| With the rapid development of highway tunnel in our country, more and more problems appear in highway tunnel construction. For example, it's difficult to determine the support parameters and the consruction opportunity between primary support and secondary lining. Taking the Chenggongling tunnel in the expressway from Ningbo to Jinhua as the engineering background, this paper mainly discusses the appropriate construction method and mechanic state in different construction case of surrounding rock and support structure, while excavation tunnel in weak and shallow-depth surrounding rock.Firstly, this thesis discusses the monitoring measurement technique and analyzes measurement dates by means of regression analysis. Secondly, the monitoring data is used in back analysis to achieve the physical and mechanical parameters of surrounding rock of Chenggongling tunnel portal section. Lastly, according to the measured displacements and surrounding rock parameters by back analysis, a FEM numerical simulation is carried on in wall rocks of II about Chenggongling tunnel portal section.There are three common excavation methods of highway tunnel under weak surrounding rock, such as bench cut method of keeping core soil, single sidewall guide pit and dual sidewall guide pit. We simulate the three excavation methods respectively using 2-D FEM, analyze the stress and strain distribution regularity of surrounding rock and support structure. After comparison, we recommend the bench cut method of keeping core soil is the preferable construction method for portal section of Chenggongling tunnel.With the construction of bench cut method of keeping core soil, we simulate the effect of construction factor, stress releasing coefficient and argue the changing law of stress and strain of surrounding rock and support structure. We also study the proper time of setting up support structure in the construction process. In order to verifying the bench cut method of keeping core soil feasibility, we Garry out comprehensive analysis for Chenggongling tunnel portal section. We focus on the safety of seconding lining under different embedment depth and lining thickness. Through comparing the result with field measured data and computing displacements without considering the effect of secondary lining, we can prove the support parameters are valid for Chenggongling tunnel construction. Combining with the practical project and measurement data, the author thinks that the construction method and support parameters are useful for excavation chenggongling tunnel portal section. The conclusion provides a certain theoretical basis and technique guidance for construction chenggongling tunnel portal section, and it can also be served as a reference and experience for the choosing support parameters and construction method on other similar weak surrounding rock tunnel. |
