Back Analysis On Mechanical Parameters Of Geotechnical Engineering Based On Differential Evolution Algorithm

The 21st century, urban living environment problems are becoming enormous challenges to urban development in China, and developing underground space resource is effective means for solving urban issues. Nowadays the exploitation and development of underground space has been extended to various fields, and played an important social and economic role. In the construction of tunnels and underground projects, the property of surrounding rock is complicated and various with non-homogeneous, non-linear and non-continuous, rock mechanics parameters are not easy to be measured. Back-analysis method based on displacement field measured becomes popular for avoiding difficulties tested and gets better reflect the true state of parameters adopted by more researcher and engineering staff, and intelligent optimization algorithm provides a more extensive space for back-analysis method.Differential evolution back-analysis approach is proposed based on a new type of optimization algorithm - differential evolutionary algorithm in this article. According to different observation indexes, two approaches are introduced including DE displacement back-analysis approach based on measured displacement values, and DE seepage back-analysis approach based on observed head values.Linking two engineering cases with Jinshandian roadway and Gezhenbao Tunnel, the feasibility and validity of DE displacement back-analysis approach is proved. In Jinshandian roadway example, mechanical parameters of the surrounding rock on excavated roadway is back-analyzed, and the inversed parameters are applied to analyze the stability of the fork roadway with similar geology engineering. The results show that the approach has a good feasibility and with guiding significance.In the example of Gezhenbao Tunnel, a three-dimension numerical model is established based on the tunnel with complicated geological conditions such as containing rock crusher band and overlying rock with a certain degree of weathering. For evaluating safety and reliability of the tunnel building, an analysis is done on various states of stress, displacement and plastic area under different conditions of digging holes, the first support and a second support according to the simulation of the tunnel excavated. Then the DE displacement back-analysis approach is used for inversing mechanics parameters of surrounding rocks of broken and integrated rock, and the results show the approach is available for complex geology.Based on differential evolution algorithm and seepage finite element calculation procedure, DE seepage back-analysis approach is introduced. The process of inversing permeability parameters is carried out by compiling produces to combine the DE algorithm and seepage procedure. A simple example of homogeneous earth dam under condition of unsteady flow is designed for inversing parameters of permeability coefficient and specific yield.