Ground surface settlement is the most significant restriction when constructing shallow metro station tunnels in urban areas. The umbrella arch method (UAM) is generally applied as a tunnel support method. However, UAM becomes inadequate in some soil conditions, such as loose sand or soft clay. Innovative support systems are required to safely build shallow metro station tunnels in urban areas. The objective of this research is to investigate alternative tunnel support systems and appropriate soil models to safely construct shallow twin-tube metro station tunnels. The continuous pipe arch system (CPAS), which consists of horizontal and continuous pipes along the metro station tunnels, was modeled in three dimensions (3D) using the finite element (FE) program Plaxis3D for various pipe diameters. The ground surface settlement results of the 3D models were compared with the in situ settlement measurements to validate the geotechnical parameters of the soils used in the models. It was observed that the hardening soil (HS) model was more accurate than the Mohr-Coulomb (MC) soil model. As a result of the 3D FE model analysis, maximum ground surface settlements were obtained below 50 mm when the pipe diameters of CPAS were larger than an internal diameter (ID) of 1200 mm at a cover depth of 10 m in sandy clay soil. It is revealed that CPAS with pipe diameters between ID 1200 mm and ID 2000 mm can be utilized as a tunnel support system in urban areas to construct shallow twin-tube metro station tunnels with low damage risk.

Mine haul roads play an important role in the mining industry. They are often designed as unsealed roads, which are frequently damaged due to seasonal moisture variation, especially when the subgrade soil is expansive clay. In this study, the performance of mine haul roads built on expansive clay soil is investigated for seasonal moisture variation using experimental and numerical investigations. Shrinkage, swelling, soil water characteristics curve (SWCC) tests, and direct shear testing were first performed to assess the hydraulic and shear performance of the control and municipal solid waste incineration (MSWI) fly ash-treated soils. The swelling reduced from 1.95 to 1.02, while the shrinkage reduced from 3.4% to 1.84% after the addition of 20% MSWI fly ash. SWCC results showed that the MSWI fly ash addition reduces the void spaces and increases residual saturation. The consolidation settlement reduced by 50% after adding 20% MSWI fly ash. The cohesion of both soil and MSWI fly ash-treated samples exhibited a bell-shaped trend with moisture increase, in contrast to friction angles which decreased with increasing saturation levels. 3D numerical models were used to predict the performance of control soil and MSWI stabilized mining haul roads using the experimental test data. The control pavement experienced increased settlement and rutting as saturation levels increased. The behaviour of the stabilized pavement differed, with the model having a 20% degree of saturation showing the least deformation due to increased stiffness from high suction. Overall, this study highlights the benefits of MSWI fly ash-based soil stabilization in improving the performance of mine haul roads under seasonal moisture changes. The findings emphasize the importance of considering the degree of saturation and stabilization techniques in pavement design to mitigate settlement and enhance overall performance.

A 3D high-resolution subsurface characteristic (HSC) numerical model to assess migration and distribution of subsurface DNAPLs was developed. Diverse field data, including lithologic, hydrogeologic, petrophysical, and fracture information from both in situ observations and laboratory experiments were utilized for realistic model representation. For the first time, the model integrates hydrogeologic characteristics of both porous (unconsolidated soil (US) and weathered rock (WR)) and fractured rock (FR) media distinctly affecting DNAPLs migration. This allowed for capturing DNAPLs behavior within US, WR, and FR as well as at the boundary between the media, simultaneously. In the 3D HSC model, hypothetical 100-year DNAPLs contamination was simulated, quantitatively analyzing its spatiotemporal distributions by momentum analyses. Twelve sensitivity scenarios examined the impact of WR and FR characteristics on DNAPLs migration, delineating significant roles of WR. DNAPLs primarily resided in WR due to low permeability and limited penetration into FR through sparse inlet fractures. The permeability anisotropy in WR was most influential to determine the DNAPLs fate, surpassing the impacts of FR characteristics, including rock matrix permeability, fracture aperture size, and fracture + rock mean porosity. This study first attempted to apply the field-data-based multiple geological media concept in the DNAPLs prediction model. Consequently, the field-scale effects of WR and media transitions, which have been often overlooked in evaluating DNAPLs contamination, were underscored.

This paper presents a 3D finite element analysis of deep soil mixing column-supported embankments (CSEs) with a geosynthetic platform. The numerical model simulated the CSE for the expansion (approximate to 1.0 km) of the existing runway at the Salgado Filho International Airport, in the city of Porto Alegre. The numerical model using Abaqus software was calibrated by comparing numerical calculations with good quality instrumentation data. Deep Soil Mixing (DSM) columns were used to improve the soil foundation. A novel approach to modeling the geosynthetic is also presented based on the mechanical properties of this material. The load transfer mechanisms and deformation of the column-supported embankments were analyzed by means of numerical and field results. Additional aspects such as the critical height and the pattern of vertical stress distribution in the columns and embankment as well as the stress distribution in the geosynthetic reinforcement were also investigated. The numerical model reproduces the vertical stress measured by the total stress cells installed above the columns and between the columns. The numerical model shows that the soil reaction of the thick compacted layer used as a work platform reduced the arching and membrane effect in the embankment.