Effects of Tunneling on Piled Foundations in Clean Sands Using Finite Element Method and Sensitivity Analyses

Abstract

Infrastructures are getting more and more popular and preferable since the urban areas are getting crowded. Ground surface is occupied by high rise buildings, hospitals, social facilities and etc. Therefore, it is essential to use the underground space for different purposes. Some of these purposes are transportation, water systems, sewer systems, and electric lines. Tunneling is a way to travel underground and it is an alternative to ease traffic in cities. Therefore, tunnels are constructed under structures with shallow or deep foundations. For this reason, effects of tunneling on a foundation become a really important topic for civil engineers. In this manner, many researchers studied the aforementioned topic. They tried to find an answer to the big question; what are the effects of tunneling on piled foundation? In this study, the answer of the question is tried to be found by using analytical methods. Different parameters are specified according to the former researches and engineering judgements. These parameters are the ratio of location of the tunnel in x-direction to tunnel diameter (x/D), depth of the tunnel to tunnel diameter (z/D) and deformation modulus of the clean sand layer. The tunnel is excavated at once as a TBM tunnel. It is important to note that effects of tunneling on existing structures are examined in this thesis. According to the 2-Dimensional plane strain model created for the problem, finite element models are created and a series of analyses are conducted by using PLAXIS 2D software. Results are tabulated and evaluated. In the light of the results, a simplified equation is suggested in the scope of this study. According to the results, outcomes are evaluated and following statements are presented. Additional settlements of the foundation due to tunneling are decreased while tunnel is located further than the foundation center axis, and with increasing ‘x/D’ and ‘z/D’, and deformation modulus. Tunneling has put extra moments on piles, especially on the further piles where tunnel is located. Increasing deformation modulus has a decreasing effect on extra pile moment because the displacement is decreasing with increasing deformation modulus of the soil. With the additional settlement values obtained from finite element method using Plaxis 2D software, an equation is proposed using Maximum Likelihood Estimation. This equation requires tunnel location in x-direction, tunnel depth, tunnel diameter and deformation modulus of the soil in order to estimate additional settlement due to tunneling. It should be kept in mind that proposed equation is only valid for cohesionless soils.