically installed cinder gravel column is effective in improving the properties of a clay foundation and its potential response to the permanently applied footing load has not been well documented in the literature. Hence, the current study specifically aimed at evaluating the effectiveness of geotextile-encased cinder gravel column in improving deformation and bearing capacity of soft clay ground. The experimental model which considered installation of a single geotextile-encased cinder gravel column into soft clay was considered. A cylindrical steel container was used in designing the experimental test. The container was filled with clay soil and the cinder gravel column was vertically installed through a replacement method. Finding of the study revealed that ultimate load-bearing capacity of the soft clay foundation after being reinforced with conventional cinder gravel was 1.85 times that of the untreated soft clay soil. The load-carrying capacity of the clay soil decreased with increment in diameter of the column whereas it is directly related to the volume replacement ratio. With regard to directional improvement, the vertical reinforcement performs better than the horizontal geotextile strips in cinder gravel column from bearing capacity improvement view point. In lessening settlement, however, application of horizontal geotextile discs at spacing ranging between half- and full-column diameter overweighs performance of the vertical encasement. In summary, application of geotextile encasement to the top 75% of the clay thickness is sufficient to come up with optimum improvement in bearing capacity and encasing the entire thickness is not necessarily required. [ABSTRACT FROM AUTHOR]

Application of vertical drains in soft clay soils is a common practice widely known to facilitate the consolidation rate. To overcome the adverse impact of a long-lasting consolidation process, highly permeable materials such as sand and crushed aggregates are used as drains. However, limited information exists regarding the applicability of scoria gravel as a vertical drain that no concisely documented information is observed in the literature. This study hence aimed at investigating suitability of scoria as a vertical drain in perpetuating the consolidation process of soft clay under highway embankment. Finite element-based numerical simulation was used to model the drain. The model was carried out by using 3D version of Plaxis software. In order to incorporate the effect of gradual load increment on the consolidation rate, the staged construction approach was employed. Both the square and triangular installation patterns were considered in the model in order to explore the critical effects of the drain installation pattern on the rate of consolidation. The numerical analysis also included varying dimensions of the vertical drain so as to investigate the effects of the dimension parameters of the vertically installed scoria drains. The conducted numerical analysis revealed that the rate of consolidation was considerably accelerated with provision of a group of scoria drains. With increase in the diameter of the drain, the consolidation rate increases, whereas the consolidation rate is inversely related to increase in drain spacing. For the drain installed at a spacing of 2 m, a diameter of 0.4 m, and a length of 8 m any arbitrary settlement magnitude is achieved 25 days earlier than the case without drains. Besides, incorporation of scoria drains lessens the pore pressure developed. The comparative analysis conducted on the effect of drain arrangement revealed that no considerable difference was witnessed in the performance of the square and triangular installation patterns even though the consolidation rate remains slightly faster in the case of the triangular installation pattern. [ABSTRACT FROM AUTHOR]

Engineering structures built on soft and compressible soils are often subjected to a long-lasting consolidation settlement. It is difficult to achieve an acceptable level of consolidation during the first few years/days of operation. Similarly, the culvert structure provided at station km 159 + 112 of the Awash-Kombolcha-Hara Gebeya Railway Project, Ethiopia, was situated along the route traversing soft clay ground of significant thickness. For the intention of reducing consolidation time and lessening the precarious impact of the postconstruction settlement, the soft clay ground was treated with preloading and prefabricated vertical drains. However, the culvert structure is currently undergoing consolidation settlement with varying magnitudes. The vertical deformation of the culvert site is monitored using settlement gauges installed at the site. Monitoring of the site continued for 120 days to track the extent of ground deformation at the culvert site. However, because of environmental and technical factors like calibration and alignment errors, the settlement instrument readings may be exposed to uncertainties, which may probably affect the safety of the culvert structure. Hence, the study is primarily aimed at evaluating the field deformation performance of the culvert structure for 120 days of the consolidation period through numerical analysis and comparing the result with the site settlement monitoring data. The critical effect of wick drain and some key parameters (fill thickness and wick drain spacing) were also scrutinized. Finite element-based numerical modeling was conducted by using the 2D GeoStudio/SigmaW package, and the Modified Cam Clay Constitutive model was adopted. The conducted numerical analysis revealed that the finite element result has good agreement with the field settlement monitoring data with only 0.0305 m maximum deviation in which the numerical analysis result remained greater for majority of the consolidation time. It can also be inferred that granular fill thickness and wick drain spacing were the key parameters impacting the settlement of the culvert structure. [ABSTRACT FROM AUTHOR]