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Seismic design loads for tunnels are characterized in terms of the deformations imposed on the structure by surrounding ground. The free-field ground deformations due to a seismic event are estimated, and the tunnel is designed to accommodate these deformations. Vertically propagating shear waves are the predominant form of earthquake loading that causes the ovaling deformations of circular tunnels to develop, resulting in a distortion of the cross sectional shape of the tunnel lining. In this paper, seismic behavior of circular tunnels has been investigated due to propagation of shear waves in the vertical direction using quasi-static analytical approaches as well as numerical methods. Analytical approaches are based on the closed-form solutions which compute the forces in the lining due to equivalent static ovaling deformations, while the numerical method carries out dynamic, nonlinear soil-structure interaction analysis. Based on comparisons made, the accuracy and reliability of the analytical solutions are evaluated and discussed. The results show that the axial forces determined using the analytical approaches are in acceptable agreement with numerical analysis results, while the computed bending moments are less comparable and show significant discrepancies. The differences between the analytical approaches are also investigated and addressed.

The effects of alkali-activated slag on the engineering properties of clayey soil were investigated. The mix proportion parameters were chosen by using Taguchi's experimental design methodology. Four factors (groundgranulated blast-furnace slag content, concentration of sodium hydroxide solution, sodium hydroxide-to-sodium silicate weight ratio and alkaline solution-to-slag weight ratio) were assessed in order to obtain the greatest compaction properties, uniaxial compressive strength and California bearing ratio (CBR). Significant improvements were observed in the mechanical properties (unconfined compressive strength (UCS) and CBR) of the clayey soil with addition of the stabilisers. Optimal values (15% slag content, sodium hydroxide concentration of 6 M, sodium hydroxide-to-sodium silicate ratio of 0•5 and alkaline solution-to-slag ratio of 2•5) increased the UCS of the compound from 8 to 100 kg/cm 2 at 7 d. The excessive addition of alkaline solutions weakened the strength parameters of the soil. The results showed that the most influential factor was the alkaline solution-to-slag weight ratio. The Taguchi method is an effective and suitable experimental method for optimising alkali-activated slag parameters. NotationA alkaline liquid-to-slag ratio M concentration of sodium hydroxide solution R sodium hydroxide-to-sodium silicate solution ratio S ground-granulated blast-furnace slag content 17 Cite this articleDavari Algoo S, Akhlaghi T and Ranjbarnia M (2021) Engineering properties of clayey soil stabilised with alkali-activated slag.

One of the most important issues in the construction of highways, mountain and urban roads is known as slope stabilization. If the necessary actions for protection are not considered, it could lead to problems and events such as landslides, settlements and even destruction of roads. There are many methods for stabilizing slopes such as Gabion walls and Tiebacks. This study can be used as the beginning of a new synthetic method where the Gabion wall is combined with Tiebacks. Gabion walls and tiebacks can be known as the most flexible methods of slope stabilization methods, because of this reason, if they can be combined with each other, it should show very good results in front of dynamic and even static forces. This combination is the novel point of this research. In this study at first, the gabion wall will be analysed in different loading conditions, and then to deal with earthquake dynamic forces the tiebacks will be used to increase the gabion walls stability.The software that is used in this study is GEO5 software, nowadays this software can be introduced as one of the best slope stability analysis software's. The results of this study showed that the designed gabion wall could be stable in dense silty gravel soil (GM) in 8.5-meter slope, and with magnitude of 0.25 horizontal coefficient of Manjil earthquake, but in the same geometry and material condition and impact of 0.4 magnitude horizontal coefficient of Bam earthquake it couldn't be stable alone. In this condition four rows of 18 meter tiebacks could stable the gabion wall very well. In this model, under loading condition 3 (with horizontal and vertical pseudo-static coefficient of Bam earthquake) that had the most vertical pseudo-static coefficient, the 23-meter tieback anchors with 12-degree inclination respect to horizontal could stable the considered gabion wall. This result could show that, the combination of gabion walls with tieback anchors gives a satisfactory result and it is an efficient and helpful method for stability of slopes in front of earthquake and dynamic forces.