Study On Load Mode Of Road Tunnel With Extra-large Cross-section And Low Flat-ratio And Its Application

With the development of road tunnel construction and assorting with muti-lanes freeways, extra-large cross-section and low flat-ratio road tunnel become a new shape in recent years. There are evident differences between low fiat-ratio road tunnel and the usual road tunnel with two-lane in one way, such as the excavation width, fiat-ratio(the ratio of height and span of tunnel), furthermore, the former is more complex in construction method and stress distributing. However, few extra-large cross-section and low flat-ratio road tunnels had been built by far in China. As a result, experience which was accumulated on design and construction is quite scarcity, and the criterion or code of design is not issued. Under these backgrounds, based on Longtoushan tunnel which is located in Guangdong province and is the longest low fiat-ratio road tunnel with eight-lane in either way in China, according to Load-Structure method, the model of load, cross-section and parameters of support were studied in detail in this paper. Study contents and conclusions were made in this paper as follows:Progress and development on study of various calculation methods of rock surrounding pressure and loose load were summarized, analyzed and appraised. Especially, based on applicability analyses of those methods, necessity of study on loose load of low fiat-ratio road tunnel was discussed in detail. Furthermore, combined with the Longtoushan tunnel, several primary problems which were induced by using those methods was analyzed and discussed.Process calculation method of rock surrounding pressure and loose load(Process Load Method), which was applicable to extra-large cross-section and low fiat-ratio road tunnel was put forward. Differences and relationships between Process Load Method and usual State Load Method (such as Terzaghi andПротодъяконовtheory) were discussed. Characteristics and operation course of Process Load Method were analyzed and discussed in detail.Analyzing and validating rationality on Process Load Method. On the one hand, based on field examination of Longtoushan tunnel, through analyzing test data of multi point borehole extensometers(MPBX), distribution regularity of permanent loose load and generation and development tendency of loose zone range of tunnel were discussed. According to analyses result of field test, rationality on Process Load Method can be proved preliminarily reasonable. On the other hand, based on numerical software, numeration model of extra-large cross-section and low flat-ratio road tunnel was established. Through analyzing development regularity of loose zone with excavation process of tunnel, from qualitative angle, testifying that process load method was rational.Application procedure of process calculation method of rock surrounding pressure and loose load was established. Firstly, application formulas on process load method were deduced. Secondly, specific procedure, method and model on Process Load Method were perfected. And then, some special problems which were found during application process were discussed. Finally, operation course of Process Load Method was illustrated by two examples.Project cost was used for object function, optimum structure of extra-large cross-section and low flat-ratio road tunnel was realized based on process calculation method. Through analyzing and comparing global optimization result which were from Process Load Method, State Load Method and the design information of Longtoushan tunnel, the figure of cross-section and tables of main support parameters of extra-large cross-section and low flat-ratio road tunnel were advised and put forward based on design of Process Load Method.In this paper, based on utility opinion, the calculation method of rock surrounding pressure and loose load on extra-large cross-section and low flat-ratio road tunnel was established; advices of cross-section and main support parameters were put forward. Some important and instructional regularities and conclusions were obtained through exploration, study and innovation on load model of extra-large cross-section and low flat-ratio road tunnel. The paper provides important reference and practical value for the design and construction of extra-large cross-section and low fiat-ratio road tunnel.Finally, the advices on further research are presented.