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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.

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In recent years, the majority of the construction projects executed in Addis Ababa city experienced a varying magnitude of time overrun in which the projects become late in their completion. Due to different problems encountered during the inception, design, and implementation phases, the projects are exposed to unexpected time overruns that in turn affect the overall performance of the projects. It is hence very essential to identify the actual causes of delay in order to minimize or avoid the corresponding adverse impacts. Therefore, this study primarily aimed at investigating and scrutinizing the potential factors causing project time overrun in the city so that the influential factors can be identified and the applicable remedial measures can possibly be forwarded. For the purpose of data collection, the study applied a semistructured questionnaire survey. The questionnaire was distributed to 121 respondents comprising practitioners and professionals actively working in the construction industry. Fifty-four delay-causing factors were identified and grouped under ten categories according to the similarity of their origin. In order to identify the most significant factors, severity analysis based on the principle of relative importance index was carried out. Accordingly, the top most significant and least significant factors were identified. The top four most influential factors identified were reluctance of consultants, inaccurate estimation of contract duration, delay in approvals and late decision making, and slow mobilization of labor whereas inadequacy of allocated funds, low motivation, and absence of incentives to contractors were the three least significant causes identified. So as to curb the adverse impact of the factors, the application of a detailed work breakdown structure, proper responsibility assignment, earned value principle, and project software were proposed as remedial measures to be implemented. The finding of the study will alarm the key players and practitioners engaging in the city’s construction industry to focus on managing the severe factors.

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.

Mat foundations are most typically used in locations featuring weak soils such as soft clays and silts, particularly when building in demanding geotechnical conditions. Because of their poor engineering characteristics and significant difficulties associated with workability, these soils are often removed or avoided by excavating down to a specific depth. However, if thick layers are present, their removal becomes unpractical, costly, and creates inconvenience during construction. To overcome this issue, various reinforcement strategies can be adopted. In this study, the use of stone columns under mat foundations was investigated via numerical modeling. Two scenarios were compared: one in which stone columns were installed without any soil removal and another in which a layer of soft ground was removed and the foundation was installed without any ground treatment. Numerical results showed the clear beneficial effect of stone columns, which can significantly reduce settlements even in the presence of a thick deformable soil layer.

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