Structural materials sustainability is gaining popularity across the globe at present. Reusing natural resources, building, demolition debris, and solid waste are the most apparent tools to make construction more environmentally friendly. Traditional concrete is believed to be less durable, stronger, environmentally friendly, and socially and commercially feasible than industrial waste concrete. The evolution of non-destructive testing (NDT) across time has not been investigated in depth by researchers. An experimental study was carried out to propose the use of non-destructive mechanisms that would enable us to assess concrete’s compressive strength without causing destruction. Varying quantities of industrial waste (coal bottom ash (CBA) and waste glass sludge (WGS)) were incorporated to cast concrete prisms (150 mm × 150 mm × 150 mm). The results obtained helped us to establish relationships between the compressive strength of concrete and the Schmidt hammer rebound value, as well as the ultrasonic pulse velocities. Microstructural analysis showed that incorporating 10% of CBA and WGS improved the porosity of concrete specimens, which shows the applicability of these industrial wastes as partial cement replacements. Scanning electron microscopy (SEM) showed traces of calcium alumino-silicate hydrate (C-A-S-H), portlandite and C-S-H, which indicates the binder characteristics of CBA and WGS. The concept of the response surface approach (RSM) for optimizing cement and industrial waste substitution was validated by the polynomial work expectation. The model was statistically significant when the fluctuation of ANOVA was analyzed using a p value with a significance level of 0.05. The study results show that the usage of 15% CBA and 10% WGS as a cementitious additive and cement replacement has the potential to increase the strength of concrete significantly.

The resilience of underground tunnels has gained paramount importance recently, driven by the need to ensure the safety and functionality of critical transportation and infrastructure systems during seismic events. Underground tunnels are prone to severe damage when the soil condition is poor and located in a high seismic zone. While the behavior of individual tunnels has been extensively studied, the concept of multiple tunnels combined into a large tunnel complex is relatively new, with limited available research focusing on rectangular-shaped tunnel complexes and requiring a more detailed examination. This study parametrically analyzes two novel and unconventional structures in soft soil, i.e., twin and triple tunnel complexes resulting from the combination of closely spaced circular twin and triple individual tunnels. Seismic records from Coyote (US, 1979), Kobe (Japan, 1995), and Kocaeli (Turkey, 1999) have been used to determine the produced surface displacements, tunnel distortions, lateral stresses on the tunnel structures, and the induced seismic forces, including thrusts, shear forces, and bending moments. The results are then compared with the conventional rectangular-shaped tunnel complex, which is also analyzed under the same conditions. The comparison shows that the twin and triple tunnel complexes are comparatively better seismic performers than the conventional rectangular tunnel complex, with reduced ground displacements produced, lesser incurred structural distortions, experienced lateral stresses, and induced seismic forces. Doi: 10.28991/CEJ-2023-09-12-01 Full Text: PDF

Tunnel construction in soft soil necessitates a thorough evaluation of soil behavior, embedment depth, ground heaves, and tunnel distortions, especially in earthquake-prone areas. This study presents a numerical parametric investigation of an unconventional tunnel complex formed by combining the closely located twin tunnels. The complex is subjected to varying horizontal ground vibrations, and the influence of lining thickness, embedment depth, and interface conditions on seismic-induced thrusts, shear forces, bending moments, tunnel distortions, and ground heaves is assessed. The applicability of analytical solutions from existing literature for singular tunnels is examined through detailed analyses of different embedment ratios. The study reveals that increased tunnel flexural rigidity leads to higher seismic-induced bending moments in the tunnel complex. Comparison of full-slip and no-slip interface conditions shows that the former exhibits reduced overall tunnel distortions. Furthermore, a comparison is made with a conventional-shaped rectangular tunnel complex. The results indicate that the twin tunnel complex behaves more rigidly under a constant embedment ratio and input motion amplitude. It also results in lower ground heaves and suffers lesser induced lining forces during seismic events, making it a superior performer in comparison. Overall, this research provides valuable insights into the behavior of twin tunnel complexes in soft soil under seismic conditions, showcasing their advantages over conventional shaped tunnels in terms of tunnel distortions, ground heaves, and overall structural response.