No abstract

Circular tunnels are the most popular shapes used in urban underground transportation systems when mechanized tunneling is used for tunnel excavation. However, circular tunnels have a small space utilization ratio. With the material development, non - circular tunnels such as sub - rectangular, U - shaped lining, etc. are now common, and their cross - section helps to improve the underground space utilization. However, there have been not many studies on the structure and the calculation method of the metro tunnels with the above cross - sections. The paper uses the analytical synthesis method to find out the advantages and disadvantages, the application conditions of the sub - rectangular shape, as well as the development direction for the complete calculation methods for this cross - section in Vietnamese conditions.

The rapid economic development of Vietnam triggers a number of challenges in all sectors including infrastructure design and execution. New development plans and lack of space in densely populated and economically valuable areas creates a need for complex engineering solutions to meet the demand. The present research is a case study investigating reengineered vast natural slope to meet all requirements for geotechnical safety such as maximum displacements and factor of safety. Complex ground conditions and significant dimensions of the slope made the entire structure very likely to cause major risk for the future development plan of the site. Due to complex conditions, the slope was divided into 4 main sections. Each section was reinforced using a combination of soil nails, ground anchors, drainage systems and micro piles, of 19m for a single pile. Due to very much limited space available new geometry of the slope was designed for inclination reaching 1:0.3. Based on numerical modelling and computation the results revealed that the maximum lateral displacements felt in a range of 37-50x10-3 m and the factor of safety was 1.56-1.65, depending on a section and analysed scenario. The computations allowed proposing combined geotechnical solutions for very much challenging sites, assuring high safety standards and fitting the entire design within a limited available area.