Comparison of Different Combined Multiple Tunnel Complexes in Soft Soil under Seismic Vibrations

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: PD

Evaluating the performance of the twin tunnel complex in soft soil subjected to horizontal ground shaking

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

Dynamic analysis of MSE wall subjected to surface vibration loading

Extensively used Mechanically Stabilized Earth (MSE) walls in Rail Transportation System (RTS) are vulnerable to surface vibrations generated by moving vehicles. Hence, it is necessary to consider the effects of surface vibrations during the design of MSE walls for RTS. Steel-reinforced panel-type MSE walls are shown to perform well during vibration loading, but costly steel materials have led to greater reliance on affordable and readily available geosynthetics for reinforcement. Limited research exists on the behavior of panel-type MSE walls with geosynthetics considering RTS-induced vibrations frequencies. Thus, this study employs Finite Element software PLAXIS 3D to simulate the impact of surface vibration frequencies on panel-type MSE walls. The qualitative study encompasses two reinforcement cases (geogrids and steel strips) of 4 m MSE wall height and four harmonic loading frequencies representing RTS-induced surface vibrations for simulation. The dynamic responses of MSE wall are presented in terms of lateral wall displacements and lateral earth pressure distributions. Furthermore, the distributions of tensile strain and the identification of potential slip surface locations are presented. The findings indicated that MSE wall and reinforcement responses are governed by RTS-induced vibrations and fundamental frequency of backfill soil. This highlights the need for consideration of both the fundamental frequency of the backfill soil and RTS-induced vibrations in the design of MSE walls

Scaling the Roots Mechanical Reinforcement in Plantation of Cunninghamia R. Br in Southwest China

The degree of mechanical reinforcement provided by plants depends upon its roots distribution in the soil and mechanical properties of the roots. The mechanical properties and distribution of root traits (root diameter and number) in the soil of the standing forest depends on the tree stem diameter. This variation of root traits with tree stem diameter is rarely investigated. Therefore, this research presents the effect of tree stem diameter on the distribution of roots within the standing forest of Cunninghamia in the Longchi forest area, Sichuan province, China. In this area, shallow landslides take place frequently. We investigated the root traits distribution for trees with different stem diameters, i.e., 220 mm, 320 mm, 450 mm, and 468 mm, to show the variation of roots distribution in the soil with stem diameter. The root architecture of the selected trees was studied by step excavation method of the root zone accompanied by measurement of roots physical parameters (roots number and roots diameter) and indices (roots area ratio (RAR), roots biomass (RB), and roots distribution (RD)). We measured the root’s maximum tensile strength by performing root tensile tests in the laboratory. The field and laboratory-measured data were used to estimate the root cohesion by both the commonly used model Wu and Waldron Model (WWM) and Fiber Bundle Model (FBM). The results indicate that the tree stem diameter correlates with both the root distribution and the tensile strength. The roots indices and root cohesion increase with an increase in the diameter of the tree. Further, RAR decreases with depth and lateral distance from the tree stem, while the maximum values were observed in 10 cm depth. The relationship between roots diameter and roots tensile strength is established through power function. The average root cohesion estimated for a tree with stem diameter 220 mm is 23 kPa, 29 kPa for 320 mm, 54 kPa for 450 mm, and 63 kPa for 460 mm. This effect of stem diameter on the increase of soil shear resistance should be considered while evaluating the stability of slopes in standing forests. The comparison between WWM and FBM for investigated species suggests that WWM estimates the cohesion values greater than FBM by 65%

A proposed seismic velocity profile database model

We describe the data model that we intend to use in a publicly available site profile database under development for the United States. The initial implementation of the database contains data from California. Currently, our prototype data model consists of JavaScript Object Notation (JSON) format files for storing metadata and data. For a site to be included in the database, the minimum metadata requirements are geodetic coordinates and elevation values, and the minimum data requirement is a shear-wave velocity profile. The JSON files are structured in a hierarchal manner to store metadata and data using a nested structure consisting of location, velocity profiles, dispersion curve data (for surface-wave methods), geotechnical data, and horizontal-to-vertical spectral ratios. The database schema at the current stage of the project, and as we continue to develop the data model we will consider including other relevant data, as well as evaluate other file formats to increase the efficiency of data storage and querying. In the current data model, location information includes site geodetic values (latitude, longitude, and elevation) and various site descriptors related to surface geology, geomorphic terrain category, slope gradient at various resolutions, and a geotechnical site category. Velocity data include the geophysical method(s) used to obtain the shear-wave velocity profile, type of data recorded, modeled primary- and shear-wave velocity as a function of depth, modeled profile maximum depth, and the calculated VS30 value. In the case of surface-wave based data, dispersion curve data can be recorded in data structure as phase velocity versus either wavelength or frequency. Geotechnical data includes boring logs penetration resistance, cone penetration test sounding logs, and laboratory index test results. Horizontal-to-vertical spectral ratio plots are given as a function of frequency

Assessing the Influence of Land Cover and Climate Change Impacts on Runoff Patterns Using CA-ANN Model and CMIP6 Data

Dhaka city is experiencing rapid land cover changes, and the effects of climate change are highly visible. Investigating their combined influence on runoff patterns is vital for sustainable urban planning and water resources management. In this work, multi-date land cover classification was performed using a random forest (RF) algorithm. To validate accuracy of land cover classification, an assessment was conducted by employing kappa coefficient, which ranged from 85 to 96%, indicating a high agreement between classified images and the reference dataset. Future land cover changes were forecasted with cellular automata-artificial neural network (CA-ANN) model. Further, soil conservation service -curve number (SCS-CN) rainfall-runoff model combined with CMIP6 climate data was employed to assess how changes in land cover impact runoff within Dhaka metropolitan development plan (DMDP) area. Over the study period (2020–2100), substantial transformations of land cover were observed, i.e., built-up areas expanded to 1146.47 km2 at the end of 2100, while agricultural areas and bare land diminished considerably. Consequently, monsoon runoff increased from 350.14 to 368.24 mm, indicating elevated hydrological responses. These findings emphasized an intricate interplay between urban dynamics and climatic shifts in shaping runoff patterns, underscoring urgency of incorporating these factors into urban planning strategies for sustainable water resources management in a rapidly growing city such as Dhaka