| The existence of insidious karst, is a hidden danger factor of highway construction and operation. The influence of ground water and external loads tend to further reduce the quality of cavern surrounding rock, giving to greater danger, with argumentation and treatment of karst subgrade before construction is necessary. Using Yong-Ji expressway project of Xiang-xi autonomous prefecture of Hunan province for research, which is the encryption line of Bao-Mao highway and Guangdong-Guangxi high-speed, also is an important inter-provincial channels of southwest region of Hunan. Based on geological information and site survey, Yong-Ji expressway line corridor through the area with erosion tectonic geomorphology hilly topography, hilly dissolution structure landforms and valley landscape. Correctly, effectively hidden karst roadbed stability analysis and construction risk assessment karst areas, could provide the basis for its decision in response to the construction, and for information technology and management of karst highway construction.Nonlinear Hoek-Brown criterion is based on the large number of tests and the results of engineering practice, which could solve the problems of low stress and non-linear that Mohr-Coulomb criterion couldn’t, and with the introduction of GSI system could be used to get rock physical parameters and mechanical characteristics more quickly. GSI is based on experience Hoek-Brown strength criterion considering a variety of geological factors rock parameters, the strength criterion combination of qualitative and quantitative analysis, a simple, economical and suitable, etc., and rock engineering design, construction and scientific research in constantly been validated and improved analytical methods. By making the system summary and analysis of the basic theory of generalized Hoek-Brown criterion of experience, research and improvement of previous experience on the basis of the criteria, to explore the rock deformation and stability the basic principles and methods of analysis karst roadbed stability analysis and evaluation. Through this study some conclusions were drawn:(1)With the subjectivity of selected parameters using Hoek-Brown criterion, sensitivity analysis methods was used, nonlinear influence discipline of derived parameters on rock strength index, could provide some theory basis for selecting parameters. With Hoek-Brown criterion for rock mass mechanical parameters of robustness values should be targeted varying degrees of quantification to ensure Hoek-Brown criterion applied flexibly and close to practical engineering.(2)The karst roadbed stability was influenced by many factors, and industry has no an uniform criteria. In order to meet certain requirements, generally divided into the following three basic criteria:rock strength criterion, rock ultimate strain criterion, rock displacement criterion. When calculating the numerical stability of the software, using the test method conducted by strength reduction step simulation to analyze the stability of karst roadbed. In analyzing the stability of surrounding rock caverns using analytical method, using complex function can be simplified analytic plane elasticity conformal mapping of complex shapes through boundary conditions when shallow cavern buried, and when it is based on Hoek-Brown criterion for solving the plastic rock cavern radius, to better reflect reality than the Fenner formula.(3) Karst roadbed risk assessment in the actual engineering practice less risk of major research chapter karst roadbed dynamic response, is divided into three aspects of risk identification, risk assessment methods and risk disposal. According to the basic principles of analysis and evaluation of bridges and tunnels, building sets karst roadbed risk evaluation system that criterion risk probability, risk of loss and risk level. According to the general nature of karst roadbed risk induction treatment system Treatment karst roadbed that excavation backfill method, pressure grouting method and the method of crossing structures.(4) According to the engineering practice of Yong-Ji expressway, the results of the use of numerical simulation and fuzzy comprehensive evaluation method was out have indicated that inadequate safety margin karst roadbed, consider the case of limestone rock under the action of groundwater and construction the environmental impact of operations, will further reduce its stable value, safety can’t be guaranteed, indicating a need for its effective prevention. The road because shallow cavern, so the use of mechanical drilling a hill, and then filling gravel, concrete paving process was carried capped treatment. Safety department rule, applied as a simple, economic effect, and in line with environmental requirements. |
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