Ground Loss and Static Soil–Structure Interaction during Urban Tunnel Excavation: Evidence from the Excavation of the Athens Metro

Ground settlement above urban tunnels is a threat for nearby buildings, because it may lead to their differential settlement, tilting, and damage, depending on their structural characteristics, on ground conditions, and on the excavation procedure. Still, for few cases only details on ground settlement are known. In this article we analyze ground subsidence data during the excavation of Lines 2 and 3 of the Athens Metro. Based on this evidence, and in comparison with previous studies, we show that observations of elevation changes and of tilting of buildings may underestimate the amount of ground loss; this is because part of the ground deformation may be compensated by the stiffness of buildings or accommodated by internal deformation of sizeable buildings hosting measuring benchmarks. This effect can be described as static soil–structure interaction (sSSI), in analogy to the dynamic SSI produced during earthquakes. sSSI can produce bias in monitoring data above an advancing tunnel front, leading to skew and not to symmetric subsidence curves if observations are made on one side on buildings and on the other side in open spaces (‘greenfields’). Furthermore, we show that ‘bowls’ of increased subsidence are observed along subsidence troughs during excavation; such ‘bowls’, not infrequently underestimated because of sSSI, may conceal a potential for sinkholes and other types of failure. Isolated towers on the contrary describe well ground subsidence and tilting.

Quantitative Analysis of Soil Displacement Induced by Ground Loss and Shield Machine Mechanical Effect in Metro Tunnel Construction

In order to relieve the increasing ground traffic pressure in the process of urbanization in China, it is inevitable to build more metro lines. However, the stratum movement caused by tunneling affects the safety of adjacent underground structures and aboveground buildings. Therefore, how to evaluate and control the stratum movement is a prominent problem. In this paper, based on the engineering project of an interval tunnel between Shizishan Station and Chuanshi Station in Chengdu Metro Line 7, China, the action mechanism of stratum movement induced by shield tunneling is analyzed, and the effect factors are divided into two categories: ground loss factors and mechanical factors. Combining the advantages of Loganathan method and mirror source-sink method, a new solution of three-dimensional displacement induced by ground loss is proposed. Based on the elastic half-space Mindlin model, the displacement at any point induced by four mechanical effect factors is deduced. Finally, the total displacement is verified by field monitoring data and quantitative analyzed in various parts.

The Utilization Of Some Of Biochar To Retain N-Total In Inceptisols

Nitrogen is very important nutrient growth of plant but eassy lost from soil. The aim of this researc to get the best biochar feedstock in maintaining N-total in the Inceptisol soil. Theresearch was carried out in the laboratory using the method of experiment. This research was carried out with complete randomized design non factorial with the treatment without biochar (controls), and 4 types of biochar from palm empty fruit bunches, rice straw, rice husks and wood, is repeated four times. The observed parameters are pH H2O,CEC, & N-total ground. The results showed that the four types of biochar can increase the pH H2O, CEC, N-total ground. Loss of Nutrient N decreased significantly due to the granting of biochar palm empty fruit bunches. Absorption capacity of biochar to reduce leaching of N in the soil of inseptisol sorted from largest to smallest is biochar palm empty fruit bunches, rice husk, rice straw and wood.